High performance biodegradable materials from oriented starch derivatives

Abstract

The present invention involves the synthesis of a series of amylose (starch) derivatives with various degrees of substitution and amylose/amylopectin ratios. These chains are chemically crosslinked and then mechanically deformed (stretched) to produce a biodegradable and mechanically superior material. Specifically, the process consists of chemically modifying starch into starch derivatives such as starch ethers, starch esters and starch carbamates. The polymers have a percentage degree of substitution of from about 35% to about 95% (degree of substitution is from about 1.05 to about 2.85) and preferably have a percentage degree of substitution of from about 65% to about 90% (degree of substitution is from about 1.95 to about 2.70). The starch derivatives are crosslinked to obtain crosslinked chains and processed into sheets, films, fibers, threads or other articles as known in the art. After processing, the articles are swollen in a thermodynamically acceptable solvent or solvent mixture to a desired volume and deformed in a uniaxial or biaxial extension. The polymers materials are preferably stretched from about 1% to about 500% in the direction of stretching. Finally, the solvent is removed, yielding a homogeneous, highly-ordered material. The present invention improves the properties and the quality of sheets, films, fibers, threads or other articles with respect, for example, to mechanical strength. The materials are developed from starch, a natural renewable source which has low cost, high production levels and which replaces petroleum-based, synthetic polymers; the materials acquire high-strength, high-modulus, toughness and flexibility; and the materials exhibit structural and functional stability during processing, storage and use, yet are susceptible to biodegradation upon disposal.

1. A method for synthesizing polymers comprising the steps of:
 (a) chemically modifying starch into starch derivatives;  
 (b) crosslinking the starch derivatives to obtain lightly crosslinked chains by contacting said starch derivatives with a crosslinking agent;  
 (c) processing the lightly crosslinked polymers into sheets, films, fibers, threads or other articles as known in the art a desired physical article;  
 (d) swelling the articles article in a thermodynamically acceptable solvent or solvent mixture to a desired volume;  
 (e) deforming (stretching) the swollen articles, in uniaxial or biaxial extension the article; and  
 (f) removing the solvent, at constant strain or stress .  
 
     
     
       2. The method of  claim 1 , wherein the starch has an amylose content from about 20% to about 80%. 
     
     
       3. The method of  claim 1 , wherein the substituted starch polymers of the present invention have a percentage degree of substitution of from about 35% to about 95% (DS is from about 1.05 to about 2.85) . 
     
     
       4. The method of  claim 1 , wherein the substituted starch polymers of the present invention have a percentage degree of substitution of from about 65% to about 90% (DS is from about 1.95 to about 2.70) . 
     
     
       5. The method of  claim 1 , wherein the starch derivative is derivatives are selected from the group consisting of mono-, di-, or tri-substituted starch ethers, mono-, di-, or tri-substituted starch esters, and mono-, di-, or tri-substituted starch carbamates. 
     
     
       6. The method of  claim 1 , wherein the starch derivative is triethylstarch ether. 
     
     
       7. The method of  claim 1 , wherein the crosslinking agent is a compound having at least two functional groups reactive with the starch derivative. 
     
     
       8. The method of  claim 1 , wherein the crosslinking agent is a di- or poly-functional compound which contains groups reactive with a group selected from carboxyl, carboxylic acid anhydride, hydroxyl, amino or and amide groups. 
     
     
       9. The method of  claim 1 , wherein the crosslinking agent is selected from the group consisting of diisocyanates, aliphatic acid chlorides, hydridosilanes, and silanol-terminated oligosilanes. 
     
     
       10. The method of  claim 1 , wherein the crosslinking agent is hexamethylene diisocyanate. 
     
     
       11. The method of  claim 1 , wherein the number of crosslinks per starch derivative chain is about one crosslink for every 25 to 250 glucopyranose units. 
     
     
       12. The method of  claim 1 , wherein the number of crosslinks per starch derivative chain is about one crosslink for every 100 to 150 glucopyranose units. 
     
     
       13. The method of  claim 1 , wherein polymer articles are oriented at a polymer concentration from about 10 volume percent to about 70 volume percent. 
     
     
       14. The method of  claim 1 , wherein polymer articles are oriented at a polymer concentration from about 15 volume percent to about 30 volume percent. 
     
     
       15. The method of  claim 1 , wherein the extension ratio is from about 1% to about 500% in the direction of stretching. 
     
     
       16. The method of  claim 1 , wherein the extension ratio is from about 10% to about 250% in the direction of stretching. 
     
     
       17. The method of  claim 1 , wherein the extension ratio is from about 25% to about 150% in the direction of stretching. 
     
     
       18. The method of  claim 1 , wherein the polymer compositions polymers are dried using a coagulation process. 
     
     
       19. The composition produced by the method of  claim 1 . 
     
     
       20. The composition of  claim 19 , wherein the starch has an amylose content from about 20% to about 80%. 
     
     
       21. The composition of  claim 19 , wherein the substituted starch polymers of the present invention have a percentage degree of substitution of from about 35% to about 95% (DS is from about 1.05 to about 2.85) . 
     
     
       22. The composition of  claim 19 , wherein the substituted starch polymers of the present invention have a percentage degree of substitution of from about 65% to about 90% (DS is from about 1.95 to about 2.70) . 
     
     
       23. The composition of  claim 19 , wherein the starch derivative is selected from the group consisting of mono-, di-, or tri-substituted starch ethers, mono-, di-, or tri-substituted starch esters, and mono-, di-, or tri-substituted starch carbamates. 
     
     
       24. The composition of  claim 19 , wherein the starch derivative is triethyl-starch ether. 
     
     
       25. The composition of  claim 19 , wherein the crosslinking agent a compound having at least two functional groups reactive with the starch derivative. 
     
     
       26. The composition of  claim 19 , wherein the crosslinking agent is a di- or poly-functional compound which contains groups reactive with a group selected from carboxyl, carboxylic acid anhydride, hydroxyl, amino or and amide groups. 
     
     
       27. The composition of  claim 19 , wherein the crosslinking agent is selected from the group consisting of diisocyanates, aliphatic acid chlorides, hydridosilanes, and silanol-terminated oligosilanes. 
     
     
       28. The composition of  claim 19 , wherein the crosslinking agent is hexamethylene diisocyanate. 
     
     
       29. The composition of  claim 19 , wherein polymer articles are oriented at a polymer concentration from about 10 volume percent to about 70 volume percent. 
     
     
       30. The composition of  claim 19 , wherein polymer articles are oriented at a polymer concentration from about 15 volume percent to about 30 volume percent. 
     
     
       31. The composition of  claim 19 , wherein the extension ratio is from about 1% to about 500% in the direction of stretching. 
     
     
       32. The composition of  claim 19 , wherein the extension ratio is from about 10% to about 250% in the direction of stretching. 
     
     
       33. The composition of  claim 19 , wherein the extension ratio is from about 25% to about 150% in the direction of stretching. 
     
     
       34. The composition of  claim 19 , wherein the polymer compositions polymers are dried using a coagulation process.