WO2003099539A1

WO2003099539A1 - Biodegradable compound and preparation method thereof, and molded material made of the same and molding method thereof

Info

Publication number: WO2003099539A1
Application number: PCT/KR2003/001001
Authority: WO
Inventors: Fijeau Kim
Original assignee: Nexsol Technologies, Inc.
Priority date: 2002-05-24
Filing date: 2003-05-22
Publication date: 2003-12-04
Also published as: AU2003241846A1

Abstract

The present invention relates to a biodegradable natural polymer matrix utilizing high contents of xylem and grain powders as main components, and more particularly, to a biodegradable compound having a composite characteristic of hardening property and thermal plasticity of resins through dehydration bridging due to water-plasticizing and condensation polymerization, and a preparation method thereof. Also, the invention relates to a molded article of three layered composite sheet molded out of a biodegradable polymer matrix compound and a molding method for preparing the molded article. Especially, the present invention involves a compound that contains a functional additive to assist binding polymer matrixes of a group of binders reinforced with biodegradable xylem and train powders, a fibroid material, additives, etc. Both sides molded out of the biodegradable polymer matrix compound are coated or laminated with hydrophobic materials to provide physicochemical and dimensional stability. Thus the matrix compound can substitute for pulp papers, cardboard, and Styrofoam products.

Description

BIODEGRADABLE COMPOUND AND PREPARATION METHOD THEREOF,

AND MOLDED MATERIAL MADE OF THE SAME

AND MOLDING METHOD THEREOF

Technical Field

The present invention relates to a biodegradable natural polymer matrix utilizing high contents of xylem and grain powders as main components, and more particularly, to a biodegradable compound having a composite characteristic of hardening property and thermal plasticity of resins through dehydration bridging due to water-plasticizing and condensation polymerization, and a preparation method thereof.

Background Art

With a growing interest in environment, social and international pressure from environmental organizations is being intensified to develop materials that can substitute non- biodegradable plastics produced and abandoned excessively. Owing to such pressure, there have been various attempts to manufacture biodegradable plastics and products.

Biodegradable polymers are being studied in the following three categories:

(a) natural polymer obtained from plants and animals (for example, cellulose, starch, protein, collagen) ,

(b) polymer generated by fermentation of bacteria or microorganisms (for example, polyhydroxy al anoates) , and (c) synthetic polymer having biodegradability (for example, polycaprolactone and polylactic acid) .

Those studied up to now follow.

It has been reported that a filler was manufactured by injection and cellular moldings of various biodegradable materials with starch as their main component.

It has been reported that biodegradable containers were molded and commercialized with starch as their main component.

It has been reported that biodegradable materials were molded and commercialized by mixing thermoplastic resins with natural materials such as chaff, wheat flour, starch, etc.

There has been an attempt to manufacture biodegradable/difficult-to-decompose resins by esterifying/etherifying natural materials of xylem powder, etc. and mixing the resulting material with liquefied materials.

There has been a report in which starch was destructurized to give thermal plasticity to starch matrix compounds so that the compounds could be easily molded and commercialized with the prior plastic molder. There has been a report in which many companies manufactured thermoplastic composite resins by mixing starch with olefin resins and various non-decomposable resins to give biodegradability to the resulting mixture.

Biodegradable containers of pulp mold are being commercialized, in which pulp slurry is manufactured by using plant pulp, regenerated pulp, etc. that are made of wood pulp, annual plants, etc.

There has been an attempt to use, as a biodegradable plastic, poly-3-hydroxy lactic acid ester (PHB) obtained through fermentation.

There has been an attempt to manufacture biodegradable plastics by using polyamino acid, particularly gluten, zein, collagen, fermented polyglutamic acid (PGA), synthesized amino acid, etc. There has been an attempt to manufacture biodegradable plastics by treating pulp, a raw material of cellulose, chemically with ester or ether. There has been an attempt to manufacture biodegradable plastics by making viscous solutions that are obtained by dissolving cellulose, natural resin, with solvents of polar aprotic amide, especially N,N-Dimethylacetamide (DMA) , n-Methyl Morpholine-n-Oxide (NMMO) , n-Methyl Caprolactam, Dimethyl Sulfoxide (DMSO) , para-Formaldehyde, etc. under the presence of lithium halide salts. Such processes produce the viscous solutions more easily and cheaply than esterification and etherification through treatment with the prior inorganic compound.

There has been an attempt to make biodegradable plastics by polymerizing caprolactone to form polycaprolactone or mixing, compounding, and dispersing caprolactone with other materials.

There has been an attempt to manufacture biodegradable plastics by using chitin and chitosan that are rich in nature and available easily.

There has been an attempt to manufacture biodegradable plastics by using alginic acid that is rich in nature and available easily. Biodegradable plastics of aliphatic polyester, etc. made by mediation of aliphatic polyester are commercialized and in sale.

There has been an attempt to manufacture biodegradable plastics by using natural saccharide or lignin, which is a waste of the pulp industry. There has been an attempt to manufacture biodegradable plastics by fermenting or processing, and polymerizing amino acid.

An attempt has been reported to manufacture biodegradable plastics by polymerizing soybean milk, fish oil, etc. There has been a report in which lactic acid is polymerized to manufacture polylactic acid, a biodegradable polymer, for the purpose of constructing a plant for commercialization in a large scale .

As described above, an innumerable plurality of studies on biodegradability are being performed now and many kinds of products are already commercialized and in market. Nevertheless, biodegradable plastics are still not widely used mainly because compared to the prior commercialized products, molded products are very expensive, production is still not in a large scale, molding processes are difficult due to relatively complicated molding and processing, the quality of newly developed products is relatively bad compared to the molded articles commercialized already, or the shapes of molded products are not acceptable to users or chosen by users, in the aspect of usage and beauty, compared to the prior molded articles. This is because users would like biodegradable plastics to have the same properties as the difficult-to-decompose plastics they are now familiar with and to be cheaper than them.

Also, as for the known arts on biodegradable sheets and molded products, there are Korea Patents Publication No. 1999- 0087469, 1999-0087468, etc.

However, the prior arts such as the patents have the following disadvantages:

1. starch that is not gelatinized should be used and should be gelatinized during the processes,

2. organic additives should inevitably be used so that the surfaces of sheets molded out of matrix compounds does not stick to the rollers during the processes. A wide range of temperature should necessarily be used for organic additives so that the possibility of bad temperature control and a high defective fraction are. accepted,

3. Combination should be precise so that molding can be finished without flowing down or being scattered by self- adhesion power,

4. A high content of starch should be used due to the dependence only on starch's adhesion power, and

5. The resistance to water is very weak after molding.

Disclosure of Invention

Therefore, the present invention has been made I view of the above problems, and it is an object of the present invention to provid'e a biodegradable natural polymer matrix utilizing high contents of xylem and grain powders as main components, a biodegradable compound having a composite characteristic of hardening property and thermal plasticity of resins through dehydration bridging due to water-plasticizing and condensation polymerization, and a preparation method thereof.

To achieve the above object, according to an aspect of the present invention, there is provided a biodegradable compound in which a) xylem powder in a concentration of 10 to 90 wt% relative to the total solid material of the compound, b) fibroid material in a concentration of 0 to 50 wt% relative to the total solid material of the compound, c) group of binders in a concentration of 0 to 90 wt% relative to the total solid material of the compound, d) functional additive in a concentration of 0 to 50 wt% relative to the total solid material of the compound, e) compounding water in a concentration of 1 to 90 wt% relative to the total solid material of the compound, etc. are homogeneously dispersed to form an aqueous slurry state.

Also, the invention is directed to a molded material of three layered composite sheet molded out of a biodegradable polymer matrix compound and a molding method of preparing the molded material.

According to another aspect of the present invention, there is also provided a method of molding a molded material of the biodegradable compound, comprising the steps of: a) forming the compound of slurry state in which xylem powder, fibroid material, starch supplied from grain powder, a group of binders consisting of aqueous thermoplastic resin and aqueous thermal gelling composite resin, a functional additive, and compounding water are dispersed homogeneously; b) casting the compound in a prescribed thickness through an outlet of an extruder; c) drying the cast compound with a drying means; and d) forming a sheet out of the dried compound.

Brief Description of Drawings

Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which: FIG. 1 is a diagram of a commercialized , wherein; FIGs. la and lb are illustrative diagrams of commercial compounding machines that can continuously make slurry that can be directly input to molding processes, FIG. lc is an illustrative diagram of a commercial compounding machine that can continuously make the slurry of precise compounding since a mixture can be supplied uniformly,

FIG. Id is an illustrative diagram of a commercialized compounding machine that can compound any slurry for each lot; FIGs. 2a and 2b are diagrams showing the rollers that sheet continuously the slurry supplied from a continuous compounding machine and the states of processes; FIGs. 3a and 3b are diagrams showing the rollers that sheet continuously the slurry cast in an extruder on a one-sided or both-sided film that is supplied after completion and the states of processes; FIG. 4a is an illustrative diagram of a mixer or an extruder of cylinder type;

FIG. 4b is a diagram showing the states of processes that show the appearance of fine tuning the cast sheet between various rollers; and FIGs. 5a, 5b, 5c and 5d are inner structural diagrams of molded articles .

Best Mode for Carrying Out the Invention

The present invention is now explained in greater details using the following embodiments, together with the attached drawings.

Recently, there have been many attempts to use xylem, pulp, processed materials of various plants, products fermented by various bacteria, starch and starch derivatives as biodegradable polymer matrixes.

The biodegradable compound of the present invention is manufactured using xylem powder as a main ingredient, aqueous thermoplastic resin, carbohydrates contained in grain powder or potatoes, and starch as a basic mixture binder. A method of simply molding out of molded articles uses the traditional method that the human race has used for several thousand years as a method of molding foods such as similar agricultural products. That is the method of molding, by heating, wheat flour containing water, starch, and the dough or slurry of pulverized grain or potatoes in a heated container. When the method is applied to foods, they can have countless plurality of shapes of bread, scorched rice, porridge, soup, pie, pancake, potato powder cake steamed on a layer of pine needles, an additive, etc. Here, proteins and carbohydrates, especially starch, contained in the dough, is not only a component of molded article, but they play a role of binders and exist in an aqueous mixture of polymer matrixes.

Therefore, giving hydrophobicity to the surfaces by molding biodegradable natural products such as xylem powder with carbohydrate binders can generate containers that can be useful enough in our daily life.

The object of the present invention is to provide a biodegradable compound by using natural polymer having a high content of xylem, wherein ^Λxylem powder' (vegetable material) and ^Λgrain powder' easily found and abundantly existing are directly pulverized and treated in advance, in consideration of their biodegradability, by then adding a ^Λfunctional additive' to the resulting material, by reinforcing with a fibroid material, ' and by then binding the resulting material with a group of ^binders,' and a method of molding molded articles. The bound material is used in preparing a biodegradable natural polymer matrix compound (the term compound' is a composition in a sense and thus compound and composition will be used in a mutually interchangeable manner) of slurry type, wherein the biodegradable compound is cheap, beautiful, and not inferior physico-chemically and morphologically than the prior petrochemical products.

The biodegradable compound has a ""composite characteristic' of water-plasticity shown in a high content of xylem powder, hardening property generated through dehydration bridging, and thermal plasticity. Thus the present invention relates to a composition of biodegradable grafted block copolymer matrix compound' of slurry type having such a composite characteristic and a preparation method thereof, and a method of preparing a three layered composite sheet molded out of the matrix compound and a molded article thereof.

The compound of the present invention has superior water- resistance, strength and performance that are superior physico- chemically, morphologically, and functionally, to papers made of the prior pulp. The composition of the compound used for forming sheet mostly comprises xylem powder as a main component, aqueous polymer having thermal plasticity (thermal gelling or syneresis hardening) as a primary binder, starch granules contained in grain powder as a secondary binder, a homogeneously dispersed fibroid material, a functional additive, additive components, and water as a solvent and a viscosity controller.

Here, syneresis' means that two molecules bind together by driving water out. Condensation polymerization is a similar phenomenon.

One of the problems related to a starch binder is that it is in general very viscous if dissolved or gelatinized in water. Once gelatinized, non-denatured starch granules are so viscous that they tend to stick to molding facilities, especially heated molding facilities. This makes starch binders a good coagulant, but at the same time, this makes manufacturing processes complex since sheets or products manufactured by using a great amount of starch binders dissolve or gelatinized tend to stick to molds or sheet forming apparatuses. Viscous nature of gelatinized starch is still thought to be probably the reason why the industry related to plastic molded articles has not been active.

However, the molded article of the present invention provides a biodegradable polymer matrix composition and a method of molding a compound out of the composition, in order to manufacture sheets that have properties similar to those of papers, cardboards, polystyrene, and plastic foam sheets and are environmentally friendly. Also, the present invention provides a composition for manufacturing sheets that can be made various containers or other products and a method thereof, by using manufacturing facilities and technologies used for manufacturing papers, cardboards, polystyrene, or plastic sheets.

The matrix for preparing the compound of the present invention consists of xylem and grain powders, a fibroid material, a binder including aqueous (or water-dispersed) thermoplastic resin and a group of carbohydrates (especially, starch) , an additive, a functional additive, and water as a solvent and a plasticizer. To form the compound having intended properties with the components mentioned above, the compound for molding is manufactured through the step of mixing them in a prescribed ratio. A group of binders is mixed in the compound, as a part of the components used for manufacturing the matrix. The matrix comprises fibroid material homogeneously dispersed for reinforcing elasticity, drawing property, and strength. To provide physico-chemical and dimensional stabilities for the molded article, hydrophobic coated films are formed on or attached to the surfaces.

Unless it is separately defined, aqueous' means both ^Λaqueous' and ^water-dispersed' .

Comprising various materials that can provide related properties to increase property of the components of the matrix, the present invention can generate inherent molded articles having significant strength, drawing property, environmental friendliness, large scale productivity, and cheap price. These examples can be easily found in ABS resins and ABR rubbers to be described later.

A ^Λgroup of binders' means the combination of binders used for sheets of the present invention. In order words, the group means a mixture of an organic binder contained in the combination and a natural binder supplied from grain powder.

A composite component' is an extended concept of compound and means that the composition used for manufacturing sheets comprises various chemically or physically different materials or phases such as xylem powder, aqueous thermoplastic (or thermally gelling or hardening) binder resins, biodegradable grain powder, fibroid material, inorganic additives, function additives, and water. This wide range of materials each and every way allows both the composition used for sheeting and the final sheets to have more than one inherent property.

The term to reinforce with fibroid material' mean to add fibroid material literally. But the sheet of the present invention is different from pulp papers and plastic pulp. Pulp papers depends not only on the binding of papers but on hydrogen bonding (condensation reaction) due to mutual entanglement of fibers based on Web' physics to provide 3-dimensional matrix and weight. In particular, to give papers a shape and weight, it is manufactured by adding thermally hardening resins and a filler together with materials for hydrogen bonding to occur.

The terms ^λslurry,' polymer matrix,' or ^molding composition, ' Voidable composition, ' or ""polymer matrix having a high content of xylem powder' are differentiated depending on the amount of water content, can be used in a mutually exchangeable way, and mean ^biodegradable polymer matrix compound' having a high content of xylem that can be molded into a shape of sheet or other shapes. This has a characteristic in that it contains water as a solvent and a plasticizer that forms a mixture having plasticity similar to plastics, by mixing a significant amount of xylem and grain powders, a small amount of organic synthetic binders, various amounts of fibroid materials and mineral additives. The compound can contain additives such as plasticizers as a functional additive, lubricants, dispersants, water-hardening materials, and foaming agents.

The total solid material includes all the solid phase materials regardless of whether they are suspended or dissolved in a mixture. Naturally, the total solid material does not include compounding water.

The compound has a limited range of plasticity and adhesive property, but has a characteristic in that it is stabilized after molding in a desired shape to have a relatively high bearing power. The Polymer matrix,' ^compound,' or ^mixture of xylem powder' refers to the compound irrespective of the degree of dryness. This compound thus comprises dried polymer matrixes and completely dried compounds (even though a certain amount of water may remain as binding water within the group of binders in the sheet . )

Formed after the compound forms sheets, the binders harden then by heat, the functional additives play their role, and the sheets are dried partially, the sheet or molded product will have the ^Λpolymer matrix having a high content of xylem powder.' The composition for making matrix comprises 5 to 90 wt% of xylem powder; 1 to 90 wt% of a starch binder contained in grain among the group of binders and an aqueous organic synthetic resin; 1 to 40 wt% of fibroid materials; 0 to 90 wt% of a filler; and the amount of water enough for generating the compound, by mixing with slurry, with all the percentages being relative to the total solid material. Aqueous resins in the compound increase the bearing power of the matrix to function as a thickener that allows homogeneous dispersion of fibers in the entire polymer matrix. There are in general many methods in molding plastics, which mostly include injection, extrusion, calendaring through casting, etc. For injection and extrusion of the compound of the present invention, conventional plastic processing methods can be used by virtue of the constituents of the present invention. And the compound is made a sheet initially since the compound mentioned above is cast to laminate on an isolation membrane continuously supplied through a conveyer in the calendaring process .

The biodegradable polymer matrix mixed completely is laminated in a uniform thickness on a coated film continuously supplied or an isolation film supplied continuously through a conveyer. Afterward, the sheet passes through a heating means heated up to more than the gelatinization temperature of starch. For example, the starch such as potato starch is gelatinized at 65 °C, corn starch at 95 °C and wax corn starch at 70 °C.

The compound cast on the isolation film flattens with its surfaces being uniform by a heated compression roller.

The sheet hardens to a significant degree by evaporating a considerable amount of water. The heating means hot enough to remove water gelainizes starch granules. The initial sheet passes through heated rollers to be dispersed with other binders and the components of the compound homogeneously so as to bind to the isolation film and, afterward, is completely molded by removing a considerable amount of water through evaporation. Then another isolation film is laminated on the surfaces of the initial sheet that is being almost dried, and the heated rollers presses the sheet to let the membrane to stick to the initial sheet, thereby completing the process of sheeting the biodegradable compound with both surfaces being coated with the films .

Additionally, the present invention provides a composition and a preparation method thereof for manufacturing environmentally friendly sheets that comprises a part of water contained in the slurry used for manufacturing pulp papers, is unnecessary for excessive dehydration during the sheeting process, and can be formed out of moldable compositions. Also, the present invention provides sheets, containers, and other products that can be decomposed into materials contained in soil or are biodegradable. The invention also provides a method of manufacturing sheets, containers, and other products with the cost cheaper than that of manufacturing papers, plastics, or other metal products, and a composition obtained therefrom. It additionally provides a composition that can reduce the energy and the initial investment expenditure for manufacturing molded articles having the identical characteristics to those found in papers or plastic sheets and especially that can comprise a high content of xylem powder, and a method thereof. Lastly, it provides a composition and a method for manufacturing inorganic material-filled sheets that can comprise a significant amount of natural additives in them and can have bigger elasticity, tensile strength, drawing property, moldability, large scale productivity.

The molded article, especially sheet, molded using the method of preparing the polymer matrix compound of the present invention can be 0.1 mm to 100 mm thick. But to have the quality similar to that of papers or cardboards, the thickness should be less than 1 cm, preferably less than 5 mm, more preferably less than 3 mm, and most preferably less than 1 mm. Additionally, the binding matrix of a group of binders of the sheet decomposes naturally after the continuous exposure to water.

