WO2001058674A2

WO2001058674A2 - Reinforced plastics and their manufacture

Info

Publication number: WO2001058674A2
Application number: PCT/US2001/004551
Authority: WO
Inventors: Tommy K. Thrash; Richard W. Tock; Daniel W. A'hern; Lyle V. Cox
Original assignee: Impact Composite Technology, Ltd.
Priority date: 2000-02-11
Filing date: 2001-02-12
Publication date: 2001-08-16
Also published as: MXPA02007702A; CA2401045A1; EP1255638A2; AU2001238183A1; WO2001058674A3

Abstract

A new organic reinforcing fiber for unsaturated polyester and other thermoplastic and thermoset resins has been developed from an agricultural byproduct. The reinforcing fiber confers desirable cost and mechanical advantages on articles produced, for instance, by the polyester-fiberglass industry. Also described are methods for producing molded, composite articles utilizing this organic reinforcing fiber, apparatus for producing such articles, and methods for reducing the emission of volatile organic carbons during the production to such articles.

Description

REINFORCED PLASTICS AND THEIR MANUFACTURE

The present invention relates to apparatus and methods, and the resulting product, for manufacturing reinforced plastics. More particularly, the present invention relates to the use of cellulosic reinforcing fiber for modifying composite plastics.

Reinforced, or composite, plastics are used in a variety of products ranging from automobile parts to spas, tubs, and showers, to septic and underground liquid storage tanks to boats to structural members for the construction industry. Both thermoplastic (polypropylene, polyethylene, polystyrene, ABS, nylon, polycarbonate, thermoplastic polyester, polyphenylene oxide, polysulfone, and PEEK, for example) and thermoset (unsaturated polyester, vinyl ester, epoxy, urethane, and phenolic, for example) plastics are modified with various materials for such uses. About 60% of all thermoset composites use glass fiber and a thermoset resin.

So-called "spray-up" in one-sided molds is a common fabrication process for making fiberglass composite products. Typical fiberglass products made by this method include boat hulls and decks, components for trucks, automobiles, recreational vehicles, spas, tubs, showers, and septic tanks. In a typical open-mold application, the mold is waxed and sprayed with gel coat and, after the gel coat cures, catalyzed thermoset resin (usually polyester or vinyl resin) is sprayed into the mold. A chopper gun chops roving fiberglass directly into the resin spray so that both materials are simultaneously applied to the mold and the spray-up may then be rolled out to compact the laminate. Wood, foam, or other core material may then be added and a secondary spray-up layer is applied to imbed the core between the laminates. The part is then cured, cooled and removed from the reusable mold.

Although not as widely used as thermoset resins, thermoplastic resin use is growing dramatically. Automated injection molding of thermoplastic composites has allowed the use of such composites in many applications previously held by metal casting manufacturers. Typical products include electrical and automotive components, appliance housings, and plastic lumber. Thermoplastic composites are compounded by melt blending the resin with additives and reinforcements and the resin, additive(s), and reinforcement(s) are fed through an extruder where they are combined, exiting the extruder in a strand that is cooled and cut into pellets for subsequent injection molding.

As such plastic composites become accepted in these applications, new markets and applications are opening up and there is increased demand for composites for use in those markets. In a broad sense, therefore, the present application is directed to thermoplastic and thermoset plastic composites that are modified with cellulosic materials, such as from plant byproducts, with improved physical characteristics compared to currently available reinforced plastics.

In another aspect, the present invention is directed to methods of manufacturing reinforced thermoplastic and thermoset plastics and the apparatus for manufacturing such plastics. In another aspect, the present invention is directed to a cellulosic material for use as a modifier for thermoplastic and thermoset plastics. In yet another aspect, the present invention is directed to methods for manufacturing composite articles from such plastics and the resulting products of such methods.

More particularly, the present invention provides a molded, composite plastic article comprising a polymeric resin and a cellulosic reinforcing fiber, the cellulosic reinforcing fiber a cellulosic material having a lignin content between about 20 and about 50 weight per cent and an inorganic content between about 5 and about 15 per cent by weight.

In another aspect, the present invention provides an improved method of molding plastic articles from both thermoplastic and thermoset resins that reduces emissions of volatile organic carbons wherein the improvement comprises applying a coating of a cellulosic reinforcing fiber to the molded plastic article before curing the polymeric resin comprising the molded plastic article.

In yet another aspect, the present invention provides a composite reinforced panel comprising a styrene resin and a cellulosic reinforcing fiber in a ratio of from about one part styrene resin to about one quarter to about three parts cellulosic reinforcing fiber wherein the cellulosic reinforcing fiber comprises a cellulosic material having a lignin content between about 20 and about 50 weight per cent and ^' an inorganic content between about 5 and about 15 per cent by weight. In yet another aspect, the present invention comprises a process for making a composite reinforced panel comprising mixing a styrene resin and a cellulosic reinforcing fiber in a ratio of from about one part styrene resin to about one quarter to about three parts cellulosic reinforcing fiber wherein the cellulosic reinforcing fiber comprises a cellulosic material having a lignin content between about 20 and about 50 weight per cent and an inorganic content between about 5 and about 15 per cent by weight, introducing the mixture of styrene resin and cellulosic reinforcing fiber into a mold, curing the mixture in the mold at elevated temperature, removing the cured mixture from the mold, and cutting the cured mixture to the desired size to form a reinforced panel. In still another aspect, the present invention provides an apparatus for molding an expanded thermoplastic polymer comprising an oven, a rack sized to fit the oven, at least two molds sized to fit into the rack, and a plurality of beams, at least one of the beams being located between the molds and at least one of the beams being located between one of the molds and the rack for transferring force caused by expansion of the thermoplastic polymer in the oven from the molds to the rack.

In still another aspect, the present invention provides a method of producing a filled plastics article involving the use as a reinforcing fiber of scrap material produced as a by-product of the processing of an agricultural product and comprising by weight between about 20 and about 50 per cent by weight, treated to reduce the material to particulate form and which has an ash content in the range of 5 to 15 per cent by weight and a lignin content in the range 20 to 50 per cent by weight.

