ABSTRACT
Carbon nanofibers (CNFs) are discontinuous hollow filaments having a diameter of approximately 100 nm (nanometer). The promise of these filaments, produced by a catalytic process in which metal particles are exposed to free carbon at elevated temperatures, derives from the fact that the filaments display physical properties approaching those of single-crystal graphite, including high thermal and electrical transport values and high tensile strength and modulus.1 These properties can improve engineered polymers for structural and conducting applications such as static discharge, electrostatic painting, and radio frequency interference shielding. These discontinuous fibers lend themselves naturally to fabricating composite materials that utilize their short length.2-4 Because shortfiber-reinforced composites can be fabricated without the expensive limitations of textile processing, they offer advantages in ease of manufacture and low cost. For example, CNF/ polymer composites may be continuously fabricated by extrusion or injection molding, allowing for both high volume production and recycling. A review of CNF composites was recently published by Tibbetts et al.5 Previous work has shown that CNFs in a polypropylene thermoplastic matrix can yield considerably improved composite strength and stiffness.6-8 Similarly, CNF has been shown to hold promise as an electrical conductivity additive.9, 10 The sub-micron dimensions of CNFs and consequent high surface area require novel procedures to capture the properties of graphite in polymer composites. Among the important factors is an appropriate interphase between the graphitic filaments and the matrix polymer. The optimal interphase for a given polymer would provide fiber-matrix adhesion to maximize mechanical properties such as tensile strength and would allow for ease of dispersion and good electron transport between the fibers. A large body of work describes surface treatment of now-common continuous carbon fibers.11 In comparison, the science and technology of surface modification for CNFs is only beginning to emerge.
