Rubber Bands

These rubber bands are made from natural rubber. Natural rubber is produced from the milky white or yellow liquid produced by the Pará rubber tree, known as latex, which used to be found only in the Amazon basin and was notoriously difficult to grow anywhere else. To make natural rubber, latex is first tapped from a rubber tree. An acid, such as formic acid, is added to the latex to make it coagulate, and then it is passed through rollers to remove excess water, and the whole thing is dried. This purified natural rubber is polyisoprene, which is both an elastomer and a thermoplastic. To make the rubber bands, this purified rubber is drawn out into a long tube, which is then cut into slices. Over time, rubber loses its ability to stretch, becoming hard and brittle. This process of perishing occurs because exposure of the rubber to light and air induces chemical changes in the polyisoprene over time. The inevitable deterioration of natural rubber can be halted by a process called vulcanisation (see Vulcanised Rubber Cube).

Rubber as a material, and rubber bands in particular, are often used to explain entropy (a measure of disorder used in physics) and the second law of thermodynamics, which states that entropy in the universe will either stay constant or increase. When it is tapped from the tree as a liquid, the major constituent of liquid rubber is a small carbon-based molecule called isoprene. As the liquid latex dries, the isoprene molecules begin to bind to one another and form long chains called polyisoprene. When a rubber band is relaxed (i.e. not stretched), these long chains are intertwined and entangled like a plate of cooked spaghetti. They are quite happy to sit tangled up together inside the rubber band. When the rubber band is stretched, the individual polymer chains are straightened up. The molecules making up the rubber therefore become much more ordered, and the entropy of the system is decreased. Because entropy always tends to increase, as soon as you release the rubber band, all the polyisoprene chains pull themselves back into their more disordered, tangled, plate-of-spaghetti formation, and the rubber band pings back to its original shape.

Although rubber didn’t appear in the West until the 19^th Century, evidence for the use of natural rubber in the service of man dates back to around 1600 BC, when the Olmecs, an ancient civilization of Mexico, used this material for everything from decorative arts to sandals. The region’s most famous artifacts are the large rubber balls that archaeologists believe may have been used in games of ritualistic and religious significance. It is thought that the Olmecs played a game similar to netless volleyball with these rubber balls. However the price of failure of these games is thought to have been human sacrifice, and the game is thought to have played an important political role in settling border disputes. Some of these have been found preserved in sacrificial pools of water, and they vary in size from a few inches to a foot; the largest were about the size of a watermelon and weighed eight pounds.