Production of low molecular weight chitosan by hot dilute sulfuric acid

Abstract

A new method was developed for production of low molecular weight chitosan, in which high molecular weight chitosan was treated with dilute sulfuric acid at 120°C. Chitosan was dissolved in the acid solution in a few minutes, and as depolymerized to low molecular weight chitosan by longer times. Low molecular weight chitosan was recovered from the acid by cooling down the solution and increasing the pH to 8-10. A low molecular weight chitosan with Mv (viscosity average molecular weight) of 174×103 was prepared from a high molecular weight chitosan (Mv = 1,388×103) with 82% recovery by using 72 mM sulfuric acid solution for 30 min. Increasing the time to 240 min reduced the Mv to 24×103, though the recovery of chitosan was reduced to 54%. Higher concentrations of acid (216 and 360 mM) resulted in higher depolymerization degrees and lower recoveries of chitosan in identical treatment times. Analysis of glucosamine and N-acetyl glucosamine showed that the prepared low molecular weight chitosan had more than 80% purity.