Jiro Shimizu

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.

Changes of tensile modulus and contractive stress of polyacrylonitrile fibres during heat treatment in air

Abstract The changes in the tensile modulus and contractive stress of polyacrylonitrile homopolymer fibres during heat treatment in air were investigated. On the basis of the consideration that with polyacrylonitrile homopolymer fibres the formation of initiation centres of the cyclisation is rate-determined by the diffusion of oxygen into the fibres, an equation was derived by modifying an experimental equation obtained previously on the modulus change of acrylonitrile copolymer fibres. The modulus change of homopolymer fibres was well approximated by the modified equation, and was characterised by a dealy time and a rate constant. An apparent activation energy of 84 kJ/mol was calculated from the temperature dependence of the delay time. The difference in value of the rate constant at a fixed temperature and of the apparent activation energy of the rate constant was almost the same for homopolymer and copolymer fibres.