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

Abstract

The long-term hydrothermal aging behavior of polyamide 6 (PA6), with and without stabilizers at 100% relative humidity/90 C 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.

Aging and Degradation of Printed Materials

“…Hydrolyzation continued in time and affected further molecular degradation (Gao, Ye, & Li, 2015). In short time (<4 days), almost no chemical reactions are observed.…”

Comparison in composite performance after thermooxidative aging of injection molded polyamide 6 with glass fiber, talc, and a sustainable biocarbon filler

“…The first drawback is their hygroscopic nature, which is caused by their polar surface that contains many amide functional groups. Moisture absorption is a potentially detrimental aspect affecting the application of PAs as it can alter the mechanical and thermal properties . The second drawback associated with PAs is its degradability during use under various environmental conditions, which limits its overall performance.…”

“…The weakness of the bond in the methylene group allows for radicals to overtake the hydrogen atom resulting in the formation of peroxide radicals, which may lead to chain scissions. The hydrolysis reaction in PA 6 increases the end‐group content increasing the free volume between chains and consequently increasing the degradation rate of the materials by lowering the molecular weight . Karstens and Rossbach proposed a thermooxidative mechanism of PA 6, a simplified schematic mechanism is represented in Scheme …”

“…Typically, durability studies are conducted over a set time period with samples finishing at scheduled intervals in order to observe the aging behavior and predict the material's lifetime. The degradative nature of PA 6 has been deeply investigated in order to better understand the aging behavior in hydrothermal, thermooxidative, and photooxidation environments . In the end, the outcomes are the same: a loss of thermomechanical properties and increase in end‐group concentrations that results in a decrease in the degree of crystallinity and alterations to the exposed surface morphology (micro‐cracks, discolouration) .…”

“…The degradative nature of PA 6 has been deeply investigated in order to better understand the aging behavior in hydrothermal, thermooxidative, and photooxidation environments . In the end, the outcomes are the same: a loss of thermomechanical properties and increase in end‐group concentrations that results in a decrease in the degree of crystallinity and alterations to the exposed surface morphology (micro‐cracks, discolouration) . For a few decades, PA 6‐based composites, for example, glass fiber (GF) or clay‐filled composites have been the topic of many studies considering their high commercial interest, specifically for automotive applications .…”