Preparation Process And Performance Study Of Graphene-based Microcapsule Epoxy Self-healing Materials

At present,epoxy resins are widely applied in various coatings,adhesives as well as electrical and electronic devices,due to their outstanding mechanical properties,chemical stability,the ease of processing and high cost effectiveness.It is widely known that epoxy resin possesses a three-dimensional network structure formed by covalent bonds.In order to prolong the service life of epoxy materials and prevent the diffusion of relevant microcracks,the polymer-based microencapsulated epoxy self-healing material has been designed according to the principle of biological damage repair.It is well known that a large number of microcapsules need to be added into polymer-based microencapsulated self-healing materials to achieve excellent self-healing performance,and the size of the microcapsules is large and the content of internal core material is low,which is easy to cause new cracks and affect the performance of the materials.In addition,the preparation process of the capsule is tedious and a large amount of organic solvent needs to be added in the reaction process,which pollutes the environment.Graphene oxide（GO）sheets contain a large number of oxygen-containing functional groups and carbocyclic skeletons on its surface,with high specific surface area and amphiphilicity.Therefore,graphene oxide is applicable as an effective stabilizer for Pickering emulsions,in order to reduce the energy at the interfaces while forming a complete shell through its self-assembly.Compared to the production of polymer-based microcapsules,the self-healing microcapsules based on the Pickering emulsions can be used to design the microcapsules of any expected structure,the process of which is simple and environmentally friendly.In this thesis,epoxy resin/amine was applied as matrix and microcapsules were treated as carrier,the appropriate epoxy repair system was established to produce epoxy resin-based self-healing material and examine its performance in repair.The research was detailed as follows:In order to reduce the high negative charge on GO surface,graphite oxide was modified with Fe₃O₄.Based on Pickering emulsion template method,glycidyl methacrylate（GMA）was microencapsulated as the repair agent,and graphite oxide-based single-component microcapsule self-healing coating with excellent repair performance was prepared.The influence of capsule preparation process parameters（such as the concentration of Fe Cl₂,the concentration of GO and the mass ratio of GO/GMA）on the performance of the microcapsules was explored.The optimal preparation process was optimized as the concentration of Fe Cl₂ was 18.75 mg/m L,the concentration of GO was 2mg/m L,and the mass ratio of GO/GMA was 4wt%.TEM,XRD,FTIR,TGA,Zeta potential and contact angle were used to characterize the microstructure of GO before and after modification.The result showed that Fe₃O₄ nanoparticles were uniformly dispersed on GO nanosheets.The surface morphology and particle size distribution of microcapsules were analyzed by optical microscopy（OM）.The average particle size of optimal microcapsules was about 5.82μm.TGA result exhibited that the core content of microcapsules was more than 94%.After analyzing the scratch morphology before and after repairing by SEM,the scratch width decreased with the content of the microcapsule increased,and when the microcapsule was 5wt%,the scratch was basically flat for 3 days at room temperature.The tensile properties of the material were evaluated using a universal testing machine,and it was found that the secondary tensile strength of the self-repairing material reached 57 MPa,which was similar to that of the pure epoxy material.The effect of the microcapsule content on the corrosion resistance of the material was also studied,after immersing for 150 h,the impedance modulus of the self-healing coating retained 148 MΩ,which was higher than that of undamaged epoxy coating.The self-repairing coatings exhibited better corrosion resistance,compared to the epoxy resin.Due to the long repair time of GMA repair agent at room temperature,in order to shorten the repair time,titanium dioxide modified graphite oxide（GO）was used as the UV-light absorption shell of the microcapsules,and encapsulated bisphenol A epoxy acrylate（BAEA）repair agent using Pickering emulsion method to prepare a microcapsule self-healing coating that could be quickly repaired by UV-light photo-induced.The effects of different processes（such as the concentration of PVA,the concentration of Ti Cl₃,GO concentration,the mass ratio of GO/BAEA）on the properties of capsules were studied.The optimal preparation process was as follows:the concentration of Ti Cl₃ was 7.5 mg m L^-1,the concentration of PVA was 1 mg m L^-1,the concentration of GO was 2 mg m L^-1and the mass ratio of BAEA/GO was 4wt%.TEM,FTIR,XRD and TGA were applied to prove that Ti O₂ nanoparticles were successfully modified on the GO surface.Combined with the morphology and particle size of GO microcapsules observed by OM,the average particle size of the optimized microcapsules was about 4.92μm,and the content ratio of repair agent in the capsule reached 91%.The result of TGA testing showed that the repair agent in the microcapsules remained active after the self-healing material solidified.SEM was used to analyze the morphology before and after the scratch repair,combined with the electrochemical test results,it was proved that the photo protective layer of the microcapsule could protect the undamaged capsule still remain active in the same area after three times of irradiation.After the material repair,the scratch area was filled,and the conductivity remained an order of magnitude with the undamaged coating.The conversion rate of the photo-sensitive resin was analyzed by FTIR,and the results showed that the conversion rate increased with the increase of the light exposure time.When the resin was repaired for the fourth time,the conversion rate was only 9%,indicating that the self-healing material could not be repaired again.Since the Ti O₂/GO encapsulated BAEA microcapsules could only be added to the waterborne epoxy resin,in order to enhance the stability of the microcapsules,BAEA was used as the repair agent,and graphite oxide was used as the emulsifier to stabilize Pickering emulsion,while chemically sticking between the oxygen containing functional group of graphene oxide and polyether amine to prepare a dual-layer shell microcapsule self-repairing coating with rapid repair by UV photo initiated.The effect of preparation process parameters（such as the value of p H,the concentration of D-2000,the concentration of GO,the mass ratio of GO/BAEA）on the performance of microcapsules was studied.The concentration of D-2000 was 0.5 mg m L^-1,the concentration of GO was 4mg m L^-1 and the mass ratio of GO/BAEA was 4wt%.FTIR and TGA tests proved that the oxygen-containing functional groups on GO reacted with the amino group in polyether amine to form a double shell,and the mass rate of the repair agent reached more than 85%.After process optimization,the particle size of the capsules was about 4.84μm,which could stably exist in ethanol solvent for 30 minutes.Through SEM,universal tensile testing and electrochemical impedance testing,it was improved that the repair performance and corrosion resistance of the material increased with the increase of microcapsule content in the system,the inside of the scratch was gradually filled,after 5 minutes of exposure to ultraviolet light.When the addition amount of microcapsules was 5wt%,the tensile property of the self-healing material was less affected,and the repair performance and corrosion resistance reached the best state.The material was achieved complete repair,with the secondary tensile strength of 53 MPa and the impedance modulus of 370 MΩ.