The surface degradation and release of microplastics from plastic films studied by UV radiation and mechanical abrasion

Abstract

During service or on discarding in the environment, solar ultraviolet radiation (UVR) and mechanical abrasion (MA) often act on plastic surface in combination, which cause the surface of plastics deterioration and micro- and nano- plastics release. Here, we examined how the set conditions (UVR, MA and UVR+MA (i.e., UVR combined with MA)) and polymer composition affected plastic degradation and microplastics (MPs) release. The surface degradation process and release of MPs of two types of plastic films (polyethylene (PE) and thermoplastic polyurethane (TPU)) under the action of UVR, MA and UVR+MA were analyzed and compared. The main results are as follow: First, the surface change of PE and TPU films by UVR+MA was observed more prominently than by UVR and MA. UVR+MA resulted in the accelerated surface degradation compared to UVR and MA. A large number of MPs were released from both PE and TPU films and significant differences were observed between UVR, MA and UVR+MA conditions. The UVR+MA treatment led to the generation of the largest amount of MPs with a smallest particle size, followed by MA and UVR. Second, plastics with different compositions exhibited different levels of resistance to UVR and MA. PE films released more MPs than TPU under the three set conditions. Finally, optical microscopy provided a direct and non-invasive method to assess the plastics degradation and the observed change in relative transmittance as a function of exposure time could be fitted linearly in some circumstances, which can be used to quantify the release of MPs. This study provided a basis for better understanding the degradation mechanisms of plastics surface and the relationship with MPs release during use and into the environment.

Keywords: Mechanical abrasion; Microplastics; Polyethylene; Thermoplastic polyurethane; Ultraviolet radiation.