| Carbon fiber reinforced vinyl ester resin composites(CF/VE)have been widely used in transportation,sports and other fields because of its outstanding adva ntages of light weight,high strength,good design and short molding cycle.But the studies show that,due to the different curing mechanism of vinyl ester resin and epoxy resin sizing agent on the surface of carbon fiber,carbon fiber can not form covalen t cross-linking with VE resin in the curing process,the interface becomes the weak link of carbon fiber reinforced vinyl ester resin composites.Therefore,the subject is to prepare a new kind of unsaturated carbon fiber emulsion sizing agent to improve the interface between fiber and resin matrix by introducing chemical bonding,thus improving the overall performance of CF/VE composite materials.Firstly,the molecular structure of sizing agent is designed and the two synthetic materials are glycidyl methacrylate(GMA)and 4,4-diaminodiphenyl methane.The feasibility of the reaction of two substances is verified by differential scanning calorimetry(DSC),and the reaction conditions are optimized.The sizing agent is prepared and its molecular structure is characterized.The results show that one of the amino groups in MDA react with the epoxy group in GMA,and the expected reaction product is obtained.Then the emulsion type sizing agent is prepared by phase inversion emulsification method,and the formulation and e mulsification process of the sizing agent are optimized.The emulsifier is compounded with OP-10 and Twain-20(mass ratio 6:4),mass ratio of emulsifiers is 10%,emulsification temperature is 60 ?,stirring rate is 10000 r/min and the water adding mode is 1 ml/min before phase inversion and 4 ml/min after that.The emulsion particle size is about 245 nm,the distribution is narrow and the emulsion has higher stability.The carbon fiber is treated with self-made sizing agent.The effects of sizing agent on the properties of carbon fiber are studied by means of wearable instrument,SEM,AFM and XPS.The results show that the carbon fiber has good bundling property,stiffness and abrasion resistance;SEM and AFM analysis show that the surface of the fiber becomes smooth after sizing,the gully disappears,the surface sizing agent covered evenly and the roughness increased significantly.The results of XPS show that the content of O elements and N elements on CF surface increases significantly after sizing and the percentage of O:C increased by 9.39%.All of these are beneficial to improve the interfacial bonding strength of CF/VE.The wettability increases obviously,the dynamic contact angle between CF and VE resin decreases from 76.37° to 60.28°.Micro-debonding test shows that,the interfacial shear strength increased from 26.99 MPa to 41.25 MPa,increasing by 52.84%.SEM images of the pull-out surface show that there is a lot of resin residue on the surface of CF after sizing,which shows that that there is a strong interface between CF and VE matrix.The interlaminar shear strength of CF/VE unidirectional composites has the same growth trend as the interfacial shear strength,increased from 45.98 MPa to 59.87 MPa,improving by 30.21%.SEM images of the fracture surfaces of CF/VE composite indicate that there is also a lot of resin residue on the surface of carbon fiber after the shear failure,and the destruction is changed from the interface to the resin damage,due to the chemical connection between the CF and the VE matrix.As the bonding strength of the interface increases,the load of the composite will be transferred to the fiber more effectively,thereby improving the performance of CF/VE. |
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