Patent ID: 8865432

Claim:
A depolymerization method for preparing a depolymerized cellulose derivative having a viscosity at 20° C. in a 2% by weight aqueous solution that is reduced by 10% to 30% compared with the viscosity of a water soluble cellulose derivative before the depolymerization so that a number of undissolved floating portions of the depolymerized cellulose derivative in an aqueous solution is decreased compared with a number of undissolved floating portions of the water soluble cellulose derivative before the depolymerization in an aqueous solution, the method of depolymerization comprising the steps of: a) providing a water soluble cellulose derivative which has a viscosity at 20° C. of 50 mPa·s or greater in a 2% by weight aqueous solution; b) contacting the water soluble cellulose derivative of step a) with an aqueous solution, an alcohol solution or a gas of hydrogen chloride at a temperature of 40° C. to 85° C. for one to two hours wherein an amount of the hydrogen chloride is from 0.04% to 1% by weight based on the weight of the water soluble cellulose derivative.