The historic Italian company Covema, which specialized in designing equipment for processing plastic materials, invented and patented the process to create wood-plastic composites or WPCs in 1960 and later marked the first WPC under the tradename Plastic-Wood. Another Italian company called Icma San Giorgio patented the first process to add wood flour to plastics in 1974.
Earlier uses of wood-plastic composites were limited to industrial applications and some building and automotive applications. It was in 1996 when United States-based Trex Company introduced the first mass-market WPC decking made of recycled wood fibers and plastic bags. The 2000s and 2010s saw rapid applications and global adoptions in the construction industry.
Understanding Wood-Plastic Composites and Its Applications in Construction: The Pros and Cons of WPC Materials
Advantages of Wood-Plastic Composites and Notable Applications
Wood-plastic composites are hybrid or composite materials made of wood-derived materials like wood fiber or wood flour and thermoplastics like polyethylene, polypropylene, polyvinyl chloride, and polylactic acid. Some manufacturers also add other lignocellulosic and inorganic filler materials to add new properties or improve existing ones.
The most common use of WPCs in construction in North America is in outdoor deck floors. They are considered better and more affordable alternatives to timber and polyvinyl chloride or PVC materials. These materials are also alternative to medium-density fiberboards or MDFs and are used in indoor furniture and prefabricated homes.
WPCs have notable properties or characteristics that have made them more appealing to PVCs and more traditional construction materials like natural wood and MDFs. The ongoing research efforts in WPC technology are focusing on improving these properties or adding novel ones. Below are the notable advantages of these materials:
1. Durability and Longer Product Lifespan
One of the main advantages of wood-plastic composites is their durability and longevity. These materials are resistant to rot, decay, and insects and are resistant to moisture unlike most natural wood and conventional medium-density fiberboards and other engineered wood. WPCs also have better UV stability than untreated wood and polyvinyl chloride.
The durability of WPCs comes from their composite structure that combines the strength of wood fibers and the resilience of thermoplastics. Note that particles of the wood content are evenly dispersed and tightly bound within the plastic. This encapsulation shields the wood material from environmental stressors while providing structural stability.
WPCs can last 25 to 50 years outdoors and 30 to 60 years indoors. Most untreated natural wood can last 5 to 10 years outdoors and 10 to 20 years indoors while treated ones have an outdoor lifespan of 10 to 20 years. PVCs have around 10 years outdoors and 30 to 50 years indoors. MDFs are not recommended outdoors and have a 10-to-20-year indoor lifespan.
2. Aesthetics and Flexible Design Applications
WPCs can be manufactured to mimic the look and feel of natural wood to provide a warm and appealing aesthetic. They also offer design flexibility because they are available in a wide range of colors, textures, and profiles. Workability is also another advantage. WPCs can be cut, drilled, nailed, and screwed using standard woodworking tools.
Remember that one of the first applications of wood-plastic composites is in decking. WPCs are now also applied in various construction elements. Their moisture resistance makes them suitable for outdoor fencing, railings, and floorings. WPCs are also the more durable alternative to PVCs and MDFs for indoor materials like wall claddings and ceilings.
3. Low Cost, Low Maintenance, and Safety
The initial cost of WPCs is between USD 4.00 to USD 8.00 per square foot. This is more expensive than natural wood, medium-density fiberboards, and PVC materials. However, similar to PVCs, their maintenance cost is low. MDFs are cheaper at USD 1 to USD 3 per square foot but remember that they have shorter lifespan. Wood has higher maintenance costs.
WPCs are typically manufactured with the desired color and finish. This eliminates the need for regular painting, staining, and sealing unlike natural wood, and further translates to cost savings over their entire lifespan. Simple soap and water are usually sufficient for cleaning WPC surfaces. The material can also be molded to meet almost any desired shape.
These materials also do not splinter. This makes them safer for bare feet on decking and play areas for children. Many wood-plastic composite decking and outdoor flooring products are also designed with textured surfaces to improve slip resistance. WPCs also expand and contract less than wood. This reduces structural deformities and possible damages.
4. Highlighted Environmental Advantages
Many WPCs utilize recycled plastics and wood waste like sawdust and wood flour. Note that these are byproducts of the timber and lumber industry. Their applications in WPC production divert them from landfills, moderate logging activities or frequency by reducing the demand for virgin timber, and demonstrate one of the best examples of upcycling.
Some producers also use recycled plastics in WPC production. These recycled plastics come from used plastic bags and various plastic containers. This also demonstrates upcycling. It is also worth mentioning that the relatively longer lifespan of wood-plastic composites means less frequent replacement and further reduction in resource consumption.
Disadvantages of Wood-Plastic Composites and Key Alternatives
Remember that wood-plastic composites are positioned as alternatives to natural wood, engineered wood like medium-density fiberboards, and polyvinyl chloride or PVC materials. This comes from the fact that WPCs combine the best qualities of wood and thermoplastics. However, for this same reason, they also feature some of the drawbacks of both.
