Preparation And Characterization Of Waterborne Polyurethane/Nanosilica Composite

Compared with pure PU, the nanocomposites could not only bring great improvement in mechanical properties, heat resistance and water-resistance, but also endow some the special properties of nano-materials such as UV shielding, conductivity, thermal insulation, abrasive resistance and other functions. Traditionally, the polyurethane-SiO₂ nano-hybrid composites are traditionally prepared via in situ process, sol–gel process, or direct mixing process. The basic sol-gel process involves the hydrolysis and polycondensation reactions of metal or silicon alkoxide, e.g. Si(OEt)4 or Si(OMe)4, which are governed by the value of pH, solvent, catalyst and temperature. The drawbacks of traditional sol-gel process are the tedious preparation procedure and the difficulty to control the reaction. The in situ process is only suitable for solution containing the metal, sulfide or hydroxide. The nanoparticles were easily to aggregate and bad dispersibility during the direct mixing process, and leaded to limit enhancement of the PU performance.In this work, we synthesized the PU/SiO₂ composite via the methods of glycol dispersing, adding polymer electrolyte dispersant, and grafting modified nanosilica.1. The waterborne polyurethane/nanosilica composite (PU/SiO₂) was prepared by dispersing nanosilica in polytetrahydrofuran glycol (PTMG) and preformed polymer separately. The properties of the two series emulsions were tested and analysed. And the different effect of the emulsion obtained by two methods on mechanic performance, thermostability, water resistance and UV absorbance was studied.2. Via the method of adding nanosilica (SiO₂) with acetone to polyurethane prepolymer and adding the polymeric electrolyte dispersant PAAS during emulsification, the IPDI-waterborne polyurethane/nanosilica (PU/SiO₂) composite with different content of SiO₂ was synthesized using isophorone diisocyanate (IPDI), polytetramethylene glycol, dimethylol propionic acid and 1,4-Butanediol. The structure of PU/SiO₂ was confirmed by the Fourier transform infrared spectroscopy (FTIR). The scanning electron microscopy indicated that SiO₂ was dispersed very well in waterborne polyurethane. The water resistance, tensile strength, thermostability and UV absorbance of the composite films were studied.3. The nanosilica was modified byγ-aminopropyl triethoxysilane (KH550), so that the surface of the nanosilica had amino with highly reactivity. The PU/SiO₂ was obtained by modified SiO₂ reacting with NCO-terminated polyurethane. Fourier transform infrared and scanning electron microscopy confirmed the structure and dispersion of the composite films. And properties of the films were investigated.