Shrinkage behaviour of polyacrylonitrile during thermal treatment

A detailed study of the shrinkage behaviour of homopolymers and copolymers of acrylonitrile has been made. Apart from chemical shrinkage, a physical shrinkage, which is independent of temperature and oxidizing gas was observed. This shrinkage occurs even at temperatures below 180°C. The effect of temperature and oxidizing gas on the chemical shrinkage is reported. The shrinkage is faster in the presence of O2 than in presence of air and N2, This chemical shrinkage can be checked with smaller loads in case of oxygen as compared to the loads required in case of air and nitrogen. The effect of load on shrinkage in presence of oxygen is reported. By use of oxygen, a maximum elongation of 65% can be achieved as compared to 40% maximum elongation reported in the literature. An empirical method has been described which can be used for the estimation of optimum peroxidation time at any temperature.