Dewatering of poly(vinyl chloride)

Abstract

Abstract In the manufacture of emulsion or dispersion type poly(vinyl chloride) (PVC) utilizing conventional peroxide initiators, the PVC dispersion produced from the polymerization reactor is concentrated by using a coagulant such as alum in a centrifuge to produce a cake. The present method then introduces a redispersant to liquefy the PVC cake and make it amenable to spray drying. The redispersant comprises an effective amount of a low molecular weight polyacrylate, such as preferably a hydrolyzed polyacrylonitrile having 20-30 percent amide groups and 70-80 percent carboxyl groups and having a molecular weight in the operable range of 800-100,000; in a preferred range of 800-60,000 and in a most preferred range of 5,000-60,000. The polyacrylate additive is utilized in an effective amount of at least 700 ppm based upon the PVC product and preferably in the range of at least 700 to 8,000 ppm. The importance of the redispersant additive is that in commercial practice it allows the elimination of a thin-film evaporator and substitution of a centrifuge step before the spray dryer with a consequent saving of heat and energy. PVC sheets made from dispersions produced herewith show greater heat stability and equivalent blush resistance than comparable sheets without a polyacrylate redispersant additive.

Inventors

• 👤 Ronald J Dembowski

Bibliographic Details