Complex Char Formation in Flame-Retarded Fiber/Intumescent Combinations: Physical and Chemical Nature of Char1

Abstract

Char forming polymers, particularly cellulosics, can best be flame retarded by chem icals that function in the condensed phase. Under heat or fire conditions, these flame retardants enhance crosslinking and aromatization reactions of the polymer at the ex pense of volatilization, leading to increased char formation. Intumescent systems are also used to increase the flame retardancy of polymers. Under the action of heat, these compounds form a foamed char, which then acts as an insulative barrier to the under lying material against heat and flame. Our recent research has shown that if certain intumescents are used on flame retardant cellulosic fibers, the combined fibrous and intumescent chars that form are more than expected in quantity, with great mechanical strength and reduced oxygen permeability and sensitivity to oxidation. Within this so- called "char-bonded" structure, there is clear evidence of bonding between cellulosic fibers and intumescent char components. In our previous publications, we discussed the methodology of forming novel, thermally responsive, barrier textile fabrics com prising flame retardant cellulosic fibers in which intumescent systems are dispersed, the formation mechanism of char-bonded structures, and evidence of the interactions occurring between these components. This work extends to understanding the physical and chemical nature of the char for a variety of flame retardant viscose and cotton/ intumescent compositions.