Effect of die drawing process on the mechanical behaviour of polypropylene

The die drawing of polymers is considered an efficient process of producing highly oriented polymeric products. The objective of this research is to investigate the effect of die drawing process on the mechanical behavior of polypropylene (PP). Polypropylene rods were drawn to different drawing ratios at various velocities and temperatures using a hot die drawing test rig designed particularly for this purpose. Tensile, compression and hardness tests were conducted on drawn specimens in order to study the effect of drawing velocity, temperature, and drawing ratio on the elastic modulus, yield strength and hardness. The results show that the tensile yield strength and modulus of elasticity are improved substantially by drawing. Further improvement can be achieved with drawing velocity however the drawing temperature reduces the over all level of orientation and in turn the tensile strength and modulus. On the other end, compressive yield strength and modulus, unlike in tension, they reduce with drawing velocity and increase with drawing temperature. The effect of the compression overhead speed of the testing machine was also considered. It was noticed that both properties were improved with the overhead speed. The influence of the drawing characteristics on hardness values was measured on the outer surface and on the cross section of the specimens. The increase of drawing temperature improves the hardness values measured on the surface and vice versa with the drawing velocity. In addition, the hardness values on the core are less affected by the drawing characteristics than that on the surface.