Characterization of polyurethane adhesives containing nanosilicas of different particle size

Three nanosilicas with different particle sizes were added to a polyurethane adhesive (PU). The filled adhesives were characterized by thermal gravimetric analysis (TGA), dynamic mechanical analysis (DMA), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and contact angle measurements. Adhesive strength was evaluated from single lap shear test of solvent wiped stainless steel/polyurethane adhesive joints. Addition of nanosilica filler altered the degree of phase separation between the hard and soft segments in the polyurethane, in different extent depending on the nanosilica particle size. Furthermore, upon curing higher degree of crosslinking was obtained in the nanosilica filled polyurethane. The nanosilicas agglomerated into the polyurethane matrix. On the other hand, the addition of nanosilica increased the surface energy of the polyurethane to a greater extent by increasing the nanosilica particle size and moderate increase in the single lap shear strength of stainless steel/polyurethane adhesive joints was obtained.