(217bz) Investigating the Factors Controlling MMT Platelet Dispersion in MMT/Pvoh Nanocomposites

The properties of polymer nanocomposites containing exfoliated inorganic platelets (e.g., montmorillonite, MMT) depend on the degree of platelet exfoliation as well as the quality of platelet dispersion in the polymer matrix.  This work explores the factors that control platelet dispersion in the polymer during solution blending and solvent evaporation via a model polymer nanocomposite system composed of MMT platelets blended with polyvinyl alcohol (PVOH).  Nanocomposite films were prepared by solution blending of aqueous PVOH solutions with dilute suspensions of fully exfoliated MMT platelets (as confirmed by AFM).  Dynamic light scattering (DLS) indicates that addition of MMT suspensions to PVOH solutions results in undesired particle aggregation and thus poor MMT dispersion in cast films (as evidenced by TEM images and water vapor permeation measurements).  We believe that PVOH bridging induces MMT platelet aggregation.  To counteract bridging aggregation, we explore the idea of pretreating the MMT surface with a small amount of compatible polymer prior to solution blending with PVOH.  We hypothesize that “pre-coating” the MMT platelet surfaces with adsorbed polymer in dilute suspensions will protect the platelets from bridging aggregation during solution blending and solvent evaporation.  MMT/PVOH films have been prepared using low molecular weight PVOH as the pre-coat polymer, and low, medium, and high molecular weight PVOH as the matrix polymer.  DLS shows that pre-coated MMT platelets are less susceptible to aggregation during blending with PVOH solutions.  Results will be shown comparing the crystallinity, dissolution behavior, water vapor permeation rate, and dynamic mechanical properties of MMT/PVOH films incorporating untreated versus pre-coated MMT.  We also hope to present results featuring the use of a PEO-PPO-PEO block copolymer (from the Pluronics® family) as the pre-coat polymer.