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Thermal oxidation, ultraviolet radiation, and mechanical abrasion - understanding mechanisms of microplastic generation and chemical transformation
Summary
Researchers evaluated how consumer-derived polymers fragment and chemically transform when exposed to UV radiation or thermal oxidation followed by soil abrasion. The study found that these combined weathering processes, which mimic real-world environmental conditions, significantly affect the rate and type of microplastic generation. The results highlight how everyday use and environmental exposure work together to break down plastics into microplastic particles.
Our study evaluated the fragmentation and chemical transformation of consumer-derived polymers exposed to UV radiation or thermal oxidation, followed by soil abrasion. Although UV exposure and elevated temperatures are common in environmental and use-phase settings (e.g., surface exposure and contact with hot food or liquids), their combined effects with mechanical abrasion (wind, surface runoff, or improper disposal into soils, riverbanks, and other sediment-rich environments) on microplastic (MP) generation remain poorly understood. To address this gap, we subjected commercial plastics to UV, thermal, or non-oxidative conditions prior to controlled soil abrasion. Micro–attenuated total reflectance–Fourier transform infrared (micro-ATR-FTIR) spectroscopy showed that abrasion introduced vinyl and oxidized products in low-density polyethylene (LDPE), expanded polystyrene (PS), and polypropylene (PP), regardless of oxidation history, while UV and thermal oxidation alone induced carbonyl formation in LDPE, PP, and PS. In contrast, polyethylene terephthalate (PET) was chemically unaffected by abrasion and thermal oxidation, while UV exposure reduced the intensity of its characteristic peaks. Among polymers, LDPE and PS exhibited the highest overall MP generation, likely due to LDPE’s thin structure and PS’s foamed morphology. Regarding weathering effects, UV-oxidized samples subjected to abrasion generated up to 2.8-fold more LDPE MPs and 1.9-fold more PP MPs than abraded non-oxidized counterparts in particle count, and 65-fold and 2.9-fold higher MP mass for LDPE and PP, respectively, as quantified by pyrolysis–GC/MS. In contrast, abraded non-oxidized PS produced higher MP counts and mass than its abraded oxidized counterparts, while PET showed no significant differences across treatments. Overall, these results demonstrate that coupled chemical and physical weathering enhances MP generation and alters polymer functional group chemistry in a polymer-specific manner. While UV exposure combined with abrasion generally increases MP formation, even mild thermal aging (100 °C) can modify the chemical fingerprint of common plastics without necessarily increasing fragmentation, advancing the mechanistic understanding of environmental plastic degradation.
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