WO1992008759A1 - Expandable and expanded (foamed) solid products - Google Patents

Abstract

This invention relates to expanded low bulk density solid products. It also relates to expandable compositions for preparing the solid foam products. In particular, it relates to such products that are environmentally degradable. It further relates to such foamed products that are resilient, have low bulk density and high crush resistance, are antistatic and are useful as loose fill packaging materials, among other applications. The invention also relates to a one-step extrusion cooking process for making the invention products.

Description

TITLE EXPANDABLE AND EXPANDED (FOAMED) SOLID PRODUCTS

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of Application Serial No. 07,615,913, filed November 20, 1990.

FIELD OF THE INVENTION

This invention relates to expanded low bulk density solid products. It also relates to expandable compositions for preparing the solid foam products. In particular, it relates to such products that are environmentally degradable. It further relates to such foamed products that are resilient, have low bulk density and high crush resistance, are antistatic and are useful as loose fill packaging materials, among other applications. The invention also relates to a one-step extrasion cooking process for making the invention products.

BACKGROUND AND PRIOR ART

Expanded products, which are hardened foams, enjoy widespread usage as loose f ll packaging material and snack foods.

Loose fills based on polystyrene, commonly referred to as plastic loose fill (PLF), constitute a major market for expanded products. These have several drawbacks. Their processes of manufacture are multi-step and costly. The expansion (foaming step), for example, involves a blowing agent, such as pentane, which presents a fire hazard, or a chlorofluorocarbon, which is environmentally imacceptable as a potential threat to the ozone layer, unless a still more costly ήydrofluorocarbon alternative blowing agent is employed. Also, although they can be formulated (at added cost) to be degradable in direct sunlight, they still suffer the serious disadvantage, and they are a cause for public concern since they are not bio- or hydrolytically degradable under other environmental conditions - conditions that may pertain in compost heaps or landfills, for example.

Still another PLF disadvantage is that they generate and accumulate static electricity, which could damage sensitive electronic derives in transit, unless formulated to meet electronic grade standards, again at additional cost.

Lacourse et al., U.S. Patent 4,863,655, discloses a biodegradable packing material comprising an expanded high amylose starch having an amylose content of at least 45% by weight, and prepared by extruding such starch in the presence of a total moisture content of 21 weight percent or less. The disclosed packing materials suffer the disadvantage of involving high cost starch starting materials.

U.S. Borax Service Bulletin IC62 Form No. 0602, Rev. 2/67, relates to starch-based adhesives produced on heating starch with aqueous soda ash or caustic. It discloses that incorporating borax, sodium metaborate or boric acid into the composition results in an adhesive having increased viscosity, quicker tack and better fluidity, probably through the formation of interchain linkages having a borate ion structure.

Organic loose fill based on popcorn has also been proposed. Although environmentally degradable, it is considered in the industry to lack the resiliency and crash strength needed in a satisfactory packaging material. It also tends to become rancid with time. Extrasion-cooked, expanded snack foods are likewise unsuitable for lack of adequate crash strength and then- tendency to break up into small and dusty particles.

Thus, needs exist in the loose fill industry for expanded product replacements for PLF that would be environmentally degradable and thereby alleviate public environmental concerns, would be naturally antistatic or would be rendered so at little or no extra cost, and could be prepared in a single potentially low-cost manufacturing step.

The present invention provides products and processes for their manufacture that meet the above needs.

SUMMARY OF THE INVENTION

An environmentally degradable expanded resilient solid foam comprising a substantially continuous preferably normally water-insoluble polysaccharide network encompassing a multiplicity of pores and voids.

