Fragmentation of plastics into microplastics

Microplastics (MPs) are < 5 mm sized plastic particles. The overwhelming majority of studies are focused on microplastic identification in various water bodies, mostly the ocean. There are relatively few studies looking into fragmentation mechanisms of larger plastic products to much smaller microplastics. Here, common plastic products like food packaging and beverage containers are mechanically fragmented down to small particles similar in size to microplastics. It is found that plastics fragment in 3 stages: (1) initial plastic deformation or slight fragmentation where the change in the plastic shape and size is dependent on the polymer yield strain, (2) exponential fragmentation with a large fragment size distribution and a fragmentation time that depends on the polymer’s ultimate stress and toughness, and (3) an attainment of an equilibrium particle size with a low fragment size distribution. The time to reach the equilibrium particle size is also dependent on the polymer’s ultimate stress and toughness. While this study looked only at mechanical fragmentation, it is hypothesized that the different environments of oceans, beaches, and rivers will contribute different environmental factors to fragmentation.