Pitch (resin)

File:University of Queensland Pitch drop experiment-6-2.jpg

Pitch has a viscosity approximately 230 billion times that of water, as demonstrated in this pitch drop experiment.

Pitch is the name for any of a number of viscoelastic, solid polymers. Pitch can be made from petroleum products or plants. Petroleum-derived pitch is also called bitumen. Pitch produced from plants is also known as resin. Products made from plant resin are also known as rosin.

Pitch was traditionally used to help caulk the seams of wooden sailing vessels (see shipbuilding). Pitch was also used to waterproof wooden containers, and is sometimes still used in the making of torches.

Petroleum-derived pitch is black in color, hence the adjectival phrase, "pitch-black".

Viscoelastic properties

Tar pitch is a viscoelastic polymer. This means that even though it seems to be solid at room temperature and can be shattered with a hard impact, it is actually fluid and will flow over time, but extremely slowly. The pitch drop experiment taking place at University of Queensland is a long-term experiment which measures the flow of a piece of pitch over many years. For the experiment, pitch was put in a glass funnel and allowed to slowly drip out. Since the pitch was allowed to start dripping in 1930, only eight drops have fallen. It was calculated in the 1980s that the pitch in the experiment has a viscosity approximately 230 billion (2.3x10¹¹) times that of water.

Production

The heating (dry distilling) of wood causes tar and pitch to drip away from the wood and leave behind charcoal. Birchbark is used to make a particularly fine tar. Tar and pitch are often used interchangeably. However, pitch is considered more solid while tar is more liquid. Traditionally, pitch used for waterproofing buckets, barrels and small boats was drawn from pine. It is used to make Cutler's resin.

External links

• The Pitch Drop Experiment
• Pine Tar Production
• Primitive tar and charcoal production

See also

• Tar

References

an:Pegunta