Extrusion of Wood Plastic Composites Douglas J. Gardner David ...Co-Rotating Twin Screw & Hot Melt Single Screw wood composite System. A co-rotating twin screw in combination with a hot melt single screw can be used to produce wood plastic composite lumber. In this case, a parallel 40:1 L/D co-rotating twin screw extruder is coupled with a hot melt 10:1 L/D, single screw extruder. The material for this system is wood flour or fiber at ambient moisture content (5 to 8%) and the polymer and additives can be in their natural states. No material.