Review on Polymer Processing Techniques Using Supercritical Carbon Dioxide (scCO2)

Supercritical fluids (SCFs) are the materials formed at the values of temperature and pressure, above its critical point. Some supercritical fluids can replace the toxic industrial solvents. Unique properties of the supercritical fluids especially supercritical carbon dioxide (scCO₂) provide the various opportunities in the field of polymerization. The supercritical carbon dioxide (scCO₂) is used as a monomer, reaction medium and catalyst for the synthesis of polymers. Various processes for the polymer synthesis have been discussed in this review article such as homogeneous polymerization, step growth polymerization, emission polymerization, dispersion polymerization and electrochemical synthesis of conducting polymers. The polymers can be readily separated from the reaction mixture as the particles or drops, in the presence of supercritical carbon dioxide (scCO₂) during the polymerization. In this review, some applications including impregnation and supercritical dyeing, purification of polymers, polymer modifications and particle production has been evaluated to study the efficiency of super critical fluids on the polymer production. This article also demonstrates the effects of various parameters on the process of polymerization such as pH, temperature and pressure. Generally, by increasing the values of pH or the reaction media, the viscosity of prepared polymers tends to increase. The characterization techniques such as Fourier Transform Infrared (FTIR) spectroscopy, X-Ray Diffraction (XRD), ¹H Nuclear Magnetic Resonance (¹HNMR) and Differential Scanning Calorimetry (DSC) are also discussed for the determination of chemical arrangement, structure of polymers and functional groups.