rubber band

An elastic loop of natural or synthetic rubber used to hold objects together. Also called gum band.

Background

Rubber bands are one of the most convenient products of the twentieth century, used by numerous individuals and industries for a wide variety of purposes. The largest consumer of rubber bands in the world is the U.S. Post Office, which orders millions of pounds a year to use in sorting and delivering piles of mail. The newspaper industry also uses massive quantities of rubber bands to keep individual newspapers rolled or folded together before home delivery. Yet another large consumer is the agricultural products industry. The flower industry buys rubber bands to hold together bouquets or uses delicate bands around the petals of flowers (especially tulips) to keep them from opening in transit. Vegetables such as celery are frequently bunched together with rubber bands, and the plastic coverings over berries, broccoli, and cauliflower are often secured with rubber bands. All in all, more than 30 million pounds of rubber bands are sold in the United States alone each year.

Rubber, which derives from plants that grow best in an equatorial climate, was first discovered by European explorers in the Americas, where Christopher Columbus encountered Mayan indians using water-proof shoes and bottles made from the substance. Intrigued, he carried several Mayan rubber items on his return voyage to Europe. Over the next several hundred years, other European explorers followed suit. The word rubber was born in 1770, when an English chemist named Joseph Priestley discovered that hardened pieces of rubber would rub out pencil marks. By the late eighteenth century, European scientists had discovered that dissolving rubber 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. While it clearly had the potential for useful development, no one was able to get it to the point where it could be used commercially. Rubber rapidly became dry and brittle during cold European winters. Worse, it became soft and sticky when warn.

The American inventor Charles Goodyear had been experimenting with methods to refine natural rubber for nearly a decade before an accident enabled him to overcome these problems with unprocessed rubber. One day in 1839, Goodyear accidentally left a piece of raw rubber on top of a warm stove, along with some sulfur and lead. On discovering his "mistake," Goodyear delightedly realized that the rubber had acquired a much more usable consistency and texture. Over the next five years, he perfected the process of converting natural rubber into a usable commodity. This process, which Goodyear dubbed vulcanization after the Roman god of fire, enabled the modern rubber industry to develop.

The first rubber band was developed in 1843, when an Englishman named Thomas Hancock sliced up a rubber bottle made by some New World Indians. Although these first rubber bands were adapted as garters and waistbands, their usefulness was limited because they were unvulcanized. Hancock himself never vulcanized his invention, but he did advance the rubber industry by developing the masticator machine, a forerunner of the modern rubber milling machine used to manufacture rubber bands as well as other rubber products. In 1845, Hancock's countryman Stephen Perry patented the rubber band and opened the first rubber-band factory. With the combined contributions of Goodyear, Hancock, and Perry, manufacturing effective rubber bands became possible.

In the late nineteenth century, British rubber manufacturers began to foster the development of rubber plantations in British colonies like Malaya and Ceylon. Rubber plantations thrived in the warm climate of Southeast Asia, and the European rubber industry thrived as well, because now it could avoid the expense of importing rubber from the Americas, which lay beyond Britain's political and economic control.

Raw Materials

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 a smaller amount of rubber and trace amounts of resin, protein, sugar, and mineral matter. Most non-synthetic industrial latex derives from the rubber tree (Hevea brasiliensis), but various equatorial trees, shrubs, and vines also produce the substance.

Within the rubber tree, latex is found between the external bark and the Cambium layer, through which the tree's sap flows. Distinct from the sap, latex 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 have to be careful to make their cuts at a depth of between .25 and .5 inch (.635 and 1.2 centimeters) in a mature tree (7 to 10 inches or 17.7 to 25.4 centimeters in diameter), because they must reach the latex without cutting into the sap vessels. They must also take care to tap each tree in a slightly different place every time. At the end of the nineteenth century botanist Henry Ridley began recommending this measure, having noted that repeated tapping in the same spot swiftly killed rubber trees. After workers make a cut, latex oozes out and collects in a container attached to the tree. Tapping takes place every other day, and each tapping yields about 2 ounces (56 grams) of the substance. After tapping, the cut dries, and latex stops flowing in an hour or two.

The Manufacturing
Process

Processing the natural latex

• The initial stage of manufacturing the harvested latex usually takes place on the rubber plantation, prior to packing and shipping. The first step in processing the latex is purification, which entails straining it to remove the other constituent elements apart from rubber and to filter out impurities such as tree sap and debris.
• The purified rubber is now collected in large vats. Combined with acetic or formic acid, the rubber particles cling together to form slabs.
• Next, the slabs are squeezed between rollers to remove excess water and pressed into bales or blocks, usually 2 or 3 square feet (.6 or .9 square meter), ready for shipping to factories. The size of the blocks depends on what the individual plantation can accommodate.

