Synthsis And Properties Of Waterborne Polyurethane Hybridized With Nanosilica And Siloxane By Sol-gel Process

Hybridized waterborne polyurethane by nanomaterial is an important method in the modification of waterborne polyurethane. In the previous researches, nanoparticles were directly added into waterborne polyurethane, which resulted in nanoparticle's agglomeration and incompatibility between nanoparticles and polyurethane, and influenced the properties hybrid materials. In the thesis, waterborne polyurethane/SiO₂ organic-inorganic hybrid materials based on sol-gel technology were prepared by using tetraethoxysilane(TEOS) as precursor, silane coupling agent 3-aminopropyltriethoxylsilane (APTES) as bridging agent between polyurethane and nanoparticles, respectively. Thus, nanoparticles were chemically bonded with polyurethane backbone. The effects of TEOS content on the structure and properties of hybrid materials were investigated.Waterborne polyurethane/SiO₂ organic-inorganic hybrid materials were prepared by two methods. The first one is as follows: waterborne polyurethane/SiO₂ materials were prepared by the hydrolization and condensation of TEOS or/and APTES endcapping the WPU molecular chain. The hybrid emulsions exhibit excellent storage stability. The hybrid was characterized by SEM, EDS, TEM, FTIR and XPS. The effect of TEOS on surface wettability, water resistance, mechanical strength and thermal properties of the hybrid was also evaluated by contact angle measurement, water absorption test, mechanical test, TGA and DSC, respectively. The result showed that well dispersed nano-silica in WPU was synthesized, with a typical diameter of about 50 nm. And the results indicated that the addition of nanosilica affected the crystallinity of polyurethane. Additionally, chemical interaction occurred between WPU and silica. Also, an increase in advancing contact angle, water resistance, tensile strength, thermal stability was obtained with the addition of TEOS, while elongation at break and glass transition temperature deceased,Another method was based on the principle of two-step method. Silica sol was prepared firstly with TEOS as precursor, hydrochloric acid as catalyst, water and absolute ethyl alcohol as solvent. Then waterborne polyurethane/SiO₂ organic-inorganic hybrid materials were prepared by the hybrid reaction between silica sol and polyurethane endcapped by APTES. The results indicated that the addition of silica sol into polyurethane enhanced the hybrid material's resistance to low temperature, thermal stability, water resistance and hydrophobicity. Elongation at break and glass-transition temperature decreased.