Effectiveness of Phosphorus-Containing Flame Retardants in Textile Back-coating Formulations

A series of phosphorus-containing flame retardants including some intumescents have been formulated with selected resins and applied as back-coatings to both cotton and cotton-polyester (35:65) blended fabrics. While all formulations raise the limiting oxygen index, only those based on ammonium polyphosphate and a cyclic phosphonate enable samples to pass a small-scale version of the simulated match test. BS5852: 1979, Source 1. While the back-coatings containing intumescents promoted higher levels of char formation this did not reflect in their performance to the match test. Thermogravimetric analysis suggests that the more effective flame retardants, as exemplified by ammonium polyphosphate, are those which liquefy by melting and/or decomposition well below 300°c. It is proposed that this liquefication enables wetting of the back face of the fabric and diffusion to the front face where, as the temperature rises towards 300°c, char formation occurs before ignition can take place.