| Synthetic leather is considered to be the best substitute material for natural leather due to excellent mechanical properties, abrasion resistance and chemical stability. But the dense polyurethane coating on synthetic leather will decrease the gas/water vapor permeability of synthetic leather, so that the sanitation properties of its products are affected greatly. In addition to the inherent properties of solid silica materials, hollow silica spheres possess smaller density, higher specific surface area and better adsorptivity and permeability because of their unique cavity structure. Therefore, hollow silica spheres have been widely applied in the fields of catalysis, environmental protection, drug delivery, etc. Based on this, hollow silica spheres were introduced into waterborne polyurethane(WPU). WPU/hollow Si O2 composite film with better water vapor permeability was prepared by using the cavity structure of the hollow Si O2 spheres to provide diffusion path for water vapor molecules.Hollow silica spheres were prepared by using cationic surfactant micelles as templates, tetraethyl orthosilicate(TEOS) and γ-aminopropyl triethoxysilane(KH-550) as silica sources, and ammonia as catalyst in an ethanol in water system. The structure and morphology of hollow Si O2 spheres were characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD) and brunauer-emmett-teller(BET). And the effects of the types and amounts of surfactant, ethanol-to-water volume ratio, ratio and total amounts of silicon sources, and reaction time on the morphology of hollow silica spheres were investigated. The results showed that hollow silica spheres possess a significant cavity with regular structure and narrow particle size distribution. The shell of hollow silica spheres is amorphous and possesses mesoporous structure, with average pore size of 34 nm. The specific surface area of hollow silica spheres is 484.71m2/g. Hollow silica spheres prepared with cetyl trimethyl ammonium bromide(CTAB) micelles as templates showed the best morphologies. With the increase of the amounts of CTAB, the particle size and shell thickness of hollow silica spheres reduced gradually. With the increase of ethanol-to-water volume ratio, the particle size of hollow silica spheres first increased and then decreased, while the shell thickness increased gradually. The particle size hardly changed but the shell thickness gradually increased with the increase of TEOS proportion in silicon sources. Increasing the reaction time could make the shell thickness of hollow silica spheres increased but had no effects on the particle size.Hollow silica spheres were introduced into WPU emulsion by physical blending method to prepare WPU/hollow silica composite emulsion and composite film. Then, the water vapor permeability, water uptake and mechanical properties of the composite coating were tested. The results showed that the introduction of the hollow silica spheres can significantly improve the water vapor permeability of WPU film. WPU/hollow silica composite film showed the better water vapor permeability when the cavity diameter of hollow silica spheres was bigger and the shell thickness was smaller. Under the precondition of better dispersion, with the increase of hollow silica spheres amounts, the water vapor permeability of WPU film increased gradually, and the water uptake and mechanical properties also improved. The WPU/hollow Si O2 composite emulsion was applied to non-woven fabric for synthetic leather, and the performance of obtained synthetic leather was tested. The results showed that both the air permeability and water vapor permeability of synthetic leather coated with WPU/hollow Si O2 composite emulsion were superior to that of synthetic leather coated with pure WPU emulsion. |
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