This standard specifies a method for the determination of the reduction in viscosity which occurs when cellulose acetate is moulded. The viscosity loss on moulding is related to the depolymerization of cellulose acetate, which generally increases brittleness in the moulded product. This method is suitable for cellulose acetate which does not contain additives, fillers, etc., which may interfere with the detemination of viscosity. It is suitable for cellulose acetate having an acetic acid yield above 50 %