Development of a single screw extruder for the production of wood-plastic composite

Abstract

This study was carried out to design, fabricate, assemble and evaluate the performance of a laboratory scale wood-plastic composite (WPC) single screw extruder that can be used for recycling wood and plastic waste materials using locally sourced materials based on availability, strength and cost effectiveness. The extruder is separated into four units; the feeding, conveying, heating and forming unit. The designed parts were; the hopper capacity, the shaft diameter, the screw dimensions (pitch, helix angle and diameter), and the capacity on the conveyor (feed throats, compression and metering units) units. The developed machine was evaluated by using it in extruding low density plastic wastes and gmelina (Gmelina arborea) sawdust. The results showed a hopper capacity of 38.3m3, shaft diameter of 60mm, screw dimensions (diameter=20mm, pitch=50mm, and helix angle = 17.650 ). The performance evaluation of the machine indicated an efficiency of 85% for the machine at an operating speed of 268rpm (4.5rps) with a throughput of 17.55kg/hr during a maximum period of 5 minutes. The mean water absorption (0.45-13.68%) and thickness swelling (0.14 - 0.94%) observed for the composites produced compared favorably with those reported in literature for WPCs recommended for non-structural indoor application purposes. The wood contents and soaking period had effects on the sorption properties and not the effectiveness or ineffectiveness of the machine. The machine conserves cost and energy due to low specific mechanical energy consumption of 191.21kJ/kg.