Preparation And Anti-corrosion Properties Of Methyl-ring Substituted Polyaniline/Zinc Oxide Composites

With the rapid development of the national economy,metal materials play an increasingly important role in international trade.When the metal material contact with a corrosive medium,an irreversible chemical reaction occurs and forms a corrosion site.Metal corrosion can cause serious economic damage and harm.The emergence of conductive polymers has brought a solution to this problem,which conductive polymers represented by polyaniline have been extensively studied and applied to the corrosion protection of metallic materials.However,there is a strong rigidity and interaction between polyaniline chains,which has some difficulties in processing and limits its application range.The modified polyaniline/inorganic particle complex solves this problem very well.On the one hand,the interaction force between molecular chains is weakened.On the other hand,inorganic particles added can also increase the tortuosity of the corrosive media path;in addition,the composite polymer and metal formed insolubles or complexes can also protect metal materials.Therefore,the preparation and corrosion resistance of methyl-ring substituted polyaniline/nano-zinc oxide were studied in this paperand the composite materials with excellent corrosion resistance were found.Zinc oxide powders with particle size of about 250 nm were prepared by liquid-phase co-precipitation method.The effects of different surfactants on the morphology and particle size of zinc oxide were studied.Three kinds of homopolymers of poly(o-toluidine),poly(m-toluidine)and poly(p-toluidine)were synthesized by chemical oxidation method using hydrochloric acid as the dopant and ammonium persulfate as the chain oxidant under the ice bath in this paper.Then,poly(o-toluidine),poly(m-toluidine)and poly(p-toluidine)composites with nano-ZnO content of 7wt.%and 14wt.%were prepared by in-situ polymerization(labeled as POT/ZnO-1,POT/ZnO-2,PMT/ZnO-1,PMT/ZnO-2,PPT/ZnO-1,PPT/ZnO-2,respectively).Fourier transform infrared spectroscopy,ultraviolet and visible light spectroscopy,X-ray diffraction spectroscopy,scanning electron microscopy,and cyclic voltammetry were used to characterize the structure and properties of the samples.The above synthesized complexes were added to an aqueous polyurethane varnish and a nanocomposite coating was prepared by a solution casting method.Polarization curves and electrochemical impedance spectroscopy tests were performed in 3.5wt.%NaCl solution,the corrosion resistance of the coatings was evaluated by immersion and salt spray tests:1.ZnO was prepared by a liquid phase coprecipitation method.The results showed that the ZnO obtained by adding cetyltrimethylammonium bromide surfactant had the smallest particle size of 237.3 nm and its shape was conical.Nano-ZnO with potassium citrate and polyvinylpyrrolidone exhibited a 255.8 nm cone shape and a 305.4 nm sheet structure.2.By measuring the polarization curve of poly(o-toluidine)/zinc oxide coating in 3.5%NaCl solution,it was found that when the content of zinc oxide is 7wt.%and the POT/ZnO composite is content of 5wt.%.The coating exhibits excellent corrosion resistance.The corrosion rate is 3.21×10-3 mm/a,which is about 2 orders of magnitude lower than 5.98×10-1 mm/a for bare steel.3.By testing the polarization curves of the poly(m-toluidine)/zinc oxide coating,it was found that the PMT/ZnO composite coating exhibited excellent corrosion resistance when the content of zinc oxide is 7wt.%and the composite content is 5wt.%.performance.The corrosion rate is 5.84×10-2 mm/a,which is higher than the equivalent content of poly(o-toluidine)/zinc oxide coating.4.The analysis of the polarization curve of the poly(p-toluidine)/zinc oxide coating showed that when the content of zinc oxide is 14wt.%and the content of composite is 5wt.%,the corrosion rate of the coating is 1.19×10-3 mm/a,corrosion resistance is better than other equivalent content series of coatings.5.After 720 hours(30 days)of salt water immersion and 396 hours(16.5 days)of salt spray experiments,it was found that when the composite content was 5wt.%,three methyl-ring-substituted polyaniline/zinc oxide composite coatings were showed excellent corrosion resistance.The order of corrosion resistance among the best composite coatings was:5wt.%(PPT/ZnO-2)/95wt.%WPU>5wt.%(POT/ZnO-l)/95 wt.%WPU>5wt.%(PMT/ZnO-1)/95wt.%WPU>bare steel,this conclusion is consistent with the polarization curve and electrochemical impedance spectroscopy results.