Impact of expandable graphite on flame retardancy and mechanical properties of rigid polyurethane foam

Flame retardant (FR) and mechanical performance properties of two different rigid polyurethane foams (RPUFs) containing expandable graphite (EG) as FR additive were studied. The impact of EG on the foam properties were evaluated. Cellular structures were less homogeneous in foams containing EG. Thermal conductivities of RPUF increased slightly with EG addition. FR properties of the foams were evaluated by limiting oxygen index (LOI) test, vertical burning test (UL94), and cone calorimeter test. The addition of EG improved the FR performance and increased the density of the foams. For example, LOI value was increased from 18.4 to 25.2 in EG10PU1, whereas for EG10PU2, LOI increased from 19.2 to 29.8. In UL94 test, EG10PU1 reached V‐1 rating, while EG8PU2 passed V‐0 rating. Results from cone calorimeter test showed that the EG in the RPUF effectively reduced heat release rate, total heat released, total smoke production, and mass loss rate with increase in EG. This improvement was more efficient for the higher density foam. In addition, low loading of EG in PU1 increased the compression performance but decreased as the amount of EG was further increased. POLYM. COMPOS., 40:E1705–E1715, 2019. © 2018 Society of Plastics Engineers