Addition of different amounts of a urethane-based thickener to waterborne polyurethane adhesive

To adjust the rheology of waterborne polyurethane adhesives, different amounts of a hydrophobically modified ethoxylated polyurethane thickener (HEUR) were added. The thickened adhesive solutions were characterized by flow rheology, pH measurements, particle size, solids content and confocal microscopy. The thickened solid adhesive films were characterized by IR spectroscopy, plate-plate rheology, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. The adhesion was measured from T-peel test of plasticized PVC/polyurethane adhesive/plasticized PVC and leather/polyurethane adhesive/SBR rubber joints. The addition of the HEUR thickener increased the viscosity of the polyurethane dispersion, and a shear-thinning behaviour was observed due to polyurethane-thickener interactions. The addition of thickener improved the rheological properties of the polyurethane, more noticeable as the content of the thickener increased. The crosslinking of the thickened polyurethane was studied by confocal microscopy. Although the addition of the thickener did not greatly affect the thermal properties of the polyurethane, an improvement in the adhesive strength of leatlier/adhesive/SBR rubber joints was obtained. (C) 2008 Elsevier Ltd. All rights reserved.