A facile physical approach to make chitosan soluble in acid-free water

We changed the situation that chitosan was only dissolved in diluted acid through mild physical treatment. In viewing of the usual methods to modify chitosan are chemical ones, we established the approach by using a water-soluble chitosan derivative as the model polymer. Its water-solubility was modulated via changing the concentration of solution and varying the precipitants. Such a physical method was adopted to treat chitiosan. One gram chitosan was dissolved in a mixture of 100 mL 10% acetic acid and 50 mL methanol, and then precipitated from a precipitant consisted of 10 mL ethanol and 90 mL acetate ester. The treated chitosan became soluble in acid-free water completely, and its solubility was 8.02 mg/mL.