Stress-accelerated photothermal oxidative aging behavior of polyamide 6

The long-term stress-accelerated photothermal oxidative aging behavior of polyamide 6 (PA6) was studied in terms of the creep behavior, mechanical properties, chemical structure, crystallization, and orientation behavior. It was found that the creep deformation of PA6 under stress with ultraviolet (UV) irradiation was lower than that of the sample aging without UV irradiation. Due to stress-induced orientation, the tensile strength of PA6 aging under stress was higher than that of the sample aging without stress. For samples aging with stress, the variation in the content of gel tended to slow down, and the reduced viscosity was lower than that of the sample aging without stress. The oxidation of PA6 can be inhibited by orientation, leading to a relatively low content of carboxylic group; however, stress would accelerate the degradation of PA6, resulting in the strengthening of UV absorption. A decrease in crystallinity of PA6 after aging was observed, which was generated by chain scission in crystalline region and the cross-linking of PA6. Stress would accelerate the degradation of PA6, resulting in further decrease in crystallinity. The orientation factor increased obviously in the case of PA6 aged with stress indicating that a clear orientation of molecules induced by stress formed.