On The Use Of Prototype Industrial Flows To Identify Viscoelastic Constitutive Equations For Polymer Melts
Résumé
This study is devoted to the validation and identification of viscoelastic constitutive equations for entangled polymer melts using "classical" rheometry tests and fieldwise measurements (flow induced birefringence coupled to laser Doppler velocimetry) in prototype extrusion flows equipped with a transparent die. We studied two different polymers : a linear polystyrene (presented in this paper) and a branched low density polyethylene (will be presented during the conference), and tested the pertinence of "molecular" constitutive equations to predict their behaviour in a contraction flow exhibiting high elongational rates. First, a "classical" identification was performed using linear viscoelasticity, capillary and extensional rheometry for a polystyrene and polyethylene. Models predictions were then tested in extrusion flows using velocity (gradients) and (first principal) stresses (difference) measurements. It was shown that an extra adjustment of parameters for the very fast viscoelastic modes were needed to take into account the behaviour in such "strong" flows.