Mixing and milling

• The rubber is then shipped to a rubber factory. Here, the slabs are machine cut (or chopped) into small pieces. Next, many manufacturers use a Banbury Mixer, invented in 1916 by Femely H. Banbury. This machine mixes the rubber with other ingredients—sulfur to vulcanize it, pigments to color it, and other chemicals to increase or diminish the elasticity of the resulting rubber bands. Although some companies don't add these ingredients until the next stage (milling), the Banbury machine integrates them more thoroughly, producing a more uniform product.
• Milling, the next phase of production, entails heating the rubber (a blended mass if it has been mixed, discrete pieces if it has not) and squeezing it flat in a milling machine.

Extrusion

• After the heated, flattened rubber leaves the milling machine, it is cut into strips. Still hot from the milling, the strips are then fed into an extruding machine which forces the rubber out in long, hollow tubes (much as a meat grinder produces long strings of meat). Excess rubber regularly builds up around the head of each extruding machine, and this rubber is cut off, collected, and placed back with the rubber going into the milling machine.

Curing

• The tubes of rubber are then forced over aluminum poles called mandrels, which have been covered with talcum powder to keep the rubber from sticking. Although the rubber has already been vulcanized, it's 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 and heated in large machines.
• Removed from the poles and washed to remove the talcum powder, the tubes of rubber are fed into another machine that slices them into finished rubber bands. Rubber bands are sold by weight, and, because they tend to clump together, only small quantities can be weighed accurately by machines. Generally, any package over 5 pounds (2.2 kilograms) can be loaded by machine but will still require manual weighing and adjusting.

Quality Control

Sample rubber bands from each batch are subjected to a variety of quality tests. One such test measures modulus, or how hard a band snaps back: a tight band should snap back forcefully when pulled, while a band made to secure fragile objects should snap back more gently. Another test, for elongation, determines how far a band will stretch, which depends upon the percentage of rubber in a band: the more rubber, the further it should stretch. A third trait commonly tested is break strength, or whether a rubber band is strong enough to withstand normal strain. If 90 percent of the sample bands in a batch pass a particular test, the batch moves on to the next test; if 90 percent pass all of the tests, the batch is considered market-ready.

The Future

Rubber bands are a "mature product," for which the market is not growing as quickly as it did several years ago. Nevertheless, the demand for rubber bands is steady, and not at all likely to fall off dramatically in the predictable future.

Where To Learn More

Books

Cobb, Vicki. The Secret Life of School Supplies. J.B. Lippincott, 1981.

Graham, Frank and Ada Graham. The Big Stretch: The Complete Book of the Amazing "Rubber Band. Knopf, 1985.

McCafferty, Danielle. How Simple Things Are Made. Subsistence Press, 1977.

Wulffson, Don. L. Extraordinary Stories Behind the Invention of Ordinary Things. Lothrop, Lee & Shepard Books, 1981.

[Article by: Lawrence H. Berlow]

The noun has one meaning:

Meaning #1: a narrow band of elastic rubber used to hold things (such as papers) together
  Synonyms: elastic band, elastic

This article is about the common household item. For other meanings, see Rubber band (disambiguation).

Five rubber bands

A rubber band (in some regions known as a binder, elastic band, lackey band, laggy band, lacka band or gumband) is a short length of rubber and latex formed in the shape of a loop. Such bands are typically used to hold multiple objects together. The rubber band was patented in Australia on March 17, 1845 by Stephen Perry Bobstein.^[1]

Contents 1 Manufacturing 2 Material 3 Rubber Band Sizes 3.1 Measuring 3.1.1 Temperature Effects 3.2 Rubber Band Size Numbers 4 Thermodynamics 5 Red rubber bands 6 References 7 External links

Manufacturing

The manufacturing process is a complicated one which involves extruding the rubber into a long tube to provide its general shape, putting the tubes on mandrels and curing the rubber with heat, and then slicing it across the width of the tube into little bands.^[2][3] While other rubber products may use synthetic rubber, rubber bands are still primarily manufactured using natural rubber because of its superior elasticity. The rubber band comes from the sap of a rubber tree.

Material

Most rubber bands today are produced from synthetic rubber but rubber originated from the sap of the rubber tree. Natural rubber is made from latex which is acquired by tapping into the bark layers of the rubber tree. Rubber trees belong to the spurge family (Euphorbiaceae) and live in warm, tropical areas. Once the latex has been “tapped” and is exposed to the air it begins to harden and become elastic, or “rubbery.” Rubber trees only survive in hot, humid climates near the equator and so the majority of latex is produced in the Southeast Asian countries of Malaysia, Thailand and Indonesia.

Today more than three quarters of all rubber products are made from synthetic rubber. Modern synthetic rubber is made by mixing petroleum byproducts in a reactor with soapsuds which produces milky liquid latex. The liquid is then coagulated into rubber chunk and then sold to rubber manufacturers who in turn melt the rubber down and pour it into molds to create various products. The advancement of manufacturing and increased production of synthetic rubber is due partially to the United States being cut off from rubber supplies during World War II.