Referring now to the figures, Figure 1 is a schematic diagram of a preferred method of preparing a cellulosic material for use as a modifier for thermoplastic and thermoset plastics. Figure 2 is a schematic diagram of a preferred method of molding a thermoplastic composite article in accordance with the present invention.

Figure 3 is a detail drawing of the molds for molding a thermoplastic composite board in accordance with the method of Fig. 2. Figures 4 A, 4B, and 4C are top, end and side views, respectively, of a rack for holding the molds of Fig. 3 for use in a method of producing a composite thermoplastic board in accordance with the method of Fig. 2.

Figures 5A, 5B, and 5C are top, end, and side views, respectively, of a preferred embodiment of an oven for use in producing a composite thermoplastic board in accordance with the method of Fig. 2.

Figure 6 is a side elevational view of a production line for producing a scored sheet for use in, for instance, spray-up molding using the composite thermoplastic board produced in accordance with the method of Fig. 2.

For purposes of illustrating the method of preparing a cellulosic material for use as a modifier for thermoplastic and thermoset plastics, reference will first be made to the use of cotton burrs as a filler for such plastics. The cotton burr is the woody or fibrous portion of the cotton boll that is neither lint nor seed, but does not include the bract, leaves, or stems as more fully described in U.S. Patent No. 4,670,944, that comprises a portion of what is commonly referred to as cotton gin by-product waste. The use of cotton burrs as a filler or modifier for such plastics is described in U.S. Patent No. 4,818,604, and both that patent and the aforementioned Patent No. 4,670,944 are hereby incorporated herein in their entireties by these specific references to those patents. Patent No. 4,670,944 describes a method of classifying lignocellulose materials for a variety of uses, including the use of the lignocellulose materials as a filler for plastics as described in Patent No. 4,818,604. Briefly, in that method, raw gin trash is cleaned of sand and fine leaf and bract particles in a spiral cut flight conveyor, pulverized in a hammer mill or equivalent, fed through a lint separator in the form of a tube formed of screen with a spike conveyor as the center shaft, the comminuted burrs, stems, and bracts falling through the screen and the lint remaining in the tube. In the present method, the method described in Patent No. 4,670,944 is modified as follows. Referring to Fig. 1, the cotton burr is separated and readily available at a cotton gin where the incoming seed cotton from the field has been harvested or stripped from the stalk by a stripper as described in Patent No. 4,670,944 such that most of the leaves, seed, trunk portions, sticks, and stems are not present as at step 10. Often the cotton burrs, as described in Patent No. 4,670,944, are stored in the open, for example, in unsheltered windrows. If necessary to prevent water damage, the burrs in the windrows are coated with fumed silica such as is available commercially under the brand names CAB-O-SIL (Cabot Corp.) and AEROSIL (DeGussa) by mixing the fumed silica with a volatile liquid carrier such as methyl alcohol and spraying the mixture on the windrows as at step 12. To decrease the likelihood of fire, a fire retardant such as BORAX may also be mixed with the burrs.

The burrs are preferably (but not required to be) compressed into ricks in the field (step 14) and are then loaded into a spiral cut flight conveyor for cleaning the sand and fine leaf and bract particles from the burrs, the latter as described in Patent No. 4,670,944, at step 16. The burrs are then pulverized in a hammer mill or equivalent apparatus as described in that prior patent at step 18 to increase bulk density and conveyed to a series of lint beaters, also of the type described in Patent No. 4,670,944, where as much cotton lint as possible is removed at step 20. The burrs are then moved by conveyor, truck and front end loader, or other means as known in the art to a hopper 22 which serves as the intake feed for a dryer 24, preferably a tower drier, for reducing the water content of the burrs to below about 15%, and preferably below 10%. The tower drier also serves as a conveyor for moving the feedstock from the hopper 22 to a second series of lint beaters 26 for removing any remaining lint from the burrs. The burrs fall through the screen of the lint beaters 26 onto a conveyor that feeds the burrs to one or more grinders 28 that grind the feedstock to a very fine material. The ground feedstock is then augured to another series of lint beaters 30 that remove even more lint and then to a series of bower shakers 32 for screening the feedstock to remove more lint and any oversized feedstock (the latter being returned to grinders 28). The remaining feedstock is then conveyed to a series of bower shakers/sifters 34 where the feedstock is screened to selected sizes, each sifter being provided with a conveyor for moving the sized reinforcing fiber to a separate holding bin 36.

Those skilled in the art who have the benefit of this disclosure will recognize that a number of modifications of this process are possible and, in some instances, even desirable. For instance, if the amount of moisture in the stored burrs 14 is low enough that forced air drying such as in the tower drier 24 is not required, the stored burrs 14 may be dessicated, and remain dessicated, by spreading a bed of dessicant on supporting structure and then covering the dessicant with a mesh and placing the burrs over the mesh. Calcium chloride, about two inches thick, is an acceptable bed. A 16 mesh or smaller wire screen is a satisfactory boundary. It is also noted that moisture does not penetrate very far into ricks of the stored cotton burrs such that it generally is not necessary to treat the stored burrs with fumed silica if the burrs are compressed into ricks. Another example of a modification to the above-described process is when the process is modified for use with other cellulosic materials. An example of such a material is the stalk, stems, and leaves of the cotton plant. As set out in the aforementioned U.S. Patent No. 4,670,944, in certain parts of the United States, cotton is customarily harvested by stripping the cotton bolls from the plant. Stripping usually involves stripping the leaves, sticks, and limbs, as well as the bolls, and leaves the stalk standing in the field. The normal practice is to shred or chop the remaining stalks and then spread them on the field and plow them under. In other parts of the U.S., and in many cotton growing areas in other countries where the cotton plant is much taller, the cotton is picked from the boll, leaving the stalk, stems, leaves, and burr standing in the field. The plant is then shredded or chopped, after which it is plowed under or otherwise disposed of. If used as a cellulosic material in accordance with the present invention, however, the stalks are harvested and either transported directly to a location at which the above-described process is conducted or stored in ricks until used as a feedstock for the above-described process. The use of such materials as cotton stalks as a feedstock for the above- described process for making a reinforcing fiber for reinforced thermoplastic and thermoset plastics is based upon the discovery that it is the combination of the lignin and the inorganic ash content of the cotton burrs that makes them so well-suited for use as a reinforcing fiber for such plastics, and the further discovery that cotton stalks and other cellulosic materials can be modified by addition of lignin and inorganic silica to function as acceptable substitutes for cotton burrs in such fillers. The lignin, which is a by-product of making paper pulp from trees and is available commercially under such brand names as LIGNOCITE (Georgia Pacific); is absorbed onto the cellulose fiber so that the fiber more readily bonds with such polymers as polyesters, polystyrene, polyethylene, polyvinyl chloride, polypropylene, and other polymers. The lignin also helps bond the cellulosic material to fiberglass and other polymeric constructs.

