Application of TG/FTIR TG/MS and cone calorimetry to understand flame retardancy and catalytic charring mechanism of boron phosphate in flame-retardant PUR–PIR foams

The aim of this work was to investigate the catalysis of boron phosphate (BP) on the thermal stability and char forming in flame-retardant polyurethane–polyisocyanurate foams (FPUR–PIR) with dimethylmethylphosphonate (DMMP) and tris(2-chloropropyl) phosphate (TCPP). The flame-retardant performance and thermal stability of FPUR–PIR were evaluated by cone calorimetry (CONE), thermogravimetric analysis (TG) and microscale combustion calorimetry (MCC). Gas-phase products of FPUR–PIR during the thermal decomposition were investigated via thermogravimetric analyzer coupled with FTIR and mass spectrometry (TG–FTIR–MS). Elemental composition and content of the charred layer in detail were analyzed by X-ray photoelectron spectroscopy (XPS). It was observed that the incorporation of 3 mass% BP in FPUR–PIR decreases the heat release rate, total smoke released and CO production. Meanwhile, the addition of 3 mass% BP advances the release of gaseous products and lower the production of smoke and toxic products like –NCO compounds, PO* and cyanic acid in the gas phase. It can accelerate the dehydration of hydroxyl compounds and promote the char formation of –NCO compounds. This can improve the thermal and oxidation resistance of condensed phase. The catalytic behavior of the dehydration and char formation of BP in the thermal degradation of FPUR–PIR is attributed to Brønsted and Lewis acidic sites on BP.