Process for preparing polyethylene terephthalate useful for beverage

Abstract

There is disclosed a process for reducing the acetaldehyde content and the generation rate of acetaldehyde of polyethylene terephthalate chip which has a crystallinity of at least about 30% in order to render the polyethylene terephthalate suitable for making containers which are useful in the carbonated beverage industry. This process comprises stabilizing the polyethylene terephthalate by heating it at an elevated temperature in air and maintaining an air to chip ratio at a predetermined value of at least about 0.8 standard cubic foot of air per minute/pound of resin per hour and at a vapor velocity of at least about 0.5 foot per second. The air used in the stabilization process has a dew point of less than about -30.degree. C. The stabilized polyethylene terephthalate produced by this process has an acetaldehyde level of less than about 2.5 parts per million, a generation rate of acetaldehyde of less than about 3.0 parts per million per minute and an intrinsic viscosity of from about 0.60 to about 0.95 deciliters per gram. There is also disclosed a process for molding a polyethylene terephthalate preform comprising melting the above described polymer, forming it into the desired preform shape, and cooling the molten polymer. This preform may then be reheated above its glass transition temperature and molded into the desired container shape.