Kinetic study of thermal degradation of poly(L-lactide) filled with β-zeolite

The thermal features and decomposition kinetics of poly(L-lactide) (PLA) filled with beta-zeolite have been studied through differential thermal analysis measurements and thermogravimetric analysis. The experimental data were collected under nitrogen atmosphere with the heating rates of 5-30 K min(-1), and the thermal degradation of PLA/beta-zeolite composites is observed to mainly occur in the temperature range of 550-675 K. The incorporation of beta-zeolite has been found to make the onset thermal decomposition temperature of PLA obviously decrease. With the Flynn-Wall-Ozawa method, the activation energy E-a of the composites has been estimated and the beta-zeolite composites have required higher E-a values for thermal decomposition reaction than pure PLA. The pre-exponential factor ln A can be readily obtained so as to establish the thermal conversion curves if the first-order mechanism is taken. Simulated results reflect that the first-order reaction mechanism has led to certain large deviations at the low conversion levels. By scanning the well-known 27 mechanism functions, the D-5 mechanism of Zhuravlev, Lesokhin, Tempelman equation is found to be the most suitable mechanism for the description of the thermal decomposition of PLA and its beta-zeolite counterparts. Along with the Flynn-Wall-Ozawa method, the D-5 mechanism has performed excellently to establish all the conversion curves over the whole range, resulting in more satisfactory simulation results than the first-order reaction mechanism.