Thermal decomposition of sponge blowing agents by pressure thermal analysis

Abstract

The thermal decomposition of six sponge blowing agents was investigated with a pressure differential scanning calorimeter and a pressure thermobalance to evaluate their thermal hazard. Decomposition heats and kinetic constants in an atmosphere of inert gas or air were obtained using thermal analysis methods. A positive gas pressure was employed in the elucidation of the decomposition behavior of these substances because some of them evaporate during linear heating at atmospheric pressure. The decomposition heats and exothermic onset temperatures of most of the sponge blowing agents tended to increase with a pressure increase in nitrogen or air. The evolution heats, ranging from about 150 to 500 cal/g (in air at 1 atmosphere), were increased to a range of about 250 to 1000 cal/g by a pressurized air atmosphere of 5.3 MPa. Under pressure thermogravimetry conditions the rate of decomposition increased with increasing gas pressure, suggesting a distinction in the decomposition mechanism. The influence of heating rate on the decomposition heat and weight change is also discussed, and kinetic constants such as activation energies at 1 atm are compared with those obtained in pressurized gas atmospheres.