Modified carbohydrate-chitosan compounds, methods of making the same and methods of using the same
Compositions of matter are provided that include chitosan and a modified carbohydrate. The modified carbohydrate includes a carbohydrate component and a cross linking agent. The modified carbohydrate has increased carboxyl content as compared to an unmodified counterpart carbohydrate. A carboxyl group of the modified carbohydrate is covalently bonded with an amino group of chitosan. The compositions of matter provided herein may include cross linked starch citrate-chitosan and cross linked hemicellulose citrate-chitosan, including foams thereof. These compositions yield excellent absorbency and metal chelation properties. Methods of making cross linked modified carbohydrate-chitosan compounds are also provided.
1. A composition of matter, comprising:
chitosan; and
a modified carbohydrate, wherein the modified carbohydrate has been modified so as to have an increased carboxyl content as compared to an unmodified counterpart carbohydrate, and wherein a carboxyl group of the modified carbohydrate is covalently bonded with an amino group of the chitosan, and wherein the composition of matter comprises a cross linked starch citrate-chitosan compound.
2. The composition of matter according to claim 1 , wherein the increased carboxyl content of the modified carbohydrate is introduced by a cross linking agent comprising at least one of citric acid, succinic anhydride, maleic anhydride and sodium monochloroacetate.
3. The composition of matter according to claim 1 , wherein the composition of matter has a tensile strength of about 0.10 to about 1.81 N/mm 2 .
4. The composition of matter according to claim 1 , wherein the composition of matter has a void fraction of about 0.9446 to about 0.9986.
5. The composition of matter according to claim 1 , wherein the composition of matter has a degradation temperature of about 305° C. to about 306° C.
6. A composition of matter, comprising:
chitosan; and
a modified carbohydrate, wherein the modified carbohydrate has been modified so as to have an increased carboxyl content as compared to an unmodified counterpart carbohydrate, and wherein a carboxyl group of the modified carbohydrate is covalently bonded with an amino group of the chitosan, and wherein the modified carbohydrate comprises hemicellulose and the hemicellulose has a carboxyl content of greater than 352 mequ/100 grams.
7. The composition of matter according to claim 6 , wherein the composition of matter comprises a cross linked hemicellulose citrate-chitosan compound.
8. The composition of matter according to claim 7 , wherein the composition of matter has a tensile strength of about 0.20 to about 1.61 N/mm 2 .
9. The composition of matter according to claim 7 , wherein the composition of matter has a void fraction of about 0.9735 to about 0.9980.
10. The composition of matter according to claim 7 , wherein the composition of matter has a degradation temperature of about 296° C.
11. The composition of matter according to claim 6 , wherein the increased carboxyl content of the modified carbohydrate is introduced by a cross linking agent comprising at least one of citric acid, succinic anhydride, maleic anhydride and sodium monochloroacetate.
12. The composition of matter according to claim 6 , wherein the hemicellulose has a carboxyl content in a range of 352 mequ/100 grams to 742 mequ/100 grams.
13. A composition of matter, comprising:
chitosan; and
a modified carbohydrate, wherein the modified carbohydrate has been modified so as to have an increased carboxyl content as compared to an unmodified counterpart carbohydrate, and wherein a carboxyl group of the modified carbohydrate is covalently bonded with an amino group of the chitosan, and wherein the modified carbohydrate comprises starch and the starch has a carboxyl content of about 180 mequ/100 grams or greater.
14. The composition of matter according to claim 13 , wherein the increased carboxyl content of the modified carbohydrate is introduced by a cross linking agent comprising at least one of citric acid, succinic anhydride, maleic anhydride and sodium monochloroacetate.
15. The composition of matter according to claim 13 , wherein the starch has a carboxyl content in a range of 180 mequ/100 grams to 473 mequ/100 grams.
16. A composition of matter, comprising:
chitosan; and
a modified carbohydrate, wherein the modified carbohydrate has been modified so as to have an increased carboxyl content as compared to an unmodified counterpart carbohydrate, and wherein a carboxyl group of the modified carbohydrate is covalently bonded with an amino group of the chitosan, wherein the composition of matter comprises a cross linked modified carbohydrate-chitosan compound, and wherein the modified carbohydrate has a degree of esterification of 17% or greater.
