Investigation of the effect of inorganic smart fillers and expanded graphite on the flame retardancy of polyisocyanurate insulation foam

Use of highly insulating polyisocyanurate (PIR) based insulation materials enhanced with eco-friendly lamellar inorganic fillers contributes to meeting energy performance requirements, environmental challenges and cost reduction without undue compromise of the overall building fire safety. This work aims to assess the fire behaviour of PIR foams enhanced with lamellar inorganic smart fillers, namely Layered Double Hydroxides (LDHs), Expandable Graphite (EG) and Ammonium Polyphosphate (APP). The morphology of the foam structure was firstly studied using Optical Microscopy and Field Emission Scanning Electron Microscope and subsequently the fire reaction properties and thermal stability of foam samples enhanced with different types of lamellar inorganic smart fillers were evaluated using cone calorimeter (CC) and thermogravimetric analysis (TGA). TGA results indicated that thermal decomposition of the neat PIR samples occurs in two distinct stages associated with the degradation of the urethane-urea linkages of the hard segment, releasing low calorific capacity products and the degradation of polyol derived products with higher calorific capacity than those derived from isocyanate. The initial degradation temperature of PIR-layered filler samples decreases compared with neat PIR foam, indicating that incorporation of flame retardants decelerates the degradation of PIR foam and as a result decreases the thermal stability of PIR foam. The cone calorimeter data showed that the effects of LDH alone has limited effect on reducing the heat release rate (HRR) or smoke production rate (SPR) as it is only act in the solid phase. With the addition of EG or EG+APP, HRR is further decreased owing to the increased char strength as well as the release of non-combustible gases, and simultaneously effectively suppress smoke and gases during the combustion process.