Low density polythene (LDPE) is a thermoplastic polymer that has been around since the 1930s. It has hundreds of uses, from six-pack rings to playground slides, although its main use is in blown film. LDPE has several important advantages over other materials which could serve the same function.
LDPE is typically soft and flexible, yet it has good impact resistance, especially at low temperatures. It is readily processed in molten form and its viscosity and flow properties are such that it can easily be blown into thin films. This makes it a good candidate for thin film applications such as plastic shopping bags and cling film. LDPE also has very low conductivity which makes it useful as an electrical insulator.
LDPE is resistant to attack or solvation by a wide variety of common chemicals. It has good or excellent resistance to acids and bases as well as many typical solvent types, including alcohols, aldehydes and esters. It can also withstand basic sterilisation techniques, including gamma radiation, ethylene oxide gas and disinfectants such as benzalkonium chloride and formaldehyde.
Due to its relative ease of manufacture, availability of raw feedstock and the enormous scale on which it is produced, LDPE is a very inexpensive plastic. Per pound, the only other plastics which are in the same range of cost are polypropylene and other forms of polythene such as high density polythene. Other common plastics such as polystyrene, nylon and PET are three to 10 times as expensive.
LDPE belongs to the class of polymers known as olefins. These are plastics made from starting chemicals which contain carbon to carbon double bonds. Such plastics typically have high resistance to moisture penetration and LDPE is no exception. Its moisture resistance is helpful in various applications such as food packaging where water is either meant to be sealed in or kept out. LDPE also can be produced with fairly high clarity, or transparency. This is helpful in applications such as wrapping where it may be beneficial to see the product under wrap.
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