Raman and ATR-FTIR unmask crystallinity changes and carboxylate group and vinyl group accumulation in natural weathering polypropylene microplastics

Naturally weathered polypropylene (NWPP) samples are useful for investigating the effects of various degradation factors that cannot be obtained in artificial laboratory experiments. In this study, NWPP samples were extracted from beach sediments (Ashiya, Hyogo, Japan). Raman and attenuated total reflection (ATR)–Fourier-transform infrared (FTIR) spectroscopies were used to analyze variations in the composition, crystallinity, orientation, and degradation of NWPP microplastics. The degree of degradation varies from sample to sample, from position to position in a sample, and the inside surface or outside surface of a sample. Significant intensity variations were observed for Raman bands at 1150 and 842 cm⁻¹,…