OPTIMIZATION OF THE TUBE-EXTRUSION DIE FOR SHORT-FIBER-FILLED POLYMERS

A new way to increase fiber orientation in the hoop direction in a sho rt-fiber-filled thermoplastic tube is presented. It consists of inject ing a lubricant at the surface of a diverging die. A calculation of fl ow and fiber orientation shows that the effect of extensional deformat ions which tend to orient fibers perpendicular to the flow rakes place over ail the thickness. Different dies are tested with a 30 wt% short -glass-fiber-reinforced polypropylene. Fiber orientation and mechanica l properties are measured. The significance of the die is shown. (C) 1 996 Elsevier Science Limited