Cloud-point measurement of the biodegradable poly(d,l-lactide-co-glycolide) solution in supercritical fluid solvents

Abstract

Experimental data of high pressure phase behavior between 35 °C and 105 °C and pressures up to 2,200 bar is presented for poly(d,l-lactic acid)(d,l-PLA) and poly(lactide-co-glycolide)15 (PLGA15), PLGA25, and PLGA50 in supercritical carbon dioxide, trifluoromethane (CHF3), chlorodifluoromethane (CHClF2), dichloromethane (CH2Cl2), and chloroform (CHCl3). d,l-PLA dissolves in carbon dioxide at pressures of 1,250 bar, in CHF3 at pressures of 500 to 750 bar, and in CHClF2 at pressures of 30–145 bar. As glycolic acid (glycolide) is added to the backbone of PLGA, the cloud point pressure increases by 36 bar/(mol GA) in carbon dioxide, 27 bar/(mol GA) in CHF3, and by only 3.9 bar/(mol GA) in CHClF2. PLGA50 does not dissolve in carbon dioxide at pressures of 2,800 bar, whereas it is readily soluble in CHClF2 at pressures as low as 95 bar at 40 °C. Cloud point behavior of d,l-PLA, PLGA15, and PLGA25 in supercritical carbon dioxide shows the effect of glycolide content between 35 °C and 108 °C. Also, the phase behavior for poly(lactic acid) — carbon dioxide-CHClF2 mixture shows the changes of pressure-temperature slope, and with CHClF2 concentration of 6 wt%, 19 wt%, 36 wt% and 65 wt%. The cloud-point behavior shows the impact of glycolide content on the phase behavior of PLA, PLGA15, PLGA25 and PLGA50 in supercritical CHClF2. A comparison was made between the phase behaviors of d,l-PLA and poly(l-lactide)(l-PLA) in supercritical CHF3. The phase behavior of CHF3 as a cosolvent for 5 wt% d,l-PLA-supercritical carbon dioxide system is presented for the effect being added 10 wt% and 29 wt% to CHF3 content.