Solubilities and Fick diffusion coefficients in blowing-agent-loaded polypropylene melts

For the accurate modeling of bubble growth in blowing-agent-loaded polymer melts during physical foaming processes, accurate blowing agent solubility and Fick diffusion coefficient D 11 data at process-relevant conditions are required. In this context, this work reports on the characterization of blowing-agent-loaded polypropylene (PP) melts by the determination of the solute mass fraction w solute and D 11 at process-relevant temperatures T and pressures p . To develop comprehensive structure-property relationships, binary mixtures based on linear PP (linPP) or long-chain-branched PP (lcbPP) or ternary mixtures based on their blends with dissolved nitrogen (N 2 ), carbon dioxide (CO 2 ), or 1,1,1,2-tetrafluoroethane (R134a) are studied at T between (433 and 533) K and p corresponding to blowing agent mass fractions w N2 ≤ 2% and ( w CO2 or w R134a ) ≤ 8%. The isochoric-saturation method (ISM) is applied to determine w solute and combined with axisymmetric drop shape analysis (ADSA) to measure the volume swelling S w required for its evaluation. To determine D 11 and the associated w solute , dynamic light scattering (DLS) is applied and combined with polarization-difference Raman spectroscopy (PDRS), which is calibrated using w solute data measured by the ISM. Here, the applicability of DLS for studying ternary polymer-based mixtures was demonstrated and it was shown that the accessed diffusion coefficients can be interpreted as quasi-binary diffusion coefficients characterizing diffusive mass transfer of the blowing agent in the molten polymer blend. For the studied systems, a w solute -independent behavior of D 11 was identified and it was demonstrated that w solute and D 11 are not significantly influenced by the characteristics of the different PP types.