A study of the extrusion of particulate cellulosic composite materials
Traditional routes to the manufacture of timber based composite materials such as particleboard rely on platen pressing a premix of carefully chosen and prepared timber particles and an adhesive to produce flat sheets. Historically such routes have made very inefficient use of forest resources, and because of the planar nature of the composite produced, the finished articles have enjoyed a reputation of being of poor quality and "cheap". The work documented in this thesis sought to examine alternatives to the traditional manufacturing methods in terms of both raw materials and processing route, and to establish technical, economic, and environmental boundaries for the use of the alternatives. Having settled upon extrusion as the most likely technique with which to proceed, the investigation was carried forward by the construction of a series of experimental instruments with the joint aims of refining the technique to a realistic working level and investigating the underlying mechanical principles behind the process. Recourse to the literature of polymer rheology, fluid mechanics, and soil mechanics gave the basis for a crude mechanism hypothesis, and iterative improvements in the instrumental techniques yielded data with which this could be refined. Although some correlation between the extrusion behaviour of this system with other more easily quantifiable systems was found, there is still considerable work required in defining the dynamic changes in the material properties as the raw material is extruded. Small scale production experiments proved successful, however, and an elementary financial model of a suitable production facility indicated that the techniques developed could be used as the basis of an environmentally acceptable, economically viable, low technology industry.