Origins of Secondary Nanoplastics from Semicrystalline Polymers*

It is now well-established that plastics degrade into micro and nanoplastics. These environmental pollutants have been found on the ocean surface and in the deep ocean. This research focuses in particular on semicrystalline polymers, which constitute nearly 75% of all plastics used currently. When these polymers environmentally degrade in the aqueous milieu (i.e., in oceans) experiments consistently show that the chain segments in the amorphous phase break first, while the crystalline population actually grows. This work proposes that semicrystalline polymers form nanoplastics (100 nm and smaller) due to the preferential fragmentation of amorphous phase tie chains which originally provided the connectivity between adjacent crystalline lamellae. By analogy to the phenomenon of environmental stress cracking, breaking of these connectors leads to local material failure and the formation of nanoplastics. The proposed work will combine experimental and theoretical tools to enunciate the proposed degradation mechanisms of semicrystalline polymers of varying chemistries when exposed to mechanical stresses, water, O₂and/or UV light.