Thermal oxidative aging behavior and stabilizing mechanism of highly oriented polyamide 6

Highly oriented polyamide 6 (PA6) was successfully fabricated through solid hot stretching technology. The effect of orientation on the structure and thermal oxidative stability of PA6 was investigated. It was found that the molecular orientation was incapable to change the degradation mechanism. Compared with the isotropic sample, a much slow drop of the intrinsic viscosity was observed for the oriented samples, and the degradation rate constant (k (1)) decreased with the increase in draw ratio. The increasing trend of FTIR absorption assigned to different carbonyl groups was obviously slowed down by orientation, and the carbonyl index of the oriented PA6 was much lower than that of the isotropic sample during the whole aging process. The degradation temperature and char yield increased dramatically for the oriented sample of PA6, which displayed relatively high activation energy (E (a)) over the whole conversion degree. The enhancing mechanism of thermal oxidative stability of PA6 was explored, indicating that the relatively high crystallinity and orientation factor and the stable dense crystalline structure of alpha crystal formed by orientation were favorable for the improvement of the oxygen barrier property and slowing down the thermal oxidative degradation of PA6. This investigation clearly showed that molecular orientation can be an efficient way to enhance the thermal oxidative stability of PA6.