Thermal degradation kinetics of recycled biodegradable and non-biodegradable polymer blends either neat or in the presence of nanoparticles using the random chain-scission model

One of the major issues in polymer recycling nowadays is related to the impact of biodegradable polymers and/or nanoparticles’ presence on the thermal degradation kinetics of non-biodegradable polymers used mainly in packaging. In this direction, the thermal degradation kinetics of PET/PLA blends was investigated using non-isothermal thermogravimetric data and a simulation model based on the random-scission mechanism. Specifically, we extended the model originally developed by Sánchez-Jiménez, Pérez-Maqueda and Criado based on the original idea of Simha and Wall to simulate the thermal degradation of polymer blends in pyrolytic conditions. A system of differential equations was set and solved based only on the kinetic parameters obtained from the neat polymers and without any additional adjustable parameter. It was found that this model describes fairly well the thermal degradation of several PET/PLA blends in a large conversion range. Deviations were observed at low conversions where degradation of PLA is promoted by ester interchange reactions with PET and at intermediate conversions where possible synergistic effects may take place. Furthermore, the addition of nanoparticles seem to retard the diffusion of the volatile degradation products out of the polymer, so that the onset of mass loss is at higher temperatures for the blend nanocomposites compared to neat blend. This was taken into account in the model by including an additional diffusion-related term to the kinetic constant of the degradation.