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 10-30 MPa 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 (13-17 MPa) and 10% of HA were proven to be favorable for creation of the PCL scaffolds with satisfying foam microstructure (mean pore size ∼200-300 μm), filler distribution and thymol impregnation yields (12-18%). This was due to the satisfactory high scCO2 solubility (0.25-0.30 g/g) and mass transfer rate (∼10-10 m2/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 (0.30-0.55 g/g), filler amount (20%) and thymol solubility in scCO2 (>5.5 g/kg) at pressures above 20 MPa resulted in decreased mass transfer rate and SSI efficiency.