Prevention of the Formation of Respirable Fibers in Carbon Fiber Reinforced Epoxy Resins during Combustion by Phosphorus or Silicon Containing Flame Retardants

Abstract The influence of different phosphorus containing flame retardants on fiber degradation during combustion of carbon fiber reinforced epoxy resins is described. A phosphazene, a phosphate and a phosphinate were investigated in HexFlow® RTM6, a high performance epoxy resin designed for resin transfer moulding processes, and composites thereof. UL94-V flammability tests of neat RTM6 samples showed a high flame retardant efficiency of the phosphate and the phosphazene. The burning behavior of carbon fiber reinforced composite samples with various amounts of flame retardants was investigated by cone calorimetry and the influence on fiber degradation was determined by scanning electron microscopy including energy dispersive X-ray spectroscopy. While phosphazene acting mainly in the gas phase showed the best flame retardant efficiency in the composite, the phosphate acting mainly in the condensed phase showed the best fiber protection. Mechanical properties were not affected significantly by the incorporation of flame retardants ensuring the application in components manufactured by resin transfer moulding. Finally combinations of phosphazene and a silicon compound were tested. No synergism regarding fiber protection or flame retardancy was observed in carbon fiber reinforced epoxy resins, but these investigations provide information about efficient fiber protection mechanisms.