In the process of forming sheet, irregular apertures are removed when water is evaporated from the matrix to promote adhesion between binders and fibers, thereby compressing the sheet during the molding process. Compression is performed by passing sheets between a set of more than one compression roller having apertures smaller than the thickness of the sheets. The sheets manufactured according to the present invention have properties similar to those of papers and plastic sheets and can be used for molding the products such as containers or other wrapping materials. The sheets are rolled up at a large spool or cut into sheets having a fixed size to be piled on palettes such as papers or cardboards for storage until necessary.

Heating the sheets of the present invention again or adding water can give plasticity to them in a limited range. After plasticization, the piled or rolled sheets are cut and molded by re-heating or re-wetting to manufacture a desired product. Additionally, the sheets can be processed like thermoplastic plastics. If the sheets of the present invention are heated above the glass transition temperature of starch, they can be molded in a desired shape. When the temperature is lowered below the transition temperature, the sheets will be solidified again.

As a result of the present invention, various products that have been manufactured with papers, cardboards, or polystyrene, when using the materials described above, can be manufactured in a large scale, with the cost cheaper than that of the prior costs. The cost reduction is not only due to the reduction in unit price of materials but a rational result of using the manufacturing processes that require less energy and the initial capital investment. Especially, the composition used for manufacturing the sheets of the present invention requires dehydration less than that in the case of manufacturing papers. Thus as compared with the case of manufacturing plastics or metals, the cost required to obtain raw materials is relatively low in the present invention. Also, the sheets of the polymer compound having a high content of xylem powder contain environmentally friendly components. Thus this method of manufacturing sheets affects environment less than the method of manufacturing sheets from the prior materials. The sheets of the present invention require wood pulp of high concentration, products for petro-chemistry, or other natural resources less than the cases of manufacturing papers, plastics, or metal sheets.

Since starch or aqueous resin components dissolve in water easily, recycling or biodegradability is promoted. Sheets or other products used decompose in water easily. Thus they can be used again in manufacturing similar products. If abandoned to ambient environment, starch and aqueous resins absorb water quickly to be dissolved, thereby leaving xylem powder having a small amount of fibers and a composition similar to soil and functional additives. Microorganisms existing in soil degrade dissolved starch and aqueous resins and dispersed fibers easily. Starch granules used as a natural binder in processing biodegradable molded articles of the present invention are not aqueous in general. Thus, if a composition containing these starch granules is not heated above the gelling temperature of starch, the composition functions only as a passive particle filler. Otherwise, a mixture should contain far more water to increase the viscosity of gelatinized starch in the molded article and to maintain the same molding properties as those before gelatinization.

The molded article using a polymer matrix compound in which xylem powder is a main component is manufactured such that the article is manufactured such that it has properties similar to papers, cardboards, or other sheet materials. The sheets described above form an isolation film coated homogeneously on the surfaces of the sheet, during and after molding. Thus they have excellent dimensional stability and hydrophobicity.

The molded article of the present invention can be described as a composite component to be mentioned later, especially a thermoplastic sheet or a molded article reinforced with fibers. In other words, the article is a thermoplastic complex binging with a group of binders the mixture in which a composite component is reinforced with fibers. The most important goal set for the present invention is to give plasticity and flexibility to the components of the present invention, even though they are natural materials, so that they can be molded freely even after the initial molding. The examples include Acrylonitrile Butadiene Styrene (ABS) resin, ABR synthetic rubber, etc. that are composite block compounds. Since each component contained in ABR resin is plastic resin and has many disadvantages, it is not frequently manufactured alone (except PS resin) . But three (four, substantially) components are mixed to have synergy effects. Similarly, SBR synthetic resin shows better rubber properties, a third characteristic, when mixed with styrene monomers and butadiene monomers .

Therefore, this is a realization of the block copolymerization' matrix compound consisting of biodegradable slurry that can be molded thermo-plastically, which is a goal of the present invention.

According to the definitions and the principles, a biodegradable polymer matrix compound comprising xylem and grain powders, a group of binders, a fibroid material, and other additives is formed and molded to various products having the properties similar to those of pulp papers or cardboards. The sheets of the present invention can substitute for plastics and the sheets manufactured out of polystyrene. The present sheets can be cut to manufacture various containers and other products by forming processes such as bending, folding, and rolling. The composition, method, and molded article of the present invention are especially useful for large scale production of disposables and food wrappers in the fast food industry. The compound of the present invention has the following characteristics different from those of other molded articles. In the cases of the prior starch and molded articles of a high content of inorganic materials, at the instant when the molded articles contact water, especially hot water, the binding force reduces considerably such that the molded articles themselves can be sustained, thus limiting the usage. In the case of an alloy with olefin resins, starch decomposes easily, but olefin resins not decompose but collapse biologically, thus confirming that olefin resins still exist.

The decomposition mechanism of the molded article of the present invention is as follows. First the molded article is dissolved initially by the water in the aqueous binder. Afterward, as the binding force of the composite components added, etc. reduces, collapse occurs slowly. Then, the xylem powder is decomposed by microorganisms. Therefore, the lifetime of the article is long sufficiently, compared to the biodegradable molded articles manufactured out of other natural materials. The article has a characteristic in that its composite components have physically strong resistance to water. But after decomposition, they decompose completely to become fertilizers, thus aiding a beneficial circulation of nature.

In the following, we turn to detailed description of the components of the present invention and their role and function.

A. Xylem powder and pretreatment

^λXylem powder' , the main component of the present invention, is defined in the following way. It is a collection of stem cells of perennial and annual plants and consists of cellulose, hemicellulose, and lignin. It refers to fine power obtained by pulverization, having property more than the physical strength of a certain requirement. Depending on the kind of raw material and the usage of molded articles, it can be processed additionally, which will be described later.

Plants accumulate a great deal of xylem (stem cells) in the stem as they live for several years or for more than a thousand years sometimes. This life activity of plants affects environment in a very ingenious way. Especially the activity affects human life much in an unavoidably inevitable manner. The products generated in these plants return to nature after they stop life activities and decompose biologically. Generation and decomposition are mutually related to form a cycle, thus providing nutrition for new organisms.

However, since manmade high quality plastics do not decompose in natural environment, the cycle of generation and decomposition is broken to hinder environmental circulation.

Xylem (plants) is regenerated annually as carbohydrates and is very cheap, is abundantly supplied, and is a limited resource that cannot be used up. It is innumerably plentiful from perennial woods and bamboos to perennial trees that are not economical, to stems of annual reeds, to annual grasses that are stepped on at mountains and fields, to fallen leaves, to vegetables that are cultivated, to cuticles of grain and dried nuts, to stems, to leaves, to byproducts of food manufacturing, and to wastes from wood processing and food manufacturing. But those that are used in reality in our life are at the very least and extremely restricted.

Except fruits, most of stem plants in any species are divided into the following 3 categories: 5 to 45% of cellulose, 25 to 35% of he icellulose, and' 20 to 30% of lignin. Except the cases where woods are used as they are, only celluloses are extracted among them to manufacture pulp papers, cellophane films, artificial fibers (viscose), and plastics, and hemicellulose and lignin are extracted to disappear during hydrolysis with acid and alkali or are used as fuels or abandoned almost, thus causing other environmental problems.

Before explaining pretreatment of xylem powder in details, thermal decomposition by dry distillation and methods of surface treatment of xylem are described further. An absorbed water' contained in woods is evaporated when heated to about 100 °C. But when the temperature exceeds 100 °C, thermal decomposition sets in slowly as a structurally absorbed water is released and at 150 °C, decomposition speed become fast. At 180 to 300 °C, hemicellulose decomposes rapidly. As cellulose decompose at 240 to 400 °C and lignin at 250 to 550 °C, peaks of heat generation appear near 250, 300, and 400 °C. At this time, decomposition is vigorous and exothermal reaction occurs simultaneously. At 500 to 1000 °C, hydrogen is separated from carbides of 3 main components to become wood charcoal and peaks of wood gas generated near 700 °C are due mainly to this hydrogen.

The specific gravity of trees differs depending on the kind of trees. The kind having the greatest specific gravity is African ironwood, which is 1.49 g/cm². The kind having the lowest is Cuban Aeschynomene Hispidad, which is 0.044 g/cm². The specific gravity of chaff is 1.10 g/cm², and the apparent specific gravity of bulked chaff is 0.17 g/cm². Any xylem powder can be used in the present invention, but xylem powder of 0.1 to 1.5 g/cm² is preferably used. When the xylem powder is compared to general plastics, plastics are nothing more than the powder foamed 1 to 5 times. This means that the xylem powder materializes more strength the plastics having the same strength and weight. This is an additional advantage and characteristic. It is lighter because of apertures generated in xylem powder by the drying of absorbed water. The surfaces of apertures can be treated with rosin, and alum (Al2(S0)₃) or NaAl(S0₄)₂ to fill the apertures. Alum is precipitated on the surfaces of xylem powder to make a part of the surfaces hydrophobic. Simultaneously, the surfaces of xylem powder become more compatible with binders dissolved in water to give an effect of being dispersed deeply and enough mutually as if it is dyed deeply.

The xylem powder prepared in this manner is used widely as a plastic filler. In general, it is compounded in 20 to 60 wt% relative to plastics. Such plastics are injected materials of general-purpose plastics of PVC, PE, PP, etc. This is so because they can be made light in weight by using the average specific gravity of xylem powder of 0.3 to 0.9, xylem powder is environmentally friendly and available in a cheaper price than plastics, and its property is not worse than that of plastics. Xylem powder is mixed with the general-purpose resins mentioned above and molded such that it has characteristics similar to those of woods. And the powder is used for purposes similar to those of woods, but more excellent performances than those of woods are taken out for use. However in this case, xylem powder and plastics lose biodegradability. Also for one disadvantage, even though the xylem powder mentioned above is environmentally friendly, the direct use of woods obtained from cut trees without pretreatment is destructive to environment and consumes energy too much. Therefore, the present invention make it possible to use the stem cells of annual plants that are low in commercial value.

Among pretreatments of xylem, purification includes the removal of lignin, which can show change in time (change of properties as time passes by) if it is present in the compound. Especially, as time progresses after molding, lignin can turn into yellow or can cause chemical, physical, or morphological change. For another disadvantage, apertures between cells can exist in xylem powder from which water or absorbed water is evaporated after a drying process. Those apertures can sustain inside of them water or other components during the processes. Therefore, they may contain the materials that can cause change in time or may require much time and energy for drying the inside of xylem powder even though they are dried in a forced way. This is why the treatment of the surfaces is preferable. Lignin is not used in the present invention, but as mentioned above, lignin decomposes at the highest temperature. Therefore, it is not possible to separate lignin by using heat, before cellulose or hemicellulose.

One of the most important reasons why xylem powder is used in the present invention is that trees have a strength of 400 to 700 kg/cm² whereas general-purpose plastics have a strength same as or lower than that. Also for another reason, cellulose, a component of xylem, does not dissolve in water, differently from starch. Thus after molding, the shape does not collapse rapidly or property does not lower immediately, even though the powder contacts water directly.

Meanwhile, the gelatinization temperature or the glass transition temperature of starch is 55 to 95 °C. Thus if starch is used as a main biodegradable binder, starch is melted due to the temperature obtained from the contents higher than the glass transition temperature, in the case where the molded article is put in hot water or high frequency wave heaters (microwave oven) are used. Here, the physical shape of the molded article changes. When this happens, xylem powder blocks heat conduction. Thus even though it is used at a temperature higher than the transition temperature, the stability of shape is not hampered much.

Another very important point is that xylem powder is rather competitive naturally even when considering the cost of treatment chemicals and the processes necessary for changing starch properties in order to provide with a specific property.

As known very well, even though water contact the molded article having a high content of xylem powder during storage, transportation, and usage, the property of xylem powder do not lower immediately, and its resistance to water is excellent compared to the sheets having a high content of starch. This is one of the characteristics of the present invention. Pretreatment is preferably done to use xylem powder for the present invention. Pretreatment applied in the present invention is divided in general into simple treatment, processing treatment, and denaturation treatment.

The simple treatment includes pulverization of xylem, heating to remove water, selection of particles having homogeneous size, etc. The processing treatment is to make the surfaces of xylem powder hydrophilic for processing. And the denaturation treatment is to process once again the xylem powder treated in the simple and processing treatments.

The simple treatment of xylem powder removes barks of xylem, needless materials, etc. , pulverizes xylem to a proper size (fine particles) for usage, and - selects the pulverized xylem having a proper size for the next processes.

This process is to pulverize xylem and select the pulverized xylem having a proper size for using molded articles for general purpose and for using them cheaply. Making xylem powder is a simple process and includes various known methods such as pulverization, smashing, grinding, compression, explosion, and extruding, among which a proper method can be used, to then select with screens. The process is very simple but can be used for most of usages.

The processing treatment of xylem powder, in order to improve performance of the xylem powder treated in the simple treatment for desired purpose, soak the xylem powder in water, or - boil or dry by distillation the xylem powder to a temperature higher than that of the molding process to remove liquid phase materials such as an absorbed water inside xylem, pine resin, etc., and beat and refine like pulp aqueous solution to make cellulose molecules in the surfaces of the xylem powder advantageous for making hydrogen bonding.

In other words, the xylem powder completed with the simple treatment is boiled or heated (with steam, substantially) for 1 to 7 hours at 100 to 145 °C according to the usage. And absorbed water, pine resin, wax and resin components that can be decomposed or discharged at the temperature are removed and the xylem powder is soaked in water. In the process, boiling the xylem powder is for removing hydrophobicity of the surfaces of the xylem powder and refining celluloses in the surfaces, rather than for removing lignin. The xylem powder that is boiled and soaked in water gives up hydrophobicity to become hydrophilic.

The processing treatment can include all or a part of the processes described above according to the specific usage.

Pulverization, boiling, and dry distillation can be achieved by heating methods known generally in the art. Refinement of xylem powder in water can be achieved by mixing with a high shear mixer or by compressing with a roller softly. The processing treatment is enough for the sheets for general purposes. Such xylem powder completed with the processing treatment can be used for compounding as it is.

The denaturation treatment of xylem powder varies depending on the usage of molded articles. One example is starch denaturation. The treatment increases or decreases the density by compressing or explosion, - completely removes lignin from xylem powder colorizes beautifully or change colors by decoloration or dyeing, treats the surfaces of xylem powder, increases processing capacity further with pulp processes such as refining, beating, sizing, charging, and correcting, and includes esterfication and etherification by changing OH functionals existing in the cellulose molecules of the surfaces of xylem powder.

The denaturation treatment can be performed in a way proper for a part of characteristics of a process according to a specific usage.

Compression of woods is a known technology for increasing the strength of woods. As xylem powder is compressed, density is increased and apertures are removed. Thus its property is changed.

In the pulp industry, pulp is obtained by the mechanical pulp process that grinds woods and the chemical pulp process that treats woods with acid and/or alkali. During these processes, most of lignin is removed. There is a thermal mechanical pulp process in the mechanical pulp process. This heats woods at 100 to 145 °C before pulverization with a machine to soften xylem powder and then pulverize them. The chemical pulp process removes most of lignin to obtain pure pulp. However, loss ratios are large because hemicellulose is also grinded in the chemical pulp process. But in the process, xylem powder is boiled or heated by steam at 100 to 145 °C, as described in the processing treatment. If hydrophobicity of the surfaces is removed in the boiling or heating, the xylem powder soaked in water is not dried but is compounded as it contains lignin. A method of removing lignin is recently known in the art, that is a physical treatment, called explosion. One example includes explosion described in US Patent No. 5769934, where woods are treated with steam at high temperature and pressure, for example, 240 °C and 30 atm, for a short time (for example, 30 seconds) and pressure is then released abruptly to explode woods (like corn popping) , thereby obtaining micro-crystalline cellulose (MCC) .

Similarly, cellulose collection is obtained. Bulked chaff is such collection. If chaff is pressurized and heated similarly and pressure is dropped instantly, then chaff is exploded. In the present invention, chaff is also considered as xylem powder.

MCC is fine powder with the degree of polymerization of about 200. But its property and phase does not differ much from pulp cellulose hydrolyzed by acid that is used widely in the prior art. By the method of manufacturing MCC, one can obtain better cellulose with lignin removed from xylem powder, more cheaply and easily than by the prior chemical treatment.

MCC obtained in this manner is compounded for matrixes for the purposes higher in class than those of the polymer matrixes completed with the simple treatment or the processing treatment. Xylem powder can be decolorized, dyed, or its surfaces can be treated, according to the usage. This means that if xylem powder needs more treatments after pulverization, boiling, and sorting, a process of filling apertures that become empty due to the removal of the contents and are generated in the stem cells of xylem powder, by treating chemically with pine resin, alum, etc., can be added.

Apertures are filled by the treatment of pine resin, and alum (A12(S0)₃) or NaAl(S0₄)₂). Alum makes a part of the surfaces of xylem powder hydrophobic by precipitating on the surfaces. Also, the surfaces become more compatible with the binders dissolved in water to provide the effect of dispersion and adherence for a sufficiently long time as if they are dyed deep into the fibers.

One of the very important reasons why xylem powder is treated in advance, particularly boiled in water and refined, is to provide a bridging condition for xylem powder to mutually bind to fibroid materials and binders physico-chemically strong. This is to induce those components mentioned above, i.e., xylem powder, fibroid materials, starch and a group of binders to form chemical bonds though condensation reaction, that is, hydrogen bonding.

For a similar example, in the case of FRP or SMC resin, coupling agents such as silane or titanate are added to increase the binding force to added unsaturated polyester resin and glass wool (fiber, cloth) . If coupling agents are added, the surfaces of glass ad resins bind strong. Eventually, thus, molded articles of glass reinforced polyester are formed, having a stronger strength. Like coupling in molded articles of FRP, hydrogen bonding formed through condensation between glucoses increases the property of molded articles through bridging between components.

The xylem powder treated in advance with a process or various processes mentioned above is preferably compounded with OH functionals in cellulose of the xylem powder surfaces that are dissociated in water, as shown in FIG. 3 to be shown later, in order to bind to other polysaccharides of the polymer matrix physically and chemically. The situation where the xylem powder is dissociated in water means a situation similar to that where pulp is at a colloidal state in water. However, it is physically impossible to dissociate xylem powder completely in water like pulp liquids. Thus it is sufficient for the usage of the present invention to soak the surfaces of xylem powder in water. If water is dried again in this case, cellulose molecules in the surfaces and molecules of the fibroid materials and starch molecules give up water to undergo condensation reaction like Chemical Formula 4 to be described later. As a result, a strong binding forms mutually between three molecules in cellulose (in xylem powder and fibroid materials) , starch, and the group of binders.

The sheets coupled in a mutually organic manner can be processed in various shapes at the instant when the binding get loose due to the supply of heat or water. It is said in this case that the sheets ^Λhave plasticity.' This characteristic is unique to the present invention and cannot be found in other woods or papers.

The molded articles manufactured with the compound of the present invention can have a limited plasticity because the group of binders contains (aqueous) thermoplastic resins, starch chain and organic synthetic binder resins, and hydrogen bonding gets loose as they contact water and heat, and thus a part of them become soft.

These materials can be restored to materials having strong binding force again by drying. They show the binding force of polymer matrixes stronger than the binding force of the group of binders alone. This is a characteristic of the present invention, which is one of its very important functions.

