Processing of polypropylene–clay nanocomposites: Single‐screw extrusion with in‐line supercritical carbon dioxide feed versus twin‐screw extrusion

Abstract

Abstract This work investigates two different melt‐blending strategies for preparing compatibilized polypropylene‐clay nanocomposites, specifically: (1) conventional twin‐screw extrusion, and (2) single‐screw extrusion capable of direct supercritical carbon dioxide ( sc CO 2 ) feed to the extruder barrel. Proportional amounts (3 : 1) of maleic anhydride functionalized polypropylene compatibilizer and organically modified montmorillonite clay at clay loadings of 1, 3, and 5 wt % are melt‐blended with a polypropylene homopolymer using the two approaches. The basal spacing, degree of exfoliation, and dispersion of organoclay is assessed using X‐ray diffraction, transmission electron microscopy, and rheology. In terms of the latter, both steady shear and small‐amplitude oscillatory shear provide information about the apparent yield stress and solid‐like terminal behavior respectively. Finally, nanoindentation is performed to determine the room temperature modulus of each melt‐blended nanocomposite. The results reveal unequivocally that the high shear of the twin‐screw process is vastly superior to the single‐screw with in‐line sc CO 2 addition in generating well‐exfoliated, percolated polypropylene‐clay nanocomposites. It is likely that increased contact time between clay and sc CO 2 is necessary for sc CO 2 to positively affect exfoliation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 884–892, 2007