The term “wood plastic composite” (WPC) refers to any composite that contains wood & thermoset or thermoplastic. Thermosets include resins such as epoxies & phenolics. Thermoplastics include resins such as polyethylene, polypropylene & polyvinyl chloride. These new materials extend the current concept of “wood composites” from the traditional compressed materials such as particleboard & medium density fiber board (MDF) into new areas & more importantly, a new generation of high performance products.
The first generation of WPC's were a combination of recycled wood flour or chips & a binder. These were ideal for relatively undemanding applications. The new & rapidly developing generation of WPC's have good mechanical properties, high dimensional stability, & can be used to produce complex shapes. They can be extruded to high dimensional tolerances, are tough & stable products. The new WPC's are high technology products for the most demanding applications.
The most common type of the new WPC's are produced by mixing wood flour / fiber & plastics to produce a material that can be processed like a conventional plastic, but has the best features of wood & plastic.

Wood Plastic Composites From A Historical Perspective
Wood – thermoset composites date to the early 1900's. An earlier commercial composite material marketed under the trade name “ Bakelite”, was made of phenol – formaldehyde & wood flour. Its first commercial use was reportedly as a gearshift knob for Rolls Royce in 1916.This paper is focused on wood – thermoplastics, which in today's parlance are simply referred to as WPC.
The birth of the WPC industry involved the interfacing of two industries that have historically known little about each other & have different knowledge, expertise & perspectives. The plastics industry has knowledge of plastics processing & the forest products industry has more experience & resources in the building products market. Not surprisingly, some of the earliest companies to produce WPC's were window manufacturers who had experience with both wood & plastics.

The plastics industry has traditionally used talc, calcium carbonate, mica, and glass fiber to modify the performance of plastics. About 2.5 billion Kgs of fillers & reinforcements are used annually. The industry was reluctant to use wood or other natural fibers such as kenaf, flax & hemp, though these fibers are from a renewable resource, are less expensive, lighter & less abrasive on processing equipments than conventional fillers. Most plastic processors ignored wood fiber because of its low bulk density & specific gravity, low thermal stability & tendency to absorb moisture.
The majority of thermoplastics have a bulk density of approximately 0.5 gms/cc. The plastics processor had to face the problem of how to consistently meter & force low bulk density wood flour into small openings typical of plastic processing equipments. In addition, the processing temperature for even the low softening plastics is often too high for incorporation of wood filler without thermal degradation. The high moisture content of wood & other natural fibers is also often problematic to the plastic industry which considers 1 to 2 % moisture content high. Even plastics processors having vented equipments capable of removing moisture during processing were averse to removing 5 to 7 % moisture from wood fiber. Resin dryers, which are fitted on plastic processing equipments, are not sufficient for wood filler or particles. Drying of wood or other natural fibbers poses a fire hazard. Plastics processors who tried to use wood or other natural fibers often lacked the knowledge of cellulosic materials & their failed attempts made the industry generally skeptical of combining wood & plastic.

For the wood products industry, thermoplastics were a foreign world, although they attempted products such as Vinyl sidings. Competing in different markets, forest & plastics industries had few material & equipment suppliers in common& they processed materials very differently & on entirely different scales.

The Turn Around
The perspectives of some plastics industries have changed dramatically in the last decade. Interest has been fuelled by the success of several WPC products, greater awareness & understanding of wood, developments from equipment manufacturers & additive suppliers & opportunities to enter new markets, particularly in the large volume building applications sector. Forest product industries are changing their perspectives as well. They view WPC's as a way to increase the durability of wood with little maintenance on the consumer's part (one of the greatest selling points). Some forest products companies in the USA are beginning to manufacture WPC. These ventures into WPC's are being driven by customer demand & opportunities based on experience in building products.