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

Melt blown biaxially orientated, unstabilised and stabilised low densi ty 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 therm al degradation have been studied using tensile tensiometric, IR spectr ophotometric, 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, crysta llinity and onset temperature (T-on) of post-fusion DSC oxidation exot herm have been observed. Photo-oxidation is accompanied by increased c rystallinity which maximises as mechanical properties start to deterio rate significantly and the rate of carbonyl group formation increases. While poor correlation exists between reduction in mechanical propert ies and increased carbonyl index values, the former correlates well wi th the DSC derived T-on values for unstabilised and stabilised films. This suggests that thermal analysis may be useful in detecting physico chemical changes occurring in exposed films more effectively than othe r techniques such as IR.