UV Aging of PET Microplastics in a Custom-Built Weathering Chamber Replicating Mediterranean Conditions

During their lifetime, microplastics undergo transformations and react in ways that change their behavior and properties over time. Current standard plastic weathering protocols, which were developed prior to the increased concern about plastic pollution, may not be fully suited for microplastic studies as they aim to monitor durability and understand bulk plastic behavior, with little concern about fragments or leachates produced during degradation. This work aims to age poly-(ethylene terephthalate) (PET) microplastics (MPs) in a custom-built weathering chamber replicating Mediterranean shoreline conditions (detailed in the authors' previous work). This work studies the physicochemical changes of PET microplastic pellets (3-5 mm) following aging for a period of 90 days in dry and aquatic environments within a purposely designed weathering chamber. The chamber implemented UV-A, mechanical abrasion, and elevated temperatures to replicate the shore conditions. Micro-Raman spectroscopy was used to follow changes in the carbonyl content, crystallinity, and phenyl content of the PET MPs. Additionally, scanning electron microscopy (SEM) paired with energy-dispersive spectroscopy (EDS) was used to observe changes at the surface of the aged PET MPs. SEM showed that abrasion led to surface roughening and fibrillation. Despite changes being noted, no clear pattern emerged within the processed Raman spectroscopic results to elicit the contributions of UV radiation, salinity, and temperature. Loss of the surface layer by fragmentation and exposure of new surfaces could explain the fluctuating micro-Raman data. This work demonstrates early-stage degradation features including fluctuating chemical changes, fragmentation, abrasion, and salt crystallization under environmentally realistic Mediterranean shoreline conditions while laying methodological groundwork for future microplastic weathering research that seeks longer durations.