Decomposition behaviour of Kevlar 49 fibres:: Part I.: At T ≈ Td

The structural changes which accompany decomposition of Kevlar 49 fibres at T= 500 degrees C and 550 degrees C, respectively, have been elucidated. At both these temperatures, cumulative thermal exposures of specific durations, t(cum)(T), are required to result in decomposition. The conspicuous features which characterize isothermal decomposition of the fibres are: (i) progressive reduction and an eventual total loss in fibre crystallinity, (ii) progressive loss in weight, (iii) introduction of surface damages, (iv) introduction of hollowness, and (v) deterioration in tensile properties.