Solid-state thermal aging promotes mechanical fragmentation and microplastic release in polypropylene

The environmental persistence of polypropylene (PP) has raised growing concern regarding its transformation into microplastics under environmentally relevant conditions. While photodegradation has been extensively studied, the role of solid‑state thermal aging under dry, sub‑melting conditions in preconditioning PP for microplastic formation remains less explored. This study systematically investigates how solid‑state thermal aging under controlled dry, atmospheric‑oxygen conditions alters PP structural integrity and how subsequent mechanical fragmentation governs microplastic release. PP specimens were thermally aged at 80 °C, 100 °C, and 120 °C for up to 350 h, followed by controlled mechanical agitation at 100, 500, and 1000 rpm in deionized water. Fourier Transform Infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) revealed thermally induced chain scission, structural weakening, and surface embrittlement, with limited detectable oxidative functionalization. Gravimetric analysis and micro-FTIR particle identification confirmed time and temperature-dependent microplastic release, with maximum mass loss of 12,800 ± 595 mg/kg at 120 °C after 350 h at 1000 rpm. A strong correlation was observed between mass loss and microplastic particle count, while particle size analysis indicated a dominance of microplastics of