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.

1 Properties
- 1.1 Physical qualities
- 1.2 Chemical resistance
2 Applications
3 See also

[edit] Properties

LDPE is defined by a density range of 0.910 - 0.940 g/cm³. 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.

[edit] Physical qualities

Maximum Temperature: 80 °C (176 °F)
Minimum Temperature: −50 °C (−58 °F)
Autoclavable: No
Melting Point: 120 °C (248 °F)
Tensile Strength: 11.7 MPa (1700 psi) Watts brand LDPE tubing lists the tensile strength at 2550 psi which is about 17.6 MPa
Hardness: SD55
UV Resistance: Poor
Translucent
Excellent flexibility
Density: 0.92 g/cm³

[edit] 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.[2]

[edit] 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: