Thermolysis parameter and kinetic research in copolyamide 66 containing 2-carboxyethyl phenyl phosphinic acid

Abstract

Polyamide 66 (PA66) containing phosphorus with flame-retardant property (FR-PA66) was synthesized with adipic acid hexamethylene salt and 2-carboxyethyl phenyl phosphinic acid as raw materials. The thermal degradation kinetics of FR-PA66 and PA66 were measured using a thermogravimetric analyzer, and the data obtained were analyzed with Flynn–Wall–Ozawa and Coast–Redfern methods. The results show that the activation energy ( Ea) of PA66 fabricated under different conditions will be different, while the mechanism functions of thermal decomposition remain the same. Comparing the limit Ea value of PA66 with FR-PA66 at different stages of thermolysis, FR-PA66 keeps the initial thermolysis Ea almost unchanged, reduces the middle thermolysis Ea to 139.1 kJ mol−1, and increases the last thermolysis Ea to 454 kJ mol−1, that is 223 kJ mol−1 higher than that of PA66 with 231 kJ mol−1. This result may be explained by the first cleavage of P–C bond and the formation of the carbonized protective layer. In addition, the most probable kinetic mechanism functions ( F( α)) of thermolysis of FR-PA66 in three different stages were when the rate of decomposition ( α) is lower than 0.4, F( α) = −ln(1 − α); when α is between 0.4 and 0.65, F( α) = [−ln(1 − α)]; and when α is beyond 0.65, F( α) = [−ln(1 − α)].