| Carbon fiber reinforced thermoplastic composites are used more and more in aerospace,medical equipment,robotics and other fields.Correspondingly,the performance requirements are getting higher,and more attention is paid to the study of interface performance.According to the principle of similar compatibility,sizing agents similar in molecular structure should be developed for different resins.At present,there are few studies on aqueous sizing agents suitable for thermoplastic resin substrates.Therefore,the preparation of aqueous thermoplastic sizing agents is of great significance for improving the interfacial properties of carbon fiber reinforced thermoplastic composites.In this thesis,a Fe3O4/reduced graphene oxide(RGO)modified polyimide aqueous sizing agent was prepared.The effects of sizing agent on the interfacial properties of carbon fiber and carbon fiber reinforced polyimide(CF/PI)and carbon fiber reinforced polyethersulfone(CF/PES)composites were investigated.Firstly,polyamic acid(PAA)precursor was prepared by a stepwise polymerization method,and a carboxyl group was ionized by reacting with dimethylethanolamine(DMEA)to prepare an aqueous PAA dispersion.The laser particle size analyzer test results showed that the average particle diameter of the PAA aqueous dispersion was 158 nm.Thermogravimetric characterization of the heat resistance of the PI film after thermal imidization of PAA,the temperature loss of 5%of the PI film having a molecular weight of 3.61×106 g/mol was increased by 41.3? compared with the molecular weight of 2.20×105 g/mol.The Fe3O4/RGO nanocomposites were prepared by coprecipitation in a magnetic field.The crystal form of the product was analyzed by X-ray diffraction(XRD).The morphology of the product was analyzed by transmission electron microscopy(TEM).X-ray photoelectron spectroscopy(XPS)analyzed the composition of the product.Aqueous sizing agents with different concentrations of PAA aqueous dispersion and Fe3O4/RGO were prepared and coated on the carbon fiber surface under a magnetic field.The surface morphology of carbon fibers was tested by scanning electron microscopy(SEM).The universal material testing machine tests the tensile strength of the monofilament of carbon fiber.Fourier transform infrared spectroscopy(FTIR)was used to test the surface functional groups of carbon fibers.XPS tests the surface element content of carbon fiber.When the PAA concentration was 1.0%and the Fe3O4/RGO concentration was 1.5 mg/mL in the sizing agent,the tensile strength of the monofilament of the carbon fiber is the highest.After coating the PAA-Fe3O4/RGO sizing agent in the magnetic field,the surface of the carbon fiber forms a uniform and orderly uneven structure,and the roughness was increased to 48.7 nm.CF/PI and CF/PES composites were prepared by hot press forming.The interlaminar shear strength(ILSS),section morphology and dynamic mechanical properties under different temperatures and loads were analyzed by universal testing machine,SEM and dynamic mechanical thermal analysis(DMTA).The optimum concentration ratio of sizing agent was determined.When the PAA concentration was 1.0%and the Fe3O4/RGO concentration was 1.5 mg/mL in the sizing agent,the ILSS of the CF/PI and CF/PES composites were the highest,which was 147.7%and 91.6%higher than that of the unsized.The effects of pure PAA sizing agent,magnetic field coated PAA-Fe3O4/RGO and purely coated PAA-Fe3O4/RGO sizing agent on the properties of carbon fiber and CF/PI,CF/PES composites were investigated.The mechanism of mechanical properties of magnetic field coating reinforced composites was also explored.The results show that the ILSS of CF/PI and CF/PES composites with magnetic field coatings increased by 27.9%and 33.9%,respectively,compared with the un-magnetic field.The reason is that the magnetic field control realizes the orientation arrangement of the Fe3O4/RGO sheet on the surface of the carbon fiber,avoiding the aggregation of the graphene sheet,thereby improving the interface properties of the composite. |
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