Influence of additives on UV-induced degradation of polypropylene: micro and nanoplastic formation and additives release

Plastics used outdoors are exposed to UV radiation, humidity, and mechanical stress, which cause them to degrade and release degradation by-products. Although additives are commonly incorporated into plastic formulations to improve their durability, their role in micro- and nanoplastics release and other degradation by-product release remains unclear. This study investigated how the initial formulation of polypropylene (PP) influences its environmental degradation. Two formulations were compared: reference PP (without added additives) and PP + 6, containing six industrially representative additives. The pellets were subjected to accelerated UV weathering and subsequently exposed to mechanical agitation in water to simulate environmental mechanical stress. Mass loss, particle size and morphology, and soluble degradation products were quantified using gravimetric, morphometric, and total organic carbon analyses, while surface morphological changes were examined by scanning electron microscopy. The reference PP (without added additives) underwent a three-phase degradation process, reaching a cumulative mass loss of 82 ± 8% after 50 days of UV exposure: an initial phase dominated by the release of volatile and NP+soluble species, followed by surface ablation generating MP, and finally a sharp increase in MNP+soluble release due to granule fragmentation, which accounted for 62 ± 7% of the total mass loss after 50 days of UV exposure. In contrast, PP + 6 exhibited delayed degradation, reaching only a cumulative mass loss of 24 ± 3% after 50 days, with two distinct phases observed. However, a continuous increase in emissions of volatile compounds and leaching of additives into the aqueous phase was observed. These results demonstrate that the initial formulation strongly governs both degradation pathways and the nature of pollutants released, underscoring the need to consider both MNP generation and soluble and volatile emissions when assessing the environmental impacts of plastic materials.