Preparation Of Epoxy Resin Self-Healing Microcapsules Modified By SiO₂ Pickering Particles And It’s Applications

Self-healing polymer materials can gradually repair some or all of their properties by themselves under certain conditions after being damaged by external conditions,which is favourable for improving their service life.In recent years,more and more attention has been paid to self-healing polymer materials.The main methods for constructing self-healing polymer materials include embedding externally assisted self repairing materials such as microcapsules,microvascular,hollow fibers and so on,or using reversible dynamic bonding and supramolecular interaction.The self-healing microcapsules are used widely in epoxy resins.However,the problems,that the effect of residual small molecular emulsifiers on the surface of microcapsules,as well as the incompatibility of the interface between microcapsules and epoxy resins causing the reduce of the initial performance of the substrate,remains to be solved.Pickering particles are easy to be modified on the surface,and stability of its emulsion is strong,so they can be used for the preparation of microcapsules instead of traditional emulsifiers.In this paper,carbon carbon double bond and epoxy groups firstly were grafted on the surface of Si O₂ Pickering particles to build a chemically bonded transition layer,which was expected to improve the initial performance of self-healing epoxy coatings through using the grafted carbon carbon double bond to participate in the composition of the microcapsule shell,and the grafted epoxy groups to chemically bond with epoxy resin substrates.Most of the reports use directly or employ single modified inorganic/colloidal particles to act as Pickering particles,while there are fewer studies about composite modified Pickering particles.We first adoptedγ-Glycidyl ether oxypropyl trimethoxysilane（KH560）andγ-methacryloxypropyltrimethoxysilane（KH570）to modify the surface of Si O₂ particles.By controlling the feeding ratio of silane coupling agent,a series of composite modified Si O₂Pickering particles with adjustable surface wettability were prepared.The hydrodynamic diameters were about 140～160 nm,and they were used to study the stability of high viscosity epoxy resin/water emulsion.The results showed that the single modified KH560-Si O₂Pickering particles had no emulsification ability for the oil phase of the epoxy resin,but both the single modified KH570-Si O₂ and the composite modified KH560-KH570-Si O₂ particles could form stable oil-inwater epoxy resin Pickering emulsion.And the best emulsification performance was obtained when the feeding ratio of silane coupling agent was KH560+KH570=19.0 wt%and KH570=12.5 wt%,corresponding to the underwater-to-oil contact angles of 108°and 130°,respectively.The emulsified emulsion formed spherical droplets with regular morphology under the optical microscope,and the height of the emulsified layer of the emulsion decreased from 2.6 cm to 1.4 cm and 1.5 cm,respectively after standing for 10 minutes.There were no obvious change in the shape of the oil droplets.When the emulsion was left to stand for 24 hours,the height of the emulsified layer did not significantly decrease,and the shape of the dispersed oil droplets remained same as that of the freshly emulsified emulsion.The microcapsules were prepared by free radical polymerization using composite modified KH560-KH570-Si O₂ Pickering particles as solid particle emulsifiers,epoxy resin E-51 and o-toluene glycidyl ether as the core materials,poly（styrene-glycidyl methacrylate）P（St-Bis-GMA）as the wall material.And the preparation process of microcapsules was discussed.The effects of the type and dosage of modified Si O₂ Pickering particles,and the ratio of wall monomers on the chemical structure,surface morphology,and thermal properties of epoxy resin microcapsules were investigated in detail.The results showed that the microcapsules were successfully prepared with 10 wt%KH560-KH570-Si O₂ Pickering particles accounting for oil phase and St/GMA=7.5/2.5.And the prepared microcapsulespossessd a regular and microspherical shape with a transparent core shell structure in the center and rough and dense surface,and an average particle size of microcapsules were in the range from 60μm to 100μm.The epoxy resin self-healing microcapsules and latent curing agent 2,4-diamino-6-[2-（2-methyl-1-imidazolyl）ethyl]-1,3,5-thiazine were added to the epoxy resin substrate in a certain proportion to prepare an epoxy resin self-healing coating.The self-healing performance of epoxy resin coatings was investigated using optical microscopy（OM）.When the mass fraction of microcapsules in the coating was 15 wt%,the coating scratches gradually reduced until they disappeared in OM photos,and the tensile strength of the coating could recover to 70.9～84.9%of that before the damage,which showed that the epoxy resin coatings embedded microcapsules had better self-healing performance.The self-healing performance of epoxy coatings enhanced with the increase of the content of encapsulated microcapsules.Compared with microcapsules prepared with single modified KH570-Si O₂ particles,microcapsules prepared with composite modified KH560-KH570-Si O₂ particles could improve the compatibility with the substrate interface due to the grafted epoxy groups on their surface.The fracture strength of the epoxy resin self-healing coating had been increased from 21.9 MPa to 28.5 MPa,and the elongation at break has been increased from 5.9%to 6.8%,thereby improving the initial mechanical properties of the epoxy resin self-healing coating.The epoxy resin self-healing microcapsules modified by Pickering particles are expected to be applied in the fields of epoxy adhesives,coatings,electronic packaging,and other fields.