TRANSVERSE ORIENTATION DIES FOR SOLID-STATE EXTRUSION OF POLYMERS .1. PROCESS MECHANICS

Solid-state extrusion of crystalline polymers is a well-known technique to produce monoaxial orientation in filaments and films. This is essentially achieved by extruding or drawing the polymer through a convergent die at temperatures below its melting point. Biaxial orientation in die drawing processes has been achieved by adding extensional forces in the transverse direction at the die exit, as in the case of tubular products. In the present study, billets of poly(tetrafluoropolyethylene) (PTFE) and ultrahigh-molecular-weight polyethylene (UHMWPE) were subjected to simultaneous deformations in the longitudinal and transverse directions, by means of dies featuring converging and diverging walls perpendicular to each other, to produce extrudates exhibiting a predominant orientation in the transverse direction. Two geometries, producing a nominal state of pure shear deformations, by maintaining constant the cross-section area at entry and exit, were examined to determine the relationship between die geometry, yielding and frictional properties of the polymer and extrusion forces. The effects of die geometry and processing conditions are analyzed in Part 2.