Characterization of surface phenomena: probing early stage degradation of low-density polyethylene films

Photo-oxidative degradation of polyethylene triggers significant deterioration in the polymer properties. Much interest is aimed at characterizing and possibly predicting photo-oxidative damages, at early stages, prior to the occurrence of profound changes in mechanical properties. Herein, we study the degradation of low-density polyethylene (LDPE) films, focusing on surface deterioration processes. Thin films of various molecular weights are exposed to accelerated weathering while their chemical, mechanical and morphological characteristics are monitored throughout by apparent contact angle (CA) measurements, Fourier-transform infrared spectroscopy (FTIR), tensile test, and electron microscopy. A significant decrease in the films' CA during degradation is observed. CA is highly sensitive to two simultaneous phenomena with opposing effect: nanoscale surface roughening and composition changes. We found the latter (specifically the evolution of polar groups) to be the dominant parameter affecting the CA behavior. Consequently, simple CA measurements coincide well with conventional FTIR analysis, and are more sensitive to changes occurring at early stages of degradation. The deterioration in the mechanical properties is also characterized and is found to present poor sensitivity and high variability at these early aging stages. Thus, simple CA measurements could potentially be used as a qualitative indicator for evaluating the aging impact on LDPE. POLYM. ENG. SCI., 59:E129–E137, 2019.