Cereal grain-based biodegradable thermoplastic compositions

What is claimed is:

1. A thermoplastic composition, comprising: about 30-100 wt-% cereal grain comprising about 60-95% starch and about 5-40% protein, the cereal grain having been treated with an effective amount of an organic solvent to extract a substantial portion of lipids from the cereal grain; the organic solvent selected from the group consisting of alcohols, alkanes, ethers, halides, aromatics, esters and ketones.

2. The composition according to claim 1, wherein the cereal grain comprises flour, meal or grits.

3. The composition according to claim 1, wherein the cereal grain comprises a cereal grain selected from the group consisting of hard wheat, soft wheat, corn, rice, high amylose corn, oat, rye, barley, sorghum, millet, triticale, amaranth, waxy corn waxy rice, or a combination thereof.

4. The composition according to claim 1, wherein the cereal grain is degerminated.

5. The composition according to claim 1, wherein the cereal grain has been treated with a bleaching agent selection from the group consisting of chlorine gas, hydrogen peroxide, and benzoyl peroxide.

6. The composition according to claim 1, wherein the cereal has been treated with an effective amount of a cross-linking agent to bind the starch and protein together so as to form a water-resistant, biodegradable, moldable thermoplastic composition; wherein the crosslinking agent is selected form the group consisting of aldehydes, epoxides, polyepoxides, acid anhydrides, phosphorus oxychloride and metaphosphates.

7. The composition according to claim 6, wherein the cereal grain is treated with the cross-linking agent in a ratio of about 90:10 to about 99.99:0.01.

8. The composition according to claim 6, wherein the cross-linking agent is an aldehyde selected from the group consisting of glutaraldehyde, formaldehyde, glyoxal, acetaldehyde, glyceraldehyde, furfuraldehyde, malonic dialdehyde, succinic dialdehyde, adipic dialdehyde, starch dialdehyde, acrolein, or a combination thereof.

9. The composition according to claim 6, wherein the cross-linking agent is an epoxide selected from the group consisting of epichlorohydrin, 3-chloro-1,2-epoxypropane, 3-bromo-1,3-epoxypropane, 3-chloro-1,2-epoxybutane, 3-4-dichloro-1,2-epoxybutane, 4-chloro-1,2-epoxypentane, chloroepoxyoctanes, vinyl cyclohexane dioxide, butadiene dioxide, or a combination thereof.

10. The composition according to claim 6, wherein the cross-linking agent is an acid anhydride comprising adipic acid and acetic anhydride, citric acid and acetic anhydride, adipic acid and propionic anhydride, citric acid and propionic anhydride, or a combination thereof.

11. The composition according to claim 1, wherein the cereal grain is treated with the solvent in a ratio of about 1:1 to about 1:5.

12. The composition according to claim 1, wherein the organic solvent comprises ethanol, methanol, propanol, isopropanol, butanol, n-pentane, n-hexane, petroleum, ether, diethylether, methylene chloride, chloroform, benzene, ethyl acetate, acetone, or a mixture thereof.

13. The composition according to claim 1, further comprising about 5-30 wt-% water.

14. The composition according to claim 1, further comprising about 0.2-20 wt-% of a plasticizer, about 3-50 wt-% of an extender, about 0.1-2 wt-% of a lubricant agent, or a combination thereof; wherein the plasticizer is selected from the group consisting of dihydric alcohols, polyhydric alcohols, derivatives thereof, and any combination thereof; the extender is selected from the group consisting of cellulosic polysaccharides, synthetic polymers, natural gums, modified gums, and any combination thereof; and the lubricating agent is selected from the group consisting of monoglycerides, diglycerides, fatty acids, phospholipids, fatty acid esters, phosphoric acid derivatives of esters of polyhydroxy compounds, vegetable oils, animal lipids, petroleum silicone, waxes, mineral oils, and any combination thereof.

