Pressure−Volume−Temperature Dependence of Polypropylene/Organoclay Nanocomposites

Abstract

The pressure−volume−temperature (PVT) dependencies of commercial polypropylene melt (PP) and its nanocomposites containing X wt % of organoclay (Cloisite-15A, or C15) and 2X wt % of a compatibilizer were determined at T = 450−530 K and P = 0.1−190 MPa. C15 was used at concentrations: X = 0, 2, and 4 wt %. Three functionalized PP's were used as compatibilizers: two maleated and one grafted with glycidyl methacrylate. Incorporation of X = 2 wt % C15 into PP resulted in reduction of specific volume by ΔV ≈ 1%, but that of free volume (hole) fraction by Δh ≈ 5%. The latter quantity was computed from the Simha−Somcynsky lattice−hole equation of state. Furthermore, at constant T and P the hole fraction was found to be linearly related to the bulk-average energetic interaction parameter and to be a sensitive indicator of structural changes. In binary (polymer + organoclay) systems Δh is linearly related to the interlayer spacing, d001. So, where statements from the previous paper are repeated or there are similarities, this is done for purposes of comparison. In three-component systems (with a compatibilizer) the proportionality has been preserved, but large changes of Δh result in relatively small changes of d001. Mechanical properties hardly correlate with either Δh or d001, as polymer/compatibilizer morphology and crystallinity complicate the behavior.