Fire retardance in polyamide-6. The effects of red phosphorus and radiation-induced cross-links

Red phosphorus contained in non-irradiated polyamide-6 at concentrations up to 12.5 does not significantly improve the fire resistance of the polymer. It weakens the thermal stability of the polymer as reflected by a decrease in the onset temperature for mass loss from 407degreesC to 363degreesC, but causes char formation as indicated by m(res) = 13 wt%, the non-volatile residue at 600 degreesC. Irradiation of polyamide-6, loaded with red phosphorus, with Co-60-gamma-rays generates intermolecular cross-links resulting in an improved fire resistance. However, the absorbed dose necessary to achieve improvement is too high ( >1 MGy) from a practical point of view. This inconvenience is overcome by applying triallyl cyanurate (TAC) as a cross-linking promoter. Typically, polyamide-6 containing 5 wt% TAC and 12.5 wt% red phosphorus exposed to a gamma-ray dose of 22 kGy yields a V-0 rating (in the mode A UL 94 test) concurrently with a small increase in the onset temperature for mass loss and a drastic increase in the residue non-volatile at 600degreesC. Copyright (C) 2002 John Wiley Sons, Ltd.