LDPE ( Low density polyethylene )


Low density polyethylene

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.

LDPE is defined by a density range of 0.910 - 0.940 g/cm. It is unreactive at room temperatures, except by strong oxidizing agents, and some solvents cause its 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
Excellent flexibility
Density: 0.92 g/cm

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]

LDPE is widely used for manufacturing various containers, dispensing bottles, wash bottles, tubing, 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