| Graphene polymer matrix composites have broad application prospects in many industries with light weight and high strength,especially in the automotive industry.Because of the demand of environmental protection and energy saving,lightweight has become the trend of the world's automotive development.However,the forming process of graphene polymer matrix composites is still restricted by high process cost,complex operation and insufficient performance of formed parts,so it is urgent to develop a new forming process.A continuous surface exposure 3D printing technology assisted by electric field is proposed,which completed the preparation of high-performance ordered graphene polymer matrix composites,and also provided a new way for continuous 3D printing of ordered composites.The theoretical analysis,experimental verification,case application and other aspects are studied in depth.The main research work and innovation are as follows:(1)A new process of 3D printing graphene-resin ordered composites based on assisted electric field continuous surface exposure was proposed to provide help for the preparation of high-performance graphene-resin composites from three aspects.The continuous integration molding of composite materials was completed by continuous surface exposure 3D printing technology,which overcame the internal stratification problem existing in traditional digital optical processing 3D printing,and ensured the mechanical properties of Z direction.In the printing process,a direct current electric field was applied to the composite paste,and the ordered arrangement of graphene in the resin matrix was completed by using the dielectric properties of graphene,which further improved the mechanical and electrical properties of the composite.The matrix material of the composite paste is photothermal double curing resin.The composite material was formed by light curing resin and cured by heat treatment after printing,so as to ensure the complete curing of the composite material,overcoming the problem of poor matrix mechanical properties caused by the light absorption caused by black graphene and the inability to achieve the complete curing of the material.(2)The different process parameters involved in the process were studied,including the rheological properties of slurry,the thickness of "dead zone",the maximum printing speed,the brightness of printing light source,the thermal curing parameters,and the intensity of auxiliary electric field.It is concluded that the maximum printing speed increases with the increase of the rheological properties of the paste and the thickness of the "dead zone",the mechanical properties of the molded parts increase with the decrease of the brightness of the light source,and the selection of the thermal curing parameters and the intensity of the auxiliary electric field directly affect the mechanical properties of the molded parts.The viscosities of graphene-resin composites with different graphene contents(0,0.5wt%,1.Owt%,2.0wt%)were 300 mPas,450 mPas,540 mPas,850 mPas,respectively.The corresponding maximum printing speed is>200mm/h,72 mm/h,50 mm/h,14 mm/h,and the corresponding minimum critical light source brightness is 2501m,2701m,3001m,3401m,respectively.The thickness of the "dead zone" reached the maximum of 78?m when the pore size of the microporous PET film was 0.45?m and the PDMS coating was 20?m.Thermal curing parameters are as follows:in the vacuum environment,the heating rate of 1?/min is successively heated to 100?,150?,180?,and the temperature is kept at each temperature for 1h,and finally it is cooled with the furnace;The auxiliary electric field is a direct current field of 500V/cm.(3)The ordered graphene-resin composites and disordered graphene-resin composites with different graphene contents were prepared by this process.The cross-section microstructure of all the formed parts was observed,and the tensile test and bending test were carried out.There is no Z-direction delamination in the finished parts.The graphene in the disordered composite is scattered in the resin matrix in disorder,while the graphene in the ordered composite is aligned along the direction of the electric field.The higher the graphene content is,the better the mechanical properties of the composites are.The ordered composites with the same graphene content also have better mechanical properties than the disordered composites.Compared with the molded parts made of pure resin,the tensile strength of 2.0wt%ordered composite molded parts increases by 101%from 44.38MPa to 89MPa,the tensile strain increases by 200%from 9.23%to 27.69%,the bending strength increases by 126%from 4.13MPa to 9.33MPa,and the bending strain increased by 98%from 10.43%to 20.6%.(4)After testing and analyzing the electrical properties of graphene-resin ordered composites,it is shown that the electrical properties of graphene-resin ordered composites are better than those of disordered composites with the same graphene content.When the content of graphene is 2.0wt%,the resistivity of the ordered composite is 6?·m,while that of the disordered composite is 96 ?·m,which is 16 times of the former.According to the characteristics of electrical and mechanical properties of ordered composites,a bumper model with signal feedback function was designed.The initiation and propagation of internal cracks in composites can be reflected by the change of resistance.Finally,the parts prepared by the ordered composite materials are connected with the warning light,and the failure of the parts is fed back by the brightness of the warning light.In summary,The electric field assisted continuous surface exposure 3D printing technology can solve the Z-direction lamination problem of the molded parts under the existing photocuring process,and the ordered arrangement assisted by electric field can further improve the strength,toughness and electrical conductivity of the molded parts.The above process provides a new solution for 3D printing of ordered composite materials. |
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