Structural and adhesion properties of waterborne polyurethane adhesives containing nanosilica dispersion obtained with different physical mixing procedures

Nanosilica dispersion was added to waterborne polyurethane dispersion by using three different physical mixing procedures differing in the flow regime (tangential, laminar, radial) and the stirring rate (300-2400 rpm). The influence of the physical mixing procedure on the structural, thermal, rheological, mechanical, surface and adhesion properties of the polyurethanes (PUs) containing 1 wt% nanosilica was evaluated. The nanosilica in the dispersion was functionalized with acrylic moieties and showed high surface tension and negative Z potential values. The PU + nanosilica blend made with higher shear rate and laminar flow regime showed high homo-geneous dispersion of the nanosilica particles and greater extent of intercalation between the soft segments of the polyurethane, this led to higher thermal stability. Unexpectedly, the better dispersion of the nanosilica in the PU matrix decreased the wettability of the PU + nanosilica materials due to the migration of acrylic moieties from the nanosilica particles to the surface. As a consequence, a decrease of the final T-peel strength was found. However, the single lap-shear strength did not change by adding nanosilica because of the scarce improvement of the mechanical properties in the PU + nanosilica materials.