| Waterborne polyurethane(WPU)is a material with controllable soft and hard segments by polyol and polyisocyanate polycondensation.Because of its low volatile organic compound emissions and superior performance,it is widely used in leather,textile,coatings and medical fields.waterborne polyurethane has poor hydrophobic and water-resistant performance,which limits its application in waterproof,outdoor products and other fields.In order to solve problems,waterborne polyurethane is usually modified with hydrophobic substances to improve its hydrophobicity and water resistance,such as organic fluorine,organic silicon and other substances etc.Organic fluorine and organic silicon have low surface energy,they migrate and enrich to membrane/air interface during the film formation process,which limits the penetration of water molecules into the inside of the film,thereby improving the hydrophobic and water resistance of the film;The introduction of crosslinking agents increases the crosslinking density of the film and the formation of a highly crosslinked matrix can improve the water resistance of the film.The first chapter briefly introduces the hydrophobic modification method of waterborne polyurethane and its application in different fields.In the second chapter,fluorine-modified waterborne polyurethanes were synthesized by using perfluorooctylpropanol as the modifier,hydrophobic high-gloss and matt coatings were prepared by phase separation during coating drying process.XPS shows that fluorine atoms migrate to the surface of film,and the mobility is limited by the fluorine capacity of the film surface;with the increase of organic fluorine,the maximum water contact angle of the film surface is 110.6°,and the surface energy decreases to 10.04m J/m~2.The tensile strength first increases and then decreases,when the fluorine content is 1%,the maximum tensile strength is 17.85MPa;by adjusting the content of additives,a high-gloss or matt coating is prepared,and the maximum water contact angle of the coating is 126°.In the third chapter,Silicon-modified main-chain and side-chain waterborne polyurethanes were synthesized by using side-chain silicone(3T10)and main-chain silicone(UC2862).XPS shows that the silicon-containing segments of side-chain silicones have greater mobility than main-chain silicones,and that the increase in the molecular chain of main-chain type silicones will facilitate their migration to the surface.When silicone content is 3%,the water contact angle of waterborne polyurethane film were modified by the side-chain silicone increases to 113.6°,and the surface energy of the film decreases to 18.62m J/m~2;The water contact angle of waterborne polyurethane film were modified by the main-chain silicone modified with different molecular weights respectively is 108.2°and 108.8°,and the surface energy of the films is respectively reduced to 16.97m J/m~2 and 16.40m J/m~2;The 24h water absorption rate of film were modified by the main chain silicone is 7.98%,the maximum tensile strength of film were modified by the chain silicone is 34.90MPa.In Chapter 4,Cross-linked waterborne polyurethanes were synthesized by using3T10 side-chain silicone as the functional substance and trimethylolpropane(TMP),N-aminoethyl-?-aminopropyltrimethoxysilane(KH792)and diethylenetriamine(DETA)as the crosslinking agents.The cross-linked network structure restricts the movement of molecular chains and the migration of silicon-containing segments to the membrane/air interface.The introduction of cross-linking agent increases the cross-linking density of the film,under the same molar amount,the cross-linking density of film modified by the KH792 is the highest.The 120h water absorption rate of the crosslinked modified film is reduced to 6.25%,the maximum tensile strength of the film is 44.14MPa,and the maximum elongation at break is 2173.98%. |
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