Surface wear mechanisms of plastics: interplay of intrinsic characteristics, environmental weathering, and microplastic generation.

Surface wear is an important pathway for microplastic (MP) release into terrestrial environments. This study examines how intrinsic polymer properties and weathering processes, including photodegradation and sediment deposition, affect surface wear mechanisms in low and high density polyethylene (LDPE, HDPE), high-impact polystyrene (HIPS), and styrene butadiene rubber (SBR). Accelerated UV weathering altered surface chemistry and microstructure, reducing elongation at break and increasing hardness through potential chain scission, chemicrystallization, and crosslinking. Sediment deposition further enhanced hardness and decreased elongation at break by 10-11%. Virgin plastics exhibit wear resistance in the order SBR < HIPS < LDPE ≤ HDPE, with specific wear rates of 0.070, 0.036, 0.013, and 0.013 mm³ /N·m, respectively. The lower wear rates of HDPE and LDPE, compared with the amorphous HIPS and SBR, emphasize the role of polymer crystallinity and molecular structure. Photodegradation reduced LDPE wear resistance by two-fold, while changes in HDPE, HIPS, and SBR were not significant. Sediment deposition had minimal impact on wear resistance. Both UV-aging and sediment deposition influenced generated MP characteristics, shifting size distributions toward larger particles. Scratch resistance and scratch coefficient of frictions were consistent with wear resistance and further highlighted the role of polymer intrinsic mechanical properties. UV-aging strongly affected semicrystalline plastics and sediment deposition increased friction in amorphous plastics.