High Density Polyethylene
High density polyethylene (HDPE) or polyethylene high-density (HDPE) is a polyethylene thermoplastic made from petroleum. Known for its large strength to density ratio, HDPE is commonly used in the production of plastic bottles, corrosion-resistant piping, geomembranes, and plastic lumber.
What is HDPE ?
HDPE is extracted from oil. Almost every 1.75 kg of crude oil produces one kilogram of high density HDPE, which is a capable of recycling.
And it should be said that the most common and mostly used and perhaps the first kind of plastic that was produced was high density PE (HDPE). The molecular chain in this type of polymer is compressed, which causes it to increase its density. Therefore, flexibility decreases sharply. Although this type of polymer has a lower impact resistance than low density PE, its resistance to chemicals, such as its resistance to fragile environmental stresses, is good. Therefore, this kind of polymer is used in a variety of commercial products such as fuel storage containers, open air chairs, toys, bags, high pressure water pipes, sewer pipes and ducts. There is another type of HDPE with high density called UHMWPE, which is common in less volume. This type of polymer is stiffer than other types of HDPE.
HDPE was first accidentally released by German chemist, "Hans Von Pechmanv". It was synthesized in 1898 when he heated Di-Azomethane, a waxy white compound, later called HDPE.
HDPE was first discovered accidentally through industrial synthesis, by Reginald Gibson and Eric Fawcett (ICI chemists) in 1933. The two scientists obtained a waxy substance by heating a mixture of ethylene and benzaldehyde at high pressure.
Various types of materials produced by these products include water pipes, sewer and industrial pipes, toy making, sports equipment, HDPE films, mineral water and family drinks bottles.
This Polyethylene has a non-branched polymeric chain. Therefore, the molecular strength of the high chain and its tensile strength is higher than other HDPE’s. Reaction conditions and type of catalyst used are effective in the production of the PE in HDPE. For the production of non-branched HDPE, the polymerization method with Ziegler–Natta catalyst is usually used.
When there is no branch in the molecule, it is called linear HDPE. Linear HDPE is harder than HDPE, but branched HDPE is made easier and cheaper. The morphology of this polymer is very crystalline. Linear HDPE is a normal product with a molecular weight of 200,000-500,000, which polymerizes under low pressure and temperatures. There is another HDPE, the density of which is between these two polymers, ranging from 0.926 to 0.940, which is called semi-high density or average HDPE.
To produce PE pipes for pressurized applications HDPE is used.
HDPE is initially homogeneous, pure but non-transparent, non-colored and, if necessary, having pigments. These materials are used in white, red, blue, yellow, green, black and sometimes even in the color of their raw materials. They are electrically insulated and will be destroyed against direct heat.
Benefits and Applications of HDPE
HDPE is used in numerous customer applications:
♦ Grocery merchandise and trash bags
♦ Containers for frozen food and dairy products
♦ Caps and closures
♦ Liners for cereal, crackers and other food packaging
♦ Plastic fuel tanks
♦ Drink cups, dairy crates and bread trays
♦ Toys and pails for items from paint to fresh produce
HDPE ( high density polyethylene ) is also used to produce safety equipment, including hard hats; home insulation; bottles for milk, juice, household/industrial chemicals and motor oil; large (rotomolded) tanks for storage of agricultural and lawn care chemicals; and pressure pipe and sheet applications.
♦ Density > 0.940 g/cm³
♦ High stiffness
♦ High crystallinity
♦ High impact strength even at low temperatures
♦ Good tensile strength
♦ Lowest permeability of all polyethylene
♦ Chemical and grease resistance
♦ Corrosion resistance
♦ Abrasion resistance
♦ Lightweight and shatter-resistant
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