Modified biopolymers and methods of producing and using the same

1. A cross-linked, charged modified starch, wherein the cross-linked, charge modified starch includes at least one negatively charged moiety and the cross-linked charge modified starch is provided by reacting a starch with a charge-modifying agent including the at least one negatively charged moiety;

wherein the cross-linked, charge modified starch has a charge density of greater than 5 meq/g, as measured by titration, for the at least one negatively charged moiety;

wherein the cross-linked, charge modified starch has a net negative charge and is anionic;

wherein the at least one negatively charged moiety is a carboxyl, a sulfonate, a sulfate, and/or a phosphate group; and wherein the cross-linked, charge-modified starch comprises a plurality of void spaces formed therein having an average diameter of about 0.1 microns to about 500 microns.

2. The cross-linked, charge modified starch of claim 1 , wherein the cross-linked, charge modified starch further comprises a biopolymer that is different than starch.

3. The cross-linked, charge modified starch of claim 1 , wherein the at least one negatively charged moiety is a carboxyl, and the cross-linked, charge modified starch is covalently cross-linked.

4. The cross-linked, charge-modified starch of claim 1 , wherein the cross-linked, charge modified starch has a charge density in a range of greater than 5 meq/g to 10 meq/g, as determined by titration.

5. A cross-linked, charge modified starch, wherein the cross-linked, charge modified starch includes at least one negatively charged moiety and charge modified starch is provided by reacting a starch with a charge-modifying agent including the at least one negatively charged moiety;

wherein the cross-linked, charge modified starch has a charge density of greater than 5 meq/g, as measured by titration, for the at least one negatively charged moiety;

wherein the cross-linked, charge modified starch has a net negative charge and is anionic;

wherein the at least one negatively charged moiety is a carboxyl, a sulfonate, a sulfate, and/or a phosphate group, and wherein the cross-linked, charge-modified starch is in the form of a particle having a diameter in a range of about 1 micron to about 2,000 microns.

6. The cross-linked, charge modified starch of claim 5 , further comprising a biopolymer that is different than starch.

7. The cross-linked, charge modified starch of claim 5 , wherein the cross-linked, charge-modified starch is in the form of a particle having a diameter in a range of about 10 microns to about 1000 microns.

8. The cross-linked, charge-modified starch of claim 5 , wherein the cross-linked, charge modified starch has a charge density in a range of greater than 5 meq/g to 10 meq/g, as determined by titration.

9. The cross-linked, charge-modified starch of claim 5 , wherein the cross-linked, charge modified starch has a charge density in a range of greater than 5 meq/g to 7 meq/g, as determined by titration.

10. The cross-linked, charge-modified starch of claim 5 , wherein the at least one negatively charged moiety is a carboxyl group.

11. The cross-linked, charge-modified starch of claim 5 , wherein the charge-modifying agent is selected from the group consisting of an acid, a mono-halogen substituted fatty acid, an acetate, an anhydride, an alkyl ester of acrylic acid, crotonic acid or itaconic acid, an acrylonitrile, sodium periodate, a sulfone, a sulfonic acid, and any combination thereof.

12. The cross-linked, charge-modified starch of claim 5 , wherein the charge-modifying agent comprises a carboxylic acid group.

13. The cross-linked, charge-modified starch of claim 5 , wherein the charge-modifying agent reacts with a hydroxyl group of the starch.

14. The cross-linked, charge-modified starch of claim 5 , wherein the cross-linked, charge-modified starch is covalently cross-linked.

15. The cross-linked, charge modified starch of claim 5 , wherein the cross-linked, charge modified starch is in the form of a particle having a diameter in a range of about 300 micron to about 800 micron.

16. The cross-linked, charge-modified starch of claim 5 , wherein the at least one negatively charged moiety is a phosphate group.

17. A method for producing a cross-linked, charge-modified starch, the method comprising:

melting a starch in the presence of a plasticizer to form a homogeneous reaction blend, wherein the plasticizer comprises water in an amount of at least 20% by weight of the starch and the homogeneous reaction blend is a single, continuous phase that comprises a plasticized starch;

reacting the plasticized starch and a charge-modifying agent that includes at least one negatively charged moiety in the homogeneous reaction blend to form the charge-modified starch; and

cross-linking the charge-modified starch to form the cross-linked, charge-modified starch,

wherein the at least one negatively charge moiety is a carboxly, a sulfonate, a sulfate, and/or phosphate group; and

wherein the cross-linked, charge modified starch has a net negative charge, is anionic, and has a charge density of greater than 5 meq/q, as measured by titration, for the at least one negatively charged moiety.

18. The method of claim 17 , wherein cross-linking the charge-modified starch comprises cross-linking the charge-modified starch in the homogeneous reaction blend to form the cross-linked, charge-modified starch.

19. The method of claim 17 , wherein the melting step further comprises combining a catalyst with the starch and the plasticizer to form the homogeneous reaction blend.

20. The method of claim 17 , wherein the cross-linking step further comprises reacting the charge-modified starch with at least one cross-linking agent.

21. The method of claim 17 , wherein the reacting and cross- linking steps occur simultaneously.

22. The method of claim 17 , further comprising foaming the cross-linked, charge-modified starch.

23. The method of claim 17 , wherein the melting step comprises melt blending the starch and the plasticizer using a reactive extrusion process.

24. The method of claim 17 , wherein the reacting and cross- linking steps are carried out using a reactive extrusion process.

