MECHANISTIC STUDY OF COMBUSTION PERFORMANCE AND THERMAL-DECOMPOSITIONBEHAVIOR 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 p hosphorus, potassium nitrate or melamine and its salts, were carried o ut using combustion and thermal decomposition approaches. It was shown that APP interacts with nylon 6 producing alkylpolyphosphoric ester w hich is a precursor of the intumescent char. On the surface of burning polymer, APE forms an inorganic glass protecting the char from oxidat ion and hindering the diffusion of combustible gases. Red phosphorus r eacts with decomposing nylon 6, probably through radical mechanisms pr oducing phosphorus ester species. The condensed phase fire retardant a ction is proved for red phosphorus. Potassium nitrate, which is a stro ng oxidizer, reacts with the polymer in condensed phase increasing the char yield. Melamine and its salts mostly provoke flow of nylon 6 lea ding 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