Compressible flow in a plate/plate rheometer: application to the experimental determination of reactive expansion’s models parameters for polyurethane foam

The quality of polyurethane foam’s structure mainly depends on the manufacturing process, during what two concomitant principal exothermic chemical reactions take place: the first one creates CO₂ dissolved into the fluid matrix (initiating micro-bubbles, expansion and coarsening of the foam) and the second one leads to the polymerization. In order to follow the rheological evolution of the PU foam during the process, the evolutions of the rheological properties of the foam during the process have been measured in a plate/plate rheometer with imposed deformation (RMS 800) and imposed stress (Stresstech). An analytical solution of the mechanical balance equation for viscoelastic compressible fluid has been proposed to describe the flow in this plate/plate rheometer with radial expansion. The trace of the elastic modulus G′ and the loss modulus G′′ as a function of time highlights the different steps of the foaming and polymerization process. The temperature dependence of both reactions follows Arrhenius’ laws. The recording of G′ and G′′ allows to identify kinetic parameters of numerical models for describing the expansion of a polymer foam and taking into account both chemical reactions.