The environmental challenge of microplastics is linked with the crisis of plastic pollution at large, and yet is emerging as a stand-alone area of research. This is because of the unique physical properties acquired by plastic objects at the micron and nanoscale in water environments. One major issue surrounding the fate of microplastics is their tendency to either float or disperse in the solvent bulk. We simulate the effect of sunlight exposure on polyethylene (PE) particles using a UV lamp in a temperature-controlled chamber. We find an increase in the dispersibility of particles, indicated by a drastic change in concentration from the water surface to the water bulk. This phenomenon is associated with a hydrophobic-hydrophilic transition in surface chemistry driven by photo-oxidation. We assess the change in hydrophobicity by contact angle measurements and we track the changes in surface functional groups using FTIR. Our findings point to the role of sunlight exposure in determining the fate of microplastics initially floating in water environments. Increases in dispersibility induced by photo-oxidation may help explain the gap between estimated plastic introduced to the environment and assessment of plastic waste found on or near the surface of oceans, rivers and lakes.

Effect of photo-oxidation on the wettability of microplastics

ACS Spring 2022

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