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Plastic recycling is the process of recovering scrap or waste plastic and reprocessing the material into useful products, sometimes completely different in form from their original state. Since plastic is not normally biodegradable, recycling it is part of global efforts to reduce plastic in the waste stream, especially the approximately eight million metric tonnes of waste plastic that enter the earth's ocean every year. This helps to reduce the high rates of plastic pollution. Plastic recycling includes melting down soft drink bottles and then casting them as plastic chairs and tables. However, this kind of "recycling" is rather a misnomer since plastic beverage bottles (soda, juice, milk) are never truly reformed into new beverage bottles, as this requires virgin plastic. So there is actually no true cycle in the "recycling" of plastic beverage containers, which actually and more precisely should be referred to as "downcycling". Plastics are also recycled during the manufacturing process of plastic goods such as polyethylene film and bags. A percentage of the recycled pellets are then re-introduced into the main production operation. This closed-loop operation has taken place since the 1970s and has made the production of some plastic products amongst the most efficient operations today. Compared with lucrative recycling of metal, and similar to the low value of glass, plastic polymers recycling is often more challenging because of low density and low value. There are also numerous technical hurdles to overcome when recycling plastic. A macro molecule interacts with its environment along its entire length, so total energy involved in mixing it is largely due to the product side stoichiometry (see enthalpy). Heating alone is not enough to dissolve such a large molecule, so plastics must often be of nearly identical composition to mix efficiently. When different types of plastics are melted together, they tend to phase-separate, like oil and water, and set in these layers. The phase boundaries cause structural weakness in the resulting material, meaning that polymer blends are useful in only limited applications. Another barrier to recycling is the widespread use of dyes, fillers, and other additives in plastics. The polymer is generally too viscous to economically remove fillers, and would be damaged by many of the processes that could cheaply remove the added dyes. Additives are less widely used in beverage containers and plastic bags, allowing them to be recycled more often. Yet another barrier to removing large quantities of plastic from the waste stream and landfills is the fact that many common but small plastic items lack the universal triangle recycling symbol and accompanying number. An example is the billions of plastic utensils commonly distributed at fast food restaurants or sold for use at picnics. The percentage of plastic that can be fully recycled, rather than downcycled or go to waste can be increased when manufacturers of packaged goods minimize mixing of packaging materials and eliminate contaminants. The Association of Plastics Recyclers have issued a Design Guide for Recyclability.〔http://www.plasticsrecycling.org/images/pdf/market_development/APR_Design_Guide_Exec_Summary2014.pdf〕 The use of biodegradable plastics is increasing. ==Processes== Before recycling, most plastics are sorted according to their resin type. In the past, plastic reclaimers used the resin identification code (RIC), a method of categorization of polymer types, which was developed by the Society of the Plastics Industry in 1988. Polyethylene terephthalate, commonly referred to as PET, for instance, has a resin code of 1. Most plastic reclaimers do not rely on the RIC now; they use automatic sort systems to identify the resin. Ranging from manual sorting and picking of plastic materials; to mechanized automation processes that involve shredding, sieving, separation by rates of density i.e. air, liquid, or magnetic, and complex spectrophotometric distribution technologies e.g. UV/VIS, NIR, Laser, etc.〔Plastics Europe: Association of Plastics Manufacturers. "''Waste Pre-Treatment and Sorting''." http://www.plasticseurope.org/plastics-sustainability-14017/zero-plastics-to-landfill/waste-pre-treatment-and-sorting.aspx. Retrieved 2015.7.8〕 Some plastic products are also separated by color before they are recycled. The plastic recyclables are then shredded. These shredded fragments then undergo processes to eliminate impurities like paper labels. This material is melted and often extruded into the form of pellets which are then used to manufacture other products. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「plastic recycling」の詳細全文を読む スポンサード リンク
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