HIGH-STRENGTH, ENVIRONMENTALLY FRIENDLY BUILDING PANELS

CROSS REFERENCE TQ RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional 61/014,214 filed December 17, 2007, which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention, generally, relates to panels that are biodegradable and free of formaldehyde and more particularly to panels with soy based composite.

BACKGROUND OF THE INVENTION

Urea-Formaldehyde (UF) resins are widely used as a binder for use in oriented strand board and particle board. These formaldehyde-based resins are inexpensive, colorless, and are able to cure fast to form a rigid polymer. Despite the effectiveness of the UF resins, particle board and oriented strand board often has a reputation for being of poor quality. Included in the quality is concern about the rate that these composites degrade when exposed to water or heat and humidity.

Another serious disadvantage of UF resin-bonded wood products is that they slowly emit formaldehyde into the surrounding environment what are commonly known as Volatile Organic Compounds (VOCs). Due to environmental, health, and regulatory issues related to formaldehyde emissions from wood products, there is a continuing need for alternative formaldehyde-free binders. Recent legislation has prohibited or severely restricted the use of formaldehyde in one or more states.

A number of formaldehyde-free compositions have been developed for use as a binder for making wood products.

U.S. Pat. No. 4,395,504 discloses the use of formaldehyde-free adhesive system prepared by a reaction of a cyclic urea with glyoxal, for the manufacture of

particleboard. Such a system, however, showed a rather slow cure and required acidic conditions (low pH) for the cure.

U.S. Pat. No. 5,059,488 shows an advantage of glutaraldehyde over glyoxal, when used in a reaction with cyclic urea. The patent discloses the use of glutaraldehyde- ethylene urea resins for wood panel manufacture. It was shown that this resin cured faster than glyoxal-ethylene urea resin, and the cure can be performed at a relatively high pH. However, the glutaraldehyde-based resins are not economically feasible.

U.S. Pat. No. 4,692,478 describes a formaldehyde-free binder for particleboard and plywood prepared of carbohydrate raw material such as whey, whey permeate, starch and sugars. The process comprises hydrolysis of the carbohydrate by a mineral acid, and then neutralizing the resin by ammonia. Although the raw materials are cheap and renewable, the reaction has to be performed at about 0.5. The pH makes handling difficult, dangerous, and costly.

U.S. Pat. No. 6,822,042 also discloses the use of a carbohydrate material (corn syrup) for preparing a non-expensive wood adhesive. Advantages of this binder include strong bonding, low cost, and renewable raw material. However, this adhesive requires the use of isocyanate as a cross-linker for this composition. Isocyanates are toxic making the use as a substitute for formaldehyde undesirable.

U.S. Pat. No. 6,599,455 describes a formaldehyde-free binder for producing particleboard containing curable thermoplastic co-polymers and cross-linkers selected from epoxy, isocyanate, N-methylol and ethylene carbonate compounds. Such compositions provide good strength and water resistance when cured. The epoxys are economically unfeasible do to the high material cost.

U.S. Pat. No. 6,348,530 describes a formaldehyde-free binder for producing shaped wood articles comprising a mixture of hydroxyalkylated polyamines and polycarboxylic acids. The binder preparation requres difficult steps to producte and as a result is not economically viable.

One product that has emerged as a substitue for formaldehyde products is Purebond® proprietary manufacturing system for hardwood, plywoods and particle board.

However, it is believed that Purebond® may include other toxic chemicals such as epichlorohydrin. While Purebond® is an improvement over the state of the art, it ultimately does not eliminate all dangerous or potentially dangerous compounds from its formulation. See http://www.columbiaforestproducts.com/products/prod-pb.aspx. See also U.S. Patent No. 7,252,735.U.S. Patent No. 7,345,136 (Heartland Resources Technologies) is believed to relate to H2H proprietary product, Soyad ®. Soyad ® is believed to include soy protien in a resin form, but does not eliminate the use of carcinogenic binders in combination with the soy protien.

Thus, after considerable attempts to solve the problem of urea formaldehyde adhesives, there exists a need to create a truly non- toxic high strength resin or composite system that does not contain any formaldehyde compositions or other carcinogenic compounds, is earth friendly and remarkably strong.

