Preparation And Properties Of PH-Responsive Core-Shell Fiber Self-Healing Anticorrosive Coating

Corrosion is one of the difficult problems that need to be solved urgently.In particular,the metal corrosion of engineering materials not only damages the economy but also endangers the safety of personnel.Therefore,protect the metal from corrosion and minimize the risk of corrosion in all industries.In recent years,intelligent anticorrosion coating has become a research hotspot of anticorrosion materials because of its self-healing,excellent anticorrosion and long-term effect,especially self-healing coating.The core-shell fiber membrane was prepared by electrostatic spinning.According to the spinning shell materials can be divided into four kinds of Poly（vinyl alcohol）（PVA）fibers,chitosan（CS）,methyl cellulose（MC）fibers,cellulose acetate（CA）fibers.According to the core materials can be divided into oleic acid（OA）+benzotriazole（BTA）,OA+2-mercaptobenzimidazole（MBI）,OA,OA+alkyd varnish（AVR）,OA+solvent free epoxy resin（EP₁）.The core materials are corrosion inhibitors.Environment-friendly nanofibers were studied the influence factors of container molding,illustrates the core material matching,shell material condition parameters,the viscosity,the type of solvent,the preparation of voltage on the influence of nanometer fiber forming rule,realized the high encapsulation rate,high load factor inhibitor of nanofibers controllable preparation,and high efficiency of self-healing capability.The main research work are as follows:（1）Taking PVA as shell material,OA and BTA as core material,coaxial core-shell fiber film was prepared on the surface of Q235 carbon steel by means of electrostatic spinning technology.Then the epoxy resin coating was coated on the fiber film to obtain the fiber epoxy composite coating.The preparation process optimization parameter on the concentration of the PVA shell solution was controlled at about 10%-20%,the injection pump rate was 0.1-0.8 mm/min（shell）and 0.001-0.005 mm/min（core）,the average diameter of the fibers was 354±40nm.Scanning electron microscopy（SEM）revealed the surface was smooth without bead structure.The core-shell structure was verified by transmission electron microscopy（TEM）confocal laser fluorescence microscopy（CLSM）,and the core-shell structure was analyzed by fourier transform infrared spectroscopy（FTIR）.Electrochemical impedance spectroscopy（EIS）was used to demonstrate that the maximum corrosion inhibition efficiency was 86.0%in 3.5 wt.%Na Cl solution after 10 days of immersion.OA was prefered to be released from the fibers under the alkaline condition with p H=12.0.OA film was formed on the surface of the damaged metal against corrosion.BTA was priority released in3.5wt.%Na Cl solution with p H=4.0,and the maximum corrosion inhibition efficiency was 83.4%after 5 days.Compared with the blank epoxy coating,the fiber composite coating has better corrosion resistance and self-healing performance.（2）The core-shell nanofibers with good morphology were prepared by using CS/PVA hybrid electrostatic spinning as the fiber shell.OA and MBI inhibitors as the fiber cores.According to SEM,TEM and CLSM analysis,the maximum fiber molding addition ratio was CS/PVA=65/35.The injection pump rate was controlled at 0.5 mm/min（shell）and 0.002 mm/min（core）,and the core-shell fibers diameter of about 180 nm was obtained with smooth surface.FTIR was used to analyze the chemical composition of core-shell structure,which proved that OA and MBI were successfully encapsulated in fibrous shell material.The self-healing process of the scratched coating on the surface of carbon steel substrate was monitored by EIS,FE-SEM-EDS and micro-FTIR spectroscopy.Results showed that the largest repair rate was 11.29 kΩcm² d^-1 in the 3.5 wt.%in Na Cl solution（p H=11.8）.In 3.5 wt.%Na Cl solution（p H=4.0）,the maximum self-healing rate was 13.11 kΩcm² d^-1.MBI in the carbon steel substrate surface formed MBI chelation film,taking the initiative to block the invasion of acid corrosion ion in the solution.The load rate of OA+MBI was about 17.2%.