Modified biopolymers and methods of producing and using the sam

Abstract

Modified biopolymers, such as, charge-modified biopolymers, cross-linked biopolymers, and cross-linked, charged modified biopolymers are provided along with methods of producing and using the same.

We claim: 
     
         1 . A method for producing a cross-linked, charge-modified biopolymer comprising:
 combining a biopolymer and a plasticizer to form a homogenous reaction blend, wherein the homogenous reaction blend comprises a plasticized biopolymer;   reacting the plasticized biopolymer and at least one charge-modifying agent in the homogenous reaction blend to form a charge-modified biopolymer; and   cross-linking the charge-modified biopolymer to form a cross-linked, charge-modified biopolymer,   wherein the cross-linked, charge modified starch is free of crystalline domains.   
     
     
         2 . The method of  claim 1 , wherein the combining step further comprises combining a catalyst with the biopolymer and the plasticizer to form the homogenous reaction blend. 
     
     
         3 . The method of  claim 1 , wherein the cross-linking step further comprises reacting the charge-modified biopolymer with at least one cross-linking agent. 
     
     
         4 . The method of  claim 1 , wherein the biopolymer comprises at least two different biopolymers. 
     
     
         5 . The method of  claim 1 , wherein the cross-linked, charge-modified biopolymer has a net positive charge. 
     
     
         6 . The method of  claim 1 , wherein the combining step comprises melt blending the biopolymer and the plasticizer using a reactive extrusion process. 
     
     
         7 . The method of  claim 1 , wherein the method is carried out in an extruder. 
     
     
         8 . The method of  claim 1 , wherein the cross-linked, charge-modified biopolymer is in the form of a particle have a diameter in a range of about 10 microns to about 1000 microns. 
     
     
         9 . The method of  claim 1 , 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. 
     
     
         10 . The method of  claim 1 , further comprising heating the cross-linked, charge-modified biopolymer 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. 
     
     
         11 . The method of  claim 1 , wherein the cross-linked, charge-modified biopolymer has a net negative charge. 
     
     
         12 . The method of  claim 11 , wherein the cross-linked, charge-modified biopolymer includes at least one negatively charged moiety selected from the group consisting of a carboxyl, sulfonate, a sulfate, and phosphate. 
     
     
         13 . A cross-linked, charge-modified biopolymer prepared according to the method of  claim 1 . 
     
     
         14 . The cross-linked, charge-modified biopolymer of  claim 13  having a charge density of at least 3 meq/g as determined by titration. 
     
     
         15 . A cross-linked, charge-modified biopolymer, wherein the cross-linked, charge- modified biopolymer is cationic, wherein the cross-linked, charge-modified biopolymer is free of crystalline domains, and wherein the biopolymer is starch. 
     
     
         16 . The cross-linked, charge-modified biopolymer of  claim 15 , wherein the cross-linked, charge-modified biopolymer has a degree of substitution of at least 0.1, as measured by nitrogen content. 
     
     
         17 . The cross-linked, charge-modified biopolymer of  claim 15 , wherein the cross-linked, charge-modified biopolymer includes at least one positively charged moiety selected from the group consisting of a quaternary ammonium, sulfonium, and/or phosphonium group. 
     
     
         18 . A cross-linked, charge modified biopolymer, wherein the cross-linked, charge modified biopolymer is anionic and wherein the cross-linked, charge modified biopolymer is free of crystalline domains, and wherein the biopolymer is starch. 
     
     
         19 . The cross-linked, charge-modified biopolymer of  claim 18 , wherein the cross-linked, charge modified biopolymer has a degree of substitution of at least 0.1, as measured by nitrogen content. 
     
     
         20 . The cross-linked, charge-modified biopolymer of  claim 18 , wherein the cross-linked, charge-modified biopolymer includes at least one negatively charged moiety selected from the group consisting of a carboxyl, sulfonate, a sulfate, and phosphate.