Hybrid silicas/waterborne polyurethane composite properties: In situ formation vs. grafting methods

A series of composites of commercial waterborne polyurethane and hybrid silica were prepared by the sol-gel process through in situ synthesis. Mechanical properties, small angle X-ray scattering and differential scanning calorimetry measurements were performed to evaluate the effects that hybrid silica has on the properties of the resulting polyurethane composites. A series of 13 different organosilanes differing in polarity and alkyl chain length was studied. Under the present evaluated conditions, composites bearing hybrid silica were more likely to exhibit a reduction in mechanical resistance when compared to bare polyurethane. Samples also exhibited a negligible variation in glass transition temperature and a reduction in Delta Cp. The enthalpy of the crystallization process exhibited an increase. Based on the small angle X-ray scattering measurements, the composites exhibited a small reduction in the interdomain spacing and an increase in the degree of phase separation.