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]

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:

• Trays and general purpose containers
• Corrosion-resistant work surfaces
• Parts that need to be weldable and machinable
• Parts that require flexibility, for which it serves very well
• Very soft and pliable parts
• Six pack rings
• Juice and milk cartons is made of liquid packaging board, a laminate of paperboard and LDPE (as the water-proof inner and outer layer), and often with of a layer of aluminum foil (thus becoming aseptic packaging).^[4][5]
• Parts of computer hardware, such as hard disk drives, screen cards, and optical disc drives
• Playground slides
• Plastic wraps

See also

• Linear low-density polyethylene (LLDPE)
• High-density polyethylene (HDPE)
• Medium-density polyethylene (MDPE)
• Ultra-high-molecular-weight polyethylene (UHMWPE)
• Stretch wrap

References

1. ^ Dennis Malpass (28 June 2010). Introduction to Industrial Polyethylene: Properties, Catalysts, and Processes. John Wiley and Sons. pp. 1–. ISBN 978-0-470-62598-9. http://books.google.com/books?id=-7cWD7MrtfEC&pg=PA1. Retrieved 21 October 2011. 
2. ^ "Market Study: Polyethylene LDPE". Ceresana Research. http://www.ceresana.com/en/market-studies/plastics/polyethylene-ldpe/. 
3. ^ "Plastic Properties of Low Density Polyethylene (LDPE)". Dynalab Corp. http://www.dynalabcorp.com/technical_info_ld_polyethylene.asp. 
4. ^ LDPE products and applications. Exxon Mobil Corporation
5. ^ DOW LDPE 5004I. IDES – The Plastics Web