The lignin is preferably absorbed onto the cellulosic material at step 22 of the above-described method by mixing the cellulosic material with the liquid lignin in a mill or other suitable apparatus that serves as the inlet feed to the drier 24. It is preferred that enough lignin be added to the cellulosic material to bring the final lignin content of the reinforcing fiber to approximately 20 - 50 weight per cent of the reinforcing fiber, and preferably 30 - 45 weight per cent. Those skilled in the art will recognize from this disclosure that the amount of lignin that is added to the cellulosic material will vary depending upon the lignin content of the raw cellulosic material. Acceptable performance of the reinforcing fiber can also be obtained, depending upon the end use of the reinforcing fiber, by absorbing one or more of the primary precursors of lignin, trans-coniferyl, trans-sinapyl, and/or trans-p-coumaryl alcohol, onto the cellulosic material. Any one or more of these precursors may also be used, in generally smaller proportions, in addition to commercially available lignin, to optimize desirable physical parameters of the final product molded with the cellulosic reinforcing fiber of the present invention.

It is preferred that the ash content of the reinforcing fiber of the present invention be in the range of from about 5 to about 15 weight per cent, and preferably, about 7 to about 13 weight per cent. To obtain this percentage of ash in the cellulosic reinforcing fiber of the present invention, again depending upon the ash content of the raw material, it may be necessary introduce the silica into the cellulosic feedstock. For instance, analysis has shown that the ash content of the stalks of certain strains of cotton is so low (on the range of 2 - 3%) that silica must be added to the raw stalks to produce a satisfactory reinforcing fiber for making composite plastics. To do so, it is preferred that a -325 sized or smaller silica sand and silica flour be absorbed onto the cellulosic material in mineral oil, tall oils, vegetable oils such as soy oil, cotton oil, or palm oil, and/or hydrocarbon and other petroleum products. Water can also be used to introduce the silica into the fibers by, for instance, soaking the cellulosic material in a slurry of water and silica sand and/or flour for times ranging from about 15 minutes up to about 6 hours. Another method for penetrating the interior fiber is to pull a vacuum in a container filled with the raw cellulosic material, introduce the liquid water- or oil-based silica into the container, and then open the container to the atmosphere to drive the silica into the interior of the fiber. As noted previously, the addition of silica can be accomplished at step 22 of the above-described process and may or may not be accomplished simultaneously with the addition of lignin, if necessary. By modifying the cellulosic material in this manner, such materials as cottonwood and other trees, cottonseed and rice hulls, corn stalks, and many other agricultural by-products are utilized as the raw material for making the cellulosic reinforcing fiber of the present invention. In contemplation of the use of such materials as the raw material for making a reinforcing fiber according to the present invention, reference will be made herein to the use of scrap material produced as a byproduct of the processing of an agricultural product As noted above, the reinforcing fiber made by the method of the present invention is utilized for reinforcement of both thermoplastic and thermoset plastics. With respect to the use of the reinforcing fiber in thermoset resins, the fiber is used as either the main body of the construct or to modify the structure and/or physical behavior of the resulting construct. The addition of as little as 2 per cent of the reinforcing fiber (weight or volume) into some thermosetting resins will result in sufficient modification of the physical behavior of the resulting construct to adapt the construct for use in certain applications. Likewise, the inclusion of as much as 98 per cent reinforcing fiber (weight or volume) with a 2 per cent inclusion of resin, used as a physical binder, is sufficient for some constructs. All known unsaturated thermosetting polyesters, including alkyd, allyls, and other such polymers as those made in a condensation reaction between difunctional acids and glycols, dissolved in unsaturated monomers, tailored according to the particular application, have shown affinity for the reinforcing fiber. Likewise, vinyl esters and polyester/urethane hybrids, those combining phenols and aldehydes, either "two stage" novolacs, or "single stage" resols of phenolics show positive reaction to the lignin groups contained in the reinforcing fiber. The amino resins of melamine and urea likewise display structural behavior, tailored to the cellulosic content of the fiber. The reinforcing fiber is utilized as both a blowing agent for polyurethanes and for improving the strength of the resulting molded composite article. The epoxy groups, characterized by a three-membered ring structure, with the addition of compounds containing active hydrogen atoms such as amines, acids, phenols, and alcohols, that react by opening the ring to form a hydroxyl group also react with the lignin groups within the fiber. A modification that is peculiar to the behavior of these epoxy families occurs with the addition of the fiber, stabilizing the exothermic reaction, to inhibit "critical mass" behavior normally exhibited beyond fifty gram weight mass.

These thermoset resins may be utilized in many know manufacturing methods, including all forms of lay-up, spray-up laminated coatings, bulk castings, bulk molding compounds (BMC), sheet molding compounds (SMC), and other such method of molding and manufacturing as lαiown to those skilled in the art. Depending upon the particular thermoset resin, catalyst (as well as the additive package), and the desired properties of the composite molded article, resins including the reinforcing fiber of the present invention are molded at temperatures ranging from ambient and up and at pressures above and below ambient, all as lαiown in the art. To illustrate the use of the above-described reinforcing fiber for modifying thermoplastic resins, reference is made to Fig. 2 showing a process for making a composite polystyrene board including the reinforcing fiber of the present invention. In this process, the ground reinforcing fiber manufactured in accordance with the above-described method is mixed with an expandable thermoplastic polymer, a tackifier is added to produce a non-pre-blown mixture, and the mixture is heated in a mold to a temperature above the glass transition temperature of the polymer for a period of time sufficient to permit expansion of the polymer beads and bonding of the expanded beads with the reinforcing fiber to form a molded, composite article such as a composite board. Further, if the molded, composite article is, for instance, a board or panel, the composite board may be laminated by a solvent-based adhesive or by thermal insult coating to form rigid macro-voids between the laminate and the composite board surface. The molded composite may also be coated with a layer of the cellulosic reinforcing fiber of the present invention as described in more detail below. In addition, an additional polymer may be applied to the coating of the cellulosic reinforcing fiber to produce a molded, laminated composite with greatly increased toughness characteristics. If the composite panel is used, for instance, to increase the bulk and/or thickness of an open molded article, it does so with minimal increase in weight and improves many of the desirable properties of the resulting molded article such as resistance to moisture, fungus, compressive force, tensile strength, and other physical parameters.