U.S. Patent Publication No. 20060264135 discloses a soy-based resin that optionally contains one or more green strengthening agents. This document discloses a method of manufacturing the soy based resin, impregnation of the resin on fibers, precuring the resin on the fibers and curing the composite in a press. However, no details are taught about producing large objects such as building panels that can be made from soy-based resins and composites.

The state of the art is to find a resin that would be an effective replacement of formaldehyde resins such as UF. However, it would be desirable to provide a panel that exceeds the current state of the art of particle board in strength. It would be further advantageous if this material was biodegradable, substantially, if not entirely from renewable sources, was environmentally friendly, It would be further advantageous if the panels having comparable strength to state of the art particle board was lighter weight, used less bulky materials, and had a lower profile. It is desirable that such curable compositions contain relatively high amount of non- volatiles, and at the same time are stable, fast-curing and do not emit any toxic fumes during the cure and afterwards. It would be desirable for the product to be not harmful to the environment when placed in a landfill. The present invention addresses one or more these and other needs.

SUMMARY OF THE INVENTION

The present invention is a high-strength, low-profile composite panel. The panel comprises a soy protein based resin and one or more sheets of plant-based fibers. The panel is made from the compression of the sheets in a vented press at a temperature that is a minimum of 8OC, a pressure that is a minimum of 3 MPa, and for a time that is a minimum of 10 minutes. The panels are a minimum length of 4 feet and a minimum width of 2 feet and a maximum thickness of one centimeter.

It has been discovered during the application of soy based resin technology to large building panels that moisture in the precured mats can create considerable previously uneonsidered challenges. Rapid curing is desirable to increase throughput and efficiency of manufactured panels. Yet rapid curing has been discovered to trap moisture in the form of steam in pockets throughout the panels. The steam pockets separate the various layers of manufactured panels. This creates unsightly bubbles or blisters and, more practically, weakens the panels.

The present invention of one embodiment employs a vented press that will adequately vent the steam at locations throughout the panel. Thus, steam can escape from the press.

Alternatively or optionally, the curing of the panels can occur in two stages, the first stage occurs at an elevated temperature relatively lower pressure to drive off the moisture before a second curing stage at elevated temperature and pressure. In one embodiment the temperature of the first stage is a minimum of about 6OC, about 70 C or about 8OC and a maximum of about 110 C, about lOOC, about 9OC or about 80 C. The pressure of the first stage is a minimum of about 0.3MPa, about 0.5MPa or about 0.7MPa and/or a maximum of about 1 MPa, about 0.8 MPa or about 0.7 MPa.

In one embodiment the temperature of the second stage is a minimum of about HOC, about 115C, about 120C, or about 125C and a maximum of about 14OC, about 135C ₃ about 130C or about 125C. The pressure of the second stage is a minimum of about 2MPa, about 4MPa or about 6MPa and/or a maximum of about 10 MPa, about 8MPa or about 6MPa.

The plant-based fibers include one or more of flax, hemp, sorghum, kenaf, jute, ramie, sisal, kapok, banana, pineapple and combinations thereof.

In one embodiment, the fiber sheet is in the form of yarn, woven fabric, knitted fabric, nonwoven fabric or combinations thereof.

In another embodiment, the length is a minimum of about 5 feet, about 6 feet or about 7 feet and or a maximum of about 8 feet, about 10 feet, about 12 feet, about 14 feet, about 16 feet, about 18 feet or about 20 feet. The width is a minimum of about 3 feet, about 4 feet, about 5 feet and/or a maximum of about 10 feet, about 8 feet, about 6 feet or about 5 feet

In still another embodiment, the resin further comprises a carboxy-containing polysaccharide that is selected from a group consisting of agar, agar agar, gellan and mixtures thereof.

In another embodiment, the resin is substantially free of starch.

In still another embodiment, there is an article of furniture made from the panel set forth above. The article has at least one load bearing horizontal member that has a minimum length of eighteen inches. The article of manufacture being selected from the group consisting of chairs, shelves, desks, tables, kitchen and other cabinets, doors, office cubicle walls and panels.

In an embodiment, the panel was compressed from two or more sheets of uniform thickness that are individually impregnated with a coating of uniform thickness, wherein the amount of resin in the cured panel is a minimum of 30 wt.%.

