Resin identification 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 polymerisation. Its manufacture employs the same method today. LDPE is commonly recycled[citation needed], and has the number "4" as its recycling symbol.

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 but breakable.
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.

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.
* Playground Slides
* Plastic Bags
* Plastic Wraps

Source : http://en.wikipedia.org/wiki/Low_density_polyethylene