2012年3月19日星期一

wood plastic composite material 111


In some manufacturing facilities, the constituents are combined and processed in a pelletizing extruder, which produces pellets of the new material. The pellets are then re-melted and formed into the final shape. Other manufacturers complete the finished part in a single step of mixing and extrusion.WPCs do not corrode and are highly resistant to rot, decay, and Marine Borer attack, though they do absorb water into the wood fibers embedded within the material[2]. They have good workability and can be shaped using conventional woodworking tools. wood plastic composite decking are often considered a sustainable material because they can be made using recycled plastics and the waste products of the wood industry. Although these materials continue the lifespan of used and discarded materials, and have their own considerable half life; the polymers and adhesives added make wood-plastic composite difficult to recycle again after use[citation needed]. They can however be recycled easily in a new wood and plastic composite, much like concrete. One advantage over wood is the ability of the material to be molded to meet almost any desired shape. A WPC member can be bent and fixed to form strong arching curves. Another major selling point of these materials is their lack of need for paint. They are manufactured in a variety of colors, but are widely available in grays and earth tones.Despite up to 70 percent cellulose content (although 50/50 is more common), the mechanical behavior of wood plastic composite decking is most similar to neat polymers. This means that they have a lower strength and stiffness than wood, and they experience time and temperature-dependent behavior [3] The wood particles are susceptible to fungal attack, though not as much so as solid wood, and the polymer component is vulnerable to UV degradation.[4] It is possible that the strength and stiffness may be reduced by moisture absorption and freeze-thaw cycling, though testing is still being conducted in this area. Some WPC formulations are also sensitive to staining from a variety of agents.The next generation of composite decking includes a durable plastic cap [5] that adds added protection. A PVC cap surrounding the wood plastic composite material helps reduce staining, fading and scratching that may occur with 1st generation composite decking. Capped composites cost considerably less than pure plastic decking as the core is still wood plastic composite materials.

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