Papers having the same hydrogen bonding do not show plasticity by heat or water. This is so because they consist of pulp fibers not having drawing property and elasticity at all. In the present invention, starch and the group of binders play the role of cohesive agents, thus showing other physical phenomena differently from hydrogen bonded materials such as papers. In the present invention, the degree of thermal plasticity is not affected absolutely by the amounts of starch, synthetic binders, and plasticizers .

Also, another pretreatment of xylem powder includes a process of denatuing xylem powder chemically. This includes the substitution of three OH functionals in the cellulose molecules of xylem powder with acetic acid, nitric acid, sulfuric acid, phosphoric acid, butylic acid, benzylic acid and laulylic acid, and other polyhydric alcohols. In this case, the xylem powder is denatured or its surface treatments are performed. By using this property, resistance to water is increased and on the contrary, biodegradability is decreased. But property can be controlled according to the usage.

The simple treatment, the purification treatment, and the denaturation treatment described above may all be performed or simply, simple pulverization and sizing alone may be performed, according to the usage. However, the molded articles of the compound of the present invention are aimed at container and sheets of general purposes that are very cheap disposables, and the general usage. Thus preferably, the xylem required in the present invention is literally cheap xylem powder whose hydrophobicity only is removed rather than cellulose materials of high price that are pure or denatured like those hydrolyzed by acid, exploded, esterified or etherified. The size of the xylem powder that can be applied for the present invention is more than 50 mesh, preferably more than 80 mesh, more preferably more than 100 mesh. But the smaller the size is, the higher the cost is. Thus the xylem is pulverized properly for the usage.

The treatments described above make it possible to properly utilized the xylem powder, etc. that are wasted until now and to use the xylem powder that has been used for insignificant purposes and the natural material wastes for the purposes in which added value is high.

In the present invention, the added amount of xylem powder for compounding is 1 to 90 wt% relative to the total solid material.

B. Group of binders

In the present invention, a binder plays a very important role in that it coheres all the composite components contained in the polymer matrix compound to provide a physical strength so as to sustain the shape of molded articles. Another important role of binder is that plasticity generated when heated allows the compound or the primary molded articles to be molded again into other shapes through re-processing.

The binding force of molded articles maintains the shape basically with the cohesive force of binder before molding and in addition to the cohesive force, the hydrogen bonding between constituents generated after drying makes the molded articles stronger. Starch and organic synthetic binders are distributed homogeneously in the matrix constituents. Thus it is preferable to compound them in such a way that the cohesive force and the hydrogen bonding force are balanced due to the arrangement of the compounded amounts of constituents. The binders' mentioned above are mixed in the matrix before use to make a group of binders, i.e., a mixture of organic synthetic binders as a main binder and natural binders as a supplementary binder. Here in the present invention, a binder' means a group of binders, if a separate modification or explanation is not expressed.

The polymer matrix displays its strength and properties by drying aqueous or water-dispersed organic synthetic polymer binders and starch binders that are dissolved in water. Polymer compositions can exhibit workability and fluidity by adding water to the matrix in an amount proper for forming a mixture that has properties similar to those of plastics. Afterward, the group of aqueous binders is induced to show a synergy effect such that it is bound to the compound through the removal of water by evaporation so as to exhibit maximum strength.

The compounding ratio of components of the polymer matrix compound and the addition of water as a solvent and a viscosity controller affect significantly rheology of a mixture that is compounded for moldability, especially the matrix containing ^λa group of binders' that can be dissolved under the presence of water.

The group of aqueous or water-dispersed polymer binders considered in the present invention is classified into the following categories, which are compounded properly for each usage before use.

(1) aqueous and water-dispersed synthetic resin that has thermal plasticity at a prescribed temperature;

(2) aqueous and water-dispersed natural resin that has thermal plasticity at a prescribed temperature; (3) aqueous and water-dispersed resin that has the characteristics of hardening by heat (gelling by heat or syneresis hardening) (4) starch, generally non-denatured starch granules

(5) polysaccharides compatible with starch and cellulose, and other organic thickeners or binders such as proteins and synthetic organic materials. A ^Λgroup of binders' combined in this manner has softening point or glass transition temperature, etc. to induce to compound the matrix having thermal plasticity, thereby having a prescribed temperature characteristic. The latter characteristic means that the compound of the present invention is molded to an initial molded article, which is then given plasticity by heating like plastics, and finally the resulting material can be processed for molding.

1. Main binder (organic synthetic binder)

The organic synthetic binder as a main binder of the present invention is contained in the compound, in an amount far smaller than that of xylem and grain powders as main components of the compound. Any aqueous resins that have thermal plasticity and syneresis hardening property can be used for this purpose.

Therefore, water-dispersed organic synthetic binders can be used. Good examples of them include polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene glycol, polyvinylmethyl ether, polyacrylic acid, polyacrylate, polyvinylacrylic acid, polyvinylacrylate, polyacrylimide, ethyleneoxide polymer, polylactic acid, latex (containing various polymerizable materials that can form aqueous emulsions like styrene-butadiene copolymer) , and a mixture or a derivative thereof.

Among the polymers mentioned above, the present inventions have noted biodegradability of various aqueous synthetic resins such as polyvinyl alcohol, cellulose ether, etc., simultaneously polymer performance when dried, thermal plasticity and syneresis hardening property when heated. The present invention is completed by noting that strong binding force appears when constituents of these polymers are interacted, plasticity or syneresis hardening property is exhibited when heated, thus they can be formed in a required shape, and they decompose easily when abandoned. < a) Polyvinyl alcohol (PVA) Polyvinyl alcohol is a synthetic polymer expressed in Chemical Formula 1 and is a representative product among aqueous synthetic polymers. Its appearance is white to pale yellow powder and its softening point 220 °C (144 °C for recently developed one) and its specific gravity about 1.19 to 1.31 °C. It is frequently used for various usages in addition to Vinylon fiber. Its biodegradability is widely known already and is still being studied in detail for decomposition structures and enzymes in relation to environmental contamination problems

¹ Chemical Formula 1

- (CH₂-CH)m - (CH₂-CH)n- I I

OH 0 I

CO I CH₃

As shown in Chemical Formula 1, polyvinyl alcohol has in reality a structure where vinylacetate and vinyl alcohol are polymerized in a mixed manner, and a copolymer of their combination. Depending on their constituent ratio, the characteristics vary and have various SVs Like pulp, starch, and xylem powder, polyvinyl alcohol can form hydrogen bonding with xylem powder, starch, and fibroid materials through syneresis reaction of OH functional contained in a straight chain. If water is removed from aqueous solution and it binds to constitutents of the matrix, resistance to water is generated and the physical phase and property is strengthened. This is also one of the most important phenomena noticed by the present inventor.

Through the OH functional, polyvinyl alcohol decomposes slowly in aqueous solution. But in air, the decomposition mechanism does not function. The evidence for this is that Vinylon fiber does not change its properties even though it is manufactured by spinning, processing by heat treatment, and drawing polyvinyl alcohol as a raw material. Polyvinyl alcohol is used in various usages for construction, reinforcing agents of cements, heat isolation fibers for agriculture, etc. It has been used as it is since it does not change in air for several years.

However, film of polyvinyl alcohol molded after heat treatment as well as general polyvinyl alcohol is degraded biologically or deteriorated in water by enzymes. This mechanism is known to be a decomposition mechanism same as that of polyhydrooxybutylate (PHB) . For a reference, polyvinyl alcohol film having a thickness of 40 μ starts to be deteriorated by Pseudomonas bacteria at 30 °C in water, in 21 days. It is confirmed that on the 28^th day, the strength reduces to 1/2, with the appearance unchanged. (Practical Technologies of Biodegradable Plastics, p 70-81, Japan, CMC 2001)

Polyvinly alcohol has the characteristics of film moldability, transparency, rigidity, surface activity. Therefore, it can be used in various fields of papers, woods, adhesives, milks, suspension liquids, etc. Especially, polyvinyl alcohol film has excellent air isolation property. Completely saponified PVA has a softening point that is very close to thermal decomposition temperature. Thus the PVA lacks melting moldability. Partially saponified PVA is lower in thermal stability. Thus it is modified to have thermal plasticity for use.

Currently, PVA resin is manufactured by molding film through melting in aqueous solution. However, PVA has various disadvantages in that it is difficult to manufacture using thermal plasticity. The disadvantages include that since general PVA has the softening point near 225 °C and decomposes at 230 to 300 °C, it is difficult to process by heating it to the temperature similar to the case of carbohydrate binders, and since the PVA is hygroscopic, the dimensional stability of molded articles become very bad.

The reason why PVA resin having very bad moldabilities can be used in the present invention is that since it is used as a functional assistant, whose added amount is small, molding is possible, and the sheets of the present invention require strong cohesive force and biodegradability as a disposable rather than precise processing and dimensional stability after molding that are needed in engineering plastics. However, the property are not fatal enough to exclude its use in the present invention. Therefore, we have looked for various PVAs and were able to find aqueous PVAs that are modified to have a softening point of 144 °C, at which constituents of the present invention do not decompose. PVA is used in the present invention for very important reasons that follow. The resin is aqueous. The OH functional existing in the straight chain can be substituted with various functional materials. Thus it can be denatured to PVA polymers having various characteristics. When hardened, all the OH functionals of constituents undergo condensation polymerization with neighboring constituents to form bridges so as to provide very strong binding force and hydrophobicity. Especially in this case, the molecules of constituents use up their OH functionals that can bind to other constituents. Thus the polymerized PVA has a strong hydrophobicity and a structural characteristic that do not allow binding to or penetration by water or other materials. Also, other very important characteristics of PVA are limited plasticity and flexibility exhibited without water when temperature reaches a prescribed temperature. Thus the compound of the present invention can be molded through re-processing. The PVA resin modified for a particular purpose is completely dissolved alone in water and shows 22 MI (melt index, g/10 min, ASTM D 1238) at maximum at 195 to 225 °C inside the cylinder of the processor. This is a melt index similar to those of general olefin resin for blow molding and resin for casting, meaning that PVA resin can be molded to film or laminated without separate addition of water.

As described above, PVA is compounded as a main binder to the sheets of the present invention to exhibit a prescribed binding force and a sufficient molding effect.

Therefore, it is possible to mold an intermediate molded article and to re-process the intermediate after water is dried, using the polymer matrix compound of the present invention that is compounded to constituents in a type of aqueous and water- dispersed slurry. In this case, if the molded article is extruded again or heated when processed, it can show a melt index of 0.1 to 25 MI. Depending on the combination of a group of binders and the amount of compounding, the compound can be molded into a final molded article in the initial stage.

Since PVA has strong viscosity and adhesive force, it is widely used as aqueous adhesives. Therefore, when molding with the compound containing PVA, it may be difficult to design processing processes since it may stick to molders. When this phenomenon occurs, it is preferable to mold after hardening the surfaces at first, by mixing with the binder having the thermal gelling (syneresis hardening) characteristic, b) Cellulose derivatives

Cellulose derivatives soluble in water can be utilized as a binder in the present invention. Cellulose derivatives preferable for the present invention are celluloses that can be esterified and have thermal gelling characteristic. These include methylhydroxymethylcellulose, hydroxymethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, hydoxyethylcellulose, hydroxyethylpropylcellulose, hydroxypropylmethylcellulose or a mixture or a derivative thereof. Other celluloses can be used that have the thermal gelling property when heated.

Since the kind of cellulose ether is aqueous, it is soluble in water. If a specific cellulose soluble in water increases in temperature, its viscosity increases and thermal gel appears. A particular cellulose has thermal gelling temperature. When the cellulose ether is heated above a prescribed gelling temperature, the OH functional of the ether in the compounded material releases water (called syneresis phenomenon) to be hardened by bindings between molecules. This phenomenon is called ^thermal gelling' or ^hardening by the syneresis phenomenon' , which is a kind of thermal hardening. This phenomenon is similar to the phenomenon and type where amylose molecules retrograded in starch give up water to be condensed. When this phenomenon occurs, it accompanies chemical and structural changes in the matrix. In other words, a specific cellulose ether is a polymer that has a gelling temperature due to the syneresis phenomenon between molecules, is aqueous at room temperature, and contracts and hardens as viscosity increases when a prescribed temperature is reached.

Favored cellulose ethers are based on methylcellulose and a mixture of celluloses having various syneresis gelling temperatures can be used.

The Methocel catalogue of Dow Chemicals, USA show various cellulose ether products that can be used for foods. These include the SG A series at 38 to 44 °C and the A series at 50 to 55 °C of methylcellulose and the E series at 58 to 64 °C, the F series at 62 to 68 °C, and the K series at 70 to 90 °C of hydroxypropylmethylcellulose, etc., having each inherent thermal gelling temperature.

If cellulose ether is heated above the inherent gelling temperature to be gelled, its binding force to and its compatibility with starch increase but lubricating and isolating properties also increase in relation to the outside. These phenomena are due- to bridging by condensation of cellulose molecules. There are many research reports showing that by using these phenomena, cellulose is coated on the surfaces of various foods to give a rich feeling to the products, to lower the adhesive forces of the surfaces, and to increase the preservation power due to the increased adhesive forces.

An artisan having ordinary skills in the field would know that in order to reduce the adhesion between the rollers and the sheets during the sheet formation process, it is preferable to choose, for designing the processes of the present invention, appropriate cellulose ethers that have the thermal gelling temperature lower than the gelatinization temperature of starch granules. c) Assistant binder

Biodegradable natural polymers that are dissolved or dispersed in water or alcohol can be added to the main binder of the present invention for supplementary use. Natural polysaccharide binders that can be used include alginic acid, picocolloid, agar, Arabian gum, guar gum, locust bean gum, karaya gum, xanthan gum, tragacanth rubber, and a mixture or a derivative thereof. Appropriate binders based on proteins include zein (prolamine derived from zein corn) , collagen (extracted from stroma or bones of animals) , derivatives of gelatin or glue, casein (main proteins of milk) , a mixture or a derivative thereof. Additionally when the natural polymer mentioned above is used as an assistant binder for compounding, it delays • starch' s dissolution in water. d) Function and role of main binders

One of the largest characteristics of the present invention is that by using condensation reaction between various types of glucoses, mutually organic binding force is derived, whereas PVA and cellulose ether use another type of condensation reactions.

The syneresis phenomenon can reduce adhesive forces between the compound surfaces and processing machines by hardening the surfaces of molded articles through the hardening of the wet compound surfaces. In other words, when heated the cast compound, the compound surfaces harden. Thus during the subsequent stages of the formation process, starch is gelatinized and dried. But this prevents the compound having adhesive property from being stuck to the rollers of forming sheets.

A specific study on compatibilities between cellulose ether and PVA can be found in Journal of Applied Polymer Science (USA) , vol. 80, no. 10, pp. 1825-1834, June 2001. Here, one can find the resulting materials of hydrogen bonding between two molecules in details.

Simultaneously, hydrogen bonding between starch and pulp cellulose is a known fact. Therefore, mutual hydrogen bonding between PVA, cellulose ether, pulp and starch produces grafted block copoly erization. In addition to this, the xylem powder in which cellulose molecules on the surfaces are activated shows a synergy effect. Differently from compounding water, this induces binding between active OH functionals in the branches of polysaccharide molecules that have OH functionals among the constituents of the present invention, including PVA, starch, xylem powder, and pulp fiber. And the binder itself is kicked out by condensation reaction to make thermoplastic grafted block copolymers of natural materials that have dried biodegradability.

In other words, the functions and roles of binders, i.e., ^λmain binders,' supplementary binders,' and ^assistant binders' is to make thermoplastic grafted block copolymers of natural materials that have dried biodegradability, by inducing binding between active OH functionals in the branches of polysaccharide molecules that have OH functionals among the constituents of the present invention, including xylem powder and pulp fiber.

Molded using the method described above, the sheets of high quality have larger elasticity, tensile strength, and hydrophobicity.

2. Supplementary binder

a. Outline

As used herein, the term ^grain' is a common name of unprocessed carbohydrates, especially the source of starch. As starch of carbohydrates contained inside grain, the grain not only plays a binder role in cohering strongly composite components inside the biodegradable polymer matrix of the present invention. But as the volume of grain added, it plays a good filler and contributes to strengthening cohesive forces of the compound by providing fibroid materials supplied from the cuticles of grain.

Grain powder, especially starch contained in the grain powder, also exhibits a certain limited thermal plasticity when heated, just like the organic synthetic binders mentioned above. Thus it makes re-molding possible.

The natural binders of the present invention use cohesive forces of starch, which will be supplied from grain powder obtained by pulverizing grain, or pure starch. To use for compounding, direct pulverization of grain is an attempt to ensure a competitive edge in price. But it is also preferable to choose pure starch depending on the use of molded articles and the desired property.

The representative grain that can be used in the present invention includes grain crops such as rice, glutinous rice, barley, wheat, corn, glutinous corn, Indian millet, millet, and oat. But for convenience, it also includes potatoes such as white potato, sweet potato, tapioca, etc. In addition to them, plants containing starch are also included in the category of grain, since all the crops mentioned above are the sources of unprocessed starch for the present invention.

In the present invention, grain has another characteristic in that after removing foreign materials, it can be pulverized for a direct use. However when grain contains much unnecessary materials that do not have an effective value to the present invention or can hamper the performance of the present invention, such as proteins, lignin, milk fat, embryo, etc., they can be separated, selected, modified, denatured, or treated in advance before use when necessary according to the usage.

The amount of starch content contained in grain, especially the ratio of amylose to amylofactin, and the amount of fibroid contents, water, unnecessary materials, etc. should be measured precisely beforehand. It is compounded properly together with other mixtures by controlling the amount with water of desired compounding. Naturally for using it in the next processes, an artisan having ordinary skill in the field should precisely measure the glass transition and gelatinization temperatures of starch before compounding and the sheeting process.

Grain is naturally cheaper than processed starch and rather more excellent in the performance and the resulting synergy effect than pure starch.

In the present invention, starch is supplied as carbohydrates contained in grain. Grain powder in the present invention contains fibroid materials, but at the same time, the starch contained in grain powder also belongs to the category of binger group. Therefore, starch plays both a supplementary binder and a filler of the compound in the present invention. When forming sheets filled with composite components, only a main binder of aqueous organic synthetic binders can be used without a supplementary binder. Even so, the cost of using a main binder only is far higher than that of using a group of binders in which main and supplementary binders are mixed. Hence, it is economically rational to use a mixture of starch and a small amount of organic synthetic binders.

The compound of the present invention shows the strength required for hardening of organic synthetic binders through water removal due to evaporation, hardening of gelatinized starch, and bridging of the surface cellulose and starch.

Starch is a chain of natural carbohydrates that contain polymerized glucose molecules found in the granule type. Starch granules contain two different kinds of glucose units: branchless single chain amylose and branched multiple chain amylofactin. Two different glucoses show different property. The role of binders of carbohydrates, fibroid materials, etc. contained in grain, especially starch, will be mentioned again later. b. Pretreatment of grain Grain is treated in advance due to various reasons. The first pretreatment is pulverization. Grains should be pulverized in a prescribed size homogeneously, so that various additives should be mixed uniformly in the compound.

Pretreatment is to obtain property enough for the molded articles to be used in the daily life after mixing grain with other components. Especially, the molded articles should have the strength such that they can maintain their initial shapes until they are used. And by giving the molded articles, especially the starch component, hydrophobicity, their property should not be reduced abruptly, which might occur when component are dissolved in contact with water. Therefore, this pretreatment is to ensure enough property that is expected when compounding.

