Optimization of carbon fiber surfaces for reinforcement in advanced polymer composites

© 2018 by DEStech Publications, Inc. All rights reserved. This paper summarizes recent efforts within our research group to optimize the interfacial adhesion of carbon fiber reinforced polymer composites (CFRPs). This effort has been approached by several avenues including surface modification of carbon fibers, and the use of molecular dynamics to determine key interfacial interactions determining optimal adhesion. Typically, surface manipulation of carbon fibers is carried out using reductive electrochemical techniques, employing irreversible single electron reduction of aryldiazonium salts. Though recent efforts have shown oxidative surface grafting of carbon fibers is possible using the Kolbe decarboxylation reaction. Both approaches create a fiber which possesses a covalently bound surface modification, able to present a myriad of chemistries to the supporting resin. Determination of interfacial shear strength (IFSS), using single filament fragmentation in epoxy resin, has shown IFSS gains of over 150%, relative to pristine unsized fiber. Interrogation of the fiber-matrix interface using molecular dynamics simulation has shown that a large degree of the IFSS gains are derived from the molecular 'drag' effect of the surface bound molecules through the polymer phase. Further benefits of this approach can also be realized by combining the surface manipulation techniques with novel sizing agents, able to plasticize the localized resin around the carbon fiber, giving a gradient interphase. When used in concert, the synergistic effects of surface modification and interphase manipulation has realized IFSS gains >250% relative to control fibers.