WPC (PLASTIC COMPOSITE) DOOR FRAME

Wood–plastic composites (WPCs) are a form of composite combining wood-based elements with polymers. The processes for manufacturing WPCs include extrusion, injection molding, and compression molding or thermoforming (pressing). Newer manufacturing processes for WPCs include additive manufacturing via fused layer modeling and laser sintering. An important constraint for polymers used in WPCs is requiring process conditions (melt temperature, pressure) that will not thermally degrade the wood filler. Wood degrades around 220°C; thus, general-purpose polymers like polyethylene and poly vinyl chloride are typically used for manufacturing WPCs. Wood fibers are inherently hydrophilic because of the hydroxyl groups contained in the cellulose and hemicellulose molecular chains. Thus, modification of the wood fiber via chemical or physical treatments is very critical to making improved WPCs. The most abundant profiles made from wood–plastic composites are boards or lumber used in outdoor decking applications. Although
early WPC products were mainly extruded for profiled sections, nowadays, many injected parts made of WPC are being introduced for various industries, including electrical casings, packaging, daily living supplies, and civil engineering applications. Mold and mildew and color fading of WPCs tend to be the durability issues of prime importance for WPCs. Most recent research on WPC durability focuses on studies to better understand the mechanisms contributing to various degradation issues as well as methods to improve durability. Most WPC products in the USA are utilized in building materials with few exceptions for residential and commercial building applications, which means that building codes are the most important national rules for the WPC manufacturers. New developments are being made especially in the area of nano additives for WPCs including nanocellulose. Recently, the trend of patent registrations for WPCs has shifted to new products or applications instead of the materials itself.

An important constraint for polymers used in WPCs is requiring process conditions (melt temperature, pressure) that will not thermally degrade the wood filler. Wood degrades around 220°C; thus, general-purpose polymers like polyethylene and poly vinyl chloride are typically used for manufacturing WPCs. Wood fibers are inherently hydrophilic because of the hydroxyl groups contained in the cellulose and hemicellulose molecular chains. Thus, modification of the wood fiber via chemical or physical treatments is very critical to making improved WPCs. The most abundant profiles made from wood–plastic composites are boards or lumber used in outdoor decking applications. Although early WPC products were mainly extruded for profiled sections, nowadays, many injected parts made of WPC are being introduced for various industries, including electrical casings, packaging, daily living supplies, and civil engineering applications. Mold and mildew and color fading of WPCs tend to be the durability issues of prime importance
for WPCs. Most recent research on WPC durability focuses on studies to better understand the mechanisms contributing to various degradation issues as well as methods to improve durability. the area of nano additives for WPCs including nanocellulose. Recently, the trend of patent registrations for WPCs has shifted to new products or applications instead of the materials itself.

Wood plastic composites (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.”

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.

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, 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 can be produced in almost any color and shape. Hollow decking boards can reduce material usage.

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.

WPC has become currently an important address of research that gained popularity over the last decade especially with its properties and advantages that attracted researchers such as: high durability, Low maintenance, acceptable relative strength and stiffness, fewer prices relative to other competing materials, and the fact that it is a natural resource. Other advantages have been strength points including: the resistance in opposition to biological deterioration especially for outdoor applications where untreated timber products are not suitable, the high availability of fine particles of wood waste is a main point of attraction which guarantees sustainability, improved thermal and creep performance relative to unfilled plastics where It can be produced to obtain structural building applications including: profiles, sheathings, decking, roof tiles, and window trims. On the other hand, WPCs are not nearly as stiff as solid wood; however, they are stiffer than unfilled plastics. In addition, they do not requi
re special fasteners or design changes in application as they perform like conventional wood.

As mentioned, the reasons for using WPC are many; however, there are other causes that men forced many countries to tend for using alternative sources to virgin materials. In the United States, for example, the U.S. Environmental Protection Agency, by the beginning of 2004, has phased out the usage of wood treated with chemicals such as the chromate copper arsenate (CCA) to prevent environmental and microbial degradation. As this type of wood was used in the building products’ market concerned with residential applications such as decking, the need for the alternative survived the WPC market. In Europe, environmental concerns are focused on limiting the use of finite resources and the need to manage waste disposal; therefore, the tendency to recycle materials at the end of their useful life has increased tremendously. Recycling polymers in Europe was less preferred than other types of materials such as metal; however, illegality of land filling and waste management priority in many European countries were the
motive to do so. In addition to the enforced environmental policies, the growth of environmental awareness led to a new orientation to use wasted natural materials for different applications and industries such as the automotive, packaging and construction industries.