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.