THERMAL RELAXATION IN EXTRUSION-ORIENTED POLYETHYLENE RODS

To study how the properties of extruded medium-density polyethylene pr oducts are influenced by the microstructure, rodlike samples, whose mo rphology can be changed under appropriate processing conditions, were produced by extrusion. A special extrusion line was developed consisti ng of an extruder equipped with a cylindrical die, thermal separator, lubrication unit, and cooling die. A wide range of representative morp hologies was achieved using various temperatures of polymer melt and o f the cooling die (calibration unit). A significant structural gradien t, determined by differential scanning calorimetry (DSC), was found in all extruded rods, depending on the thermal conditions. The molecular orientation through the section of the rods, resulting from the shear during the extrusion, was determined by Fourier transform infrared (F TIR) spectroscopy and by thermal relaxation, showing good agreement be tween both methods. (C) 1996 John Wiley & Sons, Inc.