Mechanistic study of combustion performance and thermal decomposition behaviour of nylon 6 with added halogen-free fire retardants

Mechanistic studies in nylon 6 with added halogen-free fire retardants, e.g. ammonium polyphosphate (APP), ammonium pentaborate (APE), red phosphorus, potassium nitrate or melamine and its salts, were carried out using combustion and thermal decomposition approaches. It was shown that APP interacts with nylon 6 producing alkylpolyphosphoric ester which is a precursor of the intumescent char. On the surface of burning polymer, APE forms an inorganic glass protecting the char from oxidation and hindering the diffusion of combustible gases. Red phosphorus reacts with decomposing nylon 6, probably through radical mechanisms producing phosphorus ester species. The condensed phase fire retardant action is proved for red phosphorus. Potassium nitrate, which is a strong oxidizer, reacts with the polymer in condensed phase increasing the char yield. Melamine and its salts mostly provoke flow of nylon 6 leading to extinction of the flame. Furthermore, they induce scission of H2C-C(O) bonds in nylon 6, which leads to increased cross-linking and charring of the polymer. (C) 1996 Elsevier Science Limited