Flame retardancy and degradation mechanism of poly(vinyl acetate) in combination with intumescent flame retardants: I. Ammonium poly(phosphate)

Abstract

The present paper deals with the flame retardancy study of model compound Poly(vinyl acetate) (PVAc) blended with ammonium poly(phosphate) (APP) as flame retardant. APP shows good activity within PVAc in fire tests at low mixing ratios in terms of reduction of rate of heat release (RHR). Creating difference thermograms by means of thermogravimetric analysis (TGA) learned that the classic deacetylation step of the polymer is accelerated by the presence of APP in the composite, followed by stabilisation of the formed char.A systematic model to investigate chemical decomposition reactions of blends of polymers with flame retardants is introduced to build a complete mechanistic reaction model. To perform this, both evolved gas and solid state analysis of intermediate products are coupled. For the combination of PVAc and APP, APP breaks into monophosphate during the deacetylation step of PVAc and fully cross-links with the polymer by P–O–C cross-link bonds. The formed cross-linked material further aromatises in an oxidative environment and is highly stabilised as was shown using difference thermograms: blends of PVAc and APP appear to be more than 20% stable at 600 °C in comparison with the decomposition of the pure materials. At elevated temperatures, the phosphate structure degrades, leading to the full evaporation of the carbonaceous residue within the char.