In another embodiment, the expanded product has a bulk density of about 0.7 to 2 lbs/cu ft, and is resilient to the accumulation of static electricity. Another aspect of the invention is a process for the manufacture of environmentally degradable resilient solid foam products, which process comprises (i) forming an expandable composition comprising

(a) a polysaccharide composition comprising a normally solid water-insoluble natural polysaccharide and a water-swellable gum, said composition being capable of becoming substantially molten on being heated with water at elevated temperatures and pressures, and

(b) water in a minor amount sufficient to form an extradable molten composition with the polysaccharide composition of (a) and to expand the composition when heated and extruded as described in steps (ii) and (iii) below,

(ii) heating and mixing said composition in an extrasion zone at a temperature and pressure and for a time effective to substantially completely disperse the water and form a molten extradable composition, (iii) extrading the composition through a shaped die into a lower temperature and pressure zone so as to form a shaped foam, the pressure being sufficiently low relative to the pressure in the extrasion zone to allow the foam to expand, the temperature being sufficiently low to allow the foams to cool and harden, (iv) allowing the foam to harden to a resilient low-bulk density product, and (v) recovering the product.

In another process embodiment the amount of water is also sufficient to result in a substantially non-dusting antistatic product.

In still another embodiment, the polysaccharide composition contains a minor amount of a crash strength enhancing agent such as an environmentally compatible compound of a polyvalent element of Group III or IV of the Periodic Table. In still other embodiments, the expanded composition includes at least one carboxylic acid, preferably a polycarboxylic acid, in a minor amount based on the water-insoluble polysaccharide sufficient to enhance expandability, improve resiliency and crush resistance and/or inhibit mold growth; and/or a minor amount of a surfactant to promote the formation of small pore sizes, hence greater resiliency and crush resistance in the expanded product; and/or a lipid to improve the lubricity of the expandable composition and thereby enhance its extrasion rate.

An important feature of this invention is that the expandable composition can be formulated entirely of naturally-occurring environmentally-acceptable components for the production of environmentally-degradable expanded solid products useful as loose fill packaging materials among other applications including degradable mulches. Preferably, the expanded solid products are substantially water-insoluble under ambient conditions.

Accordingly, another aspect of this invention is a loose fill packaging process wherein the packaging material is an environmentally degradable expanded solid foam defined above and more fully described below.

By "polysaccharide network" is meant consisting essentially of one or more polysaccharide-based components, described above, however changed they may have become under the extrusion cooking conditions described herein.

By "environmentally-degradable" is meant subject to hydrolytic and biochemical degradation under ambient environmental conditions as may pertain, for example, in compost heaps, landfills and open country side.

DETAILED DESCRIPTION OF THE INVENTION

The extradable, expandable, environmentally degradable composition normally comprises (1) a normally solid substantially water- insoluble polysaccharide composition that is rendered substantially molten in the presence of water under extrasion conditions of elevated temperature and pressure and mechanical shear, and (2) water in an amount sufficient to render the total composition substantially molten under said extrasion conditions, the water being substantially homogeneously dispersed/dis¬ tributed/incorporated in the molten mass so that on extrading it into a lower temperature and pressure zone expansion occurs as the water vaporizes against the lower external pressure with eventual formation of a cooled hardened foam, or expanded product. By normally substantially water-insoluble ingredients and products is meant insoluble at ambient temperatures, more specifically below about 25°C.

The polysaccharide composition preferably comprises at least one natural polysaccharide component (A) that is normally insoluble in water and can be gelatinizable and rendered molten, at elevated temperatures and pressures under extrusion conditions, and at least one normally solid polysaccharide component (B) that is water-swellable at ambient temperatures and pressures and capable of promoting gelatinization and melting of component (A) under extrasion temperatures, pressures and mechanical shear mixing. Such formulation to be expanded may also advantageously contain minor proportions of other compatible adjuvants, described more fully below, that may aid in dispersing water throughout the polysaccharide composition, promoting formation of a substantially homogeneous molten mass within the extrader, in facilitating movement of the mass through the extrader and its associated die(s), in modifying the structure of the expanded product and/or in improving the properties of the expanded product.

