Plastic degradation in Hong Kong natural open-air and coastal marine environments

Abstract

Plastics have revolutionised the modern society with their versatile properties and cheap manufacturing costs. They are widely produced as disposable items, which end up in natural environments upon inappropriate disposal as one of the major pollutants. The polluting effects of plastics constitute of macroplastic pollution, which results from the high environmental persistence of plastic debris, as well as microplastic pollution, which mainly results from macroplastic fragmentation. Understanding degradation behaviours of different plastic polymers in common disposal environments is the key to evaluating their polluting effects. In this thesis, I conducted in situ experiments to assess the 40-day degradability of conventional plastics (incl. PET, HDPE, PVC, LDPE, PP, PS and EPS) in marine environments, and the six-month degradability of bioplastics (incl. PLA, PVA/Starch blends, and additive-modified LDPE) in open-air and marine environments. Chapter 2 reveals the early degradation signs of conventional plastics and their engagement in synergistic oxidative processes and oxidation product removal processes. Polystyrenes and polymers with heteroatoms show larger degradability than pure polyolefins. Also, PS appears to be a better polymer choice with lower macro- and micro-plastic risks, which suits for short-term applications. Chapter 3 reveals the suboptimal degradability of bioplastics in natural environments. Biodegradable plastics that are biobased appear to have a larger degradability than the fossil-based ones. By outlining polymer susceptibility to various degradation processes, this thesis allows estimation of the polymers’ degradability in different deposition locations with diverse weathering forces, as well as their associated environmental impacts. In this thesis, I evaluated the role and degradation efficiency of bioplastic components, which adds information for the development of better bioplastic formulations. This thesis highlights the needs for further investigation in the degradation behaviours of different plastic polymers, and to identify sustainable polymer choices for long-term applications.