Effect of organoclays on the properties of polyurethane/clay nanocomposite coatings

摘要

Linear, one-binding-site or two-binding-site (N~+) organifiers with two hydroxyl end groups were synthesized, and novel organoclays were prepared through a cation-exchange reaction between pristine sodium montmorillonite and the synthesized organifiers. After sonication of the as-prepared organoclay in N,N~1- dimethylformamide for 10 min, the average size of the clay decreased to about 1 μm. The X-ray diffraction patterns confirmed that the d-spacing of the silicate layers of the organoclay expanded from 1.1 to about 1.9 nm and the peak intensity decreased with the molecular weight of the organifier increasing. Polyurethane/clay nanocomposites were synthesized by a one-shot polymerization method. Both intercalated and exfoliated structures of the layered silicates in the polyurethane matrix were observed from transmission electron microscopy micrographs, and the d- spacing ranged from 4 to 10 nm. The thermal and mechanical properties of the nanocomposite were enhanced by the introduction of the organoclay into the polyurethane matrix. An approximately 40-46°C increase in the onset decomposition temperature, a 200% increase in the tensile strength with a 0.5 wt % clay loading, and a 49% increase in Young's modulus with a 3 wt % clay loading were achieved. The effects of the molecular weight and the number of binding sites of the organifier on the properties of the nanocomposites were also evaluated.