The invention extrasion process for the production of environmentally-degradable loose fill packaging products of this invention broadly comprises (i) intimately mixing a normally water-insoluble gelatinizable and meltable polysaccharide composition described above, preferably such compositions comprising components (A) and (B) above, with controlled proportions of water sufficient to provide a molten composition, under extrasion conditions of temperature, pressure and mechanical shear, optionally with one or more adjuvants noted above, (ii) feeding the mixture to an extruder equipped with one or more dies adapted to provide an internal pressure within the body of the extrader and screw means for conveying, compressing, heating and working the ingredients into a continuous molten mass, and for extrading the molten mass through the die(s) into a lower pressure zone where expansion of the mass to a foam and cooling of the foam to a hardened expanded product can take place. Preferably the extruder will be of the high temperature, high shear rate type, as is well known in the extrasion art.

Intimate mixing of polysaccharide components (A) and (B) with water (or an aqueous solution containing other adjuvants soluble or dispersible in water) may be accomplished by any of the methods known to the art for making intimate mixtures of heterogeneous materials. It is preferably conducted in two stages. Polysaccharide (A), which is preferably a starchy product, is first mixed with the aqueous component under conditions of high shear, as produced, for example, in an Osterizer" or "Waring" blender, so that the water (along with any components solubilized or dispersed therein) becomes substantially completely incorporated in the polysaccharide. The gum component, i.e., polysaccharide (B), is then added to the thus "tempered" starch and mixing is continued to obtain a uniform blend of the (A) and (B) compositions.

The blend may be immediately fed to an extrader, which may be of the single or multiple screw type, designed to develop a pressure of 800 to 3000 psig, preferably 1200 to 2000 psig. The extrasion temperature of the feed material increases as it moves along the barrel of the extrader, as a result of frictional heat generated by the moving screw, to a high generally in the range of about 100° to 225°C, preferably 150° to 200°C, during which time the feed material becomes gelatinized, then molten, as it nears the extrader die. If necessary, the contents can be heated by an external heat source. Desirably, the die is preheated to a temperature about as high as the molten mass reaching it. The die can be of any design known to the art. The diameter of the expanded product is controlled by the die and the temperature and pressure of the operation. The length of the expanded piece can be controlled by interfacing the exit die with a variable speed cutting knife.

The expansion ratio of the expanded product varies with the feed composition, the process conditions and the die. Typical expansion ratios correspond to bulk densities in the range of about 0.7 to 2 lbs/cu ft for the cooled and hardened foam product.

Slight loss of water, up to a maximum of about 0.5% by weight of the expanded product, occurs as it ages, under typical uses of loose fill materials. The aged product retains its resiliency and ability to withstand repeated shock, and shows little or no tendency to become sticky with time or to break up into fines.

The term normally solid and substantially water-insoluble polysaccharide (A) is meant to include natural starch and cellulosic products. Starchy products include any such product derived from cereal grains, legumes and tubers containing at least 50% by weight of natural (non- destracterized) starch on a dry basis. The starch portion comprises amylose consisting essentially of linear glucose units linked by alpha 1-4 bonds and amylopectin, generally regarded as having branched glucose-based chains and containing a major proportion of alpha 1-6 bonds. Representative starch substances include corn starch, corn mean (whole or degerminated), corn grits, wheat starch, rice starch and potato starch, with those derived from corn and rice preferred, especially corn meal and grits. Further preferred are starchy substances whose starch portions have amylose contents of up to 35% by weight, more generally between 20 and 30%.

Cellulosic products include cellulosic agricultural residues such as comminuted or ground oat-, rice- and wheat-bran, sawdust, wood pulp and dietary fiber, which may or may not be delignified.

Substantially delignified celluloses are characterized by having enhanced capacity to absorb water and are preferred for use herein. Such cellulosics are described in U.S. Patents 4,859,282, 4,859,283 and 4,957,599, which patents are incorporated herein by reference. The cellulosic component adds strength and aids in reducing flaking and dusting of the expanded product.

It will be appreciated by those in the art that the starch products, unless highly refined, normally contain minor proportions of other substances, notably proteins and lipids as well as internally bound water. The various starch products are also characterized in being plasticized or gelatinized on being heated with water at elevated temperatures, the temperature depending on the water content, the pressure, and to an appreciable extent on the degree of mechanical shear to which it is subjected. In general, the greater the water content, the higher the temperature and pressure and the greater the mechanical shear the lower the temperature required to render the product substantially molten.

