INHIBITION OF HYDROCYANIC ACID EVOLUTION FROM POLYURETHANES DURING OXIDATIVE-DEGRADATION

It has been shown that the evolution of hydrocyanic acid during the thermal oxidative degradation of aliphatic and aromatic polyurethanes is inhibited by metals such as Cu and Co powders, their oxides, and decomposable compounds. Other metals are much less efficient inhibitor. The inhibition efficiency also depends on the degree of dispersion. Cu or its oxides and decomposable compounds are the most powerful inhibitors; very effective are copper films (400 to 1000-Å thick) deposited on polymer films. It is shown that HCN evolved from NaCN is catalytically decomposed in an air stream; if the velocity of such a stream is low and the HCN concentration is small, then the main decomposition product is N2 (ca. 90 %) plus small amounts of nitrogen oxides, H2O, and CO2. The catalytic decomposition reaction of HCN evolved from polyurethanes is exactly analogous to that for NaCN, i.e., at low air flow rates and low HCN concentrations mainly N2 is the decomposition product. The results obtained for HCN evolved from NaCN agree well with those of previous workers. It can be definitely concluded that the inhibition by copper of HCN evolution from polyurethanes and other nitrogen containing polymers is not due to a change in the oxidative degradation mechanism of the polymers but is due to the catalytic decomposition of HCN evolved from polymers. © 1978, The Society of Polymer Science, Japan. All rights reserved.