WPCs are still partly made of wood materials. They are still susceptible to surface mold, mildew, and staining. Moreover, because of their plastic component, they are less stiff and strong than solid wood and can sag under heavy loads if not properly supported. They can also become hot in direct sunlight and may fade or chalk over time when used outdoors.
Another disadvantage of WPCs is that they are heavier than MDFs, engineered wood, and certain natural wood. This can make installation harder. Moreover, similar to both MDFs and PVCs, they are also difficult to repair once damaged. Note that wood can be sanded or refinished with fillers or other substances. Below are the specific disadvantages:
1. Relatively High Initial or Upfront Cost
Natural wood is cheaper than WPCs at around USD 2.00 to USD 6.00 per square foot. This is true in geographic markets like Canada and the United States where timber and lumber are abundant. MDFs are even cheaper at USD 1.00 to USD 3.00 per square foot. WPCs have high upfront costs due to existing market demand and inherent manufacturing factors.
The cost of WPCs also varies according to manufacturers and geographic markets. Some products are more expensive because they have additives for ultraviolet resistance, fire resistance, and better water or moisture resistance. These materials are also more expensive in geographic markets with an abundant supply of natural wood or have no established WPC market.
Hence, considering the higher upfront costs, WPCs might not suit low-budget projects or uses with short-term lifespans in which long-term durability is not a priority. One example is low-cost housing programs that often prioritize using more abundant materials like natural wood or concrete. WPCs are also not the preferred materials for ready-to-assemble furniture.
2. Scratch Resistance and Fire Hazard
These materials are still suspectable to scratches and scuffing from pointed or sharp objects due to the softer texture of the plastic component. Some scratches can be difficult to repair invisibly. This disadvantage makes them not ideal for high-impact areas or in applications where aesthetics are important. Examples include commercial lobbies and factories.
Heat retention is also another issue. WPCs can get hot in direct sunlight and become uncomfortable for bare feet on decks and outdoor floorings. They also pose a moderate fire hazard because they contain both wood fibers, which are combustible, and plastics, which can melt and burn further when ignited. WPCs are generally more flammable than wood.
3. Heavy Weight and Low Structural Strength
WPCs are denser and heavier than most natural wood and engineered wood. This makes them difficult to transport and install. Note that thermoplastic materials are denser than wood fibers. The plastic matrix also tightly bonds with the wood particles due to the exertion of extreme pressure during the manufacturing process. This bonding increases overall density.
It is also important to underscore the fact that wood-composite materials are not ideal for structural or load-bearing applications. Wood has high tensile and bending strength because of its wood fibers that run in one direction. WPCs are made of short particles fused with plastics. These composites do not transfer stress well. Plastics also deform under constant stress.
The above is supported by available and comparative data. WPCs have a density of between 1000 and 1300 kilograms per cubic meter. Softwoods like pine have between 400 and 600 while hardwoods like Oak have between 600 and 750. WPCs also have a modulus of elasticity and flexural stiffness of 3000 to 4000. Solid pine has 9000 to 11000 while PVC has 2000 to 3500.
4. Important Environmental Issues
It is true that WPCs are considered environmentally friendly from a first-used perspective because they can be made using recycled wood and plastic materials. However, from an end-use aspect, their plastic components are not biodegradable. Recycling them can be more complex than pure plastics and wood due to their composite nature. Specialized facilities are required.
Most high-performance WPCs are also made from virgin plastics. This contributes to petroleum consumption and increases the carbon footprint of production. Some product variations are also made with chemical additives like ultraviolet stabilizers, pigments, and flame retardants. These can leach into the environment during production, use, or disposal.
FURTHER READINGS AND REFERENCES
- Chotikhun, A., Kittijaruwattana, J., Arsyad, W. O. M., Salca, E.-A., Hadi, Y. S., and Hiziroglu, S. 2022. “Some Properties of Wood Plastic Composites Made from Rubberwood, Recycled Plastic and Silica.” Forests. 13(3): 427. DOI: 3390/f13030427
- Elsheikh, A. H., Panchal, H., Shanmugan, S., Muthuramalingam, T., El-Kassas, Ahmed. M., and Ramesh, B. 2022. “Recent Progresses in Wood-Plastic Composites: Pre-Processing Treatments, Manufacturing Techniques, Recyclability and Eco-friendly Assessment.” Cleaner Engineering and Technology. 8: 100450. DOI: 1016/j.clet.2022.100450
- Icma San Giorgio. n.d. “History.” Icma San Giorgio. Available online
- Jian, B., Mohrmann, S., Li, H., Li, Y., Ashraf, M., Zhou, J., and Zheng, X. 2022. “A Review on Flexural Properties of Wood-Plastic Composites.” Polymers. 14(19): 3942. DOI: 3390/polym14193942
- Murayama, K., Ueno, T., Kobori, H., Kojima, Y., Suzuki, S., Aoki, K., Ito, H., Ogoe, S., and Okamoto, M. 2019. “Mechanical Properties of Wood/Plastic Composites Formed Using Wood Flour Produced by Wet Ball-Milling Under Various Milling Times and Drying Methods.” Journal of Wood Science. 65(1). DOI: 1186/s10086-019-1788-2