It is believed that gelatinization followed by melting of the starch substrate occurs in the present process when the polysaccharide-water- based formulation is heated under extrasion conditions to a temperature of at least about 100°C. Subsequently extrading the molten mass produced jn^tu through a heated die into a lower temperature and pressure zone forms an expanded product through vaporization of the high temperature and pressure water contained in the molten mass.

The normally water-insoluble polysaccharide [component (A) above] is preferably employed in combination with a minor proportion of a water-swellable gum [component (B) above], preferably such gum that is polysaccharide-based and environmentally degradable. Included are alginates, alkyl and hydroxyalkyl celluloses wherein the alkyl moieties contain 1-3 carbon atoms, carboxyalkyl celluloses wherein the alkyl moiety contains 1- 3 carbon atoms, carrageenan (and the like sulfated polysaccharides), guar gum, agar, gum arabic, gum Ghatti, gum Kharaya, gum tragacanth and xanthan gum. Xanthan gum is preferred for its pronounced ability to bind and hold water at elevated temperatures, which is believed important in the production of highly expanded yet tough and resilient solid foam products. Another preferred gum is carboxymefhylcellulose for its ready availability and low cost.

The proportion of gum component (B) relative to component (A) can vary widely depending upon whether polysaccharide (A) is for example a starchy product, which is gelatinizable and meltable by water alone under such conditions. With substantially completely gelatinizable and meltable polysaccharide (A) compositions, such as the starch substances, the quantity of gum (B) may vary from about 0.01 to about 5% by weight of polysaccharide (A), preferably about 0.1 to 2%, more preferably about 0.4 to 1%. With (A) type polysaccharides that are difficult or not gelatinizable and extradable under extrasion conditions, e.g., cellulose, higher proportions of gum may be required ranging up to 10% or more by weight, with intermediate proportions used with mixtures of meltable and non-meltable polysaccharides. Preferably, the nαn-gelatinizable cellulosic component of polysaccharide (A) will constitute less than 50% by weight of (A), more preferably between 0.01 to 5% by weight, most 0.02 to 0.8%.

The gum functions importantly to enhance the degree of expansion and provide for a tougher resilient foam able to withstand repeated shock, particularly when a crash strength-enhancing agent, as described below, is employed therewith. The gum component also retards the evaporation of water from the extradate and minimizes dusting of the final product, attributable perhaps to its water-binding property. The water component substantially is multi-functional. It serves to gelatinize and then render the polysaccharide composition molten during its passage through the extruder, and to expand the molten mass on its being extruded into the low temperature and pressure external to the extrasion zone. The water component can be used to carry other, especially water- soluble or dispersible adjuvants, into the composition to be expanded. Such adjuvants include: foaming aids, e.g., alkali metal carbonates and bicarbonates, which can liberate CO2 in the presence of acid; acids (inorganic or organic as exemplified below); surfactants; lipids; antistatic agents, e.g., mineral and 'onium salts; fire retardants; preservatives and fungicides, e.g. propionic and benzoic acids.

The composition can also contain crash strength enhancing agents such as environmentally compatible compounds of polyvalent elements of Groups HI to IV of the Periodic Table, preferably of Group III and preferably those compounds wherein said element is bonded to oxygen atoms. Such compounds include: boric acid, boric anhydride (B2O3), sodium metaborate, sodium borate (including anhydrous as well as hydrated Na2B4θy); alumina, hydrated alumina (including aluminum hydroxide gel), aluminum carbonate, aluminum acetate and other carboxylates, aluminum borate, aluminum phosphate, sodium aluminum phosphate; silicic acid (including colloidal silica), alkali and alkaline earth metal aluminates and silica-aluminates, alkali and alkaline earth metal silicates such as sodium silicate and magnesium silicate. The compounds of the Group HI elements are preferred, especially those of boron, in particular the sodium borates. The crash strength enhancing agents are believed to crosslink the polysaccharide components of the formulation through coordination and/or reaction with the hydroxyl groups of adjacent polysaccharide molecules and thereby results in a foamed product having enhanced crash resistance. Such agent need only be used in relatively small concentrations, generally amounting to not more than about 3% by weight of the polysaccharide (A) component, e.g., starch, preferably to about 0.1 to 2% by weight, more preferably 0.2 to 0.8%.

