Effect of energism and char formation on the fire retardant properties of rigid polyurethane foam

A fire retardant additive was synthesized by using char forming raw materials. It is used as a fire retardant charring agent and designated as FRCA. Effect of FRCA on thermal degradation and fire retardancy of rigid polyurethane foam (RPUF) has been investigated. The results demonstrated that the FRCA is very effective in enhancing the fire retardancy of RPUF. Thermal stability data obtained in nitrogen and air demonstrated that FRCA has a good ability of char formation itselt and FRCA shows a high initial temperature of the thermal degradation. The quantities of char residue produced by FRCA showed that RPUF is more stable in nitrogen than air. The FRCA can change the thermal degradation behaviour of RPUF, enhance decomposition peak and promote char formation. This is attributed to the fact that endothermic reactions took place in RPUF-FRCA charring process and the char layer formed by FRCA prevented heat from transferring into inside of RPUFFRCA. TGA results further explained the effective flame retardancy of the RPUF containing FRCA. Char formation is also accompanied by water release, which dilutes the combustible vapours. The stabilized char residue acts as protective thermal barrier which does not allow further flame spread. This may leads to reduced burning rate which resulted into enhanced flame retardancy. Significant increase in oxygen index showed effect of char generating additives towards the flammability of RPUF. An oxygen index of RPUF-FRCA is probably increased due to the presence of phosphorus and nitrogen into the FRCA composition. Phosphorus and nitrogen have synergistic effect between them which enhances the oxygen index of RPUF-FRCA.