Additional treatment is to physically coat and chemically treat the starch by • sing the property of polymers in starch contained in grain powder. For example, hydrophobicity and fluidity are given, starch is decolorized and dyed, the gel strength is modified, etc. All this can be called the denaturation of starch. Starch are classified into water resistant starch, acid- processed starch, oxidized starch, derived starch, etc., depending on the denaturation method. Denatured starches are the starch where grain powder is provided with strong water repellency by mixing grain with a water repellant agent, the alpha starch obtained by dehydrating rapidly after the starch component is gelatinized in advance before compounding, the decomposition- product by heat, acid, and enzymes, the starch derivatives in which the chains of starch are attached to various functionals, by esterfication or etherification, etc., the starch provided with hydrophobicity by substituting the OH functionals of starch molecules, etc. There are many pretreatment methods known in the art, which are commercialized in the market and used widely. c. Binding function of grain powder

Starch and cellulose have a structure that is made from a polysaccharide molecule unit shown in Chemical Formula 2. In the structure of Chemical Formula 2, Rl, R2, and R3 are basically an

OH functional, but when denatured, they can be substituted with the same or different functional.

Chemical Formula 2

Different from starch having a similar structure, cellulose has different hydrophilicity and solubility in water. These differences are due to the difference of the bonding methods of carbons 1 and 4 of the straight chain in the arrangement of connection loops between polysaccharide molecules. On the contrary, starch shows a very rapid biodegradability and solubility in water. Therefore, the characteristics of starch need to be changed such that shape deformation and decomposition of molded articles are delayed even in contact with water.

As described above, denaturation methods of starch are known and commercialized according to the usage. To provide hydrophobicity for the above structured starch, starch (grain power in reality) can be treated in advance. As explained in b above, there are many pretreatment (denaturation) methods of starch. This means that the three OH functionals indicated as Rl, R2, and R3 are substituted with acetic acid, nitric acid, or other polyhydric alcohol, or the surfaces of starch is coated.

Surface characteristics of starch, cellulose, and xylem powder

The surface of pulp or xylem powder, i.e. cellulose, s anionic. Therefore, if cationic starch is used where the OH functionals of starch molecules are substituted with quaternary amine-based organic compounds, then the binding force between additives is increased to improve the physical strength by which starch interacts with cellulose, since the starch has a strong affinity with cellulose fibrils and additives. In this case, the substituent that binds to the OH functionals of starch through ether bonding is quaternary amine. In this manner, one can induce a 3-dimensioally stable bonding.

This characteristic is widely used currently in paper manufacturing processes, especially the process of strengthening the bond between starch and pulp and the process of pulp sizing,

Gelatinization of starch

In general, starch granules are not soluble in cold water. But if the outside membranes of the granules are destructed by grinding, etc., then starch is swelled to form gel. The precise temperature where starch binders are swelled and gelatinized depends on the kind of starch. Gelatinization results from swelling due to decomposition of linear amylose polymer granules that were compressed in the granules initially. Many changes occur during the process of increasing temperature to 100 °C in the suspended state in enough water. When non-denatured granules are exposed in warm water, they swell and soluble starch (amylose) diffuses through the wall of the granules to form paste. In hot water, the granules break down to swell enough to gelatinize the mixture.

Initially, swelling is slow, but if a specific temperature is reached, irreversible change occurs more rapidly to increase the viscosity of starch liquid. This accompanies the collapse of molecular configuration inside. At this point, the crystallinity of starch particles is lost and the sensitivity to hydrolysis by enzymes and the solubility change of starch are accompanied.

Various natural starches have a great variety of gelatinization temperatures. For example, potato starches have the temperature of 59 to 68 °C, corn starches that of 62 to 95 °C, and glutinous corn starches that of 63 to 72 °C. All grain crops and potatoes are used for supply of starch in the present invention. At the temperature, starch granules start to swell irreversibly. Swelling increases with temperature. The viscosity of starch liquid increases depending on the swelling and bursting of ^• starch granules and the degree of exposure of materials inside.

In the aspect of processability, the gelatinization temperature is one of the important characteristics that require a strict management in the binder molding process. Gelatinization implies that starch granules become more compatible and sensitive to enzyme actions, and this is an important characteristic in the molding stage of the present invention. Especially the gelatinization temperature is intimately utilized in applying the temperature to control cohesive forces in the processes that use starch as a binder. The cohesive forces before and after gelatinization and the force after drying, especially the difference in viscoelasticity should be grasped before using starch in the molding processes of the present invention. Otherwise, unexpected variations in the shape stability, the dimensional stability, and the foaming magnification ratio of the molded articles might occur.

Completely gelatinized starch can be used for the constituents of the biodegradable polymer matrix compound of the present invention. However in this case, the starch tends inevitably to stick to the molding machine during the processes. Thus the processes should be designed in preparation for such incidences.

Non-denatured starch-based binders of are cheap in price and thus they are favored compared to denatured starch-based binders. Especially, non-denatured starch is not gelatinized until the instant when temperature is heated to the gelatinization temperature.

Since a pure starch composition can absorb water vapor from the air near by, water exists in 10 to 12 wt% of the total weight of the composition. When an additive is added to a starch composition, water exists in 3 to 6 wt% of the total weight since the composition contains a smaller amount of starch, d. Pulverization of grain and size As for grain pulverization, the grain mentioned above should be pulverized enough to have a proper size for each usage before use. By using known methods, cuticles and contents should be pulverized homogeneously. When grain is pulverized, the temperature increase should be prevented to avoid the gelatinization of starch contained in the grain. When pulverized, temperature increases due to the frictional heat of grain, which may cause grain to be gelatinized. Grain is pulverized to be more than 50 mesh, preferably more than 100 mesh. By mixing it with other components evenly, it can be used, as a compound component, for direct compounding. e. Amount of grain powder for compounding

In the present invention, the concentration of natural binders in the form of grain powder is 5 to 90 wt% relative to the total solid binder group, preferably 20 to 80 wt%, more preferably 30 to 70 wt%. f. Physical property of molded articles

When the polymer matrix of the present invention containing grain powder, fibroid materials, starch and a group of binders forms a solid material, the matrix can have a tensile strength of 40 to 50 MPa. The sheets of the present invention reinforced with fibroid materials can have the tensile strength of 100 Mpa at maximum, depending on the kind and concentration of the starch, fibroid materials, and binders in the sheets.

Even with the methods described above, the current technology does not allow starch to be perfectly hydrophobic and to have a perfect polymeric binding with other components, like the prior plastics. However, starch can prevent water penetration for a significant period of time and can have a binding force sufficient to be used for the period. Thus it does not present many difficulties to be used as a disposable.

3. Supplementation of function for binders

In the matrix compound of the present invention, aqueous synthetic binders and starch binders are favored and used basically. Even so, additional organic binders can be used in a supplementary manner.

Having various properties and thermal deformation characteristics, cellulose ether can be used as a supplementary member. When PVA is a main binder, a cellulose ether-based resin can be preferably an assistant binder. When cellulose resin is a main binder, PVA is preferably an assistant binder. Cellulose ether dissolves in water. Proper cellulose ethers include ethylhydroxyethylcellulose, hydroxymethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxyethylpropylcellulose, a mixture or a derivative thereof.

Cellulose ether as a favored assistant binder is methylcellulose. Most of methylcellulose ethers have the hardening temperature of about 70 to 85 °C. Other cellulose ethers having the thermal gelling characteristic can be used as an assistant binder.

As an assistant binder, a synthetic binder selected from the group consisting of polyvinyl pyrrolidone, polyethylene glycol, polyvinylmethyl ether, polyacrylic acid, polyacrylate, polyvinylacrylic acid, polyvinylacrylate, polyacryl imide, polylactic acid, ethylene oxide polymer, latex, a mixture or a derivative thereof can be used as a supplementary member.

Polysaccharide selected from the group consisting of alginic acid, picocolloid, agar, Arabian gum, guar gum, locust bean gum, karaya gum, xanthan gum, tragacanth rubber, and a mixture or a derivative thereof can be used as a supplementary member .

Natural proteins selected from the group consisting of prolamine, collagen, gelatin, glue, casein, a mixture or a derivative thereof can be used as a supplementary member.

An artisan having ordinary skills in the field would know how to choose cellulose ether that has the syneresis hardening temperature lower than the gelatinization temperature of starch granules.

4. Function and role of binders during the hardening reaction of the compound

When sheet are manufactured using extrusion and roller processes, organic synthetic binders (including cellulose-based resin) may provide the optimal performance. Even so, they are very expensive, compared to other constituents used in manufacturing sheets.

Starch is a good binder and cheaper than organic synthetic binders are. But when starch is used as a binder in the sheet formation process, it sticks sheets to rollers due to the strong sticking property. Thus starch makes large scale production difficult.

The present invention uses, as the supply source of starch, grain powder instead of a large amount of organic synthetic binders. The combination of a small amount of organic synthetic binders and a large amount of grain powder binders alleviates the disadvantages that appear when each is used separately. Also, the combination prevents the adhesion of starch to the rollers during the formation process of molded articles and thus reduces the cost of manufacturing sheets greatly. Additionally, if a large amount of grain powder is included, the sheets are stronger than those including a large amount of organic synthetic binders, and are not much fragile.

Therefore, when a specific organic synthetic binder is used, it acts as a binder of forming coated films in the formed sheets. When the starch inside the sheets is gelatinized and is dried by water removal due to vaporization afterward, the starch becomes a main binder to bind other solid components inside the matrix of the sheet.

Since xylem and grain powders themselves have fibroid materials, they can provide an additional dimensional stability to molded articles. At the same time, xylem powder is not only less expensive than processed starch, but an excellent natural binder. Thus with the cost far less than that of the sheets using organic synthetic binders as an only binder, a fairly high quality of sheets can be manufactured. Therefore, the method of molding the composition used for forming the sheets of the present invention includes the step of mixing water, fibroid materials, and binders using a high shear mixing method, in order to form a mixture in which xylem powder and fibroid materials are dispersed homogeneously. Afterward, non-denatured starch granules contained in the grain powder, additives, and other assistant additives are mixed to form the compound..The fibroid materials in the dried sheet are dispersed homogeneously, as a reinforcing agent, in the entire matrix. Here, water can be added additionally to control the viscosity. If not the process of casting on the coated films supplied by a conveyer, sheets are formed through molding rollers. In this case, the sheets formed out of the compound in the sheet formation process pass through between a set of heated rollers. Starch granules are protected by the coated films hardened on the surfaces of the sheets. This protection prevents starch from being sticked to the rollers when starch granules are gelatinized.

In order to form the surfaces of organic synthetic binders on the surfaces of the sheets before gelatinization of starch, the starch-based binders favored in this process are non- denatured starch that is gelatinized at a temperature higher than the syneresis hardening temperature of organic synthetic binders

5. Chemical bonding between xylem powder, pulp cellulose, and a group of binders

Binder achieves the role and purpose by materializing the binding strength between constituents. After molded in a desired shape, it is better to maintain the shape stronger.

The reason xylem and grain powders are mixed for use in the present invention is very important and different from that the same volume of inorganic additives is mixed as an organic synthetic binder to a mixture to manufacture a matrix. One of the important reasons is explained with the following Chemical Formulae.

Chemical Formulae 3a and 3b.

Chemical Formula 4

Chemical Formula 3a shows HO and H of two hydrated glucose molecules loosely held together. As they are dehydrated, water (H₂0) is condensed out as shown in Chemical Formula 3b to form a strong ether bond in the type of single oxygen link as shown in Chemical Formula 4. If starch is coated on a paper, a part of starch reacts with cellulose pulp to form a bridge on the surfaces of the paper. Similarly, parts of OH functionals undergo condensation reaction with starch monomers in the dehydration process to form very strong physicochemical bonds.

The case where xylem powder and starch undergo grafted polymerization through organic bridging shows a physical strength in molded articles, as if they form grafted polymerization, much significantly different from that where inorganic additives are added to a mixture and just occupy a volume. The dehydration bridging' phenomenon due to condensation reaction is the source of the difference.

As described above and will be done again later, the increase in the bursting strength of paper due to hydrogen bonding between dissociated pulp and starch, and the bridging between PVA and cellulose ether, namely the reaction shown in

Chemical Formulae 3 and 4, is widely known already.

The present inventor understands that the polymer matrix compound is a very characteristic polymer obtained by condensation polymerization between natural materials, and is a thermoplastic grafted block copolymer of xylem powder/pulp/starch/binders .

C. Fibroid material

In the present invention, fibroid materials are contained in, the xylem and grain components. Nevertheless, various types of fibroid materials are used in the present invention to entail a good result. 'Fibroid materials' are a common name for various

'fibers.' 'Fibers,' 'fibroid materials,' and 'fibroid raw materials' means both inorganic and organic fibers. Fibroid materials are added to the compound in order to increase elasticity, ductility, flexibility, cohesive property, drawing property, bending property, rupture energy, bending and tensile strengths. Sheets or products manufactured thereform are damaged when cutting molded articles (when section forces are applied) . Fibroid materials that can be contained in sheets or the matrix of molded products include naturally produced organic fibers such as pulp, hemp, cotton, leaves of plants, cellulose extracted from woods or stems. Rich fibers harvested in agriculture and the industry related to forestry can be utilized in the present invention.

Depending on the situation, 'regenerated fibers' can be used instead. 'Regenerated fibers' include waste papers, regenerated papers, regenerated pulp, regenerated fibers, viscous fibers, 'twined fibers,' etc.

Among constituents of plants, especially cellulose exists in fibrous resin inherently. There are three OH functionals in the resin molecule in such a way that antihydrophilicity and antihydrophobicity coexist. Cellulose, especially pulp fibers, swells in water. When they swell, shapes are formed and then by removing water, papers are manufactured. When swelled cellulose fibers are dried, they give off water and form strong bonds between OH functionals of cellulose fibers through condensation reaction. The binding mechanism of the polymer matrix sheets of the present invention is due to hydrogen bonding between cellulose and starch contained in xylem powder, and mutual bonding between the composite components of the group of binders, fibroid materials, and other mixtures. However, fibroid materials act as a component to reinforce cohesive forces and to provide tensile strength and elasticity. But the binding is not as strong as hydrogen bonding. Thus fibroid materials do not provide a strong binding to the extent that the prior papers depend solely on hydrogen. In harmony of the physicochemical binding forces, for example, the cohesive force between organic synthetic binders and starch, the physical cohesive force due to the viscoelasticity between cellulose contained in xylem powder, starch, binders, and pulp fibers, and the hydrogen bonding force, the sheets molded out of the polymer matrix compound of the present invention shows strength and property, not worse than those of the prior polymers produced by the prior petrochemistry.

Characteristics of cellulose

In general, the strong binding force of papers made from pulp is due not only to the cohesive force of the sizing agent and the thermoplastic resin contained in papers but also to the OH bonding between fibrils of pulp bound again.

The- characteristics of fibroid materials of plants, especially cellulose, are being continuously studied. Cellulose is dissolved in a solvent under a special environment. For example, polar aprotic amide solvents, especially N,N- Dimethylacetamide (DMA) , n-Metyhl Morpholine-n-Oxide (NMMO) , n- Methyl Caprolactam, Dimethyl Sulfoxide (DMSO) , para-Formaldehyde, etc. under the presence of lithium halide can dissolve cellulose. There are attempts to manufacture biodegradable plastics by making viscose through the prior treatment processes of inorganic materials using such dissolution or by obtaining viscose or cellulose solution in the processes cheaper and simpler than esterification and etherification. However, even though many progresses have been made, such dissolution cannot be considered as being perfect. The reason is that except spinning or film, it is difficult to freely mold and process using such dissolution like plastics. For reference, the production processes of papers made from pulp are explained. In manufacturing pulp papers, the kraft or hydrogen sulfite process is mostly used for forming pulp. In the kraft process, pulp fibers are 'cooked' for dismantling during the NaOH process. In the hydrogen sulfite process, acid is used for dismantling fibers. To release lignin kept inside the fiber walls in these processes, fibers are processed primarily. However, the removal of lignin from fibers reduces the strength of fibers. Since the hydrogen sulfite process is much severer than the primary process, the papers manufactured by the sulfite process have only about 70% of the strength of those by the kraft process. If woods become wood pulp in the kraft or hydrogen sulfite process, they are processed in beater to release hemicellulose and lignin inside the fiber and to unbind by chafing the fibers. In general, pulp slurry consists of 99.5% of water and about 0.5% of wood pulp. Such pulp slurry are further beat to release hemicellulose and to form a fiber mixture in which molecules binds to themselves through a web effect (web physics) and hydrogen bonding by which fibers entangle mutually when chafed. However, this sever treatment in pulp production causes defect to be generated along the length of the entire fibers, thus losing most of tensile, tearing, and bursting strengths. Pulp manufacturing depends on web physics to obtain bonding and structural integrities necessary for sheeting papers. Thus a relatively high ratio (more than 80%) of fibers should be added to the paper sheets. The slurry beaten in water is put on a screen net and extrusion rollers squeeze out water for primary dehydration. This dehydration process generates the sheet having 50 to 60% of water contents. After the primary dehydration, the paper sheets are further dried by heating with heated rollers. Here, to obtain typical properties of papers, substituting fiber materials can be added to the sheets. The materials include various plant fibers (known as secondary fibers) such as reeds, bamboos, straw, flax hemp fibers, Manila hemp, hemp, and sugar canes. The resulting papers are called 'plant papers.'

In the paper industry, pulp is obtained from trees and papers are made from pulp. This requires too much energy and contaminates environment.

Considering the level of the current technologies, to mold for a desired purpose by using the characteristics of pulp fibers, starch, and xylem powder as they are, are much economical and realistic than to mold by transforming or substituting glucose molecules.

The fibroid materials used for manufacturing the sheets of the present invention and other products are favored to have a large ratio of 'length/diameter (L/D) , since thinner and longer fibers can give larger strength. The ratio is 10: 1, preferably 100: 1.

Cotton, wood fibers, flax hemp, Manila hemp, and Indian millet are favored since they decompose easily under normal conditions. However, other fibers such as glass fibers may be favored depending on the desired usage and performance of the sheet. Also depending on the usage, regenerated paper fibroid materials can be used.

Despite advanced modern paper production methods, there exists no fiber slurry in the 'moldable' state that can be molded like plastics having plasticity, at any instant of paper manufacturing stages. This is so because cellulose does not have thermal plasticity and does not dissolve in any solvent as perfectly as to allow molding.

The sheets of the present invention have so many characteristics in that they can substitute papers. Nevertheless, their manufacturing processes differ from the prior processes of manufacturing pulp papers, in many aspects. At first, compared to the pulp paper slurry containing more than 97% of water, even 99.9%, a far less amount of water is used in manufacturing the compound of the present invention (less than 50 wt%) . Also, the sheets of the present invention are more cohesive than the aqueous pulp slurry and are formed together with the polymer matrix in the compound. Thus once molded, they maintain the shapes as long as no more molding or actions are applied.

In paper production, only cellulose is extracted and hemicellulose and lignin are removed. But different from that, the present invention removes water and absrobed water from xylem powder and the remnants are pulverized for use. Thus the use ratio of raw materials is high and the loss ratio is relatively low. Preferably, this is more environmentally friendly that the paper manufacturing industry. Another characteristic of the present invention is that the invention does not depend on web physics to bind the components of the sheet. Bur rather, the binding and cohesive forces of the group of binders provide most of tensile and bending strengths. The group of binders interacts not only other solid components to a certain degree but themselves as a binding matrix. As a result, a smaller ratio of fibers can be included inside the fibroid material, while maintaining the advantages of tensile, tearing, and bursting strengths given to the material.

