Comparison of surficial modification of micro-sized polyethylene in between by UV/O3 and UVO submerged system

This study examined the effects of ozonation and UV applied in series (O3+UV) or simultaneously (UVO) under four different ozone dosages from 4 to 7 mg/min to understand the surface alterations on polyethylene microplastics in aquatic environments via the photochemical oxidation process. The plastic samples were analyzed by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angle measurements. FTIR spectroscopy showed that the levels of carbonyl (ketone and esters) and vinyl groups increased gradually with increasing ozone dose injected; the highest was observed at 6 mg/min of ozone. On the other hand, the levels at 7 mg/min of ozone were slightly lower than those at 4 to 6 mg/min. This could be related to the deeper penetration into the crystalline bulk polymeric chain. The contact angle changed from 125.90˚ to the lowest value of 120.04˚ and 123.8˚ for O3+UV and UVO, respectively. Furthermore, XPS showed that C-O was only presented in the 7 mg/min sample, whereas C-O, OH, C=O, and C-C=O remained for 4 to 6 mg/min. Overall, O3+UV can oxidize the surface of the polyethylene microplastic particles more effectively than those of UVO, irrespective of the ozone dosages.