PU elastomers comprising spherical nanosilicas: Balancing rheology and properties

For polyurethane (PU) engineering elastomers, although urethane chemistry allows tailoring of elastomer properties, there is an inherent correlation between increasing strength and decreasing elongation-to-break. The ability to break this correlation provides great potential for creating high-performance materials that possess attractive combined properties. The incorporation of nanofillers is one of the promising approaches. However, while property enhancement is achieved, nanocomposite systems often experience significant increase in viscosity leading to process difficulty. In this paper, the use of nanospherical particles to mitigate the rheology was explored. We were able to achieve significant property enhancement in the ultimate mechanical properties and thermal stability while maintaining low viscosity during process. By first forming well dispersed nanosilica in polyol, followed by elastomer casting, material with significantly higher strength, elongation-to-break, thus, toughness, and degradation temperature than one without nanosilica was obtained. The performance improvement is attributed to the ability to form a low viscosity, stable nanofluid where the nanosilicas are present as primary nanoparticles in the polyol. The morphology of the formed elastomers was studied. It is hypothesized that nanoparticles reduce defects that contribute to premature failure of the elastomer, thus improving ultimate properties.