Microstructure Design And Mechanical Properties Of Graphene-based Fibers

After hundreds of millions of years of evolution,natural biological materials have achieved the perfect unity of structure and function,such as wood,fish scales and shells.Among them,the shell mother-of-pearl benefits from the precision structure of the alternating layers of soft and hard substances inside,which makes it has excellent properties such as stiffness,strength and toughness at the same time,so it has become the focus of researchers’ research and imitation.Scientists often choose materials with large aspect ratio and excellent mechanical properties as the hard phase in the staggered laminated structure to prepare shell-like structure materials with both excellent performance and rich functions.Among them,graphene is often selected as an ideal material for preparing shell-like structural materials due to its high strength,large aspect ratio,and light weight.At present,graphene-based composite materials have achieved considerable development.Among the many graphene derivatives,graphene fiber has attracted great attention due to its light weight,high strength and flexibility,since it was created by Gao and Xu in 2011.In this paper,the strengthening and toughening mechanism of the shell structure has been utilized.The modified Hummers method has been used to prepare graphene oxide(GO),which has been used as the hard phase in the "brick-mud" structure,and the polyurethane(TPU)with better bonding properties has been selected as the soft phase.The GO-TPU composite fiber with shell-like structure has been prepared by wet spinning process.These fibers have different microstructures.The tensile test results show that the strength and toughness of these composite fibers first increase and then decrease with the increase of TPU content.The tensile shear chain model and finite element simulation have been combined to analyze the mechanical properties of these GO-based composite fibers.The results show that the internal stress distribution can be optimized by adjusting the microstructure between the hard "brick" of GO and the soft "mortar" of TPU,and then the macro-mechanical properties of the fiber can be improved.In addition,it can be found from the above research that the interface bonding between TPU and GO is another key factor affecting the mechanical properties of composite fibers.Therefore,carbon nanotubes(CNTs)have been added to the layered structure to improve the interface bonding characteristics and stress transfer efficiency between the "brick" and the "mortar",and further exert the excellent load-bearing characteristics of GO sheets,thereby improving the tensile strength and toughness of the composite fiber.What’s more,chemical reduction of these GO-based composite fibers has been performed to further increase their mechanical properties.In addition,it can be seen from the above research that when TPU and GO are in a certain mass ratio,the composite fiber exhibits better mechanical properties.However,the current industrial manufacturing is moving towards a more convenient and environmentally friendly direction.Therefore,a dry spinning process with a simpler preparation process has been used to spin the GO-TPU mixed solution with a specific mass ratio.At the same time,the ABAQUS simulation software has been used to observe the influence of internal defects on the macromechanical properties of the fiber.The results show that the dry-spun fiber has minor internal hole defects than the wet-spun fiber,so its mechanical properties show obvious advantages compared with the wet-spun fiber.This result shows that the dry spinning process can effectively control the internal microstructure of the fiber,improve the internal stress distribution and load transfer efficiency,then realize the optimization of its macro mechanical properties.In summary,in this paper wet spinning has been used to prepare GO-based composite fibers.What’s more,the tensile-shear chain model and finite element simulation have been combined to analyze the strengthening and toughening mechanism of its microstructure and interface.In addition,chemical reduction of the GO-based composite fibers has been performed to further increase their mechanical properties.Based on the above work,the GO-TPU composite fiber has been prepared by the dry spinning method with a simpler process,and the failure mechanism of its internal defects has been analyzed by ABAQUS.These studies will provide useful guidance for the optimization strategy of the internal microstructure of the GO composite fiber and the improvement of the preparation process.