Toxic gas evolution from polymers: Evolution of hydrogen cyanide from linear polyurethane

HCN evolution from linear polyurethane has been studied over a range of temperatures from 261 to 480°C as function of exposure time, oxygen pressure, film thickness, and chain length. Infrared spectra have also been measured as function of exposure time. In addition, gas evolution during thermal degradation in vacuo has been investigated in a quartz spoon reaction vessel. Rate constants and energies of activation have been evaluated for all reactions. Gas evolution and adsorption are diffusion‐controlled during thermal and thermal‐oxidative degradation up to at least 330°C. Thermal degradation consists essentially of a reversal of the polycondensation process. The thermal‐oxidative degradation is a complicated reaction involving chain scission, crosslinking, carbonization, and gas evolution. HCN evolution, although appreciable, is only a minor side reaction of the total oxidation process. A tentative mechanism for HCN evolution has been proposed.