Simulation of the thermal degradation kinetics of biobased/biodegradable and non-biodegradable polymers using the random chain-scission model. Capabilities and limitations

In literature, several models have been applied in the simulation of the thermal degradation of polymers. Often, the models used were taken from solid-state physics and found to simulate very well the experimental data, though without any real physical meaning. In this investigation, a systematic approach is carried out regarding the simulation of the thermal decomposition of polymers using the random chain-scission model. Specifically, the model developed by Sánchez-Jiménez, P é rez-Maqueda and Criado based on the original idea of Simha and Wall is analyzed and applied to several polymers including polyolefins, styrenics, aromatic or aliphatic polyesters both biobased/biodegradable and non-biodegradable. The aim is to compare the thermal stability of several polymers and provide kinetic parameters having physical meaning based on a meaningful kinetic model. In order to estimate the kinetic parameters independently and consistently, the following procedure is proposed: initially, one has to perform experiments at several heating rates in order to estimate the activation energy of the reaction using a differential or an advanced integral isoconversional approach. Following, a system of differential equations is set and solved based on the random scission model, using only one adjustable parameter, i.e. the pre-exponential factor. It was found that using the same set of parameters, thermogravimetric data for all these polymers at several different heating rates can be simulated very well in the range of relative degree of degradation from 30% to 90%. This observation verified the hypothesis that at this region of degradation the dominant mechanism for several polymers is that of random scission. The best set of kinetic parameters is proposed for several polymers with the activation energy mainly ranging in between 160 and 210 kJ/mol.