Supercritical carbon dioxide (CO 2) is well established for use as a processing solvent in polymer applications such as polymer modification, formation of polymer composites, polymer blending, microcellular foaming, particle production and polymerization. Its gas-like diffusivity and liquid-like density in the supercritical phase allow replacing conventional, often noxious, solvents with supercritical CO 2. Though only a few polymers are soluble in supercritical CO 2 , it is quite soluble in many molten polymers. CO 2 dissolution in a polymer has been interpreted physically but FT-IR studies lead to an explanation in terms of weak interactions between basic and acidic sites. Various experimental methods and equations of state are available to measure or predict the solubility of CO 2. Dissolved CO 2 causes a considerable reduction in the viscosity of molten polymer, a very important property for the applications stated above. CO 2 mainly acts as a plasticizer or solvent when contacted with a polymer. Gas solubility and viscosity reduction can be predicted theoretically from purecomponent properties. In this review, experimental and theoretical studies of solubility and viscosity of several polymer melts are discussed in detail. Detailed attention is also given to recently reported applications along with aspects related to polymer processing.

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Fourier transform infrared (FTIR) spectroscopy was used to reveal intermolecular interactions between carbon dioxide (CO 2 ) and the carbonyl groups of poly(L-lactide) (PLLA), poly(D,L-lactide) (PDLLA), and poly(e-caprolactone) (PCL). After exposing polymer films to high pressure CO 2 , the wave number of the absorption maxima of the polymer carbonyl groups shifted to higher values. Also, due to the interaction between CO 2 and the carbonyl groups of the polymers, a new broad peak in the bending mode region of CO 2 appeared. To distinguish between polymer-associated and nonassociated CO 2 , and to quantify these contributions, the bending mode peaks were deconvoluted. From these contributions, it was found that in the case of PCL more CO 2 is interacting with the polymer carbonyl groups than in the case of PDLLA and PLLA. Under our experimental conditions, 408C and pressures up to 8 MPa, a significant depression of the PCL melting temperature was observed.

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