Azodicarbonamide has a decomposition temperature in air of about 195 to 200 C. and about 190 C. in dioctyl phthalate. For many applications it is desirable to have azodicarbonamide decompose at a much lower temperature. Decomposition at a lower temperature would permit a reduction in the heat degradation of the plastic composition in which the chemical blowing agent is incorporated. Further lower decomposition temperatures would permit shorter processing cycles and allow enhanced decomposition rates thereby permitting lower processing temperatures or shorter residence times or a combination thereof. Also, it is commercially desirable to reduce the initial and range of decomposition temperatures of azodicarbonamide to or lower than the initial decomposition temperature of oxybisbenzenesulfonyl hydrazine, since azodicarbonamide is a more economical source of gas.
It is now known that some heavy metal compounds have an activating effect on chemical blowing agents, that is, they tend to lower the decomposition temperature at which the blowing agent evolves gas.