Preparation And Characterization Of Polyester-based Polyurethane/SiO₂(TiO₂) Nanocomposite Coatings

Organic-inorganic nanocomposite materials may combine the advantages of two components, even acquire some novel properties because of their special structures, and are becoming one of the most intersting research areas in recent years.In this dissertation, the Sol-Gel process was applied to produce silica or titania sols, which was then directly introduced into polyester by in situ and blending methods, and cured by IPDI trimers to obtain polyester-based polyurethanes with excellent properties. The structure and properties of polyester resins and polyester based polyurethanes embedded by nanosilica particles, silica networks and tatania networks were investigated in detail. Some main conclusions are summarized below:(1) Introducing silica with particle structureThe silica particles were introduced into polyester resin by in situ and blending methods. It was found that more polyester segments were bonded at the surfaces of silica particles by in situ method than by blending method, the steric resistance obtained by chemically bonded polyester segments impaired the interaction between particles, resulting in decreasing viscosity of nanocomposite resin and homogeneous dispersed silica particles. The viscosity of nanocomposite resins first increased, then decreased with the increase in particle size, and a critical viscosity at 10 wt%for resins obtained by in situ method while at 6 wt % for resin obtained by blending method were observed.The Tg, tensile property, abrasion resistance and UV resistance ofcorresponding polyester-based polyurethane/silica nanocomposites could be obviously improved when silica particles were embedded, especially for nanosilica at the size of 28nm~66nm . In situ method caused better properties than blending.The silica particles could move towards the surface and interface of nanocomposite coats to lower free energies. Although no particles were observed in the surface by AFM, the XPS indicated higher silica content at the surface than at the interface.(2) Introducing silica with network structureThe silica with network structure was introduced into polyester resin, further cured by IPDI trimers to obtain transparent polyester-based polyurethane/silica hybrid coats. There were primary silica-rich phases and agglomerates of silica-rich phases in hybrid coats with radius of gyration (Rg) lower than 20nm. All of their fractal dimension values (Dm) were lower than 3, and the former value was lower than the latter, which mean the silica-rich phases existed with the loose network structure. In comparison with blending method, in situ method had much stronger interactions between organic-inorganic phases and inorganic-inorganic phases as well for hybrid resins and their corresponding hybrid coatings, resulting in higher viscosity of hybrid resin, higher Tg, modulus and cross linking density for hybrid coats and extent of micro-phase separation. For in situ method, the higher the embedded silica was, or the more ethoxy groups existed at the surface of silica, the stronger the interaction was, the better the properties were. However, little was changed for hybrid coatings obtained by blending method.Obvious agglomerates of silica-rich phase were observed by AFM for the hybrid coats obtained by in situ method while those agglomerates were only observed for the hybrid coats obtained by blending method at relatively high silica content. The surface silica content was higher for hybrid coating obtained by blending method than by in situ method since the former caused weaker interaction between organic-inorganic phase and smaller size of silica-rich phases, which availed the immigration of silica particles at the surface.