In more detail, and by specific reference to Fig. 2, it can be seen that a thermoplastic polymer such polystyrene, available commercially in bead form, is mixed with the reinforcing fiber as a step 40 in a ratio of approximately two parts polystyrene beads to one part reinforcing fiber in a ribbon blender or similar agitating mixing device. A quantity of surface active agent comprising approximately 1% by weight of the total polystyrene bead content is added to this mixture at step 42 to promote uniform dispersion of the two components and to promote adhesive bonding between the reinforcing fiber and the polymer when molding. The polymer, reinforcing fiber, and surface agent mixture is then introduced into a mold as at step 44 shaped to the size of the desired molded product and the mold heated at step 46 to a temperature in excess of the glass transition temperature of the polymer for sufficient time to expand the polymer to the shape of the mold. The mold is then cooled as at step 48 to cure the expanded polystyrene. Although not necessary, it is preferred that a reduction from atmospheric pressue be utilized during the heating step 46 to cause the polymer beads to swell or "blow" more quickly and at a lower temperature. It is desirable to avoid high temperatures to avoid degenerating the strength of the composite article. If a reduction is pressure is utilized in the method of the present invention, a reduction from atmospheric pressure of about 5 inches of mercury is generally adequate to provide these desirable benefits. Those skilled in the art who have the benefit of this disclosure will recognize that greater reductions in pressure may result in more such beneficial results but at the cost of increased cost of production.

Those skilled in the art will also recognize that, although reference is made herein to polystyrene, the method of the present invention is also practiced with equally satisfactory results using many other thermoplastic melt processable polymers such as polypropylene, polyethylene, polyvinyl chloride, copolymers, tertiary polymers, including interpenetrating polymer networks, and their admixtures. A wide range of additives, including antioxidants, thermal stabilizers, nucleators, coupling agents, lubricants, and other processing modifiers are also utilized to advantage in connection with the molding of thermoplastic polymers in accordance with the teachings of the present invention. Those skilled in the art who have the benefit of this disclosure will recognize that, because the reinforcing fiber described herein is comprised of cellulosic material, temperatures above about 400 - 450° F will oxidize the reinforcing fiber, but the addition of one or more of these processing modifiers allows the cellulosic reinforcing fiber described herein to be melt processed at temperatures in excess of 500° F with satisfactory results.

Thermoplastic processing via injection, compression, extrusion, pulltrusion, melt coating, rotorotational molding, and other such methods are contemplated by the use of the term "molded" herein. It will also be recognized that thermosetting polymers may be substituted, in part or in whole, into the substituted polymer matrix or as an included modifier to a selected percentage ratio to the primary polymer to adjust the desired physical properties of the resulting molded product, the method of manufacturing that molded product, of the value benefit of the final product. In short, those skilled in the art will recognize from this disclosure that, even though certain polymers and methods of manufacture are described herein, the polymers and methods described herein are exemplary and that a wide range of possible combinations of polymers, combinations of polymers, modifiers and stabilizing additives, and methods of manufacturing may be utilized to achieve the desired results. The ratio of cellulosic reinforcing fiber to polymer is varied in accordance with the desired properties of the resulting product, it being contemplated that, in the case of the polystyrene polymer described herein, a ratio of about one part reinforcing fiber to about one part polymer is as high as is likely to be useful in most applications because, if a higher ratio is utilized, the resulting molded article is more rigid and brittle. There are, however, applications in which a rigid and/or brittle molded article is desirable. For that reason, the method of the present invention contemplates a ratio of reinforcing fiber to polymer that may be as high as about one part reinforcing fiber to about 0.25 parts polymer. By contrast, a lower ratio of reinforcing fiber to polymer, for instance, about one part reinforcing fiber to about three parts polymer, generally results in a molded article that is more pliable. Again, there are applications in which that pliability is desirable such that the method of the present invention contemplates that the reinforcing fiber and polymer may be blended in a ratio as low as about one part reinforcing fiber to about thirty parts polymer. Of course the ratios set out herein also depend on the particular polymer that is being blended with the reinforcing fiber. For instance, in the case of certain polymers, the resulting molded article may be brittle even when reinforcing fiber and polymer are utilized in a ratio of, for instance, about 1 :5 such that the present invention contemplates that those skilled in the art will find it beneficial to alter the ratio of reinforcing fiber to polymer experimentally to arrive at an optimum ratio for a particular application. The physical properties of the resulting molded composite article are also affected by the particular cellulosic reinforcing fiber that is utilized. For instance, if it is desired to mold a smooth textured board, the reinforcing fiber that is utilized may be a mixture of about equal parts of ground reinforcing fiber that passes through a 30 mesh screen and an 80 mesh screen. For a stronger board, larger particle sizes are utilized, including particle sizes up to as much as about half an inch. Similarly, the present invention contemplates the use of particles of cellulosic reinforcing fiber of different shapes as described in U.S. Patent No. 4,818,604 to optimize certain properties. As disclosed in that patent, for instance, if the strength and toughness of the molded composite article is important, particles shaped as flakes help achieve those properties. If the molded composite article is to be painted or coated for appearance such that the smoothness of the surface of the article is important, not only is it desirable to use a small size particle, but it is also desirable to use particles that are of the same, preferably round shape. These different shapes can be obtained by the use of hammer mills or other types of grinders to pulverize the cellulosic feedstock as lαiown in the art.

