Abstract: A wood-plastic composite material is produced in a twin screw extruder with parallel intermeshing segmented screws. The screw segments are positioned on two spline shafts and perform the various required functions of mixing, deaerating and removal of moisture followed by extrusion. A polymer is fed to the main throat of the extruder where the plastic is conveyed along a barrel formed by the case of the extruder. Cellulosic fiber is positively fed into the extruder approximately one-quarter of the way down the extruder barrel by a twin screw side stuffer. A vent is provided for entrained air in the cellulosic material to escape. The molten mixture of polymer and cellulosic material is then conveyed to a devolatilization area having a first atmosphere devolatilization area and a second vacuum devolatilization area separated by a melt seal.