In another embodiment, there is a method of manufacturing a high-strength, low- profile composite panel. The method comprises providing sheets of plant-based fibers, wherein the plants include one or more of flax, hemp, sisal, jute, sorghum, ramie, kapok, banana, pineapple kenaf and combinations thereof. The sheets are sized to have a length and a width that is a minimum of 1 cm greater than the length and the width of the finished panels. The method includes impregnating a soy-based resin into the sheets.

The step of impregnating requires uniform distribution of the resin, hi one embodiment, the steps include drying the sheets individually. The step of drying prevents folding or kinking of the sheets. A plurality of sheets is stacked so that the sheets are aligned to within one centimeter of the other sheets. Next, the sheets are pressed at a temperature that is a minimum of 8OC, a pressure that is a minimum, of 3 MPa, and for a time that is a minimum of 30 minutes. The panel is trimmed to eliminate variance in thickness along the edge of the finished panel. The length of the finished panel is a minimum of about two feet and the width is a minimum of about four feet.

In another embodiment, there is a panel made from the preceding process.

Alternatively, there is an article of furniture made from the panel set forth above. The article has at least one load bearing horizontal member that has a minimum length of eighteen inches. The article of manufacture is selected from the group consisting of chairs, shelves, desks, tables, kitchen and other cabinets, doors, office cubicles and panels.

In one embodiment, the present invention is a method of making panels set forth above, the method includes an additional step of providing sheets that are a minimum of 2 centimeters larger than the finished panel.

In an embodiment, there is a step of impregnation that requires at least two applications of resin. In another embodiment, the step of drying occurs at a pressure that is a maximum of 0.9 atm.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an elevated view of a pair of press plates used in one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

The term "biodegradable" is used herein to mean degradable over time by water, microbes and/or enzymes found in nature (e.g. compost), without harming the environment. To be considered strictly biodegradable a material is required to degrade a minimum of 60% within 180 days under compo stable conditions that are defined by ASTM D790.

The terms "biodegradable resin" and "biodegradable composite" are used herein to mean that the resin and composite are sustainable and at the end of their useful life, can be disposed of or composted without harming, and in fact helping, the environment.

The term "stress at maximum load" means the stress at load just prior to fracture, as determined by the stress-strain curve in a tensile test.

The term "fracture stress" means the stress at fracture as determined by the stress- strain curve in a tensile test.

The term "fracture strain" means the strain (displacement) at fracture, as determined by the stress-strain curve in a tensile test.

The term "modulus" means stiffness, as determined by the initial slope of the stress- strain curve in a tensile test.

The term "toughness" means the amount of energy used in fracturing the material, as determined by the area under the stress-strain curve.

The "tensile test" referred to is carried out using Instron or similar testing device according to the procedure of ASTM Test No. D882 for resin sheets and D3039 for composites. Testing is carried out after 3 days conditioning at 21°C and 65% R. H.

The term "strengthening agent" is used herein to describe a material whose inclusion in the biodegradable polymeric composition of the present invention results in an improvement in any of the characteristics "stress at maximum load", "fracture stress",

"fracture strain", "modulus", and "toughness" measured for a solid article formed by curing of the composition, compared with the corresponding characteristic measured for a cured solid article obtained from a similar composition lacking the strengthening agent.

The term "curing" is used herein to describe subjecting the composition of the present invention to conditions of temperature and effective to form a solid article having a moisture content of preferably less than about 0.5 wt.%.

The phrase "free of formaldehyde" or "formaldehyde free" means the materials used do not contain formaldehyde or a compound that will release formaldehyde in the manufacturing process or during the effective life of the product

The Fiber Mats

In accordance with the present invention, the soy impregnated fiber mat plies are made of biodegradable fiber mats and biodegradable polymeric resin that comprises soy protein. Preferably the mats are biodegradable and from a renewable natural resource.

In one embodiment, the fabrics are any biodegradable material that has fibers useful in making fabric, cords or string. In one embodiment, the biodegradable fibers are made of cotton, silk, spider silk, hemp, ramie, kenaf, sorghum, burlap, flax, sisal, kapok, banana, pineapple wool, hair or fur, jute, polylactic acid (PLA), viscose rayon, lyocell, or combinations thereof.

