A rubber band (in some regions known as a binder, an elastic or elastic band, a lackey band, laggy band, lacka band or gumband) is a short length of rubber and latex formed in the shape of a loop and is commonly used to hold multiple objects together. The rubber band was patented in England on March 17, 1845 by Stephen Perry.[1][2][3]
Contents |
Rubber bands are made by 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.[3][4]
While other rubber products may use synthetic rubber, rubber bands are primarily manufactured using natural rubber because of its superior elasticity.[3]
Natural rubber originates 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.
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.
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.
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 31⁄2 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 in its 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 |
Temperature affects the elasticity of a rubber band in an unusual way. Heating causes the rubber band to contract, and cooling causes expansion.[9]
An interesting effect of rubber bands in thermodynamics is that stretching a rubber band will cause it to release heat (press it against your lips), while releasing it after it has been stretched will lead it to absorb heat, causing its surroundings to become 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 external work, TΔS must be negative. Since T is always positive (it can never reach absolute zero), the ΔS must be negative, implying that the rubber in its natural state is more entangled (fewer 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.[10][11]
The result is that a rubber band behaves somewhat like an ideal monatomic gas, inasmuch as (to good approximation) elastic polymers do not store any potential energy in stretched chemical bonds or elastic work done in stretching molecules, when work is done upon them. Instead, all work done on the rubber is "released" (not stored) and appears immediately in the polymer as thermal energy. In the same way, all work that the elastic does on the surroundings, results in the disappearance of thermal energy in order to do the work (the elastic band grows cooler, like an expanding gas). This last phenomenon is the critical clue that the ability of a elastomer to do work depends (as with an ideal gas) only on entropy-change considerations, and not on any stored (i.e., potential) energy within the polymer bonds. Instead, the energy to do work comes entirely from thermal energy, and (as in the case of an expanding ideal gas) only the positive entropy change of the polymer allows its internal thermal energy to be converted efficiently (100% in theory) into work.
In 2004 in the UK, following complaints from the public about postal carriers 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 inadvertently dropped. Currently, some 342 million red bands are used every year.[12]
This type of rubber band was popularized by use in the military. They are typically hand cut into various sizes from inner tubes, and are thus black in colour. They have the advantage of being versatile, strong and resistant to weather and abbrasion. They are commonly used for lashings, and can also be used for makeshift handle grips, providing a strong high-friction surface with excellent shock absorption.[13]
In animal husbandry, rubber bands are used for docking and the male castration of livestock. The procedure involves banding the body part with a tight latex (rubber) band to restrict blood flow. The part eventually drops off.
Rubber bands have long been one of the methods of powering small free-flight model aeroplanes, the rubber band being anchored at the rear of the fuselage and connected to the propeller at the front. To 'wind up' the 'engine' the propeller is repeatedly turned, twisting the rubber band. When the propeller has had enough turns, the propeller is released and the model launched, the rubber band then turning the propeller rapidly until it has unwound.
One of the earliest to use this method was pioneer aerodynamicist George Cayley, who used them for powering his small experimental models. These 'rubber motors' have also been used for powering small model boats.