CORRELATION OF PHYSICOCHEMICAL CHANGES IN UV-EXPOSED LOW DENSITY POLYETHYLENE FILMS CONTAINING VARIOUS UV STABILISERS

摘要

Melt blown biaxially orientated, unstabilised and stabilised low density polyethylene (LDPE) films with various thicknesses were exposed in two accelerated artificial weathering devices with xenon are (Xenotest) and fluorescent tube UV-B (QUV) sources under controlled temperature and humidity. The structural changes during combined photo- and thermal degradation have been studied using tensile tensiometric, IR spectrophotometric, and thermal analytical (DSC) techniques. The effects of hindered amine light stabilisers (HALS) and film thickness on the time-dependent changes in elongation, carbonyl group concentration, crystallinity and onset temperature (T-on) of post-fusion DSC oxidation exotherm have been observed. Photo-oxidation is accompanied by increased crystallinity which maximises as mechanical properties start to deteriorate significantly and the rate of carbonyl group formation increases. While poor correlation exists between reduction in mechanical properties and increased carbonyl index values, the former correlates well with the DSC derived T-on values for unstabilised and stabilised films. This suggests that thermal analysis may be useful in detecting physicochemical changes occurring in exposed films more effectively than other techniques such as IR. [References: 16]