Patent ID: 7482019

Claim:
A method for preparing modified microcrystalline chitosan, comprising the steps of: firstly, dissolving chitosan into an aqueous acidic solution; second, degrading chitosan in an aqueous acidic solution under conditions to achieve a desired molecular weight range and polydispersity, said solution having a concentration of at least about 0.001 wt % of chitosan, wherein the degrading is enzymatic, hydrolytic, or oxidative, said degrading comprising at least one of the following: introducing at least one of cellulases, chitanases, or xylanases with an enzymatic activity greater than 0.01 units/cm 3 into the aqueous acidic solution at a temperature between 30 degrees C. and 60 degrees C. for up to 100 hours, and then increasing the temperature to above 70 degrees C. to deactivate the enzyme; incubating the chitosan in the acidic solution having chydrochloric acid or chloroacetic acid at an amount greater than 0.001 wt % of the chitosan at a temperature between 40 degrees C. and 80 degrees C. for up to 100 hours; or introducing an oxidative agent into the acidic solution at a temperature greater than 30 degrees C. to 60 degrees C., wherein the oxidative agent is 10% hydrogen peroxide or sodium perborate in an amount between 0.01 wt % to 0.5 wt % of the chitosan; thirdly, alkalizing at vigorous agitation said acidic aqueous solution of chitosan with an aqueous base to form an alkaline solution having chitosan concentration of about 0.01-20 wt %, said alkaline solution having a pH greater than 7.0, wherein the base is a hydroxide or ammonia; and fourthly, precipitating said microcrystalline chitosan from said alkaline solution.