Study On Waterborne Polyurethane Modified With Short Fluoroalkyl Compounds And Its Coating Properties

Waterborne polyurethane is fabricated using water as a solvent.It is widely used in coatings,textile modification and wood processing due to its good mechanical properties and environmental protection characteristics.Because of introduction of hydrophilic components,the hydrophobicity and water resistance of waterborne polyurethane are poor,which limits its rapid development.It is one of the effective ways for improving hydrophobicity of waterborne polyurethane to introduce fluorinated compounds with more than 8 fluorinated carbon atoms.However,long perfluoroalkyl compounds are environmentally persistent and have long biological half-lives,which can accumulate in human and animal tissues.Compounds containing shorter fluorocarbon chains(C≤6)are much less toxic and have a higher safety profile.However,due to the short molecular chain-segments of short fluoroalkyl compounds,the migration efficiency of fluorine element is low,which cannot be well oriented on the surface,and the effect of hydrophobic modification is limited.Therefore,improving the transfer efficiency of fluorine element in the short fluoroalkyl chain-segments is of great significance for the construction of short fluoroalkyl compound modified superhydrophobic polyurethane.To construct the superhydrophobic surface of short fluoroalkyl chain-modified waterborne polyurethane,the short fluoroalkyl chain-segments were introduced into both ends of the polyurethane molecular chains as capping agent through sophisticated molecular design,which reduced the restriction of main chain rigidity on fluorine element migration and improved the migration efficiency of fluorine element.Moreover,by adjusting the structure of the isocyanate connected with the capping agent,the shackles of the main chain against the fluorine element migration were further broken.The short fluoroalkyl modified superhydrophobic waterborne polyurethane was successfully prepared.The main research contents include the following two parts,(1)The short fluoroalkyl chain was introduced into the ends of waterborne polyurethane molecular chains as a capping agent,which reduced the strong restriction and rigidity,improving fluorine migration efficiency.At the same time,hydroxy-terminated polydimethylsiloxane was introduced into the middle of molecular chains as a synergistic modifier to improve the mechanical properties of the films through increasing the degree of microphase separation of polyurethane.The test results of contact angle and X-ray photoelectron spectroscopy showed that the fluorine successfully migrated to the film surface,which reduced the surface energy of the films and greatly increased the static water contact angles.Polydimethylsiloxane was introduced as a soft segment.Due to its thermodynamic incompatibility with the isocyanate rigid block,the polarity difference between the hard and soft segments of the molecular chain increased,which improved the phase separation degree between the hard and soft segments,thus enhancing the mechanical properties of the films.The waterborne polyurethane coating with excellent hydrophobicity,water resistance and mechanical properties was obtained by the synergistic action of fluorinated capping agent and silicone.(2)By adjusting the structure of the isocyanate section itself connected with the fluorinated capping agent,the migration efficiency of fluorine element was further improved,and the superhydrophobic waterborne polyurethane was obtained.The research results of dynamic thermomechanical analysis,contact angle and X-ray photoelectron spectroscopy showed that the hexamethylene diisocyanate has the strongest movement ability,and the content of fluorine element on the surface of the waterborne polyurethane with hexamethylene diisocyanate as a hard segment was the highest.As a result,the water contact angle of the coating reached 157.3°,endowing a superhydrophobic function.