Residual water in the expanded product, alone or in combination with additives carried therein imparts antistatic properties to the product, especially desirable in loose fill materials. The proportion of water should be sufficient to gelatinize and render molten the polysaccharide composition at the contemplated temperatures and pressures of the extrasion step and to provide a desired degree of expansion in the expansion phase of the extrasion step. Normally the amount of water based on the dry weight of the polysaccharide (A) component will be in the range of from about 10 to about 25%, preferably not more than about 20%, more preferably from about 12% to 18%. Since, in general, the higher water contents tend to product thinner walled products, which may be imdesirable, it is advisable to adjust the water content carefully to achieve optimally tough resilient foams having high crust resistance.

Since the polysaccharide components (A) and (B) normally contain water, their contents can first be determined by standard methods and the amount of water to be added adjusted accordingly.

In general, the water content should be coordinated with the gum content: the higher the water content the greater will be the gum content required for optimum expanded product pore strength; conversely, the higher the gum content the greater can be the water content and the higher can be the degree of expansion tolerated in the product. The water content, however, should also be coordinated with the extrasion temperature and pressure so that the expanded product, after cooling and hardening, contains at least about 4% and not more than about 14% by weight, preferably from about 7% to 12%, more preferably 10-12%. The optimum water content in the initial formulation is readily determined by trial. The water content, whether of the starting materials or of the expanded product, is conveniently determined by measuring the amount of water lost under standard water-loss methods of analysis.

The expansible composition may also include acid components, such as organic acids that are water-soluble and environmentally compatible. Included are organic acids containing up to 6 carbon atoms such as acetic, propionic, citric, ascorbic, tartaric, lactic, hydroxyacetic, gluconic, saccharic and benzoic acid. The carboxylic acids are preferred, in particular propionic and citric. Polycarboxylic acids such as citric, tartaric and saccharic are believed to function as cross-linking agents, enhancing the strength of the expanded starch matrix, in particular in combination with the gum component. " "

The composition can also contain leavening agents to promote gasification, thereby expansion of the mixture on extrasion, when an alkali- metal carbonate or bicarbonate is incorporated into the composition to be expanded. Preferred leavening agents are those that are slow-reacting, releasing CO2 relatively slowly while the expandable composition is heated under extrasion conditions. Included are sodium acid pyrophosphates, such as Na2H2P2θγ including hydrates thereof, monocalcium phosphate CaH4(Pθ4)2, as the hydrate or slow-release coated anhydrous material, and acidic sodium aluminum phosphates, e.g., NaHi4Al3(Pθ4)g-H2θ. The proportion of acid generally corresponds to about 0.1 to about 4%, preferably o.l to 1%, by weight of polysaccharide component (A).

The expandable formulation may also advantageously include a surfactant or lipid, preferably one of more that are environmentally acceptable. Typical are the long-chain (C^-Cig) fatty acids, their mono-, di- and tri- esters of glycerol or other polyol or polyhydroxycarbohydrate, such as, for example, sorbitol and sorbitol ethylene oxide condensation products, and lipids in general. The quantity is generally in the range of about 0.1 to 3% by weight of the polysaccharide (A) component, more usually about 0.1 to 1% by weight. The surfactant aids in dispersing water and other additives throughout the mixture to be expanded and promotes the formation of fine pores throughout the expanded product, thereby contributing to the resiliency and roughness of the foam structure. It will be noted that unrefined starchy products normally contain hpid material, for example as fatty acids or fatty acid esters of glycerol. Such material is believed to be incorporated into the extruded product as part of the network defining the cellular structure. The present formulation may contain still greater concentration of lipid material, since such material also increases the lubricity of the mass in the extrasion zone, resulting in an increased rate of production of extruded product.

