WPC - Durable and Stylist Alliance of Wood and Plastic

Wood-plastic composites continue to drive the growth of wood replacement applications due to their low-maintenance and aesthetic properties. Wood processing and plastics manufacturers are expected to shift towards wood plastic composite manufacturing due to similar manufacturing technology, as well as lower production costs. In addition, plastic manufacturers are expected to move more rapidly due to technical know-how.

WPC is increasingly employed as both an interior and exterior building material. For these applications, materials have to exhibit multifunctional characteristics such as a combination of exceptional mechanical properties and flame retardancy, which can be achieved with the addition of specific additives during composite processing.

Wood Fibres, Polymers and Additives

Wood plastic is a hybrid material made from composite natural wood and plastic fibers. Dust from fiber fillers such as pulp, peanut husks, and bamboo is mixed with new or waste plastic powders from materials such as polyethylene, polyvinyl chloride, polypropylene, and acrylonitrile butadiene styrene. Wood fibers (or wood flour) are typically used as reinforcing fillers in quantities ranging from 50 to 80% while polymeric materials act as binders. Once the ingredients are mixed together to obtain a relatively thick consistency, they are then extruded or moulded.

Additives, such as colorants, reinforcing agents, and lubricants may be added to obtain a higher level of specification for the intended product use. Due to the unique composition of composites, wood-plastic composites can be manipulated to assume a wide range of shapes and dimensions, including arched and bent shapes. As a result of their high cellulose content, Wood Plastic Composite Products can be considered very similar to wood, but they are also moisture and rot resistant.

Wood Plastic Composite (WPC) consisting of polyethylene (PE) and wood sawdust is mainly used in building and structural components. On the other hand, WPC includes wood sawdust and polypropylene (PP), which are commonly used for automotive and consumer products. Wood sawdust and polyvinyl chloride (PVC) make up a WPC that is commonly found in window construction, as well as in some decking applications. Combining acrylonitrile butadiene styrene (ABS) and wood sawdust yields a WPC that can be used in a variety of applications.

Material selection depends in large part on the choice of the manufacturer, and on the general properties of each ingredient as well as availability. Maple, oak and pine are common types of sawdust, and are relatively low-cost to obtain.

Repeatability, Thermal Stability and Hardness

WPC assumes many of the same characteristics of wood thanks to its high cellulose content. It can therefore be subjected to similar processes including planning, drilling and sanding. Nails, screws, and other fasteners often achieve greater grip when used with WPC than with wood, resulting in WPC's ability to use smaller fasteners to hold higher. Additionally, WPC offers better water resistance than original wood with minimal expansion. The lack of moisture present within the WPC also results in its resistance to decay. The ability of WPC to perform in high temperature environments is also better than that of wood. Due to their longevity they are often used as a replacement for tropical timber, thereby contributing to the conservation of ecologically important tropical forests.

Connectors for Better Performance

To achieve the various characteristics listed above, the way the wood is processed and the interfacial adhesion must be controlled. The difference between the surface energy of the wood and the matrix of the plastic polymer determines the final physical properties of the composite, often requiring the addition of a coupling agent to enable stronger interfacial adhesion. Coupling agents inspirit dissimilar materials to form an alloy. Compatibility may also be used, a process by which wetting is achieved within a mixture. There are several ways in which coupling and compatibility can occur, including modification of the fiber or polymer and adding coupling agents. Depending on the type of wood and plastic involved, various coupling agents and compatibilizers may be appropriate.