Preparation And Properties Of Bio-based Polyurethane Transparent Antifouling Coatings

Surface contamination not only affects the appearance and performance of products,but also takes time and effort to remove stains,especially the use of chemical cleaning agents can damage the surface of materials and pollute the environment.Coating is one of the most simple and economical methods to protect the surface of materials.In particular,polyurethane coatings have excellent mechanical properties and corrosion resistance,which can be widely used in many fields,because it can regulate its performance through the structure and proportion of soft and hard segments.However,the traditional polyurethane coatings are mostly prepared from petrochemical products,and the transparency of the coatings is poor due to the separation of hard and soft segments.The research of this topic starts from the concept of sustainable development,the polyurethane coating was prepared directly with unmodified castor oil as raw material polyol.At the same time,the environmentally friendly polydimethylsiloxane（PDMS）was used as antifouling agent,and the PDMS was covalently grafted to form a uniform microphase separation“nano pool”in the coating.The PDMS molecular chain segments were migrated from the coating to the surface to realize the antifouling of the coating.In this paper,the preparation process of solvent castor oil-based polyurethane transparent antifouling coating was studied in detail,and the water-based process was explored.The main research work of this subject is described as follows:（1）Preparation of solvent castor oil-based polyurethane transparent antifouling coating.With castor oil（CO）as raw material polyol,hexamethylene diisocyanate trimer（HDIT）as polyisocyanate,monohydroxy PDMS（PDMS-OH）as antifouling agent,butanone and dimethyl carbonate as solvent,a series of transparent antifouling coatings of castor oil-based polyurethane with high hardness were prepared through two pre-reactions and high temperature curing process.The test results show that the PU-PDMS coating has smooth surface structure;coating transmittance>98%;the coating has better mechanical properties than other bio-based coatings,and the hardness of the coating can be adjusted by R-value(n_-NCO:n_-OH).When R-value is 1.8,the hardness of the coating can reach 7 H.（2）The surface wettability and antifouling properties of solvent castor oil-based polyurethane transparent antifouling coating were studied.The contact angle test shows that as R-value increases,the water contact angle（WCA）tends to increase,the water sliding angle（WSA）and the contact angle hysteresis value（Δθ）decrease.The higher PDMS content in the coating,the greater WCA,the lower WSA andΔθvalues.Water-based pollutants（water,coffee,milk,tea,ink,fingerprint liquid and so on）can slide quickly from the coating surface without leaving traces;oil-based pollutants（hexadecane）due to its compatibility with PDMS,although can quickly slide but will leave traces;the oil-based inks after oil-based mark strokes can shrink rapidly on the coating surface and be easily wiped off.The coating can still maintain antifouling performance after thousands of frictions.In addition,artificial blood and artificial tissue fluid were selected to characterize the sliding performance of two kinds of liquids simulating human environment,and the results showed that they were similar to water-based and oil-based simulated contaminated liquids,which proved that they had certain development potential in the field of surface protection of biomedical materials.The XPS test results that the silicon content on the coating surface was much higher than the theoretical value verified that the PDMS graft chain with low surface energy could migrate from the coating interior to the coating surface,thus giving the coating excellent antifouling performance.（3）The corrosion resistance of solvent castor oil-based polyurethane transparent antifouling coating was studied.The results of salt water immersion,polarization curve and electrochemical impedance spectroscopy（EIS）showed that the introduction of PDMS could endow the coating with better corrosion resistance.The larger the circular arc radius of Nyquist diagram is,the better the corrosion resistance is.The test results show that when R-value is 1.5 and PDMS dosage is 4.0 wt%,the capacitance circular arc radius of the coating(PU_1.5-PDMS_4.0)is 10times of that of the iron matrix itself and 4 times of that of PU_1.5,respectively,and the equivalent resistance value increases significantly.When immersed in salt water for 29 days,the radius of the capacitance arc is similar to that of the iron substrate itself,indicating that the corrosion medium reaches the surface of the substrate at this time,further indicating that the coating has a certain long-term corrosion resistance.（4）The waterborne preparation process of castor oil-based polyurethane transparent antifouling coating was explored.The anionic and cationic WPU-g-PDMS dispersions were prepared by using 2,2-dihydroxymethylpropionic acid（DMPA）or N-methyldiethanolamine（MDEA）as hydrophilic chain extender and self-emulsifier,respectively,and the film-forming process of the dispersions was explored.The results showed that when the molar ratio of functional groups of three raw materials of-NCO（HDIT）:-OH（CO）:-OH（DMPA or MDEA）was2.20:1.00:1.19 and the amount of PDMS was 3.0 wt%,the stable WPU-g-PDMS dispersion was obtained by direct dispersion method.The polyurethane coating with uniform surface and pencil hardness of 6 H can be obtained by rolling coating process.The introduction of PDMS can effectively enhance the hydrophobicity and antifouling properties of the coating surface.High temperature curing can accelerate the migration of PDMS segments from coating interior to surface.