15. The composition according to claim 14, wherein the plasticizer is a polyhydric alcohol selected from the group consisting of glycerol, glycerol monoacetate, diacetate or triacetate, sorbitol, sorbitan, mannitol, maltitol, ethylene glycol, propylene glycol, polyvinyl alcohol, sodium cellulose glycolate, cellulose methyl ether, sodium alginate, sodium diethysuccinate, triethyl citrate, polyethylene glycols, polypropylene glycols, polyethylene propylene glycols, and mixtures thereof.

16. The composition according to claim 14, wherein the extender is selected from the group consisting of methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, microcrystalline cellulose, natural cellulose, cellulose acetate, cellulose nitrate, poly(acrylic acid), poly(methacrylic acid), poly(vinyl acetate, poly(vinyl alcohol), poly(vinyl acetate phthalate), ethylene/vinyl acetate copolymer, ethylene/vinyl alcohol copolymer, polyhydroxybutylate, xanthum gum, guar gum, gum arabic, alginate, carrageenan, pectin, agar, and konjac flour.

17. The composition according to claim 1, further comprising about 0.001-10 wt-% of a coloring agent selected from the group consisting of azo dyes, natural coloring agents, metallic oxides, and any combination thereof.

18. A method of making a biodegradable thermoplastic composition, comprising:

(a) combining a cereal grain with an effective amount of an organic solvent to form a mixture and extract a substantial portion of lipids from the cereal grain; the organic solvent selected from the group consisting of alcohols, alkanes, ethers, halides, aromatics, esters and ketones;

(b) removing the solvent from the mixture to provide a cereal grain residue; and

(c) drying the residue.

19. The method according to claim 18, wherein the cereal grain:solvent weight ratio is about 1:1 to 1:5.

20. The method according to claim 18, wherein combining step (a) comprises extracting the lipids from the cereal grain over a period of about 0.5-48 hours.

21. The method according to claim 18, wherein combining step (a) further comprises heating the admixture to the boiling temperature of the solvent.

22. The method according to claim 18, wherein removal step (b) comprises filtering or centrifuging the admixture to remove the organic solvent.

23. The method according to claim 18, further comprising after the removal step (b), the steps of:

(i) washing the residue with an effective amount of an organic solvent to remove residual lipids from the residue; and

(ii) removing the solvent from the washed residue.

24. The method according to claim 18, further comprising, after removal step (b), the steps of:

(i) combining the residue with a minor effective amount of a cross-linking agent to link starch and protein molecules of the cereal grain to form a cross-linked residue; wherein the crosslinking agent is selected from the group consisting of aldehyde, epoxide, polyepoxides, acid anhydrides, phosphorus oxychloride, and metaphosphates;

(ii) washing the cross-linked residue with an effective amount of an organic solvent to remove residual cross-linking agent from the residue; and

(iii) removing the solvent from the washed, cross-linked residue.

25. The method according to claim 24, wherein the cereal grain:cross-linking agent ratio is about 90:10 to about 99.99:0.01.

26. The method according to claim 24, wherein step (i) further comprises reacting the cross-linking agent with the cereal grain for a time period of about 0.5 to 24 hours.

27. The method according to claim 26, wherein the cross-linking agent in step (i) is combined with an organic solvent which is the same as or different from the organic solvent of step (ii), and step (i) further comprises heating the cross-linking agent and the cereal grain to reflux, to the boiling temperature of the solvent.

28. The method according to claim 18, wherein step (a) further comprises combining the cereal grain and the organic solvent mixture with a minor but effective amount of a cross-linking agent to link starch and protein molecules of the cereal grain to form a cross-linked, biodegradable, cereal grain-based thermoplastic composition.

29. The method according to claim 28, wherein the cereal grain:cross-linking agent ratio is about 90:10 to about 99.99:0.01.

30. The method according to claim 28, wherein step (a) further comprises reacting the cereal grain with the organic solvent and the cross-linking agent for a time period of about 0.5 to 24 hours.

31. The method according to claim 28, wherein the step (a) further comprises heating the mixture to reflux, to the boiling temperature of the solvent.

32. The method according to claim 18, further comprising a step (d) of remoistening the residue with an effective amount of water, wherein the composition comprises about 5-50% by weight water.

