Thermal degradation and ageing of segmented polyamides

The degradation behaviour and kinetics of degradation of segmented polyamides with varying block lengths have been studied by non-isothermal thermogravimetry in air and nitrogen and by infrared spectroscopy. In air, all the polymers show two stage decomposition, whereas in nitrogen, the decomposition occurs in a single stage. In both atmospheres the degradation, however, follows first order kinetics. The infrared spectroscopic analysis of the degraded products reveals that the decomposition occurs in the polyether linkage followed by polyamide hard block. The mechanism of degradation is of course a complex one. In the case of thermooxidative degradation, a decrease in hard block molecular weight has a great influence on the activation energy values. The effect of ageing on the mechanical properties of these polymers has also been studied. On ageing, it is observed that both tensile strength and elongation at break drop sharply in the initial stage. After this initial drop, both properties show a marginal change with time and temperature of ageing, Retention of physical properties is better with high hard block molecular weight polymers. (C) 2000 Elsevier Science Ltd. All rights reserved.