Impact of cosolvent concentration of ternary and binary solution for biodegradable poly(D,L-lactic acid) under supercritical solvents

Abstract

This study provides experimental cloud point data for poly(D,L-lactic acid) (PDLLA) polymer and supercritical solvent and cosolvent mixtures at ∼333 K to ∼424 K and pressures up to ∼157 MPa for PDLLA. Various solvents investigated include CO2, DME, CH2F2, CHF3, C3F8, C3H8, c-C4F8, and F-22. CO2 is a preferred solvent due to non-toxic, non-flammability, low cost but the results indicate low PDLLA solubility in CO2 at ∼100 to 110 MPa and at experimental temperature range of 333.15 K to 423.15 K. However, for DME and F-22 solvents, the cloud points appear at ∼10 to 30 MPa suggesting these are better suited to dissolve polymers for supercritical processes. The results indicate that DME is the favored solvent due to its superior performance. In the pure component system, the cloud point curve exhibited a distinctive nature, displaying behaviors such as UCST, horizontal, or LCST under the experimental conditions. However, the phase behavior of PDLLA in the presence of both solvent and co-solvent demonstrated a transition from UCST to LCST types. This observed change suggests variations in the solubility of the polymer under the same experimental conditions, highlighting the dynamic influence of co-solvents on PDLLA's solubility characteristics. For systems with higher molecular weight PDLLA, increased self-association resulted in reduced solubility and upward shift of cloud point curves. This study will be helpful in optimizing solvent + cosolvent and operating conditions involving PDLLA in supercritical processes, especially in biomedical applications.