Intercalated Polymer Nanocomposites Prepared in Supercritical Carbon Dioxide
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Q10.8.1
Intercalated Polymer Nanocomposites Prepared in Supercritical Carbon Dioxide. Manuel Garcia-Leiner and Alan J. Lesser. Polymer Science and Engineering Department, University of Massachusetts at Amherst, Amherst, MA 01003, U.S.A. ABSTRACT An alternative route to prepare polymer-clay nanocomposites using supercritical carbon dioxide (scCO2) is described. The presence of clay nanoparticles significantly influences the morphology, foaming process and crystallization of a polymer when processed in scCO2. Intercalated structures are successfully produced in the presence of scCO2 even when favorable interactions between the polymer and the clay are not present. The effect of scCO2 on the intercalation process is analyzed for a variety of polymer systems both with modified and unmodified clays. By controlling the hydrophilicity of the polymer and clay systems, specific understanding of the effect of scCO2 on the structure and morphology of the nanocomposites is obtained. Experimental results show significant increases in the clays d-spacings for scCO2-treated samples. This behavior is consistent regardless of the nature of the polymer, showing significant amounts of intercalation even in purely hydrophobic polymers. INTRODUCTION Nanotechnology is leading the way to better and unique materials for a variety of applications. Recent developments have shown the possibility of incorporating diverse inorganic materials into engineering polymer systems producing polymer nanocomposites that in many cases provide an alternative for better material properties. Recent investigations [6] suggest, however, that since most of the improvements in nanocomposites come from interactions at the molecular scale and since toughening occurs over a specific length scale, effective toughening mechanisms would require a specific filler size that may not be achieved by individual nanoscale particles [11]. As a consequence, it is suggested that the extremely reduced scale of a fully exfoliated structure may not be favorable for toughening, while an intercalated system may promote considerable interaction between silicate layers at a length scale large enough to promote toughening. ScCO2 has proven to be an environmentally friendly alternative for a wide range of applications, combining in a unique manner properties that are typically observed in both liquid and gas states. With some exceptions, scCO2 is a non-solvent for most polymers, however, it can plasticize most of them very efficiently. Due to its high compressibility, these solvent properties can be controlled by small changes in processing conditions, acting as a “reversible plasticizer” that can be easily removed after depressurization. In this work we present an alternative route to prepare polymer nanocomposites by introducing scCO2 in a modified processing system [12]. Results suggest that the presence of scCO2 promotes significant changes in the properties of a system that may enhance the ease of polymer intercalation when layered nanosilicates are introduced as
Q10.8.2
nanos
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