the present invention relates to a process for reactively separating hydrolyzable polymers , such as pet , in mixtures of the polymer and certain non - hydrolyzable polymers , specifically polyolefins by converting the hydrolyzable polymers to their corresponding water soluble components in the presence of liquid water at temperatures from about 200 ° c . up to the critical temperature of water and autogenous pressure . the process has utility in recycling and waste material separation processes .