Measurement and modeling of CO2 absorption in poly(lactic-co-glycolic acid)

High-pressure CO2 absorption into polymers was measured by a gravimetric method. The amount of CO2 absorbed in the polymer was extrapolated using the CO2 release profile from polymeric samples measured at standard conditions by an external balance. The polymers studied were poly-(methyl methacrylate) (PMMA) and poly(lactic-co-glycolic acid) (PLGA) with different molecular weights (MW) and lactide–glycolide copolymer ratios. Experimental results for PMMA well agree with literature data of Wissinger and Paulaitis [J. Polym. Sci.: Part B: Polym. Phys. 25 (1987) 2497] and Chang et al. [J. Supercrit. Fluids 13 (1998) 113]. For PLGA, CO2 absorption measurements were performed at 313 K and in the pressure range 0.6–4.0 MPa. The method gave reproducible results within the accuracy of ±0.002 for mass fraction, ±0.1 MPa for pressure and ±0.15 K for temperature. A perturbed-hard-sphere-chain equation of state (PHSC EOS) was used to correlate CO2–PLGA absorption isotherms. Pure EOS parameters were estimated by a group contribution method, whereas only one interaction parameter was necessary to fit the measured data. The model fairly describes the experimental data points for all PLGAs considered in this work. These results may be very useful to examine the possibility of successfully using a biodegradable amorphous PLGA polymer for developing effective pharmaceutical products by high-pressure CO2 techniques.