In one embodiment, the fabrics are preferably hemp, ramie, kenaf, sorghum, burlap, flax, sisal, kapok, banana or pineapple fibers.

In an embodiment, the fibers are yarn, woven, nonwoven, knitted or braided. The mats are preferably of uniform thickness and water absorbent to facilitate easy impregnation of the mats by soy fiber. Ln one embodiment the mats are nonwoven and have a mass per area that is a minimum of about 100 g/m ² , about 200 g/m ² or about 300 g/m ² and/or a maximum of about 500 g/m ² , about 600 g/m ² or about 800 g/m ² .

In one preferred embodiment, the mats are nonwoven and are made of natural fibers (e.g. kenaf fibers) that are blended with a biodegradable material that is capable under heat and pressure to bind the natural fibers into a workable nonwoven fiber mats of uniform thickness. The polylactic acid readily melts during the heat press stage and binds the kenaf fibers together. Other degradable fibers that have improved binding under conditions of heat and pressure include but are not limited to polylactic acid, wool, viscose rayon, and lyocell may also be used as binding materials in non-woven fiber mats.

The amount of degradable fibers used as binders in the non-woven mat is a minimum of about 1 wt. %, about 3 wt.%, about 5 wt.%, about 10 wt.% and a maximum of about 20 wt.%, about 17 wt.%, about 15 wt.%, about 12 wt.% or about 10 wt.%. The amount of natural fibers used in the fiber mat is a minimum of about 80 wt.%, about 82 wt.%, about 85 wt.%, about 87 wt.% or about 90 wt.%.

Resin

In one embodiment, the resin includes soy protein and a soluble strengthening agent (i.e., substantially soluble in water at a pH of about 7.0 or higher. In one embodiment, the soluble strengthening agent is a polysaccharide. Preferably, the polysaccharide is a carboxy-containing polysaccharide. In one preferred embodiment, the soluble strengthening agent is selected from the group consisting of agar, agar agar, gellan, and mixtures thereof.

Soy protein is the basis for the resin of the present invention. Soy protein can be obtained in soy flour, soy protein concentrate and soy protein isolate. Each of these sources has increasing concentrations of soy protein. Preferably, soy protein concentrate is used because of it has an excellent tradeoff between cost and concentration of soy protein.

The amount of soy protein added to the fiber mats, fabrics, or yarns, results in composite panels that have a minimum of about 30 wt.% soy protein, about 35 wt.% soy protein, about 40 wt.% soy protein, about 50 wt.% soy protein and/or a maximum of about 70 wt, % soy protein, about 65 wt.% soy protein, about 60 wt.% soy protein,

about 55 wt. % soy protein or about 50 wt.% soy protein based upon the final weight of the finished panel.

Soy protein has been modified in various ways and used as resin in the past, as described in, for example, Netravali, A. N. and Chabba, S., Materials Today, pp. 22- 29, April 2003; Lodha, P. and Netravali, A. N., Indus. Crops and Prod. 2005, 21, 49; Chabba, S. and Netravali, A. N, J. Mater. ScL 2005, 40, 6263; Chabba, S. and Netravali, A. N.,

J, Mater. Sd. 2005, 40, 6275; and Huang, X. and Netravali, A. N., Biomacromolecules, 2006, 7, 2783.

Soy protein contains about 20 different amino acids, including those that contain reactive groups such as -COOH, -NH ₂ and -OH groups. Once processed, soy protein itself can form crosslinks through the -SH groups present in the cysteine amino acid as well as through the dehydroalanine (DHA) residues formed from alanine by the loss of side chain beyond the β-carbon atom. DHA is capable of reacting with lysine and cysteine by forming lysinoalaiήne and lanthionine crosslinks, respectively.

Asparagines and lysine can also react together to form amide type linkages. All these reactions can occur at higher temperatures and under pressure that is employed during curing of the soy protein.

In addition to the self-crosslinking in soy protein, the reactive groups can be utilized to modify soy proteins further to obtain desired mechanical and physical properties. The most common soy protein modifications include: addition of crosshnking agents and internal plasticizers, blending with other resins, and forming iαterpenetrating networks (IPN) with other crosslinked systems. Without being limited to a particular mechanism of action, these modifications are believed to improve the mechanical and physical properties of the soy resin.