Similarly, other modifications can be made to the method of the present invention to optimize certain properties of the resulting molded, composite article. For instance, it has been found that in applications in which resistance to moisture and or attack from biologies such as mold and/or mildew is required, the reinforcing fiber may optionally be mixed with fumed silica before mixing with the polymer. Between about one half of one part to about one part of fumed silica is added to about 100 parts of the ground reinforcing fiber for this purpose. For applications in which high strength is required, commercially available lignin, for instance, LIGNOCITE (Georgia Pacific), may be added to the cellulosic reinforcing fiber in a ratio of about one half of one part to about one part per 100 parts of the mixture of reinforcing fiber and polymer.

Referring now to Figs. 3 and 4, there is shown a preferred embodiment of a mold for molding a composite board in accordance with the present invention. A plurality of molds 50 is shown in Fig. 3, each mold 50 being comprised of thin gauge metal top and bottom surfaces 52, 54 having a mold cavity 56 therebetween. The use of thin gauge material as the mold surfaces 52, 54 allows a greater degree of control over convection heat transfer on both heating and cooling of the mold 50, as well as a reduction in cooling time. To support the molds 50 and contain the internal pressures, a series of beams 58, preferably I-beams running along the long axis of the molds 50, is used above and below the surfaces 52, 54 and a plurality of molds 50 and beams 58 are stacked in a rack 60 with a screw press 62 bearing against the stack 64. Depending upon the shape of the article being molded (molds for a composite panel such as described above being shown in Figs. 3 and 4), it may be necessary to vary the shape of the foot 66 of screw press 62 or to utilize multiple screw presses 62 to achieve the necessary support for the stack 64 of molds 50 and to distribute that support over the surfaces 52, 54 uniformly and to transfer the force caused by expansion of the thermoplastic polymer in the molds 50 from the molds 50 to the structural members comprising rack 60. As can best be seen in Figs. 4B and 4C, in the preferred embodiment shown, three stacks 64 of ten molds 50 are supported by each rack 60, each stack 64 in rack 60 having two screw presses 62 bearing against the topmost beams 58 in the stack 64. Those skilled in the art who have the benefit of this disclosure will recognize that the number, size, and shape of the molds 50 will vary in accordance with the size and shape of the particular composite article being molded and that the specific arrangement of the molds 50 in rack 60 is therefore a matter of routine optimization of the molding process.

Referring now to Fig. 5, there is shown a preferred embodiment of an oven, indicated generally at reference numeral 70, for use in raising the temperature of the mixture of polymer and reinforcing fiber above the glass transition temperature of the polymer. The particular oven 70 shown in Fig. 5 is designed for use in molding composite panels of the type described above such that it is shaped to accommodate a plurality of the mold racks 60 described above. Those skilled in the art who have the benefit of this disclosure will recognize that the size and shape of an oven can either be optimized to the size and shape of the particular composite article being molded or that an oven in accordance with the present invention may be designed to accommodate a variety of mold shapes and numbers for use in molding different shaped composite articles.

Depending upon the size and shape of oven 70, however, means must be provided to circulate sufficient heated air, and subsequently, cool air to achieve uniform temperatures for heating and cooling the molds contained in the oven cavity 72. For instance, the oven 70 shown in Fig. 5 is heated (for instance, with natural gas) at about 350,000 BTU/hour and an airflow circulation of about 3000 cubic feet of air per minute is provided to maintain a relatively constant temperature throughout the oven chamber 72 during molding. An intake duct 74 within oven chamber 72 acquires the air for circulation through a plurality of louvers 76 for controlling the volume of circulating air and feeds a blower 78. The outlet duct 80 from blower 78 preferably directs the recycled air to impinge on the super heated air entering the oven cavity 72 from the burner 82 and the resulting mixture of recycled and superheated air is forced through a choke point 84 to prevent stratification and out into the mold cavity 72 through an expansion chamber 86. Although not shown since they are a function of the volume and shape of oven cavity 72, the arrangement of the molds and/or mold racks therein, the type of composite article(s) being molded, the volume of air being circulated in the oven 70, and many other factors, the oven cavity 72 can be provided with a plurality of baffles for directing the air flow evenly throughout the oven cavity. Alternatively, the outlet of expansion chamber 86 is shaped and positioned in the oven cavity 72 to direct the heated air into the oven cavity 72 in a vortex that reduces the likelihood of "dead air space" in the oven cavity 72 to assure adequate heat transfer and temperature control throughout the oven cavity 72. In the particular oven 70 shown in Fig. 5, the heated air in the oven cavity 72 is recycled and re-heated approximately every 60 seconds, but those skilled in the art will recognize that circulation time is, like the other factors listed above, a function of the size and shape of the oven, the particular polymer that is mixed with the reinforcing fiber of the present invention for molding, the temperatures required for molding, and many other factors such that the recycle time set out herein is only illustrative of the particular oven 70 shown in the figures for molding a composite panel and that many other recycle rates are contemplated by the present disclosure.

A particular problem that arises in connection with the molding of composite articles is the evolution of volatile organic carbons (VOCs). For instance, the oven 70 described above and shown in Fig. 5 is designed to produce approximately 100 cubic feet of molded composite panels per hour, and at that production rate, approximately 60 pounds of pentane gas is generated each hour. VOCs are harmful to the environment and cannot safely be released into the atmosphere; consequently, the design of oven 70 is such that almost none of the 60 pounds of pentane gas per hour that is generated is released to the atmosphere. This reduction in VOC emission is accomplished by the recycling of the air in the oven cavity, and specifically, by the burning of the pentane gas pulled from the oven cavity 72 during molding in the expansion chamber 86 of the air circulating means. A vent 88 is provided at a low point in the wall of oven 70 for venting any pentane gas (or other VOCs) and the vent 88 directs the VOCs to a flare stack 90 where final combusion, if necessary, is accomplished to further reduce VOC emission.

