LDPE stands for Low Density Polyethylene, also called Low-Density Polyethylene in English. Many users and producers still refer to ethylene instead of ethylene.
Polythene is formed by polymerisation of ethylene (poly means "many"; literally, therefore, many-ethene). Ethylene is obtained by cracking a light derivative of petroleum, such as naphtha.
The low density of LDPE results from carrying out the polymerisation process under high pressure, creating molecules with many side branches. These side branches lower the degree of crystallisation, meaning that the molecules do not lie tightly together due to their irregular shape. This causes fewer molecules to fit in the same space, resulting in a lower density of the material.
We see a good example of this effect with water and ice. Ice, being in a more crystallised state, is lighter than water.
LDPE is a thermoplastic, a type of plastic that softens when heated, unlike rubber, for example. This allows LDPE to be easily reused and moulded into other shapes after heating.
Advantages of LDPE (film)
LDPE is a tough plastic with many side branches in its molecular structure. This makes the material soft to the touch but strong at the same time. It is also water-repellent, well-insulating and resistant to acids, making LDPE film ideal for packaging material. It is also allowed to come into contact with foodstuffs, making it suitable for use in the food industry.
Thanks to its specific molecular structure, LDPE is suitable for shrink wrap. All types of PE shrink lengthwise when heated, but the side branches in LDPE allow the film to shrink widthwise as well.
A major advantage of LDPE film is that little material is needed to make packaging. This means that less energy is consumed during production and CO2 emissions are lower than with other packaging materials because the material is so light and compact.
Another important advantage is that LDPE is highly recyclable.
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