Study Of Polyurethane Modified By Dispersible Nano-TiO₂

Nano-sized TiO₂is non-toxic and odorless and possesses good photocatalytic activity, strongultraviolet-absorbing ability and infrared reflection ability, as well as sterilizing ability and deodorizationability. As a result, nano-sized TiO₂is widely applied in coating, cosmetics, and antibacterial agents, as wellas in paper making and environment protection. Thus we anticipate that nano-sized TiO₂may be used tomodify paints for traditional leathers to improve the performance of the leathers. However, nano-sized TiO₂has a large specific surface area and high surface energy and is liable to agglomeration, which hinders itsapplication in paints and coatings for leathers. Bearing those perspectives in mind, we separately adoptpolyvinylpyrrolidone （PVP） and silane coupling agent KH-550to in-situ surface-modify nano-sized TiO₂so as to improve its dispersibility in and compatibility with polymer matrix and increase its bondingstrength with the polymer matrix. Furthermore, TiO₂/PVP/polyurethane composite coatings andTiO₂/KH-550/water-borne polyurethane （denoted as PU） composite coatings were prepared by blending,and the resistance to solvent attack and ultraviolet irradiation of the composite coatings, as well as theirthermal stability and wear resistance were primarily investigated. The main contents and research results ofthis thesis are as follows:（1） Rutile TiO₂nanoparticles were prepared by low-temperature liquid-phase hydrolysis of titaniumtetrachloride （TiCl₄） as the starting material. As-obtained TiO₂nanoparticles were in-situ surface-modifiedby PVP. Then TiO₂/PVP/PU composite coatings were prepared by blending. The composition andmicrostructure of TiO₂nanoparticles before and after modification with PVP were analyzed by means ofX-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectrometry （FT-IR）.The resistance to solvent attack and ultraviolet irradiation of the composite coatings, as well as theirthermal stability and wear resistance were primarily investigated. It has been found that TiO₂/PVP has gooddispersibility in water-borne PU, while introducing TiO₂/PVP contributes to greatly improve the resistanceto solvent attack and ultraviolet irradiation as well as wear resistance of PU-matrix coatings. In themeantime, TiO₂/PVP/PU composite coating has better thermal stability than PU coating, and the compositecoating containing4%TiO₂/PVP （mass fraction） has the strongest absorbance for ultraviolet; and its friction coefficient is reduced by21.64%, its water-absorption is reduced by56.95%, and its water contactangle is increased from65.2°to83.8°as compared with the unfilled PU coating.（2） Nano-TiO₂was modified by silane coupling agent KH-550by grafting. ThenTiO₂/KH-550/water-borne PU composite coatings were prepared by blending. The chemical structure ofas-prepared TiO₂/KH-550/PU composite coatings was analyzed by means of FT-IR, and their thermalstability was evaluated with a thermal analysis system. Moreover, the water resistance, ultravioletresistance and wear resistance of TiO₂/KH-550/PU composite coatings were primarily evaluated. It hasbeen found that KH-550is bonded to the surface of nano-sized TiO by forming chemical bond. IntroducingTiO₂/KH-550helps to improve the water resistance, thermal stability, and ultraviolet resistance of PUcoating to some extent. When the dosage of TiO₂/KH-550reaches3%, relevant TiO₂/KH-550/PUcomposite coating has the strongest absorbance for ultraviolet. Besides, the TiO₂/KH-550/PU compositecoating containing2%TiO₂/KH-550has the smallest water-absorption （39.11%lower than that of PU）, andits water contact angle is increased from61.2°（PU coating） to82.6°（PU coating doped with TiO₂/KH-550）.Moreover, as-prepared TiO₂/KH-550/PU composite emulsion can be well used to improve the waterresistance and wear resistance of sheep leathers, and the friction coefficient of the treated sheep leathers isreduced from0.44to0.30（a reduction by31.20%）.