Study On Properties Of Organic-Inorganic Hybrid Waterborne Polyurethane Emulsions And Their Composite Coatings

Marine corrosion has caused serious losses to the development of the global economy,and it has always jeopardized the safety of marine workers.Solving the corrosion protection of equipment in marine environments such as ships and architecture has become a worldwide problem.Coating the surface of the substrate is a simple and effective method for preserving the substrate,so how to develop high-performance,environmentally-friendly anti-corrosion coatings has gradually become a challenge in the field of materials science.In this study,a series of waterborne polyurethane composite emulsions?WPU?were synthesized based on the excellent structural design and water-based feature of polyurethane.The properties of the emulsion and the coating were systematically characterized,the correspondence between the corrosion resistance and the coating structure was investigated,and the optimal formulation was determined to meet the anti-corrosion requirements of the equipment under marine conditions.Polyurethane prepolymer was synthesized using isophorone diisocyanate?IPDI?,polycarbonate diol?PCDL?,dimethylolpropionic acid?DMPA?as main raw materials,preparation of complex neutralizer using calcium hydroxide?Ca?OH?₂?and triethylamine?TEA?.A series of aqueous polyurethane emulsions with different Ca-?OH?₂ contents are obtained after emulsification.FT-IR characterized and confirmed the structure of the polyurethane.The DSC test results show the introduction of Ca?OH?₂ inhibits the crystallization properties of the polyester polyurethane and improves the transparency of the coating.Mechanical tensile tests show that the introduction of Ca?OH?₂ does not reduce the elongation at break while enhancing the tensile properties of the coating.Thermogravimetric analysis and water contact angle tests indicated that Ca?OH?₂ increased the initial decomposition temperature and water contact angle of the coating.When the ratio of Ca?OH?₂/TEA is more than 4:6,the polarization curve shows that the coating has good corrosion protection performance to the substrate in 5%NaCl solution.The silane-terminated aqueous polyurethane prepolymer is synthesized from polytetrahydrofurandiol?PCDL?,isophorone diisocyanate?IDPI?,dimethylolpropionic acid?DMPA?,?-aminopropyltriethoxysilane?KH-550?,and The silica sol was synthesized by sol-gel method using tetraethyl orthosilicate?TEOS?and?-glycidyloxypropyltrimethoxysilane?KH-560?.A series of aqueous polyurethane-silica sol composite emulsion?PUS?was prepared during the emulsification of the prepolymer.FT-IR confirmed the hydrolysis and condensation of TEOS with KH-560 to form a silica sol containing epoxy groups,and successfully constructed the silica sol-polyurethane composite coating.Water absorption and mechanical tensile tests show that the addition of silica sol improved the water resistance and tensile strength of the coating.Thermogravimetric analysis showed that the thermal stability of the coating increased significantly with the addition of silica sol.The polarization curves and salt water immersion corrosion experiments show that the silica sol content is an important factor affecting the corrosion resistance of the coating.When the silica sol content is 9wt%,the coating has the best corrosion resistance to the substrate.