A New Technique for Characterizing the Transient Rheological Response of Polymer Melt at High Shear Rates

Characterization of the transient rheological response of polymer melts is important for computerized modeling and optimization of the manufacturing processes involving fast polymer melt flow such as injection molding and extrusion. In this paper, a new cone-and-plate rheometer utilizing the Kolsky torsion bar technique is reported. This rheometer can be accelerated to an angular velocity of 1600 rad/s within 100 μs. It enables characterization of the transient response of polymer melts for shear rates up to 104 1/s, temperatures up to 300°C, pressures up to 10 MPa, and shear strains up to 1000%. Experimental data are presented for a low-density polyethylene melt at shear rates between 780 1/s and 6840 1/s. The results show that the shear stress in the material increases not only with the shear rate but also more significantly with the shear strain. The significance of this finding is also discussed.