Low-density polyethylene

It was the first grade of polyethylene, produced in 1933 by John C. Swallow and M.W Perrin who were working for Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerization.

The EPA estimates 5.7% of LDPE (resin identification code 4) is recycled in the United States.

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.

When exposed to consistent sunlight, the plastic produces significant amounts of two greenhouse gases: methane and ethylene.

Because of its lower density (high branching), it breaks down more easily than other plastics; as this happens, the surface area increases.

LDPE has SPI resin ID code 4
Schematic of LDPE branching structure
A GEECO bowl, c.1950, still used in 2014
A piece of packaging foam made from LDPE
A Ziploc bag made from LDPE
Facial wash gel bottle made of LDPE