Functionalized Hexagonal Boron Nitride Modified Waterborne Polyurethane Composite Emulsions And Their Properties

Waterborne polyurethane emulsion,as a kind of environmentally friendly coatings with excellent comprehensive properties,which plays an increasingly important role in industry production and social life.However,waterborne polyurethane coatings are facing some urgent problems,such as insufficient water resistance,poor physical and mechanical properties,limited corrosion resistance and poor wear resistance,which seriously hinder their further development.As we know,modification of waterborne polyurethane by inorganic nano-materials is a common method.Inorganic nano-fillers can improve the physical and chemical properties of polymer composites because of their specific functional groups,shape and specific surface area.Unfortunately,there are still some problems,such as poor dispersion and poor compatibility with polymer matrix.In this thesis,functional hexagonal boron nitride was used as filler to modify waterborne polyurethane by covalent bonding strategy.The effects of functionalized hexagonal boron nitride modified waterborne polyurethane such as interfacial compatibility,mechanical properties,water resistance,wear resistance and corrosion resistance were investigated,and the crosslinking mechanism,corrosion resistance mechanism and wear resistance mechanism were preliminarily discussed at the micro-scale.1.Waterborne polyurethane(WPLU)coatings were prepared using a novel functional trimethoxysilane end-capping agent(DAA-GPTMS)derived from Diallylamine(DAA),3-(Glycidoxypropyl)triethoxysilane(GPTMS)and modified with edge-hydroxylated boron nitride(hBN-OH)nanosheets.It was found that the density and crosslinking degree of the composite coatings were significantly improved by the introduction of the end-capping agent with unique structure.The contact angle and water absorption experiments showed that the introduction of DAA-GPTMS could significantly improve the hydrophobicity and water resistance of polyurethane films.The transmission image showed that the uniform dispersion of inorganic nanoparticles was achieved by covalent bonding between hBN-OH and DAA-GPTMS at the end of the polymer chain.The mechanical properties and physical properties of polyurethane films could be significantly enhanced by introducing both of them into the composite system.The coatings containing both of them exhibited lower corrosion current density and higher self-corrosion potential.When the content of DAA-GPTMS and hBN-OH was 7.5 wt%and 0.2 wt%.respectively,the corrosion resistance of the coatings was the best.Compared with pure polyurethane,the corrosion resistance of the coatings increaseed by several orders of magnitude.2.Boron hydroxide nitride was modified by toluene diisocyanate(TD1).Polyurethane composites were prepared by in situ synthesis of hexagonal boron nitride(hBN-NCO)with isocyanate group on the surface.Scanning and transmission images showed that hBN-NCO possessed good interfacial compatibility with waterborne polyurethane substrate.The introduction of hBN-NCO nanosheets enhanced the wear resistance and mechanical properties of polyurethane composites.When the content of hBN-NCO was 2 wt%,the tensile strength increased about twice as much as that of pure polyurethane,but the elongation at break decreased only about 27%.Tafel tests and electrochemical impedance tests showed that the corrosion current density decreased by an order of magnitude when the addition amount reached 2 wt%.At the same time,hexagonal boron nitride with excellent electrical insulation performance could slow down the electrochemical corrosion rate to a certain extent.All these indicated that the comprehensive properties of polyurethane composites prepared by in-situ method had been greatly improved.