25. The method of claim 17 , wherein the method is carried out in an extruder.

26. The method of claim 25 , wherein the method is a single-stage direct extrusion process.

27. The method of claim 25 , wherein the extruder comprises at least two reaction zones.

28. The method of claim 27 , wherein the method comprises reacting the plasticized starch and at least one charge-modifying agent at a first reaction zone and cross-linking the charge-modified starch at a second reaction zone.

29. The method of claim 25 , wherein the method is a multi-stage extrusion process.

30. The method of claim 17 , wherein the reacting and/or cross-linking step(s) is/are carried out at a temperature in a range of about 80° C. to about 150° C.

31. The method of claim 17 , wherein the reacting and/or cross-linking step(s) is/are carried out in an extruder with a residence time in a range of about 0.1 minutes to about 5 minutes.

32. The method of claim 17 , wherein the reacting and/or cross-linking step(s) is/are carried out in an extruder having a screw RPM in a range of about 250 to about 500.

33. The method of claim 17 , further comprising heating the cross-linked, charge-modified starch at a temperature in a range of about 100° C. to about 150° C. for a period of time in a range of about 1 minute to about 8 hours.

34. The method of claim 17 , wherein the cross-linked, charge-modified starch is in the form of a particle wherein the cross-linked, charge-modified starch is in the form of a particle having a diameter in a range of about 1 micron to about 2,000 microns.

35. The method of claim 34 , wherein the cross-linked, charge-modified starch is in the form of a particle having a diameter in a range of about 300 microns to about 800 microns.

36. The method of claim 17 , wherein the at least one negatively charged moiety is a carboxyl, and the cross-linked, charge modified starch is covalently cross-linked.

37. The method of claim 17 , wherein the cross-linked, charge modified starch further comprises a biopolymer that is different than starch.

38. The method of claim 17 , wherein the cross-linked, charge modified starch has a charge density in a range of greater than 5 meq/g to 10 meq/g, as determined by titration.

39. A cross-linked, charge modified starch, wherein the cross-linked, charge modified starch includes at least one negatively charged moiety and the cross-linked, charge modified starch is provided by reacting a starch with a charge-modifying agent including the at least one negatively charged moiety;

wherein the cross-linked, charge modified starch has a charge density of greater than 5 meq/g, as measured by titration, for the at least one negatively charged moiety;

wherein the cross-linked, charge modified starch has a net negative charge and is anionic; wherein the at least one negatively charged moiety is a carboxyl, a sulfonate, and/or a phosphate group; and

wherein the cross-linked, charge-modified starch absorbs a 0.9% saline soluation, at room temperature, in an amount of at least 20times the weight of the cross-linked, charge-modified starch.

40. The cross-linked, charge modified starch of claim 39 , wherein the cross-linked, charge modified starch further comprises a biopolymer that is different than starch.

41. The cross-linked, charge modified starch of claim 39 , wherein the at least one negatively charged moiety is a carboxyl, and the cross-linked, charge modified starch is covalently cross-linked.

42. The cross-linked, charge-modified starch of claim 39 , wherein the cross-linked, charge modified starch has a charge density in a range of greater than 5 meq/g to 10 meq/g, as determined by titration.

43. A cross-linked, charge modified starch, wherein the cross-linked, charge modified starch includes at least one negatively charged moiety and the cross-linked, charge modified starch includes at least one negatively charged moiety and the cross-linked, charge modified starch is provided by reacting a starch with a charge-modifying agent including, the at least one negatively charged moiety;

wherein the cross-linked, charge modified starch has a charge density of greater than 5 meq/g, as measured by titration, for the at least one negativey charged moiety;

wherein the cross-linked, charge modified starch has a net negative charge and is anionic; wherein the at least one negatively charged moiety is a carboxyl, a sulfonate, a sulfate, and/or a phosphate group; and

wherein the cross-linked, charge-modified starch has a free swell capacity (FSC) in a range of about 25 g/g to about 100 g/g.

44. The cross-linked, charge modified starch of claim 43 , wherein the cross-linked, charge modified starch further comprises a biopolymer that is different than starch.

45. The cross-linked, charge modified starch of claim 43 , wherein the at least one negatively charged moiety is a carboxyl, and the cross-linked, charge modified starch is covalently cross-linked.

46. The cross-linked, charge-modified starch of claim 43 , wherein the c cross-linked, charge modified starch has a charge density in a range of greater than 5 meq/g to 10 meq/g, as determined by titration.

47. A cross-linked, charge modified starch, wherein the cross-linked, charge modified starch includes at least one negatively charged moiety and the cross-linked charge modified starch is provided by reacting a starch with a charge-modifying agent including the at least one negatively charged moiety;

wherein the cross-linked, charge modified starch has a charge density of greater than 5 meq/g, as measured by titration, for the at least one negatively charged moiety;

wherein the cross-linked, charge modified has a net negative charge and is anionic;

wherein the at least one negatively charged moiety is a carboxly, a sulfonate, a sulfate, and/or a phosphate group; and

wherein the cross-linked, charge-modified starch has a Centrifuge Retention Capacity (CRC) in a range of about 15 g/g to about 60 g/g.

48. The cross-linked, charge modified starch of claim 47 , wherein the cross-linked, charge modified starch further comprises a biopolymer that is different than starch.

49. The cross-linked, charge modified starch of claim 47 , wherein the at least one negatively charged moiety is a carboxyl, and the cross-linked, charge modified starch is covalently cross-linked.

50. The cross-linked, charge-modified starch of claim 47 , wherein the cross-linked, charge modified starch has a charge density in a range of greater than 5 meq/g to 10 meq/g, as determined by titration.