Carbon Nanofiber Reinforced Composites for Enhanced Conductivity, Strength, and Tensile Modulus
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Carbon Nanofiber Reinforced Composites for Enhanced Conductivity, Strength, and Tensile Modulus Gary G. Tibbetts, Ioana C. Finegan1, and Choongyong Kwag Materials and Processes Laboratory, General Motors R&D Center 30500 Mound Rd. Warren, MI, 48090, USA 1 Industrial and Engineering Technology, Central Michigan University, Mount Pleasant, MI, 48859, USA ABSTRACT Carbon nanofibers of diameter 200 nm may be used as an additive to thermoplastics for applications requiring electrical conductivity and enhanced mechanical properties. The electrical properties of nanofiber in thermoplastics such as nylon and polypropylene and are very attractive compared with those provided by other conventional conducting additives. Because of the low diameter of the nanofibers used, the onset of electrical conductivity (percolation threshold) can be below 1 volume %. Because of the highly conductive nature of the fibers, particularly after a graphitization step, the composites can reach resistivities as low as 0.15 Ohm cm. These conducting composites may be used for applications such as radio frequency interference shielding, primerless electrostatic painting, and static discharge. In order to make composites having excellent mechanical properties, good adhesion between fiber and matrix is essential. Carbon nanofiber-matrix adhesion was studied after surface treating the fibers using a variety of methods. Among as-grown fibers, those produced with longer gas phase feedstock residence times in the fiber growth reactor were less graphitic but adhered to a polypropylene matrix better, giving improved tensile strength and modulus Two chemical treatments were found to be somewhat effective in increasing tensile strength, but both decreased the modulus. . A modest degree of oxidation was also found to increase adhesion to the matrix and increase composite tensile strength, while extended oxidation attacked the fibers sufficiently to decrease composite properties. INTRODUCTION Vapor-grown carbon fibers (VGCF) of about 200 nm in diameter may be used for many applications. Since their intrinsic modulus and tensile strength are high, they may be compounded with thermoplastics and used to form composites of good mechanical properties. Furthermore, since their intrinsic electrical conductivity approaches that of graphite, they may be used to make electrically conductive composites. Even though the constraints of inexpensive fabrication require that the composites be comprised of non-oriented fibers, yet good properties T2.3.1 Downloaded from https://www.cambridge.org/core. Karolinska Institutet University Library, on 28 Feb 2020 at 19:52:56, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-733-T2.3
may nevertheless be obtained for both applications. In this paper we will show that relatively small quantities of VGCF can improve both the mechanical and electrical properties of thermoplastics. EXPERIMENTAL The PYROGRAF VGCF were produced at the pilot plant of Applied Science,
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