Also, it appears that, like the gums, lipid material in or on the polysaccharide-based matrix tends to retard the evaporation of water from the final cooled and hardened expanded foam product.

In addition, the formulation to be expanded may also contain minor proportions of proteinaceous constituents, which may initially be present in the starchy or cellulosic product or may be added as such to augment the original content. Examples of such adjuvants are wheat gluten and soy protein. Protein enrichment of the formulation is often beneficial in strengthening and stabilizing the expanded structure, evidently through bonding interaction with the carbohydrate moiety.

To minimize the loss of water from the expanded product on standing, the product can be advantageously post-treated by spraying with water, with or without a humectant such as glycerin or any one or more or the polysaccharide (B) components dissolved therein, so as to increase the total water content if necessary and maintain it within the desired concentration range for extended periods of time.

Further, the formulation may also include minor amounts of other environmentally degradable polymers such as hydrolytically degradable polyesters and polyamides. One preferred group are such products made by self-condenstion of hydroxycarboxylic acids or by ring-opening polymerization of lactones and dimeric cyclic esters of alpha-hydroxy carboxylic acid. Examples are polylactide, polyglycolide, poly(gamma-valerolactone), poly(epsilon-caprolactone) and copolymers of any two or more thereof.

The expanded product of the invention normally ranges in color from substantially white to yellow, depending largely on the colors of polysaccharide (A) and polysaccharide (B). Products based on such starchy substances as corn meal and corn grits are inherently yellow. The color of the product, however, can be varied, as desired, by incorporating into the formulation to be expanded a small color-imparting amount of a compatible dye or other coloring agent. Preferably, the coloring matter is environmentally acceptable, such as an approved food colorant. For example, adding a red dye to a yellow corn mean/grits-based formulation yields a reddish product, a blue, a greenish one.

EXAMPLE 1 This example utilized a single screw extrader having a 9-inch long screw providing a double helix shallow cut flight in a 3.75-inch barrel and an exit die assembly designed to produce an internal pressure of about 1800 psig. The exit die assembly consisted of a die plate having 6 1/8-inch openings in it periphery and a backup plate having 20 1/8-inch openings at its center and providing a 0.03-inch clearance to the die plate. The exit die interfaced with a variable speed knife for cutting the extradate to a desired length, and the combination was chosen to produce peanut-shaped, two-inch long extradates in its cooled hardened state.

An extrusion mixture was prepared by mixing corn grits with an aqueous solution in an amount sufficient to provide a total moisture content of 15%. The aqueous solution contained 0.4% sodium bicarbonate, 0.2% carboxymethyl cellulose and 0.05% of a polysorbate ester of oleic acid, the percentages being based on the total composition by weight. The mixture was blended in a cone blender for 30 minutes to obtain a uniform blend.

The blend was fed to the extrader at a rate of 3 lbs per minute. The temperature of the mass within the extrader rose as it moved along the barrel, as a result of frictional heat generated by the working of the mass by the moving screw, and reached a maximum of about 190°C near the exit die, which has been preheated to about 180°C at start-up.

The expanded final product had a bulk density of 1.1 lbs per cubic foot, which corresponded to an expansion ratio of 6 times the diameter of the die opening. The product was sufficiently resilient and crash resistant, as evidenced by its ability to withstand repeated shocks, and had a moisture content of 10.1%, properties considered acceptable for many applications as a loose fill packaging material.

Lower moisture contents, e.g., down to 7%, where desired for use under high humidity conditions, can be achieved by flash drying. Such treatment also serves to create a case hardening of the foam surface, thereby minimizing possible moisture absorption under high moisture storage conditions.

EXAMPLE 2

In this Example the extrader and procedure of Example 1 was employed except that (a) the exit die assembly die plate contained 49/64-inch openings and was designed to produce a 1600 psig internal pressure; (b) the exit die was preheated to a temperature of about 165°C; (c) the extrasion feed mixture consisted of whole grits and sufficient water added to provide a total moisture content of 14% by weight; (d) the corn grits-water mixture was blended in a cone blender for 30 minutes; and, (e) the corn grits-water blend was fed to the extrader at a rate of 4 lbs per minute (200 rpm shaft speed).

