Thermal degradation kinetics of long carbon chain bio-based semi-aromatic polyamide PA9T/9C and the influence of cycloaliphatic ring on it

Abstract

In this paper, the process and mechanism of thermal degradation of the long carbon chain bio-based semi-aromatic polyamide PA9T/9C in nitrogen (N₂) and air atmosphere and the thermal degradation kinetics of PA9T/9C at different heating rates (\({\Phi}_{\text{h}}\)) in N₂ atmosphere were studied by thermogravimetric analysis. The results show that the thermal degradation process of PA9T/9C in N₂ is a one-step reaction, which accords with the thermal degradation mechanism of conventional polycondensation products, and the thermal degradation temperature increases with the increase of \({\Phi}_{\text{h}}\). The thermal degradation process of polyamide can be changed under different atmospheric conditions. The thermal degradation process of PA9T/9C in air atmosphere is similar to the thermal degradation process in N₂ atmosphere, except that the degradation in an air atmosphere is a two-step reaction with additional oxidative crosslinking. At the same time, the cycloaliphatic ring structure can improve the heat tolerance of the polymer. The Kissinger, Flynn–Wall–Ozawa and Coats-Redfern methods were used to calculate the thermal degradation activation energy of PA9T/9C, and the apparent thermal degradation activation energy shows an increasing trend with rising alicyclic-ring content within the estimated experimental uncertainty. Finally, the Coats-Redfern method demonstrates that for the thermal degradation behavior of long-carbon-chain bio-based semi-aromatic polyamide PA9T/9C, the R₂ phase boundary reaction model achieves the best mathematical fitting performance among the investigated models.