A comparative study of behaviour and kinetics after replacement of air (oxidative) with helium (non-oxidative) with respect to the thermal decomposition of recycled polystyrene

This work investigated the effects of environment gas type on the thermal decomposition of recycled polystyrene and the related reaction behaviours under both oxidative and non-oxidative conditions by using TGA and DSC analysis to examine oxidative processes with heating rates of 5, 7, and 10 °C /min, TGA only to examine non-oxidative processes at 5, 10, 15, 20, and 25 °C/min. Reaction under oxidative gas was found to occur at much higher rates than in non-oxidative conditions, resulting in higher arrangements of activated complexes. To assess the oxidative reaction, the glass temperature, crystallisation temperature, melting temperature and decomposition stages were measured, with the Coast-Redfern method used to analyse the experimental results statistically in Minitab. Linear relationships were thus obtained, which determined that both reactions have a first order relationship. A comparison was also made of the kinetic and thermodynamics properties for both reactions, which suggested that the activation energies for oxidative conditions were lower than for non oxidative conditions, with a similar pattern seen for thermodynamic properties. Glass transition temperatures and crystallisation temperatures were found to be dependent on heating rates.