Degradation and fragmentation behavior of polypropylene and polystyrene in water

Abstract

The polystyrene (PS) retrieved from the beach exhibited no change in surface texture. In contrast to it, the retrieved polypropylene (PP) had a rumpled surface texture. Highly reactive sulfate radical generated by K2S2O8 was employed as degradation initiator of PP and PS, and their degradation behavior was studied in water. The PS carbonyl index value gradually went up down, and its molecular weight (MW) curve discontinuously shifted to a lower MW with the increase of the degradation time unlike the PP. It was found that the PP microplastic production rate was approximately three time higher than the PS from weight ratio dependence on degradation time. The higher microplastic production rate of PP arose from its crystallizability. The voids were produced by change in specific volume occurring by chemi-crystallization and then provoked the cracks leading to quick fragmentation. The SEM photographs suggested that the PP microplastic size facilely reached nm order by the cracking around lamella.

Verification of the existence of copper-based antifouling paint particles in the sea and their implications for marine microplastic degradation

“…This color change is due to the valence change of copper ions. We have previously reported that seawater drastically improved PP degradation performance during the AOP under pH control 15,25 . Cl − reacts with OH• generated by degradation actions such as solar irradiation and AOP in seawater and yields Cl 2 .…”

“…We, therefore, adjusted the pH to shift the equilibrium toward ClOH in Eq. ( 1) 15 . In addition, Cu + reacts with ClOH and is converted to Cu 2+ according to Eq.…”

“…1452 cm −1 ) [31][32][33] . In the case of the AOP in seawater 15 , a reaction between Cl − and OH• occurs and produces Cl•; then, two Cl• atoms couple to produce Cl 2 , which then reacts with H 2 O and forms ClOH, with the equilibria depending on pH. The pH value of K 2 S 2 O 8 in the seawater solution (normal salinity concentration) decreased from ca.…”

“…8 to ca. 3 during the daily exchange (see Materials and methods section) 15 . This procedure ensures a bias towards the ClOH-rich equilibrium for a period before exchanging with a fresh K 2 S 2 O 8 seawater solution.…”

“…MP mainly comprises polypropylene (PP), polyethylene (PE), and polystyrene (PS) products and is produced by sunshine exposure [12][13][14] . In our previous study 15 , PP degradation was performed in seawater via an advanced oxidation process (AOP) using SO 4 • − 15 , where SO 4 • − functions as a highly e cient initiator for degrading the plastic. The combination of seawater and the SO 4 • − initiator resulted in the excellent acceleration of the degradation process under pH control.…”