Effects of suspended sand concentrations on the surface aging of conventional and biodegradable plastic debris

Plastic waste ages in the environment, causing severe environmental pollution issues, but aging from suspended sand is less studied than that of ultra violet, thermal, or microbial effects. This study explored suspended sand's impact on the surface aging of traditional plastics (PET, PP) and biodegradable plastics (PLA+PBAT, SBP) through indoor experiments conducted over 0, 14, 28, and 42 days. Results showed that the carbonyl index of PET, PP, and SBP increased with aging, especially for SBP after 42 days, while that of PLA+PBAT decreased. The XPS analysis indicated that O/C ratios increased as all plastics aged, with PP showing the most significant increase. Contact angles of all plastics decreased, signaling enhanced hydrophilicity, with PLA+PBAT showing the largest reduction. Suspended sand accelerated aging through abrasion at low concentrations but slowed oxidation at high concentrations due to shading. Although its impact demonstrated weak regularity, the aging rate of traditional PP was even superior to that of biodegradable plastics, with an aging rate in order: PP > SBP > PLA+PBAT > PET. The aging process showed two phases: near-surface photo-oxidation in the rapid oxidation phase, followed by microcrack formation and particle rupture in the plateau phase. The impact of suspended sand should be considered in assessing lake plastic risks.