Effect of nanoclay on the thermal degradation kinetics of recycled biodegradable/non-biodegradable polymer blends using the random chain-scission model

In this research, nanocomposite blends of recycled biodegradable PLA with non-biodegradable PET were prepared at several ratios with commercial organomodified montmorillonite added at several amounts. Thermogravimetric measurements were carried out to record their thermal degradation kinetics. The presence of the nanoclay at relatively low amount (up to 5 %) was found to enhance the thermal stability of the polymer blend. A theoretical kinetic model was developed, based on the random chain-scission mechanism taking into account also autocatalytic effects due to the formation of carboxylic groups during the degradation of the polyesters. The innovative part of this research was that for the first time the role of the clay as a mass-transport barrier to the volatile products generated during decomposition was considered through a diffusion-based model. Diffusional barriers set to the volatile products were taken into consideration through modeling equations based on sound principles, such as the diffusion coefficient and the free volume theory. A system of differential equations was set and solved for the polymer blends based on the kinetic parameters obtained from the neat polymers and only three adjustable parameter of clear physical meaning. Simulation results were in good agreement to the experimental data at different blend compositions and clay loadings. Predictive capabilities of the model under isothermal conditions were explored.