Influence of MWCNTs on Fracture Toughness of MWCNTs/Nickel-Pitch Fiber/Epoxy Composites

Abstract

ABSTRACT: The influence of MWCNTs on fracture toughness properties of MWCNTs/Nickel-Pitch Fibers/epoxycomposites (MWCNTs/Ni-PFs/epoxy) was investigated according to MWCNTs content. Nickel-Pitch-based carbonfibers (Ni-PFs) were prepared by electroless nickel-plating. The surface properties of Ni-PFs were determined byscanning electron microscopy (SEM) and X-ray photoelectron spectrometry (XPS). The fracture toughness ofMWCNTs/Ni-PFs/epoxy was assessed by critical stress intensity factor ( K IC ) and critical strain energy release rate( G IC ). From the results, it was found that the fracture toughness properties of MWCNTs/Ni-PFs/epoxy were enhancedwith increasing MWCNTs content, whereas the value decreased above 5 wt.%. MWCNTs content. This was probablyconsidered that the MWCNTs entangled with each other in epoxy due to an excess of MWCNTs. Key Words: Pitch Fibers, Multi-walled Carbon Nanotubes (MWCNTs), Electroless Nickel-plating, Epoxy Composites,Fracture Toughness 1. INTRODUCTION These days, pitch-based carbon fibers (pitch fibers) havereceived considerable attention due to their advantages such ashigh carbon yield, low cost, and good graphitizability that arecharacteristic of pitches derived from coal tar or petroleum.These excellent properties of pitch fibers are transferred tomatrix through their interface. Accordingly most of pitch-based carbon fibers reinforced composite properties are con-trolled by interfacial adhesion between pitch fibers and matrixresins [1,2]. Carbon nanotubes (CNTs) are a typically nanofillers andwere discovered as fullerene-related structures by Iijima atNEC laboratory of Tsukuba in 1991 [3]. Carbon nanotubesalso have several excellent properties including electronic con-ductivity, thermal conductivity, corrosion resistance, highstrength, Young's modulus and so on [4-6]. In this study, epoxy matrix was reinforced with Pitch fibersand multi walled carbon nanotubes (MWCNTs) to enhancethe fracture toughness of the composites. In order to improveinterfacial adhesive strength between fillers and matrix resins,the filler surface is commonly modified by numerous surfacetreatments [7-9]. Therefore the pitch fibers and MWCNTswere electrolessly nickel-plated and acidic treated, respectively.The objective of this study is to evaluate the influence ofMWCNTs on the fracture toughness of MWCNTs/Ni-PFs/epoxy composites. The pitch fiber surfaces were characterizedby SEM and XPS to confirm the morphology of the fiber sur-faces and the elemental compositional changes. The criticalstress intensity factor (