Indian Journal of Fibre & Textile Research Vol. 22, December 1997, pp. 264-273 Responsive heat barrier fabrics A R Horrocks, S C Anand, B K Kandola & D Sanderson Faculty of Technology, Bolton Institute, Deane Road, Bolton BL3 5AB, U.K. Recently a heat baryier composite fabric structure has been developed [UK Pat 2279084 B, 20 June 1995] which can withstand air exposure temperatures up to 1200°C. This novel assembly is a multilayer fabric which comprises a flexible nonwoven core of flame-retardant fibres throughout which an intumescent is dispersed. This paper reviews the various stages of development of th is novel composite textile structure since 1992, where a number of flame-retardant celll!losic fibres have been combined with selected intumescents in suitable composite structures. High flame and heat resistance and very low heat release properties are features of these composite structures. It has been demonstrated that on heating such systems, both components char by chemically and physically compatible mechanisms, resulting in a chemical interaction to form a fibrous char-reinforced intumescent char or 'char-bonded' structure which is unusually resistant to oxidation. Keywords : Composite fabrics, Flame-retardant fibres, Heat-barrier fabrics, Intumescents 1 IntroductioJl The currently available protective and barrier fabrics are textile products having different levels of performance. Fabrics based on organic structures, i.e. flame-retardant cotton and wool, polyaromatic structures like aramid and novoloid fibres, have 'desirable textile properties. When exposed to fire, they do not propagate fire but at temperatures above 2S0°C, they carbonize to give char. The char is very brittle and has tendency to oxidize slowly above 400-S00°C, hence no coherence is left. Of these fibres, even the most heat-resistant ones like aramids, survive only a few minutes when heated in air up to 900°C. Fabrics based on only inorganic fibres (silica or alumina) are very good protective fibres as barriers for fire and heat. Some can withstand temperatures up to 1100°C for considerable time, but they are very expensive and have higher densities and moduli. Thus, they are unsuitable for end-uses where lightness and flexibility are required, e.g. protective clothing, transport upholstery fabric, etc. Fig. 1 presents a schematic representation of the various fabric types in terms of fibre content, cost and performance. Hence, there is a need of a barrier fabric having textile characteristics at normal temperatures and which can offer protection against flame and heat at temperatures up to 1200°C for short periods of time. This paper reviews 1-4 the development of a novel genus of barrier fabric which comprises a flexible nonwoven core containing both organic and inorganic fibrous components throughout which an intumescent is dispersed. The core is constructed so that it permits flexibility at both low and high temperatures. Up to SOO°C, it accommodates expansive forces generated by the developing intumescent char component which enables it to increase in volume and thickness while fabric integrity and flexibility are maintained. As the temperature is ntised above SOO°C, the char (which comprises both fibre and intumescent components) slowly oxidises leaving the inorganic fibre components as a residue. After long periods of time or on increasing the temperature above lOOO°C, an inorganic skeleton of the original structure remains which still offers a degree of coherent thermal protection. Fig. 2(a) shows the structure of nonwoven core with an intumescent dispersed through it. Alternative more practical versions of this are shown in Figs 2(b) and 2(c) where these assemblies contain flame- retardant, non-thermoplastic face and backing fabrics which add reinforcing elements to the