Thermal Decomposition of Composites in Fire

Abstract

The behaviour of composite materials in fire is governed largely by the chemical processes involved in the thermal decomposition of the polymer matrix and, if present, the organic fibres. This chapter provides a description of these decomposition mechanisms. The description is kept at a general level, and the reader can refer to the many excellent textbooks on polymer decomposition for more information [1--5]. Following this, the decomposition behaviour of polymer systems used in composites is described. A great number of different polymers can be used in composites, and it would be too exhaustive to describe the decomposition of each type. Instead, the chemical nature and decomposition behaviour of the thermoset polymers and thermoplastics most commonly used in composites are reviewed. This will include the thermosets: polyesters, vinyl esters, epoxies and phenolics, and the thermoplastics: polypropylene (PP), poly ether ether ketone (PEEK) and polyphenylene sulphide (PPS). The thermal decomposition of the organic fibres most often used in composites; namely aramid and UHMW polyethylene fibres, are also discussed. The decomposition of other types of organic fibres that are presently used in niche applications are not reviewed, such as nylon 6,6 or PBO (Zylon®), or fibres that are still under development, such as M5 (poly(2,6-diimidazo[4,5-b:4{\textasciiacutex},5{\textasciiacutex}-e]pyridinylene-1,4-(2,5-dihydroxy)phenylene)). Finally, the physical aspects of degradation of composites in fire are described, including char formation, delamination damage and matrix cracking.