The mechanism of washing parameters and fabric movement on microplastic fiber release in top-loading washing machines

Microplastic fibers released from synthetic fabrics account for 35% of the total microplastics in the World’s oceans. The current study mainly focuses on the effects of a single washing parameter and a specific washing machine model on the release of microplastic fibers, and the results of the study on the release of microplastic fibers from different washing machine models are not generalizable. In this paper, a dimensionless washing machine model was constructed to investigate the release mechanism of microplastic fibers based on the magnitude analysis. The results show that the average length of microplastic fibers shedding is 300–400 μm, and the highest proportion is 24–35%. The interaction of surface friction coefficient and water volume ratio showed a positive correlation on the mass of microplastic fiber release, with more fibers with weak adhesion falling off due to increased friction and high impact of water flow. When the filling ratio is low, the horizontal fabric motion height is low, the horizontal distance from fabric centroid to drum center and the top-view distance from fabric centroid to drum center are large. Due to the constant change in the state of motion of the fabric, the mechanical forces on the fabric are altered, which ultimately affects the release of microplastic fibers. The investigation of the release mechanism of microplastic fibers can help to develop effective strategies to reduce the shedding of microplastic fibers, thus mitigating their potential impact on the environment.