Concentric billet coextrusion

The coextrusion processes are the second group of methods for processing "unprocessable" polymers. They are divided into split billet coextrusion and concentric billet coextrusion. In principle they involve the extrusion of the unprocessable component in a sandwich with a processable polymer, to promote extrusion. A form of substrate drawing is involved. 

Concentric Billet Coextrusion. The concentric billet extrusion uses a billet of processable polymer with a hole drilled in the center. A rod of "unprocessable" polymer is placed in this hole and the composite extruded (Figure 4). The concentric composite billet was first used to prepare "one polymer composites" in which the two components consist of two samples of HOPE of different molecular weight (35). Many features of these composites have been studied (36,37). 

---