Synthetic And Characterization Of Microcapsules For Self-healing Coatings

Anticorrosion coatings are one of the most important corrosion protection means.Its performance and service life determines whether it can protect the base metal material from corrosion for a long time,and whether it is worth being used.Not only anticorrosion coatings,but also various types of coatings are composed of polymer matrix,which tend to crack under the effect by the physical force and the environmental conditions during use.The micro-cracks are often generated inside the matrix material,and cannot be seen by the naked eye.Once expanding,micro-cracks will connect,thus cause the coating to fall off and lose the protective property.In order to solve this problem,in this paper,we prepared a smart self-healing coating embedded with microcapsules.The microcapsules were embedded in the resin matrix.Once the cracks generate and spread to the surface of the microcapsules,the microcapsules will be broken and release its internal healing agents.The healing agents fill in the cracks,cure with oxygen,and prevent the cracks continued expansion.Urea-formaldehyde resin as shell material and epoxy resin as core material were used to prepare microcapsules.SDBS solution with mass concentration of 0.8% was used and stirred at 2000 rpm for 5-10 min to obtain uniform and stable emulsion.But the obtained microcapsules had a great inhomogeneous in size,ranging from 2?m to 200?m,which were easily to aggregate.Urea-formaldehyde resin as shell material and tung oil as core material were used to prepare self-healing microcapsules by in situ polymerization with two steps.SDBS were chose as the emulsifier in the synthesis reaction.The optimum concentration of the emulsifier is 1% according to the morphology and particle size of microcapsules prepared with different concentrations of emulsifier.The parameters of synthesis,such as core-shell ratio,acidification time,the final pH of acidification which could affect the performance of the microcapsules were preliminary researched.The size of microcapsules obtained mainly distributed in the range of 20-80?m,with the average particle size of 57.9 ?m.The shell of microcapsules was compact,and the thickness was mainly in the range of 1.5-5 ?m.The rough surface of the microcapsules could increase the interfacial strength between microcapsules and the resin matrix.The roughness of themicrocapsules increased with the increase of the concentration of the emulsifier and the core-shell ratio.The shorter the acidification time was,and the lower the final pH of acidification was,the tougher the surface of the microcapsules would be.The infrared spectrum of the microcapsules possessed the characteristic peaks of UF and tung,which proved that the UF-tung oil microcapsules had been synthesized successfully.The TG curve of the microcapsules shows its good thermal stability.The response surface method was used to optimize the microcapsule core content.Four experimental variables such as core content,stirring speed,acidification time and the final pH of acidification were selected.The model of microcapsules on their core content was established by computer software.Then we could get the experiment conditions with the specific requirements of core content,and we could also find the best preparation technology.The UF-tung oil microcapsules were prepared using the optimal preparation parameters of core content obtained by response surface methodology.Then the microcapsules were added to the resin matrix to prepare composite coatings through an addition with embedded microcapsules in the resin or a layer-by-layer addition.Observed by optical microscope,the microcapsules were uniformly dispersed in the resin matrix.SEM photograph showed that the microcapsules were well bonded with the resin matrix.Both of the two kinds of composite coatings in the self-healing test experiments showed good self-healing effect.