Photo-aging of PVC in deionized water,estuary water,and seawater

To better understand the changes of PVC after long-term aging in marine environments, an UVA accelerated aging experiment was con-

ducted.  PVC  samples were  exposed  to  UVA radiation  for  15  days  in deionized water, estuarine water, and seawater. The changes in PVC particle size after  15 days of aging were analyzed by the OMiPA. As shown in Fig.2a, the values of ∣ln∣ for the three environments were 0.108 ± 0.006, 0.123 ± 0.021, and 0.188 ± 0.007, respectively. The results indicate that the particle size of PVC changed differently in the three water environments, with more small particles produced in the aged  PVC  in  water  environments,  especially  in  seawater  where  the particle size reduction was more pronounced. Additionally, the oxygen- containing functional groups formed on the surface of aged MPs cause changes in surface potential and hydrophilicity. As shown in Fig.2b, the zeta  potential  of pristine  PVC  was  − 0.090  ± 0.187  mV,  while  after aging, the zeta potentials of PVC in the three water qualities were  −  3.296 ± 0.987, − 4.361 ± 1.015, and −  7.138 ± 1.627 mV, respectively. This indicates that UV aging results in more negative charges on the surface of MPs, increasing their polarity and tendency towards insta- bility, especially in adsorbing positively charged pollutants. FTIR anal- ysis, as shown in Fig.2c, revealed the appearance of new absorption peaks at  1600,  1715, and  3435 cm− 1  on the surface of aged PVC in different water environments, corresponding to stretching vibrations of -C=C-  groups,  stretching vibrations  of -C=O  groups  (associated with -COOH groups), and stretching vibrations of -OH groups. This suggests the formation of oxygen-related functional groups on the surface of PVC during  aging,  making  the  MPs  more  susceptible  to  fragmentation(Ouyang et al.，2022). The CI value (1715 cm− 1/974 cm− 1) serves as a quantitative indicator of the degree of MPs aging. As shown in Fig.2d, the  CI  values  of aged  PVC  after  15  days  in  the  three  water  bodies increased significantly compared to pristine MPs, further indicating the accumulation of oxygen elements on the surface material during pho- toaging. Through the aforementioned analysis, it was found that PVC undergoes photoaging in different water bodies, with a faster aging rate observed in seawater. These findings shed light on the changes of PVC after  long-term  photoaging  in  marine  environments,  including  alter- ations  in  particle  size,  surface  potential  and  hydrophilicity,  and  the formation  of functional  groups,  which  could  significantly  affect  the stability and adsorption capacity of MPs.