Preparation And Properties Of Carbon Nanotubes Modified Carbon Fiber/Epoxy Composites

Carbon fiber/epoxy composite exhibits good mechanical properties, and hasobtained applications in many realms. However, the properties of epoxy matrix aremodest and the interfacial strength between fiber and matrix is relatively weak. Theyare considered to be fatal bottlenecks constraining the further improvement of overallproperties of composite. Besides, interlaminar performances of laminate compositeare poor. Then, as nano-scale material, carbon nanotubes (CNTs) were utilized tomodify carbon fiber/epoxy composite, due to their outstanding mechanical andelectrical properties.In the present work, freeze drying method was innovatively used for thepreparation of CNTs modified carbon fiber/epoxy composite from the point ofoptimizing CNT dispersion state in composite. Specifically，In two-dimensional carbon fiber fabric/epoxy composite, the feasibility ofpreparing continuous CNT networks using freeze drying method was discussed. Theresults demonstrated that: CNTs could be assembled to continuous and porous CNTnetworks in fabric with the assist of freeze drying technique. Most part of them werepreserved in composite due to the robustness of network structures, thus significantlyimproved through-thickness electrical conductivity of composite and had an effect oninterlaminar shear strength (ILSS).In unidirectional carbon fiber fabric/epoxy composite, the effect of CNTs withdifferent organization forms and characteristics on through-thickness properties ofcomposite was studied. Different drying methods of heat drying and freeze dryingwere utilized to affect CNT organization form. CNT characteristic was controlled bychoosing different solutions of non-functionalized CNTs (NOCNTs) or hydroxylmodified CNTs (OHCNTs). As a consequence, CNT networks modified compositedisplayed significantly better electrical performance than composite with CNTaggregates; NOCNT networks made the corresponding composite possess higherILSS value, whereas OHCNT networks impaired ILSS while enhancing flexuralstrength and modulus of composite. Beside, the formation mechanism of CNTnetworks was discussed, and could be described as “freeze drying within confinedspace”.In three-dimensional carbon fiber fabric (carbon fiber felt)/epoxy composite, theeffect of different drying methods, including heat drying and freeze drying, on composite was studied. The results indicated that compared to the commonlyused heat drying method, freeze drying method exhibited an advantage of keepingoriginal macro-structure of the felt and ameliorating CNT dispersion state.Accordingly, the conductivity and flexural strength of the composite fabricated byfreeze drying were significantly better than the composite fabricated by heat dryingmethod.