The Preparation Of Titania/Polyurethane UV Blocking Coatings

Nowadays, inorganic-organic hybrid materials are becoming the hotspot in materials research, especially in coating and adhesive field. Because of the unique properties possessed by inorganic nano-materials, like silica and titania, the hybrid materials consisted of polymer and these inorganic nano-materials ulteriorly attracted the attention of researchers.In this paper, the preparation of titania/polyurethane UV blocking coating and the preparation of nano-silica reinforced ether adhesive were discussed. Also, the effects of preparation methods and experiment conditions on the structure and performance of materials were investigated.(1) Ethanol-based titania sol and titania-silica hybrid sol have been synthesized in this study. During the process to acquire titania sol, acetylacetone was used to chelate with tetrabutylorthotitanate, which led to modified organic titania precursor. Subsequently, transparent sol was obtained under acid-catalyzed condition. The preparation of silica-titania hybrid sol was based on this protocol. In order to get hybrid sol, acidic silica sol was prepared first with the catalysis effect of acid. Then, acetylacetone chelated tetrabutylorthotitanate was added into silica sol. Through hydrolysis and condensation process and the effect of silane, silica-titania hybrid was obtained. After mechanic mixing of sols with water-borne polyurethane dispersion, UV-blocking coating was acquired. Transparent UV-blocking films could be prepared by rods. UV-vis spectra and accelerated weathering tester were utilized to investigate the UV-blocking performance of the hybrid coatings. At the same time, the modification effect of silica on the weathering property of the films was also studied. Moreover, in order to extend the UV-shielding range, cerium oxide ethanol dispersion was doped into the silica-titania sol, through which coatings with better UV-blocking performance were obtained.(2) A novel and facile miniemulsion-combined sol-gel process to fabricate water-borne UV-blocking additive was also presented. In this approach, the oil phase composed of acetylacetone(Acac) modified titanium (IV) butoxide (TBT),dimethyl benzene(DB) and hexadecane(HD) were confined in the miniemulsion droplet microreactors with the aid of a cationic emulfier hexadecyltrimethylammonium bromide(CTAB). Then, a silica layer was coated onto the miniemulsion droplets by the co-condensation of amino-silane and tetraethyl silicate (TEOS). At the same time, TBT in the miniemulsion droplets diffused to the O/W interface and then initiated the sol-gel reaction, hence TiO₂-SiO₂ hybrid colloids were obtained. TEM,FTIR,EDX and XPS methods were utilized to investigate the structure of as-prepared hybrids Some influencing parameters, such as the concentrations of TBT in the oil droplet, the content of amino silane in the silica precursor, etc., on the morphology of the hybrid colloids were investigated. UV-visible spectra and dye degradation experiments showed that the polyurethane films doped with these hybrid colloids had a very good UV-blocking property.(3) Nanosilica reinforced waterborne silylated polyether adhesives were prepared with silylated polyether emulsion, tetraethyl orthosilicate (TEOS), silica sol and fumed silica powder. Effects of TEOS content, silica sol content and the type and content of fumed silica on the shear strength of the adhesive and their strengthening mechanisms were investigated using a scanning electronic microscope and an electronic instron tester. Colloidal silica particles was less efficient than fumed silica particles for reinforcing the polyether adhesive but can increase the shear strength of fumed silica embedded adhesive. Comparing the adhesives with the hydrophilic fumed silica or the extremely hydrophobic fumed silica, the adhesive with moderate hydrophobic fumed silica had the highest shear strength. It seemed that TEOS, silica sol and fumed silica played crosslinking (with polyether chain), dispersing (for fumed silica) and reinforcing roles on waterborne adhesive, respectively.