Preparation of Polystyrene Nanoparticles with Environmental Relevance Using a Gradual Degradation Method

This study investigates the environmental degradation of polystyrene (PS) microparticles and flakes using a gradual degradation method. The concentration of SO₄•^- decreased exponentially, simulating the environmental conditions. The nanofragment size of PS particles evolved dynamically, fluctuating from below 250 nm at 3 days to 300-500 nm at 6 days, then forming two peaks below 200 nm at 9 days, before shifting to a single peak below 100 nm at 12 days. At 15 days, the distribution expanded to two peaks between 500 nm and 200 nm. The polydispersity index (PDI) varied unpredictably, and fragments below 100 nm fluctuated between 10 and 50 nm independent of time. SEM analysis revealed an initial peeling process, with the outermost layer peeling off. The core size of the PS particles decreased rapidly from 11,000 nm to 2500 nm within 6 days and stabilized at 1000 nm after 9 days. The PS flakes showed minimal shape change until 24 days, but surface roughness increased by 30 days, leading to fragmentation. By 42 days, the flakes partially broke into ca. 100 μm pieces. The initial morphology significantly influenced the breakdown pattern, suggesting multiple breakdown mechanisms other than peeling.