Study On The Influence And Acting Mechanism Of Molybdenum Disulfide/Epoxy Interface Control On The Properties Of Adhesives

Epoxy adhesives have become very important adhesive materials in the field of composites manufacturing due to their good adhesive applicability,excellent aging resistance and simple operation.Although epoxy adhesives have the above advantages,the shortcomings of low mechanical property,high brittleness and low heat resistance affect the further popularization and application of epoxy directly.Compared with the traditional modification methods,the addition of low content of two-dimensional nanofillers will significantly improve the mechanical and thermal properties of polymer materials.Among them,molybdenum disulfide(MoS₂)with sandwiched lamellar structure is considered to be a promising nano-additive for enhancing the mechanical property and heat resistance of polymer materials.MoS₂ surface is inert,without any active groups,and has poor compatibility with polymer matrix.In this paper,from the perspective of interface regulation,MoS₂ nanosheets were surface modified by organic molecules with different structures,thereby improving the compatibility of MoS₂ and epoxy.And then they were mixed with epoxy to prepare functional MoS₂/EP nano-composite adhesives.The effects of surface functionalization on the dispersibility of MoS₂ sheets and the thermal,mechanical,dielectric and bonding properties of epoxy adhesives were mainly studied,and the related strengthening mechanisms were discussed.The main research work was as follows:Firstly,MoS₂ was stripped by lithium ion intercalation method and liquid-phase exfoliation.Then,according to the compatibility of the modified organics with epoxy and ultrasonic solvent,three organic compounds with different structures(3-mercaptopropyltriethoxy-silane,diaminodiphenyl sulfone,and polythiol)were selected to functionalize MoS₂ surface,and the modified products were characterized.The prepared silane-functionalized MoS₂nanosheets,amino-functionalized MoS₂ nanosheets and polythiol-functionalized MoS₂nanosheets were dispersed in epoxy to form a composite adhesive system.The effects of dispersion state,morphology and dosage on heat resistance,mechanical properties and dielectric properties were studied.The results sh owed that the connection of organic molecules between MoS₂ nanosheets and epoxy matrix enhanced the interfacial interaction between MoS₂ and epoxy matrix,thereby increasing the effective volume of modified nanosheets.Therefore,the addition of a small amount of functionalized MoS₂ nanosheets could effectively improve the mechanical property and heat resistance of the composite system.When the content of amino-functionalized MoS₂ was 2.0 wt.%,the glass transition temperature of EP system was increased by 31?.The maximum of shear strength was 15.2 MPa at 150?,with an increase of 290%.The maximum of tensile strength was 96.3 MPa,with an increase of 74%.The maximum of impact strength was 8.3 k J/m²,with an increase of 207%.When the content of polythiol functionalized MoS₂ was 0.5 wt.%,the glass transition temperature of EP system was increased by 17?.The maximum of shear strength was 17.1 MPa at 150?,with an increase of 388%.The maximum of tensile strength was 92.6 MPa,with an increase of 75%.The maximum of impact strength was 5.6 k J/m²,with an increase of 93%.When the content of silane functionalized MoS₂ was 0.7 wt.%,the glass transition temperature of EP system was increased by 14?.The maximum increase of shear strength was213%at 150?.The maximum increase of tensile strength was 57%.The maximum increase of impact strength was 76%.MoS₂ was exfoliated by a simple ultrasonic method in a low viscosity bisphenol E cyanate ester monomer(CE)firstly.And then,the polysulfone(PSF)was dispersed in the above suspension to prepare functionalized MoS₂nanosheets(PSF-MoS₂).And the structure of PSF-MoS₂ was characterized.Compared with MoS₂,the compatibility between PSF-MoS₂ and CE was significantly improved.Then,PSF-MoS₂/CE suspension was uniformly mixed with epoxy to form a PSF-MoS₂/CE/EP single-component latent adhesive.The kinetic equation of curing system of PSF-MoS₂/CE/EP adhesive was calculated.The effects of dispersion state,morphology and dosage of PSF-MoS₂ on mechanical property,heat resistance and dielectric property of PSF-MoS₂/CE/EP adhesive were studied.The addition of a very small amount of PSF-MoS₂ nano-filler can effectively improve the heat resistance and mechanical property of the adhesive.When the addition amount of PSF-MoS₂ was 0.10 wt.%,the tensile strength was 108.9MPa,with an increase of 20%.The impact strength was 22.1k J/m²,with an increase of 220%.PSF-MoS₂/CE/EP adhesive had excellent high temperature shear strength.When the content of PSF-MoS₂was 0.21 wt.%,the shear strength of the system was increased from 13.4 MPa to 19.7 MPa at 200?,with an increase of about 47%.The composite adhesives prepared by four interface control methods were respectively bonded to aluminum alloy,epoxy carbon fiber composite,and dual-horse carbon fiber composite,and their shear strength were tested.The performance of silane functionalized MoS₂/EP composite adhesive for bonding aluminum alloy materials was better than the other three kinds.Four kinds of composite adhesives showed good adhesive propert y for epoxy carbon fiber composite,and the failure modes were all substrate failures.The performance of polysulfone functionalized MoS₂/EP composite adhesive for bonding bismaleimide carbon fiber composite material was better than the other three kinds,and the failure mode was substrate damage.Through the analysis of the shear strength data of four composite adhesive systems bonded with a thick adhesive layer,it was concluded that as the thickness of the adhesive layer increased,the shear strength showed a downward trend,the addition of functionalized MoS₂ can reduce the drop of shear strength with thick adhesive layer.In addition,the comparison of the shear strength data of the adhesive immersion in water,aviation kerosene,hydraulic oil and salt spray aging before and after showed that the addition of functionalized MoS₂ can improve the liquid immersion resistance and salt spray aging resistance of the adhesive system.