CHARACTERIZATION OF MICROCELLULAR BIODEGRADABLE POLYMERIC FOAMS PRODUCED FROM SUPERCRITICAL CARBON DIOXIDE SOLUTIONS

The formation of foams of biodegradable poly(e-caprolactone) (PCL) from CO2 solns. in molten PCL was investigated. This study included characterization of the CO2 diffusion and equil. soly. in molten PCL in contact with supercrit. CO2 (scCO2). Expts. were performed at 70, 80, and 90 °C at CO2 pressures up to 25 MPa. The effective mutual diffusivity of CO2 in molten PCL was measured as a function of the CO2 pressure. The data revealed a dramatic increase in apparent effective diffusivity at elevated pressure, likely related to the formation of fluid bubbles, phase-sepd. from the previously homogeneous, molten PCL soln. of CO2. Microcellular PCL foams were produced by starting from an equil. CO2-PCL soln. at 70 °C over a wide range of initial pressures (from 6.9 to 32 MPa) by quenching down to foaming temps. (from 24 to 30 °C) followed by rapid depressurization to atm. pressure. Foam structures were characterized by SEM, and cell sizes and d. were detd. quant. The various foam structures were analyzed and interpreted in connection with the independently measured kinetics and equil. of CO2 sorption in PCL by considering the effects of starting pressure and foaming temp. on bubble nucleation and growth.