Wood plastic composite is a relatively new material that has many potential uses. The markets for WPC decking lumber have been expanding recently and new applications are being pursued. Door and window components, deck handrails and fencing are other markets for the WPC industry. The flexibility of manufacturing methods and product performance attributes provide the potential for a variety of new markets.
This publication is intended as an introduction to wood plastic composite technology for those people who are interested in WPC technology and their applications.
What are WPCs?
(WPCs) are roughly 50:50 mixtures of thermoplastic polymers and small wood particles. The wood and thermoplastics are usually compounded above the melting temperature of the thermoplastic polymers and then further processed to make various WPC products.
WPC can be manufactured in a variety of colors, shapes and sizes, and with different surface textures. Depending on the processing method, WPCs can be formed into almost any shape and thus are used for a wide variety of applications, including windows, door frames, interior panels in cars, railings, fences, landscaping timbers, cladding and siding, park benches, molding and furniture.
One commonly available example of WPCs is the decking lumber that is often better known by its various brand names – e.g., Trex™, ChoiceDek™, Eon™ or SmartDeck™ – or as the generic term “composite lumber.”
wood plastic composites Advantages
WPCs offer a number of potential benefits. The presence of wood in a plastic matrix can result in a stiffer and lower-cost material than if plastic alone was used. Also, the compression properties (resistance to crushing) for most WPCs are superior to that of wood loaded perpendicular to the grain. The plastic in the product is not subject to water absorption or biological attack, so the WPC can have lower maintenance requirements than solid wood. WPC lumber will not warp, splinter or check.
The use of wood – a natural and renewable resource – can reduce the “carbon footprint” of plastics, because less fossil energy and material are required to make the final product. WPCs are also potentially recyclable, because recovered material can be melted and re-formed. WPCs may be identified as sustainable materials, due to the wood particles predominately being a byproduct of sawmill and other wood-processing waste streams, and because much of the plastic is derived from consumer and industrial recycling efforts.
WPCs offer great flexibility in the shapes and colors of the materials produced. Materials usage can be also be reduced through the engineering of special shapes – e.g., hollow-core decking boards.
wood plastic composites Disadvantages
The wood component within WPCs does impart some positive attributes compared to plastic; however, the inherent problems with wood (moisture sorption and susceptibility to mold and decay) remain. Water can penetrate into WPCs can be produced in almost any color and shape. Hollow decking boards can reduce material usage.
WPCs, albeit at a much lower rate and level compared to solid wood or other wood composites. The resulting sorption of water can promote the growth of mold and decay fungi; however, aesthetics − not structural issues − dominate consumer callbacks. Color fade from sunlight is also accelerated when wood is added to thermoplastics, causing a whitening or graying of the surface of the composite.
WPCs are also usually quite heavy and not as stiff as solid wood. This limits the potential use of WPCs in many structural applications and creates the potential creep or sagging problems, especially in a warm environment. On the other hand, this flexibility can be an advantage: WPC can be bent on-site to make attractive patterns.
WPC is touted as having environmental benefits, because it is made from residues (wood) or recycled materials (plastic). However, virgin plastics are commonly supplemented in WPC operations to maintain tighter quality control and offset highly fluctuating recycled plastic inventories. WPC also requires large amounts of energy to produce. WPC is theoretically recyclable; it could be re-melted and reformed into new decking lumber. However, no recycling of this new product is currently underway, with exception of recycling of off-specification material during manufacture. The collection, cleaning and transportation of old WPC to a recycling center for remanufacture are likely to be prohibitively expensive.
