Abstract
Extinction oxygen index (EOI) and the derived value at zero ignition time [EOI]o have been determined for a series of commercial quality flame-retarded cotton fabrics in the temperature range 20 to 200°C. The flame retardants used were Proban-CC (Albright and Wilson Ltd.) and Pyrovatex-CP (Ciba-Geigy). For all the flame-retarded cotton fabrics studied, EOI and [EOI]o decreased with increase in temperature. The influence of conditioned area density M at a given temperature can be predicted via the linear relationship [EOI]0=E0+E1M Substitution of moisture correted area density data had negligible influence on the calculated values of Eo and E1. The dependence of [EOI]o on area density, E1, has a negative temperature dependence. The similarly temperature dependent term Eo is the “intrinsic oxygen-index,” which is independent of ignition and area density variables. For a given flame retardant this represents the fabric properties where maximum access of oxygen is possible. In all cases studied, Eo > E1 and so the temperature dependence of [EOI]o is largely determined by Eo. Values obtained for the fractional increase in Eo, with respect to its value at 20°C, with increasing temperature indicate that the temperature sensitivity of the burning behavior of cotton is greater than that of Proban-CC-treated cotton, which itself is greater than that of Pyrovatex CP-treated cotton. It is inferred that effective flame-retardants should not only function under ambient conditions but also reduce the temperature sensitivity of the inherent fibre-burning behavior at elevated temperatures.