Long term ageing of polyamide 6 and polyamide 6 reinforced with 30% of glass fibers: temperature effect

Because the prediction of the durability of polyamide materials is a very important issue for designers and users, the effect of environment conditions on their mechanical properties is an active field of research. For this reason this experimental investigation was conducted in order to study the effect of temperature on long term ageing of polyamide 6 (PA6) and polyamide 6 reinforced with 30 wt% of glass fibers (PA6GF30). Ageing was realized in distilled water (pH ≈ 6; 100% RH) at 30 °C, 50 °C, 70 °C and 90 °C for up to 80 days. Results highlighted the impact of ageing temperature on both conditioned materials. Thus, several surface damages such as crazing and yellowness were recorded especially at high temperatures indicating the materials degradation. These structure changes were induced by the combined effects of water and temperature. As the water diffuses within the polymer, the glass transition temperature T_g drops progressively with ageing temperature to reach the lowest value for samples aged at 90 °C for both tested materials. This tendency was also observed for Young’s modulus, tensile strength and the elongation at break. Thus, a significant loss in stiffness and strength of both materials was recorded as a function of conditioning temperature. This loss of mechanical properties is mainly caused by hydrolysis process and/or interfacial debonding. The appearance of this irreversible phenomenon rises with ageing temperature. Moreover, contrarily to PA6GF30, the temperature effect was also pointed out on SEM observations of PA6 samples. Thus, the hygrothermal ageing induces a change in the mode of fracture from ductile to moderate brittle one according to the ageing temperature. Accordingly, it seems that the ageing temperature has a great effect on the severity of damage of tested materials after long term immersion.