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A popular overview about Polyethylene.
The hardest and least flexible among different types of polyethylene. It has better tensile strength than other forms of polyethylene. Its density is 0.941-0.965 g/cm3.
At room temperature above 90% is crystalline and the rest is amorphous (solid without regular crystalline structure). PE melts between 125° - 135°C, its viscosity is given by molecular weight. The density at the melting point drops to 0.80g/cm³.
Has a density of 0.910-0.925 g/cm3.
The most important physical properties are resistance against bending and impact. Excellently insulates el. current.
At room temperature 50-60% is crystalline and the residue is amorphous (solid without regular crystalline structure). It has long and short side chains.
Has density of 0.91-0.94 g/cm3. Strongest against point puncture.
At room temperature 35-60% is semicrystalline and the residue is amorphous (solid without regular crystalline structure). LLDPE is resistant to oxidation and UV radiation. It has many short side chains. (Compared to LDPE, there are more of them, but they are shorter.). The individual short branches can move relative to each other without tangling.
It is a thermoplastic, so it can be formed when heated. Polyethylene is resistant to most chemicals and solvents. Only some compounds such as decahydronaphthalene or some aromatic or halogenated hydrocarbons are able to dissolve polyethylene. Chemical decomposition of the polymer structure of polyethylene can only occur using a strong oxidizing agent such as oleum or red fuming nitric acid. PE excels in low water absorption.
Polyethylene can be melted and welded. There are two basic processing methods. Both at high temperatures. Extrusion and injection. In the first case, we extrude the plastic under high pressure to create a continuous profile such as pipes or plates. The injection then uses molds. (Similar processes are used in the metalworking industry.)
It is produced at low temperatures and low pressure from natural gas using a Ziegler-Nattan catalyst by one or more stage polymerizations. It is not the only method, an older Phillips catalyst or a chromium-based catalyst can also be used.
It is produced by radical polymerization using the tubular method or using an autoclave at high pressure.
Polyethylene is produced by the addition or radical polymerization (types of polymerization) of ethylene (olefin - general formula C2H4). A Ziegler-Natt or metallocene catalyst is used in the polymerization.
It is prepared by polymerizing a mixture of ethylene (ethene) with 1-butene and a small amount of 1-hexene and 1-octene, using a Ziegler-Natt or a metallocene catalyst.
Polyethylene can be produced in the form of soft and flexible as well as solid, hard and durable products. Among other things, it can also be part of everyday objects, packaging, piping and toys. Polyethylene products are still replacing traditional materials such as paper or metals.
Polyethylene is the world's most widely used polymer.
The figure shows the ethene polymerization process.
They have virtually no chemical impact on the environment. However, they are very stable and therefore do not disintegrate in nature other than by mechanical wear. (Or long-term exposure to UV radiation over many years.)
Polyethylene was first discovered in 1898 by the German chemist Hans von Pechmann by accident during the study of diazomethane. However, this method has no practical use because diazomethane is notoriously unstable and toxic.
The first industrial synthesis was discovered again by accident in 1933 by Erik Fawcett and Reginald Gibson in England. At extreme pressure (approx. 1400 bar) they were able to produce polyethylene from a mixture of ethylene and benzaldehyde. The reaction was started with traces of oxygen, so it was poorly reproducible, and it was not until 1939 that chemist Michael Willcox Perrin made it a reproducible high-pressure synthesis that was and still is a valid basis for LDPE production.
It is a compound composed of macromolecules. Macromolecules are attracted by Van der Waals forces and, in addition, are physically wound like fibers in threads. They may be also bounded with each other by regular bonds to form a network like structure.
It is a molecule typically composed of thousands or more atoms. Macromolecules are formed by a polymerization process, which is a chemical reaction where the macromolecule is formed from smaller molecules (monomers) by a repetitive process.
