Evaluating polyethylene weathering processes after simulated solar exposure and in situ lake deployment

• Stability/degradation of polyethylene after simulated solar exposure/lake deployment. • Systematic investigation of a variety of polyethylene samples. • Advanced statistical methods used for data analysis. Studies on environmental polyethylene (PE) weathering have been of interest from the standpoint of sustainability and recycling. To help determine the individual and combined role of solar radiation and biofilms in the polyethylene degradation processes, we study changes in the molecular architecture of high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE) via a combination of simulated solar exposure and in situ freshwater lake deployment. Here experimental design variables include the sample variations in polyethylene material parameters, and aging variables such as simulated solar exposure (or UV aging) duration, lake deployment duration, and water column (lake depth). Chemical and structural changes in samples were measured by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and Raman microscopy, and the results were quantified and further processed using statistical analysis to reveal their relationships to a variety of aging conditions. Post-environmental aging (as material exposed to environment) is heterogeneous in nature, and it is necessary to leverage statistical analysis to reach data interpretation with confidence. The study indicates that the types of polyethylene and UV aging are the key factors that led to the polyethylene structural changes. The lake deployment duration within 14 months at three depths in a 30 m freshwater lake does not yield a significant effect on the carbonyl index of polyethylene measured using ATR-FTIR but does impact the PE crystallinity detected by Raman microscopy. Based on Raman and ATR-FTIR results, it is hypothesized that biodegradation of PE does occur during the lake deployment, but in a very slow fashion. In the lake, the structural reorganization of the PE samples is more pronounced compared to the photo-oxidation reaction induced by the UV irradiation. However, additional experiments are needed to validate further our results/hypothesis.