Reflecting the aging behavior of polystyrene nanoplastics in the seawater through Young's modulus by atomic force...

Nanoplastics (NPs), with different physicochemical properties at various aging stages, have severe impacts on human health and the ecological environment. Restricted by the traditional technique, such as time-consuming, sample concentration, and the destructive of the sample, it is hard to precisely determine their aging behavior. Interestingly, we found that the nano-mechanical properties of the NPs were largely influenced by the oxidation and the cross-linking, however, their deep relationship remains lacking. Herein, this study investigates the aging behaviors of commodity plastics, microplastics and NPs in seawater via testing the changes of the physicochemical properties by combination of atomic force microscope. The results indicated that the changing behavior of Young's modulus (YM) for NPs exhibited distinctly with a rapid to a slow growth trend, an initial slow increase followed by an acceleration for microplastics, while there was almost no significant change for commodity plastics. And it was further validated by the changing trend of hydroxyl index and degree of cross-linking of the aged plastics with different sizes, which undoubtedly showed a consistent trend with the YM changes. These findings provide a new perspective for measuring the degree of cross-linking of aged NPs.