P. Vandewitte et al., IN-SITU ANALYSIS OF SOLVENT NONSOLVENT EXCHANGE AND PHASE-SEPARATION PROCESSES DURING THE MEMBRANE FORMATION OF POLYLACTIDES/, Journal of applied polymer science, 61(4), 1996, pp. 685-695
Membrane formation of polylactides has been studied using in situ anal
ysis techniques. An experimental method based on the use of dark groun
d optics and reflected light illumination is used to monitor the mass
transfer and phase separation dynamics during formation. Additionally,
the phase separation and structure formation has been studied using o
ptical microscopy. The results of the dark ground optics technique for
the polymer/solvent/nonsolvent systems poly-L-lactide/chloroform/meth
anol and poly-DL-lactide/chloroform/methanol showed that the diffusion
kinetics were similar for the semicrystalline poly-L-lactide (PLLA) a
nd the amorphous poly-DL-lactide, The influence of the molecular weigh
t of the polymers on the diffusion kinetics was found to be negligible
. Increasing the polymer concentration of the casting solution decreas
ed the rate of diffusion. The phase separation of poly-DL-lactide was
studied with optical microscopy and found to proceed via liquid-liquid
demixing. For poly-L-lactide solutions of relatively low concentratio
n (5-6% w/w), phase separation proceeded via liquid-liquid demixing fo
llowed by crystallization. For more concentrated PLLA solutions, phase
separation proceeded directly via solid-liquid demixing processes. Ad
ditionally, for 6% w/w solutions of poly-L-lactide in dioxane immersed
in methanol, precipitation also occurred solely via solid-liquid demi
xing. (C) 1996 John Wiley & Sons, Inc.