EFFECT OF THE FIRE-RETARDANT, MELAMINE, ON THE COMBUSTION AND THE THERMAL-DECOMPOSITION OF POLYAMIDE-6, POLYPROPYLENE AND LOW-DENSITY POLYETHYLENE

Combustion tests show that polyamide-6 (PA-6) mixed with melamine is s elf-extinguishing. The thermal degradation process in PA-6 is modified strongly by the presence of melamine, so that the temperature of deco mposition is lowered and the composition of the resulting volatile pro ducts is changed. On the other hand, melamine is not effective for eit her polypropylene (PP) or low-density polyethylene (LDPE). Activation energies based on thermogravimetry (TG) curves for the thermal decompo sition of each sample at different heating rates are in the range of a bout 88.1 to 263 kJ mol(-1). The fluctuations found in activation ener gies indicates that a charring mechanism may contribute to the overall process. Minor amounts of thermal decomposition products other than e psilon-caprolactam were also evolved from the pure PA-6, their formati on being suppressed in mixtures with melamine. The charring process oc curs in parallel with the volatilization of decomposition products of PA-6, on which melamine seems not to have a significant effect. It app ears evident that, compared with PP and LDPE, PA-6 is much more suscep tible to thermal decomposition in the presence of melamine. (C) 1997 E lsevier Science Limited.