Phase behavior of biodegradable poly(L-lactic acid) in supercritical solvents and cosolvents.

Poly(L-lactic acid) (PLLA), a biodegradable polymer from plant sources, is widely employed in biomedical applications for its biocompatibility and versatile mechanical properties. However, comprehending its phase behavior in various solvents poses a challenge for broader applications. In this study, the phase behavior of the polymer was investigated in various solvent and cosolvent media and combinations at a wide range of temperatures and pressures to gain insight into the polymer properties. PLLA of varying intrinsic viscosity (IV): [0.15 dl/g, with an estimated weight average molecular weight (M w) range of approximately: 1600 to 2400 g/mol; 1.0 dl/g (M w): 100,000 g/mol); and 1.8 dl/g (M w): 80,000 to 100,000 g/mol] was employed for this study. The phase behavior of the polymer across different compositions of PLLA and solvent (CH 2 F 2 , CHF 3 , CO 2 , DME, F-22) in a wide range of temperatures from 333 to 425 K and high pressure 1.55 to 172 MPa was investigated. Miscibility of PLLA in DME and F-22 is predicted to be higher with increasing in concentration than the other cosolvents. Furthermore, in the case of the supercritical solvent CHF 3 and DME the phase transition pressure curve of PLLA was observed to exhibit a lower critical solution temperature (LCST) type with a positive gradient with increasing temperature. However, lower phase transition pressure was noticed for lower molecular weight PLLA in supercritical solvent CHF 3 and DME, i.e., of the order IV 0.15 dl/g<IV 1.0 dl/g<IV 1.8 dl/g. The phase transition pressure of PLLA (IV 1.8 dl/g) in solvent CO 2 with increasing the concentration of co-solvent (F-22, DME) from 0 to ∼97 wt% shifted from UCST to LCST type. The LCST curve of PLLA (IV 0.15) in DME intersects with the vapor(V)-liquid(L) curve at T : 353 K and P below 5 MPa, indicating the coexistence of V+L phases. • The phase behavior of poly (L-lactic acid) was investigated at supercritical conditions. • Various supercritical fluids employed for this study were CH 2 F 2 , CHF 3 , CO 2 , DME and F-22. • Low molecular weight poly (L-lactic acid) exhibited minimum transition pressures in CHF 3 and DME. • Poly (l-lactic acid) exhibited superior miscibility in DME and F-22 compared to other solvents. [ABSTRACT FROM AUTHOR]