Study On Mineralization And Properties Of Waterborne Polyurethane Coatings

With the continuous development of society,the exploitation of Marine resources has become the focus of the world.However,the harsh Marine environment has seriously corroded vessels,infrastructure and other equipment and caused great economic losses,making the safety of staff can not be effectively guaranteed.Therefore,strengthening the corrosion protection of equipment in the Marine environment has become a worldwide problem.In this paper,a simple and effective anticorrosion method was selected,and organic coating was applied on the surface of the substrate to improve the anticorrosion ability of the equipment.Based on the consideration of environmental friendliness and excellent comprehensive performance,we choose the waterborne polyurethane coating with adjustable performance.However,due to the hydrophilic groups contained in the molecular structure of waterborne polyurethane,the water resistance and corrosion resistance of its coating are slightly inadequate.Therefore,we adopt the method that shells,corals and other Marine organisms in nature form stable minerals such as Ca CO₃ through surface mineralization to improve their corrosion resistance to improve the corrosion resistance of waterborne polyurethane coating.Therefore,based on the strong designability of polyurethane molecules,this study synthesized a series of waterborne polyurethane emulsions with mineralization function,characterized the properties of the emulsion and coating,and explored the influence of the mineralization of polyurethane coating on the corrosion resistance of coating.Polyurethane prepolymers were prepared with isophorone diisocyanate（IPDI）,polycarbonate diol（PCDL）,calcium citrate and 2,2-dimethylolpropionic acid（DMPA）as the main raw materials,and triethylamine was used as the main raw material.The salt-forming agent reacts with the polyurethane prepolymer,and the product is emulsified to obtain a series of aqueous polyurethane emulsions with different calcium citrate contents.The properties of polyurethane film and its mineralization effect and anticorrosion properties in simulated seawater were explored.The mechanical properties test results show that the mechanical strength of WPU3 reaches 20MPa.The DSC test results show that the crystallization of polyester polyurethane is strongly inhibited with the increase of calcium citrate ratio.XRD and SRM test results showed that calcium carbonate appeared on the surface of the polyurethane film after immersion in simulated seawater for 20 d.The water contact angle test results show that increasing the proportion of calcium citrate will increase the water contact angle of the coating,and the water contact angle of the coating will also increase after mineralization.The results of impedance test and simulated seawater immersion test show that the WPU3composite coating has the best anticorrosion properties and the mineralization time is from 10d to 20d,and the resistance R_p of the composite coating increases from 2.04×10⁴Ωcm² to 7.78×10⁴Ωcm².Polyurethane prepolymers were prepared from isophorone diisocyanate（IPDI）,polycarbonate diol（PCDL）and 2,2-dimethylolbutanoic acid（DMBA）.Triethylamine and Na OH were used as salt forming agents to react with polyurethane prepolymers.The products were emulsified to obtain waterborne polyurethane emulsion and further film drying.The properties of polyurethane film and its mineralization effect and anticorrosion properties in simulated seawater were investigated.FT-IR test results showed that waterborne polyurethane was successfully prepared.The mechanical properties test results show that the mechanical strength of WPU3 reaches 40 MPa.DSC results showed that the addition of Na OH inhibited the crystallization of polyester polyurethane.The thermal stability test results showed that the initial decomposition temperature of WPU3 decreased to 224℃.The water contact Angle test results show that the water contact of WPU3 film is reduced to 72.1°.XRD and SEM results show that dense Ca CO₃ appears on the surface of WPU3 film.The results of seawater corrosion simulation show that the anticorrosion properties of polyurethane coating is improved by Ca CO₃ filling in the scratches.Polyurethane prepolymers were prepared from isophorone diisocyanate（IPDI）,poly（propylene glycol）（PPG）and N,N-dimethyl-N’,N’-di（2-Hydroxypropyl）-1,3-propanediamine.Acetic acid,citric acid and 2,2-dimethylolpropionic acid（DMPA）were used as salt-forming agent to react with the polyurethane prepolymer to prepare three kinds of ionized polyurethane,and then they were emulsified in water to obtain three kinds of waterborne polyurethane latexes which were abbreviated as WPU1,WPU2 and WPU3,respectively.Three kinds of waterborne polyurethane films were prepared from the latexes and immersed in simulated seawater to absorb CO₂ and mineralize to form polyurethane-calcium carbonate（PU-Ca CO₃）composite films and their anticorrosion properties were studied.The process of three kinds of waterborne polyurethane films to absorb CO₂ and mineralize to form polyurethane-calcium carbonate（PU-Ca CO₃）composite membranes and their anti-corrosion properties were studied.FT-IR test results show that three kinds of cationic waterborne polyurethane have been successfully synthesized.The particle size test shows that the particle sizes of WPU1,WPU2 and WPU3 latexes are 19.38,93.08 and 84.33 nm,respectively.XRD,SEM and electrochemical test results show that after the simulate seawater immersion,the Ca CO₃ mineralization layer appears on both WPU2 and WPU3 film surface.The mineralization layer formed on the surface of WPU3 film is relatively dense and has excellent anticorrosion properties,and its corrosion rate and corrosion current density are 1.70×10^-3 mm/year,1.44×10^-7 A/cm².