Another aspect of the present invention also relates to the harmful effect of VOC emission. Surprisingly, it has been discovered that the addition of the reinforcing fiber of the present invention to certain polymers has the effect of decreasing VOC emission. Application of the reinforcing fiber to, for instance, uncured polyester resin (PER) has the effect of reducing VOC emission compared to VOC emission from molding of PERs that do not include the reinforcing fiber of the present invention. However, for maximum reduction of VOCs, the reinforcing fiber is mixed with the PER in the form of the liquid resin rather than the beads described above. For instance, if the reinforcing fiber is added in an amount comprising about 10% by weight to a general purpose PER such as STYOL 20-4221 or 40-4232 (Cook Composites and Polymers Company, Kansas City, MO) and catalyzed with 0.9 to 2.0% methyl-ethyl ketone peroxide (MEKP), the resulting mixture contains about 50 - 60% solids and the balance is liquid styrene, and when this mixture is molded in the manner described above, free styrene vapor emissions are reduced by the absorption of about 2.2 to 2.8 times the weight of the liquid styrene component in the resin, with a reduction of vapor emissions by as much as 50%. Further testing has shown that the addition of about 10% by volume of the reinforcing fiber of the present invention to polyester resins results in a weight loss reduction of styrene of approximately 43%. It appears that the reduction in styrene vapors (VOCs) from polyester resins is a transient phenomenon and that at least three factors are involved in this method of reducing VOC emissions from PER production. First, the reinforcing fiber appears to physically absorb styrene from the PER solution and effectively reduce initial vaporization. This absorption is selective to styrene because of the relatively low molecular weight of styrene compared to the molecular weight of the polyester component of the resin solution. Second, the styrene absorbed into the reinforcing fiber, however, is still driven off by elevated temperature such that, at or about the peak temperature, the vapor pressure of the styrene and, hence, the styrene emissions, will also peak and then subside. This effect is most noticeable for large molded composite articles in which the heat of the polymerization process builds rapidly in the mold due to a decrease in the thermal conductivity of the cured resin. Third, the free styrene in the PER solution also reacts to become a portion of the polymer structure during cure. This reaction effectively removes and/or prevents the styrene monomer from becoming a part of the VOC that is generated. In light of these three factors, styrene vapor emission is best reduced by mixing the reinforcing fiber with the PER to temporarily "lock up" the styrene monomer by absorption into the reinforcing fiber as described above. Second, rapid curing processes that avoid excursions into high temperatures provides the best opportunity for locking the styrene monomer into high molecular weight polymers and eliminating the migration and loss of the monomer to the vapor phase. Because rapid PER cure rates also produce high peak cure temperatures, the present invention contemplates optimization of the cure rate, followed by the cooling of the molds, in a manner known to those skilled in the art to reduce VOC emissions.

In another aspect of the present invention, a further reduction in VOC emission is achieved by spraying or otherwise applying a cover coating of the reinforcing fiber described above to the molded composite article. The preferred method of application of the cover coat is by the use of a so-called "particle pump" such as that manufactured by Venus- 1 Magnum Corporation (St. Petersburg, FL). The reinforcing fiber is loaded into a storage hopper that is coupled to a compressed air stream venturi outlet and the reinforcing fiber is mixed into the compressed air stream and propelled through an application nozzle to be deposited onto the surface of the still wet molded composite article. The dry stream of reinforcing fiber appears to bond to the wet surface via capillary attraction, providing further absorption of styrene monomer and functioning in a manner similar to a physical barrier to prevent escape of VOCs by evaporation of these objectionable emissions.

If this airflow cover coating of the reinforcing fiber of the present invention is the final surface of the molded composite article, this coating is left intact as a barrier to further emissions during the final exothermic cure of the article. However, should it be desired to apply further laminations, either to build bulk volume (and thus increase the overall physical performance of the article) or to attach structural elements to the molded composite article (e.g., to attach the pedestal to a molded sink basin), the process is then repeated, several times if necessary, overcoating the dry sprayed layer of reinforcing fiber with a new wet coating of resin. Care must be taken that a sufficient volume of resin is applied to the dry coat of reinforcing fiber to avoid formation of voids in the interior of the laminate.

The saturated layer of reinforcing fiber appears to function in a manner similar to the core of a laminate, providing both bulk volume without requiring the use of more expensive resins and reinforcing materials and performing a coupling and performance role that increases the physical performance characteristics of the final article. With regard to the latter, these laminated structural cores appear to function according to the teachings of the so-called Milewski packing theory (H.S. Katz and JN. Milewski, Handbook of Fillers for Plastics, New York: Chapman and Hall (1987)) to enhance the ultimate physical performance of the final molded composite article. In accordance with this theory, the use of a combination of reinforcing shapes and sizes of particles as provided by the cellulosic reinforcing fiber of the present invention completes the matrix structure of the polymer, reinforcing and allowing stress transfer behavior throughout the entire structure, reinforcing the what would have otherwise been unprotected resin deposits, and filling the spaces between the reinforcing fibers. The combination of the cellulosic reinforcing fiber of the present invention and the resulting reinforcement provides a more ductile molded composite that is more forgiving of the more normal "micro-cracking" failure modes. By enhancing the behavior of these reinforcing materials in this manner, the present invention makes possible the substitution of what would have otherwise been the non- performing portion of the fibrous glass materials with the less expensive cellulosic reinforcing fiber without a direct percentage loss in physical properties, yet increasing other desirable properties of behavior such as impact resistance.

The expected physical properties of these composite molded articles can be tested and expressed alone, for instance, as tensile strength, flexural strength, compressive strength, and impact stength, or in a resulting combination that is necessary to produce a specific designed combination of properties or behavior when exposed to certain stresses. Testing by accelerating the speed of the stress that is applied to the composite, molded article in a uniaxial direction combines all these forces and stengths, noting a ductile vs. brittle failure model. Long term flexural fatigue can, for instance, be reasonably predicted with this model while the rate of failure by instant impact loadings can be shown in a "better or worse" behavior model, thus establishing a composite design guidance reflecting these combinations of forces to the entire model. Adjusting the performance behavior of the molded, composite article can be accomplished with a high degree of confidence by following this model and by doing so, testing indicates that properly applied and void free, lamination of the molded, composite article in this manner can result in a doubling of the ultimate impact strength of the finished article.

