| With the continuous promotion of the carbon neutral policy,the demand for carbon fibre composite materials in transportation,wind power and other industries is increasing.As the widespread application of carbon fibre composite materials,the issue of recycling and reuse for them has attracted more and more attention.Recycled carbon fibre(r CF)is a high-value product recovered from waste composites or semi-finished products.It inherits most of the excellent properties from the virgin carbon fibre,including high specific strength,specific stiffness,high electrical conductivity,good thermal conductivity and so on.However,the r CF is usually in a discontinuous,messy and fluffy state,yet has no sizing agent on its surface.These characteristics make it difficult to process in secondary reuse,resulting in poor mechanical properties and low added value of the prepared r CF composite products.In order to solve above problem,from the perspective of high-efficiency and value-increment reuse of r CF,this paper systematically studies the effects of the arrangement state(dispersion and orientation)as well as surface/interface microstructure regulation of r CF on the mechanical and electromagnetic protection properties of its composites,in order to develop a structure-function integrated r CF composite with high-value feature.(1)Aiming to solve the problems of low fibre volume content,poor dispersion and interface bonding of r CF in composites,through combining process parameter optimization of wet-laid technology and fibre surface modification,r CF non-woven fabric with fibre well dispersed is successfully prepared for reinforcing composites.Benefit from the uniform dispersion of fibres and its excellent interfacial bonding with the matrix,PDA-r CF/EP composites show excellent mechanical properties,with tensile strength and flexural strength reaching 147.9 MPa and 177.2 MPa respectively.The perfect fibre conductive network also endows the composite with excellent electromagnetic shielding performance(_up to 40 d B).(2)The existing wet-laid technology was improved,and the geometry of the tapered nozzle was designed and optimized through Computational Fluid Dynamics.Thus,r CF non-woven fabric(length>100 m,width>500 mm)with high orientation structure(alignment degree=83.5%)is successfully prepared in large scale,whose fibre volume fraction in the composite can exceed 40%.The tensile strength and flexural strength of quasi unidirectional composites prepared from aligned r CF non-woven fabrics reach 774.8 and678.2 MPa respectively.In addition,the effects of fabrics-ply angle and order on the mechanical properties and electromagnetic shielding effectiveness of the composites were studied.The interlaminar shear strength of the prepared quasi isotropic composites can be optimized to 37.1 MPa,and the average_of composites can be improved to 45 d B.(3)Targeting to dispose the problem that the shielding material will reflect electromagnetic waves and produce secondary electromagnetic pollution,the r CF-based electromagnetic wave absorbing material is developed.Through simple self-assembly and autocatalytic pyrolysis process,MOF derivatives with hierarchical heterostructure are decorated on the surface of r CF,which can simultaneously realize the synergy of various electromagnetic wave loss mechanisms and the improvement of impedance matching,endowing the r CF composites with advantages of low reflection loss,broad effective absorption bandwidth and thin matching thickness.The minimum reflection loss and specific reflection loss of the Co-NC@CF-3composite is as low as-50.1 and-1002 d B respectively at the matching thickness of 1.8 mm,and its effective absorption bandwidth is up to 4.82 GHz at the matching thickness of 1.6 mm.Compared with other carbon fibre based composites,the Co-NC@CF composite shows ultra-efficient electromagnetic wave absorption performance.(4)ZnO nanowire arrays were successfully constructed on the surface of r CF as multifunctional interfacial phase for simultaneously strengthening the fibre/matrix interface,improving the impedance matching and boosting the interfacial polarization loss.The mechanism of how interface microenvironment affect the charge transfer behavior and interfacial polarization of r CF/ZnO heterointerface was deeply studied.And the relationship between interfacial polarization intensity and interfacial adhesion and polarization loss was discussed,which deepened the understanding of the synergistic regulation mechanism of mechanical properties and electromagnetic wave absorption properties of materials.The interfacial shear strength of ZnO@r CF-o composite is as high as 97.5 MPa,and its minimum reflection loss is as low as-55.3 d B at the ultra-thin matching thickness of 1.5mm,and the effective absorption bandwidth is up to 5.0 GHz at the matching thickness of 1.6 mm. |
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