Thermal oxidation of hydroxyl-terminated polybutadiene rubber I. Chemiluminescence studies

The chemiluminescence (CL) intensity from a hydroxyl-terminated polybutadiene (HTPB) rubber was measured during isothermal oxidation at temperatures ranging from 70 to 130 degrees C. The CL isotherms were characterised by an approximately constant level of intensity followed by a rapid increase to a maximum intensity. The initial intensity as well as the maximum intensity levels of the different isotherms obeyed an Arrhenius expression, suggesting an invariable overall oxidation mechanism. Total luminous intensity (TLI) values in nitrogen atmosphere were obtained;It selected times during the isothermal oxidation. The TLI data showed a good correlation with the CL isotherm, indicating that the time course of the isotherm can be explained in terms of peroxide build-up and decomposition. The build up of peroxides during oxidation was shown from FTIR data to be accompanied by a build-up of carbonyl groups. Above a certain TLI level, FTIR data showed a significant decrease in unsaturation, while swelling measurements showed an increase in the apparent crosslink density. This formation of a secondary network later accelerated, with gradual depletion of oxygen in the specimen, causing sever embrittlement of the rubber. (C) 1999 Elsevier Science Ltd. All rights reserved.