The interplay of thermodynamics and shear on the dispersion of polymer nanocomposite

Abstract

Most of work on polymer/layered silicate nanocomposites (PLSN) focused on the importance of the chemistry used to modify the surface of the clay, usually montmorillonite (MMT) and characterization of the nano-scale structure obtained in the last decade. The role and importance of processing has been paid attention only recently. Our purpose of this study is to determine the effect of the chemistry and shear on the dispersion of clay in polymer matrix via dynamic packing injection molding (DPIM), in which the melt is firstly injected into the mold then forced to move repeatedly in a chamber by two pistons that moved reversibly with the same frequency as the solidification progressively occurs from the mold wall to the molding core part. A special orientation region between the skin region and the core region is produced via imposing the reversible shear effect during the cooling of the melt. The initial MMT and organic modified MMT (abbreviated as OMMT) were directly injection molded with powdered iPP in the DPIM without pre-extrusion. Without shearing, only an intercalated structure was obtained through organic modification and the diameter of OMMT particles has a significant reduction compared to the initial MMT. Under the effect of shear, however, an intercalated morphology in the oriented region and an exfoliated morphology in the core region can be achieved. Our result suggests that both the chemistry and shear are important to determine the dispersion of clay in polymer matrix. PP/clay nanocomposites with excellent impact strength can be prepared via simple one step, direct injection molding without a conventional pre-extrusion, by dynamic packing injection molding. The observed change of impact strength could be related to the local hierarchical structure developed during the processing.