Rheology of PP/Clay hybrid produced by supercritical CO2 assisted extrusion
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Polypropylene (PP)-layered silicate nanocomposites were developed using a new processing method involving a supercritical carbon dioxide (scCO2)-assisted co-rotating twin-screw extrusion process. The nanocomposites were prepared through two step extrusion processes. In the first step, the PP/clay mixture was extruded with CO2 injected into the barrel of the extruder and the resulting foamed extrudate was cooled and pelletized. In the second step, the foamed extrudate was extruded with venting to produce the final PP/clay nanocomposites without CO2. In this study, organophilic-clay and polypropylene matrix were used. Maleic anhydride grafted polypropylene (PPg-MA) was used as a compatibilizer. This study focused on the effect of scCO2 on the dispersion characteristics of the clays into a PP matrix and the rheological properties of the layered silicate based PP nanocomposites. The dispersion properties of clays in the nanocomposites as well as the rheological properties of the nanocomposites were examined as a function of the PP-g-MA concentration. The degree of dispersion of the clays in the nanocomposites was analyzed by X-ray diffraction and transmission electron microscope. Various rheological properties of the nanocomposites were measured using a rotational rheometer. In the experimental results, the scCO2 assisted continuous manufacturing extrusion system was used to successfully produce the organophilic-clay filled PP nanocomposites. It was found that scCO2 had a measurable effect on the clay dispersion in the polymer matrix and the melt intercalation of a polymer into clay layers.
Keywordsnanocomposites rheology polypropylene extrusion supercritical fluid
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