(275a) Supercritical Carbon Dioxide (scCO2) Processing of Polystyrene/Clay Nano-Composites: Structures and Properties

Improving clay dispersion and clay-polymer interfacial interactions are keys to enhancing barrier property of nanocomposites,. A supercritical CO₂ (scCO₂) processing method was utilized to pre-disperse commercialized organic clays, and then those pre-dispersed clays were compounded with polystyrene (PS) to form nanocomposites with significant dispersion and interfacial enhancement. The effects of scCO₂ processing on clays pre-dispersion and polymer-clay dispersion and interaction in nanocomposites were investigated. SEM and WAXD of the clays indicated that after scCO₂ process the clays lost their long region ordered layer structure, the size of particles and the tightness of packing are reduced, among different clays, those with lower inter-modifiers interaction tend to be dispersed. WAXD and TEM of the PS/clay nanocomposites show that PS have penetrated into the inter galleries and the pre-dispersed clays lead to a disordered intercalated/ exfoliated structure with improved interfacial interaction rather than a disordered intercalated structure as “as-received” clay did. The effects of clay modifier, clay weight fraction and scCO₂ processing on clay dispersion and polymer-clay interactions in nanocomposites were investigated. Structure- barrier property relationship was set up based on several phenomenological models study. Results indicated that scCO₂ processing lead to a more homogenous dispersion and achieved a nearly 83% reduction of oxygen permeation in PS/clay system with only 3.3 vol% clay, which corresponding to an effective aspect ratio of 109.09±4.35. Moreover, among those phenomenological models, Cussler random array model shown the best fit and given a more realistic prediction of effective aspect ratio in nanocomposites.