Ageing characterization of commercial ethylene copolymer greenhouse films by analytical and mechanical methods

This paper focuses on the description of the ageing behaviour of commercially available ethylene vinyl acetate (EVA) greenhouse films due to accelerated weathering. Two commercially available multi-layer films were chosen as model materials. The degradation behaviour was analyzed by infrared (IR) spectroscopy in transmittance and attenuated total reflectance (ATR) mode, by ultra violet (UV) visible/near infrared-spectroscopy, differential scanning calorimetry (DSC) and by comprehensive mechanical characterization. Using IR spectroscopy, hydroxyl-, vinylidene- and acid-groups were identified as main degradation products. By IR and UV/VIS/NIR-spectroscopy the consumption of stabilizers was detected. Post-crystallization was detected by DSC measurements. The analytical results of the weathered films were correlated to ultimate mechanical properties determined by investigating unnotched and notched specimens. The results suggest that degradation of the investigated polymer films is strongly confined to the surface. While both films were of different layer structure, the ageing processes on the surface of the 200 μm thick film are not reflected by mechanical properties, in contrast to the 30 μm thick film. Nevertheless, tensile tests appeared to be the most versatile method for describing ageing phenomena. Both chemical ageing and physical ageing as well as local (initial) and global ageing effects are reflected by mechanical properties.