33. The method according to claim 32, wherein the composition comprises about 5-30% by weight water.

34. The method according to claim 32, further comprising a step (e) of molding the composition to provide a shaped article that is capable of remaining structurally intact without significant deterioration when exposed to water at a temperature of about 20.degree.-30.degree. C. for a period of about 2-7 days.

35. The method according to claim 34, wherein the composition is molded into the article by injection molding, blow molding, compression molding, transfer molding, extrusion molding, vacuum molding, rotation molding, thermo-forming, or expanded foam molding.

36. A method according to claim 32, wherein step (d) further comprises combining the remoistened residue with about 0.2-20 wt-% of a plasticizer, about 0.1-2 wt-% of a lubricating agent, about 3-50 wt-% of an extruder, or any combination thereof; wherein the plasticizer is selected form the group consisting of dihydric alcohols, polyhydric alcohols, derivatives thereof, and any combination thereof; the extender is selected from the group consisting of cellulosic polysaccharides, synthetic polymers, natural gums, modified gums, and any combination thereof; and the lubricating agent is selected from the group consisting of monoglycerides, diglycerides, fatty acids, phospholipids, fatty acid esters, phosphoric acid derivatives of esters of polyhydroxy compounds, vegetable oils, animal lipids, petroleum silicone, waxes, mineral oils, and any combination thereof.

37. A method according to claim 32, further comprising a step (e) of extruding the composition with or without heat, and granulating the extruded composition into pellets or chips.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

Various formulations of thermoplastic compositions have been developed in an attempt to at least partially replace non-degradable petroleum-based products with biodegradable components which can be used for the manufacture of extruded and/or molded articles such as films, utensils, containers and other packaging articles. Several of these compositions have been formulated which use starches such as a destructurized starch. Although starch compositions are biodegradable, they also tend to readily absorb moisture from humid air or by direct contact with water. This causes the moisture content of a molded article to increase and the article to lose its dimensional stability, and tear or collapse.

In an attempt to improve the structural stability of articles made from starch-based compositions, other ingredients have been included in the formulations. For example, compositions have been developed that include destructurized starch in combination with a water-insoluble synthetic thermoplastic polymer such as polyolefin or a polyester. Additionally, starches have been combined with protein to form starch-protein biopolymers that can provide moldable, biodegradable thermoplastics.

Modified cereal flours, such as pregelatinized or acid-modified corn flours, have been combined with a cross-linking compound such as glyoxal, to form a resinous material that may be used as a molding compound. A drawback of such compositions is that the lipids, fatty acids, and other minor components of the cereal flour can undergo an undesirable thermal reaction during processing that is detrimental to the strength and water-resistance of the molded article.

Therefore, an object of the invention is to provide a thermoplastic material that is thermally stable and can provide articles that have an increased level of physical strength and water-resistance, being capable of tolerating exposure to water over an extended period of time with minimal or no disintegration. It is a further object to provide a thermoplastic material that is biodegradable.

SUMMARY OF THE INVENTION

The present invention provides a thermoplastic composition that comprises about 30 to 100 wt-% of a cereal grain that comprises starch and protein. The cereal grain is preferably degerminated, treated with an organic solvent such as methanol, ethanol and the like, to extract a substantial portion of the lipids and other organic solvent-soluble materials from the grain, and optionally treated with a cross-linking agent, as for example, an aldehyde such as glutaraldehyde and formaldehyde, an epoxide such as epichlorohydrin, an acid anhydride such as a mixture of adipic acid and acetic anhydride, and the like. An effective amount of the cross-linking agent is reacted with the cereal grain to bind together the starch and protein of the cereal grain particles so as to form a cross-linked composition. The solvent-treated, optionally cross-linked, cereal grain-based thermoplastics may be used to make extruded, molded or otherwise pressure-formed articles. To facilitate molding, it is preferred that the finished composition comprises about 5-30% by weight water.

