Recent Progress in Fabrication, Structure, and Properties of Carbon Fibers

Hierarchical Micro/Mesoporous Carbons Synthesized with a ZnO Template and Petroleum Pitch via a Solvent-Free Process for a High-Performance Supercapacitor

Hierarchical micro/mesoporous carbons were prepared using ZnO nanoparticles as hard templates and a petroleum industrial-residual pitch as the carbon source via a solvent-free process. The ZnO templates can be easily removed using HCl(aq), thereby avoiding limitations present in conventional porous silica templating approaches that require highly corrosive HF(aq) for template removal. Notably, the proposed solvent-free synthetic method from low-cost pitch to high-value porous carbons is a friendly process with respect to our overexploited environment. With the combination of ZnO nanoparticles and pitch, the surface area (76-548 m² g^-1) of the resultant mesoporous carbons increases with an increase in the weight ratios of ZnO to pitch. Furthermore, the hierarchical micro/mesoporous carbons with a large surface area (854-1979 m² g^-1) can be feasibly fabricated by only adding an appropriate amount of an activating agent. Meanwhile, N-doped hierarchical porous carbons can be achieved by carbonizing the blend of these materials with melamine. For supercapacitor application, the resultant carbons exhibit a high capacitance up to 200.5 F g^-1 at 5 mV s^-1 using LiClO₄/PC as the electrolyte in a symmetrical two-electrode cell. More importantly, the coin-cell supercapacitor based on porous carbons achieved a capacitance of 94 F g^-1 at 5 mV s^-1 and 63% capacitance retention at 500 mV s^-1, thereby holding the potential for commercialization.

Dynamic Self-Stiffening and Structural Evolutions of Polyacrylonitrile/Carbon Nanotube Nanocomposites

The self-stiffening under external dynamic strain has been observed for some artificial materials, especially for nanocomposites. However, few systematic studies have been carried out on their structural evolutions, and the effect of the types of nanofillers was unclear. In this study, we used a semicrystalline polymer, polyacrylonitrile (PAN), and various types of carbon nanomaterials including C₆₀, carbon nanotube (CNT), and graphene oxide (GO). An external uniaxial dynamic strain at small amplitude of 0.2% was applied on the prepared nanocomposite films. It was observed that PAN/CNT exhibited significant self-stiffening behavior, whereas PAN/GO showed no response. Systematic characterizations were performed to determine the structural evolutions of PAN/CNT film during dynamic strain testing, and it was found that the external dynamic strain not only induced the crystallization of PAN chains but also aligned CNT along the strain direction.

Carbonization with Misfusion: Fundamental Limits of Carbon-Fiber Strength Revisited

D-loops, a new type of structural defect in carbon fibers, are presented, which have highly detrimental effect on their mechanical properties and can define a new fundamental upper limit to their strength. These defects form exclusively during polyacrylonitrile carbonization, act as stress concentrators in the graphitic basal plane, and cannot be removed by local annealing.

Ordered Silica Nanoparticles Grown on a Three-Dimensional Carbon Fiber Architecture Substrate with Siliconborocarbonitride Ceramic as a Thermal Barrier Coating

Hierarchical structure consisting of ordered silica nanoparticles grown onto carbon fiber (CF) has been fabricated to improve the interfacial properties between the CFs and polymer matrix. To improve the reactivity of CFs, their surface was modified using poly(1,4-phenylene diisocyanate) (PPDI) via in situ polymerization, which also resulted in the distribution of numerous isocyanate groups on the surface of CFs. Silica nanoparticles were modified on the interface of CF-PPDI by chemical grafting method. The microstructure, chemical composition, and interfacial properties of CFs with ordered silica nanoparticles were comprehensively investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Results indicated an obvious increase in the interfacial shear strength, compared to that of CF precursor, which was attributed to silica nanoparticles interacting with the epoxy resin. Furthermore, siliconborocarbonitride (SiBCN) ceramic was used as thermal barrier coating to enhance 3D CF architecture substrate antioxidant and ablation properties. Thermogravimetric results show that the thermal stability of the CF with SiBCN ceramic layer has a marked increase at high temperature.

