Gas antisolvent fractionation of semicrystalline and amorphous poly(lactic acid) using compressed CO2

Semicrystalline and amorphous poly(lactic acid) (L-PLA and D,L-PLA, respectively) were fractionated from chloroform solutions using compressed CO2 as an antisolvent. The following process variables were used to precipitate normalized molecular weight fractions (NMW) of L-PLA ranging from 0.81 to 1.54 relative to the starting material: polymer concentration, initial organic solution volume, and the rate of antisolvent addition. An analysis of variance (ANOVA) used to quantify the importance of these variables determined that polymer concentration had the most significant impact on the NMW of L-PLA precipitated in this gas antisolvent (GAS) precipitation process. The results of the ANOVA also suggest a predictive approach to polymer fractionation in this complex system. The analysis also highlights the differences and similarities between the fractionation of semicrystalline and amorphous polymers using compressed antisolvents. (C) 2002 Elsevier Science Ltd. All rights reserved.