Preparation Of Epoxy Emulsion Carbon Fibre Sizing Agent And Interfacial Properties Of CFRP

Carbon fiber/epoxy composites are widely used in the fields of sports equipment,automobile manufacturing,aerospace and aviation because of their light weight,high strength and wear resistance.With the development of new energy automobile and airplane,high performance carbon fiber and composite materials are required.Sizing agent,which is at the interface between fiber and resin in carbon fiber composites,plays an important role in the comprehensive properties of composites.Sizing agents are usually used to protect fibers,but the interfacial properties are limited.Therefore,how to optimize the sizing agent structure,increase the reactive groups with the matrix resin and improve the comprehensive properties of the composites through a simple sizing process has become an urgent problem for high-performance carbon fiber composites.In this paper,a new epoxy emulsifier,multi reactive group epoxy resin and hyperbranched curing agent were designed and synthesized to provide more active groups for sizing agent and improve the interfacial properties of CF/epoxy composites.Aiming at the problem that the introduction of more active groups into the sizing agent will reduce the stability of the original sizing agent lotion,a new epoxy emulsifier was synthesized by grafting polyethylene glycol（PEG）and polypropylene glycol（PPG）onto the side chain of epoxy resin（EP）.Epoxy emulsion sizing agent was prepared by phase inversion emulsification.When the molecular weight of PPG was 2000,the emulsion showed nano single dispersion,with the smallest median particle size and the highest stability,compared with non grafted PPG.The stability period extended from 15 days to 10 months without particle size change.After sizing CF with this emulsion as sizing agent,it was found that the sizing modification method will not affect the tensile strength of carbon fiber.The wettability of CF can be improved,with the surface energy of 45.67 m N·m^-1.The interfacial adhesion between CF and EP was enhanced,and the interfacial shear strength（IFSS）and interlaminar shear strength（ILSS）reached 75.92 MPa and 85.99 MPa respectively,which was 42.33%and 17.41%higher than that of bare fiber.In addition,the introduction of hydrophobic segment PPG2000 into emulsifier alleviates the hygroscopicity of sizing CF.The emulsifier laid a foundation of emulsion stabilization for the optimization of epoxy emulsion sizing agent.The bio-based epoxy resins PA-EP-3 and PA-EP-5 with epoxy values of 0.925and 0.737 were synthesized by using protocatechuic acid PA and brominated alkenes with different chain lengths as raw material.A series of new epoxy emulsion sizing agents were prepared by partially replacing EP.It was found that partial substitution had little effect on the initial particle size of emulsion.The emulsion with 20 wt%addition showed nano dispersion after standing for 60 days.Using emulsion with 20wt%PA-EP-3,20 wt%PA-EP-5 and without bio-based epoxy resin（PA-EP）as sizing agents,CF was sized respectively.The effects of sizing agent type and solid content on fiber sizing amount were studied.When the solid content of 20 wt%PA-EP-3 and20 wt%PA-EP-5 sizing agent is 0.75 wt%,the sizing amount of 1.3 wt%and 1.2 wt%can be achieved,which is higher than that of the sizing agent without PA-EP（0.7wt%）.The introduction of PA-EP into the sizing agent improved the wettability of CF,added the chemical bonding at the CF/EP interface and improved the interface properties.Compared with CF treated with sizing agent without PA-EP,IFSS increased by 14.29%and 11.40%respectively,and ILSS increased by 10.87%and10.04%respectively.The application of the bio-based epoxy resin in CF/EP composites is realized.A series of hyperbranched resins（HB-EP-1,HB-EP-2 and HB-EP-3）were synthesized by modifying epoxy resin with the reaction product of diethanolamine and succinic anhydride as branching unit.To prepare a self-curing epoxy emulsion sizing agent,they were added to the high epoxy value epoxy emulsion as epoxy curing agent in the emulsification process.It was found that the introduction of hyperbranched structure resulted in the initial particle size of emulsion become larger.When the addition amount was 15 wt%,the emulsion could maintain the nano-sized dispersion suitable for the CF surface within 60 days,and the infrared spectrum proved that the curing agent did not react with the epoxy group during this period.CF was treated with emulsion sizing agent containing 15 wt%hyperbranched curing agent.The monofilament tensile properties and wettability of CF were improved after sizing.Among them,the CF treated with 15 wt%HB-EP-2 sizing agent presented the highest IFSS and ILSS,reaching 83.17 MPa and 93.82 MPa respectively,which were48.78%and 25.75%higher than those of bare fiber.The introduction of hyperbranched structure enhances the chemical bonding and physical entanglement at the interface between CF and EP,but increases the moisture absorption of CF after sizing,therefore CF need to be stored in an environment with low relative humidity.The epoxy emulsion sizing agent prepared in this paper can significantly improve the interfacial properties of CF/EP composites,and has potential application value in the field of preparing high-performance CF/EP composites.