A study on montmorillonite/polyethylene nanocomposite extrusion-coated paperboard

Extrusion coating was used to obtain montmorillonite/polyethylene-coated paperboard. The coating was prepared from a master batch containing maleated polyethylene, low-density polyethylene and 32 wt.% polyvinylpyrrolidone-surface-modified montmorillonite clay, which was blended with different amounts of low-density polyethylene to yield composites with 4 wt.% and 8.3 wt.% montmorillonite. X-ray diffraction revealed that the clay stacks in the coating were more extensively intercalated than in the original surface-modified clay. Transmission electron microscopy showed that the clay stacks were, to a large extent, separated by the high shear forces during extrusion into smaller evenly distributed entities. This was, unfortunately, achieved at the expense of the formation of a great many voids and pinholes, as revealed by transmission electron microscopy and dye staining. This had strong negative effects on the oxygen barrier properties but only a modest effect on the water vapour permeability. Tensile tests showed that the coating was always ductile and that the coating paperboard adhesion decreased with increasing clay content. The creasability was good and unaffected by the presence of the filler in the coating. Thermogravimetry showed that the degradation temperature in air of the filled coatings were of the order of 10degreesC higher than that of unfilled polyethylene. Copyright (C) 2004 John Wiley Sons, Ltd.