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

Authors: 
Yang, F., Merck & Co
Kriegel, R., Coca Cola
Kannan, R., Johns Hopkins University School of Medicine



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.