UV aging behaviour of ethylene-vinyl acetate copolymers (EVA) with different vinyl acetate contents

The mild UV aging of ethylene-vinyl acetate copolymer (EVA) with two vinyl acetate (VAc) contents (14, 18 wt%) was performed in a xenon arc source chamber. The degradation mechanism was analyzed via attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), gel content and high temperature gel permeation chromatography (HTGPC). Photo-chemically induced deterioration was first initiated from vulnerable VAc units. Ketone formation preceded lactone generation, especially in EVA with high VAc content. Un-stable structures induced further degradation in the main chain. Competition between radiation induced cross-linking and chain scission in EVA was observed, and the later was confirmed to be dominant. Higher VAc content resulted in remarkable drop in molecular weight and growth in polydispersity. Apparent re-arrangement in crystallisation and consequent decrease in thermal stability are discussed through differential scanning calorimetry (DSC) and thermo-gravimetric analysis (TGA), which accorded well with the chain scission tendency. Interaction between photo-chemical degradation and physical annealing accounted for the first increasing then decreasing tendency in the mechanical properties of both EVAs.