Another benefit of the use of the cellulosic reinforcing fiber in this manner has been discovered when a "suppressed" resin is used to reduce VOC emission and additional layers or laminations are to be applied to the molded article. When such resins are used, an expensive and tedious process of removing the suppressing wax layer is necessary to achieve further bonding of the laminations. However, the application of the reinforcing fiber of the present invention to the wet coating of suppressed resin and further application of wet coatings results in a laminate having superior physical properties without the need for the tedious and expensive process of removing the wax layer.

Testing has shown that with the addition of about 10% reinforcing fiber to the resin and application of the reinforcing fiber as an overcoat, a reduction in emissions of up to about 80%) can be achieved, both as an apparent result of the absorption capacity of the reinforcing fiber and its function as a mechanical barrier to emissions. It is preferred that the reinforcing fiber overcoat be applied to the molded article no later than about ten minutes prior to the onset of the exothermic reaction since testing has shown that about 70%) of the evolved weight loss occurs within the first increase in the exotherm and before the resin reaches 50% of peak temperature.

Although it will be understood that the above-described molded, composite panels may be molded in an infinite number of shapes and sizes for use in such applications as construction components such as siding and/or structural members and decorative trim, concrete forming, outdoor playground equipment, protective structures and/or buildings, and many other purposes, the composite panels are also used in the above-described open mold process for producing such useful articles as shower and tub enclosures, boat hulls, and many other molded articles. To facilitate this use of the molded, composite panels produced in accordance with the present invention, reference is again made to the figures, and specifically, to Fig. 6 showing a production line for final processing of the molded composite panel produced from the molds 50 shown in Figs. 3 and 4. The production line comprises a flat conveyor 100 on which the panels are placed flat and which carries the panels past a station 102 at which a scrim is adhered to one side of the panel and then to a linear scoring saw 104 that cuts part way through and from the other side of the panels. The conveyor 100 next carries the panels through a cross-cut scoring saw, or cuber, 106 that cross-cuts partly through each panel and past a series of spring-loaded, spaced rollers that serves as a score cracker 108 to break the scored panel into a plurality of strips of approximately equal width. The strips are then carried past a pair of parallel, horizontally spaced rollers 110 that break the scored strips into an array of approximately equally sized tiles or cubes that is held together by the scrim and can be applied to the first layer of a thermoset resin (usually, polyester or vinyl ester) in the spray-up process. The scrim allows the array of tiles to conform to the shape of the open mold for subsequent application of a second spray-up layer to produce a shaped laminate that is lighter and stronger than conventional glass molded structures.

Although the production of a molded, composite article has been described herein as a batch process, those skilled in the art will recognize from this disclosure that the process can also be conducted as a continuous production method. Continuous loading, pre-heat conditioning, temperature processing, and repeat are accomplished on a continuous transfer line using radio frequency of 50 -- 100 megahertz or microwave energy in the 915 megahertz range to heat the process moisture in the reinforcing fiber. This heat transfer is used to blow the EPS beads in a moving belt conveyor of stainless steel ribbon as the top and bottom surfaces of, the mold with moving edge guides encapsulating the expanding polymer and the resulting continuous sheet is cut to length by a cross-cut scoring saw upon exiting the process line. The thickness of the sheet is changed by opening or closing the gap between the endless ribbons. If the laminate panel is to be used as a single sheet, for instance, in a manner similar to the uses of commercial chip board or pressed board, the percentage volume and particle size of the reinforcing fiber is adjusted to provide high compressive strength and to assist in adhesion to the structural laminates. If the molded, composite panel is to be converted to scored sheet, mounted on scrim cloth in the manner described above in connection with the description of the production line shown in Fig. 6, the percentage volume and particle size of reinforcing fiber is reduced to assist in the ductile behavior required for contoured laminates.

Although the inventions described herein are described in conjunction with the preferred embodiments that are illustrated in the figures, certain variations in those embodiments which are equivalents are intended to fall within the scope of the following claims.

Claims

What is Claimed Is:

1. A molded, composite plastic article comprising a polymeric resin and a cellulosic reinforcing fiber, said cellulosic reinforcing fiber comprising a cellulosic material having a lignin content between about 20 and about 50 weight per cent and an inorganic content between about 5 and about 15 per cent by weight.

2. The molded, composite article of claim 1 wherein said cellulosic reinforcing fiber comprises less than about 15% water.

3. The molded, composite plastic article of claim 1 wherein said polymeric resin comprises either a thermoset or a thermoplastic resin or a mixture of a thermoset and a thermoplastic resin.

4. The molded, composite plastic article of any of claims 1 - 3 comprising about one part of said cellulosic reinforcing fiber to about 0.25 to about 30 parts of said polymeric resin.

5. The molded, composite plastic article of any of claims 1 _.- 4 additionally comprising fumed silica in a ratio of from about one half to about one part of fumed silica to about 100 parts of cellulosic reinforcing fiber.

6. The molded, composite plastic article of any of claims 1 - 5 additionally comprising a coating of said cellulosic reinforcing fiber.

7. A molded, composite plastic article substantially as described herein.

8. In a method of molding plastic articles, the improvement comprising applying a coating of cellulosic reinforcing fiber. to the molded plastic article before curing the polymeric resin comprising the molded plastic article to reduce emissions of volatile organic carbons.

9. The improved method of claim 8 wherein said cellulosic reinforcing fiber comprises a cellulosic material having a lignin content between about 20 and about 50 weight per cent and an inorganic content between about 5 and about 15 per cent by weight.

10. The improved method of either Of claims 8 or 9 additionally comprising applying additional polymeric resin over the coating of cellulosic reinforcing fiber.

11. The improved method of claim 8 wherein the polymeric resin is a styrene resin and the coating of cellulosic reinforcing fiber is applied no later than about ten minutes prior to the onset of the exothermic reaction.

12. The improved method of any of claims 8 - 10 wherein the polymeric resin is applied prior to the onset of polymerization of the polymeric resin.

13. The improved method of any of claims 8 - 10 or 12 additionally comprising accelerating the curing of the polymeric resin.

14. The improved method of claim 13 additionally comprising limiting the temperature at which the polymeric resin cures.

15. The improved method of any of claims 8 - 10 or .12 additionally comprising limiting the temperature at which, the polymeric resin cures.

