Accelerated degradation of low-density polyethylene in air and in sea water

Accelerated weathering of LDPE laminates, with samples exposed to ultraviolet radiation (UVR) in air and while floating in seawater at the same temperature, was investigated in this study. The depth profiles of the concentrations of oxidation products in the two sets of samples was assessed by FTIR (Fourier Transform Infrared Spectroscopy) and suggest the oxidation on weathering to be diffusion-controlled in both air and in seawater, localizing the reaction to a thin surface layer. While the thickness of this layer is several hundred microns in air-weathered samples it is too small to be discernible by FTIR spectroscopy in sea water-weathered samples. A naturally weathered polyethylene microplastic pellet from floating ocean debris was also similarly studied by FTIR and the depth profile compared with that from accelerated weathering of LDPE laminates. Tensile properties of the LDPE weathered in air and in sea water were also compared to better understand the impact of diffusion-controlled oxidation on their mechanical integrity. How the origin of apparent retardation of the rate of weathering degradation of LDPE in seawater relative to that in air, is related diffusion-controlled oxidation due to the low concentrations of dissolved oxygen in seawater, is also discussed.