THE FLAMMABILITY OF POLYACRYLONITRILE AND ITS COPOLYMERS

The burning behaviour and the influence of flame-retardant species on the flammability of fibre-forming homopolymer and copolymers of acrylonitrile are reported. A pressed powdered polymer sheet technique has been developed which allows a range of polymer compositions in the presence and absence of flame regardants to be assessed for limiting oxygen index, burning rate and char residue determinations. The method has been used to provide a rapid, reproducible and convenient means of screening possible flame-retardant systems. It has been shown that the mechanism of thermal degradation of acrylic polymers is dependent on the rate of heating. At low heating rates cyclisation is the main reaction pathway, whereas at high heating rates commensurate with those encountered in fires volatile-forming chain scission predominates. Furthermore, the effectiveness of a particular flame retardant is directly proportional to its char-forming tendency. The most effective of the flame retardants studied was ammonium polyphosphate, and a mechanism by which this operates is suggested.