Rubber may seem like a fairly mundane substance, but it’s actually quite an interesting material. Natural rubber is an elastomer (or “elastic hydrocarbon polymer”) that comes from latex, a milky substance that is harvested from rubber trees. It goes through several processes in order to turn into the substance that we see in day to day use.
From Tree to Tyre
Rubber is harvested by “tapping” a tree. This involves cutting into the bark so that the latex sap oozes out. This sap is gathered in buckets, and taken for purification. For more than 100 years, the main source of latex was trees that grew in the wild. Eventually, demand for latex exceeded the supply that was practical from wild trees, and latex “farms” were developed, making it much easier to harvest latex in bulk.
Tapping a tree to gather latex involves cutting a spiral pattern into the bark. An experienced tapper can do one tree every 20 seconds, and will cut around 500 trees per day. They will then rest, eat lunch, and go back to the first tree and collect the bowl of latex. Most trees will drip latex for around four hours before the cut “clots”.
The raw latex is purified into a substance called polyisoprene. It is possible to produce polyisoprene synthetically, but most of the polyisoprene produced today is from natural sources. The purified rubber is shipped around the world for use in everything from the textile industry to the tyre industry.
Elasticity and Other Properties
Rubber is a valuable polymer because it has several desirable properties. Rubber is flexible, and has a decent level of tensile strength and elasticity. This means that it can be used in high pressure situations. In some forms, it copes well with water. It is also a good insulator, making it useful for safety gear.
Damage and Decay
Polymer oxidation can be a serious problem. Ozone gas will attack some elastomers, including natural rubber, making it crack and rot. If the rubber is used in a piece of mission critical equipment, then this can have disastrous effects.
One such example is the Challenger Space Shuttle. The shuttle’s multi-stage booster rockets had two rubber o-rings. These rings had a tendency to stiffen and unseal in cold weather, and took a long time to warm up. The Challenger launch took place on a cold day, and the O-Rings were not sufficiently warmed up when the launch took place. This meant that hot gasses leaked back through the seal, damaging the rings even more, contributing to the explosion which eventually took place. After the challenger accident, engineers added a third O-Ring to the booster rockets, adding an extra layer of redundancy.
Rubber is not the only polymer that is susceptible to decay. Most polymers would oxidize under similar circumstances. Synthetic rubber tends to be more durable than natural rubber, however, and is gaining favour in the textile industry because of its superior level of durability and other favourable properties.