Supercritical CO₂-Mediated Intercalation of PEO in Clay

Abstract

Introduction. Polymer/clay nanocomposites prepared by a variety of methods that embed these inorganic nanolayers to a polymer host have been actively studied in recent years as these materials exhibit dramatic, concurrent improvements in many properties. 1 Typical preparation methods include in-situ polymerization, solution intercalation, and melt intercalation, among which solution intercalation has been known for over a century and has proved to be one of the most successful methods of incorporating delaminated clay into polymers. 2 Many polymers have been intercalated into clay via this method: Examples include water-soluble polymers such as poly(ethylene oxide) and poly(vinyl alcohol) 3,4 and organic solventsoluble polymers such as high-density polyethylene, 5 poly(L-lactide), 6 etc. Despite many laboratory successes with solution intercalation, its application on an industrial scale is still hindered by two major problems: (1) involvement of large quantities of aqueous/organic solvent; (2) a limited number of solvent/polymer pairs available for polymer dissolution and subsequent intercalation.During the past decade, supercritical carbon dioxide (sc CO 2 ) has attracted a great deal of attention as an "environmentally benign, inexpensive, and nonflammable alternative" solvent for polymer synthesis and processing. 7,8 The low viscosity, near-zero surface tension, relative chemical inertness, and high diffusivity of sc CO 2 results in negligible competitive adsorption with guest molecules on the host substrate and therefore facilitates solute transfer relative to normal solvents. Furthermore, since CO 2 is a gas at ambient conditions, the tedious drying procedure associated with conventional liquid solvents is circumvented, and the product is free of residual solvent upon depressurization.These unique properties of sc CO 2 have been exploited to prepare polymer blends. [9][10][11][12] The usual method employs sc CO 2 as a swelling agent to facilitate the diffusion of a guest monomer into a CO 2 -swollen polymer matrix. Subsequent polymerization develops a blend of submicron phase-separated polymers. Recently, an in-situ polymerization method used sc CO 2 as a processing aid to achieve a uniform reinforcement distribution in a polymer/clay composite at high clay loading (∼40 wt %). 13 Intercalation of unreactive small molecules into layered clay in the presence of sc CO 2 has also been

A comparative study of polyethylene oxide/nanoclay composite preparation via supercritical carbon dioxide and melt processing

“…Therefore, it was concluded that the ScCO 2 preparation yielded more homogenous samples as no non-intercalated PEO remained in the composites prepared using ScCO 2 . The findings of the DSC analysis is in agreement with those reported by Zhao and Samulski [6] who found that, compared with composites prepared by solution methods, composites prepared via ScCO 2 processing had lower T m and smaller ΔH m .…”

“…Zhao and Samulski reported the preparation of polymer/nanoclay composites with PEO of molecular weight 10,000 using ScCO 2 processing [6]. Their study compared two methods of sample preparation in which the PEO was intercalated into montmorillonite clay via either a small scale (2.5 ml chamber) ScCO 2 process or solution modification using water or alcohol as solvent.…”

Recent Advances in Polymer/Layered Silicate Nanocomposites: An Overview from Science to Technology

“…20 Zhao et al 21 presented unambiguous evidence for sc-CO 2 mediated intercalation of PEO into Na z -MMT compared with polymer intercalation in solution, in which an entropy driven process is dominant. This mechanism is probably similar to that in polymer melts.…”

“…54 kJ mol 21 / 32 . 09 kJ mol 21 ), which is the energetic interaction parameter between polymer clay and polymer polymer. It is also reported the value of the free volume reduction for the polystyrene based nanocomposite system.…”

Recent advances in polymer/layered silicate nanocomposites: An overview from science to technology

“…All PBSCNs studied here follow this relation except PBSCN4 (MMT5 3 . 6 wt-%), in which w filler &(aspect ratio) 21 . For this reason in PBSCN4 rotation of dispersed intercalated with flocculated stacked silicate layers is completely hindered and only translational motion is available, and hence show very high modulus.…”