Combination of an organothio compound and a zinc mercapto ester as a heat stabilizer in PVC processing

Halogen containing polymers, especially those containing chlorine, are used widely and have great commercial significance. Polyvinyl chloride (PVC), in particular, is used in packaging, siding, pipe, and many extruded shapes. Such large scale and diverse use of the halogen-containing polymers depends upon the incorporation therein of good heat and light stabilizers. PVC, for example, is known to have a tendency to degrade upon prolonged exposure to heat and light during processing and use. Darkening or other color change and the loss of tensile, flexural, and impact strengths are the results of such degradation. Unless good low-cost stabilizers are available for addition to the polymer composition, the service life of articles made from the composition is limited, and its use severely restricted, as will be the conditions for making it. The zinc bum experienced during the processing of a composition comprising a halogen-containing polymer and a zinc mercaptoester is eliminated by the addition of an organothio compound selected from dithioglycol, polyformals and polyacetals of said dithioglycol, and a mercaptoalkanol.