The effects of aluminum hydroxide and ammonium polyphosphate on the flame retardancy and mechanical property of polyisocyanurate–polyurethane foams

Ammonium polyphosphate and aluminum hydroxide were added simultaneously to polyisocyanurate–polyurethane foams as flame retardants. The effects of aluminum hydroxide and ammonium polyphosphate on the fire retardancy and mechanical property of polyisocyanurate–polyurethane foams were investigated. Thermogravimetric and thermogravimetric–Fourier-transform infrared spectroscopy were used to investigate the thermal stability and decomposition of the foams. Cone calorimeter tests, the limiting oxygen index, and scanning electron microscopy were used to study the fire performance of aluminum hydroxide and ammonium polyphosphate. The results show that the compressive strength of the foams increases upon the addition of both aluminum hydroxide and ammonium polyphosphate. The flame retardancy of the polyisocyanurate–polyurethane foams can be significantly improved under the effect of aluminum hydroxide and ammonium polyphosphate. After the addition of 5-phr aluminum hydroxide and 15-phr ammonium polyphosphate, the limiting oxygen index value increases from 21.2% for the reference sample to 28.0%, while the peak heat release rate reduces from 159.8 kW/m2 for the reference sample to 76.8 kW/m2. The effects between aluminum hydroxide and ammonium polyphosphate occur in the condensed phase. Spherical projections with “villi-like” particles are formed covering the surface of char to hinder flame and energy transmission.