A pal of mine, the daughter of a rancher, recently disclosed that she seldom wore skirts in high school because she feared that during her daily drive to school a mouse would run up her leg. At the ranch, she parked next to a granary. Her solution to a mouse attack was to wear pants, to fasten bicycle clips or rubber bands around her lower pant legs while she drove, then try to remember to remove them before her first class.
This led to a discussion of mice, favorite teachers, rubber bands, their many properties and uses, and inevitably to the central question of this week’s inquiry — how in the heck do they make rubber bands?
First a bit of history. Rubber (latex) comes from plants (Hevea brasiliensis) that grow in an equatorial climate. Europeans first came into contact with latex when imperialist nations laid claim to the soil of the New World and found that indigenous folks were building waterproof shoes and bottles made from juices of a plant. Along with gold, tobacco, turkeys, popcorn and pumpkins, the explorer/raiders returned to their royal patrons with artifacts made of this strange new stuff.
For the next couple hundred years the shoes and flasks were scattered around various European museums and labs. The word “rubber” was coined in 1770, when an English chemist, Joseph Priestley, discovered that hardened pieces of the stuff would erase pencil marks. By the late 18th century, European scientists had discovered that dissolving latex in turpentine produced a liquid that could be used to waterproof cloth.
However, until the beginning of the 19th century, natural rubber presented several technical challenges because no one was able to get it to the point where it could be stored. Rubber rapidly became dry and brittle during cold European winters and soft and sticky in the summer.
The American inventor Charles (the Blimp) Goodyear had experimented with methods to refine natural rubber for nearly a decade before a lab accident made him rich. One day in 1839, he spaced out and left a piece of raw rubber on top of a wood stove along with some sulfur and lead. (Don’t try this at home.) While cleaning up the mess, Goodyear realized that the rubber had acquired a much more usable consistency and texture. Over the next 5 years, he perfected the process of converting natural rubber into what we have today. Goodyear called this process “vulcanization” after the Roman god of fire.
The first rubber band was developed in 1843 when Thomas Hancock, much like my pal, sliced up one of the Mayan bottles and used the strips as garters. Hancock himself never vulcanized his invention, but he did develop the masticator machine, a forerunner of the modern rubber milling machine. In 1845, Hancock’s associate, Thomas Perry, vulcanized his garters, patented the rubber band and opened the first rubber band factory.
Here is how rubber bands are made: Although 75 percent of today’s rubber products are made from the synthetic rubber perfected during World War II, rubber bands are still made from organic rubber because it offers superior elasticity. Natural rubber comes from latex, a milky fluid composed primarily of water with small amounts of rubber, resin, protein, sugar, and mineral matter.
Latex is found between the external bark and the cambium layer, through which the tree’s sap flows. Latex is not sap. It serves as a protective agent, seeping out of and sealing over wounds in the tree’s bark. To “tap” the substance, rubber harvesters cut a V-shaped wedge in the bark. They must make their cuts at a depth of between a quarter and half inch so as to reach the latex without cutting into the sap vessels. After the bark is cut, latex oozes out and collects in a container attached to the tree. Tapping takes place every other day, and each tapping yields about two ounces of the substance. After tapping, the cut dries, and latex stops flowing in an hour or two.
The latex is strained, put into large vats and combined with acetic or formic acid. This results in a cheese-like conglomeration of particles, called a slab. The slabs are squeezed between rollers to remove excess water and pressed into bales or blocks, usually 2 or 3 cubic feet.
The bales are shipped to a rubber factory, mainly in South Asia, where they are chopped into small pieces and run through a machine that mixes the rubber with sulfur to vulcanize it, pigments to color it, and other chemicals to increase or diminish the elasticity. The rubber is then heated and squeezed flat in a milling machine. Still hot from the milling, the strips are then fed into an extruding machine that forces the rubber out in long, hollow tubes.
The tubes are stretched over aluminum poles of various diameters which have been covered with talcum powder to keep the rubber from sticking. Although the rubber has already been vulcanized, it’s still rather brittle at this point, and needs to be “cured” before it is elastic and usable. To accomplish this, the poles are loaded onto racks that are steamed then fed into another machine that slices them into finished rubber bands of various thicknesses and lengths.
Rubber bands are everywhere. Thirty million pounds of rubber bands are sold in the United States each year. The largest consumer in the world is the U.S. Postal Service. Another large consumer is the agricultural products industry. (The big blue bands around broccoli.) The flower industry uses rubber bands to bind bouquets or to keep individual flowers from opening in transit. Every office either has too many or no rubber bands.
I found no data about the annual tonnage of rubber bands used to prevent mice from running up teenage girls’ legs.