Since a smaller amount of fibroid materials are used while the good strength characteristics are maintained, sheets, containers, or other related molded articles can be manufactured out of the compound, which is more economical that papers.

The reasons for being more economical are

(1) the xylem powder to be used in the present invention is much cheaper that pulp, (2) the unprocessed xylem powder, potatoes, etc. to be used in the present invention are much cheaper than processed starch and organic synthetic binders, (3) the capital investment for processing facilities is much smaller than that of the paper industry,

(4) Hydrophobicity of the surfaces of the xylem powder is removed and the amount of fiber contents is minimized with the pretreatments that do not use acid and alkali, thus reducing the amount of contaminants related to fiber manufacturing, and

(5) the energy consumption is low since the amount of water used in the processes of the present invention is small.

The L/D ratio and strength of a fibroid material are important factors in determining the amount of fibroid materials to be used. The higher the tensile strength, the smaller the amount of fibroid materials is used for obtaining the tensile strength necessary for the molded articles. Some fibers have higher tensile, tearing, and bursting strengths and other kinds of fibers having lower tensile strength may be more elastic. In the case where sheet are used for bending at a large angle, a high concentration of fibroid materials are required.

The sheets of the present invention use about 1/100 to about 1/3 of the amount of fibroid materials that are required in papers. Nevertheless, the sheets have the tensile, tearing, and cohesive strengths similar to those of papers. A reason is that the fibroid materials used in the present invention experience less processing than those in manufacturing papers. Another reason is that xylem powder contains a certain amount of fibers as a binder and a structural constituent.

Fibers with a smaller L/D ratio or short length are mixed easily with the compound. Fibers such as the kraft pulp and Manila hemp have high tearing and bursting strengths. Fibers such as cotton have lower strength and higher elasticity. When better mixing, higher elasticity, higher tearing and bursting strengths are required, the combination of fibers having various L/D ratios is added to the mixture. For example, the kraft pulp mixture disperses better fibroid materials in the entire compound to generate good sheets, which have excellent resistance to folding. In any case, the fibroid materials used in the present invention do not experience severe processing that is used in manufacturing papers, which the fibroid materials used in papers experience. Thus they maintain the initial strength. Also, the fibroid materials of the present invention do not require chemical processing almost at all, compared to the paper industry.

In order to use the sheets of the present invention for a specific usage, especially for a thick and strong material quality, for example, for substitutions of wrapping boxes, corrugated cardboards, or fiber drums, one can utilize processed

'twined fibroid materials.' The processed 'twined fibroid materials' are twined strings of Manila hemp, twined straw ropes, those that can withhold stronger forces by papers twining after slitting in one direction, Korean paper ropes twined after slitting in one direction, films twined after slitting in the length direction, yarns of twined fibers, waste fiber yarns, etc. These are similar to fine twined ribbons. The raw materials of processed twined fibroid materials may include those that can give the sheet more dimensional stability and vertical strength, such as the kraft paper, plastic films, synthetic fibers, regenerated papers, waste papers, news papers, regenerated fibers, glass fibers, animal fibers, metal fibers, etc.

At the same time when three OH functionals in the glucose molecules are dried together with xylem powder and starch, fibroid materials are also mixed with them to allow polymer chains to be connected by bridging as shown in Chemical Formula 4. This enables stronger polymer matrix compounds to be formed.

The polymer matrix has a strong three dimensional structure in which the fibroid materials are dispersed in xylem powder and starch to form hydrogen bonding, thus they are strongly interconnected, and organic synthetic binders cohere in between the bondings .

This can be inferred from the enlarged view of the foam sheet shown in FIG. 5. The amount of fibroid materials added to the compound of the present invention depends on the properties of the final molded article such as the required tensile strength, drawing property, and elasticity. The cost is one of the criteria that determine the amount. Hence, the concentration of the fibroid materials in the sheet of the present invention is 0.1 to 50 wt% of the total solid material, preferably 0.5 to 40 wt%, more preferably 1 to 30 wt%.

Functional additives

To supplement performances required for the sheet of the matrix compound of high content of xylem powder of the present invention, various function additives and a filler can be used. As described above, the required performances include hydrophobicity (or water resistance) providers, agents of supplementing flexibility, agents of strengthening elasticity, agents of expanding surface areas, filler, etc.

As used herein, a filler can be one of additives and one additive may have two functions or may be a filler that performs filling only.

1. Plasticizer In the matrix compound of the present invention, water, especially compounding water, is an excellent plasticizer. In addition to compounding water, various plasticizers can be added to the compound, to provide plasticity necessary for the final sheets and products. Plasticity plays a very significant role in exhibiting elasticity without the sheets or the molded articles of the present invention being deformed or destroyed by outside forces for the time of use. Plasticity, i.e., elasticity and flexibility obtained by softening, can be increased by adding plasticizers to the matrix. To soften the formed sheets or the matrix of molded articles, plasticizers are preferably the materials that can be dispersed by a group of binders. These plasticizers, also acting as a lubricant, have boiling points high enough not to be vaporized from the matrix during the molding processes. And they remain stable, being evenly distributed in the polymer matrix even after the molded articles or the sheets are formed. Favored plasticizers do not evaporate during the formation processes and remain in the formed sheets and products.

The appropriate plasticizers used in the present invention include polyethylene glycol (less than 600 of MW) , glycerin, sorbitol, fumaric acid ester, and soybean milk, which function as plasticizers with compounding water. Glycerin is also removed in part during the water removal process. In the next sheet formation treatment process, glycerin is applied to provide increased elasticity and acts as a wetting agent. Glycerin treatment gives the sheets elasticity, thus stabilizing them against a certain impact or deformation. A specific study on compatibilities between cellulose ether and PVA can be found in Journal of Applied Polymer Science (USA) , vol. 80, no. 10, pp. 1825-1834, June 2001. Here, one can find the resulting materials of hydrogen bonding between two molecules in details. Simultaneously, hydrogen bonding between starch and pulp cellulose is a known fact. In addition to this, xylem in which cellulose molecules on the surfaces are activated shows a synergy effect. Therefore, mutual hydrogen bonding between PVA, cellulose ether, pulp and starch produces grafted block copolymerization.

Differently from compounding water, this induces binding between active OH functionals in the branches of polysaccharide molecules that have OH functionals among the constituents of the present invention, including PVA, starch, xylem, and pulp fiber. And the binder itself is kicked out by condensation reaction to make thermoplastic grafted block copolymers of natural materials that have dried biodegradability.

2. Foaming agents (formation of apertues or vesicles)

When thermal isolation is required more than strength, elasticity, or flexibility in molded articles (i.e., when required to thermally isolate hot or cold materials) , it may be preferable to include small apertures in the sheet in addition to light weight filler, in order to increase the thermal isolation property of the molded articles. Apertures should be included with a careful control to provide required thermal isolation without serious reduction of the sheet strength. When thermal isolation is not important, it is preferable to minimize apertures so as to maximize the strength and minimize the volume.

The foaming ratio of the compound of the present invention can be controlled by the compounding machine of high shear, by the foaming method in which high pressure gas is added, or by the foaming method using chemical foaming agents such as calcium carbonate. And it is easy to ensure its property such as proper tensile strength. Thus it is possible to mold the compound and manufacture its products. Chemical foaming agents that are available in the market and can be used in the present invention, and their chemical reaction temperatures are shown below.

Azodicarbonamide 205 to 215 °C

4, 4' -Oxybis (benzenesulfohydrazide) 150 to 160 °C Diphenlysulfon-3, 3' -disulfohydrazide 155 °C Trihydrazinotriazine 275 °C p-Toluenesulfonylsemicarbazide 228 to 235 °C

5-phenyltetrazole 240 to 250 °C

Isatoic Anhydride 210 to 225 °C

Resin particles containing foaming gas can be also used and are available easily in the foaming polystyrene resin makers or in the market.

Another foaming agent that can be used in the present invention is a mixture of citric acid and bicarbonate, which is pulverized to small particles and coated with wax, starch, or aqueous coating. This can be used for forming apertures in the following two manners :

(1) a cell type structure is generated in the matrix by forming the carbon dioxide gas through the reaction with water,

(2) Particles are filled as a part of the matrix, which is hardened. Afterward, the molded article is heated to above 180 °C, for the foaming particles to be reacted, thereby generating a well controlled light weigh structure of cell type (that can decompose the particles by absorbing heat) .

As another simple foaming agent, the powder of calcium carbonate can be used. The liquid existing in the compound penetrates in the apertures of the carbonate. In this state, vaporization by heat is in equilibrium due to the balance between the evaporation of the foaming agents and the vapor pressure of water. When the pressure is reduced abruptly, the foaming agents undergo thermal expansion, thus allowing the foaming agent to be evaporated.

Apertures can be introduced in the compound by adding to the matrix the foaming agents that expand when heat is applied to the matrix during the molding processes. These apertures are mixed homogeneous in the compound and are maintained under pressure while heated, thus allowing homogeneous foaming to be achieved.

While sheets are formed out of the compound, it is preferable to compress the compound with heated rollers in order to remove water that is generated in the compound. If the surfaces of sheets are not compressed, apertures or weak parts can be formed on the surfaces. It is necessary to form skins stronger than the inside by increasing the density of the surfaces through compression.

3. Inorganic filler

The inorganic fillers that are generally used in the paper, paint, and coating industry may be used in preparing the compound of the present invention. The inorganic fillers used in the paper industry have an average particle diameter less than 2 μ. But the average diameter of the particles used in the present invention may be more than 100 μ, depending on the wall thickness of sheets. Thus they are generally cheap and have lower specific surface areas. The inorganic fillers used in the paper industry in general have more uniform sizes that those of the present invention.

To increase the natural particle filling density of additives in a mixture, various ranges of additive particle sizes will be used. By using larger particles with various sizes, the cost of inorganic additives can be reduced in the present invention, compared to the paper industry.

The allowance of various ranges of particle sizes makes it possible to use additives and fillers far more various in the present invention than in the paper industry. Therefore, the additives included in the polymer matrix of the present invention may be chosen such that they provide far various properties for the final products such as sheets or molded articles. The raw materials of the present invention can contain far more functional additives or fillers than those of paper.

The reason is that the binding force of binders to cohere sheets mutually is stronger than hydrogen bonding force of web physics.

Functional additives having different characteristics can provide their own inherent characteristics for sheets. Thus they may be chosen properly. For example, kaσline is sleek and requires less processing in finishing, and materials such as clay provide surfaces. The fillers having large particles such as calcium carbonate generate lusterless surfaces. The favored fillers in the present invention are calcium carbonate that is dry and pulverized. It is because wet pulverized calcium carbonates are available at the price of 1/3 of other fillers. The calcium carbonates are favored to have the particle sizes of 10 to 150 μ and the average sizes of about 50 μ. Clay and gypsum can be easily purchased and cheap. They have a good workability and can be formed in various shapes . Also, they can provide the binding and cohesive properties and strength. Thus they are very useful fillers.

Due to the properties of the compound and the sheet manufactured, it is possible to include porous light weight fillers in them. Thus they can provide the thermal isolation effect for the molded sheets, more than that the foamed materials. The fillers that can provide light weight and thermal isolation to the sheets include Perlite, vermiculite, hollow glass beads, cork, clay, etc.

Other kinds of fillers that can be added to the compound include inorganic gel such as silica gel, calcium silicate gel, and aluminum silicate gel, and micro gel. Gel and micro gel absorb water. Thus in order to reduce the amount of water content, they may be added to increase cohesive forces. Additionally, the high hygroscopic property of silica gel allows it to be used as a water controller in the final gelled sheets. Gel and micro gel absorb water from air, thus maintaining the expected amount of water under the normal conditions in the sheets. Of course, the water absorption speed from air is related to the relative humidity of air. The control over the water content in the sheets makes it possible to more carefully control drawn down, elasticity modulus, flexibility, folding property, elasticity, and drawing property of sheets.

It is preferable to include various sizes and classes of fillers that can fill the narrow spaces between constituents of the compound. If the particle density is optimized, the narrow spaces filled with water ( 'capillary water' ) can be removed to reduce the amount of water required in the processes to a proper level.

Considering the explanations above, the amount of inorganic fillers that are added to the compound of the present invention depend not only on their usage and particle density but various factors including the kind and amount of other additive components. Therefore, their concentration in the sheet of the present invention is 10 to 90 wt% of the total solid material, preferably 20 to 70 wt%, and more preferably 30 to 50 wt%

4. Dispersing agents A 'dispersing agent' refers to a material that can be added for homogeneous dispersion and for reducing viscosity and bearing power of the matrix. By dispersing constituents, especially inorganic filler particles or fibroid materials, dispersing agents reduce the viscosity of a mixture. They maintain the proper level of workability so as to reduce the amount of water used. However, they act against the group of binders that bind solid materials in liquid phase. Thus they tend to weaken the binding force also in solid phase.

Dispersing agents act by being adsorbed on the surfaces or near the colloidal double layers of particles. They generate negative charges on the particle surfaces to prevent the cohesion of the particles by repelling them. The repelling of the particles reduces attractive or frictional force that lets them to have larger interaction, thereby 'lubricating' them. This increases the material density to a less degree to maintain the workability. Thus even with a smaller amount of water, the compound can be worked on smoothly enough. Dispersing agents are preferably added to mix before addition of a group of binders and water.

The amount of dispersing agents added is 5 wt% relative to water at maximum, preferably 0.1 to 4 wt%, more preferably 0.5 to 2 wt%.

5. Water repellents

Water repelling is a concept different from hydrophobicity, one in which water is repelled. The method of adding water repellents to raw materials are widely known especially in the fields of weaved fibers, papers, and pulp molds. The repellents widely used currently include fluoride-based resin or silicon- based products. The examples are Lodyne of a multinational enterprise, Ciba Specialty Chemicals Inc., Fluorad of 3M Inc., silicon-based oil or resin thereof of Dow-Corning Inc., etc.

To obtain a repelling effect requires simple addition. Thus the process is very simple. However, the problems that have to be overcome are the lowering of property such as binding force due to a large amount of addition and the high price.

6. Chromaticity controllers

To materialize the desired color of molded articles completed, pigments or dyes can be used. The prior known dyes can be used to colorize or white pigments can be used. Preferable whit pigments are calcium carbonate, oxidated titanium, talc, etc.

Ξ. Water

Water is added to the compound, to dissolve the constituents in a mixture, especially binders, or at least to disperse them. The added water having such a function is called 'compounding water' to distinguish it from the water contained in the constituents. Also, water aids in homogeneously dispersing in an entire mixture other solid components such as fibroid materials and additives. Such water plays a very important role in generating the compound that has required rheological properties including viscosity and cohesive force.

Also, another important role of water is to provide a cause of condensation reaction, that is, an environment for bridging, as shown in Chemical Formula 3. The OH and H between two glucoses form water under the influence of the supply of physical energy such as heat, to be kicked out of them. The water is then evaporated after letting them to be bound, as shown in Chemical Formula 4.

The important components of the compound of the present invention, that is, xylem powder, fibroid materials, and grain powder (starch) all are modifications of glucose molecules. The condensation reaction between glucose molecules is a very important reaction for inducing dehydrated hardening in the present invention.

In order to provide proper workability, water should be added to constituent particles, fibroid materials or other solid particles at an appropriate time to dissolve or at least disperse binders, thereby filling apertures. When dispersing agents or lubricants are added, a smaller amount of water can be used initially to maintain proper workability.

The amount of water added to the compound should be controlled so that the mixture has enough workability. One has to recognize the fact that if the initial amount of water is lowered, the amount of water to be removed for formation of hardened sheets is also lowered.

Water may be supplied though grain that is directly input. Especially unprocessed white or sweet potatoes in storage have a large amount of water. In a certain case, it may be preferable to supply a relatively large amount of water initially. The reason is that an excessive amount of water can be evaporated. Nevertheless, one of the important characteristics of the present invention can be compared to the case of manufacturing papers. The fact is that the initial amount of water is far less in the present invention than in the water found in the fiber slurry used in manufacturing pulp papers. This brings a mixture that have bearing power and stability larger than those of paper slurry.

To obtain self adhesive raw materials (i.e., morphologically stable) , the total amount of water to be removed is far less in the compound of the present invention than in the slurry of pulp papers. Furthermore, the intermediate sheets of the present invention have inner cohesive property far higher than the wet pulp slurry does.

The amount of water necessary to be added in a mixture depends on the amounts of starch or other water-absorbing components, fibroid materials, and additives, and the particle filling density of additives. Also, the amount depends on the rheology of the compound.

In most cases, a minimal amount of water preferably is added to provide the workability necessary for the compound. Thus the amount of water to be removed from the processed sheets is reduced. If so, the manufacturing cost is reduced since water removal requires energy.

Apertures were discussed in the section of the foaming agent above, but water is also an important foaming agent in the present invention. In other words, the relationship between water and apertures involves the magnification ratio of foaming.

When compounding, xylem powder, a group of binders, fibroid materials, functional additives and water are dispersed uniformly. In the compounding process, the shear force of rotation with a high speed may let a certain amount of air to be included.

The sheet in which air is included is heated. The heat increases the vapor pressure of water contained in the compound, thereby let it to evaporate. As water evaporates, the space of water becomes empty. Therefore, as water does so, the sheet of the present invention develops apertures that are distributed homogeneously in the sheet. Using the processes described above, one can control the magnification ratio of foaming by controlling the amount of water content. Without using a separate foaming agent, one can control the magnification ratio of apertures and foaming of the sheet to be molded, by controlling the water content in the total compounding amount. This is one of the very important characteristics in the present invention.

Therefore in the present invention, water play various roles such as a plasticizer, a bridging aiding agent through condensation reaction, a foaming agent by drying, a viscosity controller of the compounded material, a adhesive that provides the composite components with a basic binding force.

The amount of water added for forming the compound of the present invention may differ depending on the drying method and process, but it is 5 to 80 wt% of the compound when the magnification ratio of foaming is low, preferably 10 to 70 wt%, more preferably 20 to 50 wt%. When the magnification ratio is desired to increase, instead of requiring the strength of molded articles, up to 10 times the total solid material of slurry may be added. An artisan in the field would be able to control the preferable amount of compounding water in order to obtain the proper strength and workability necessary for molded articles in the manufacturing processes.

Preparation of the compound

The terms 'slurry,' 'polymer matrix,' 'compound,' 'moldable composition, ' or 'biodegradable polymer having a high content of xylem powder' can be used in a mutually interchangable way and they are a mixture filled with xylem powder that can be molded in any shapes. The mixture has a characteristics in that it has considerable amounts of xylem and grain powder, a small amount of natural or organic synthetic binders, various amounts of fibroid materials and function additives, and water as a solvent and a plasticizer that forms a mixture to have plasticity like plastics. The total solid material includes all the solid phase materials regardless of whether they are suspended or dissolved in the mixture.

The compound may include functional additives such as plasticizers, lubricants, dispersing agents, and aqueous gelling material, and other mixing agents such as foaming agents. The matrix that contains water has thermal plasticity after drying. Thus even after the matrix is molded in a desired shape by heat, it has a relatively high inner bearing power characteristically. Irrespective of the degree of drying, 'polymer matrix,' 'compound,' 'polymer mixture having a high content of xylem powder, ' or 'slurry' refers to the compound.

The compound of the present invention has aqueous or thermal plasticity and includes the polymer matrix of slurry type that is partially dried and the compound that is completely dried

(even though a certain amount of water may remain as binding water within the group of binders in the sheet.)