The thermoplastic compositions of the invention are produced by combining a cereal grain, in the form of, for example, flour, meal, grits, or the like, with an effective amount of an organic solvent with or without water. Preferably, the amount of the organic solvent and the reaction period of the cereal grain with the solvent is effective to remove a major portion of the lipids and/or other thermally unstable components from the cereal grain. A cross-linking agent may be reacted with the cereal grain, for example, by adding the agent to the organic solvent used for extracting the lipids, and then mixing the solvent/cross-linking agent with the cereal grain, or by adding the agent to the cereal grain residue after the solvent extraction of the lipids from the cereal grain. The organic solvent, and any unreacted cross-linking agent, is then separated from the cereal grain, for example, by filtration or centrifugation, to provide a residue of the solvent-treated cereal grain. It is preferred that the residue is then washed with a portion of organic solvent, or aqueous solvent, to remove residual lipids and other thermally unstable materials, and excess cross-linking agent from the residue. The cereal grain residue is then dried to remove the organic solvent, and remoistened to a predetermined moisture content.

The remoistened residue may be mixed with other ingredients such as a plasticizer, a lubricating agent, an extender, and the like, in order to facilitate molding of the composition into a shaped article. The cereal grain-based thermoplastic compositions of the invention may be molded or shaped by conventional processing techniques, such as by compression molding, injection molding, blow molding, vacuum forming, thermo-forming and the like. The articles that are formed from the present compositions are translucent in appearance and have a high degree of mechanical strength, and water-resistance. Advantageously, the cereal grain-based thermoplastics of the invention are biodegradable, and are suitable for use in making articles that are disposable, and/or edible by a human or other animal after use, as for example food containers, tablewares, and the like.

Although the articles made from the composition of the invention will disintegrate over time when exposed to moisture, such as from the atmosphere and the package contents, or from submersion in water or other direct contact with water, the articles of the invention, particularly those that include a cross-linking agent, have a higher resistance to disintegration by moisture and will remain substantially intact for a more extended period of time than articles made from prior art starch-based thermoplastics. Most cereal grains comprise about 5 to 40 wt-% protein, and portions of the protein component, such as gluten and zein, are water-insoluble which may help increase the water-resistance of articles formed from the present compositions. Advantageously, both the starch and protein components are derived from a single source, i.e., the cereal grain. Thus, the thermoplastic formulations of the present invention eliminates the need to combine the starch and protein components as separate ingredients.

DETAILED DESCRIPTION OF THE INVENTION

The thermoplastic compositions of the invention comprise a cereal grain from which a substantial portion of the lipids and other thermally unstable substances have been removed by extraction with an organic solvent such as methanol, ethanol, and the like, or an aqueous solvent, or a mixture thereof. Preferably, the cereal grain is also degerminated to remove a major portion of the cereal lipids. The present thermoplastics are prepared by extracting a major portion of the lipids and other thermally unstable substances from a cereal grain with an organic solvent, removing the solvent extract, and remoistening the residue with an amount of water to facilitate molding of the composition into the desired article.

Preferably, the cereal 9rain is treated with a bi-functional cross-linking agent such as an aldehyde, an epoxide, an acid anhydride, or other suitable agent. The reaction of the cross-linking agent with the starch and protein of the cereal particles causes the formation of starch-protein linkages, starch-starch linkages, and/or protein-protein linkages.

The cereal grain-based thermoplastics of the invention may be used to make extruded, molded or otherwise pressure-formed articles of various shapes, forms and sizes. The articles formed from the solvent-treated, cereal-based thermoplastics of the invention, particularly those that are formed from solvent-treated and cross-linked cereal grain, have an increased level of water-resistance and structural stability compared to articles formed from other starch-based thermoplastics.

As used herein, unless otherwise noted, the wt-% of the components of the composition are based on the total dry weight of the composition.

Cereal Grains. The compositions of the invention include a native or natural cereal grain. The phrase "cereal grain," according to the invention, includes any starch/protein-containing cereal grain in a particulate form such as a milled flour, meal, grits, and the like, that may be processed according to the method of the invention to provide a thermoplastic composition as described herein. The cereal grain may be treated with a bleaching agent, as for example, with chlorine gas, hydrogen peroxide (H.sub.2 O.sub.2) or benzoyl peroxide, or other like oxidizing agents, or nutritionally reinforced, as for example with vitamins or minerals.

