Carbon fiber (CFs) is a kind of high-performance inorganic fiber. After compounding with polymer, ceramic or metal material, the composite material with high strength, high rigidity, low density, corrosion resistance and fatigue resistance is prepared in aerospace, automotive, military , Sports and other fields have important uses, so in the laboratory and industrial production, carbon fiber materials are the key research objects. As another star carbon material, graphene has attracted much attention since its birth. Among them, a lot of research work on high-strength polymer-based composite materials shows that graphene with unique physical and chemical properties can greatly improve the mechanical strength of the material under the condition of very low addition amount. Can the microscopic two-dimensional graphene improve the mechanical strength of the macroscopic one-dimensional carbon fiber?
Recently, the research team of Professor Xiaodong Li and Professor Adri CT van Duin of the University of Virginia and the research team of Professor Leonid V. Zhigilei of Pennsylvania State University have found that adding 0.075 wt% of mechanically exfoliated graphene can increase the tensile strength and Young's modulus of carbon fiber by 225 % And 184%. By characterizing and analyzing the microstructure and macroscopic mechanical properties of various graphene content composite carbon fibers, and combining the results of computer simulations, the authors found that the improvement of the mechanical strength of carbon fibers by trace graphene stems from the following three factors:
(1) Graphene reduces the size of holes / defects inside the carbon fiber and improves its integrity;
(2) Graphene optimizes the arrangement of carbon fiber precursor polyacrylonitrile (PAN) fiber molecular chains;
(3) Graphene can improve the mechanical strength of the carbon fiber body.
This research work not only explores the mechanism of graphene-reinforced carbon fibers, but also provides theoretical guidance for the preparation of higher-strength, high-modulus carbon fibers; at the same time, it also provides research work for the preparation of high-performance carbon fibers through adjustment of microstructure A good idea. This research work was published in "Science Advances" as a paper entitled "Graphene reinforced carbon fibers".
The author disperses different amounts of mechanically peeled graphene in a PAN / DMSO solution and obtains PAN / graphene composite fibers by wet spinning; then CF / graphene composite carbon fibers are obtained after high temperature treatment of pre-oxidation-carbonization-graphitization . The tensile test results of the composite carbon fiber show that adding a small amount of graphene can greatly increase the tensile strength and Young's modulus of the carbon fiber while maintaining the elongation at break: the tensile strength and Young's modulus of the original carbon fiber are At 589 MPa and 82 GPa, the tensile strength and Young's modulus of the composite carbon fiber after adding 0.075 wt% graphene were 1916 MPa and 233 GPa, respectively, an increase of 225% and 184% compared to the original carbon fiber. The microstructure test results of various composite carbon fibers show that the introduction of graphene reduces the size of pores / defects inside the carbon fiber and improves its integrity.
The composite carbon fiber added with 0.1 wt% graphene has higher regularity, but the tensile results show that its strength and modulus are lower than the composite carbon fiber containing 0.075 wt%. What is the reason? According to the results of nano X-ray tomography, the authors found that although the high content of graphene is beneficial to improve the fiber regularity and reduce the axial cracks of the fiber, it will greatly increase the longitudinal spherical nano defects of the fiber, which will reduce the mechanical strength of the fiber . In order to deeply explore the mechanism of graphene's influence on the mechanical properties of carbon fiber, the author conducted research and analysis on the entire preparation process of composite carbon fiber and found that a small amount of graphene will increase the viscosity of the PAN / DMSO solution, which can increase the solidification of PAN fiber Regularity in the process to reduce defects in the final carbon fiber; microstructure characterization and mechanical testing of the pre-oxidized and carbonized PAN / graphene composite fiber, it was found that the fiber containing 0.075 wt% graphene showed all stages The highest mechanical strength and structural regularity. The XRD and TGA test results of the graphitized composite fiber show that the addition of graphene can increase the carbon residue and the degree of graphitization of the carbon fiber.
In order to understand the impact of graphene on the structure of carbon fibers at the molecular level, the author conducted simulations and molecular simulations. ReaxFF simulation results show that graphene has unique edge reactivity-PAN can form five-membered, six-membered and seven-membered carbon rings with graphene edges during heat treatment; at the same time, the addition of graphene also increases the six-membered ring Arrange regularity and residual carbon rate. Molecular simulation results show that graphene can promote partial rearrangement of PAN molecular chains, thereby reducing the spacing of PAN molecular chains, which is beneficial to reduce defects in carbon fibers and improve crystallinity, thereby improving the mechanical properties of carbon fibers.
The authors found that the introduction of a small amount of graphene can significantly improve the mechanical strength of carbon fiber with PAN fiber as the precursor, and combined with experimental and simulation results from the molecular point of view to explore the strengthening mechanism of graphene, for the future preparation of low cost and high strength The carbon fiber material provides a theoretical basis.
Original link: https://advances.sciencemag.org/content/6/17/eaaz4191