The polymer matrix of slurry type that contains a large amount of water forms a sheet and the binders harden when heated to function as an additive. Formed at least when the matrix is partially dried, the sheets or products may have the 'matrix having a high content of xylem powder.'

The proper compounding of the compound can be designed to rationalize the processes by using in an appropriate way the apparatuses of mixing, extruding, and molding, and to minimize the controlling of various components.

A. Constitution of the compounding ratio of the compound The first step of preparing the compound out of the matrix constituents is to mold in such a way that not only the molded articles have strength, elasticity, drawing and decomposing properties but the compound has a necessary workability and self-adhesion power. The preferable properties of the compound are proper workability, those similar to plastics, self-adhesion power for extrusion, stamping, and molding, and the same property precisely reproduced according to temperature, water content, and compounding ratio. The amounts of water, binders, and dispersing agents determine workability and the extrusion property of a mixture. So do those of the fibroid materials, plasticizers, and other fillers such as hollow glass beads, inside the mixture. However, any single component cannot completely determine the rheology and other properties of the compound. Rather, each component is constituted to exhibit a synergy effect in an interrelated way.

Even with the compounding of a similar matrix, the result might be a highly viscous dough if water is compounded less and a slurry if it is compounded more.

B. Effect of components in the matrix process

To obtain a mixture having a proper workability and fluidity in the matrix molding process, the amount of water to be added depends on the concentration of additives, the particle density, the kinds and amounts of fibroid materials and binders. However in general, as water is added more, the viscosity and bearing power of a mixture are reduced more. Thus the fluidity of the mixture increases and the dimensional stability decreases. Especially the energy consumption of a heating means is high.

Binders can considerably affect the rheology of a mixture, depending on the degree of their gelatinization and dissolution, and their kind and concentration. The binders used in the present invention can be dissolved or at least dispersed well in water generally. The starch granules of grain powder directly pulverized are maintained to be not at the gelatinized state in the mixture containing water until they are molded.

The binders used in the present invention may have not only various cohesive forces, viscosities, and bearing powers but also various solubilities or dispersivenesses .

The starch granules contained in grain are gelatinized and hardened in the sheet formation process. Natural polymer binders like starch are not polymerized or decomposed when added to the compound. But if they are heated to a proper degree, they are gelatinized simultaneously with drying and then hardened. As for gelatinization, most aqueous resins are easily gelatinized in water of room temperature. Starch is gelatinized only in water of temperature higher than that. However, a part of denatured starch is gelatinized at the temperature. Although aqueous resins show maximum rheological effects instantly, starch-based binders become thick when the temperature of a mixture increases. The functional additives that can directly affect the rheology of the compound are dispersing agents, plasticizers, lubricants, etc.

The amount, kind, and particle density of fillers can greatly affect the rheology and workability of the compound. The fillers that are porous or have large surface area tend to absorb water more than non-porous fillers do. Thus they reduce the amount of water that can be used for lubricating particles. This causes the mixture to be highly viscous.

The particle density of constituents also affects the volume of the space for other liquids such as water, lubricants, polymers, or the mixture to flow (move) , thereby affecting the rheology of the mixture greatly. The aqueous hardening additives like calcium carbonate can be used as a water absorber. They react with water to reduce the effective amount of water inside the mixture, thus affecting the rheology of the mixture greatly according to the hydration degree, which is a function of time.

By holding molded articles together, cohesiveness allows sheets to be expanded or pulled through rollers and maintains the morphology until the materials are dried to have enough tensile strength. Also, the solid materials such as xylem and grain powder affect the rheology in a manner similar to those of additives. Some fibroid materials may absorb water depending the porosity and the swelling tendency.

C. Function and ability of the components that provide a certain characteristics

Mostly, the sheet that has lower concentrations of binders and fibroid materials is harder, has higher thermal isolation property and lower cohesiveness, is more resistant to damages by heat, has lower tensile strength, and is decomposed less in water.

The sheet that has lower concentration of binders and higher concentration of fibroid materials has higher tensile strength and drawing property, lower compression and bending strengths, lower elastic modulus, higher elasticity, and is considerably resistant to decomposition by water.

The sheet that has higher concentration of binders and lower concentration of fibroid materials is more aqueous and decomposable, and easier to mold (this allows the sheet to be thin) , has relatively higher compression and tensile strengths, higher drawing property, and lower elastic modulus. It also has proper elasticity.

The sheet that has higher concentrations of binders and fibroid materials has the properties most similar to those of pulp papers, and has higher tensile strength, drawing property, inner flexibility, and elasiticity, and lower elastic modulus. It also has proper compression strength, very low resistance to water and low resistance to heat.

By adding rosin and alum to the compound, the final molded articles may be provided with a certain degree of waterproof. These interact with constituents to form components that have high resistance to water in the matrix.

D . Organic relationship of molded articles with composite components

The properties that can affect the property of the final molded articles and are preferably included in the polymer matrix are high tensile strength, elasticity, drawing property, bending property, and flexibility. According to the final usage, it may be preferable to manufacture the sheet having the properties of papers or cardboard products. However, it may be preferable to the matrix having the properties that cannot be obtained from general wood pulp or other raw materials of papers. These properties include resistance to water, increased drawing property, higher elastic modulus, or lower density.

Different from papers, cardboard, or pulp molds that depend greatly on the properties of used pulp, the molded articles or sheets of the present invention have the properties relatively less correlated with those of used fibroid materials. Longer and more elastic fibers can provide the sheet with more elasticity than shorter and harder fibers do. However, one can include in the sheet of the present invention the properties that depend greatly on pulp, by controlling the processing technologies of the present invention and the concentrations of non-fibroid components. The properties such as surface strength, rigidity, surface finish, and porosity are irrelevant to the kind of fibroid materials used.

Elasticity, tensile strength, or elastic modulus can be controlled such that the sheets or the molded articles manufactured therefrom satisfy the performance criteria. Depending on the usage, a higher tensile strength would be more important. Sometimes, the usage requires elasticity and at other times hardness. A certain sheet should be dense and another should be thick, light, and isolating thermally. The important point is to target a material that is proper for a specific usage, in consideration of the cost and the parameters of other manufacturing process.

In general, if the concentration of fibroid materials is increased in a mixture, the tensile, tearing, and bursting strengths and the elasticity of the final sheet are increased.

The kind of additives also affects the properties of the sheet. In general, light weight additives such as Perlite or hollow glass beads that is hard and inelastic entail the sheet that is low in density, high in thermal isolation, and not easily fragile. The additives such as silica, gypsum or clay are very cheap. Thus they can greatly reduce the cost of manufacturing a sheet.

E. Mixing of the compound

The compound-manufacturing facility of integrated molding type includes the extrusion unit in which the raw materials contained in the matrix are continuously measured, mixed, mixed again after removal of air, and output, in an automatic fashion. Or a part of components are mixed beforehand in a container, and the mixed components are then pumped into a mixer of dough and slurry.

Various mixers for mixing the compound of the present invention are known and commercialized. For example, drum mixers, Banary mixers, Henschel mixers, Wigweg mixer, Hobart mixers, kneaders, and extruders having twin screws are preferably used.

In the case of compounding the slurry matrix of low viscosity, various machines can be used in mixing the compound of the present invention. The Wigweg mixer shown in FIG. la is one of the proper low viscosity mixers.

In the case of compounding of high viscosity, extruders of twin screw are preferable. These mixers can be controlled to provide various rotation powers and different shear forces for different components.

The low and high viscosity compoundings all have advantages and disadvantages. To obtain the most ideally mixed compound, composite components should have been homogeneously dispersed. To do so, additive components should be mixed in the order of mixing first those that are difficult to mix and should be prepared in a proper agreement of the characteristics necessary for the desired final molded articles. These requirements should be determined by the viscous state due to the proper amount of water added, depending on the environment of the casting and drying processes.

To form a mixture that is dispersed well and homogeneous, it may be preferable to mix in a powerful mixer of high shear the components that are difficult to mix.

When the added materials are not mixed well due to their long lengths and hardness, it is preferable to use stronger mixing methods in order to disperse homogeneously.

For example, some fibers may need to be separated completely. Since the mixing with high shear results in a more homogeneously mixed mixture, it increases the viscosity of the compound in the middle of mixing. Therefore, it increases the strength of the final hardened sheet. This is so because such mixing disperses fibroid materials, particles and binders more homogeneously to generate more homogeneous matrixes in the hardened sheets.

For the balance between the excessive mixing that may cause the damage in fibers and the homogeneous mixing, it is preferable to mix most of the compounds for 10 minutes at maximum and to cast with the extrusion of 3 minutes at maximum out of the mixture.

F. Completion and storage of the matrix

To mix the constituents of the compounding ratio described above and to then supply the mixed matrix to the next molding process, the matrix is stored in the state where compounding is completed or the shape is modified properly. It is also required to store and maintain in a homogeneous state inside the hopper. For the proper shape, the matrix can be supplied directly to the sheeting process by extrusion like plastic master badges or the mixed dough can be supplied directly to the hopper of the caster in the case of the low viscosity matrix. If the mixing process, and the casting or molding process of the matrix are separated, the matrix should be stored in such as way that the mixed state does not change. This means that the water contained in the matrix compound, which is mostly organic materials and carbohydrates, should not be dried and the changes in time such as viscosity change, viscoelasticity change, dehydration reaction, foaming, fermentation, bridging, layer separation, phase change, etc. due to the gelatinization of starch should not occur.

The compound completed in this manner is stored in the state of the slurry containing water such that it can be molded into sheets or primary molded articles. Or, as the compounding water of the slurry is dried through the extruder, moldable pellets can be made to use for molding purposes. The primary molded articles should have a properly high melt index in the molder by increasing the binder content among the constituents. The moldable pellets can have function additives such as dispersing agents or wax added, in order to be proper for molding.

The matrix having the constituents and completed by processing methods, as described above, can be called a grafted block copolymer matrix compound of slurry type, consisting of natural raw materials such as biodegradable xylem powder, fibroid material, grain powder (starch), and binder. The difference of the compound undergone the process of the slurry of the present invention from the compound undergone the dry process through the extruder without containing water is whether it is through the bridging or the constituents play a simple filler. Note that this difference is very big. The molding through the slurry of the present invention exhibits far more excellent physical and structural strengths, resistance to water, relative stability of changes in time than that of the dry process does.

Manufacturing of intermediate molded articles out of the compound

The compound of the present invention can be molded by various known methods, which include the molding process of slurry (similar to the manufacturing of carbon copies of bread) , the paper manufacturing process, the casting process of plastic sheets, the manufacturing process of PVA films or foam sheets, the manufacturing process of polyethylene or polystyrene foam sheets, the foaming process of sheets containing ethylenevinylacetate, etc. As for the process very similar to that of the present invention, one can refer to US patent no. 5545450 entitled 'Molded articles having an inorganically filled organic polymer matrix', registered on 13 August 1996, where detailed explanations can be found on the formation process of starch sheets having a high content of inorganic materials.

The term 'sheet' molded out of the compound of the present invention includes a plate that is flat, circular, bended, and organized. The compound is one that is manufactured by homogeneously mixing the group of binders and the constituents. The sheets may include other layered sheets, surface coatings, printed matters, etc.

The sheet may have various shapes according to its usage. It may be as thin as 0.01 mm and may be thicker than 1 cm, when its strength, durability, and size are important. The present invention forms primary sheets by continuously casting the matrix compound containing a high ratio of xylem powder and the sheets are hardened by evaporating water through a drying means, thereby completing stable sheets. Thus the present invention relates to a novel composition for which a technological problem is solved to manufacture sheets in a large scale by using such a method of manufacturing stable sheets.

A. Formation of intermediate articles (initial sheets)

The polymer matrix sheets, i.e., the intermediate molded articles to be molded into other products, can be manufactured by sheeting the compound mixed as described in details, above. The present inventor presents the following four methods of molding sheets.

The first method consists of the steps of forming sheets by casting the compound on the already molded isolation film that is continuously supplied on a conveyer; then stabilizing the shapes of the formed sheets by promoting the bridging between binders, xylem power, and fibroid materials through water removal by heating; and completely hardening the binders by complete evaporation. The sheet formed in this manner consists of one surface having a coated film and the other surface being a dried polymer sheet. Thus when completing by remolding, the other surface is coated properly for use. In this case, whether the starch constituents are gelatinized does not affect the next processes much. The second method casts the compound on the conveyer coated with a biodegradable coating liquid that can be dried quickly, as in the first method. Then increasing the temperature of the conveyer hardens the coated film of the liquid and heats the compound, thus progressing the molding. Due to the heated conveyer in this case, the coating liquid between the compound and the conveyer hardens and the film in-between hardens, thus preventing the adhesion of the compound to the molder or rollers. The surfaces of the conveyer or rollers are coated with fluoride resin, etc. Thus the adhesion power to other materials is not strong and the molded sheets are easily separated together with the fluoride resin. In this case, whether or not the starch constituents are gelatinized does not affect the next processes.

The third method casts the compound on the conveyer coated with cellulose ether that has the thermal gel (syneresis hardening) characteristic, as in the first method. Simultaneously, the upper side of the sheet is coated and pressed down by the rollers that are coated with the coating liquid of cellulose ether, thus stabilizing the sheet. And increasing the temperature of the conveyer and rollers above the syneresis hardening temperature of the ether progresses the molding. Due to the heated conveyer, the coating liquid between the compound and the conveyer hardens and the film in-between hardens, thus preventing the adhesion of the compound to the molder or rollers. The surfaces of the conveyer or rollers are coated with fluoride resin, etc. Thus the adhesion power to other materials is not strong and the molded sheets are easily separated together with the cellulose films. Since both surfaces of the sheet formed in this way consists of the cellulose films, the sheets are fragile to the attack of water. The sheets are coated properly when remolding. In this case, it is inevitable, to use the starch that is not gelatinized. The fourth method casts the compound under the condition that the temperature is lower than the gelatinization temperature of starch and higher than the thermal gel temperature by adding, to the binder compounding of the polymer matrix, the resin that has the thermal gel temperature characteristic, thus hardening the surfaces of the sheet, thereby removing the adhering property of the compound and forming the sheet.

B. Formation of the sheet out of the compound

FIGs. 2a and 2b of FIG. 2 show the system for manufacturing the sheet out of the polymer matrix compound in details.

The polymer matrix compound that can be applied to the present invention can be formed, by using various polymer processing technologies already known and widely used. The examples include: a process of drying papers and forming sheets, a process of sheeting PVC casting films, a process of foaming PVC sheets, a process of foaming low density polyethylene (LDPE) sheets, a process of molding polystyrene foam sheets, a process of manufacturing and processing various nonwovens, a process of drying resin pellets and mixing pigments, etc., a process of making functional master badges, and a process of making sheet molding compounds (SMC) .

The known machines and technologies used in the processes described above and other similar methods are preferably used. The examples of low viscosity mixer are preferably drum mixers, Banbary mixers, Henschel mixer, Wigweg mixers, Hobart mixers, etc. The examples of high viscosity mixer are preferably kneaders, extruders having twin screws, etc.

A series of slurry sheeting systems, as shown in FIGs. 2a and 2b of FIG. 2, may include mixers, twin screw extruders, various sheet forming rollers, drying means, compression rollers, additional drying means, a series of finishing rollers, and finishing spools.

The manufacturing processes used for manufacturing the polymer matrix sheets of the present invention that can be formed into containers or other products are shown in FIGs. 2, 3, and 4, which include the units performing the following steps of:

(1) preparing for extrusion by putting in the hopper the compound that is supplied in the mixed state;

(2) extruding or casting the mixture in sheet or various shapes though a proper outlet (die) ; (3) forming the desired thickness of casting sheets by passing the extruded mixture through formation and compression rollers; (4) gelatinizing the starch by passing the sheets through initial heating means, then removing a part of water from the mixture, and then drying the sheets with a heating means;

(5) increasing the strength of the sheets by removing undesired apertures through the compression of the sheets while the sheets are rather wet;

(6) further drying the sheets after the compression;

(7) finishing the sheets by passing them through more than one finishing roller; and (8) winding on spools the sheets dried to form the rolls that are stored to be used when needed.

FIG. la is the favored mixing process of slurry and shows the 'Wigweg' extruder that supply rapidly back and forth the mixed slurry along the length of formation rollers. As shown in FIGs. 2a and 2b, the slurry compound can be injected directly into the space between formation rollers.

The second method for obtain a best mixture include the steps of:

(2) extruding the mixture and cutting the extruded mixture into separate units of proper shape;

(3) transferring the extruded units to the hopper;

(4) forming sheets by passing the units through a pair of self supplied compression rollers; and

(5) drying or finishing the sheets.

The extrusion step assists the air removal from the compound and the extruded units are uniformly supplied for the inlet of the compression roller.

C. Fine adjustment of molding The slurry that is output with an initial thickness through the extruder die in the sheet formation step is compressed to the first desired thickness to mold sheets. These sheets are passed through more than one group of compression or formation rollers (FIG. 4b) to form the sheet of the second desired thickness out of the compound. Or, the compound can be input directly to the space between the sheet formation rollers of FIG. 4b.

FIG. 4a is an enlarged view of the extruder of screw type that includes an injector of injecting the compound onto the casting extruder. The constituents put in the hopper are transferred to the inside of the cylinder to mix them homogeneously before being sent to the next steps.

The slurry constituents are injected into the hopper of FIG. 4a. The screws make the mixture progressed toward the outlet while mixing it. Extrusion should supply the compound for the molding facilities continuously and in a properly controlled manner. This can be achieved by the flow of materials though the outlet or by other mechanisms that induce 'extrusion.' For example, gravity can be used to make the compound flow.

In FIGs. 2a and 2b, the slurry compound is injected directly to a group of extrusion and reduction , rollers from the mixer to directly transform the compound of slurry state to sheets without using an extrusion die. The sheets that are formed by formation rollers like the systems shown in FIGs. 2a and 2b are transferred to drying rollers, compression rollers, additional drying rollers, a series of finishing rollers, and go through a spooling process afterward.

When a separate isolation or adhesion (sticking) prevention means is not provided, the binder having a thermal hardening characteristic is included in the compounding, to form the initial coating film of cellulose ether on the surfaces of the sheets, and the sheet formation rollers are then heated to the temperature at which starch granules are gelatinized. Also, a part of water can be removed by evaporation during the processes. As shown in FIG. 4b, the reason for compressing the sheets is that compression can provide the dimensional stability for the sheets. At the same time, when the sheets are compressed, as shown in FIG. 5, flat and strong skins are formed on the surfaces of the sheets. As shown in FIG. 5a, the compression forms a denser layer on the surfaces than in the inside. Thus the denser layer has a characteristic in that it reduces the physical impact from the outside.

Directly after the compound is cast, water in liquid state is not removed almost at all in the initial formation stage of the sheets. But as shown in FIGs. 2a and 2b, a series of heated sheet formation rollers is used as a heating means during the sheet formation process to remove the water amount. The thickness of the sheets reduces as they are passed through rollers. Accordingly, the sheets are drawn down in the 'machine direction' with the width maintained uniform. As a result of drawing the sheets down, the fibroid materials are oriented in the machine direction. Combined with the initial extrusion processes, the reduction process can, in this manner, generate the sheets that are oriented singly in the machine direction. However, if the speed of the compression rollers increases, the fibroid materials become disordered in the sheets.

