Supercritical impregnation of polymers - ZyXEL NSA210

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404 I. Kikic, F. Vecchione / Current Opinion in Solid State and Materials Science 7 (2003) 399–405 inside the swollen substrates. The process parameters were controlled by the concentration of the radical initiator and by the solubility of the monomers in SCCO 2 . As a result, PTFE shows the least ability to be modified due to its limited swelling capability and high crystallinity degree (impregnation occurs only in amorphous domains). In contrast the highest mass gains are obtained for PC and PVC as substrates, and styrene and MMA as the impregnating monomers. PVC–PMAA was chosen as a model system for the investigation of the limits of supercritical polymer modification, because this system seems to be most interesting for the possibility to generate a water-soluble polymer PMAA inside a hydrophobic PVC matrix. CO 2 treatment causes no changes in the chemical structure of PVC since the thermogram of CO 2 -treated PVC equals that of pure PVC. PMAA starts to decompose by dehydration at 125 °C, and the decomposition is complete by the degradation of the polymer backbone at 400 °C, causing relatively high mass losses in comparison to PVC and CO 2 -treated PVC [24]. One advantage of supercritical polymer modification is the possibility to synthesize new polymer mixtures with thermally unstable components. With the generation of the water-soluble poly(methacrylic acid) (PMAA) inside the hydrophobic PVC or PMMA substrates, it was possible to obtain polymer mixtures inaccessible by common techniques such as melt mixing, because the PMAA would definitely decompose during the extrusion at temperatures >175 °C. 4. Conclusions An overview of supercritical impregnation processes in the presence of supercritical fluids has been presented. Supercritical carbon dioxide dissolved in glassy polymers increases the diffusivities of additives in the polymer matrix because of the CO 2 plasticization effect. Supercritical fluid impregnation is a useful method for the preparation of pharmaceutical forms. This method presents the advantages related to the plasticizing ability of the CO 2 that enhances drug diffusion rates into the polymer and the ease of solvent removal. Supercritical dye impregnation is a process based on the affinity of the dye for the polymeric matrix. Moreover, supercritical dye impregnation replaces water in dyeing processes, overcoming the problem of wastewater treatment. SCF properties are successfully adopted for charging a polymer matrix with metallic organic complexes in order to prepare metal-containing nanocomposite metals. An interesting application of supercritical impregnation is the polymer blend preparation by the impregnation of a polymer matrix with a monomer and an initiator to perform the polymerization within the polymer matrix. With this particular method it is possible to obtain polymer blends not easy obtainable with common techniques, i.e. melt mixing. References [1] Zhou H, Fang J, Yang J, Xie X. Effect of the supercritical CO 2 on surface structure of PMMA/PS blend thin films. J Supercrit Fluids 2003;26:137–45. [2] Wang Y, Yang C, Tomasko D. Confocal microscopy analysis of supercritical fluid impregnation of polypropylene. Ind Eng Chem Res 2002;41:1780–6. [3] Diankov S, Barth D, Subra P. Supercritical impregnation isotherm of O-HBA on PMMA in batch stirred reactor. In: 6th International Symposium on Supercritical Fluids, 2003. p. 1599– 604. [4] Kazarian SG, Martirosyan GG. Spectroscopy of polymer/drug formulations processed with supercritical fluids: in situ ATR-IR and Raman study of impregnation of ibuprofen into PVP. Int J Pharm 2002;232:81–90. [5] Alessi P, Cortesi A, Kikic I, Vecchione F. Plasticization of polymers with supercritical carbon dioxide: experimental determination of glass-transition temperatures. J Appl Polym Sci 2003;88:2189–93. [6] Kikic I, Vecchione F, Alessi P, Cortesi A, Eva F, Elvassore N. Polymer plasticization using supercritical carbon dioxide: experiment and modeling. Ind Eng Chem Res 2003;42:3022–9. [7] Condo PD, Sanchez IC, Panayiotou GC, Johnston KP. Glass transition behaviour including retrograde vitrification of polymers with compressed fluid diluents. Macromolecules 1992;25:6119–27. [8] Kikic I, Vecchione F, Elvassore N. Thermodynamic analysis of the effect of supercritical fluids on the glass transition temperature. In: 2nd International Meeting on High-Pressure Chemical Engineering, 2001. [9] Wissinger RG, Paulaitis ME. Molecular thermodynamic model for sorption and swelling in glassy polymer––CO 2 systems at elevated pressures. Ind Eng Chem Res 1991;30:842–51. [10] Doghieri F, Sarti GC. Nonequilibrium lattice fluids: a predictive model for the solubility in glassy polymers. Macromolecules 1996;29:7885–96. [11] Alessi P, Cortesi A, Kikic I, Scotti F, Vecchione F. Sorption of supercritical carbon dioxide in copolymers: use of the NELF model. In: 5th International Symposium on Supercritical Fluids, 2000. [12] Guney O, Akgerman A. Synthesis of controlled-release products in supercritical medium. AIChE J 2002;48:856–66. [13] Shim JJ, Choi JH, Ju JH, Son BK, Ahn JM, Kim BH, et al. Dyeing of polyester, aramid and polypropylene fibers in supercritical CO 2 . In: 6th International Symposium on Supercritical Fluids, 2003. p. 2101–6. [14] Park MW, Bae HK. Dye distribution in supercritical dyeing with carbon dioxide. J Supercrit Fluids 2002;22:65–73. [15] Van der Kraan M, Bayrak O, € Fernandez Cid MV, Woerlee GF, VeugelersW JT, Witkamp GJ. Textile dyeing in supercritical carbon dioxide. In: 6th International Symposium on Supercritical Fluids, 2003. p. 2119–24. 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I. Kikic, F. Vecchione / Current Opinion in Solid State and Materials Science 7 (2003) 399–405 405 [17] Yoda S, Hasegawa A, Suda H, Uchimaru Y, Haraya K, Tsuji T, et al. Preparation of polymer metal composite film as a precursor of metal doped carbon membrane via supercritical impregnation. In: 6th International Symposium on Supercritical Fluids, 2003. p. 1981–6. [18] Nazem N, Taylor LT, Rubira AF. Metallized poly(etherether ketone) films achieved by supercritical fluid impregnation of a silver precursor followed by thermal curing. J Supercrit Fluids 2002;23:43–57. [19] Kazarian SG. Polymer processing with supercritical fluids. Polym Sci, Ser C 2000;42:78–101. [20] Xu Q, Chang Y. Complex interactions among additive/supercritical CO 2 /polymer ternary systems and factors governing the impregnation efficiency. In: 6th International Symposium on Supercritical Fluids, 2003. p. 1577–83. [21] Li D, Liu Z, Han B, Song L, Yang G, Jiang T. Preparation of nanometer dispersed polypropylene/polystyrene interpenetrating network using supercritical CO 2 as a swelling agent. Polymer 2002;43:5363–7. [22] Tang M, Wen T-Y, Du T-B, Chen Y-P. Synthesis of electrically conductive polypyrrole–polystyrene composites using supercritical carbon dioxide: I. Effects of the blending conditions. Eur Polym J 2003;39:143–9. [23] Tang M, Wen T-Y, Du T-B, Chen Y-P. Synthesis of electrically conductive polypyrrole–polystyrene composites using supercritical carbon dioxide: II. Effects of the doping conditions. Eur Polym J 2003;39:151–6. [24] Muth O, Hirth Th, Vogel H. Polymer modification by supercritical impregnation. J Supercrit Fluids 2000;17:65–72.
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