Preparation And Properties Of Epoxy Resin Matrix For High Impact Resistance Composites

Epoxy resin has been widely developed and applied in the fields of protective coatings,electronic packaging materials,adhesives and high-performance composites because of its good mechanical strength,strong adhesion,excellent dimensional stability,excellent chemical corrosion resistance,electrical insulation and wide formula diversity.However,due to the high crosslinking density,the cured epoxy resin has the disadvantage of high brittleness or poor toughness,which greatly restricts the application of epoxy resin in the field of high-performance materials.Therefore,the toughening modification of epoxy resin is a key problem to be solved at present.Over the years,many researchers have also used many ways to increase the toughness of epoxy resin such as adding flexible components,rubber elastomer,block copolymer and thermoplastic materials.However,the introduction of flexible components will sacrifice the strength and modulus of epoxy resin itself.The toughness of epoxy resin can also be enhanced by the introduction of rigid particles,but this method will increase the viscosity of the system and cause inconvenience to the subsequent processing process.Therefore,how to realize the synergistic improvement of strength,modulus and toughness of epoxy resin using green,environmental,and simple methods is still a harsh task.In this paper,epoxy resin containing flexible alkyl side chain named DX(X=4,8,12,18)was prepared by thiol-ene click chemistry and used as the toughening agent of bisphenol A typed epoxy resin(DGEBA).The results show that both the toughness and mechanical properties of DGEBA can be increased by the introduction of DX.The main research results are as follows:(1)A series of epoxy resin with flexible alkyl side chain named DX(X=4,8,12,18)was prepared by the reaction of monofunctional mercaptan TX(X=4,8,12,18)with the unsaturated double bond of an allyl-based epoxy resin(DADGEBA)under UV irradiation.Fourier transform infrared spectroscopy(FT-IR)and nuclear magnetic hydrogen spectroscopy(~1H-NMR)were used to analyze the raw materials and products before and after the reaction.The results proved the successful synthesis of epoxy resins containing flexible alkyl side chains.(2)Different mass fractions of D18 and DGEBA was fully mixed,then the mixtures were cured with methyl hexahydrophthalic anhydride(Me HHPA)to prepare EP_D18-Xcopolymerization toughening systems(CPTS).The effect of the content of flexible side chains on the mechanical properties of D18/DGEBA CPTS was systematically studied.In conclusion,the physical entanglement formed by the structural difference between side chain and main chain caused by the introduction of D18 can realize the simultaneous improvement of strength,modulus and toughness of epoxy resin.The results proved the excellent compatibility of the CPTS.In addition,the tensile results show that the mechanical properties can reach the maximum value when the mass ratio of D18 and DGEBA is 5/95.At this time,the tensile strength,tensile modulus,elongation at break and impact strength can reach 101.2MPa,2.8 GPa,4.3%and 22.5 k J/m~2,which are increased by 15.5%,7.7%,22.9%and58.5%respectively compared with the pure EP system.(3)On the basis of the above research,DX(X=4,8,12,18)that contains different lengths of flexible side chains were blended and cured with DGEBA with the mass ratio of 5/95 to obtain DX/DGEBA CPTS(EP_DX-5system).The effect of the length of flexible side chains on the mechanical properties of the CPTS was revealed.The test results show that the comprehensive mechanical properties of all the EP_DX-5systems are greatly improved compared with pure EP system,while the tensile strength,tensile modulus,elongation at break and impact strength of EP_D4-5system can reach 104.8 MPa,2.9 GPa,4.6%and 25.2k J/m~2,which are 19.6%,11.5%,31.4%and 77.5%higher than that of pure EP system,respectively.In addition,the Tg of all the EP_DX-5systems was slightly lower than that of pure EP system.(4)On the basis of the above research,4,4'-diamine diphenylmethane(DDM)and 4,4'-diamine dicyclohexyl methane(PACM)were selected as curing agents for D8/DGEBA system(changing the content of D8)to obtain CPTS(EPD_D8-Xand EPP_D8-Xsystem).The influence of curing agent structure on the mechanical properties of the CPTS can be revealed.The results show that the mechanical properties of EPD_D8-Xsystem cured by DDM increase first and then decrease with the increase of D8 content.When D8 content was 5 wt%,the tensile strength of the CPTS reached the maximum value.The tensile strength,elongation at break and tensile modulus of the system were increased by 29.9%,100%,and 30%compared with that of the pure EPD system.However,the mechanical properties of EPP_D8-Xsystem cured by PACM are lower than that of pure EPP system.SEM morphologies show that only in EPD_D8-Xsystems exhibit typical sea-island structural phase separation morphology.In conclusion,the curing agent with relatively high polarity(DDM)is beneficial to the formation of phase separation structures.However,the curing agent with relatively low polarity(PACM)cannot form phase separation structures,which is an important means to improve the toughness of epoxy resin.