Nano-oxide Modified Polyurethane Elastomer

In this thesis, the optimum grafting conditions and grafting effects of nano-particles(including SiO2,TiO₂,Al₂O₃) modified via direct grafting and TDI activation method were discussed. The results of nano-silica modified with Poly(oxypropylene glycol) (PPG) via direct grafting method showed that grafting ratio was raised as a function of the grafting temperature, the optimum grafting temperature was 140°C. The results of nano-silica modified with PPG via TDI activation method showed that grafting ratio increased at first then decreased to a lowest point, then increased again and decreased afterwards as a function of NCO/OH ratio, the optimum NCO/OH ratio is 1:0.9. It was found that ultrasonic vibration had some good effect on the dispersion and grafting ratio of nano-paticles. Fourier transform infrared spectroscopy(FTIR) and thermal gravimetric analysis(TGA) results demonstrated that the grafting molecule chains(PPG and TDI) were combined with the hydroxyl groups on surfaces of nano-particles via chemical bonds. A larger grafting ratio was obtained via TDI activation method. Sedimentation experiment and transmission electron microscopy(TEM) results demonstrated that stable steric hindrance layer was established on the surface of nano-particles after the grafting modification. It not only increased the dispersibility of the particles, but also improved the compatibility between the nano-particles and the polyurethane elastomer matrix. Studies of polyurethane elastomer(PU) composites either prepared by in-situ polymerization or filled by modified nano-particles via TDI activation method showed that the tensile strength and elongation at break were improved, and it also indicated that the latter method was much better. By comparison of the properties of PU composites, the best filler content of each nano-particle was obtained. It was found that the nano-silica increased the thermal stability of PU composites when using in-situ polymerization method.