Low-temperature grafting of carbon nanotubes on carbon fibers and their composites

Abstract

The hybridization of carbon nanotubes (CNTs) and carbon fibers (CFs), which called as CNT-grafted CF has emerged as such an advanced and hierarchical material that can improve the reinforcing effect of CFs in composites and solve the dispersion problems of CNTs. Hierarchical structuring of the reinforcement is an effective method for improving the mechanical, electrical and thermal properties of the composites. Radially grown CNTs on CFs improve the radial stiffness and axial tensile strength of CF-reinforced composites, the interfacial shear strength (IFSS) of polymer composites, and the electrochemical performance as CF electrodes. Even CNT-grafted CF has these merits, many researches for CNT-grafted CF as reinforcement of composites could not show good mechanical properties because of the degradation of mechanical properties of the CFs while chemical vapor deposition (CVD) process which is for grafting of CNTs on CF. Some of researchers succeed to prevent degradation by using buffer layer coated on CF or control of catalysts layer deposited on CF but these methods are not suitable for macroscale process. Because of these limits, previous researchers could not show the mechanical performance of CNT-grafted CF reinforced composites in macroscale. Through our previous research, we succeed to grow CNTs on CF without degradation of the mechanical properties of CFs by using low-temperature process with Ni-Fe bimetallic catalyst. We lowered growth temperature of CNTs to below 500oC and succeed to inhibit the inter-diffusion between carbon and catalyst particles while CVD process. By using CNT-grafted CF manufactured by low-temperature process, we studied about the thermal/electrical/mechanical properties of CNT-grafted CF reinforced plastic composites. Tensile strength of CNT-grafted CFRP was increased 17% in unidirectional composites and 32% in woven composites compared to as-received CFRP. Increased interfacial shear strength (IFSS) was critically contributed to the strength of CFRP and we identified their failure mechanism by observation of fractured surface of CFRP. In addition, we manufactured CNT-grafted carbon fiber/carbon composites and characterized their thermal/electrical/mechanical properties. CNT-grafted CFs have excellent wettability to the liquid pitch which forms matrix of the C/C composites. Thus, CNT-grafted CF/carbon composites have much better mechanical/thermal properties especially through-the-thickness direction. Lastly, we developed continuous manufacturing process of CNT-grafted CF for mass production. Water vapor-assisted CVD was adopted to accelerate CVD process and T-zone furnace was designed to minimize shade effect. We optimized lab-scale continuous process for CNT-grafted CF with detailed parameters