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A sustained upsurge in the use of fibre reinforced polymer (FRP) composite materials has occurred over the last forty years. The use of polymer composites has grown at a phenomenal rate since the 1960s, and these materials now have an impressive and diverse range of applications in aircraft, spacecraft, boats, ships, automobiles, civil infrastructure, sporting goods and consumer products. The use of composites will continue to grow in coming years with emerging applications in large bridge structures, offshore platforms, engine machinery, computer hardware and biomedical devices. Figure 1.1 shows the growth in the use of composite materials by various industry sectors in the United States since 1960. Over this period consumption has increased about 30 times, and the growth rate is expected to continue. The greatest increases are occurring in the transport and construction markets, although the use of composites is also substantial in the corrosion protection (eg. piping), marine, and electrical/electronic markets as shown in Fig. 1.2.

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′,5′- 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.

The fire reaction properties of fibre reinforced polymer composites are described in this chapter. The properties that are described are time-to-ignition, heat release rate, mass loss, extinction flammability index, thermal stability index, limiting oxygen index, smoke density, smoke toxicity and surface spread of flame. The fire resistance properties of burn-through resistance and resistance to jet-fire attack are also described, although other resistance properties such as structural capacity in fire and post-fire mechanical properties are discussed in separate chapters later in this book.

Composite materials include an organic resin that will lose strength and thermally decompose when exposed to elevated temperatures. As with many other types of construction materials, the fire performance of composites is assessed through the material’s propensity to spread flame and its fire resistance capabilities. Flame spread is the ignition of the composite material by an initiating fire and propagation of flame along the surface. Fire resistance is a measure of the ability of a wall or ceiling to prevent heat transmission through the assembly and structural integrity. Chapter 5 will address how to predict the heat transmission through the thickness of the composite when exposed to fire. This chapter will focus on modelling the flame spread over composite surfaces and the structural response of composites during fires.

The thermal decomposition of fibre reinforced polymer composites in fire is a complex topic that involves the combined effects of thermal, chemical and physical processes. The thermal processes include heat conduction from the fire through the composite; heat generated or absorbed from the decomposition reactions of the polymer matrix, organic fibres and core material; heat generated by the ignition of flammable reaction gases; and convective heat loss from the egress of hot reaction gases and moisture vapours from the composite into the fire. The chemical processes include thermal softening, melting, pyrolysis and volatilisation of the polymer matrix, organic fibres and core material together with the formation, growth and oxidation of char. The physical processes can involve thermal expansion and contraction, internal pressure build-up due to the formation of volatile gases and vaporisation of moisture; thermally-induced strains; delamination damage; matrix cracking; surface ablation; and softening, melting and fusion of fibres. Many of these processes do not occur in isolation from each other, but usually influence other processes that add to the complexity of the behaviour of composites in fire. Understanding these processes and how they interact is essential to understanding the fire reaction and fire resistive properties of composite materials.

A large quantity of information is available on the fire reaction properties of polymer composites (as described in chapters 2 to 5), and the level of fire hazard associated with their use is known for a large number of materials. We also have a good understanding of the chemical, thermal and physical mechanisms that control reaction properties such as time-to-ignition, heat release rate, flame spread rate, smoke production and toxicity. In short, we have quite a good quantitative understanding of the fire reaction behaviour of composites. Unfortunately, less is known about the fire resisting properties, such as burn-through resistance, dimensional stability and structural integrity, especially when the structure is under load. Moreover it is not usually possible to estimate the fire resistive behaviour based solely on the known fire reaction properties. A composite that has good fire reaction properties, such as low heat release rate and smoke yield, may not necessarily have good fire resistive properties. Composites with a polymer matrix having high thermal stability, decomposition temperature and char yield may not necessarily have better fire resistive properties than more flammable materials. For example, phenolic laminates generally show better fire reaction properties than unsaturated polyester laminates, including longer ignition time, lower heat release rate, slower flame spread and less smoke, but their mechanical properties can often degrade more rapidly in fire. Until recently, little was known about the structural properties of composites in fire. Understanding the structural performance in fire is a critical safety issue because the loss in stiffness, strength and creep resistance can cause composite structures to distort and collapse; possibly resulting in injury and death. Structural properties of composites in fire are therefore arguably as important to safety as the fire reaction properties that have generally been more widely studied.

The fire reaction properties and thermal degradation mechanisms of polymer composites have been subjects of in-depth characterisation and analysis for many years because of the need for fire-safe materials. The growing use of composites in aircraft, ships, civil construction and other applications has required knowledge of their reaction properties such as heat release rate, smoke production and toxic gas emission to ensure safety in the event of fire. Furthermore, the thermal decomposition behaviour of organic resins, fibres and core materials that determine the fire reaction properties of composites are generally well understood.

This chapter gives an overview of methods to enhance the flame retardant properties of fibre reinforced polymer composite materials. The methods used are extraordinary diverse, and vary in complexity from simple additive compounds blended into the polymer matrix or heat-resistant coatings, through to sophisticated methods that involve chemical modification of the matrix or heat-induced intumescence of the composite surface. Also outlined are methods to improve the thermal stability and fire resistance of organic fibres used in composites.

The terminology polymer nanocomposite describes a composite in which one of the composite materials, the nano-material, has a minimum of one dimension which is on the nanoscale and it is completely dispersed throughout the polymer. The typical nanomaterial is a clay but graphite, single-wall and multiple-wall nanotubes and nanoscale spherical particles, such as polyhedral oligomeric silsesquioxane, POSS [ 1 ],[ 2 ], silica [ 3 – 5 ] and titania [ 6 ],[ 7 ], have also been used.

An overview of the fire safety standards and regulations applied to polymer composite materials used in aircraft, ship, civil infrastructure and transport applications is given in this chapter. The fire standards are described in a general way, and it is not the purpose of this chapter to give an exhaustive description of all the regulations because it is outside the scope of this book. Regardless of the application, the fire safety standards applied to composites (and other combustible materials) should have the following characteristics: performance-based; accurately and realistically prescribe the fire performance limits of the composite component; only consider those fire reaction and fire resistive properties relevant to the application; consider the fire safety of the composite in the end-use condition rather than of the material itself; not require extensive and costly testing; internationally recognised; and provide a tool for the research and development of fire-safe materials.