Simulated degradation of low-density polyethylene and polypropylene due to ultraviolet radiation and water velocity in the aquatic environment

Low-density polyethylene (LDPE) and polypropylene (PP) are the two main polymers with extensive applications. It might lead to plastic pollution and degradation in the aquatic environment. Former laboratory simulation studies of plastic degradation have been presented. However, most of the studies were only applied a single degradation agent without specific environmental conditions, which indicated a research gap. This research aimed to investigate LDPE and PP degradation under the influence of UV radiation and water velocity with specific environmental conditions. Five reactors of simulated aquatic environments were adjusted to desire calculated UV B dose of 158.98-438.91 W.S/cm2 and water velocity variations of the Surabaya River, one of Indonesia's urban rivers that has been polluted by microplastics. The water velocity was set in high (0.3-0.6 m/s) and low ones (0.1-0.3 m/s) to represent the fluctuated river discharge at rain and dry seasons. Total simulation time of 480 h (8 h/day for 60 days simulation) has initiated LDPE and PP degradation. LDPE experienced more weight loss (3.07%) under the combined exposure of UV and high water velocity, than PP (2.37%) under high water velocity. Synergetic effects of photodegradation, physical-mechanical, and hydrolysis degradation mechanisms could affect more severe crack tip formation of LDPE and PP rather than in single agent simulation. Major surface morphology deterioration of LDPE and PP, changes in transmittance intensities, carbonyl index in this study have revealed the importance of combined exposure of UV radiation and water velocity to plastic degradation in the aquatic environment.