Sd. Yeo et al., SUPERCRITICAL ANTISOLVENT PROCESS FOR SUBSTITUTED PARA-LINKED AROMATIC POLYAMIDES - PHASE-EQUILIBRIUM AND MORPHOLOGY STUDY, Macromolecules, 26(23), 1993, pp. 6207-6210
Poly crystalline spherulites and microfibrils are obtained from a subs
tituted 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 solutio
n produces polycrystalline spherulites in the 1-10 mum-diameter range,
and the degree of crystallinity is affected by turbulence caused by c
arbon dioxide injection. A microfibrillar structure is obtained by spr
aying the polymer solution through a small orifice into cocurrently fl
owing supercritical carbon dioxide. This morphology is suggestive of s
hear-induced chain orientation during nucleation. In addition, phase b
oundaries of the polymer + solvent + antisolvent ternary and the solve
nt + antisolvent binary systems are determined up to 120-degrees-C and
300 bar.