Particle orientation in talc-filled thermoplastics extruded through cylindrical, rectangular and annular dies

Talc-filled thermoplastic (polystyrene) compounds have been processed by compression molding and in a range of slit, capillary, rectangular and annular dies. Talc volume fractions of 0.05, 0.10, 0.20, and 0.40 were investigated. We have studied the state of orientation of the talc particles through the cross-section of these samples. For the slit dies and compression-molded samples, the disk particles are parallel to the die or mold surface. This is also the situation for the capillary dies at low talc particle loadings. At volume fractions of 0.05 and 0.10 talc the disks are oriented in concentric (onion ring) shape from core to skin. At 0.20 and 0.40 volume fractions of talc the disk particles in the core of the extrudates have a disordered radial orientation while in the skin they are oriented in the circumferential direction. At a volume fraction of 0.40 the talc compound showed more radial direction orientation than at 0.20 talc. Similar observations were made for rectangular and annular dies. The mechanisms leading to this behavior are discussed.