Solubility and diffusivity of supercritical carbon dioxide (sc-CO2) in molten PP/EPDM blends
Surat Areerat, Kouei Nitta, Masahiro Ohshima
Department of Chemical Engineering, Kyoto University
Japan

Keywords: CO2 Solubility, Diffusivity of CO2, PP/EPDM Blend Polymer

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Solubility and diffusivity of supercritical carbon dioxide (sc-CO2) in molten polypropylene/ethylene-propylene-diene rubber (PP/EPDM) blends were measured at temperature 200 oC and pressure in the range from 2 to 15 MPa by using a new gravimetric technique of gas sorption measurements, i.e., magnetic suspension balance (MSB). Five PP/EPDM blends, whose PP compositions are different, 0, 25, 50, 75 to 100 wt%, were examined.
Using the Sanchez-Lacombe equation of state and an additional volume-mixing rule with an adjustable parameter, CO2 solubility in immiscible polymer blends was calculated from the MSB measurements. The effects of PP composition in the blends on CO2 solubility and diffusivity were investigated through five blends. When EPDM composition in blend increases, CO2 solubility in the blend decreases and the diffusion coefficient of CO2 into the blend increases. The experiments elucidate that the simple weight average of Henry’s constants of neat PP and EPDM polymers can provide the good estimate of the CO2 solubility for PP/EPDM blend in any EPDM compositions.
The diffusivity of CO2 into blend polymers varies depending upon the PP compositions and dissolved CO2 concentration in blend. However, the permeability of CO2 in blend can be successfully estimated by Robeson’s equation with a continuous phase factor, which corresponds to the PP weight percentage in blend where the morphological phase inversion occurs. The continuous phase factor was obtained by characterizing TEM micrographs of the polymer blend morphology. Using the factor and Robeson’s equation, the permeability and diffusivity of CO2 can be calculated for PP/EPDM systems in any blend ratios at any CO2 pressure.