Wood-plastic composites or WPC as it is known as is a relatively new product developed during the last ten years or so.

WPC are essentially a combination of wood and thermoplastic materials along with some additives. To cite an illustration of WPC products, is an extruded profile that is used for veranda decking products.

It is made up of 70% wood flour, 25% polyethylene (PE), polypropylene (PP)/PVC and the rest 5% of additives. The additives can range from adhesive agents, UV-protective additives and colour pigments.

Current Market Scenario
In the west, USA and Europe Thermoplastic natural fibre composites are having a good market demand. No doubt that during the last five years, demand for wood-plastic composites has grown by 35-40 %. By the end of 2007 WPC would do business worth $2.0 billion in North America and western Europe. In the European market the main driving force for further product development of WPC is the Automobile market. In context of the present scenario, there lies a huge potential for extruded WPC profiles in products like decking, window or door profiles.

Main Ingredients of WPC Profiles
The following material forms the main ingredient of extruded WPC profiles.

• Wood Flour
  Wood flour is essentially a wood cellulose that is finely ground. For a product to be termed as a wood flour the particle size should be above 20 mesh but below 850 microns. The following table lists some of the chemical and mechanical properties of Wood flour.

  Physical/Chemical Properties	Specifications
  Acidity (pH)	3.5 - 4.6
  Density	0.66 P>Density
  Solubility in Water	Less than 0.1%
  Ash Content	.23 to 0.25 Hardgrove Index
  Moisture Content	4% to 6% (depends on relative humidity)
  Specific Gravity	0.5-0.8
  Colour	Brown (light) to tan

  
  
• Thermoplastic Resins
  The choice of resin selected for use in thermoplastic composites is dependent on many factors. Wood tends to a show a nature for degradation at higher temperatures, so a thermoplastic resins which can be processed at a temperature below 2000, centigrade is to be selected for processing of the composites. Let's have look at the choices available for thermoplastics available for extruded plastic profile.

  Polyethylene(PE)	Polypropylene	PVC
  Relatively less expensive	Good service temperature	Strongest resin
  Excellent toughness and impact strength	Lowest Density as compared To PE and PVC	Highest service temperature,
  Can be used both in virgin & recycled form	Best suited to building and automobiles	Excellent weather resistance
  Shows a tendency to stabilize against thermal degradation		Has a tendency towards brittleness

  
  
• Additives
  The main function performed by additives in thermoplastic composites are as under:
  • Improve mechanical properties
  • Provide chemical stability during processing
  • Improve the flow of raw material blend
  
  

Manufacturing of WPC
Extruded WPC profiles are typically manufactured using extrusion process. In the Extrusion process there is a continuous heating, compressing and conveying of raw ingredients that has already been premixed. The extrusion process consists of shaping of the material with the help of extrusion dies, cooling of a product upon its exit from the die and down stream handling including cutting, embossing, sanding and other treatments. This process saves the cost of machining and fabrication. Shape of the final product obtained would be replication of the die opening. The products/profiles made by this process can be cut into small pieces, moulded, routed, sanded etc., with the same tools, feeds and speeds as with wood.

While coming to the extruder type there are variety of equipment available the most common are single-screw extruders, counter-rotating twin-screw extruders or set ups using custom extruders. Out of the three the single-screw system is the cheapest. But typically it has some limitations. Twin-screw extruders on the other hand are good option for extruded woo thermoplastic composites or WPC because here the mixing action is able to blend the wood filler and polymer perfectly in a single process. Along with that it gives low screw speed as well as low-shear mixing, so essential for keeping down the temperatures.

Application of WPC Profile

Industry	Application
Building & Construction	Window and door frames, Cladding
Industrial/Infrastructure	Industrial flooring, railings, bulkheads, Railway sleepers etc.
Automotive	Door & head liners, interior panels, rear shelves, Truck floors etc
Garden/ Outdoor	Decking, Fencing, garden furniture, shelters sheds, playground equipment etc.
Interiors and Internal finishes	Interior panels, Office furniture, Kitchen cabinets, shelving, shutters/Blinds etc.

WPC Extruded Profiles in Construction Applications Salient Features Cross section optimization for construction applications. Hollow sections for reduced weight. Surface texture provides improved slip resistant surface.