Polypropylene is a thermoplastic polymer, used in a wide variety of applications, including Australian banknotes. Polypropylene is unusually resistant to many chemical solvents, bases and acids.

Polypropylene can be manufactured to a high degree of purity, making it useful for the semiconductor industry. It is also resistant to bacterial growth, making it suitable for disposable syringes and other medical equipment. It can be injection molded or fabricated (machined and welded). Other applications are piping, filter material and plastic products that require a higher quality than polyethylene. Polymer banknotes are made from the polymer biaxially-oriented polypropylene (BOPP) which greatly enhances durability of the banknotes

Polypropylene was discovered in the early 1950s by Giulio Natta. In modern science, inventions often occur in different places at about the same time. Polypropylene was an extreme case of this phenomenon, being separately invented about nine times. It was a patent attorney's dream scenario, and litigation wasn't resolved until 1989.

Polypropylene managed to survive the legal process, and two American chemists working for Phillips Petroleum, J. Paul Hogan and Robert Banks, are now generally credited as the "official" inventors of the material. Polypropylene is similar to its ancestor, polyethylene, and shares polyethylene's low cost, but is much more robust. It is used in everything from plastic bottles to carpets to plastic furniture, and is very heavily used in automobiles.

   CH3        H           CH3   H   CH3   H
     \      /              |    |    |    |
      C == C       ->   -- C -- C -- C -- C --
     /      \              |    |    |    | 
    H        H             H    H    H    H

  propylene monomer      polypropylene polymer

Resin identification code

The symbol for polypropylene developed by the Society of the Plastics Industry so that items can be labelled for easy recycling is:

and indicated in Unicode by ♷.

External links

• Society of the Plastics Industry site
• IDES Inc.
• http://www.psrc.usm.edu/macrog/pp.htm
• biography of Giulio Natta at Nobel Prize website