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

The chemiluminescence (CL) intensity from a hydroxyl-terminated polybutadie ne (HTPB) rubber was measured during isothermal oxidation at temperatures r anging 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, suggestin g an invariable overall oxidation mechanism. Total luminous intensity (TLI) values in nitrogen atmosphere were obtained;It selected times during the i sothermal oxidation. The TLI data showed a good correlation with the CL iso therm, indicating that the time course of the isotherm can be explained in terms of peroxide build-up and decomposition. The build up of peroxides dur ing oxidation was shown from FTIR data to be accompanied by a build-up of c arbonyl groups. Above a certain TLI level, FTIR data showed a significant d ecrease 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 sev er embrittlement of the rubber. (C) 1999 Elsevier Science Ltd. All rights r eserved.