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High-density polyethylene
High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a polyethylene thermoplastic made from petroleum. It is sometimes called "alkathene" or "polythene" when used for pipes.〔(Pipe materials ). level.org.nz〕 With a high strength-to-density ratio, HDPE is used in the production of plastic bottles, corrosion-resistant piping, geomembranes, and plastic lumber. HDPE is commonly recycled, and has the number "2" as its resin identification code (formerly known as recycling symbol).
In 2007, the global HDPE market reached a volume of more than 30 million tons.〔(【引用サイトリンク】 publisher = (Ceresana Research ) )〕
==Properties==
HDPE is known for its large strength-to-density ratio.〔(Thermoforming HDPE ). Dermnet.org.nz〕 The density of HDPE can range from 0.93 to 0.97 g/cm3 or 970 kg/m3.〔(Typical Properties of Polyethylene (PE) ). Ides.com. Retrieved on 2011-12-30.〕 Although the density of HDPE is only marginally higher than that of low-density polyethylene, HDPE has little branching, giving it stronger intermolecular forces and tensile strength than LDPE. The difference in strength exceeds the difference in density, giving HDPE a higher specific strength.〔(Compare Materials: HDPE and LDPE ). Makeitfrom.com. Retrieved on 2011-12-30.〕 It is also harder and more opaque and can withstand somewhat higher temperatures (120 °C/ 248 °F for short periods, 110 °C /230 °F continuously). High-density polyethylene, unlike polypropylene, cannot withstand normally required autoclaving conditions. The lack of branching is ensured by an appropriate choice of catalyst (''e.g.'', Ziegler-Natta catalysts) and reaction conditions.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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