Effect of organoclay-type and clay-polyurethane interaction chemistry for tuning the morphology, gas barrier and mechanical properties of clay/polyurethane nanocomposites

Abstract Organo-modified montmorillonite (Mt) and bentonite reinforced clay/polyurethane nanocomposite (CPN) films were produced by master-batch based melt-mixing route, followed by compression molding. A novel route for preparation of master-batch by solution mixing was explored by using sonication and high-speed stirring. It was found that master-batch prepared by solvent mixing route resulted in good dispersion of clay-platelets in master-batch and finally in CPN. The concentration of both organoclays was varied from 1 to 5 wt% in final CPN, which were prepared by melt-mixing of master-batch and neat polyurethane (PU) in a twin-screw extruder. The presence of hydroxyl group in the clay-modifier of Mt, attributed to nearly exfoliated structure up to 3 wt% due to improved interaction by hydrogen bonding with ether groups or urethane linkages. Whereas, organo-modified bentonite showed partially intercalated and flocculated morphology, due to the absence of any polar group in the clay-modifier. As a consequence, Mt/PU nanocomposites showed much better mechanical and gas barrier properties in comparison to bentonite/PU nanocomposites. Moreover, a significant reduction in helium gas permeability and improvement in mechanical (tensile and tear) properties were observed for CPN produced with both organoclays in comparison to neat PU. At lower volume fraction of organoclays, a good correlation was obtained between gas permeability values determined experimentally and predicted by two different mathematical models.