CARBON NANOFILLER MODIFIED CARBON FIBER EPOXY COMPOSITE FOR STRUCTURAL APPLICATION

Abstract

Carbon fiber (CF) reinforced epoxy composites are the most widely used fiber reinforced polymer composites (FRPs) in aerospace, automobiles, lightweight structures and many other industries. Properties, like, high strength and stiffness, coupled with low density, corrosion and fatigue resistance, make it better as compared to the conventional metallic counterparts. Despite these advantages, the anisotropic properties of FRPs and the brittle nature of the matrix often results in delamination and premature failure of structures. Hence, there is a need to improve the transverse and out of plane properties, without sacrificing the axial properties and maintaining low weight. The interfacial interaction between CF and epoxy has to be strong to achieve this. A number of techniques have been adopted to strengthen the interface, most of which involve modifying CF surface. Studies on modifying the matrix using nanofillers is quite limited, due to the difficulty in dispersion. Hence, this study aims at modifying the epoxy matrix using carbon nanofillers, as they have similar surface chemistry and properties as CF. It also focuses on improving the dispersion of carbon nanofillers inside epoxy matrix, by taking advantage of the synergy that exist among nanofillers having different morphologies. Thus, the overall aim of the current research is to explore the potential of synergistic effect of carbon nanofillers, with different morphologies, on CF epoxy composite for structural application. The carbon nanofillers of interest here are carbon nanotubes (CNT) with 1D structure, graphene (Gr) with 2D shape and nanodiamond (ND) with 3D morphology. The potential of ND, as a reinforcement to epoxy matrix, is investigated and compared with CNT and Gr, in terms of mechanical and thermal properties for a range of content 0.1-1 wt%. ND improves tensile strength (56%), elastic modulus (94%), hardness (470%) and % strain (66%) of epoxy, simultaneously, ii which is very remarkable as compared to Gr or CNT. Investigation on fractured surface of CNT-epoxy and Gr-epoxy composite revealed agglomeration as the prime reason behind the restricted efficiency of the reinforcement phases. Nanodiamonds showed great reinforcement efficiency to epoxy matrix. NanoDMA was performed on ND-epoxy composite to assess and understand the micron level phase distribution of ND in epoxy matrix and its effect on mechanical properties. The spherical morphology of ND has less tendency to agglomerate. So, its positive contribution towards dispersion, in binary combinations with CNT and Gr in epoxy composite, is investigated. Both mechanical and thermal properties are improved for CNT- epoxy and Gr-epoxy composite with the addition of ND, due to the improved exfoliation. No agglomerations were seen even at much higher reinforcement content. The improved exfoliation of Gr, with addition of ND, is quantified through scanning probe microscopy (SPM). Its effect on toughening behaviour of epoxy was predicted through numerical analysis, which were in good agreement with experimental results. After verifying the potential of ND, as an individual reinforcement and in binary combination, its role in boosting the synergy between Gr-CNT hybrid is investigated. Addition of ND to Gr-CNT hybrid helped in achieving a well exfoliated close knitted 3D network of reinforcement, which improved both tensile strength and fracture toughness quite significantly. This well exfoliated close knitted 3D network of nanofiller is then added to epoxy matrix. The CF laminated composite, fabricated through vacuum assisted resin transfer technique, using 3D network of nanofiller modified epoxy matrix. It is then evaluated for mechanical, thermal and interfacial properties. Improvement in interlaminar fracture toughness by ~260% and interfacial shear strength by ~16% with the addition of 3D network of nanofiller establishes the potential of the approach/route followed.