COMPLEX CHAR FORMATION IN FLAME RETARDED FIBER-INTUMESCENT COMBINATIONS .1. SCANNING ELECTRON-MICROSCOPIC STUDIES

A recently disclosed development(1-3) comprising a composite of flame retardant cellulose fibres and an intumescent has shown unusually high flame and heat resistance with a char structure that can withstand ai r exposure temperatures up to 1200 degrees C. Char structures of selec ted flame retardant cellulose fibres when alone and blended with inert E-glass and aromatic char-forming novoloid fibres in the presence of an ammonium polyphosphate-based intumescent have been studied using sc anning electron microscopy. Evidence suggests that a 'char-bonded' str ucture is formed in which flame retardant cellulose fibrous chars have interacted with intumescent char during its formation. Similar intera ctions are not seen with E-glass and novoloid fibre residues. The char -bonded structure is considered to have reduced air permeability and s o has considerably enhanced surface oxidative resistance at high tempe ratures. An outline mechanism is proposed and is based on known pyroly sis mechanisms for the flame retarded cellulose fibre and intumescent components. Copyright (C) 1996 Elsevier Science Ltd.