Flame retardancy of different-sized expandable graphite particles for high-density rigid polyurethane foams

The effects of expandable graphite (EG) of different particle sizes, on the fire-retardant properties of high-density rigid polyurethane foam (R-PUF) (0.45 g cm(-3)) were studied. Samples of EG with different particle sizes were obtained by pulverization in an ultra-high-speed mixer for 4 and 13 min, respectively. It was shown that as received (EGO) and 4 min pulverized EG (EG4) efficiently improved the fire-retardant properties of RPUF composites, while 13 min pulverized EG (EG13) did not. The char of the burned composites filled with EGO and EG4 covered the whole surface of the samples and formed a complete physical barrier. This barrier material prevented combustible gases from feeding the flame and also isolated oxygen efficiently from the burning material. EG13 did not produce enough char to cover the whole surface of the burning sample, resulting in poor fire-retardant property of the RPUF composites. Thermal degradation tests of the foams by thermogravimetric analysis indicated that EG showed negligible effects on the thermal stability of the RPUFs. (C) 2006 Society of Chemical Industry.