This invention relates to a process for the recovery and reuse of scrap of polyethylene terephthalate (PET) coated with a chlorine-containing polymer as well as to useful articles made from such recovered material.
There is a large amount of PET scrap available to the industry for reuse from such sources as, e.g., PET bottles, fibers, and film. A substantial amount of this scrap is difficult to use because some PET film and bottles which require greater impermeability to oxygen and water are coated with a thin layer of a chlorine-containing polymer. This usually is a vinylidene chloride homopolymer or a vinylidene chloride copolymer with a minor amount (about 0.1-10 weight percent) of another vinyl comonomer, which itself may or may not be chlorinated. The identity of those additional comonomers may vary according to the manufacturer and usually is considered proprietary by the film coating industry. Further, polyvinyl chloride and copolymers of vinyl chloride with minor amounts of other unsaturated monomers can be used in those applications. In addition, a chlorine-containing polymer is coated on photographic polyester film base for adhesive purposes. When a vinylidene chloride polymer is used as the coating material, the amount of such coating normally is about 0.01-0.24 weight percent of the total coated polymer weight. However, this amount is not critical and can be adjusted as appropriate for a particular application. Normally scrap material consisting of PET coated with a chlorine-containing polymer cannot be used as such and has to be boiled with sodium hydroxide or subjected to other chemical treatment to remove the polymer coating. For example, vinylidene chloride polymer degrades at about 200.degree. C., which is below the normal processing temperature of PET. If scrap PET containing vinylidene chloride polymer is inadvertently used in processing, hydrogen chloride is released, resulting in degradation and discoloration of the PET and corrosion of the equipment. The art has not heretofore described any practical method of melt processing that would make possible the use of PET scrap contaminated with vinylidene chloride polymers or vinyl chloride polymers without prior complete removal of the chlorine-containing polymer contaminant.
It thus can be readily seen that a process for recovering and reusing such PET scrap material, of which there are available millions of kilograms every year, would be of great industrial interest.