Low-density polyethylene


Low-density polyethylene
LDPE has SPI resin ID code 4

Low-density polyethylene (LDPE) is a thermoplastic made from petroleum. It was the first grade of polyethylene, produced in 1933 by Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerization.[1] Its manufacture employs the same method today. LDPE is commonly recycled[citation needed] and has the number "4" as its recycling symbol. Despite competition from more modern polymers, LDPE continues to be an important plastic grade. In 2009 the worldwide LDPE market reached a volume of US$22.2 billion (15.9 billion Euro).[2]

Contents

Properties

LDPE is defined by a density range of 0.910–0.940 g/cm3. It is not reactive at room temperatures, except by strong oxidizing agents, and some solvents cause swelling. It can withstand temperatures of 80 °C continuously and 95 °C for a short time. Made in translucent or opaque variations, it is quite flexible, and tough but breakable.[citation needed]

LDPE has more branching (on about 2% of the carbon atoms) than HDPE, so its intermolecular forces (instantaneous-dipole induced-dipole attraction) are weaker, its tensile strength is lower, and its resilience is higher. Also, since its molecules are less tightly packed and less crystalline because of the side branches, its density is lower. LDPE contains the chemical elements carbon and hydrogen.

Chemical resistance

  • Excellent resistance (no attack) to dilute and concentrated acids, alcohols, bases and esters
  • Good resistance (minor attack) to aldehydes, ketones and vegetable oils
  • Limited resistance (moderate attack suitable for short-term use only) to aliphatic and aromatic hydrocarbons, mineral oils, and oxidizing agents
  • Poor resistance, and not recommended for use with Halogenated hydrocarbons.[3]

Applications

LDPE is widely used for manufacturing various containers, dispensing bottles, wash bottles, tubing, plastic bags for computer components, and various molded laboratory equipment. Its most common use is in plastic bags. Other products made from it include:

See also

References


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