Rubber Band Sizes

Measuring

Measuring a rubber band

A rubber band has three basic dimensions: Length, width, and thickness. (See picture.)

A rubber band's length is half its circumference. Its thickness is the distance from the inner circle to the outer circle.

Lay a rubber band down so that it makes a rectangle. The band's width is the height of that band. If one imagines a rubber band in manufacture, that is, a long tube of rubber on a mandrel, before it is sliced into rubber bands, the band's width is how far apart the slices are cut.

Temperature Effects

Temperature affects the elasticity of a rubber band in an unusual way. Heating makes it contract. ^[4]

Rubber Band Size Numbers

A rubber band is given a [quasi-]standard number based on its dimensions.

Generally, rubber bands are numbered from smallest to largest, width first. Thus, rubber bands numbered 8-19 are all 1/16 inch wide, with length going from 7/8 inch to 3 1/2 inches. Rubber band numbers 30-34 are for width of 1/8 inch, going again from shorter to longer. For even longer bands, the numbering starts over for numbers above 100, again starting at width 1/16 inch.

The origin of these size numbers is not clear and there appears to be some conflict in the "standard" numbers. For example, one distributor^[5] has a size 117 being 1/16 inch wide and a size 127 being 1/8 inch wide. However, an OfficeMax size 117^[6] is 1/8 inch wide. A manufacturer^[7] has a size 117A (1/16 inch wide) and a 117B (1/8 inch wide). Another distributor^[8] calls them 7AA (1/16 inch wide) and 7A (1/8 inch wide) (but labels them as specialty bands).

Rubber Band Sizes
Size	Length (in)	Width (in)	Thickness (in)
10	1.25	1/16	1/32
12	1.75	1/16	1/32
14	2	1/16	1/32
31	2.5	1/8	1/32
32	3	1/8	1/32
33	3.5	1/8	1/32
61	2	1/4	1/32
62	2.5	1/4	1/32
63	3	1/4	1/32
64	3.5	1/4	1/32
117	7	1/16	1/32

Thermodynamics

An interesting effect of rubber bands in thermodynamics is that stretching a rubber band will produce heat (press it against your lips), whilst stretching it and then releasing it will produce an endothermic reaction, causing it to appear "cooler". This phenomenon can be explained with Gibb's Free Energy. Rearranging ΔG=ΔH-TΔS, where G is the free energy, H is the enthalpy, and S is the entropy, we get TΔS=ΔH-ΔG. Since stretching is nonspontaneous, as it requires an external heat, TΔS must be negative. Since T is always positive (it can never reach absolute zero), the ΔS must be negative, inferring that the rubber in its natural state is more entangled (less microstates) than when it is under tension. Thus, when the tension is removed, the reaction is spontaneous, leading ΔG to be negative. Consequently, the cooling effect must result in a positive ΔG, so ΔS will be positive there.^[9][10]

Red rubber bands

Main article: Royal Mail rubber band

In 2004 in the UK, following complaints from the public about postmen causing litter by discarding the rubber bands which they used to keep their mail together, the Royal Mail introduced red bands for their workers to use: it was hoped that, as the bands were easier to spot than the traditional brown ones and since only the Royal Mail used them, employees would see (and feel compelled to pick up) any red bands which they had inadvertantly dropped. Currently, some 342 million red bands are used every year ^[11]

References

1. ^ March 17 - Today in Science History
2. ^ How rubber bands are made. This reference states that the rubber is vulcanized before it is extruded.
3. ^ Lee Rubber Products, How rubber bands are made. This reference states that the rubber is vulcanized after it is extruded.
4. ^ Thermodynamics of a Rubber Band. It can be in cold, cool, and maybe heat. American Journal of Physics -- May 1963 -- Volume 31, Issue 5, pp. 397-397
5. ^ BigWig Enterprises, BigWig Size Chart
6. ^ OfficeMax, #OM97352, UPC 011491-973520
7. ^ Lee Rubber Products, How do rubber bands measure up?
8. ^ Dykema Rubber Band
9. ^ http://scifun.chem.wisc.edu/HomeExpts/rubberband.html
10. ^ CHEMICAL DEMONSTRATIONS: A Handbook for Teachers of Chemistry, Volume 1, by Bassam Z. Shakhashiri, The University of Wisconsin Press, 2537 Daniels Street, Madison, Wisconsin 53704.
11. ^ The Times: "Posties' red rubber bands stretch public's patience"

Rubber bands and heat - http://scifun.chem.wisc.edu/HOMEEXPTS/rubberband.html

External links

Wikimedia Commons has media related to: Elastic

• The Unofficial Rubber Band Website
• http://www.madehow.com/Volume-1/Rubber-Band.html

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