Extraordinary Improvement of the Graphitic Structure of Continuous Carbon Nanofibers Templated with Double Wall Carbon Nanotubes

Abstract

Carbon nanotubes are being widely studied as a reinforcing element in high-performance composites and fibers at high volume fractions. However, problems with nanotube processing, alignment, and non-optimal stress transfer between the nanotubes and surrounding matrix have so far prevented full utilization of their superb mechanical properties in composites. Here, we present an alternative use of carbon nanotubes, at a very small concentration, as a templating agent for the formation of graphitic structure in fibers. Continuous carbon nanofibers (CNF) were manufactured by electrospinning from polyacrylonitrile (PAN) with 1.2% of double wall nanotubes (DWNT). Nanofibers were oxidized and carbonized at temperatures from 600 °C to 1850 °C. Structural analyses revealed significant improvements in graphitic structure and crystal orientation in the templated CNFs, with the largest improvements observed at lower carbonization temperatures. In situ pull-out experiments showed good interfacial bonding between the DWNT bundles and the surrounding templated carbon matrix. Molecular Dynamics (MD) simulations of templated carbonization confirmed oriented graphitic growth and provided insight into mechanisms of carbonization initiation. The obtained results indicate that global templating of the graphitic structure in fine CNFs can be achieved at very small concentrations of well-dispersed DWNTs. The outcomes reveal a simple and inexpensive route to manufacture continuous CNFs with improved structure and properties for a variety of mechanical and functional applications. The demonstrated improvement of graphitic order at low carbonization temperatures in the absence of stretch shows potential as a promising new manufacturing technology for next generation carbon fibers.

Multi-step mechanism of carbonization in templated polyacrylonitrile derived fibers: ReaxFF model uncovers origins of graphite alignment

“…Recently, the addition of nanofillers such as carbon nanotubes [3][4][5][6][7][8] (CNTs) or other graphitic structures [8][9][10][11][12][13][14] to polymers has been explored as a potentially useful approach for the production of composites with superior thermal stability and enhanced mechanical and electrical…”

“…The procedures used to combine fillers with polymer have varied from electrospinning of components [5,8,10,11,15,16] to multistep protocols [3,4,11]. The most recent experiments involve dispersion of the filler components in solvent with subsequent electrospinning, and heat-treatment to give various degrees of structural re-ordering, including carbonization.…”

“…Instead of trying to achieve high volume fraction for nanoreinforcement, low quantities of CNT or graphene-oxide (GO) nanoparticles were used to alter the structure of carbon nanofibers via templating. [8,12] Good quality continuous nanofibers were produced by electrospinning of PAN/nanoinclusion solutions and carbonized at various temperatures. Good alignment of inclusions along the fiber axis were observed.…”

“…Generally, the thermal treatment of spun nanofiller-modified precursor fibers [8,12] is similar to the treatment of PAN-only fibers [17,18], and involves three stages: (i) stabilization, (ii) carbonization, and optional (iii) graphitization. The stabilization stage [19] is initiated by heating of stretched fibers at 180°C-300°C.…”

Mechanisms for Imparting Conductivity to Nonconductive Polymeric Biomaterials

“…As a 2D atomic structure, graphene has typically been applied as a coating of polymers [ 139,143 ] although it can be stacked or formed into plate or ribbon like structures and integrated into polymer networks. [ 131 ] The metallic and carbon based materials outlined are high strength materials with high conductivity.…”