Supercritical carbon dioxide as a green solvent for processing polymer melts:Processing aspects and applications

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 pure-component 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. (c) 2005 Elsevier Ltd. All rights reserved

Modeling of a Buss-Kneader as a polymerization reactor for acrylates. Part II: Methyl methacrylate based resins

The Buss-Kneader has proven to be a suitable reactor for the polymerization of acrylates. In this second part, the polymerization of methyl methacrylate and the ter- polymerization of methyl methacrylate (MMA), hydroxyethyl methacrylate and n-butylmethacrylate is carried out in a pilot Buss-Kneader. The reactor had to be pressurized up to about 10 bars to avoid evaporation of MMA. Instabilities in output rate and temperature profiles were observed as a result of fluctuating the pressures. Because of good mixing there may be no diffusion limitation for radicals. As a result, even at high conversions, no gel effect was observed

Solubilities of sub- and supercritical carbon dioxide in polyester resins

In supercritical carbon dioxide (CO2) assisted polymer processes the solubility of CO2 in a polymer plays a vital role. The higher the amount of CO2 dissolved in a polymer the higher is the viscosity reduction of the polymer. Solubilities Of CO2 in polyester resins based on propoxylated bisphenol (PPB) and ethoxylated bisphenol (PEB) have been measured using a magnetic suspension balance at temperatures ranging from 333 to 420 K and pressures up to 30 MPa. An optical cell has been used to independently determine the swelling of the polymers, which has been incorporated in the buoyancy correction. In both polyester resins, the solubility of CO, increases with increasing pressure and decreasing temperature as a result of variations in CO, density. The experimental solubility has been correlated to the Sanchez-Lacombe equation of state.</p