Structure, permeability, and rheology of supercritical CO2 dispersed polystyrene-clay nanocomposites

Abstract

Improvement in clay dispersion and clay-polymer interfacial interactions are keys to producing superior nanocomposites. A supercritical CO2 (scCO2) processing method was utilized to pre-disperse commercial organic clays, for further solvent mixing with polystyrene (PS) to form nanocomposites with significant dispersion and interfacial enhancement. The effect of scCO2 processing on clay pre-dispersion, and clay dispersion and interfacial interaction in nanocomposites were investigated. SEM and WAXD of the clays indicated that after scCO2 processing the clays lose their long region ordered layer structure appreciably, associated with reduction in particle size. WAXD and TEM of the PS/clay nanocomposites showed that the polymer penetrated into the pre-dispersed clay, leading to a disordered intercalated/exfoliated structure with improved interfacial interaction rather than a disordered intercalated structure as seen with as-received clays. Relationships between those structures, rheological and barrier properties were investigated. The scCO2-processed nanocomposites showed a plateau in the low-frequency storage modules and increased complex viscosity, each associated with significant clay dispersion in the nanocomposite. With only 1.09% volume fraction of clay, significant reduction (∼49%) of oxygen permeation was achieved.