What is WPC material? Wood-plastic composites are panels or wood products made from recycled plastic and small wood particles or fibers. Compared to the time-honored natural wood or traditional wood composites such as particleboard or fiberboard, wood-plastic composites are relatively new products.
This article summarizes some of the basic manufacturing steps, physical and mechanical properties, and main uses of WPC.
Wood-plastic composite materials are widely used in countries around the world. They are made by mixing wood particles as fine as flour with recycled plastic. In 2022, the sales of the North American WPC market has reached 1.662 billion US dollars. At a CAGR of 11.4% during 2021-2026, the wood plastic composite (WPC) market is expected to reach USD 7.4 billion by 2026.
Compared with traditional wood products, wood-plastic composites have high durability, flexural strength, shear strength, low moisture content and low water absorption. These properties make it useful for railings, windows, doors, siding, fencing, floors and interior molding, and increase demand in the automotive and construction industries. The growing construction industry in emerging countries such as China, India, Brazil, Argentina, and the African region is also driving the market growth over the forecast period.
The main production steps and performance of WPC
Typically, the manufacture of WPC is a two-step process. Combinations of wood and thermoplastics such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polyvinyl chloride (PVC) are mixed together to form a dough-like consistency called a compound. Mixing can be carried out by a batch or continuous process.
In addition to the main constituent wood, which has a particle size range of 20 to 60 mesh, plastic coupling agents, stabilizers, blowing agents or dyes are added to enhance the performance of the final product in specific applications.
For example, lubricants can improve the appearance of surfaces. There are three common molding methods for WPC. Figure 1 shows the extrusion method, which forces the molten composite material through a die. In the case of the injection molding method, the molten composite material is forced into a cold mold. The third is to press the molten composite between mold halves.
Figure 1. Extrusion manufacturing process of wood-plastic composites.
Most WPCs are produced through an extrusion process, which uses various extruder types, such as single or twin screw, to form the final shape of the material. Figures 2, 3, and 4 illustrate an example of a WPC product and a flowchart of a typical manufacturing process, respectively.
Figure 2. Different types of wood composite products.
Figure 3. Application of wood-plastic composites as decorative panels.
Figure 4. Typical production flow chart of wood-plastic composites.
Most of the physical and mechanical properties of WPC depend primarily on the interaction between wood and thermoplastic materials. One of the most effective ways to improve this interaction is to add coupling agents as additives. In general, such additives help the compatibility between hydrophilic wood (which absorbs water easily) and hydrophobic plastic (which lacks hydrophilicity), resulting in a single-phase composite, resulting in a product with better properties than solid wood. dimensional stability.
Traditional pressure-treated wood dominated by copper chromate arsenate (CCA) is facing increasing user dissatisfaction due to health reasons and environmental pollution. In addition, since December 2002, the use of arsenic-treated wood has been banned when there is direct human contact, such as decorative materials, playground equipment, or picnic tables.
The use of WPC wood, either in solid cross-section form or with a tubular structure as shown in Figure 2, has been a very popular material as an alternative to treated wood products.
Some advantages and disadvantages of WPC
The biggest advantage of WPC is its eco-friendly method of using waste wood and recycled plastic materials. Compared to solid wood, wood composite plastics are low maintenance. One of the main reasons for the rapid growth of WPC is its low life cycle cost.
In general, WPC boards are about 15% more expensive to produce than pressure-treated lumber, but require less maintenance. The actual payback period is estimated to be 3 to 5 years compared to pressure treated surfacing materials. Its excellent dimensional stability and low variability can also be considered as another major advantage of WPC products.
Due to the great interest in outdoor use, most research in many countries has focused on the durability and extended service life of WPCs.
In fact, WPC was originally marketed as natural decay resistance to fungal or insect attack. However, it has been shown that WPC will still absorb some moisture and eventually rot, but at a much slower rate than solid wood.
Thermal expansion, creep (deformation over time), high density and difficult to apply coatings will be some of the other disadvantages of WPC.