Supercritical CO2 sorption kinetics and thymol impregnation of PCL and PCL-HA

Abstract

The potential of supercritical carbon dioxide (scCO2) processing of polycaprolactone (PCL) and polycaprolactone-hydroxyapatite (PCL-HA) composites for obtaining functional porous scaffolds at moderate temperatures (35–40°C) was analyzed and quantified. The effect of scCO2 sorption kinetics on the swelling, foam morphology and thermal behavior of the PCL and PCL-HA composites was studied. Sorption isotherms were determined using magnetic suspension balance at 10–30MPa and 35–40°C. Influence of the pressure, HA amount (10–20%) and procedure for HA powder preparation on the sorption kinetics was discussed. Supercritical solvent impregnation (SSI) of PCL and PCL-HA with thymol was investigated as environmentally friendly way to produce functional scaffolds with controlled microstructure. Moderately high pressures (13–17MPa) and 10% of HA were proven to be favorable for creation of the PCL scaffolds with satisfying foam microstructure (mean pore size ∼200–300μm), filler distribution and thymol impregnation yields (12–18%). This was due to the satisfactory high scCO2 solubility (0.25–0.30g/g) and mass transfer rate (∼10−10m2/s) in the polymer phase as well as its great plasticizing effect (−ΔTm=26.4–27.4°C). Higher saturation of the polymer phase with scCO2 (0.30–0.55g/g), filler amount (20%) and thymol solubility in scCO2 (>5.5g/kg) at pressures above 20MPa resulted in decreased mass transfer rate and SSI efficiency.