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Formation of microporous polymer fibers and oriented fibrils by precipitation with a compressed fluid antisolvent
Author(s) -
Dixon David J.,
Johnston Keith P.
Publication year - 1993
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1993.070501110
Subject(s) - polystyrene , materials science , chemical engineering , polymer , microporous material , binodal , molar mass , spinodal decomposition , dilution , supersaturation , mass transfer , precipitation , porosity , polymer chemistry , phase (matter) , composite material , chromatography , chemistry , organic chemistry , thermodynamics , physics , phase diagram , meteorology , engineering
Polymer morphology is controlled over a continuum from microspheres to interconnected bicontinuous networks to fibers with a versatile new process: precipitation with a compressed fluid antisolvent. The results are explained qualitatively as a function of phase behavior, mass‐transfer pathways, and the formation rates of skin on the flowing jet. By spraying dilute polystyrene in toluene solutions into liquid carbon dioxide, extremely small 100 nm microspheres are formed. For concentrations above the critical composition, fibers are produced that are not only microcellular, but, in some instances, even hollow. Mass‐transfer pathways that cross the binodal near the critical composition produce interconnected networks, likely due to spinodal decomposition. In this region, fibers composed of highly oriented microfibrils are produced at high shear rates. Preaddition of CO 2 influences the morphology because of dilution, in a similar manner as a liquid antisolvent, except that the viscosity reduction is larger due to added free volume. Because CO 2 diffuses through the glassy polystyrene skin faster than does a conventional liquid antisolvent such as methanol, it produces more porous fibers, which are also more cylindrical. © 1993 John Wiley & Sons, Inc.