Characterization of the thermal oxidative degradation kinetics of thermoplastics

Abstract

Thermal oxidative degradation kinetics of polyethylene, poly(ethylene terephthalate), and polystyrene were investigated by thermogravimetric analysis. The samples included low-density polyethylene, medium-density polyethylene, high-density polyethylene, a starch-based biodegradable thermoplastic polyester, polyethylene natural gas pipe, a poly(ethylene terephthalate) water bottle, and a polystyrene drinking cup. The kinetics were conducted under dynamic conditions at heating rates of 10, 20, 30, and 40 degrees C min(-1) between 25 and 650 degrees C in air. The Kissinger, Flynn-Wall-Ozawa, and Coats-Redfern methods were used for investigation of degradation of these polymers. Thermal oxidative degradation of the polymers was compared. Low-density polyethylene, medium-density polyethylene, high-density polyethylene, and polyethylene pipe obeyed a diffusion mechanism for oxidative thermal degradation. The starch-based biodegradable thermoplastic polyester, polystyrene cup, and poly(ethylene terephthalate) bottle followed random nucleation, diffusion, and phase boundary-controlled reaction mechanisms, respectively.