Abiotic degradation of LDPE and LLDPE formulated with a pro-oxidant additive

This article investigates the influence of a pro-oxidant additive on the accelerated and environmental degradation of linear low density polyethylene (LLDPE) and low density polyethylene (LDPE). Extruded cast films (100 μm) were prepared with various amounts of a pro-oxidant (a so-called “Oxo” additive) (0%, 1% and 2% w/w). The films were subjected to either environmental weathering or air oven aging (60 °C) tests for 260 days. The chemical and physical changes induced by aging were monitored by: Gel Permeation Chromatography (GPC), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Successive Self-nucleation and Annealing (SSA) thermal fractionation and tensile tests. Neat PE samples did not exhibit significant changes during the period evaluated. Crystallinity obtained from standard DSC tests during accelerated degradation exhibited variations due to a combination between annealing and recrystallization after chain scission. For both accelerated and environmental degradation a complete loss of mechanical properties was obtained although at different exposure times. SSA was shown to be the most sensitive technique applied since it evidenced early structural changes during degradation in LLDPE and LDPE that were undetected by GPC, tensile tests (i.e., strain at break) or FTIR at identical exposure times. SSA tests after accelerated degradation revealed that LLDPE linear sequences in between branching points are substantially more affected at longer exposure times than those in LDPE, a result that may imply differences in degradation mechanisms during the later stages of the degradation process.