Changes of tensile modulus and contractive stress of acrylic fibres during thermal stabilisation for carbon fibre production

Abstract

The changes in the tensile modulus and contractive stress of acrylonitrile copolymer fibres during heat treatment in air investigated. The variation of the tensile modulus with the heat treatment time during heat treatment at constant temperatures could be approximated by the experimental equation ( E t – E 0/( E s – E 0 = 1 – exp (− kt), where E t is the tensile modulus at a heat treatment time t, E 0 and E s are the initial and final moduli, respectively, and k is a rate constant. The temperature dependence of the rate constant followed an equation of the Arrhenius form, and an apparent activation energy of 98·3 kJ/mol was calculated. The contractive stress plotted against log kt varied in a systematic fashion with temperature, and the contractive stress curves showed a pronounced characteristic at t = 1/ k. The effect of temperature on the contractive stress was discussed in relation to the relaxation of molecular orientation at high temperatures.