The preparation of nano-clay/polypropylene composite materials with improved properties using supercritical carbon dioxide and a sequential mixing technique

A semi-continuous process using scCO2 is reported for processing polymer–clay composites with high clay loading (i.e. 10 wt %) by reducing the collapse of the exfoliated clays. Two major modifications are involved in the new procedure: exfoliating the nano-clay directly into the hopper filed with pellets followed by processing the composite immediately and sequentially mixing the clay into the melt. This latter approach helped to minimize the clay collapse when processing the composites with high clay loadings. Transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD) results are provided to investigate the effect of sequential mixing on reducing the clay collapse in the nanocomposite. Surface modified montmorillonite (MMT) nano-clay/polypropylene (PP) composite at 10 wt % nano-clay with improved clay dispersion was obtained with increased modulus and tensile strength of 63 % and 16%, respectively, compared to the pure PP matrix.