The effect of ammonium polyphosphate (APP) and tris(2,4-di-ter-butylphenyl)phosphite (TBP) flame retardants and polyphosphoric acid (PPA) was examined on the thermal decomposition reactions of polystyrene (PS), styrene-acrylonitrile copolymer (SAN), acrylonitrile-butadienestyrene copolymer (ABS) and polyacrylonitrile (PAN) by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and thermogravimetry (TG) techniques.
The effect of APP and PPA proved to be significant on the thermal decomposition of polymers investigated. The char formation from each polymer-APP and polymer-PPA mixture increases considerably. The thermal stability of PS increases in the presence of APP and PPA by 17 and 28 8C, respectively.
Analogous and significant changes were observed in the pyrolysis product distribution of PS, SAN and ABS in the presence of APP and PPA, indicating, that the polyphosphoric residue of APP modifies the thermal decomposition mechanisms of these polymers even during fast pyrolysis when the chemical processes take place simultaneously.
The presence of PPA promotes hydrogen shifts resulting in isomerisation and formation of indene compounds from PS, moreover, development of a conjugated ladder structure from PAN chain even during fast pyrolysis. This is the first time that a GC/MS evidence can be presented directly confirming the first step of carbonization reaction of PAN.
The results also give an insight into the influence of PPA on the electron donating ability of phenyl side groups having a significant effect on the thermal decomposition product distribution of PS and styrene copolymers.