Preparation And Application Of Anticorrosive Functional Microspheres

Metal corrosion is the common phenomenon in daily production and life. It destroys significantly the mechanical, optical and other physical properties, and shortens the life of the equipment, even causes some catastrophic accidents. Anti-corrosive coating is one of the most effective ways to prevent metal corrosion. However, the anti-corrosive coatings often suffer damages induced by environmental factors in service time. These damges can accelerate the coating to peel off from the metal substrate so that the protective function of the coating fails. Therefore, how to improve the active anticorrosion and the self-healing properties of the coatings is a pressing issue in the research area of the metal anticorrosion.In this thesis, the submicron microspheres or microcapsules loaded with corrosion inhibitor or self-healing agent had been designed and fabricated based on emulsion polymerization techniques. These microspheres containing "active" species were adopted in the green coatings in order to obtain the long term and smart anti-corrosive coatings. The work consists of four parts of contents:mesoporous and hollow inorganic microspheres loaded with corrosion inhibitor prepared by reverse microemulsion polymerization; hollow raspberry-like polymer microspheres loaded with corrosion inhibitor synthesized by multi-step emulsion polymerization; the preparation of hollow and azo polyurea microspheres loaded with corrosion inhibitor via inverse miniemulsion interfacial polymerization; the fabrication of microcapsules containing self-healing agents by in situ polymerization in an oil/water emulsion. The main contents and results are as follows:1. The synthesis and controlled-release behavior of1H-benzotriazole (BTA)-loaded hollow silica nanocapsules (HSNs-M) with magnesium hydroxide precipitated on the inner wall of the silica shells. Transmission electron microscope (TEM) and Brunauer-Emmett-Teller (BET) measurements indicate the hollow structure of silica nanocapsules and the mesoporous morphology of the silica shell. The actual loading capacity of BTA is287.17mg (BTA)/1g (HSNs-M). The results of UV absorption spectra show that the release of BTA can be triggered by acidic condition in the corrosive solution. Finally, the anti-corrosive SiOx/ZrOx coatings embedding with hydrophobically modified HSNs-M have a better waterproof performance since the water contact angle can reach140°. In comparison to the passive SiOx/ZrOx coatings with or without BTA, the enhanced corrosion protection performance of this developed anti-corrosive system in the0.1M NaCl solution was observed by both electrochemical impedance spectroscopy (EIS) and Tafel analysis. The composite coating, which inhibition efficiency for aluminum is99.26%, can almost completely prevent the occurrence of corrosion on the aluminum surface.2. The fabrication of submicron-sized raspberry-like hollow microspheres was performed via a multi-stage emulsion polymerization. BTA was embedded in (methyl) acrylic copolymer core consisting of methyl methacrylate (MMA), butyl acrylate (BA) and methyl acrylic acid (MAA) units. In addition, a raspberry-like PS shell was formed on the surface of the core during osmotic swelling process of (methyl) acrylic copolymer core in alkaline solution. TEM, scanning electron microscopy (SEM) observation and BET measurement indicate that the raspberry-like microspheres having voids in inner part and fine pores on the surface. The raspberry-like microspheres have a better waterproof performance since the water contact angle can reach to122.3°. FT-IR and element analysis confirm the encapsulation of BTA into the raspberry-like hollow microspheres. The actual loading capacity of BTA is19.66mg (BTA)/1g (polymer microspheres). The results of UV absorption showed that the release of BTA can be triggered by the stimuli of changing pH of the corrosion solution. Finally, the combination of hierarchical raspberry-like surface structure and loading with BTA gives an excellent anti-corrosive property of the prepared microspheres, which was investigated by electrochemical measurement performed using linear sweep voltammetry, EIS and Tafel analysis. When BTA-loaded raspberry-like hollow microspheres are embedded in a water-borne polyurethane film, the obtained composite film can good protect the copper from corrosion both in acidic and alkaline corrosion solutions.3. The synthesis of the hollow polyurea microcapsules was performed by interfacial polyaddition of the monomers toluene-2,4-diisocyanate (TDI) and diamine in a W/O inverse miniemulsion. As a result, a sufficient storage of the corrosion inhibitor BTA was encapsulated in the hollow particles. The loaded BTA can be released timely by the stimuli of temperature or UV-light. Moreover, TEM images indicate that the size of hollow polyurea nanocapsules was100-500nm. The hollow polyurea nanocapsules loaded with corrosion inhibitor were introduced into the organic film. The enhanced anti-corrosive effect of the organic film embedded with the nanocontainers was obtained, which was investigated by electrochemical measurement performed using EIS and Tafel analysis, because of the controlled release of the corrosion inhibitor triggered by the environmental stimuli. Especially, the inhibition efficiency of the composite film can reach84.46%after being treated by UV-light.4. The fabrication of poly(urea-formaldehyde)(PUF) microcapsules containing UV-curable polyurethane prepolymer and photoinitiators are facilely performed by in situ polymerization of formaldehyde and urea in an oil/water emulsion. It was confirmed by optical microscopy (OM) and SEM that the mean size of the microcapsules could be controlled by agitation speed. The yield and the encapsulation rate of microcapsules prepared at the agitation rate of600rpm were around65.23wt%and97.52wt%, respectively. When the waterborne coating embedded with microcapsules containing UV-curable healing agents was scratched, the healing agent could be released from ruptured microcapsules and filled the scribed region. In comparison to the coating without microcapsules, the better anticorrosion properties of the coating embedded with microcapsules were successfully investigated by both EIS and Tafel curves analysis.