Degradation profile of polyethylene after artificial accelerated weathering

Elucidation of the chemical changes that take place during the aging of polyethylene sheared electrical cables, and the correlation of these changes with physical properties need experiments with accelerated aging assays. These were carried out using the most representative polyethylene grades found in today's market: low density (LDPE), linear low density (LLDPE) and high density (HDPE). The samples were exposed to UV- and xenon arc radiation using a varying exposure time and different temperature cycles. The changes in the material structure and properties were analyzed by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), FTIR-spectroscopy, density and hardness measurements. During degradation polar groups in the polyethylene are generated, as well as chain scission and cross-linking. As net effects of these processes respective increases in crystallinity, density and hardness and surface cracking at late stages of degradation are observed. By varying the angle of incidence in attenuated total reflection (ATR) experiments using FTIR-spectroscopy it was possible to detect variations in composition of distinct layers from the surface down to a depth of 1.2 mum. Deeper layers were reached by microtoming the samples in layers down to 60 muM. The main chemical modifications were carbonyl formation of various kinds which were identified in the FTIR-ATR spectra of degraded polyethylene samples. (C) 2002 Elsevier Science Ltd. All rights reserved.