MECHANISMS FOR VISCOSITY REDUCTION OF POLYMER BLENDS - BLENDS OF FLUOROELASTOMER AND HIGH-DENSITY POLYETHYLENE

The rheological behavior of fluoroelastomer high-density polyethylene (HDPE) blends was investigated in detail. A capillary rheometer was us ed to determine the apparent viscosity of the blends as a function of time at various shear rates. The time to attain the steady state and t he normalized steady-state apparent viscosity of the blends depend on shear rate and the fluoroelastomer concentration. The reduction in the apparent viscosity is caused by adhesive failure at the interface bet ween the HDPE melt and the fluoroelastomer layer which was formed on t he die wall surface during the extrusion of the blends. The presence o f the fluoroelastomer layer on the die wall surface was confirmed by x -ray photoelectron spectroscopy and rheological measurements. Based on our previous work and this work, we have discovered that there are at least two different mechanisms-adhesive failure at the interface betw een the extrudate and the lubricating layer or cohesive failure in the lubricant layer-for viscosity reduction in polymer blends. (C) 1997 T he Society of Rheology.