Low density polyethylene

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LDPE has SPI

resin ID code 4

Low-density polyethylene (LDPE) is a thermoplastic made from oil. It was the first grade of polyethylene, produced in 1933 by Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerisation [1]. Its manufacture employs the same method today.

Properties

LDPE is defined by a density range of Q to 3 It is unreactive 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 to the degree of being almost unbreakable.

It 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.

Physical qualities

  • Maximum Temperature: 176 °F (80 °C)
  • Minimum Temperature: −58 °F (−50 °C)
  • Autoclavable: No
  • Melting Point: 248 °F (120 °C)
  • Tensile Strength: 1700 psi (11.7 MPa)
  • Hardness: SD55
  • UV Resistance: Poor
  • Translucent
  • Excellent flexibility
  • Density: 0.92 g/cm³

Chemical resistance

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 & general purpose containers
  • Food storage and laboratory 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 soda can rings
  • Extrusion coating on paperboard and aluminum laminated for beverage cartons.
  • Computer components, such as hard drives, screen cards and disk-drives.

See also


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