Kinetics of azodicarbonamide decomposition in the presence of an initiator for obtaining solid foams

Abstract

The kinetics of decomposition of azodicarbonamide, an exothermic chemical blowing agent, which is used for obtaining solid foams, was investigated. It was shown that the modified coal tar pitch can be used as a polymer matrix to produce foamed pitch composite materials. The decomposition temperature of azodicarbonamide is approximately 200– 210 °C. Such a decomposition temperature is too high to foam a modified coal tar pitch due to a change in its rheological properties. The azodicarbonamide decomposition temperature can be reduced by adding initiators. Zn stearate, Ca stearate, their mixture and polyvinylchloride were used as initiators. The influence of the initiators on the kinetics of azodicarbonamide-initiator decomposition at temperatures of 130–150 °C was investigated. The induction period, the time of reaching the maximum decomposition degree and the decomposition rate of the azodicarbonamide-initiator have been determined as a function of the temperature and the initiator amount. A maximum rate of mixture decomposition was observed in the case of Zn stearate; the addition of binary initiator Zn stearate/Ca stearate decelerates the process. The use of polyvinylchloride as an initiator is characterized by very low rates. The comparison of the decomposition degree for various initiators in isothermal conditions revealed that Zn stearate is the most active initiator. It has been established that there is a line of the optimal Zn stearate amount to reach the maximum decomposition degree at temperatures of 130–150 °C for the complex blowing agent azodicarbonamide-Zn stearate. The gas number of the complex blowing agent, azodicarbonamide-Zn stearate with an optimal composition has been determined at 140 and 150 °C