What are wood-plastic composites?
Wood-plastic composites are composites made from wood fibers and thermoplastics such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC). Or polylactic acid (PLA).
In addition to wood fibers and plastics. WPC may also contain other lignocelluloses. Or other inorganic filler materials. WPC is a subset of a large class of materials called natural fiber plastic composites (NFPC). Which may not contain cellulosic fiber fillers such as pulp fibers, peanut shells, coffee shells, bamboo, straw, etc.
In the composite structure, certain chemical additives are also required. They provide the integration of polymers and wood flour (powder). While promoting optimal processing conditions.
The company that invented and patented the WPC process was Covema of Milan. founded in 1960 by the Terragni brothers, who called it WPC under the trademark “Plastic-Wood”. The first patent for the process of adding wood fibers to thermoplastics.
WPC is still new to the long history of building materials, compared to natural wood. And is most widely used in North America for outdoor deck flooring. But it is also used for railings, fences, landscape timbers, cladding and siding, park benches, molding and trim, and interior furniture. Comparison solid wood treated with preservatives or solid wood of decay-resistant species. WPC is more environmentally friendly and requires less maintenance. These materials can be produced using simulated wood grain details.
WPC is produced by thoroughly mixing ground wood particles with heated thermoplastic resins. The most common production method is to extrude the material into the desired shape. But injection molding is also used. WPC can be made from virgin or recycled thermoplastics, including high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyvinyl chloride (PVC), polypropylene (PP), acrylonitrile butadiene styrene (ABS), polystyrene (PS), and polylactic acid (PLA). PE-based WPCs are by far the most common. Additives such as colorants, coupling agents, UV stabilizers, foaming agents, blowing agents. And lubricants help to tailor the final product to the target application. Extruded WPCs can be molded into solid and hollow profiles. A wide variety of injection molded parts are also produced, ranging from automotive door panels to cell phone housings.
In some manufacturing facilities. These components are mixed and processed in a pelletizing extruder to produce pellets of the new material. The pellets are then remelted and formed into their final shape. Other manufacturers complete the finished part in a single step of mixing and extrusion.
Because of the addition of organic materials. WPC is processed at lower temperatures during the extrusion and injection molding process. For example, WPC tends to be processed at temperatures about 28 °C lower than the same unfilled material. Most will start burning at about 204 °C. Processing WPC at too high a temperature increases the risk of shearing, burning, and discoloration. By pushing too hot material through too small a gate during the injection molding process. The ratio of wood to plastic in the composite will ultimately determine the melt flow index (MFI) of the WPC. A large amount of wood typically results in a lower MFI.
Advantages of wood-plastic composites
WPC does not corrode and is highly resistant to rot, decay, and marine moth attack. Although they do absorb water into the wood fibers embedded in the material.
WPC has good workability and can be shaped using traditional woodworking tools.
WPC is often considered a sustainable material. Because it can be made from recycled plastics and waste materials from the wood industry. The added polymers and adhesives make WPC difficult to recycle after use. However, they can be easily recycled in new WPCs, just like concrete.
One advantage over wood is that the material can be molded to meet almost any desired shape. It can also be molded in a variety of desired colors.
WPC components can be bent and fixed to form strong arch curves. Another major selling point of these materials is that they do not require painting.
WPC sandwich panels
WPC panels show a range of good properties. But the relative heaviness of the overall composite panel limits their use. As lightweight is not necessary. WPC in the form of sandwich construction composites. Which allows the benefits of traditional wood composites to be combined with the lightness of sandwich panel technology. WPC sandwich panels consist of a wood polymer composite skin and a typically low-density polymer core. That can very effectively increase the stiffness of the panel.
WPC panels are primarily used in automotive, transportation, and construction applications. But are also being developed for furniture applications. The new efficient and often in-line integrated production process. This allows for the production of stronger and stiffer WPC sandwich panels at a lower cost than traditional plastic panels.