Cold extrusion and cold drawing of polymeric rod: The influence on subsequent tensile and compressive mechanical properties

Abstract

Nylon 6-6, polycarbonate and high density polyethylene were extruded and drawn through a 40% reduction die in one pass at room temperature. Certain mechanical properties of the extrudate were measured by subsequent tension and compression tests. For both forming processes and for all three polymers, the tensile true stress-true strain curve is raised compared with the behavior of the original material while the comparable compressive curve is lowered. It was also found that the onset of tensile instability was extended to larger tensile strains when these polymers were first cold worked by extruding or drawing. The elastic modulus was increased when PC was extruded or drawn while this property exhibited a decrease, due to cold working, for both other polymers. All three materials exhibited pronounced directional effects when subjected to compressive loading both parallel to and perpendicular to the longitudinal axis of the extrudate. In a qualitative manner this seems to correlate with greater chain alignment brought about by the forced flow through the die throat. Exploratory temperature measurements indicate that a maximum rise of 20 deg F resulted for this severe reduction of area; this would not cause the glass transition temperature of the PC and Nylon to be exceeded.