Research On Interphase Design Of Carbon Fiber/Vinyl Ester Resin And The Interaction Mechanism

Carbon fibers reinforced resin composite,with superior strength-to-weight ratio,excellent mechanical and thermal stability and outstanding design ability,has become the first choice replacing metal materials for vehicle lightweight.Vinyl ester resins(VE)is a kind of thermosetting resin with and outstanding curing performance,which can meet the need of mass production of auto parts.Therefore,carbon fiber reinforced vinyl ester resin composite(CF/VE)has wide application prospects in vehicle lightweight.However,the poor interfacial strength between CF and VE has limited the mechanical performance of composites.To solve this problem,this thesis aims at improving the interfacial property of CF/VE composite through interphase designing,analyzing interaction mechanisms of different interfaces,establishing the correspondence between the interface microstructure and the macroscopic properties of the composite.Three methods were used for interphase design: sizing agent grafting modification on CF surface,self-migration of acrylamide in VE,processing by unsaturated sizing agent.The poor interfacial strength of CF/VE composite is due to the lack of chemical bonds in interphase because of the epoxy sizing agent on untreated CF.Acrylamide as modifier was grafted onto CF surface by reacting with the epoxy groups of sizing agent.Vinyl functionalized CF surface was obtained without sacrificing the strength of carbon fiber and chemical bond was formed in composite interphase.The grafting reaction can be performed spontaneously at normal temperature according to the quantum mechanics calculation.The optimal concentration of acrylamide aqueous solution is 1.0wt% and the reaction condition is 10 min at 80℃.After the grafting modification,CF/VE composite showed 78.65% higher interface shear strength(IFSS)and 43.50% higher interlaminar shear strength(ILSS).The carbon fiber surface has an oriented adsorption effect on acrylamide molecules in the modifier.Herein acrylamide was added into VE for interphase modification by self-migration.Molecular dynamics simulations were performed to study the interactions between CFs and VE.After equilibrium,an interphase layer was formed surrounding both desized and sized CF surface with different structure and properties compared with bulk resin.The thickness of interphase layer on sized CF surface is larger than that on desized CF surface.In both interphase layers,acrylamide exhibited larger relative concentration than that in bulk resin,indicating that acrylamide molecules have migrated to fiber surface.The driving force of the migration is the resultant force of van der Waals and electrostatic interaction from CF surface and VE.After migration,interaction energies in both interfaces decreased significantly,which means the improvement of interfacial bond energies.The AM molecules in interphase chemically bonded CF surface and VE matrix.As a result,IFSS and ILSS of sized CF/VE composite were enhanced by 83.96% and 55.61%,respectively.This interphase design method improved the uniformity of interfacial chemical bonding and avoided the effect of surface grafting modification on the processability of CF.An unsaturated sizing agent was designed and prepared.The main component of the sizing agent,N-(4’4-diaminodiphenyl methane)-2-hydroxypropyl methacrylate(DMHM),was synthesized by the reaction between glycidyl methacrylate and 4’4-diaminodiphenyl methane.Molecular dynamics simulations were performed to study the role of sizing agent in the formation of interphase and the effect on the interfacial properties.Epoxy sizing agent and modified epoxy sizing agent were also studied for comparison.As a result,DMHM exhibited the highest interfacial bonding strength with the fiber surface and outstanding swelling effect in liquid VE.DMHM was synthesized and the sizing agent emulsion was prepared using phase inversion emulsification method.After sized by the new sizing agent,CF exhibted good processability.Surface energy was increased by 57.35%.IFSS and ILSS of CF/VE composite were enhanced by 96.56% and 66.07% respectively.Mode II interlaminar fracture toughness was improved by 59.05% than the epoxy sizing composite,by 19.86% than the modified epoxy sizing composite.The preparation parameters of CF/VE sheet molding compound(SMC)were optimized and SMC plates with different interfacial properties were prepared.The test results of static mechanical properties showed that the tensile properties,flexural properties and impact toughness of SMC composites were improved to some extent after interfacial modifications.Among them,process of unsaturated sizing agent showed the most obvious effect: the tensile strength and modulus were increased by 49.67% and 43.62%,the bending strength and modulus were increased by 64.35% and 46.34%,the impact toughness was increased by 31.31%.At last,the dynamic mechanical properties of composites were also improved by interfacial modification.