Preparation Of Organic-inorganic Composite Coatings Based On Biomimetic Mineralization And Its Anti-corrosion Performance

Waterborne polyurethane（WPU）coating have been widely used in the field of corrosion protection due to their ecofriendly,good abrasion resistance and broad applicability.In order to meet the stringent requirements for anti-corrosion coatings in marine environment,based on modified WPU organic substrates,the organic-inorganic composite coatings containing CaCO₃ were prepared by biomimetic mineralization to improve the anti-corrosion performance of the coatings.The self-mineralized composite coatings significantly improve the corrosion resistance of WPU coatings.The research contents of this paper mainly include the following points:（1）CD-WPU emulsions with different contents ofβ-cyclodextrin（β-CD）were successfully prepared,and the CD-WPU emulsions were coated on tinplate acted as an organic template for biomimetic mineralization.The special hydrophobic ring structure and hydroxyl-rich functional groups inβ-CD promote the mineralization of CaCO₃ on CD-WPU.The existence ofβ-CD in CD-WPU organic films can effectively adsorbs and complexes Ca²⁺by its-OH contained in hydrophobic cavities.With the increase content ofβ-CD,the anti-corrosion performance of the mineralized composite films present the trend of first increasing and then decreasing.Especially,when the content reaches 3 wt%（3CD-WPU）,the mineralized composite film is the most compact and with the best anti-corrosion performance with the corrosion rate is only 1.39×10^-3 mm/year.Under the same conditions,the corrosion rate of WPU coating is 7.36×10^-2 mm/year,and its corrosion resistance is much weaker than that of organic-inorganic composite coating formed by mineralization with 3CD-WPU used as organic template.This excellent corrosion resistance is mainly ascribed to the uniform nucleation sites provided by CD-WPU,further formed a dense CaCO₃ inorganic layer.（2）The cheap and abundant natural biopolymer chitosan（CS）was mixed with cationic WPU by a simple blending method.The composite emulsions were coated on tinplate acted as biomimetic organic template.The effects of CS in organic template to mineralized CaCO₃ were investigated by means of SEM,XRD,polarization curves and so on.The results show the-OH functional group in CS-WPU organic coats can effectively complexs Ca²⁺in solution and promoting the CaCO₃ mineralization on the surface of WPU film.The continuous organic-inorganic composite coatings formed by biomimetic mineralization exhibit excellent corrosion resistance.Especially,the dense organic-inorganic composite film based on 4CS-WPU organic template exhibits outstanding anti-corrosive performance with corrosion rate of 7.70×10^-44 mm/year mm/year,being much less than 2.47×10^-2 mm/year for WPU coating under same conditions.This excellent corrosion resistance is mainly attributed to the uniform nucleation sites provided by CS-WPU,promoting the formation of dense CaCO₃inorganic layers.In addition,the adsorption energy between polymer molecule and CaCO₃ and the radial distribution function of-OH to Ca²⁺in solution system were calculated by molecular dynamics simulation.The results clearly showed that the functional group of-OH was effectively complexed with Ca²⁺in solution via the strong non-van der Waals force.At the same time,the adsorption energy of modified WPU on CaCO₃ was also significantly improved.The quantum computation results further reveal and support the mechanism of the promotion ofβ-CD and CS to the CaCO₃ mineralization.