Polyethylene Essay

1213 words - 5 pages

PolyethyleneOn March 27th, 1933, two organic chemists named R.O Gibson, and E.W Fawcett were experimenting with various chemicals in an autoclave at Imperial Chemical Industries Research Laboratory. They had become surprised when a white, waxy substance started to leak out of the autoclave (Hinsley 2009). Little did they know that this unique substance would go on to have a wide range of applications in the world from children's toys to bullet-proof vests. This is the product that we call polyethylene (also known as plastic), and as time goes on, more applications are being discovered and changing our world. What makes polyethylene so applicable? It is the ability to be altered in density to stretch or be strong, and not react with other chemical structures that gives polyethylene its ability to change our world today.Polyethylene (C2H4) is used almost everyday in people's lives as something made of plastic. What makes this product so applicable? To start, the process of polyethylene must be taken into account. There are two types of polyethylene that are commonly used today, high-density polyethylene (HDPE) and low-density polyethylene (LDPE). LDPE was the first and only type of polyethylene around for approximately 20 years. Both types of polyethylene are created by taking the monomer, ethane gas (C2H6), and heating it up in a pressurized container ("What is Polyethylene", n.d). Ethane gas has a two carbon atoms in the chain and each of the two carbon atoms share two valence electrons with the other. If two molecules of ethane are brought together, one of the carbon bonds in each molecule can be broken and the two molecules can be joined with a carbon-carbon bond. After the two monomers are joined, there are still two free valence electrons at each end of the chain for joining other monomers or polymer chains. This is process is called polymerization ("Polymer Structure", n.d). Since LDPE is produced at extremely high pressures, this high-pressure polymerization created polyethylene with many branches; the branches are created due to intermolecular and intramolecular chain transfer during polymerization. The mechanism for the polymerization of LDPE is free radical polymerization. The uses of LDPE are limited due to high number of branches. The difference in HDPE and LDPE is the degree of branching (shown in Figure 3 and Figure 4). In general, the degree of branching in polyethylene determines its mechanical properties. The way HDPE is created is a slightly different method than LDPE. A German chemist named Karl Ziegler created polyethylene with the use of a catalyst at atmospheric pressure. The idea of the mechanism involves catalyst formation and chain propagation in which the Chromium d-orbitals interact with the p-electron cloud of ethylene. The mechanism is classified as anionic polymerization. Anionic polymerization means the polymerization continues until the concentration of ethylene runs out. Because of this, the molecular weight of the...

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