(81a) Supercritical Carbondioxide Dispersion of Nano-Clays and Clay-Polymer Nanocomposites

Dispersed polymer/clay nanocomposites are of great interest because they can offer significant property enhancements. Achieving a high level of clay dispersion has been a key challenge. In this paper, we explore a novel supercritical carbon dioxide (scCO2) processing method that utilizes scCO2 to disperse nano-clays. The structure and properties of the clays and the resultant nanocomposites are characterized using a combination of wide-angle X-ray diffraction (WAXD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and rheology. Our results indicate that nano-clays can be delaminated by the scCO2 process and the extent of dispersion is dependent on the CO2-philicity of the nano-clay. Significant dispersion was achieved with Cloisite 93A, whereas relatively little dispersion was achieved for Cloisite Na+. It appears that the presence of an acidic hydrogen on the ammonium salt (as in the case of 93A) or an increased positive charge on the N of the ammonium salt (I-30P) increases the CO2-philicity of the nano-clay and therefore increases dispersion. In addition, results demonstrate that natural clay (Cloisite Na+) can be dispersed by combining CO2-philic PDMS with the clay prior to processing. The resultant dispersed Cloisite-Na+-PDMS nanocomposite had significant enhancements of the rheological properties, and showed a solid-like low-frequency plateau, characteristic of dispersed nanocomposites with good polymer-clay interactions. Therefore, other CO2-philic polymers may be capable of dispersing natural clay, which could lead to significantly superior nanocomposites at a reduced cost.