17. The composition of matter according to claim 16 , wherein the modified carbohydrate comprises a carbohydrate component comprising at least one of hemicellulose and starch.
18. The composition of matter according to claim 16 , wherein the increased carboxyl content of the modified carbohydrate is introduced by a cross linking agent comprising at least one of citric acid, succinic anhydride, maleic anhydride and sodium monochloroacetate.
19. The composition of matter according to claim 16 , wherein the modified carbohydrate has a degree of esterification in a range of 17% to 46.6%.
20. A method of making the cross linked starch citrate-chitosan compound according to claim 1 , the method comprising:
providing an aqueous citric acid solution including citric acid, water and a catalyst;
reacting a starch component with the citric acid solution to provide a starch citrate solution; and
mixing the starch citrate solution with a chitosan solution including chitosan, water and a weak acid to produce the cross linked starch citrate-chitosan compound.
21. The method of claim 20 , further comprising freeze drying the cross linked starch citrate-chitosan compound to form a foam.
22. The method of claim 21 , further comprising curing the foam by heating the foam at a predetermined temperature for a predetermined time to increase the tensile strength of the foam.
23. A method of making the composition of matter according to claim 6 , the method comprising:
providing an aqueous citric acid solution including citric acid, water and a catalyst;
reacting a hemicellulose component with the citric acid solution to provide a hemicellulose citrate solution; and
mixing the hemicellulose citrate solution with a chitosan solution including chitosan, water and a weak acid to produce a cross linked hemicellulose citrate-chitosan compound.
24. The method of claim 23 , further comprising freeze drying the cross linked hemicellulose citrate-chitosan to form a foam.
25. The method of claim 24 , further comprising curing the foam by heating the foam at a predetermined temperature for a predetermined time to increase the tensile strength of the foam.
26. A method of making the cross linked modified carbohydrate-chitosan compound according to claim 16 , the method comprising:
esterifying a carbohydrate component by combining the carbohydrate component with a cross linking agent in an aqueous solution, wherein a mixture including the carbohydrate component and the cross linking agent is formed thereby;
dehydrating the mixture to form the modified carbohydrate; and
cross linking the modified carbohydrate with chitosan by reacting the modified carbohydrate with chitosan under aqueous conditions, thereby forming a cross linked modified carbohydrate-chitosan compound.
27. The method of claim 26 , wherein esterifying the carbohydrate component further comprises adding a catalyst to the aqueous solution.
28. The method of claim 27 , wherein the catalyst is selected from the group consisting of sodium hypophosphite, sodium bisulfate and sodium bisulfite.
29. The method of claim 26 , further comprising removing the cross linked modified carbohydrate-chitosan compound from the cross linking reaction mixture.
30. The method of claim 26 , further comprising freeze drying the cross linked carbohydrate-chitosan compound to form a foam.
31. The method of claim 26 , wherein the carbohydrate component is selected from the group consisting of hemicellulose and starch.
32. The method of claim 26 , wherein the cross linking agent is selected from the group consisting of citric acid, sodium monochloroacetate, maleic anhydride and succinic anhydride.
33. The method of claim 26 , wherein cross linking the modified carbohydrate with chitosan is carried out at a temperature of about 80° C. to about 120° C.
34. The method of claim 26 , wherein cross linking the modified carbohydrate with chitosan is carried out at a solid to liquid ratio of at least 1:100.
35. The method of claim 26 , wherein cross linking the modified carbohydrate with chitosan is carried out at a pH of about 3 to about 6.
36. The method of claim 26 , wherein cross linking the modified carbohydrate with chitosan is carried out at a mass ratio of the modified carbohydrate to chitosan of about 0.4:1 to about 1.2:1.
37. A water absorption process which comprises contacting water with the cross linked modified carbohydrate-chitosan compound according to claim 16 .
38. A metal chelation process which comprises contacting a solution containing a metal with the cross linked modified carbohydrate-chitosan compound according to claim 16 .
39. The metal chelation process of claim 38 , wherein the metal is selected from the group consisting of Pb, Hg, Cd and As.
40. A salt absorption process which comprises contacting a solution containing salt with the cross linked modified carbohydrate-chitosan compound according to claim 16 .