On the strategies for incorporating nanosilica aqueous dispersion in the synthesis of waterborne polyurethane/silica nanocomposites: Effects on morphology and properties

In this work the synthesis of waterborne polyurethane/nanosilica nanocomposites by using two different strategies is presented, starting from a vinyl terminated polyurethane prepolymer (PUP) based on isophorone diisocyanate and polypropylene glycol, and varying the nanosilica content. In one case, the PUP was dispersed in an aqueous solution containing glycerol-functionalized colloidal nanosilica particles and the dispersion was further polymerized; in the other case, the PUP was dispersed in an aqueous media, then colloidal nanosilica was added to the dispersion and then polymerized. A physical mixture was also prepared for comparative purpose. Films were prepared by casting of the aqueous dispersion. The morphology of the dispersions and films depended on the incorporation route of nanoparticles as was observed by SAXS, SEM and TEM. While the blends had significantly less hydrogen bonding between the hard segments of the PU and nanosilica particles, samples prepared by the two different methods proposed in this work showed an strong interaction between both materials in agreement with FTIR and DSC results. Synthesis pathway plays an important role in order to obtain high performance waterborne polyurethane/nanosilica composites, since final properties of the films also depended on the nanoparticle incorporation strategy.

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