Improving the Fire Performance of Structural Insulated Panel Core Materials with Intumescent Flame-Retardant Epoxy Resin Adhesive

The effects of adhesive (layer) on fire performances of structural insulated panel (SIP) have been mostly ignored. This research studied modifications to the epoxy resin adhesive (EA) with expandable graphite (EG), ammonium polyphosphate (APP) and calcium carbonate (CaCO3) to prepare an intumescent flame-retardant epoxy resin adhesive (FREA) which was applied to expanded polystyrene (EPS), a typical core material of SIPs. It was found that the FREA had a char yield of 33% which was 7.6 times of that of EA and a higher viscosity than EA. The limiting oxygen index reached a maximum of 37.7% and UL94 passed the V-0 rating when the EPS was coated with FREA, of which the fire performance was even better than flame-retardant EPS. Additionally, the heat release rate, production rates of CO, CO2 and soot and sample back temperatures were all reduced compared to the EPS coated with EA. Avoiding the sample surface recession in the cone calorimeter, the custom-made spray gun system proves that the FREA can significantly increase the ignition time and lead to self-extinguishment. The degradation products of APP crosslink with CaCO3 to produce phosphates which bond with expanded EG forming the char layer to prevent heat and flame. The use of flame-retardant adhesives can lead to a sufficient fire safety level for the core material without affecting its functions.