Here we present a novel laser process to generate carbon nanofiber nonwovens from polyacrylonitrile. We produce carbon nanofabrics via electrospinning followed by infrared laser-induced carbonization, facilitating high surface area and well-controlled hierarchical porosity. The process allows precise control of the carbonization conditions and provides high nanoscale porosity. In comparison with classical thermal carbonization, the laser process produces much higher surface areas and smaller pores. Furthermore, we investigate the carbonization performance and the morphology of polyacrylonitrile nanofibers compounded with graphene nanoplatelet fillers.
Porous carbon materials represent prospective materials for absorbers, filters, and electronic applications. Carbon fibers with high surface areas can be produced from polyacrylonitrile and spun as thin fibers from solution. The resulting polymer fibers are first stabilized to obtain conjugated ribbons and then carbonized to graphitic structures in a second high‐temperature step in an inert atmosphere. In this study, we investigated a previously described fast laser‐heating process that delivered fibers with a higher crystallinity and surface area compared to the thermally carbonized fibers. In a subsequent KOH‐activation step, the crystalline domains were exfoliated, and the surface of the fibers became macroporous. This led to a reduced specific surface area but a higher capacitance compared to thermally carbonized nanofibers. We report the electrochemical properties of the electrochemical cells and discuss their potential applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46398.
Carbon fiber reinforced plastics are excellent materials for applications in lightweight constructions in the automobile or aviation sectors due to their 2.5-fold higher specific strength compared to aluminum. However, the high manufacturing costs of carbon fibers are one of the main limiting factors for the exploration of new fields of applications. The precursor fibers mostly consist of polyacrylonitrile which is transformed into carbon fibers in furnace processes. Almost one half of the manufacturing costs can be assigned to the stabilization and carbonization of the carbonaceous precursor fibers. The furnace processes takes up to 2 h and produces high energy costs due to the needed temperatures of about 1500 °C. In this paper, a new laser-based manufacturing process for carbon fibers is presented. The process is developed at the Fraunhofer Institute for Laser Technology (ILT) and shows potential for the implementation of a fabrication process with reduced energy and time costs compared to the conventional furnace based approach. Furthermore, the fiber stabilization can now be realized with higher heating rates. Thus, shorter stabilization times are potentially needed. The exothermal energy from the stabilization reaction can be extracted more efficiently via the cool ambient air which reduces the risk of thermal damage of the fibers tremendously. Furthermore, the excellent adjustability of the spatial and temporal energy deposition via laser allows an adaptive process control which has the potential to fabricate fibers with increased mechanical properties in shorter times. First investigations of the stabilization process indicate that a careful choice of the process parameters allows for inducing distinct temperature profiles in the fibers which influences the resulting carbon fiber structure. Furthermore, first investigations on laser-based carbonization show that the fabrication of fibers with tensile force of up to 8 cN is possible.
Carbon-based materials are used as electrode materials in a wide range of electrochemical applications, e.g., in batteries, supercapacitors, and fuel cells. For these applications, the electronic conductivity of the materials plays an important role. Currently, porous carbon materials with complex morphologies and hierarchical pore structures are in the focus of research. The complex morphologies influence the electronic transport and may lead to an anisotropic electronic conductivity. In this paper, we unravel the influence of the morphology of rotationally spun carbon fiber mats on their electronic conductivity. By combining experiments with finite-element simulations, we compare and evaluate different electrode setups for conductivity measurements. While the “bar-type method” with two parallel electrodes on the same face of the sample yields information about the intrinsic conductivity of the carbon fibers, the “parallel-plate method” with two electrodes on opposite faces gives information about the electronic transport orthogonal to the faces. Results obtained for the van-der-Pauw method suggest that this method is not well suited for understanding morphology-transport relations in these materials
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