The properties (mechanical and thermal) of the soy resins can be further improved by adding nanoclay particles and micro- and nano-fibrillar cellulose (MFC, NFC), as described in, for example, Huang, X. and Netravali, A. N., "Characterization of flax yarn and flax fabric reinforced nano-clay modified soy protein resin composites," Compos. Set. and TechnoL, in press, 2007; and Netravali, A. N.; Huang, X.; and

Mizuta, K., "Advanced green Composites," Advanced Composite Materials, submitted, 2007.

The resin can include additional non-soluble strengthening agents of natural origin that can be a particulate material, a fiber, or combinations thereof. The non-soluble strengthening agent may be, for example, a liquid crystalline (LC) cellulose nanoclay, microfibrillated cellulose, nanofibrillated cellulose.

Further in accordance with, the present invention, a composition containing agar, agar agar or gellan and soy protein can be employed, optionally, together with natural and high strength liquid crystalline (LC) cellulosic fibers to form biodegradable composites. The LC cellulose fibers can be produced by dissolving cellulose in highly concentrated phosphoric acid to form a LC solution of cellulose, as described in Borstoel, H., "Liquid crystalline solutions of cellulose in phosphoric acid," Ph. D. Thesis, Rijksuniversiteit, Groningen, Netherlands, (1998). The resulting LC solution was spun using an air gap-wet spinning technique to obtain highly oriented and crystalline cellulose fibers that had strengths in the range of 1700 MPa.

The resin can include additional non-soluble strengthening agents of natural origin that can be a particulate material, a fiber, or combinations thereof. The non-soluble strengthening agent may be, for example, a liquid crystalline (LC) cellulose nanoclay, microfibrillated cellulose (NFC), nanofibrillated cellulose (MFC).

Gellan, a linear tetrasaccharide that contains glucuronic acid, glucose and rhamnose units, is known to form gels through ionic crosslinks at its glucuronic acid sites, using divalent cations naturally present in most plant tissue and culture media. In the absence of divalent cations, higher concentration of gellan is also known to form strong gels via hydrogen bonding. The mixing of gellan with soy protein isolate has been shown to result in improved mechanical properties. See, for example, Huang, X. and Netravali, A. N., Biomacromolecules, 2006, 7, 2783 and Lodha, P. and Netravali, A. N., Polymer Composites, 2005, 26, 647.

Gellan gum is commercially available as Phytagel ^τ from Sigma- Aldrich Biotechnology. It is produced by bacterial fermentation and is composed of glucuronic acid, rhanmose and glucose, and is commonly used as a gelling agent for

electrophoresis. Based on its chemistry, cured Phytagel is fully degradable. In. preparing a composition of the present invention wherein cured gellan gum is the sole strengthening agent, Phytagel™ is dissolved in water to form a solution or weak gel, depending on the concentration. The resulting solution or gel is added to the initial soy protein powder suspension, with or without a plasticizer such as glycerol, under conditions effective to cause dissolution of all ingredients and produce a homogeneous composition.

Preferably, the weight ratio of soy protein: strengthening agent in the resin of the present invention is a minimum of about 20:1, about 15:1, about 10:1, about 8:1, about 4:1, about 3:1 and/or a maximum of about 1:1, about 2:1, about 2.5:1, about 3:1 and about 4:1.

The composition may also include a plasticizer. The weight percentage of plasticizer in the resin (excluding water) is a minimum of about 5 wt.%, about 8 wt.%, about 10 wt. %, about 12 wt.% or about 15 wt.% and/or a maximum of about 20 wt.%, about 18 wt.%, about 15 wt.%, about 12 wt.% or about 10 wt.%.

The biodegradable polymeric composition of the present invention preferably is substantially free of a starch additive. The biodegradable polymeric composition is substantially free of supplementary crosslinteng agents such as, for example, acid anhydrides, isocyanates and epoxy compounds.