Native or natural cereal grains that are useful according to the invention include, for example, corn (maize), waxy corn, rice, waxy rice, hard wheat, soft wheat, durum wheat, rye, oat, barley, sorghum, millet, triticale, amaranth, high amylose corn, and the like. The cereal grain may comprise a normal starch (about 20-40% by weight amylose), a waxy starch (about 0-8% by weight amylose), or a high-amylose starch (greater than about 50% by weight amylose). Preferably, the cereal grain is capable of being cross-linked together with a cross-linking agent that will bind with the starch and protein of the cereal grain to form starch to starch cross-links, protein to protein cross-links, and starch to protein cross-links.

A preferred composition prior to molding, comprises about 30 to 100 wt-% cereal grain, more preferably about 50 to 95 wt-%, more preferably about 60 to 90 wt-%, based on the total dry weight of the composition. It is also preferred that the cereal grain comprises about 60 to 95% starch, and about 5 to 40% water-insoluble proteins such as gluten and zein.

Organic Solvent. Cereal lipids are often concentrated in cereal germs, and degerminated cereal grains generally contain less than about 5% lipids in the endosperm. Native cereal grains contain lipids that may undergo undesirable reactions, such as oxidation, during thermal processing of a composition that includes the cereal grain. Such thermal reactions may alter the composition to the extent that the strength, durability, and/or water-resistance of an article that is formed from the composition is diminished. To avoid such undesirable changes in the composition, the cereal grain, preferably degerminated, is mixed with an organic solvent for a time effective to extract the lipids such as free fatty acids, glycolipids, phospholipids, nonpolar lipids, and the like, and other thermally unstable materials, from the cereal grain.

Organic solvents that may be used according to the invention include alcohols (absolute or aqueous) such as methanol, ethanol, isopropanol, n-propanol, butanol, and the like; alkanes such as n-pentane, n-hexane, petroleum ether, and the like; and ethers such as diethylether and the like; halides such as methylene chloride, chloroform, and the like; aromatics such as benzene, and the like; esters such as ethylacetate, and the like; and ketones such as acetone, and the like.

Preferably, the cereal grain is combined with the organic solvent in a grain:solvent parts by weight ratio of about 1:1 to 1:10, more preferably about 1:1 to 1:5, more preferably about 1:1.5 to 1:3. The solvent is allowed to react with the grain, with or without stirring and with or without heating, for a time effective to remove a substantial majority of the lipids and thermally unstable materials such as natural oxidizing agents, including free fatty acids, glycolipids, phospholipids, non-polar lipids, and the like, from the cereal grain.

The lipids are extracted from the cereal grain particles by the solvent, typically as an off-white to yellow colored oily substance. The time required for removal of the lipids from the grain will vary depending, for example, on temperature, types and amounts of residual lipids, the extraction solvent used, and mechanical stirring. The solvent extraction time is about 0.5 to 24 hours, preferably about 1 to 12 hours, more preferably about 1 to 6 hours. To accelerate the extraction of lipids from the cereal grain, the grain/solvent mixture may be agitated and/or heated, preferably to reflux, to the boiling temperature of the solvent.

Preferably, an effective amount of the lipids of the cereal grain are extracted by the solvent such that, during processing, any thermal reaction of the lipids that are present in the composition will not substantially alter the properties of the thermoplastic composition and articles that are formed from the composition, particularly the water-resistance, physical strength or other mechanical properties. The solvent containing the extracted cereal lipids is then removed by centrifugation or filtration, preferably with an aspirator. The defatted cereal residue is preferably washed with additional solvents. Preferably, the lipid content of the composition is less than about 2 wt-%, more preferably less than about 1 wt-%.

Cross-Linking Agent. The cereal grain may further be treated with a cross-linking agent, preferably a bi-functional cross-linking agent. The cross-linking agent preferably binds the protein of the cereal grain together in a protein to protein linkage, binds the starch together in a starch to starch linkage, and links the starch to the protein in a starch to protein linkage. The treatment of the cereal grain with a cross-linking agent provides a cereal grain-based thermoplastic composition that may be molded or otherwi