(217j) Viscoelasticity During Scale-up in Extrusion of Polymer Blends

In processing of polymers especially blends and composites, continuous mixers are used such as corotating twin-screw extruders [ZSK). scale-up rules are commonly based on the principle of similarity. In the case of twin- screw extruders these rules have to be adjusted because of geometrical and thermodynamic restrictions Geometrical restriction is dependent on screw diameter and center- line distance. The other restriction is the heat transfer from the polymer melt during compounding process.

Scale-up process using the dimensionless temperature and dimensionless power consumption are more useful than the scaling rule of mass flow rate to screw diameter. Materials used in our study were blends of composites containing cross-linked polymers. In these materials elastic modulus was greatly higher than viscous modulus. Polymers with different levels of cross-linking with and without fillers were dynamically analyzed in a rotational rheometer. Equilibrium plateau modulus was computed using time temperature superposition. Equilibrium plateau modulus characteristic of polymer network showed power law dependence on melt flow index in a small twin-screw extruder. On increasing the size of the extruder power law index decreased which was associated with lower dimensionless temperature( ratio of set temperature to die temperature) and lower dimensionless power parameters.