Study On Flame Retardancy Of Carbon Nanotubes/Carbon Fiber/Epoxy Resin Three Phase Composites

Epoxy resin is widely used in electronics and aerospace,due to its good bonding properties,easy processing and molding.However,it is combustible.Once it is ignited,the mechanical properties of the composites would be deteriorated.Therefore,flame retardant modification of epoxy resin has been a technical problem in this field.Due to its high strength,small specific gravity,small thermal expansion coefficient,high thermal conductivity and high design freedom,carbon fiber has become one of the main reinforcing fibers for advanced composite materials.Carbon nanotubes are considered to be an ideal flame retardant additive because of its unique structure and good thermal conductivity.In this paper,carbon fiber and carbon nanotubes were taken as flame retardant additives.The carbon fiber/epoxy composites and carbon nanotubes/carbon fiber/epoxy three-phase composites were prepared by the way of solution blending.The composites were analyzed by oxygen index,UL-94,Cone calorimetry and thermal gravimetric analysis to investigate their flame retardancy.The tensile and flexural tests were carried out to investigate the effect of reinforcements on their mechanical properties.The microstructure of the composites was characterized by scanning electron microscopy.The results showed that carbon nanotubes and carbon fiber had a synergistic effect on enhancing the flame retardancy of epoxy resin compared with carbon fiber reinforced epoxy resin composites.The oxygen index of F5N10 was the best,which were 6.86%higher than that of epoxy resin.F7N7 had the same combustion level of FH-2 as F7,but the burnout length was reduced by 14mm.The peak value of heat release rate of F7N7 was 34.65%lower than that of epoxy resin,and peak of smoke generation rate was minimum.The total smoke production of F5N5 was 43.04%lower than epoxy resin.The initial decomposition temperature of F7N7 was about 14℃higher than that of F7.And the tensile and flexural strength was enlarged.The activation energy of the epoxy resin in the first pyrolysis stage was101.0KJ.mol^-1,and the apparent activation energy of F7N7 was relatively increased by 2.7KJ.mol^-1.The activation energy of the three-phase composites in the second stage was higher than that of the epoxy resin.It could be seen from the microscopic characterization that the carbon nanotubes were combined with the carbon fiber to promote the carbon formation of the epoxy resin,and the flame retardant enhancement of the epoxy resin was attributed to the condensed phase flame retardant effect.