Patent ID: 8835514

Claim:
A homogenously reacetylated chitosan having a molecular weight of not smaller than 200 kDa and a deacetylation degree of 30-60% for use in the preparation of a pseudo-thermosetting neutralized chitosan composition forming a phosphate-free transparent hydrogel at a temperature higher than 5° C., wherein said homogenously reacetylated chitosan is obtained by a homogenous reacetylation process of a chitosan having a molecular weight of not smaller than 200 kDa and a deacetylation degree of 80 to 90%, which process comprises: filtrating a chitosan having a molecular weight of not smaller than 200 kDa and a deacetylation degree of 80 to 90% dissolved in an acidic medium to eliminate insoluble particles; precipitating chitosan contained in the filtrated acidic solution to obtain chitosan free of insoluble particles; preparing a cooled acidic solution of the chitosan free of insoluble particles at a temperature lower than 5° C. to obtain a cooled acidic solution of chitosan free of insoluble particles; preparing a cooled acetic anhydride solution containing a predetermined amount of acetic anhydride in methanol at a temperature lower than 5° C.; reacetylating chitosan by adding dropwise, under homogenous conditions, the cooled acetic anhydride solution to the cooled acidic solution of chitosan free of insoluble particles to provide a crude homogenously reacetylated chitosan having a deacetylation degree of 30-60%; treating said crude chitosan to eliminate salts produced during reacetylation and insoluble particles of chitosan to obtain a homogenously reacetylated chitosan having a deacetylation degree of 30-60%.