The expanded product was judged suitable as a loose fill packaging material. EXAMPLE 3

The procedure of Example 2 was followed except that the com grits were first added to the cone blender with a monooleyl glyceride in an amount providing 0.25% by weight of the monooleate and the mixture then mixed for 3 minutes before adding water to provide a 14% total concentration of water and blending for another 30 minutes.

The extruded expanded product was considered acceptable as a loose fill packaging material.

EXAMPLE 4

The procedure of Example 3 was followed except that maltodextrin, in an amount of 3% by weight of the com grits, was blended with the corn grits along with the monooleate in the cone blender.

The expanded product was judged acceptable for use in loose fill packaging.

EXAMPLE 5

The procedure of Example 3 was followed except that 0.5% by weight of sodium bicarbonate and 1% citric acid by weight of the com grits were added to the cone blender along with the monooleate.

The expanded product was judged acceptable as a loose fill material.

EXAMPLE 6

The procedure of Example 5 was followed except that soy protein, as soy isolate, 3% by weight of the grits, was also added to the cone blender along with the sodium bicarbonate and the monooleate before further blending the formulation with water. The soy isolate contained 90% by weight of protein, 1% carboxyhydrate, 4% water, the rest ash-forming constituents.

The expanded product was judged an acceptable loose fill material. EXAMPLE 7

The procedure of Example 3 was followed except that 0.3% by weight each of NaHCθ3 and monosodium aluminum phosphate was also added to the com grits along with the monoglyceride in the cone blender.

The expanded product produced from this formulation was judged acceptable as a loose fill material.

EXAMPLE 8 An extrasion mixture was prepared by mixing com grits (98), carboxymethyl cellulose (1%), delignified and bleached cellulosic fiber prepared from oat hulls as described in U.S. Patent 4,859,282 (0.5%) and sodium aluminum acid pyrophosphate (0.5%), all percentages by weight. The water content of the total mixture was adjusted to 15% by weight by the addition of water and blending in a plow blender. The blend was fed to the extruder of Example 1 and extruded to form an expanded product under the conditions of Example 1. The product, compared to that of Example 1, showed improved resilience, greater crash strength and reduced dusting when broken and when tested as a loose fill packing material.

EXAMPLE 9 The procedure of Example 8 was followed except that the quantity of com grits was 97.5% by weight and 0.5% by weight of soybean oil was to the extrasion mixture to be blended. The resulting expanded product exhibited loose fill packing properties similar to those of the Example 8 product.

EXAMPLE 10 The procedure of Example 8 was followed except that the quantity of com grits was 97% by weight, that of carboxymethyl cellulose was 1.75% by weight and 0.25% by weight of borax (sodium borate decahydrate NaB4θylOH2θ)was added to the mixture to be blended. The extruded expanded product exhibited high resistance to crashing, flaking and dusting and was highly satisfactory as loose packaging material.

Claims

CLAIMS:

1. An environmentally-degradable expanded resilient solid foam free of synthetic polymer comprising a substantially continuous polysaccharide-based network of cell walls encompassing a multiplicity of pores and voids, said network before expansion consisting essentially of a normally solid water-insoluble thermally gelatinizable and meltable natural polysaccharide containing a major amount of a normally water-insoluble polysaccharide, a minor amount of a water-swellable environmentally- acceptable gum and water in the amount of from about 10 to 25 percent by weight based on the polysaccharide.

2. A foam of Claim 1 further characterized in that said foam has a bulk density of about 0.7 to 2 lbs/cu ft, and is resistant to the accumulation of static electricity.

3. A foam of Claim 1 wherein the polysaccharide before expansion consists essentially of a starchy substance wherein the starch has an amylose content of up to 35 percent by weight.

4. A foam of Claim 3 wherein the starchy substance is a cereal grain or tuber starchy substance containing at least 50 percent by weight of starch.

