Construction industry to benefit from wood fibre composite profiles

Wood and plastics are being increasingly combined to make wood fibre composite profiles for a variety of construction applications such as decking, fencing and door/window frames. The trend has already started in the U.S. where the market for wood extrusion has leapt from 90,000 tons in 1998 to 1,80,000 tons in 2000 and extruded wood profiles are now becoming more popular in Europe and Asia. The problem of disposing large volumes of waste stream of wood flour (some wood processing units generate as much as 50 tonnes of waste per day) is being solved by it's use as primary material. The content of wood is more than plastic in the wood fibre composites, where plastic act as a glue. The material not only looks and feels like wood, but it can be drilled, cut and trimmed with similar tools used for wood. It can also be given an aesthetic finish by varnishing and can also be sanded, painted, and stained. Besides being more cost-effective then timber, which is expensive and prone to price fluctuations, it does not absorb water or decay, like timber does. Most of the production is done using the US developed Strandex system which can handle wood contents of upto 70%. The wood is first pre-dryed to reduce its moisture content below 2% and the wood scrap is then blended with PP or powdered PP. The mixture is then fed into a conical twin-screw extruder via a stuffing unit. Cincinnati Extrusion has developed its Titan conical twin-screw extruder for handling wood fibre, which has a wide, open feed area that gives the advantage of handling highly-filled materials in the form of either powders or pellets.

The company is also in the process of offering complete lines for extruding profiles with wood content of upto 85% which uses individual dosing feeders to deliver wood and polymer pellets separately into the extruders. For profiles with high wood loadings, there is no need for calibration baths, and cooling is carried out using air blowers, with little or no haul-off force required. Davis-Standard's Woodtruder, is a dual-extrusion system combining wood fibre processing and plastics extrusion in one machine. The machine features a primary 28:1 parallel twin-screw extruder and a moulded single-screw, side-injection extruder. A crammer feeder conveys the wood fibre composite at a controlled rate into the primary extruder. The first section of this unit uses a special heating and vaccum venting system to eliminate moisture from the wood fibre. Mounted mid-way along the primary extruder, the side-injection extruder separately heats and mixes the polymer. This is injected at a controlled rate to give the required fibre-polymer ratio, which can be as high as 80% wood for interior applications or 50-60% for outdoor uses. The machine can be used with HDPE, PP, PS, PVC, or ABC along with a variety of fibrous materials such as peanut shells, rice husks, wood shavings and jute. The production of wood fibre composites has been made easier with the availability of Fasalex pelletized compounds that can be simply fed into an extruder by gravimetris or volumetric dosing. The pellets typically consists of 60% saw dust or wood flour; 20% maize or corn and 20 % polymer; which can be a biodegradable resin - to produce a fully natural product.