| Epoxy resin composites have been broadly used in civil and military fields. As a new kind of high-temperature structural material, carbon fiber/ glass fiber coaxial pultruded composites have been adopted to support the high-voltage cables in electricity transmission industry. Moreover, due to its excellent mechanical performance, carbon nanotube has emerged in various kinds of composite as a reinforcing material. In this research, a kind of carbon fiber/glass fiber coaxial pultruded composite with high coaxial degree and high glass transition temperature which could reach the standard of supportive material in high-voltage cable has been made by modified pultrusion equipment. In this paper, carbon nanotubes are functionalized by silane coupling agent and some of them are combined with silica to improve their binding with epoxy. When add those functional carbon nanotubes into epoxy resin and pultruded composite, the test result shows mechanical properties of those materials have been improved. Researches on curing process of Huntsman epoxy resin castings have determined the main parameters of the pultrusion process. Modification of the pultrusion equipment and employment of two-step pultrusion process have made sure that the carbon fiber inner core is enwrapped evenly by glass fiber out shell. The coaxial composite has good concentricity and the interface between fiber and epoxy resin is also very well. Moreover, the glass transition temperature of this composite could reach 220℃.After oxidation by sulfuric and nitric acid, carbon nanotube is treated by silane coupling agent KH550 to get s-MWNT. Then some of those treated carbon nanotubes are reacted with KH550 and silica to graft silica onto carbon nanotube and form s-MWNT-SiO2. Those functional MWNTs were analyzed by Fourier Transform infrared spectroscopy(FTIR), X-ray photoelectron spectroscopy(XPS), Thermal gravimetric analysis(TGA), Transmission electron microscopy(TEM). Those results could approve that the silane reactive group and some silica particle have been successfully grafted on the carbon nanotube. Those silane reactive groups could have chemical binding with epoxy resin to improve the mechanical performance of the resin and those silica particles could also act as reinforce filler for the resin.Various weight concentration of functional carbon nanotube is added into epoxy resin castings, and the tensile, flexural properties and dynamic mechanical properties are tested. Besides, the fracture morphology of the epoxy resin casting is observed by SEM. The results show that when the concentration of s-MWNT and s-MWNT-SiO2 is 0.5wt%, the tensile strength of epoxy resin has been improved by 16.6% and 18.8% respectively; the flexure strength has been improved by 12.3% and 14.5% respectively; the flexural modulus has been improved by 19.0% and 21.7% respectively. At the same time, glass transition temperature of epoxy resin castings has also been improved. From microstructure analysis, the epoxy resin with 0.5wt% functional MWNT have excellent dispersion, so carbon nanotube could act as 'bridges'to support the epoxy resin.Different weight concentration of functional carbon nanotubes are filled in pultruded composite. Then the flexural and shear properties are tested. Besides, the fracture morphology of the composites are observed by SEM. When the weight concentration of functional carbon nanotube is 0.25wt%, the flexure strength has been improved by 13.7% and 14.7% respectively; the flexural modulus has been improved by 11.0% and 13.0% respectively; the shear strength has been improved by 22.0% and 25.9% respectively. From microstructure analysis, it is observed that at this concentration carbon nanotube has best dispersion and the interface between epoxy resin and glass fiber has been well improved. In this situation, it is indicated that the functional could transfer the stress efficiently to the fibers. |
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