5. A foam of Claim 4 wherein the starch substance is a refined corn starch, corn meal, corn grits or a mixture thereof.

6. A foam of Claim 3 wherein the polysaccharide before expansion is a starchy substance mixed with a minor proportion of a cellulosic component.

7. A foam of Claim 1 wherein said gum is selected from the group consisting of alginate, alkyl cellulose, hydroxyalkyl cellulose, carboxy- alkyl cellulose, carrageenan, guar gum, agar, gum arabic, gum Ghatti, gum Kharaya, gum tragacanth, xanthum gum and mixture thereof.

8. A foam of Claim 1 wherein the polysaccharide before expansion is mixed with a minor proportion of a C\ to Cβ carboxylic acid.

9. A foam of Claim 1 wherein the polysaccharide before expansion is mixed with a minor proportion of a lipid.

10. A foam of Claim 1 wherein the polysaccharide before expansion is mixed with a minor amount of an environmentally compatible compound of an element of Groups BI to IV of the Periodic Table wherein the element is chemically bonded to one or more oxygen atoms effective to result in an expanded product having enhanced resistance to crashing.

11. A foam of Claim 10 wherein said environmentally compatible compound is selected from the group consisting of boric acid, boric anhydride, sodium metaborate, sodium borate or mixtures thereof.

12. A process for the manufacture of environmentally- degradable expanded solid foam products, which process comprises

(i) forming an expandable composition comprising

(a) a normally solid water-insoluble natural polysaccharide composition,

(b) a minor amount of water-swellable environmentally-acceptable polysaccharidic gum, and

(c) water in a minor amount from about 10 to 25 percent by weight based on component (a) sufficient to form an extradable substantially homogeneous thermally gelatinizable and meltable material polysaccharide composition and expand the composition when heated and extruded as described in steps (ii) and (iii) below,

(ii) heating and mixing the composition of (i) above in an extrasion zone at a temperature and pressure and for a time effective to form a substantially molten extradable composition,

(iii) extrading the composition through a shaped die into a lower temperature and pressure zone so as to form a shaped form, the pressure being sufficiently low relative to that in the extrasion zone to allow the foam to expand to a bulk density of about 0.7 to 1.2 lbs/cu ft, the temperature being sufficiently low to allow the foam to cool and harden, (iv) allowing the foam to harden to a resiUent low-bulk density product free of synthetic polymer, and (v) recovering the product.

13. A process of Claim 12 wherein the normally solid water- insoluble polysaccharide composition before expansion consists essentially of a starchy substance wherein the starch has an amylose content of up to 35 percent by weight.

14. A process of Claim 13 wherein the starchy substance is a cereal grain or tuber starchy substance containing at least 50 percent by weight of starch.

15. A process of Claim 14 wherein the starch substance is a refined corn starch, corn meal, corn grits or a mixture thereof.

16. A process of Claim 12 wherein the normally solid water- insoluble polysaccharide composition before expansion is a starchy substance mixed with a minor proportion of a cellulosic component.

17. A process of Claim 12 wherein said gum is selected from the group consisting of alginate, alkyl cellulose, hydroxyalkyl cellulose, carboxy-alkyl cellulose, carrageenan, guar gum, agar, gum arabic, gum Ghatti, gum Kharaya, gum tragacanth, xanthum gum and mixtures thereof.

18. A process of Claim 12 wherein the expandable composition before expansion is mixed with a minor proportion of a C to Cg carboxyhc acid.

19. A process of Claim 12 wherein the expandable composition is mixed with a minor proportion of a hpid.

20. A process of Claim 12 wherein the expandable composition before expansion is mixed with a minor amount of an environmentally compatible compound of an element of Groups HI to IV of the Periodic Table wherein the element is chemically bonded to one or more oxygen atoms effective to result in an expanded product having enhanced resistance to crashing.

21. A process of Claim 20 wherein said environmentally compatible compound is selected from the group consisting of boric acid, boric anhydride, sodium metaborate, sodium borate or mixtures thereof.