Polyethylene

A soft, tough thermoplastic. It comes in several forms referred to a low density (LDPE), medium density (MDPE), high density (HDPE and so on.

Kayaks are often made of PE. Whitewater kayaks use it to allow them to boof with elan. Sea kayaks made of PE are much less expensive than composite kayaks.

I know that most people reading this page are not that interested in Chemistry but most recreational boats are made from a form of HDPE known as super-linear. All of the poly-ethelene compounds are made of ethelene molecules (ethel is two carbon atoms and ene is a double bound between them - this is also know as a vinyl bond in the chem lab) that are strung together (making them poly or many) by a free radical chain reaction. A free radical is a molecule with only one electron (they are usually paired) on the end and it will bond with almost anything that it comes into contact with. These are used in limited quantities to start the chemical chain reaction and are therefore called initiators. When an initiator (free radical) contacts a molecule of ethelene it bonds to it and takes one of the electrons from the other side of the molecule making that end want to bond with whatever it comes into contact with. This process repeats until either two chains that are forming bond to each other, thus leaving the electrons paired, or until a forming chain contacts another free radical and again terminating the chain reaction. The more initiators that are used the faster the poly ethelene is formed. On the other hand, for super-linear HDPE, an extremely few initiators are used so that fewer, but longer, chains are formed. By limiting the initiators extremely long chains can be formed thus creating a material with a great deal of strength. When you scratch your boat it is very unlikely that a chain is broken but merely that the chains are seperated from each other. If it were possible to make a boat out of a single, very very long, molecule of poly ethelene then it would be almost indestructable. It would also take a very long time to make that chain and be very difficult to work with. Just remember that the fewer/longer the chains of polyethelene the more durable the boat.

         H   H   H       H        H              H      H
         |   |   |       |        |               \   /       Lines represent single bonds
     H-C=C-C=C-C=C-...-C=C-....-C=C-H              C=C
       |   |   |       |        |                 /   \       Equals represents double bonds
       H   H   H       H        H                H     H

             Poly-Ethylene                       Ethelene