Study On The Preparation Of Microcapsules And Its Application In Epoxy Resin Self-repairing Coating

The coating will inevitably produce micro-cracks during the long-term use.At the same time,the micro-cracks are difficult to repair from outside.So the mechanical properties and the service life of the coating will be decreased.The self-repairing coating containing self-repairing microcapsules can not only effectively prevent the generation of micro-cracks through the automatic response of the micro-cracks,but also can extend the life and reduce the maintenance cost of the coating.Therefore,it is of great significance to study the self-repairing coating containing microcapsules.In this study,the microcapsules were synthesized by in-situ polymerization with poly?melamine-urea-formaldehyde??MUF?and epoxy resin as shell and core material respectively.The surface morphology of the microcapsules were observe by optical microscope?OM?and scanning electron microscope?SEM?.Chemical structure was characterized by Fourier transform infrared spectroscopy?FTIR?.The thermal stability property was studied by thermogravimetric analysis?TGA?.Then the microcapsules were applied to the epoxy resin coating.The mechanical properties of the coating containing microcapsules were studied by Universal Tensile Testing Machine and Paint Film Impact Testing Machine.The electrochemical property of the coating was investigated by Electrochemical Workstation.The results showed that,the prepared microcapsules are sphere with an average size of about 100?m.The surface of them is rough and compact.They have good thermal stability.Compared with the coating witnout microcapsules,when the microcapsule content is 3wt%,the bending intensity,tensile intensity,impact intensity and bonding intensity of the coating are increased by 16.7%,14.6%,10.6%and 17.9%respectively.The self-repairing property of the coatings is enhanced with the increase of the latent curing agent.When the content of curing agent is 6wt%,the self-repairing property and electrochemical property of the coating enhance with the increase of microcapsules content.However,due to the poor compatibility between the MUF shell material and epoxy resin coating,the basic properties of the self-repairing coating will be affected with the addition of microcapsules with MUF as the shell material.In order to solve the above problems,microcapsules were synthesized by in-situ polymerization with MUF modified by nano-Al₂O₃ and epoxy resin as shell and core material respectively.OM and SEM were used to observe the surface morphology.The structure was characterized by X-ray photoelectron spectroscopy?XPS?and FTIR.The thermal property was tested by TGA.The self-repairing epoxy coating with the above modified microcapsules was prepared.TGA,Universal Tensile Testing Machine and Paint Film Impact Testing Machine were used to study the thermal property and the mechanical properties.The self-repairing property and electrochemical property were investigated by Electrochemical Workstation.The results showed that,when the ratio of core to shell is 1.5:1 and the nano-Al₂O₃ content is 4.5wt%,the surface roughness and the thermal stability of the modified microcapsules are higher than that of the unmodified microcapsules.The mechanical properties of the coating containing modified microcapsules are higher than that of the coating with unmodified microcapsule.Compared with the coating without microcapsules,when the modified microcapsules content is 5wt%,the bending strength,the tensile strength,the bonding strength and the impact strength of the coating are increased by 55.1%,111.9%,51.9%and 10.6%respectively.The electrochemical property and self-repairing performance of the coating enhance with the increase of the modified microcapsules content.The above results indicated that,the modification of shell material by nano-Al₂O₃ can improve the compatibility of the microcapsules and the coating,so the mechanical properties of self-repairing coatings containing microcapsules are improved.Since the hydroxyl in the structure of core epoxy E-51 can absorb the moisture in the environment,The self-repairing performance of the microcapsules containing epoxy resin and the protective property of self-repairing coating on metal will be weakened.In order to solve the above problems,the core material was modified by?-?2,3-epoxypropoxy?propyl trimethoxy silane?KH-560?.Microcapsules were synthesized by in-situ polymerization with MUF and epoxy resin modified by KH-560 as shell and core material respectively.The surface morphology,chemical structure,particle size and thermal property of the microcapsules were investigated.Then the microcapsules modified by KH-560were applied to the epoxy resin coating.The mechanical properties,self-repairing property and electrochemical property of the coating were studied.The results showed that,when the ratio of core to shell is 1.5:1 and the emulsifier content is1.4wt%,the modified microcapsule is regular spherical structure with uniform size and an average particle size of about 100?m.They have good thermal stability.The effect of the epoxy microcapsules before and after modified by KH-560 on the mechanical properties of the self-repairing coating was basically the same,but the electrochemical and self-repairing property of the coating with the modified microcapsules are higher.It indicated that the modification of the core material by KH-560 can increase the epoxy quantity.The self-repairing effect and corrosion resistance of the coating are more significant.The repairing agent and curing agent are dispersed in the substrate of the above two-component self-repairing coating.Based on this,a kind of one-component self-repairing coating containing linseed oil filled microcapsules were studied.The poly?urea-formaldehyde?microcapsules containing LO were synthesized by in-situ polymerization.The surface morphology,chemical structure,particle size and thermal property of the microcapsules were characterized and tested.Then the microcapsules were applied to the epoxy resin coating.The mechanical properties,self-repairing property and electrochemical property of the self-repairing coating were investigated.The results showed that,when the ratio of core to shell is 5:5,the emulsifier content is 1.5wt%and the pH is 3.0,the microcapsules are sphere with an average size of about 80?m.The surface of the them is rough and compact.They has good thermal stability.When the microcapsules content is 3wt%,the bending intensity,the tensile intensity,the bonding intensity and the impact intensity of the coating are increased by 20.1%,25.1%,11.8%and 24.8%respectively.The electrochemical performance of the self-repairing coating enhance with the increase of microcapsules content.