| Carbon fiber(CF)reinforced composites are widely used in various fields due to their excellent mechanical performance such as high specific strength,high specific modulus,lightweight,corrosion resistance.However,the chemically inert surface of CF,which was due to the high temperature carbonization or graphitization during manufacturing,goes against the adhesion between CF and resin matrix.It is also a bottleneck problem for the exhibition of excellent properties of carbon fibers reinforcement.It is usually to enhance the interfacial properties by sizing process with sizing agent emulsion,whose chemical structure is similar to the applied resin matrix.Vinyl ester resin contains double bonds and hydroxyl group,which has chemical reactivity.Based on the structural characteristics of carbon fiber and vinyl ester resin,three kinds of vinyl ester based polymers with different structures were designed as main composition of sizing agent emulsion in this thesis.By investigating the mechanism of ring-opening reaction of epoxy groups and the preparation of sizing agent emulsion as well as the interfacial properties of composites,the factors influencing the performance of sizing agent emulsion and the interfacial shear strength(IFSS)of composites were studied.The results indicated that:(1)Since the nucleophilic reagent can make the epoxy group to open the ring reaction under acidic conditions,three kinds of sizing agent main polymers with different structures were prepared.By analyzing the FTIR spectra of these three polymers,it was found that the epoxy function groups were disappeared,proving the generation of the designed polymer structure.The thermal stability of the vinyl ester based polymers were analyzed by TGA.The thermal stability of acrylic acid type is higher than that of hyperbranched type while that of the hydroxyethyl methacrylate type is the lowest.(2)Three kinds of sizing agent emulsion were prepared based on above obtained main polymers by phase inversion method.The effects of emulsifier,the concentration of polymer,stirring rate and the addition of stabilizer on the particle size and stability of the emulsion were investigated by dynamic light scattering(DLS)and electrophoretic light scattering(ELS)measurements.It was found that the addition of anionic emulsifiers can significantly reduce the average particle size and increase the stability of emulsion.Increasing the content of emulsifiers can decrease the average particle size and improve the stability of emulsion.Increasing the stirring rate allows the emulsion to have a smaller average particle size and higher stability.The addition of stabilizers could improve the decreasing of the particle sizes and stability.When the emulsifier was selected as EL-40 and NP-10 A,the content of emulsifier is 15%,the stirring rate is 19000 r/min and the stabilizer is added,the average particle size of the emulsion is 150.3 nm and the absolute value of zeta potential is 78.9m V with the highest stability.(3)The influence of the sizing agent on the physical and chemical structure of the carbon fiber surface was investigated by SEM observation and XPS measurements.It was found that the grooves on the surface of carbon fibers were reduced and the oxygen content was significantly increased after sizing.The surface of carbon fibers had the highest oxygen content and C-O structure content after sizing with acrylic type sizing agent while the lowest oxygen content and the highest C=O structure after sizing with hyperbranched sizing agent.(4)The effect of the sizing agent on the wettability and interfacial properties of carbon fiber reinforced vinyl ester composites were concluded by dynamic contact angle and interfacial shear measurements,respectively.It was found that the dynamic contact angle of the fiber with both water and diiodomethane is decreased and the surface free energy is increased.The interfacial shear strength(IFSS)is increased significantly after sizing.The IFSS value of carbon fiber with no sizing treatment was 20.7 MPa.After sized with acrylic sizing agent,hydroxyethyl methacrylate sizing agent and hyperbranched sizing agent,the IFSS were increased to 35.4 MPa,38.6 MPa and 32.8 MPa,respectively with a highest 86.5% improvement. |
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