Preparation of Stereocomplex Polylactide Using Supercritical Fluid Technology

Polylactides (poly D-lactide and poly L-lactide) have been used in many applications. Homopolymer polylactide has limitations in physical properties, such as thermal property. Stereocomplex polylactide has been known as one of the choices to enhance the properties of polylactides. Numerous studies have been carried out on stereocomplex formation and characterizations. But, these have limitation in case of high molecular weight polylactides. The use of supercritical fluid technology in stereocomplex formation was expected to produce stereocomplex from high-molecular-weight polylactide which is main problem in conventional methods.

We used supercritical carbon dioxide combined with solvent to produce stereocomplex formation of high-molecular-weight polylactides. The degree of stereocomplex formation was evaluated as a function of solvents, pressures, solvent concentration, temperature, and times. The high degree of stereocomplex formation was achieved at 30% of dichloromethane, 350 bar, and 65 C.

Our system can solve limitation problem of other methods like long time processing and difficulties for high-molecular-weight polylactide. Compared to the solution casting method, stereocomplex formation by supercritical CO2-solvent had a higher degree of stereocomplex formation, short time, and dry product was obtained in situ. The obtained stereocomplex polylactide as heat stable polymer has melting point of 230 C and onset degradation temperature of 305 C. The significant improvements were also occurring in mechanical properties. The stereocomplex polylactide obtained by supercritical method has better properties compared to either the solution casting method or their homopolymers.

Purba Purnama and Soo Hyun Kim
Biomaterials Research Center, Korea Institute of Science and Technology, Seoul 136-791, Korea
University of Science and Technology, 113 Gwahangno, Yuseong-gu, Daejeon 305-333, Korea
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