Weathering and Dating of Plastics in Variably Saline Environments

Abstract

Research has been conducted over the course of the 2021-2022 academic year to determine the weathering characteristics of plastic materials as a function of salinity and time. Since their widescale introduction, plastics have entered river and oceanic systems around the world and had adverse effects. To this end, I conducted two experiments. The first exposed polyethylene (PE), polystyrene (PS), polyvinylchloride (PVC), and Nylon 6,6 plastic samples to UV light over under different saline conditions. Samples of the plastics and their leachates were analyzed by FTIR and EEMS/UV-Vis respectively. The second analyzed plastic samples from fishing nets that had been exposed to saline environments, UV, and mechanical degradation using FTIR. With this data I attempted to determine a method of dating environmental plastic samples based upon those spectra and depth of plastic sample. In all, research found differences in the weathering between plastic types and salinity over time. Saline lab samples showed greater oxidation with PE, PS and PVC, while Nylon 6,6 was oxidized more heavily in fresh solution. Field samples showed increases in hydroxyl and carbonyl groups that were correlated with time. Leachates were analyzed and phenol, toluene, and similar aromatic compounds and more complicated polymer acids were found in UV and dark samples respectively with minor increases in fluorescence in saline relative to fresh solutions. A mechanism of UV catalyzed leaching by ring forming reactions was put forward based on prior work by Cai et al. and Huang et al. Finally, a model for the age of weathered plastics based on FTIR spectral analysis was put forward for nylon and PVC as þ = �㕃þþ�㕘 �㔼ÿþþý�㕖þ�㕦 �㕅þþ�㕖Ā−0.1828 0.0268 and t = ln (�㕃þþ�㕘 �㔼ÿþþý�㕖þ�㕦 �㕅þþ�㕖Ā 0.8328 ) 0.6285 respectively.