In the case of the matrix having the compounding that has very low adhering property to rollers and plasticity, the extruded sheets can be reduced to the final thickness in a single step using heated rollers of very large diameter and various rollers of small diameter.

To obtain the thinnest thickness of the sheets while preventing the molded sheets from being dried excessively, the optimization of roller diameter is favored more than the reduction in the number of the reduction processes in the manufacturing process. Not only the reduction of the space necessary for the processes but also the number reduction decrease the number of rollers that has to be synchronized for preventing the sheet accumulation behind the rollers (when the rollers rotate slowly) and the sheet tearing (when they rotate fast) .

In general, the adhesiveness of the compound increases as the water amount increases in a mixture. Therefore when a mixture contains a larger content of water, rollers should be heated to a higher temperature to prevent adhesion. This is an advantage because the sheets having a larger content of water should be heated to remove more water so as to obtain a proper self-adhesion power. Additionally, the increase in the roller temperature is permitted such that the increase in the roller speed prevents the sheets from being stuck to the rollers.

To reduce the adhesion between the rollers and the sheets, another method is to treat the surfaces of the rollers. The rollers are made of stainless steel with their surfaces treated with gloss and are coated with non-adhering materials such as chromium, nickel, or Teflon.

Finally, since the workability is high and the compound has plasticity, the stamping process does not compress the sheets much. In other words, when the sheets are dried excessively during the period of passing through the space between the compression rollers, a part of them may be expected to compress, but the density of the sheets will be maintained to a fixed value during the stamping process. When compression is needed, the sheets may be passed through a group of compression rollers (FIG. 4b) after drying. Therefore, the important parameters in the stamping process are the diameter, speed, temperature and 'nip height' (or gap distance) of rollers. The increase in the diameter and nip height of rollers reduces the shear rate that is provided for the compound during the sheet formation process and the increase in the speed of rollers increases the shear rate.

In addition to the processes described above, one can apply, for the formation of the sheets of the present invention, the technology similar to mixing, heating, drying, melting, drawing, foaming, exfoliation, evaporation, winding, ultrasonic wave irradiation, ultraviolet ray irradiation, etc. If necessary, the technology may include the process such as mixing, kneading, surface coating, wet injection, wet removal, dissolution, fusion, addition reaction, clustering, granuling, hydrogenation, oxidation, reduction, hydrolysis, bridging, and cooling of the mixture, etc.

An advantage of the sheets of the present invention is that they affect environment less than papers, cardboards, plastics, or polystyrene molded articles. The sheets and molded articles of the present invention can be regenerated. Even if they are not regenerated, they decompose easily when exposed to water, pressure, and other environmental factors, to become a component that is mutually supplementary to soil components. The components of organic synthetic binders dissolve in water more slowly that carbohydrates do, but decompose rapidly by the actions of microorganisms. Fibroid materials also decompose rapidly and are contained in a smaller amount in the compound of the present invention than in papers. Inorganic additives are inactive and compatible with soil in any cases. Comparatively, polyethylene or plastics continue to exist for several years or even several centuries. Papers or even cardboards may continue to exist for several months or even several years if decomposition conditions are not perfect. In comparison to this, the containers that are manufactured out of the sheets of the present invention decompose in several hours or days depending on the water content, to turn into compost, thus fertilizing soil.

D . Drying process

By using a processor, especially an extruder, that has the removal function of air bubbles, compounding water and air bubbles are simultaneously removed from the compound for drying. But when the sheets are intermediate molded articles, compounding water and air bubble are not removed but dispersed in the mixer of low shear force and the formed sheets are dried with a separate heating means. When dried without the removal of air bubbles, the sites where air bubbles and compounding water have located remain as apertures to have foamed shapes. This means that the sheets are dried and hardened in the foaming magnification ratio as high as the compounding water is foamed. Thus the amount of compounding water added can determine the foaming magnification ratio of the molded article.

When the initial sheets are molded as an intermediate molded article, the sheets can be dried partially or even almost completely with a heating means by casting them on the conveyer. Even so, the sheets should be dried further to obtain a required tensile strength and a prescribed drawing property. Even though the sheets may be dried naturally as time passes by, it is impossible to wait for natural drying since a large scale production is aimed at in the process design. Drying can be performed with various methods of heating the sheet to discharge water quickly.

There may be various drying means of the sheets. But in the present invention, they are broadly classified into the methods of using heating rollers and a drying tunnel.

First, the method of using heating rollers is described.

Contrary to more than one compression roller that are arranged in a group in a serial manner, the drying means are arranged in such a way that the sheets pass through the surface regions of rollers sequentially (various rollers shown in FIGs. 2a and 2b).

In this method, two surfaces of the sheets are dried stepwise. The heating rollers of large diameter are favored. Since the diameter is large, the contacted area is large and the heat efficiency is high. But many series of smaller rollers may be used.

Next, the method of using a drying tunnel (dryer) is explained. The matrix that is cast on the conveyer in the extruder is adjusted to a prescribed thickness in the compression roller to enter the drying tunnel. The entered conveyer is heated by various heating means and the length and line speed of the conveyer determine the duration time inside the heating means. The line speed is controlled according to the dried state. During the time, the matrix receives heat from the heating means and the water in the matrix is dried by the heat.

The heating means in the drying tunnel may include heating by electricity and gas, and a method of mixing high frequency wave (dielectric heating) irradiation with electricity or gas. As for heating by electricity and gas, one can use generally known methods .

High frequency wave dielectric heating is to heat an object in a strong high frequency electromagnetic field and is also called radio wave heating. If an object is placed in a high frequency electric field, the object itself generates heat due to the loss of dielectric substances of an insulator. This principle has been applied to drying or adhering of woods, vulcanization of rubbers, molding and processing of synthetic resin, gluing (high frequency wave gluing) of vinyl films, drying of fibers, processing, insects-killing and sterilization of agricultural and fishing products, cooking of foods (microwave oven) , etc. The characteristics of this heating method is that even though the heated object has low thermal conductivity, the heated object itself generates heat and is heated in a good efficiency, and the desired location can be heated selectively.

The temperature of the drying means depends on various factors including the water content of the sheets when the sheets are passed through a specific roller. To prevent the damage and decomposition of the constituents of the matrix compound, the temperature of the drying means should be less than 300 °C. To prevent the destruction of organic components (organic binders or cellulose ether, etc.), the compound should not be heated above 250 °C. Nevertheless, the rollers can be heated above the temperature as long as a proper amount of water exist in the compound, since the vaporization of the water in the mixture can cool the materials. Still, since the amount of water reduces during the drying process, the roller temperature needs to be reduced in order to prevent the excessive heating of the sheet materials.

When the processes need to be quickened, one can use the drying tunnel, oven or chamber together with the drying means. To obtain the drying effect by thermal convection, one may favor to accelerate the drying process by circulating the heated air. The temperature inside the tunnel and the retention time of the sheets in the tunnel determine the speed and amount of evaporation of water in the sheet materials. The temperature inside the tunnel should not exceed 250. °C to prevent the destruction of organic binders. The drying tunnel is heated to 100 to 250 °C. In some cases, the final step is the drying process described above before the sheets are used for manufacturing containers or other products or are wound to the spool (the roll at the end of FIGs. 2a, 2b, 3a and 3b) . When the sheets are required to be smoother or to have finishing more like papers, additional steps can be added after the drying or finishing step.

Surface treatment (the difference of coating and lamination)

Molded and dried as described above, the sheets may require additional surface treatment to supplement the performance according to the characteristics necessary for them and the final usage. According to the sheeting process described above, one side of the sheets may have been laminated initially and there may be sheets that are coated with a coating liquid and that have one surface of hardened binders. These additional surface treatment processes for supplementing the performance include coating, lamination, or a combination thereof.

A. Lamination and lamination process

Surface treatment can provide molded articles with physicochemical protection and molded sheets with various properties. A 'lamination' sheet refers to the sheet that has more than two layers, at least one side of which is a sheet. A sheet can be formed by combining at least two layers. The thickness of a sheet varies according the desired usage and the required properties. The lamination materials combined or adhered to the sheet include other sheets and the materials that provide the properties necessary for the sheets when two are laminated together, i.e., coating materials, adhesives, or a combination thereof. The examples of improving or strengthening the properties of the sheet are polymer sheets, metal foil sheets, ionomer sheets, elastic polymer sheets, nylon sheets, wax sheets, aqueous hardening sheets, and metalized film sheets.

Wet starch may be used as an adhesive for lamination. By using adhesives through various methods such as wet gluing lamination, dry gluing lamination, heat and compression lamination, sheet-sheet and sheet-coated film mutual bindings can be formed. As useful adhesives, there are aqueous adhesives (natural and synthetic) , high temperature melting or dissolved adhesive.

Liquid adhesives that will combine two layers are used for wet binding lamination of the sheet and other layers. Natural aqueous adhesives useful for wet binding lamination include vegetable organic binder adhesives, protein-based adhesives, animal adhesives, casein and natural rubber latex. Useful synthetic aqueous adhesives include resin emulsions such as stable suspended liquids of polyvinyl acetate particles in water. Most of aqueous adhesives are weak in smell, taste, color, and toxicity, and have a wide range of adhesive properties and excellent performances.

Thermo-plastic adhesives are hot melt adhesives that are applied in the molten state and hardened when cooled. Hot melt adhesives harden more rapidly than other adhesives. Useful oily adhesives include polyurethane adhesives, oily ethyleneacetate systems, and other rubber resins.

Starch in the sheets also acts as a thermo-plastic material. If the sheets are heated above the glass transition temperature of starch, the sheets can be molten and deformed. Cooling of thermo-plastic materials makes molded articles fixed in a new shape. Molten and cooled starch acts as an adhesive that adheres and seals the sheet, so that pipes, tubes or cans can be manufactured.

The surface layers of the sheets that are supplied continuously by the conveyer should have higher drawing properties and melt flow viscosity than those of the compound at the temperature for remolding. Otherwise, the compound layers and the surface layers might be separated when remolded.

B. Coating and Coating process

The sheets or the molded articles therefrom can be coated or applied for surface treatment with coating materials. By various methods including sealing and protection of sheets or articles, coating can be used for strengthening the surface characteristics of the sheets. Coating protects the surfaces from wet, base, acid, grease and organic solvents. It provides strengthened surfaces that are smoother and glossier, so that the sheets or their constituents are prevented from being scattered. It also provides thermal isolation and insulation. The coating materials of the surface layers reinforce the sheets at the lines of bending or folding. For the articles that are formed by folding, coating materials having plasticity and elasticity are favored. These materials can be used as lamination materials or adhesives. Some coating makes the matrix flexible, thus making the molded sheet more elastic. For example, coating based on the materials such as soybean milk or cellulose is applied on the sheet surface alone or in combination with polyethylene glycol, to make the sheets or the sites of folding in the sheets permanently flexible.

When these properties are provided for the sheets of the present invention through the surface treatment, they exhibit substantially the properties similar to those of polystyrene foam sheets, plastic sheet, or papers.

The purpose of coating process is to protect the content by forming a uniform film on the sheet surface. Coating can be applied during the sheet formation process or the production formation process, or after products are formed. A specific coating process and material can be chosen depending on the variables of the sheet surfaces and the coating compounding materials. The sheet variables are strength, wetting property, porosity, density, smoothness, homogeneity, etc. The compounding variables of the coating materials are the content amount of the total solid material, solvent (solubility and volatility of water) , surface tension, rheology, etc.

In the field of manufacturing papers, cardboards, plastics, polyethylene, metal sheets, or other wrapping materials, coating means such as blade, air-knife, Dahlgren (a coating machine using various rollers) , printing, and gravure, and coating methods such as powder coating, 'coating method using phase equilibrium' of Korea Patent Application no. 10-2001-0060271, applied on 27 September 2001, and 'coating method of surface isolation materials using phase change and equilibrium during the molding process of starch molded articles' of Korean Patent Application no. 10-2001-0064858 can be applied for sheet coating. Coating can be applied by pasting, smearing, or spraying coating materials on the sheet or articles, or by putting them in a container containing proper coating materials and then by performing post-treatments.

Also, the coating methods of the sheet surfaces can integrate the coating and extrusion processes - by casting through gluing the compound simultaneously with the molding of coating materials (hollow molding, lamination, casting, etc.) - by casting (co-extruding) the compound on a coated film or a film that is molded on the conveyer, or by casting the compound on a film coating material that has become, after hardening, a coated film, which was coated with a coating liquid on the surface of the conveyer contacting the compound. All these integrated coating methods maintain the initial shapes of the compound.

Proper organic coating materials include PVA, polyvinylacetate, polyacrylate, polyamide, nitrocellulose, cellulose acetate, cellulose acetate butylate, hydroypropylmethylcellulose, polyethyleneglycol, acryl resin of emulsion type, liquid phase polyurethane, polylactic acid, latex, starch, soybean protein, soybean milk, cellulose ether, synthetic polymer containing bidegradable polymer, rosins, wax

(beeswax, petroleum-based wax, or synthetic wax) , food oil, melamine, polyvinylchloride, elastic polymer, etc.

The compounding of PVA alone and monomers having plasticity, for example, copolymers with ethyl acrylate, butyl acrylate, dibutyl maleate, etc. can be used as a coating liquid. Vinylacetate resin alone has been used for being cheap. But, since coating materials using copolymers has low temperature of coated film formation, excellent weatherability, water- resistance, and storage stability, they might be used. Nevertheless, the advantage may lower the biodegradability of the molded articles of the present invention. Thus, in order not to hamper the biodegradability, it is preferably to add a small amount of monomers .

Proper inorganic coating materials include sodium silicate, calcium carbonate, aluminum oxide, silicon oxide, kaoline, clay, ceramics and a mixture thereof. Inorganic coating materials can be mixed with organic coating materials. In addition to these coating materials, proper coating materials can be used according to the usage.

Waterproof coating is preferable for the articles contacting water. If the sheets are used for the containers contacting foods, the coating materials will include those that are certified formally.

Polymer coating materials like polyethylene are useful for forming a thin layer of low density. Low density polyethylene is useful for generating the containers that seal water and are pressure-tight. Polymer coating materials can be utilized as an adhesive for heat sealing.

Wax and wax mixtures, especially natural and synthetic wax provide a barrier to water, oxygen, and organic liquids such as grease or oil. These allow containers to be sealed thermally. Synthetic wax is useful for wrapping foods and drinks and includes paraffin wax and microcrystalline wax.

C. Post-processing

By optimizing the compounding of the compound according to the purpose, one can manufacture the matrix that can be drawn down up to a prescribed ratio in the heated or wet state or even in the dried state. In other words, the sheet can be drawn down with the ratio range without being destructed.

The term 'draw down' means that the matrix of the sheet can be expanded without being destroyed to have a finished surface. In other words, the term implies that there exist a point to which the matrix can be deformed without being destroyed by the application of a drawing force. To obtain the sheet that has necessary strength, flexibility, drawing property, weight or other performance criteria, the thickness of the sheet can be modified by adjusting the gap (space) between the rollers of the molding facility. According to the thickness and performance, one can adjust the components of the matrix and their relative concentrations. The sheets can be designed to have various thicknesses. When thermal isolation, and higher elasticity or strength are required, the sheet may be 1 cm thick at maximum. Of course, compositions may be molded into the very thick sheets being more than 10 cm thick.

The sheets for wrapping boxes are preferably 2.5 mm thick and milk packs 5 mm and juice boxes 2.5 mm. The sheets that require higher strength and elastic modulus and lower elasticity

(covers of magazines or books) are preferably 0.1 to 2 mm thick.

The thickness and elasticity of a specific sheet depends on the performance criteria required for the molded article and object in question.

As described above, the sheet can be molded to have various thicknesses and strengths to be used for various usages.

When boxes and containers with lids are manufactured out of the sheets, they need to be fold or bent. To form 'folding- inducing lines' where the sheets can be folded, it may be preferable to process the sheet in advance. Pre-processing is to first generate on the sheets the locations where the sheets can be folded or bend.

The pre-processed sheets prevent the exfoliation of the surface skins and intermediate layers that can occur when the sheet are bent in a forced manner. The processing generates in the sheets the 'folded locations (hinges) ' that have larger flexibility and elasticity than the unprocessed sheets. Also it provides the locations where the sheets are naturally bent or first folded.

Depending on the usage, there are the cases where it is preferable to heighten resilience and provide resistance to folding by enriching more fibroid materials at the folded locations .

During the pre-processing, the sheets are preferably maintained in a dried or semi-dried state or in a semi-hardened state. It is because while lines are made on the sheets containing water, the rooms are provided for the locations compressed by a prescribed pressure to move without physical damages, since the contents have a prescribe viscosity. This induces the sheets to be compressed rather than cut. At the same time, the polymer matrix is condensed at the compressed locations. Thus the skins stronger in the compressed location than in the uncompressed location are formed to provide a force resistant to bending.

The pre-processing should be performed to a proper depth according to the cases and usages. The reason is that if too deep or shallow, the sheet might be cut instead of the increase in the resistant force to a prescribed bending. Also the preprocessing on both surfaces of the front and back is helpful in increasing the range and angle of bending movement.

Articles manufactured as a sheet

By using the molding method of the sheet that utilizes the biodegradable polymer matrix compound of the present invention, one can manufacture various types of sheet having various properties. When very thin, elastic sheets of light weight are needed, the thickness of the sheets may be less than 0.1 cm. When relatively thick, strong, hardening sheets are required, the thickness may be about 1 cm. The sheets can have a density of 0.2 to 2 g/cm², depending on the kind of additives added in compounding. The higher the density, the stronger the sheet is. If the density is low, thermal isolation is large. By designing the precise thickness and density in advance, one can manufacture the sheet that has necessary properties, in an economically possible method.

The sheets of the present invention can be utilized in the fields where polystyrene foam material (Styrofoam) , pulp papers, or cardboards are used. Also, by virtue of the properties inherent to the raw materials of the compound of the present invention, one can manufacture various articles that can substitute for plastics, polystyrene, or metals. Especially, the sheets of the present invention can be utilized for manufacturing the following various articles:

Disposable and non-disposable food or drink containers such as lunch containers, instantly fried noodle (instant noodle in- the-cup) containers, disposable take-out food containers, food containers heated instantly in microwave ovens (high frequency wave) for wrapping retort foods, cereal boxes, sandwich containers, 'clam shell' type containers (folding (hinge) type containers that are used for fast foods such as hamburgers and sandwiches) , freeze-dried food boxes, large wrappers for circulating fishes, food containers for exhibition in small packages at large general merchandise stores, food trays for exhibition in small packages, milk packs, fruit juice containers, yogurt containers, drink carriers (basket type carriers, '6 pack' ring type carriers) , ice cream boxes, cups (disposable drinking cups, corrugated cups, corn cups) , French fry containers; wrappers, wrapping materials such as space fillers, a filler, bags for snacks, bags having an opening end such as vegetable bags, bags inside dried cereal boxes, cosmetics wrappers, hardware wrappers, trays for supporting products such as cookies and candy bars, cans, tapes, cardboards, various boxes such as hard board corrugated boxes for wrapping, sweets boxes, and cosmetics boxes; molded article containers for condensed freeze-dried juice, oatmeal, potato chips, ice cream, salt, detergents, and motor oil; postal matters wrappers, books, magazines, envelopes, post cards, 3 ring binders, book covers, folders, trays, lids, straws, cases, egg boxes, disposable plates, toys, Plamodel, etc.

