Mechanical oxidation and microparticle production: a quantitative study of mechanical plastic weathering using novel reactor design

Abstract

Mechanical degradation of plastic waste is a major source of microplastics and potentially a large contributor to the oxidation of plastic waste in soil and water environments. Mechanical oxidation of plastic occurs when mechanical force induces homolysis of covalent bonds on the carbon backbone and radical formation then leads to radical induced oxidation. Despite the abundance of mechanical degradation of plastic and its potential for oxidation in the natural environment, a quantitative understanding of this is the least pursued compared to other plastic oxidation mechanisms such as UV oxidation. This thesis attempts to generate a quantitative correlation between input of mechanical work and both oxidation of plastic and nano/microplastic production. In this device a low-density polyethylene sample sealed at the bottom of a glass cylinder is covered with sediment; the device is then fixed onto a shaker table, driving a circular motion of sediment. With a high-speed camera, sediment motion is captured and the calculated path length of the sediment in tandem with the coefficient of kinetic fiction between the sediment and the plastic substrate is used to calculate abrasive energy input. By employing X-ray photoelectron spectroscopy (XPS), quantification of the degree of oxidation due to a calculated abrasive energy input is made possible. In addition to the investigation of oxidation, a combination of total organic carbon measurements and nanoparticle tracking analysis is used to quantify the rate of nano and microplastic production and chemical leachate generation in a five-month weathering experiment. The novel findings from these experiments present an overlooked pathway, and the novel device generated will enable a high throughput testing platform for new materials and enable exploration that enhances our understanding of the effect of complex environmental conditions on plastic degradation.