Thermal Degradation Kinetics of Completely Biodegradable and Biobased PLA/PHB Blends

Abstract

In this article, the influence of blend ratio of plasticized poly(lactic acid)/poly(3-hydroxybutyrate) (PLA/PHB) and chitin nanoparticles (ChNP) nanocomposites on the thermal stability and degradation kinetics has been investigated using thermogravimetric analysis under nitrogen atmosphere at four different heating rates (i.e., 5, 15, 30, and 50°C/min). The derivative thermogravimetric curves have indicated single-step and two-step degradation processes for individual polymers and polymer blends, respectively. It suggests immiscibility or partial miscibility between the polymers. The degradation kinetic parameters were studied over the 30 – 500°C temperature range by using the Kissinger-Akahira-Sunose (KAS) and Vyazovkin isoconversional methods under non-isothermal conditions. The average values of the effective activation energies of the deconvoluted PHB and PLA peaks in the PLA:PHB 70:30 (B73) blends were higher than those of the pure polymers, while in the PLA:PHB 60:40 (B64) blends were lower, which was attributed to the different morphology of the blends. Furthermore, the effective activation energy of the nanocomposites diminished due to the catalyzing effect of the chitin nanoparticles. By means of the invariant kinetic parameters (IKP) method, it was possible to evaluate the preexponential factor and the activation energy of the blends without any assumptions concerning kinetic model. The invariant activation energies calculated were in accordance with the ones estimated by the isoconversional methods. Finally, Avrami-Erofeev function was determined as the most probable kinetic mechanism of the systems studied by applying the Sestak-Berggren equation.