Effect of the fire-retardant, melamine, on the combustion and the thermal decomposition of polyamide-6, polypropylene and low-density polyethylene

Abstract

Combustion tests show that polyamide-6 (PA-6) mixed with melamine is self-extinguishing. The thermal degradation process in PA-6 is modified strongly by the presence of melamine, so that the temperature of decomposition is lowered and the composition of the resulting volatile products is changed. On the other hand, melamine is not effective for either polypropylene (PP) or low-density polyethylene (LDPE). Activation energies based on thermogravimetry (TG) curves for the thermal decomposition of each sample at different heating rates are in the range of about 88.1 to 263 kJ mol −1. The fluctuations found in activation energies indicates that a charring mechanism may contribute to the overall process. Minor amounts of thermal decomposition products other than ϵ-caprolactam were also evolved from the pure PA-6, their formation being suppressed in mixtures with melamine. The charring process occurs in parallel with the volatilization of decomposition products of PA-6, on which melamine seems not to have a significant effect. It appears evident that, compared with PP and LDPE, PA-6 is much more susceptible to thermal decomposition in the presence of melamine.