Mechanism of quiescent nanoplastic formation from semicrystalline polymers

Abstract

Polymers are known to spontaneously produce microplastics (sizes 1 μm – 3 mm) and nanoplastics (10 nm – 1 μm). Still, the mechanisms by which environmentally-triggered Å-level random bond breaking events lead to the formation of these relatively large fragments are unclear. Significantly, $$\approx$$ 70% of commercial polymers are semicrystalline, with a morphology comprised of alternating crystalline and amorphous layers, each tens of nanometers thick. It is well-accepted that chain scission events accumulate in the amorphous phase. We show that this leads to mechanical failure and the concurrent release of particulate nanoplastics comprised of polydisperse stacks of lamellae even under quiescent conditions. Noncrystalline analogs, which do not have a well-defined microstructure, do not form nanoplastics. While the amorphous phase of the semicrystalline nanoplastics continues to degrade, crystal fragments do not, and hence, they temporally persist in the environment. These results stress the critical role of polymer microstructure and fracture mechanics on particulate nanoplastic creation. Polymers are known to spontaneously produce micro- and nanoplastics but the mechanisms by which environmentally-triggered Å-level random bond breaking events lead to the formation of these relatively large fragments are unclear. Here, the authors show that chain scission accumulates in the amorphous phase of a semicrystalline morphology which leads to mechanical failure and the concurrent release of nanoplastics even under quiescent conditions.