Method of Making Resin

A biodegradable resin in accordance with the present invention may be prepared by the following illustrative procedure:

Into a mixing vessel at a temperature of about 70-85 ⁰ C is added 50-150 parts water, 1- 5 parts glycerol, 10 parts soy protein concentrate or isolate, and 1-3 parts gellan, agar agar, agar or mixtures thereof. To the mixture is added, with vigorous stirring, a sufficient amount of aqueous sodium hydroxide to bring the pH of the mixture to about 11. The resulting mixture is stirred for 10-30 minutes, then filtered to remove any residual particles. Optionally, clay nanoparticles and/or cellulose nanofibers,

nanofibrils (NFC) or microfibrils (MFC) may be added to the resin solution as additional strengthening agents.

Method of Making Impregnated Fiber Mats

The resin solution so produced is used to impregnate and coat one or more fiber mats or fabric sheets. The mats may comprise, for example, burlap, flax, ramie, sisal, kapok, banana, pineapple, kenaf, sorghum, hemp fiber or combinations thereof, hi one embodiment, the mat is preferably flax. In one embodiment, the fabric sheet is preferably flax. The mat is preferably jute or kenaf.

Resin solution is applied to a fiber mat or sheet in an amount of about 50-100 ml of resin solution per 15 grams of fiber so as to thoroughly impregnate the mat or sheet and coat its surfaces. The mat or sheet so treated is pre-cured by drying in an oven at a temperature of about 35-70 ⁰ C to form what is referred to as a prepreg.

The prepreg mats are arranged into sheets of sufficient size and are layered on top of one another. Care is taken to prevent any folding of the sheets which is often difficult to do when manufacturing sheets of considerable size. The prepreg sheets are sized to exceed recommended dimension by a minimum of 1 cm in length and width of the desired. Through experience it has been found that manufacture of a composite board of uniform thickness of a size greater than about 4 feet in length and two feet in width requires assembling pieces that are slightly oversized. Otherwise, the edges of the board cannot be made with uniform thickness desirable in a building product.

In one embodiment, a minimum of two prepreg sheets are stacked and aligned. In another embodiment, there are 4, 5, 6, 7, 8, 9, or 10 prepreg sheets.

Five sheets are stacked as described above and are subject to high pressure and temperature to cure. By way of example, the stack is hot pressed for 2-10 minutes at about 80 ⁰ C and a load of 0.5-1 MPa. Following a rest period of about 5 minutes, the stack is hot pressed for 5-15 minutes at 120-130 ⁰ C and a load of 2-10 MPa, followed by removal from the press. The resulting solid article has the appearance of a solid piece of material and a thickness of about 0.1-0.5 inches. Then, the outer perimeter is

cut to the desired size. The article is of uniform, thickness and exhibits excellent strength properties.

The layers of material are stacked from a first layer to the last layer as follows:

NWMWF/NWM/WP/NWM,

where NWM is non-woven mat, WP is a woven fabric.

Thus in one embodiment, the layers are alternated between woven fibers and non- woven mats. A biodegradable composite article of the present invention may comprise a thermoset composite sheet in the form of a flat sheet, as just described. Alternatively, the thermoset sheet may be corrugated, with a lateral profile comprising alternating ridges and valleys.

The present invention of one embodiment employs a vented press that will adequately vent the steam at locations throughout the panel. Thus, steam can escape from the press.

The vented press may be arranged with a plurality of vent holes. The vent holes can be spaced apart in grid patterns, diamond patterns or hexagonal patterns. The vent holes preferably have a diameter that is sufficiently large to permit adequate steam ventilation but sufficiently small to preferably not produce bumps on the surface of the pressed articles. In one embodiment, the holes have a minimum diameter of about 0.5 mm, about 0.75 mm or about 1 mm and/or a maximum diameter of about 3mm, about 2 mm or about 1 mm. Preferably the number of holes per decimeter square is a minimum of about 40, about 60, about 80 or about 100 and/or a maximum of about 400, about 200 or about 100.

Alternatively or optionally, the curing of the panels can occur in two stages, the first stage occurs at an elevated temperature relatively lower pressure to drive off the moisture before a second curing stage at elevated temperature and pressure. In one embodiment the temperature of the first stage is a minimum of about 6OC, about 70 C or about 80C and a maximum of about 110 C, about lOOC, about 90C or about 80 C. The pressure of the first stage is a minimum of about 0.3MPa, about 0.5MPa or about 0.7MPa and/or a maximum of about 1 MPa, about 0.8 MPa or about 0.7 MPa.

