| Metal corrosion causes huge economic losses,waste of resources and energy,ecological environment pollution,and seriously threatens the safety of human production and life.Coating is the most widely used,simple and effective among the anti-corrosion methods.As the corrosion micro areas appeared by by external forces or corrosive media is traditional coatings,the corrosion reaction will quickly spread from the corrosion micro areas,resulting in coating failure.The use of self-healing anti-corrosion coating can effectively solve the above problems.The core component of self-healing coating is self-healing microcapsule.The self-healing microcapsules are stimulated and release the inhibitors encapsuled to prevent the spread of corrosion to prevent the spread of corrosion as the self-healing system is driven by the force,electromotive force,pH and other different factors of the corroded micro area.With the pursuit of environmental protection,ecology and safety issues,the coatings should also develop in the direction of no VOC and green environmental protection.Based on the problems of easy failure and insufficient corrosion resistance of metal coatings,in consideration of the development direction of green and environmental protection of coatings.L-CySStine@polypyrrole nanotube selfhealing microcapsules were designed and prepared(L-CySS@PNT)in this paper,in which conductive polymer polypyrrole(pnt)with hollow tubular nanotube structure and excellent corrosion resistance is used as the shell material,and L-CySStine(L-CySS)with green and environmental protection and excellent corrosion inhibition performance.Further,reduced graphene oxide(RGO)was utilized as nano fillers,which enable the composites coatings to possess dual anti-corrosion mechanisms of active anti-corrosion and passive anticorrosion and L-CySStine@polypyrrole nanotubes@graphene aqueous epoxy resin(L-CySS@PNT@RGO-WEP)self repairing anti-corrosion coating was prepared.The anti-corrosion mechanisms of PNT,L-CySS and RGO components on metals were studied respectively.The formation mechanism and pH responsive release mechanism of L-CySS@PNT,the self-healing anti-corrosion mechanism of L-CySS@PNT@RGO-WEP composite coatings were also explored.The specific work is as follows.1.Granular polypyrrole(GP)and polypyrrole nanotube(PNT)were prepared by chemical oxidation method.The effects of different morphology on the conductivity and thermal stability of polypyrrole were studied.The experimental results showd that the morphology of polypyrrole affects the conductivity,physical and mechanical properties of polypyrrole,and then affected the corrosion resistance of polypyrrole composite coatings.Compared with GP,PNT has better anti-corrosion performance due to its higher electrical conductivity and fiber reinforcement.The physical and mechanical properties and anti-corrosion properties of the composite coatings first increased and then decreased with the addition of PNT.The optimal addition is 1.5%,and the lowfrequency impedance of PNT-WEP-1.5 is 1.93×108Ω·cm2。The anticorrosion mechanism of PNT composite coatings is cathodic protection,anodic protection and shielding reinforcement based on fiber increasing mechanism.2.Benzotriazole(BTA)was used for comparative experimental research as a widely commercial used corrosion inhibitor.The slow release rate of L-CySS and BTA at different concentrations,temperatures and pH was studied by static weight loss method.The structure-activity relationship between the molecular structure and the corrosion inhibition performance of L-CySS and BTA was explored by adsorption thermodynamic calculation and quantum chemical calculation,and the corrosion inhibition mechanism was clarified.The anticorrosion properties of L-CySS and BTA composite coatings at different pH were evaluated by electrochemical tests,and the anti-corrosion mechanism was researeced.The results showed that compared with BTA,the S atom and disulfide bond in L-CySS molecule give it excellent corrosion inhibition performance.In addition,the carboxyl group and amino group in the molecule make it have better corrosion inhibition performance under alkaline conditions.The inhibition mechanism of L-CySS is passivation.The L-CySS-WEP composite coating is sensitive to pH,and the order of corrosion resistance is:LCySS-WEP-7>L-CySS-WEP-5>L-CySS-WEP-3.The low-frequency impedance of the L-CySS-WEP-7 composite coatings was 5.12 × l09 Ω·cm2,2 orders of magnitude higher than that of BTA-WEP-composite coatings.3.L-CySS@PNT Self repairing microcapsules were prepared by three methods and the influence of preparation methods on the performance of microcapsules were studied.The interface interaction mechanism of L-CySS/PNT,and BTA/PNT and the interaction of the above composites system were contrastive studied through the methods of simulation calculation,loading capacity,adsorption kinetics,adsorption thermodynamics,to clarify the formation mechanism of L-CySS@PNT self-healing microcapsules.The pH responsive release mechanism of L-CySS@PNT microcapsules were explored by release experiment and release kinetics simulation anylasis.The simulation results showed that L-CySS@PNT The composite system has better compatibility and is more stable compared with BTA.L-CySS@PNT selfhealing microcapsules were prepared by in-situ polymerization with the maximum loading capacity.The analysis of adsorption kinetics and adsorption thermodynamics showed that the adsorption of L-CySS in PNT was monolayer adsorption,pH and the ratio of L-CySS to PNT would affect the formation mechanism and loading capacity of L-CySS@PNT self-healing microcapsules,among which,the saturated adsorption capacity reached the largest of 33.1 μg/mg at pH 9。The release kinetics study showed that,L-CySS@PNT selfhealing microcapsules can release L-CySS through capsule disintegration in all tested pH ranges,and the release speed and intensity are different under different pH conditions.Under acidic conditions,the release rate is fast and the release intensity is high.L-CySS@PNT self-healing microcapsules have pH response characteristics.4.Graphene based self-healing anticorrosive coatings were prepared with a system of both passive anti-corrosion system by L-CySS＠PNT self-healing microcapsules and an active anti-corrosion system of RGO.Electrochemical tests were carried out to evaluate the corrosion resistance of L-CySS@PNT@RGO composite coatings and to study the corrosion enhancement mechanism of RGO,the self-healing anti-corrosion mechanism of the composite coatings.LCySS@PNT@RGO-WEP coatings exhibited excellent corrosion resistance in neutral salt spray experiments in comparation with pure WEP,PNT-WEP and PNT@RGO-WEP coatings.The electrochemical test results were consistent with the neutral salt spray test results.The corrosion potential of L-CySS@PNT@RGO-WEP composite coatings was-198.82 mV,the corrosion current density was 7.29×10-13 a/cm2,the polarization resistance was 1.77×1014Ω·cm2,and the corrosion rate was 8.53×10-15 mm/year,4 orders of magnitude less than pure WEP coatings according the result of Tafel test.L-CySS@PNT@RGOWEP composite coatings showed excellent corrosion resistance.The results of self-healing experiments showed that,L-CySS@PNT@RGO-WEP composite coatings has anti-corrosion and self-healing performance.After 500 hours of salt spray,the low-frequency impedance of the coating still remained above 108Ω·cm2,and the long-term anti-corrosion performance was excellent.The selfhealing process of the coatings was due to the release behavior of L-CySS in LCySS@PNT microcapsules.A green,environmental friendly and efficient self-healing anti-corrosion coating was provided through the research of this subject,the anti-corrosion mechanism of each component and the cooperative self-healing anti-corrosion mechanism were clarified.The research results can be applied to the practical application of metal corrosion protection,and can provide certain theoretical guidance for the design and synthesis of green,environmentally friendly and efficient self-healing corrosion protection system. |
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