Determination of CO2 solubility in isotactic polypropylene melts with different polydispersities using magnetic suspension balance combined with swelling correction

This work is aimed at determining solubility of CO2 in polymer melt through experimental measurements. The apparent solubility of CO2 in two kinds of isotactic polypropylene (iPP) melts with different molecular weight distributions was measured by using a magnetic suspension balance (MSB) at temperatures of 200 and 220 °C, and CO2 pressures up to 30 MPa. Meanwhile, the swelling volume of the iPP/CO2 solutions was experimentally measured under the same conditions by using a high-pressure view cell with direct visual observation. It was then used to correct the gas buoyancy acting on the iPP melts in the MSB measurement so that the real solubility of CO2 in the iPP melts could be determined. Solubility of CO2 in the iPP melts was also corrected using swelling ratio predicted by Sanchez–Lacombe equation of state (S–L EOS) for comparison. iPP with a larger molecular weight distribution showed a lower swelling degree and lower real solubility than those of iPP with a lower molecular weight distribution. It showed a large deviation to the solubility with the experimental swelling ratio correction at high CO2 pressures due to the overestimation of swelling ratio predicted by Sanchez–Lacombe (S–L) equation of state.

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► Swelling ratio of the iPP/CO2 solution was experimentally measured with direct visual observation.
► It was used to correct the solubility of CO2 in the iPP melts measured by using MSB.
► iPP with wider molecular weight distribution exhibited lower swelling ratio and CO2 solubility.
► Experimental swelling corrected solubility agreed well with S–L EOS corrected at low CO2 pressure.