Transferability of accelerated weathering to outdoor weathering for commodity polymers PS, PP and PE

The worldwide accumulation of microplastic poses indeterminable ecological risks. Polymer defects introduced by photooxidation govern the properties of weathered plastic particles and their interaction with natural colloidal particles and living organisms while additive degradation and leaching increase the risk potential of microplastic. To aid these risk assessments, knowledge on pathways and timescales for microplastic formation and degradation under exposure to different environmental stress factors is crucial. In this context, accelerated laboratory weathering has gained significant attention as less time-consuming alternative to outdoor weathering experiments with better controllable and adjustable parameters such as temperature and relative humidity. However, the applicability of accelerated weathering to simulate outdoor settings is rarely evaluated. To test the transferability of accelerated weathering in an industrially available weathering chamber to outdoor weathering, we performed a direct comparison study using polystyrene (PS), low-density polyethylene (LDPE) and polypropylene (PP) as these commodity polymers alone make up half of the entire global plastic production. While PS and LDPE are non-additivated and serve as models for the degradation behavior of amorphous and semicrystalline polymers, respectively, the semicrystalline PP is additivated with the primary antioxidant Irganox 1010 and the secondary antioxidant Irgafos 168. All three polymers were subjected to accelerated weathering over a time period of 4.5 months at different temperatures and outdoor weathering for a supposedly corresponding 1.5 years. Both experiments were continuously sampled and monitored via gel permeation chromatography, particle size analysis, differential scanning calorimetry, SEM imaging, and solid-state 13C NMR spectroscopy to determine degradation time scales and mechanisms. The results of both experiments could be successfully linked using weather data obtained from the meteorological station at the University of Bayreuth located in the vicinity of the outdoor experiments. Also see: https://micro2024.sciencesconf.org/559207/document