Synergistic effects of expandable graphite and dimethyl methyl phosphonate on the mechanical properties, fire behavior, and thermal stability of a polyisocyanurate–polyurethane foam

In this study, a series of flame-retardant polyisocyanurate–polyurethane (PIR–PUR) foams were prepared using various concentrations (0–25% by weight) of expandable graphite (EG) and dimethyl methyl phosphonate (DMMP) (0–7% by weight). The effect of these additives on the properties of the PIR–PUR foams, including physico-mechanical, morphological, flame retardancy, and thermal stability, was studied. Increasing amounts of EG in the PIR–PUR foam caused a significant drop in the compression strength. However, DMMP caused the mechanical properties of PIR–PUR foam to improve compared to foam filled with EG alone. The flame retardancy of PIR–PUR foams containing both EG and DMMP was enhanced significantly compared to EG filled foams. Thermogravimetric analysis (TGA) indicated that EG enhances the thermal stability of PIR–PUR foams but that DMMP decreased it. The morphology of the residual char provided conclusive evidence for the weak thermal stability of foams filled with DMMP.