Thermal degradation and ageing of segmented polyamides

The degradation behaviour and kinetics of degradation of segmented polyamid es with varying block lengths have been studied by non-isothermal thermogra vimetry in air and nitrogen and by infrared spectroscopy. In air, all the p olymers show two stage decomposition, whereas in nitrogen, the decompositio n occurs in a single stage. In both atmospheres the degradation, however, f ollows first order kinetics. The infrared spectroscopic analysis of the deg raded products reveals that the decomposition occurs in the polyether linka ge followed by polyamide hard block. The mechanism of degradation is of cou rse a complex one. In the case of thermooxidative degradation, a decrease i n hard block molecular weight has a great influence on the activation energ y values. The effect of ageing on the mechanical properties of these polyme rs has also been studied. On ageing, it is observed that both tensile stren gth and elongation at break drop sharply in the initial stage. After this i nitial drop, both properties show a marginal change with time and temperatu re of ageing, Retention of physical properties is better with high hard blo ck molecular weight polymers. (C) 2000 Elsevier Science Ltd. All rights res erved.