Thermal degradation and fire behaviour of unsaturated polyester with chain ends modified by dicyclopentadiene

This work deals with the thermostability and the thermal behaviour of unsaturated polyester materials with dicyclopentadiene end cap (DCPD). These new UP resins will be used for naval applications, limiting styrene emission during processing. The thermostability has been studied by thermogravimetric analysis (TGA) both in air and in nitrogen to determine thermal and thermooxidative mechanisms, and activation energy was calculated for different rates of reaction. In the beginning of thermal degradation, La was about 100 kJ mol(-1), which corresponds to polystyrene depolymerization; for alpha=0.5, which corresponds to UP network degradation, La was 170 kJ mol(-1); for the thermooxidation phase, Ea was about 250 kJ mol(-1). Limiting Oxygen Index (LOI) has been determined to study fire behaviour. LOI decreases when the styrene content decreases and material fire behaviour was better when the samples were post cured. Oxygen indexes are higher for UP modified by dicyclopentadiene (DCPD) chain ends than for classical ones. Products formed during the thermal degradation have been identified using coupled pyrolysis gas chromatography mass spectrometry analysis. During thermal degradation, water, carbon monoxide and carbon dioxide are the most important products; the major degradation step for UPs was ester linkage rupture. Styrene and products derived from styrene were detected. For UP prepolymers modified by dicyclopentadiene end caps, products based on DCPD structure and on polycyclic molecules were also detected. (C) 1998 Elsevier Science Limited. All rights reserved.