The following examples present the matrix compound obtained according to the processes of the present invention and the method of forming sheets out of the matrix compound and the compositions thereof. In other words, the method of manufacturing sheets, containers, and other products having various properties and sizes and various mixture compositions thereof are presented.

A high content of xylem powder is manufactured into the compound out of the polymer matrix containing the components shown in the following table

This example shows a standard compounding the present invention. As xylem powder, Avidon trees (bulk specific gravity of 0.3 g/cm² and 0.7 g/cm² before and after pre-treatment) were pulverized to 200 mesh and then boiled at 100 °C for 5 hours. Fibers were pulp and starch was corn starch that is not gelatinized when added to the mixture. Organic binders were a mixture of PVA (Kuraray, Exceval CP-410481) and methylcellulose (For example, Dow' s Methocel F4M Grade, gel temperature is 62 to 68 °C, and it shows strong lubricating powder) in the ratio of 50: 50.

The xylem powder, starch, and fibers were mixed under high shear in a Hobart mixer. Then a group of binders was added and the mixture was mixed again for 5 minutes. After water of room temperature was added, the mixture was mixed under low shear until the components were mixed well, to complete slurry. The reason for using low shear is to protect the fibers in the components. By using an extruder of screw type that can remove air, the mixture was extruded through an outlet of 30 cm x 0.6 cm, to form a continuous sheet having the corresponding width and thickness. Afterward, the extruded sheet had the gap corresponding to the thickness of the formed sheet and was passed through the space between the rollers that had been heated to about 70 °C. Afterward, the initial sheet was passed through the space between the rollers having a temperature above 100 °C to gelatinize starch and to remove water due to evaporation from the sheet. Since the xylem powder has low specific surface area and cellulose ether had been gelatinized, the mixture had a low sticking property to the rollers. Therefore, cellulose ether among the binder group prevented starch from being stuck to the rollers during the formation process.

The resulting sheets of a high content of xylem powder were completed as the initial molded articles of various thicknesses more than 1 mm.

Remolding was performed by heating the initial molded articles to above 220 °C, to provide plasticity and flexibility and the articles were processed to the purposed shapes.

<Examples 2, 3, and 4> The sheets filled with a high content of xylem powder are manufactured out of the following molded article compositions.

Example 2

Example 3

Example 4

The xylem powder, starch, pulp fibers were mixed under high shear in a Hobart mixer. Afterward, a group of binders was added and the mixture was additionally mixed. And water was added to the mixture, which was then mixed sufficiently under low shear. The mixture was extruded using an extruder through a die of 30 cm x 0.6 cm to form a continuous sheet having the corresponding width and thickness. Afterward, the extruded sheet was passed through a group of formation/reduction rollers that have the gap corresponding to the thickness of the formed sheet. The sheets of these examples were completed as the initial molded articles of various thicknesses of more than 1 mm.

<Examples 5, 6, 7, 8, 9, 10, 11, 12, and 13> The sheets of a high content of xylem powder are manufactured out of the following compositions.

Example 5

Example 10

The sheets are manufactured according to the method described in Example 2. The sheets formed in these examples were completed as the initial molded articles of various thicknesses of more than 1 mm.

<Examples 14, 15, 16, 17, and 18> Only The starch of Example 1 is substituted with the following grain powders, in the converted amount of starch.

* The amount of water added = 6000 - (the converted amount of starch - 1500) Substi . =substituted

With foreign materials removed, the grain powders were homogeneously pulverized with the cuticles and included in the compounding without separate pre-treatments. The cuticles of rice plants and barley and the embryos of corn were difficult to pulverize or separate in the lab. The processes were the same as those in Examples 1 and 2. The sheets are manufactured using the method described in Example 2. In these examples, the sheets were molded in thicknesses of more than 1 mm.

After increasing the amount of binders without containing grain powder, the sheets are manufactured out of the following compositions. Additionally, the compositions contain, in a large amount, xylem powder among all the components. 11 kg of water is contained in the compositions.

As natural filament, Manila hemp (string) was pulverized and compounded. It was confirmed that even though a large amount of xylem powder is contained, property can be maintained and molding was possible, if a large amount of organic binders and fibroid materials are used.

The sheets, i.e., the intermediate molded articles that can be molded into various products (including foods or drinks containers) were manufactured. The hardened sheets were remolded to finish with coating and then manufactured into various foods and drinks containers. For the cups into which drinks are put in fast food stores, the sheets were cut in a proper size and the cut sheets were wound up in a cup shape and by using aqueous adhesives, they were glued to manufacture a pipe shape. For isolating heat, it is preferable to use the sheets of the present invention of a thickness of more than 1 mm in manufacturing the cups .

<Example 21> The sheets were heated to 220 °C and the heat provided the sheets with plasticity. The sheets that had been provided with plasticity and flexibility by heating were put on a female mold and then compressed with a male mold. They were cut in the neighbor afterward. After the shapes of the molded articles were stabilized, they were taken out. In this manner, the molded articles of tray shape were completed simply.

The sheets having various thicknesses were manufactured according to Examples described above. The dried sheets of each thickness were cut in a circular shape and molded into disposable trays by using facilities and machine presses that are used in manufacturing disposable plate with the raw material of papers. The formed plates are similar to the prior paper plates, trays and cups in the shape, strength, and appearance. However, the plates that are manufactured out of the sheet of a high content of xylem powder are harder than the prior paper plates and exhibit larger and stabler structural integration when foods are put on them.

By using the compositions, the sheets of corrugated cardboards that have an inner structure in which cardboards are put between two flat sheets were formed. The flat outer sheets were formed, by winding the raw materials with two flat sheets of proper thickness. The hardened cardboard sheets (similar to the corrugated inner sheets of general pasteboard boxes) of a high content of xylem powder that are corrugated and have proper thickness were wetted again to be taut. The taut sheets were passed through the rollers having the corrugated surfaces or saw teeth that engage mutually, to form the corrugated sheets. Adhesives were applied on the corrugated sheets, which were then put between two taut sheets and hardened. The corrugated sandwich structures are more excellent in strength, toughness, and stiffness than the prior cardboard sheets.

After forming a plate and a tray, each weighing 20 g, they were coated with 1 to 5 g of a coating composition. The composition is a suspended liquid in which 20% nitrocellulose

(RS 1/2NC) , 20% glycerin, and 10% rosin are dissolved in 50% methanol. For coating, any known methods can be used. To prevent blushing, the coating composition were coated on the completely dried molded articles at room temperature and placed at the temperature. After coating, the containers were dried for a proper period of time. The physically stable biodegradable lacquer surfaces for which waterproof treatment was performed well were generated.

After a plate and a tray were formed, each weighing 20 g, they were coated with 1 to 5 g of a coating composition. The composition is a composition that contains 20% PVA, 20% glycerin, and 60% water. For coating, any known methods can be used. The composition is applied at 90 to 150 °C. After coating, the containers were dried for a proper period of time.

The molded articles such as the trays manufactured according to Example 21 were passed through a wax coating machine to apply wax on the surfaces . The wax layer was made waterproof by sealing the surfaces of the molded articles against moisture.

The containers such as the trays manufactured according to Example 21 were coated with acryl emulsion using a fine spray nozzle. Similar to the wax of Example 26, the acryl coating layers were made waterproof by sealing the surfaces of the molded articles against moisture. Since acryl coating does not meet the eye differently from was coating, it is an advantage. Since the thin acryl coating is possible, the gloss of the surfaces of the molded articles can be controlled by using different kinds of acryl coating. However, biodegradability might be disputed depending on the kind of acryl monomer.

Industrial Applicability

The present invention provides compositions and methods for manufacturing cheaply the sheets that are environmentally friendly and simultaneously have the properties similar to those of papers, cardboards, polystyrene, plastics or metal sheets, which are modern conveniences but environmentally destructive. The sheets can be molded into various containers and other products by using manufacturing facilities and technologies that are used for manufacturing papers, cardboards, polystyrene, plastics, or metal sheets.

The present invention provides the compositions and methods for manufacturing the moldable biodegradable natural compositions, especially the environmentally friendly sheets that can be formed from a high content of xylem powder. The invention also provides the sheets, containers, and other products that are decomposed into the materials existing in soil or biodegradable. It further provides the methods of manufacturing sheets, containers, and other products more cheaply than those of papers, plastics, or metal products. Moreover, it provides the composition and methods for manufacturing the sheets filled with a high content of xylem powder that are consist of natural polymer but have large elasticity, tearing strength, toughness, and moldability, and large scale productivity.

Since the compound and molded articles of the present invention is biodegradable, they influence environment in a nondestructive manner.

While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.

Claims

What Is Claimed Is:

1. A biodegradable compound in which a) xylem powder in a concentration of 10 to 90 wt% relative to the total solid material of the compound, b) fibroid material in a concentration of 0 to 50 wt% relative to the total solid material of the compound, c) a group of binders in a concentration of 0 to 90 wt% relative to the total solid material of the compound, d) a functional additive in a concentration of 0 to 50 wt% relative to the total solid material of the compound, e) compounding water in a concentration of 1 to 90 wt% relative to the total solid material of the compound, etc. are homogeneously dispersed to form an aqueous slurry state.

2. The biodegradable compound according to claim 1, wherein the binder group consists of the starch separated from grain powder, aqueous thermoplastic resin, and aqueous thermal gelling composite resin.

3. A method of preparing a biodegradable compound of slurry state, which comprises the steps of measuring each constituent of xylem powder, fibroid material, a group of binders, additives; dispersing the measured constituents; mixing the dispersed constituents; and adding compounding water to the mixed constituents to complete the slurry state.

4. The biodegradable compound according to claim 1, wherein the xylem powder is the powder obtained by homogeneously pulverizing at least one selected from the group consisting of perennial trees, annual plant stems, fallen leaves, cultivated vegetables, stems of grains, cuticles of dried nuts, reed stems, leaves, byproducts of food manufacturing that have a high content of cellulose, and byproducts of wood processing.

5. The biodegradable compound according to claim 1, wherein a pretreatment is performed on the xylem powder.

6. The biodegradable compound according to claim 5, wherein the pretreatment is to remove hrdrophobicity of the surfaces of the xylem powder so as to activate the OH functionals.

7. The biodegradable compound according to claim 1, wherein the xylem powder comprises at least one selected from the group consisting of exploded cuticles of dried nuts, bulked chaff and plants containing a large amount of cellulose.

8. The biodegradable compound according to claim 1, wherein the xylem powder comprises at least one selected from the group consisting of compressed cuticles of dried nuts, bulked chaff and plants containing a large amount of cellulose.

9. The biodegradable compound according to claim 1, wherein the xylem powder has a specific gravity of 0.1 to 1.5 g/cm³.

10. The biodegradable compound according to claim 1, wherein the xylem powder has a size less than and equal to 100 mesh.

11. The biodegradable compound according to claim 1, wherein the xylem powder has a size of 100 to 300 mesh.

12. The biodegradable compound according to claim 1, wherein the xylem powder has a size greater than and equal to 300 mesh.

13. The biodegradable compound according to claim 1, wherein the fibroid material consists of a mixture of at least one selected from the group consisting of pulp, hemp, cotton, leaves of plants, cellulose fibers extracted from woods or stems, waste papers, regenerated papers, regenerated pulp, regenerated fibers, viscous fibers, Manila hemp fibers, corn fibers, flax hemp fibers, hemp fibers, pine tree fibers, and twined fibers.

14. The biodegradable compound according to claim 1, wherein the fibroid material comprises a fiber having a L/D ratio of greater than and equal to 10: 1.

15. The biodegradable compound according to claim 1, wherein the fibroid material comprises a fiber having a L/D ratio of greater than and equal to 100: 1.

16. The biodegradable compound according to claim 2, wherein the compound consists of a mixture consisting of a) the starch in a concentration of 0 to 90 wt% relative to the total solid material, b) the thermoplastic resin in a concentration of 0 to 90 wt% relative to the total solid material, and c) the composite resin in a concentration of 0 to 90 wt% relative to the total solid material.

17. The biodegradable compound according to claim 2, wherein the grain powder is extracted from at least one selected from the group consisting of unprocessed white potato, sweet potato, corn, glutinous corn, rice, glutinous rice, unhulled barley, whole wheat, and tapioca.

18. The biodegradable compound according to claim 2, wherein the starch is extracted from at least one selected from the group consisting of white potato, sweet potato, corn, glutinous corn, rice, glutinous rice, unhulled barley, whole wheat, and tapioca.

19. The biodegradable compound according to claim 2, wherein the resin comprises a mixture of at least one selected from the group consisting of PVA, PVA derivatives, PVA polymers, polyvinyl pryrrolidone polymers, polyvinylacetate polymers, polyethylene oxide polymers, etc.

20. The biodegradable compound according to claim 1, wherein the binder comprises resin that plays a binder role in the matrix and simultaneously has a certain thermal plasticity after drying and molding, thus showing a certain thermal plasticity through reheating after drying and molding.

21. The biodegradable compound according to claim 1, wherein the binders comprises the function of a binder that has OH functionals in the binder resin chain, thus the binders form bridging by themselves through condensation reaction to structurally harden more strongly.

22. The biodegradable compound according to claim 2, wherein the thermoplastic resin shows a Melt Index (ASTM D.1238) of dried state is 10 to 30 gram/lOmin.

23. The biodegradable compound according to claim 2, wherein the thermoplastic resin shows a Melt Index (ASTM D 1238) of dried state is 0.11 to 10 gram/lOmin.

24. The biodegradable compound according to claim 2, wherein the composite resin is a cellulose ether derivative in which cellulose ether includes a mixture of at least one selected from the group consisting of methylhydroxyethylcellulose, hydroxymethylethylcellulose, craboxymethylcellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxyethylpropylcellulose, and a mixture, a polymer, or a derivative thereof.

25. The biodegradable compound according to claim 1, wherein the functional additive is at least one selected from the group consisting of polyethylene glycol, glycerin, sorbitol, fumaric acid ester, soybean milk, and food oil.

26. The biodegradable compound according to claim 1, wherein the functional additive is, as a foaming agent, at least one selected from the group consisting of resin particles containing a foam gas (foam particles) , citric acid, a mixture of bicarbonates, bicarbonates that are processed as small particles and coated with wax, starch, or aqueous coating, powder of calcium carbonate, Isatoic Anhydride, Azodicarbonamide, 5-phenyltetrazole, 4, 4' -Oxybis (benzenesulfohydrazide) , Diphenlysulfon-3, 3' -disulfohydrazide,p Toluenesulfonylsemicarbazide, and Trihydrazinotriazine.

27. The biodegradable compound according to claim 1, wherein the functional additive is at least one selected from the group consisting of calcium carbonate, titan oxide, clay, gypsum, Perlite, vermiculite, hollow glass beads, cork, clay, silica gel, calcium silicate gel, and aluminum silicate gel, as an inorganic filler.

28. The biodegradable compound according to claim 1, wherein the functional additive comprises fluoride-based compounds or silica-based compounds, as a water repellent.

29. The biodegradable compound according to claim 1, wherein the functional additive comprises at least one selected from the group consisting of calcium carbonate, titan oxide, talc, inorganic pigment, and organic pigment, as a chromaticity controller.

30. The biodegradable compound according to claim 1, wherein the compounding water functions as a solvent and lubricant to provide a prescribed shape of the mixture with plasiticity, and is used as a solvent to be mixed and kneaded with aqueous resin being a binder of the mixture so as to disperse the resin and as a foaming assistant to generate apertures by evaporation.

31. The biodegradable compound according to claim 1, wherein the binder comprises a protein assistant binder selected from the group consisting of prolamine, collagen, glue, casein, and a mixture or a derivative thereof.

32. The biodegradable compound according to claim 1, wherein the binder comprises a polysaccharide assist binger selected from the group consisting of alginic acid, pico-colloid, agar, Arabian gum, guar gum, locust bean gum, karaya gum, (xanthan gum) , tragacanth gum, and a mixture or a derivative thereof.

33. The biodegradable compound according to claim 1, wherein the binder comprises a synthetic binder selected from the group consisting of polyvinyl pyrrolidone, polyethylene glycol, PVA, polyvinylmethyl ether, polyacrylic acid, polyacrylate, polyvinylacrylic acid, polyvinylacrylate, polyacrylimide, polylactic acid, ethyleneoxide polymer, latex, and a mixture or a derivative thereof.

34. The biodegradable compound according to claim 1, wherein the granules of the binder have an inherent gelatinization temperature, cellulose ether has a thermal gelling temperature, and the gelatinization temperature of the starch granules is higher than the thermal gelling temperature of cellulose ether, thus preventing the compound from being stuck to the processors during the processes.

35. A method of molding a molded material of the biodegradable compound, which comprises the steps of: a) forming the compound of slurry state in which xylem powder, fibroid material, starch supplied from grain powder, a group of binders consisting of aqueous thermoplastic resin and aqueous thermal gelling composite resin, a functional additive, and compounding water are dispersed homogeneously; b) casting the compound in a prescribed thickness through an outlet of an extruder; c) drying the cast compound with a drying means; and d) forming a sheet out of the dried compound.

36. A molded material of the biodegradable compound, which comprises a compound layer mixed with the polymer matrix of a biodegradable material and a hydrophobic isolation film formed on both sides of the compound layer.

37. The molded material of the biodegradable compound according to claim 36, wherein the compound layer and the isolation film are glued together by a resin solution.

38. The method according to claim 35, wherein the slurry to be cast at step b) is included by thermal gelling resin, thus allowing the surfaces to be thermally gelled first for hardening when molding the sheet.

39. The method according to claim 35, wherein the drying means is a drying tunnel using electricity.

40. The method according to claim 35, wherein the drying means is a drying tunnel using gas.

41. The method according to claim 35, wherein the drying means is a drying tunnel using a high frequency wave.

42. The method according to claim 35, wherein the drying and foaming are simultaneously performed when heating to a prescribed temperature at step c) .

43. The method according to claim 35, wherein the sheet has a tearing strength of 1 Mpa to 100 Mpa.

44. The method according to claim 35, wherein the sheet has a density of 0.1 to 2.0 g/cm².

45. The method according to claim 35, wherein the sheet has a thickness of less than 1 mm.

46. The method according to claim 35, w.herein the sheet has a thickness of 1 to 10 mm.

47. The method according to claim 35, wherein the sheet has a thickness of 10 to 100 mm.

48. The method according to claim 35, wherein the fibroid material includes 'twined fibers.'

49. The method according to claim 35, wherein the sheet has an elongation of 0.1 to 50%.

50. The method according to claim 35, wherein the sheet has an elongation of 50 to 200%.

51. The molded material of the biodegradable compound according to claim 36, wherein since the compound layer is compounded with an assist binder, the resistance to water can be maintained for a considerable period of time even though the isolation film is damaged.

52. The molded material of the biodegradable compound according to claim 51, wherein the assistant binder is compounded with at least one selected from the group consisting of: a) Natural polysaccharide such as alginic acid, picocolloid, agar, Arabian gum, guar gum, locust bean gum, karaya gum, xanthan gum, tragacanth rubber, and a mixture or a derivative thereof; b) protein-based binder such as zein (prolamine derived from corn) , collagen (extracted from stroma or bones of animals) , gelatin, glue, and a derivatives thereof; c) casein (main proteins of milk) , a mixture or a derivative thereof.

53. The molded material of the biodegradable compound according to claim 35, wherein the compound is molded by forming bridging through condensation polymerization or syneresis reaction, thus having fewer free OH functionals on the surfaces of the molded articles to have hydrophobic surfaces structurally.