Manufacture of WPC Products

The processes that can be used for the manufacture of WPC products are compounding, extrusion, injection molding and pultrusion. Drying ofwood is an important prerequisite of WPC production since... 

There currently are no manufacturing standards for WPCs and the standard test methods for evaluating the mechanical and physical properties of WPC products are under development by the American Society for Testing and Materials (ASTM), committee D7 on Wood. The lack of manufacturing standards combined... 

The compounding process is very important in the manufacture of WPCs. The performance of a compound has big influence on the properties or productivity of the WPC. So, in this section, not only the technique but also the purpose and some points of attention are included in the discussion of a compounding process. 

The technique widely used in compound manufacture of WPCs is the compound process using an extrusion machine. Since continuous production of compound using an extrusion-molding machine is possible, it can secure high productivity. Furthermore, as a pellet-shaped compound is handled easily at molding (extrusion or injection), it is easy prepared by compounding by extrusion molding. 

There are a variety of WPC products in the market These commerdal products could originate from virgin or recycled polymers and virgin or reclaimed wood. For instance, Andersen Windows Company utilizes waste PVC from their manufacturing plant in producing WPC window components. Certain Teed Company uses recycled fibers in their Boardwalk plastic composites. Some examples of WPC products and their major components are listed in Table 13.4, with a focus on the United States, which has the biggest WPC market for building applications. 

The manufacture of WPCs is comprises two steps blending raw materials and making composites blends into a product [32]. Raw materials can be mixed in either batch or continuous mixers. The forming techniques include extrusion, injection molding, and compression molding. However, some factors, such as fiber type, fiber content, fiber orientation, moisture content of fiber, should be taken into consideration when choosing the suitable manufacturing process [33]. 

The range of whey products that are used include, for example, ultra-filtered and dried WPC, which contains between 20% and 89% protein ion exchange and membrane filtered WPI, which contains at least 90-95% protein (Tunick, 2008) and other whey fraction-enriched products such as p-lactalbumin. These enriched protein whey products can be texturized and used in the manufacture of high-protein content puffed com products (Onwulata et al, 2010). 

Apparently, none of WPC manufacturers adds calcium carbonate as a filler in then-products. LDl Composites, which use Biodac that consists of about 25% CaC03 and 25% of kaolin (clay), also did not use individual minerals as fillers. Nevertheless, there are many publications, mainly by suppliers of minerals and university researchers, describing benefits of calcium carbonate in WPCs. 

Dover Chemical Corporation produces resinous chlorinated paraffins under a name Chlorez . All Chlorez grades have a physical form of white powder (particles smaller than 50 mesh) with chlorine content around 70%. The manufacturer recommends Chlorez as flame retardants (in a combination with antimony trioxide) and lately as a nonreactive coupling agent under a brand name Doverbond (such as Doverbond DB 4300 or Doverbond 3000). The manufacturer claims that Chlorez in the amount of 10% along with 3% of a lubricant in the WPC shows an effect of a coupling agent and increases the flexural strength and modulus of the product, as well as the UV and moisture resistance (private communication, Dover Chemical Corp.). DB 4300 lists at 1.50/lb [12,13]. 

By far, wood particles are the major raw material source used for manufacturing WPCs. Wood particles can originate from sawdust, planer shavings, short solid pieces of lumber, conventional wood composite scrap [6], and scrap pallets [12], Both softwoods and hardwoods can be used for WPC production. Currently, most WPCs using softwoods are made with southern yellow pine, while WPCs produced with hardwoods are made with oak, maple, or aspen. The anatomical features as well as physical, mechanical, and chemical properties of softwoods and hardwoods differ considerably among species, and may affect the wood-polymer interface, and, as a consequence, the composite s properties and performance. 

There is no such thing as a typical feedstock that should be used to manufacture a specific WPC and the materials selected depend very much on cost, availability, market value of the product (i.e., low-cost or high-value end of the market) and product performance requirements. 

Ponderosa pine, a common species used extensively in window and door manufacture and routinely made into wood floor, is a good overall performer. Other species, such as maple, oak, and many other hardwoods and softwoods can be successfully used. The density of hardwoods can be almost twice that of softwoods and so will result is a heavier product. Moreover, some wood fibers are more durable than others depending on the environmental conditions (wet or dry). Also the modulus is generally higher for hardwoods resulting in a stiffer WPC product. 

In order to produce a WPC product by the extrusion process, it is required to first melt the polymer, then mix the molten polymer with the dried wood fiber such that a homogeneous melt is achieved and any remaining moisture can be removed by vacuum venting. The extruder then compresses the homogeneous blend to pass through the die. Various extrusion configurations have been developed for WPC product manufacture [274], some of which are described below. 

As the processing of WPCs becomes more of a science than an art, systematic studies are needed to understand the possible benefits of processing aids. These benefits will be needed if WPG product manufacturers are able to lower their costs enough to compete better with conventional construction materials. 

The mechanical properties of Wood-Plastic-Composites substantially depend on the quality of the raw material, the composite and the manufacturing process. The density of WPC lies between 0.9 and 1.4 g cm and is higher than that of one of the two components, plastic and wood, alone. The porous wood structure is densified during the production process and plastics and additives partly penetrate into the cavities. Thus, water absorption is made harder, and the material swells less and more slowly. ... 

The production of WPC by UF is today a well-established application in the food and dairy industry. WPC can be further fractionated in j3- and a-lactoglobulin fractions by properly selectingpH,ionicstrength and temperature (Zidney, 1998), or used for the manufacture of caseino-macropeptides with pharmotherapeutic value. 

The enthusiasm in this field is explained by the number of potential applications. For example wood-polymer composites (WPC), mostly manufactured through extmsion and injection moulding processes are used in automotive (dashboards or screen-doors of the vehicles) and construction applications (interior floor coverings, profiles for doors and windows, ornamental panels, external shutters, pavements, garage, or entrance doors). Replacement of wood products for building applications such as particleboard and fiberboard materials or injection mouldable wood is another area where natural fibers are generating increased interest. 

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