16. An improved method of reducing emissions of volatile organic carbons during the curing of polymeric molded articles substantially as described herein.

17. A composite reinforced panel comprising a styrene resin and a cellulosic reinforcing fiber in a ratio of from about one part styrene resin to about one quarter to about three parts cellulosic reinforcing fiber wherein said cellulosic reinforcing fiber comprises a cellulosic material having a lignin content between about 20 and about 50 weight per cent and an inorganic content between about 5 and about 15 per cent by weight.

18. The composite reinforced panel of claim 17 additionally comprising fumed silica in a ratio of about one part of fumed silica to about 100 parts of said cellulosic reinforcing fiber.

19. The composite reinforced panel of either of claims 17 - 18 wherein said cellulosic reinforcing fiber comprises approximately equal parts of particles passing through a 30 mesh screen and particles passing through an 80 mesh screen.

20. The composite reinforced panel of either of claims 17 - 18 wherein said cellulosic reinforcing fiber comprises particles in sizes up to approximately half an inch in size.

21. A composite reinforced styrene panel substantially as described herein.

22. A process for making a composite reinforced panel comprising: mixing a styrene resin and a cellulosic reinforcing fiber in a ratio of from about one part styrene resin to about one quarter to about three parts cellulosic reinforcing fiber wherein said cellulosic reinforcing fiber comprises a cellulosic material having a lignin content of between about 20 and about 50 weight per cent of said cellulosic reinforcing fiber and an inorganic content of between about 5 and about 15 weight per cent of said cellulosic reinforcing fiber; • introducing the mixture of styrene resin and cellulosic reinforcing fiber into a mold; curing the mixture of styrene resin and cellulosic reinforcing fiber in the mold at elevated temperature; removing the cured mixture from the mold; and cutting the cured mixture to a desired size.

23. The method of making a composite reinforced panel of claim 22 additionally comprising accelerating the cure rate.

24. The method of making a composite reinforced panel of either of claims

22 - 23 additionally comprising cooling the cured mixtμre of styrene resin and cellulosic reinforcing fiber in the mold.

25. The method of making a composite reinforced panel of any of claims 22 - 24 additionally comprising applying a coating of the cellulosic reinforcing fiber to the mixture of styrene resin and cellulosic reinforcing fiber before curing.

26. The method of making a composite reinforced panel of claim 22 additionally comprising applying a scrim to the cut, cured mixture of styrene and cellulosic reinforcing fiber.

27. The composite reinforced panel miαe by the process of claim 22.

28. A method of making a composite reinforced panel substantially as described herein.

29. An apparatus for molding an expanding thermoplastic polymer comprising: an oven; a rack sized to fit into said oven; at least two molds sized to fit into said rack; a plurality of beams, at least one of said beams being located between said molds and at least one of said beams being located between one of said molds and said rack for transferring the force caused by the expansion of said thermoplastic polymer in said oven from said molds to said rack.

30. The apparatus of claim 29 additionally comprising means for cooling said oven.

31. The apparatus of claim 29 wherein said oven is heated by forced air..

32. The apparatus of claim 31 additionally comprising means for distributing forced air evenly throughout the oven cavity.

33. The apparatus of claim 3 i additionally comprising a blower for distributing forced air evenly throughout the oven cavity.

34. The apparatus of claim 33 wherein the air output from said blower is injected into the forced air heating said oven.

35. The apparatus of claim 34 wherein the mixed air output from said blower and the forced air heating said oven is passed through a choke point.

36. The apparatus of claim 33 additionally comprising a combustion chamber for the mixed air output from said blower and the forced air heating said oven.

37. The apparatus for molding an expanding thermoplastic polymer substantially as described herein.

38. A method of producing a filled plastics article, involving the use as a reinforcing fiber material of scrap material produced as a by-product of the processing of an agricultural product and comprising by weight between about 20 and about 50 per cent by weight, treated to reduce the material to particulate form and which, has an ash content in the range of 5 to 15 per cent by weight and a lignin content in the range 20 to 50 per cent by weight.

39. A method according to claim 38 in which the agricultural by-product is treated with inorganic silica to increase the ash content to the desired range.

40. A method according to claim 39 involving the use of silica grain, silica sand. or silica flour, and a carrier material by which the silica may be absorbed into the reinforcing fiber material.

41. A method according to claim 40 wherein the carrier material comprises mineral oil, tall oils, vegetable oils, hydrocarbons or petroleum products.

42. A method according to any one of claims 38 - 41 wherein the reinforcing fiber material is coated with fumed silica.

43. A method according to claim 42 involving mixing the fumed silica with a volatile carrier and spraying the mixture onto the material.

44. A method according to any one of claims 38 - 43 involving the processing of the material to ensure that the particle size ranges from a size passing through an 80 mesh screeen up to half an inch.

45. A method according to any one of claims 38 - 44 involving the processing of the material to ensure that the particles of the material are different shapes.

46. A method according to any one of claims 38 - 45 wherein the agricultural by-product is treated with sufficient lignin to increase the lignin content of the material to the desired range.

47. A method according to claim 46 involving mixing the reinforcing fiber material with liquid lignin prior to drying the reinforcing fiber material.

48. A method according to any one of claims 38 - 47 involving absorbing onto the agricultural by-product one or more primary precursors of lignin, trans- coniferyl, trans-synaptyl, and trans-p-coumaryl alcohol.

49. A molded plastics article, molded from a mixture comprising a polymeric resin and a reinforcing fiber material according to any one of claims 38 - 48, together with a surface active agent, in which the constituents are mixed together, introduced into a mold, and retained in the mold at an elevated temperature to cure the polymeric resin.

50. A molded plastics article according to claim 49 wherein the rate of cure of the plastics article is accelerated.

51. A molded plastics article according to either of claims 49 or 50 wherein the plastics article is cooled after curing.

52 A molded plastics article according to any of claims 49 - 51 wherein the maximum temperature at which the polymeric resin cures is limited.

53. A molded plastics article according to any of claims 49 - 52 additionally comprising applying a coating of the reinforcing fiber material to the molded plastic article before curing.

54. A molded plastics article according to claim 53 additionally comprising one or more additional layers of polymeric resin applied over the coating of reinforcing fiber material.