High-speed roll-to-roll manufacturing of graphene using a concentric tube CVD reactor

We present the design of a concentric tube (CT) reactor for roll-to-roll chemical vapor deposition (CVD) on flexible substrates, and its application to continuous production of graphene on copper foil. In the CTCVD reactor, the thin foil substrate is helically wrapped around the inner tube, and translates through the gap between the concentric tubes. We use a bench-scale prototype machine to synthesize graphene on copper substrates at translation speeds varying from 25 mm/min to 500 mm/min, and investigate the influence of process parameters on the uniformity and coverage of graphene on a continuously moving foil. At lower speeds, high-quality monolayer graphene is formed; at higher speeds, rapid nucleation of small graphene domains is observed, yet coalescence is prevented by the limited residence time in the CTCVD system. We show that a smooth isothermal transition between the reducing and carbon-containing atmospheres, enabled by injection of the carbon feedstock via radial holes in the inner tube, is essential to high-quality roll-to-roll graphene CVD. We discuss how the foil quality and microstructure limit the uniformity of graphene over macroscopic dimensions. We conclude by discussing means of scaling and reconfiguring the CTCVD design based on general requirements for 2-D materials manufacturing.

Polyacrylonitrile fibers containing graphene oxide nanoribbons

Graphene oxide nanoribbon (GONR) made by the oxidative unzipping of multiwalled carbon nanotube was dispersed in dimethylformamide and mixed with polyacrylonitrile (PAN) to fabricate continuous PAN/GONR composite fibers by gel spinning. Subsequently, PAN/GONR composite fibers were stabilized and carbonized in a batch process to fabricate composite carbon fibers. Structure, processing, and properties of the composite precursor and carbon fibers have been studied. This study shows that GONR can be used to make porous precursor and carbon fibers. In addition, GONR also shows the potential to make higher mechanical property carbon fibers than that achieved from PAN precursor only.

Effective Surface Functionalization of Carbon Fibers for Fiber/Polymer Composites with Tailor-Made Interfaces

Composites between carbon fibers (CFs) and heterogeneous materials have been widely studied and their fabrication techniques have been developed. However, their hydrophobic surfaces make it difficult to disperse CFs into hydrophilic resins, which results in weak junctions with ceramics. To develop high-strength composite fibers, it is important to design interfacial chemical bonds. Thus, surface-modification techniques of CFs have recently become the main focus and their interfaces have been characterized by various analytical methods. In this Minireview, various techniques that modify the CF surface by coating with inorganic polymers (metal oxide compounds) are highlighted, and the applications of novel nanocomposite fibers are also described. Furthermore, interfacial bonds between CFs and polymer resins are reviewed and discussed in terms of CF-reinforced plastics and their future prospects.

Carbon nanotube core graphitic shell hybrid fibers

A carbon nanotube yarn core graphitic shell hybrid fiber was fabricated via facile heat treatment of epoxy-based negative photoresist (SU-8) on carbon nanotube yarn. The effective encapsulation of carbon nanotube yarn in carbon fiber and a glassy carbon outer shell determines their physical properties. The higher electrical conductivity (than carbon fiber) of the carbon nanotube yarn overcomes the drawbacks of carbon fiber/glassy carbon, and the better properties (than carbon nanotubes) of the carbon fiber/glassy carbon make up for the lower thermal and mechanical properties of the carbon nanotube yarn via synergistic hybridization without any chemical doping and additional processes.

Structural Polymer-Based Carbon Nanotube Composite Fibers: Understanding the Processing-Structure-Performance Relationship

Among the many potential applications of carbon nanotubes (CNT), its usage to strengthen polymers has been paid considerable attention due to the exceptional stiffness, excellent strength, and the low density of CNT. This has provided numerous opportunities for the invention of new material systems for applications requiring high strength and high modulus. Precise control over processing factors, including preserving intact CNT structure, uniform dispersion of CNT within the polymer matrix, effective filler–matrix interfacial interactions, and alignment/orientation of polymer chains/CNT, contribute to the composite fibers’ superior properties. For this reason, fabrication methods play an important role in determining the composite fibers’ microstructure and ultimate mechanical behavior. The current state-of-the-art polymer/CNT high-performance composite fibers, especially in regards to processing–structure–performance, are reviewed in this contribution. Future needs for material by design approaches for processing these nano-composite systems are also discussed.

Realizing ultrahigh modulus and high strength of macroscopic graphene oxide papers through crosslinking of mussel-inspired polymers

Covalently crosslinked graphene oxide papers (GOPs) with enhanced mechanical properties are prepared by a strategy involving crosslinking by means of intercalated polymers. The strength and modulus of the crosslinked GOPs increase by 115% and 550%, respectively, compared to the pristine GOPs. These results broaden the potential applications of graphene, and the crosslinking strategy will open the door to the assembly of other nanometer-scale materials.