Shear degradation of vinylidene chloride copolymers

Abstract

AbstractThermally induced dehydrochlorination is a well‐established and prominent degradation mode for vinylidene chloride copolymers. During extrusion, other processes may represent significant degradation pathways. Under shear in air, both oxidative chain‐scission and cross‐linking are prominent processes for both vinylidene chloride/vinyl chloride and vinylidene chloride/methyl acrylate copolymers. Both processes are dependent upon shear rate and temperature. The shear‐stress dependency can be modeled by a kinetic expression that incorporates shear stress into the Arrhenius preexponential factor. Vinylidene chloride/methyl acrylate copolymers appear to be somewhat more susceptible to oxidative chain‐scission than are comparable vinylidene chloride/vinyl chloride copolymers, presumably because of a rapid oxidative attack at exposed methyl acrylate units. Shear‐induced degradation of these materials in air is characterized by early predominant chain‐scission with cross‐linking assuming a greater importance as a function of time. Degradation under shear in a nonoxidative environment is a much simpler process—oxidative chain‐scission is suppressed and cross‐linking is very similar to that observed in air. © 1994 John Wiley & Sons, Inc.