The Preparation And Electrical Properties Of The Functionalized Carbon Nanotubes Modified Carbon Fiber/epoxy Composites

Carbon fiber reinforced plastic (CFRP) has been widely used in the aviation, aerospace and automobile due to their low density, wonderful corrosion resistance and mechanical properties. However, as for one kind of anisotropy material, CFRP has low transverse mechanical properties and a trendy of exfoliation between inter-layers. The epoxy (EP) matrix was easy to be destroyed and could not play a role of transferring load when they were suffered from the powerful force. At present, the use of functionalized carbon nanotubes (CNTs) modified the interlamination section of CFRP is an effective solution for these problems. CNTs have effectively took part in the curing cross-link reaction by their different type of surface functional groups, the modulus and strength of resin matrix have been significantly improved. Nevertheless, the bad dispersion state of CNTs and the low interfacial interaction with resin matrix have a great influence of the CFRP properties. For solving these problems, a series of fundamental experiments were carried out in this research.(1) The amino-functionalized multi-walled carbon nanotubes(MWCNT-NH2) and epoxy-functionalized multi-walled carbon nanotubes(MWCNT-BGE) were prepared through the surface amidation and epoxidation of commercial carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH). The effect of special surface functional groups on the improvement of their dispersion state has been researched.Then, two original kinds of product (MWCNT-NH2/epoxy pre-dispersion mixture and MWCNT-BGE/epoxy pre-dispersion mixture) were obtained by pre-treated with epoxy (TDE-85). The results showed that the MWCNT-NH2 and MWCNT-BGE could obviously improve the wettability and dispersion state with resin matrix. Transmission electron microscope (TEM) showed that there had a strong chemical interaction between MWCNT-NH2 and EP, which led to the formation of a large tight sphere for MWCNT-NH2/epoxy pre-dispersion mixture. In contrast,MWCNT-BGE/epoxy pre-dispersion mixture exhibited a fluffy network structure, and some "tentacles" continually expanded to outside. And then,the various functionalized CNTs were added into different solvent and liquid curing agent to investigate the influence factor of CNTs dispersion stability. The results showed that the polarity of solvent、viscosity of liquid curing agent、diameter of nano-particle and environmental temperature could directly or indirectly influence the dispersion stability of CNTs suspensions.(2) The MWCNT-NH2 and MWCNT-BGE were homogeneously dispersed into TDE-85/MTHPA/MNA system and prepared the castings.The effect on curing mechanism.mechanical property、thermal property and dielectric property of different functionalized CNTs modified epoxy castings was investigated. The results showed that the MWCNT-NH2 and MWCNT-BGE could greatly take part in the formation of curing cross-linked network. After adding 0.5 wt% MWCNT-NH2 and MWCNT-BGE, the heat of curing reaction was increased by 44.9 J/g and 59.3 J/g, respectively. The glass transition temperature of composite castings were enhanced 11.8 ℃ and 14.1 ℃ and thermal decomposition temperature were improved 11 ℃ and 10.25 ℃ ,separately. Functionalized CNTs had played a perfect role of reinforcing epoxy resin matrix, and the mechanical and dielectric properties of CNTs/EP composites were also greatly improved.(3) The reticular MWCNT-BGE/epoxy pre-dispersion mixture was transferred to the interlayer of CFRP by well-designed spraying. The effect of MWCNT-BGE/epoxy pre-dispersion mixture on the properties of composite laminates was investigated. The results showed that the three-dimensional continuous conductive paths were formed by the wonderful electrical property of CNTs and carbon fiber (CF), the through-thickness electrical conductivity of 0.5 wt%MWCNT-BGE/epoxy pre-dispersion mixture modified CF/EP composite could reach to 2.87 S/cm. In addition, the interlaminar mechanical property of MWCNT-BGE/CF/EP composite laminates was also observably improved due to the pull-out and bridging effect of MWCNT-BGE and the interlaminar shear strength (ILSS) was higher than the standard level all the time. And this kind of novel multifunctional MWCNT-BGE/epoxy pre-dispersion mixture modified CF/EP composite laminates will be of great value for aviation and aerospace fields.