Long-Term Hydrothermal Aging Behavior and Life-Time Prediction of Polyamide 6

The long-term hydrothermal aging behavior of polyamide 6 (PA6), with and without stabilizers at 100% relative humidity/90ºC was studied. It was found that the first stage of aging was the Fickian process and corresponded to the physical absorption of water until equilibrium, resulting in slight change of reduced viscosity and chemical structure of the sample of PA6. The second stage of aging was the initiation process of hydrolytic degradation of PA6, which resulted in a decrease of reduced viscosity and increase of end group content. In the final stage of aging, the relative weight gain (W_r) dropped, the reduced viscosity decreased monotonically, and end groups increased continuously, resulting from the hydrolysis of amido links and molecular degradation of PA6. The presence of four types of stabilizers effectively weakened the oxidation reaction and resulting molecular degradation of PA6 during aging. The lifetime of PA6 in a hydrothermal environment was predicted through a method based on the Arrhenius model by considering both temperature and humidity as environmental factors, and, furthermore, was predicted through the time–temperature superposition method.