Carbon Nanofiber Treatment Effects on Composite Properties
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Carbon Nanofiber Treatment Effects On Composite Properties David J. Burton, D. Gerald Glasgow, Choongyong Kwag, and Max L. Lake, Applied Sciences Inc., PO Box 579, Cedarville, OH 45314
ABSTRACT Carbon nanofibers (CNF) are vapor grown carbon fibers grown catalytically from gaseous hydrocarbons using metallic catalyst particles. While this type of carbon fiber has been known for many years, only recently have composite properties been studied. Rules for composite synthesis teach that composite properties depend on several key parameters, including fiber-matrix interphase and fiber aspect ratio. Good adhesion between these fibers and matrix resins is essential for the performance of CNF based composites, so the mechanical properties of composites are strongly influenced by fiber surface morphology and chemistry. This work examines the fiber-matrix adhesion problem as influenced by CNF fiber surface area and surface energy, and the impact of aspect ratio on composite electrical properties.
INTRODUCTION Vapor grown carbon fibers (VGCF) have been studied for over twenty-five years, owing to the novel growth mechanism, noteworthy physical properties, and the promise of low cost manufacturing of this type of carbon fiber. Representative milestones were early reports of Professor Morinobu Endo at Shinshu University in Japan, who made observation of the superior physical properties of VGCF [1], and suggested uses in high performance CFRP, CFRM, electricity and electronics, as well as in aviation, space, and biotechnology. Tibbetts et al. elaborated on this theme [2], noting that while the discontinuous nature of the fiber would likely preclude the most demanding aerospace structural applications, VGCF would be well suited to applications for chopped fiber composites using plastics, ceramics, metals, and cement matrices. This assessment was supported with the observation of the highly graphitic nature and physical properties of VGCF, comparable or superior to conventional PAN-based carbon fiber. Cited anticipated uses range from electrical, including emi shielding, through thermal and structural applications. Tibbetts also commented on the development of a continuous process for production of a nanofiber version of VGCF, and noted that the vapor grown carbon nanofiber (VGCNF) was expected to have equivalent properties as those measured for the macroscopic version, but would be less expensive to produce [3]. Daumit compared the properties and potential of PAN and pitch-based carbon fibers as well as VGCF, [4] and observed that VGCF offers an excellent performance/cost ratio which will permit competition with chopped carbon fiber, fiberglass, carbon black, and asbestos. Other researchers who anticipated the advantages of vapor grown carbon nanofibers in composites for various applications included R.T.K. Baker [5] and D.D.L. Chung [6], as well as our own R&D group [7]. Models describing the strength and modulus of other short fiber reinforced composites, that is, paper, suggest that carbon nanofiber can be used to produce exce
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