This study quantitatively defines the temperature induced chemical transformations and evolution of radial heterogeneity during the stabilisation of carbon fibre precursors.

Here we report on how residence time influences the evolution of the structure and properties through each stage of the carbon fibre manufacturing process. The chemical structural transformations and density variations in stabilized fibres were monitored by Fourier Transform Infrared Spectroscopy and density column studies. The microstructural evolution and property variation in subsequent carbon fibres were studied by X-ray diffraction and monofilament tensile testing methods, which indicated that the fibres thermally stabilized at longer residence times showed higher degrees of structural conversion and attained higher densities. Overall, the density of stabilized fibres was maintained in the optimal range of 1.33 to 1.37 g/cm3. Interestingly, carbon fibres manufactured from higher density stabilized fibres possessed lower apparent crystallite size (1.599 nm). Moreover, the tensile strength of carbon fibres obtained from stabilized fibres at the high end of the observed range (density: 1.37 g/cm3) was at least 20% higher than the carbon fibres manufactured from low density (1.33 g/cm3) stabilized fibres. Conversely, the tensile modulus of carbon fibres produced from low density stabilized fibres was at least 17 GPa higher than those from high density stabilized fibres. Finally, it was shown that there is potential to customize the required properties of resultant carbon fibres suiting specific applications via careful control of residence time during the stabilization stage.

Carbon fibre composites are lightweight, high performance materials with outstanding mechanical properties.

The energy requirements for the production of high quality carbon fiber and other carbon-based materials made by carbonization is a key factor limiting the commercial application of these materials. With the aim of enhancing the carbonization efficiency, we have prepared polyacrylonitrile (PAN) based precursor materials doped with high aspect-ratio cellulose nanofibers (CNF) derived from Australian spinifex grass (T. pungens). This was achieved by systematically investigating the rheology and electrospinning properties of composite fibers of PAN and CNF prepared at various CNF concentration levels and subsequently stabilized and carbonized. The carbon properties were characterized by X-ray diffraction and Raman spectroscopy. Upon carbonization, the incorporation of CNF into the PAN precursor led to changes in the crystallite and graphitic structure of the carbon materials, and these changes found to be closely related to the CNF concentration. CNF loadings of 0.5–2 wt % resulted in spinnable solutions with well-ordered carbon structures exhibiting a reduced Raman D/G ratio and an increased [002] band intensity by XRD. These spinifex CNF additives highlight a new approach for enhancing the energy efficiency of the carbonization process for PAN-based precursors.

Process parameters, especially in the thermal stabilization of polyacrylonitrile (PAN) fibers, play a critical role in controlling the cost and properties of the resultant carbon fibers. This study aimed to efficiently handle the energy expense areas during carbon fiber manufacturing without reducing the quality of carbon fibers. We introduced a new parameter (recirculation fan frequency) in the stabilization stage and studied its influence on the evolution of the structure and properties of fibers. Initially, the progress of the cyclization reaction in the fiber cross-sections with respect to fan frequencies (35, 45, and 60 Hz) during stabilization was analyzed using the Australian Synchrotron-high resolution infrared imaging technique. A parabolic trend in the evolution of cyclic structures was observed in the fiber cross-sections during the initial stages of stabilization; however, it was transformed to a uniform trend at the end of stabilization for all fan frequencies. Simultaneously, the microstructure and property variations at each stage of manufacturing were assessed. We identified nominal structural variations with respect to fan frequencies in the intermediate stages of thermal stabilization, which were reduced during the carbonization process. No statistically significant variations were observed between the tensile properties of fibers. These observations suggested that, when using a lower fan frequency (35 Hz), it was possible to manufacture carbon fibers with a similar performance to those produced using a higher fan frequency (60 Hz). As a result, this study provided an opportunity to reduce the energy consumption during carbon fiber manufacturing.