Synthesis and characterization of clay-nanocomposite solvent-based polyurethane adhesives

In this work nanocomposite adhesives obtained using an organically modified montmorillonite (OMM) in a polyurethane matrix were studied. An amount of organoclay ranging from 3% up to 18% by weight was added to the polyol resin before mixing with isocyanate. In particular, a typical adhesive formulation used in laminated films for food packaging was studied. The effect of different preparation procedures was compared in order to correlate exfoliation with rheological and mechanical properties. The basal distance of OMM before and after mixing with the polyol and after curing was characterized by X-ray diffraction. Composites with low content of OMM show an intercalated structure. A mix of exfoliated and intercalated layers was observed in the composites with the highest OMM content, before and after curing. The basal distance of OMM decreases after solvent mixing and curing, suggesting that exfoliation and intercalation are improved with respect to the uncured system. The viscosity of polyols-OMM systems was studied as function of shear rate in a cone-plate rheometer in order either to check the possible degradation of the polyol oligomer on to correlate the viscosity with the aggregation state of OMM. Viscoelastic properties of polyol oligomer were obtained by shear dynamic mechanical tests in the frequency range 0.1–16 rad/s. Finally the tensile properties of polyurethane clay-nanocomposites were measured.