Stress drives polymer phase separation and microplastic release

Abstract Microplastic release from semicrystalline plastics threaten the environment and human health. We investigated polypropylene and polyethylene plastics, which together account for 54% of the global market. Mimicking common levels of residual stress found in plastics via cantilever beam experiments, we demonstrated that compressive stress drives nano and microscale segregation of amorphous polymer droplets onto the plastic’s surface. Simulations reveal this stress-driven volumetric flow is consistent with that of a Bingham plastic material, with a temperature-dependent threshold yield stress. Flow is thermally activated and stress dependent, with a reduced energy barrier at higher compressive stresses. Transfer of surface segregated amorphous droplets into the surroundings generates microplastics. Studies with water-containing plastic bottles showed that the highly compressed neck and mouth regions were predominantly responsible for the release of microplastics.