Solubility of blowing agents in polymer melts by the combination of the isochoric-saturation method with axisymmetric drop shape analysis

• Combination of axisymmetric drop shape analysis with the isochoric saturation method. • Optical investigation of volume swelling of pendant drops with dissolved CO 2. • Experimental volume swelling data for [EMIM][NTf 2 ] , polystyrene, and polypropylene. • Experimental solubility data of CO 2 in [EMIM][NTf 2 ] , polystyrene, and polypropylene. A novel approach to investigate the solubility of blowing agents in polymer melts by combining the isochoric saturation method (ISM) with axisymmetric drop shape analysis (ADSA) is presented. The latter is used to obtain the volumetric properties of the saturated melt at the investigated pressure and temperature required for the evaluation of the mass balance in ISM. For this, the volume of a sessile drop (SD) or pendant drop (PD) is analyzed over a wide range of temperatures and combined with the mass of the drop to access the density. The volume swelling ( S w ) due to the solvation of the gas in the polymer melt is accessed by determining the volume change with increasing gas pressure. The method is validated using the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][NTf 2 ]) with dissolved carbon dioxide (CO 2 ) as a reference system at temperatures between (323.09 and 373.07) K and pressures up to 5.082 MPa. In addition, S w and the solubility of CO 2 in polystyrene (PS) and polypropylene (PP) is investigated at about 476 K and pressures up to 5.330 MPa. At the largest pressure, PS and PP show an increase in volume of about (2 and 3)% which agrees with literature values. The solubility of CO 2 in PP is almost twice as large as that for PS. On average, the solubility in form of the amount or mass fraction of CO 2 could be determined with relative expanded uncertainties (coverage factor k = 2) of 0.042, 0.12 and 0.071 for [EMIM][NTf 2 ], PS, and PP, respectively.