Thermal stability of binary and ternary biodegradable polymer blends assessed by isoconversional kinetic analysis

Abstract

Here we report on kinetic analysis of thermal degradation of polymer blends based on incremental isoconversional method coupled with mathematical deconvolution of thermogravimetric curves based on Fraser–Suzuki peak function. The measured kinetic envelope was decomposed into contributions approximately corresponding to degradation of each constituent of a polymer blend. Kinetic parameters from isoconversional analysis were further used for estimating the effect of blending on thermal stability of the constituents. Compared to routinely used parameters such as degradation onset temperature or DTG-peak temperature, the deconvolution analysis allows to determine stability of all components in a mixture regardless of their relative content. Here we also show that deconvolution analysis can be carried out directly on integral α(T) curves, thus bypassing the work with differential data dα/dt. Isoconversional analysis of deconvoluted α(T) curves allows to calculate various parameters for assessing the potentially accelerating or inhibiting effect on thermal degradation, for example, by means of decomposition half-time t_0.5. The results can be made more robust by utilizing relative criteria for stability such as t_0.5(blend)/t_0.5(neat polymer). Using this approach, detrimental effect of PHBV and PBAT on thermal stability of PLA above 300 °C was confirmed. On the other hand, stability of PHBV in both binary and ternary mixtures was improved compared to neat polymer.