Attenuated total reflection infrared spectroscopy for micro-domain analysis of polyethylene samples after accelerated ageing within weathering chambers

Elucidation of the chemical changes that take place during the ageing of polyethylene by weathering can be accomplished by infrared (IR) spectroscopy. Accelerated ageing was applied to the most representative low density polyethylene (LDPE) found in markets today. The samples were exposed to UV- and xenon-arc radiation of varying duration and temperature cycles. The structural changes in the material surface were analysed by scanning electron microscopy (SEM) and chemical composition was studied by FTIR spectroscopy. By varying the crystal material in the conventional attenuated total reflection (ATR) experiments it was possible to analyse distinct layers from the surface. Micro-domain analysis was made possible by using a novel ATR microprobe based on a silver halide fibre of circular cross-section with an outer diameter of 700 mum. Layers at larger depth were reached by cross-sectioning the LDPE-samples and measuring the concentration profiles of oxidation products down to 500 mum with a spatial resolution lesser than 15 mum. The main chemical modifications were from carbonyl formation of various kinds identifiable in the ATR-FTIR spectra of degraded polyethylene samples. (C) 2003 Elsevier B.V. All rights reserved.