In one embodiment the temperature of the second stage is a minimum of about HOC about 115C, about 120C, or about 125C and a maximum of about HOC, about 135C, about 130C or about 125C. The pressure of the second stage is a minimum of about 2MPa, about 4MPa or about 6MPa and/or a maximum of about 10 MPa, about 8MPa or about 6MPa.

Frequently, a press is employed to produce a number of ply boards at a single time. The present invention employs a number of ventilated spacers between each panel to be formed. The spacers have vertical vent holes as described above. The vertical vent holes are fluidly connected to horizontal vents. Thus, the steam in a stack of panels can vent through the vent holes and disperse horizontally through the horizontal vents.

In one embodiment, the press is made of porous steel that has natural pores to act as vents.

Figure 1 describes a press plate 10 according to one embodiment of the present invention. The press plate 10 is machined from steel or aluminum. Preferably the press plate is resistant to corrosion from contact with moisture. The press plate has a thickness that is a minimum of about 4 mm and a maximum of about 5 mm. Vent holes 12 are arranged in a grid pattern over the entire area of the plate. Horizontal vents 14 form a criss-cross pattern and aligned vent holes 12. The side opposite the horizontal vents contact the panel to be formed (not shown). Alternatively, the side with the horizontal vents 14 can face the board.

In one embodiment of the present invention, one or two surfaces of the contoured article is laminated with a veneer or coated to improve water resistance. The veneer can improve appearance as well as water resistant properties of the corrugated board. The veneer of one embodiment is a wood veneer, or printed paper veneer. The veneer may be laminated or coated to produce a waterproof finish. The coating of one preferred embodiment incorporates a natural whey ingredient to improve its earth friendly properties according to formulas known in the art. In another embodiment, the coating is not a biodegradable coating.

Potentially, the vent holes may cause the panels to have bumps where the vent holes were located during pressing. However, an additional step of sanding and/or polishing can remove any bumps that may form during the curing stage.

For example polyurethane or epoxide coatings are used to cover the surface of the corrugated board. In another embodiment, Formica is the laminated outer layer. While it is understood that non-biodegradable materials are less desirable from an ecological standpoint, the use of petroleum products on the outer layers is often worthwhile for furniture or other objects to produce a long-lasting durable product where the bulk of that product is made from renewable and biodegradable materials.

Also envisioned in accordance with the present invention are biodegradable composite solid articles that comprise a stacked array of biodegradable composite sheets containing both flat and corrugated sheets. For example, the array could include a middle corrugated sheet disposed between and adhered to two flat sheets, providing bending stiffness in the direction of the corrugations. In another configuration, two superimposed corrugated sheets whose corrugations are orthogonal to one another are secured between two flat outer sheets, resulting in a structure of enhanced stiffness hi both directions.

Also in accordance with the present invention, a biodegradable molded thermoset polymeric article is obtained by subjecting the biodegradable polymeric composition described above to conditions of temperature and pressure effective to form the thermoset polymeric article. Effective temperature and pressure conditions preferably comprise a temperature of about 35°C to about 130 ⁰ C and a pressure of about 0.1 MPa to about 20 MPa, more preferably, a temperature of about 8O ⁰ C to about 120 ⁰ C and a pressure of about 4 MPa to about 20 MPa.

In one preferred embodiment, the molded thermoset polymeric article comprises a thermoset sheet, which may be included in a stacked array of thermoset sheets. Alternatively, the biodegradable press-shaped thermoset polymeric article may be shaped by a mold.

Preferably, the biodegradable press-shaped thermoset polymeric article is characterized by a stress at maximum load of at least about 20 MPa and/or a modulus of at least about 300 MPa.

In one embodiment, the panels are of a size that is about 8 feet by four feet, four feet by two feet, and twelve feet by four feet. These panels have excellent nail and screw retention properties, can be painted effectively and are strong. They can be cut or drilled without frayed edges and are consistent in width throughout the surface area. In another embodiment, the panels are effective in making office cubicles and partitions. In another embodiment, they are used for making cabinetry. In another embodiment, the panels are excellent for use in manufacturing furniture, particularly low profile furniture. Other applications include chairs, shelves, desks, tables and doors.

While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it should be recognized that the invention is not limited to the described embodiments.