Methods for producing modified microcrystalline chitosan and uses therefor

Abstract

Disclosed are methods of producing modified microcrystalline chitosan. Chitosan in aqueous solution is degraded enzymatically, hydrolytically or oxidatively. The chitosan solution is then alkalized with agitation using aqueous hydroxides and/or their salts to attain a pH not lower than 7.0. The precipitated modified microcrystalline chitosan is highly pure and may be concentrated and dried according to known methods. Methods according to the invention also include methods by which an aqueous solution of chitosan is first alkalized using hydroxides and/or their salts to a pH not lower than 7.0. Then the precipitated microcrystalline chitosan is subjected to enzymatic or oxidative degradation to achieve a desired average molecular weight and polydispersity. The product is highly pure and may be concentrated and dried according to known methods.

1 - 30 . (canceled)  
     
     
         31 . A chitosan-calcium (II) complex, comprising: calcium (II) ions bound to microcrystalline chitosan, wherein said complex contains ≧0.01 wt % chitosan having an average molecular weight ≧10 kD, a polydispersity ≧2.0, deacetylation degree 24 65% and wherein said complex has a water retention value ≧300%, pH ≧7.1 and a calcium (II) ion content ≧0.1 wt % relative to chitosan.  
     
     
         32 . A chitosan-calcium (II) complex according to  claim 31 , wherein said calcium (II) ions are bound with the microcrystalline chitosan by coordinate bonds or hydrogen bonds.  
     
     
         33 . A chitosan-calcium (II) complex according to  claim 31 , wherein said complex is water soluble.  
     
     
         34 - 38 . (canceled)  
     
     
         39 . A chitosan-calcium (II) complex prepared according to a method comprising the steps of: 
 (a) providing a suspension containing ≧0.01 wt % microcrystalline chitosan, said chitosan having an average polymerization degree ≧100 kD, a polydispersity ≧2.0, and deacetylation degree ≧65%; and    (b) mixing said microcrystalline chitosan with ≧0.01 wt % calcium (II) salt to form said complex; wherein said complex has a water retention value ≧300% and a pH 27.0.