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 Bronsted and Lewis acidic sites on BP.