Characterization of Microcellular Biodegradable Polymeric Foams Produced from Supercritical Carbon Dioxide Solutions

The formation of foams of biodegradable poly(ƒÕ-caprolatone) (PCL) from CO2 solutions in molten PCL was investigated. This study included characterization of the CO2 diffusion and equilibrium solubility in molten PCL in contact with supercritical CO2 (scCO2). Experiments were performed at 70, 80 and 90¢XC at CO2 pressures up to 25 MPa. Diffusion kinetics were studied as a function of the CO2 pressure and the data revealed a dramatic increase in apparent effective diffusivity at elevated pressure consistent with the incipient phase separation in the gas-molten PCL solution. Microcellular PCL foams were produced starting from an equilibrium CO2-PCL solution at 70 ¢XC over a wide range of initial pressures (from 6,5 to 32 MPa) by rapid depressurization and quenching of the polymer solution down to foaming temperatures ranging from 24 to 30„aC. Foam structures were characterized by scanning electron microscopy and cell sizes and density were determined quantitatively. The various foam structures were analyzed and interpreted in connection with the independently measured kinetics and equilibrium of CO2 sorption in PCL by considering the effects of starting pressure and foaming temperature on bubble nucleation and growth.