Supercritical Antisolvent Process for Substituted Para-Linked Aromatic Polyamides: Phase Equilibrium and Morphology Study

Polycrystalline spherulites and microfibrils are obtained from a substituted para-linked aromatic polyamide in a supercritical antisolvent (SAS) process. Carbon dioxide is contacted with 0.03–0.12 wt % polymer in dimethyl sulfoxide and in N,N-dimethylformamide solutions in both batch and continuous modes of operation. Slow expansion of the solution produces polycrystalline spherulites in the 1–10-µm-diameter range, and the degree of crystallinity is affected by turbulence caused by carbon dioxide injection. A microfibrillar structure is obtained by spraying the polymer solution through a small orifice into cocurrently flowing supercritical carbon dioxide. This morphology is suggestive of shear-induced chain orientation during nucleation. In addition, phase boundaries of the polymer + solvent + antisolvent ternary and the solvent + antisolvent binary systems are determined up to 120 °C and 300 bar.