(584b) Poly(vinyl alcohol)-Platelet Nanocomposites: Preparation, Characterization and Gas Barrier Properties
Using poly(vinyl alcohol) as the binder, we have prepared polymer nanocomposites filled with different platelets, namely, sodium montmorillonite, laponite, or calcium niobate (a layered perovskite). The three types of platelets exhibit a large range of aspect ratio, from ~40 nm for laponite to ~300 nm for the perovskite. The polymer-platelet interfacial interaction varies among these materials, potentially influencing the nanocomposite morphology. The variation in aspect ratio may impact gas barrier performance. The goal of this work is to investigate these ideas. The platelets are first dispersed in deionized water with vigorous stirring and sonication. Perovskite exfoliation requires preliminary ion exchange and intercalation with tetrabutylammonium hydroxide. We have shown that it is critical to centrifuge the suspensions to eliminate the unexfoliated portion. Light scattering and atomic force microscopy results confirm that more than 90% of the platelets are exfoliated. Next, the platelet suspensions are blended with PVOH solutions at various solids ratios to form precursor solutions. Solid nanocomposites were prepared by the solvent-casting method, or by rapid precipitation (dropwise addition to a non-solvent for both PVOH and platelets). The nanocomposites were characterized by various techniques, including differential scanning calorimetry and wide-angle X-ray diffraction, to quantify platelet exfoliation or intercalation as well as the effect on PVOH crystallinity. The relative effectiveness of the two preparation methods for the formation of nanocomposite structure are compared and discussed. The oxygen permeabilities of the PVOH-platelet nanocomposites were measured on a custom-build gas permeation station. Oxygen permeability results are summarized, discussed and compared with analytical models.