Thermal degradation behaviors of polyethylene and polypropylene. Part I: Pyrolysis kinetics and mechanisms

Study of the decomposition kinetics is an important tool for the development of polymer recycling in industrial scale. In this work, the activation energy and the reaction model of the pyrolysis of high density polyethylene (HDPE), low density polyethylene (LDPE) and polypropylene (PP) have been estimated from non-isothermal kinetic results. Firstly, the activation energy values obtained by Friedman, Kissinger–Akahira–Sunose and Flynn–Wall–Ozawa isoconversional methods, are 238–247 kJ/mol for HDPE, 215–221 kJ/mol for LDPE and 179–188 kJ/mol for PP. Secondly, the appropriate conversion model of the process was determined by Coats–Redfern and Criado methods. The pyrolysis reaction models of HDPE and LDPE are accounted for by “Contracting Sphere” model, whereas that of PP by “Contracting Cylinder” model.