Polyethylene

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Polyethylene or polythene is a polymer consisting of long chains of the monomer ethylene (IUPAC name ethene). The recommended scientific name 'polyethene' is systematically derived from the scientific name of the monomer. In certain circumstances it is useful to use a structure–based nomenclature. In such cases IUPAC recommends poly(methylene). The difference is due to the 'opening up' of the monomer's double bond upon polymerisation.

In the polymer industry the name is sometimes shortened to PE, in a manner similar to that by which other polymers like polypropylene and polystyrene are shortened to PP and PS, respectively. In the United Kingdom the polymer is commonly called polythene, although this is not recognised scientifically.

The ethene molecule (known almost universally by its common name ethylene), C2H4 is CH2=CH2, Two CH2 groups connected by a double bond, thus:

polyethylene is created through polymerization of ethene. It can be produced through radical polymerization, anionic addition polymerization, ion coRordination polymerization or cationic addition polymerization. This is because ethene does not have any substituent groups that influence the stability of the propagation head of the polymer. Each of these methods results in a different type of polyethylene.

Classification

Polyethylene is classified into several different categories based mostly on its density and branching. The mechanical properties of PE depend significantly on variables such as the extent and type of branching, the crystal structure, and the molecular weight.

Ultra high molecular weight polyethylene (UHMWPE)

Ultra low molecular weight polyethylene (ULMWPE - PE-WAX)

High molecular weight polyethylene (HMWPE)

High density polyethylene (HDPE)

High density cross-linked polyethylene (HDXLPE)

Cross-linked polyethylene (PEX)

Medium density polyethylene (MDPE)

Low density polyethylene (LDPE)

Linear low density polyethylene (LLDPE)

 Very low density polyethylene (VLDPE)

Out of the above classifications we are using High density polyethylene (HDPE) in our pipe

HDPE:

HDPE is defined by a density of greater or equal to 0.941 g/cm3. HDPE has a low degree of branching and thus stronger intermolecular forces and tensile strength. HDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. The lack of branching is ensured by an appropriate choice of catalyst (e.g. chromium catalysts or Ziegler-Natta catalysts) and reaction conditions. HDPE is used in products and packaging such as milk jugs, detergent bottles, margarine tubs, garbage containers and water pipes
 

High-density polyethylene (HDPE) is a polyethylene thermoplastic made from petroleum. It takes 1.75 kilograms of petroleum (in terms of energy and raw materials) to make one kilogram of HDPE

Properties

Normal density : 945 kg/m^3

Melt flow rate: 0.4 to 0.8 g/10 min

Anti-oxidant : less than or equal to 0.3 percent

HDPE has little branching, giving it stronger intermolecular forces and tensile strength than lower-density polyethylene. It is also harder and more opaque and can withstand somewhat higher temperatures (120 °C for short periods, 110 °C continuously). High-density polyethylene, unlike polypropylene, cannot withstand normally-required autoclaving conditions. The lack of branching is ensured by an appropriate choice of catalyst (e.g., Ziegler-Natta catalysts) and reaction conditions.