​Coextrusion is a process of extruding two or more plastic materials through a single die

Coextrusion is a process of extruding two or more plastic materials through a single die. The auxiliary equipment includes cooling with a water bath and sizing in which the plastic tube is forced against external sleeve or against a mandrel with vacuum to achieve the appropriate diameter of the tube, post forming with jigs, fingers, shoes, and rollers, cutting with fly cutters, and winding devices. The materials have high molecular weight, high viscosity, and high melt strength. Polyethylene can be used for films and pipes, either as LDPE (flexible) or HDPE (rigid). Polypropylene can be used as an oriented film. PVC can be used in the rigid form and plasticized form with twin screw. PTFE or UHMWPE processed by screwless or ram extrusion. The products that are made include fibers and monofilaments for nylon, acrylics, polyesters at a production rate of 800–6000 ft/min, profiles that include flat strips, simple channels, hollow sections for vinyl and PVC, polystyrene, and polyethylene. The profiles can be made with cellular, or foam, core and solid skin. This can be used with exterior wall siding, window tracks, door tracks, handrail covers, and weather stripping.

The tubular products can include tiny tubing for an artificial kidney or drinking straws to pipes with a 20-m diameter. The specialty tubes can include pipes made with coextrusion foam core, very long tubes made with helical winding, and then bonding with a suitable extruded profile, flexible reinforced tubing made by extruding an inner liner, braiding around with fiber reinforcement, and then extruding over with a cover or jacket. The materials are PVC, LDPE, or HDPE. The flat products include films with a thickness of 0.25–3 mm. Plastic sheets can be made thicker. The widths can be made large as the thickness as high as 13 mm.