Patent ID: 8304464

Claim:
A method for mixing a polyester with a caustic material, comprising: providing a polyester; drying the polyester; mixing the dried polyester with the caustic material to form a mixture; and heating the mixture in multiple temperature stages defined as a function of a reaction sequence of the reaction between the polyester and the caustic material, wherein in a first of the temperature stages the polyester is heated to a temperature between 95° C. and 120° C., in a second of the temperature stages the polyester is heated to a temperature between 110° C. and 130° C., and in a third of the temperature stages the polyester is heated to a temperature between 120° C. and 140° C., and wherein a reactor heats the mixture of the polyester and caustic material, the reactor including a twin shaft mixing screw for mixing of the mixture of polyester and caustic material, screw shafts that mesh with one another being used for the twin shaft mixing screw, at least one of the screw shafts having a sawtooth profile, and wherein the inner wall of the reactor is kept essentially free of adherences of the polyester.