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Comparing outdoor and accelerated weathering of polystyrene, polyethylene and polypropylene – towards predicting the fate of environmental microplastics
Original title: Comparing outdoor and accelerated weathering of polystyrene, polyethylene and polypropylene – towards predicting the fate of environmental microplastics
Summary
Scientists tested how common plastics (like those in packaging and containers) break down into microplastics when exposed to sunlight and weather, comparing real outdoor conditions to sped-up lab simulations. They found a way to use everyday weather data to more accurately predict how fast plastics fragment into smaller pieces in different climates and seasons — which matters because knowing how quickly plastics break down helps researchers better estimate our exposure to microplastics in the environment over time.
Accelerated weathering becomes increasingly popular in microplastic research to produce defined, environmentally relevant reference particles and determine their degradation kinetics. However, to predict the persistence of environmental microplastics, models must be developed that correlate real-life with accelerated weathering. Therefore, we conducted long-term accelerated and outdoor weathering studies using amorphous polystyrene (PS), semi-crystalline low-density polyethylene (LDPE) and polypropylene (PP) particles. In all cases, the particles weather according to the same principles. Photooxidation induces chain scissions, crosslinks and polar, oxygen-containing functional groups. At the same time, the particles degrade following a three-stage model where surface abrasion is followed by fragmentation. While the mechanical stress was similar and kept constant for all experiments, temperature and irradiance varied for the outdoor setting. By introducing a time-dependent acceleration factor composed of the Schwarzschild and Arrhenius laws, we could derive a model with the materialspecific activation energy (EA) and Schwarzschild coefficient p as only free parameters. EA and p determine how strongly the timescales between outdoor and accelerated weathering divide, rendering the model’s predictive power polymer-type dependent. The model uses publicly available weather data and thus predicts seasonal and regional variations of the outdoor degradation rates with higher accuracy compared to common models using an average temperature or a constant acceleration factor. Synopsis: The characteristics of commodity plastics like PS, PE and PP weathered in natural environments can be predicted by parameterizing the irradiance and temperature from accelerated weathering studies.