COMBUSTION AND FIRE RETARDATION OF POLY(2,4-DIMETHYL-1,4-PHENYLENE ETHER) HIGH-IMPACT POLYSTYRENE BLENDS - II - CHEMICAL ASPECTS

The chemical reactions occurring during the intumescent process taking place in the combustion of the poly(2,6-dimethyl-1,4-phenylene ether) -high-impact polystyrene blends (PPE-HIPS) are studied in detail throu gh the chemical characterization of the burnt and original material by infrared, pyrolysis-gas chromatography-mass spectrometry, and direct insertion probe spectrometry. Evidence is given of thermal rearrangeme nt in the blend of the polyether PPE chains to polybenzylic structures occurring in the heating conditions of pyrolysis or combustion, as pr eviously shown, to take place in thermal degradation of PPE. The rearr anged chain segments are shown to give a larger contribution to the in tumescent char, while volatile blowing products are mostly formed by p olystyrene and polybutadiene components. From PPE-HIPS blends, the vol atilization of the fire-retardant triphenyl phosphate (TPP), which whe n heated alone volatilizes at a temperature below that of PPE-HIPS deg radation, is delayed probably by hydrogen bonding with PPE. This allow s TPP to play the typical flame inhibition role of volatile phosphorus compounds. Moreover, it is found that TPP favors the PPE rearrangemen t and henceforth increases the char yield of the burning blend, which is a typical condensed phase fire-retardant action. (C) 1998 John Wile y & Sons, Inc.