Use of precipitated silica with silanol groups as an inorganic chain extender in polyurethane

In this study, novel polyurethane/silica (PU/SiO2) hybrid materials, prepared without an external crosslinking agent, were developed via the chemical reaction between urethane groups of PU prepolymer and hydroxyl groups at the surfaces of silica. The added inorganic filler-silica thus played the dual roles not only inorganic chain extender but also reinforcing agent in the preparation of the hybrid. Two different blending methods, were compared with respect to the mechanical properties of the PU/SiO2 hybrid materials: stirring mixing and three-roller shear mixing. The hybridization mechanism was confirmed using Fourier-transform infrared spectroscopy (FT-IR), solid-state 29Si NMR spectroscopy and X-ray diffraction (XRD). The dispersion of silica particles in the PU matrix was investigated by scanning electron microscopy (SEM). Because of the shear effect of three-roller shear process, the size of the silica aggregates tended to be more uniform. The tensile strength and elongation at break of the PU/SiO2 hybrid were 51 MPa and 590%, respectively, which represent increases of fourfold and 39% compared to those of neat PU. The thermogravimetric analysis (TGA) results for the PU/SiO2 hybrids indicated greater thermal stabilities and lower decomposition rates after hybridization. This work contributes new insights into the preparation of high-performance PU/SiO2 hybrids. Keywords: Polyurethane, Silica, Hybrid material, Chain extender, Preparation