（3）MC was a non-ionic cellulose ether,with unique hot gelation properties and poor fiber formability.In this study,the core-shell structure MC fiber was successfully prepared by controlling solution concentration,environmental humidity and operating parameters of electrostatic spinning equipment.The shell material was MC and the core material was OA.The results showed that when the concentration of MC aqueous solution was 8 wt.%and the positive spinning voltage was 30±3 k V.The fiber morphology was good without droplet and bead.Fibers were combined with PDMS coating to form a composite coating,and its self-healing anticorrosion performance in 3.5 wt.%Na Cl solution（p H=11.7）was studied.EIS,scanning kelvin probe（SKP）and infrared microscopic spectrum test results showed that scratched MC composite coating with the increase of immersion time had the repair rate of 48.00Ωcm² h^-1.The maximum voltage potential of SKP decreased from 308.0 m V to 265.0 m V,and the infrared microspectra at the scratch showed the spectrum of OA,which proved the formation of OA protective film at the scratch.（4）Coaxial fibers was prepared by electrostatic spinning with CA as shell material,OA and AVR as core materials.Then the fibers was silanized to obtain hydrophobic fiber film.Finally,the fibers was added to poly（dimethyl siloxane）（PDMS）coating to obtain composite coating.The hydrophobic fibers were characterized by contact angle analyzer,SEM,TEM,CLSM and FTIR.The results showed that the core-shell structure was constructed successfully and contact angle was about 136°.EIS results showed that the self-healing rate of scratched coatings was 4.90 kΩcm² d^-1 soaked for 12 days in 3.5 wt.%Na Cl wet/dry cyclic conditions（p H=11.8）.The repair rate of scratched coatings was22.80 kΩcm² d^-1 soaked for 5 days in 3.5 wt.%Na Cl wet/dry cyclic conditions（p H=4.0）.SKP and EDS analysis were used to compare the voltage potential strength and iron content at the scratch of the composite coating.The chemical composition of the protective film formed at the scratch was measured by micro-infrared spectroscopy,and the conclusion was consistent with the FTIR diagram of OA and AVR.It is proved that the inhibitors released from the fibers will form a protective film and play its self-healing role.（5）The p H responsive superhydrophobic core-shell fiber self-healing coating of CA system was prepared successfully.Core-shell fiber films were prepared on Q235 carbon steel with CA as the shell material,OA and EP₁ as the core materials.The superhydrophobic suspension solution was prepared by adding silicas to epoxy resin（EP₂）and PDMS,then the superhydrophobic fiber coating F-EP₂+PDMS@Si O₂ was obtained by spraying it on the core-shell fiber membrane surface.The static contact angle of the superhydrophobic coating was up to 157.3±3°and the sliding angle was 3.5±0.5°.EIS results showed that the scratched coating soaked for 4 days in 3.5 wt.%Na Cl solution（p H=12.0）,the repair efficiency was 55.65 kΩcm² d^-1.In 3.5 wt.%Na Cl solution（p H=4.0）for12 days,the repair rate was 87.10 kΩcm² d^-1.The results of SKP and EDS analysis showed that the corrosion resistance of the superhydrophobic fiber coating was significantly higher than that of the non-fibrous superhydrophobic coating,indicating that it had a certain self-healing performance.It was proved that the coating was superhydrophobic,and the coating has excellent wear resistance,good chemical stability,and can withstand knife scraping and sandpaper abrasion.In summary,we designed a p H response nanofibers container and its coating based on higher p H micro-cathode area and lower p H anode area.It reveals the spontaneous response to the p H change response mechanism of the coating for corrosion environment.Expounds the multiple nanometer fiber self-healing corrosion inhibitor molecules in response to the release of the p H value and film-forming mechanism.It also clears the the film-forming process and the inhibition on metal surface corrosion.This study has extended the application of electrospinning technology in the field of corrosion protection in Marine environment and has important reference value for the development of new self-remediation materials.