Rubber bands rely on the property of elasticity to function. Over time, frequent stretching and environmental exposure can cause these bands to lose their ability to snap back, leaving them slack and less effective. Fortunately, the unique material structure allows for a simple method to restore some of its lost tension and return it closer to its original, tighter size using heat.
The Underlying Science of Shrinkage
The material that gives a rubber band its flexibility is an elastomer, a substance composed of long, tangled polymer chains. In their natural state, these chains are highly disordered. When a rubber band is stretched, these long molecules are forced to straighten out and become more aligned in the direction of the pull. If the band is stretched repeatedly, the polymer chains may not fully recoil, resulting in a permanent deformation and loss of elasticity.
Applying heat provides the energy necessary for these straightened chains to become highly mobile and return to their preferred, more compact, and disordered state. This phenomenon, where a material contracts instead of expands when heated, is due to an increase in molecular disorder, or entropy. The thermal energy causes the ends of the chain to pull closer together, which is the physical manifestation of the rubber band shrinking.
Step-by-Step Guide to Heat Shrinking
The most effective way to apply the necessary thermal energy is by using boiling water. Begin by collecting the supplies: a small saucepan, water, a pair of kitchen tongs, and a bowl of cold water. Safety is important, so handle the hot water and rubber band with care to prevent burns.
First, bring water to a boil on the stovetop. Carefully drop the slack rubber band into the water using the tongs. The high temperature rapidly transfers energy to the polymer chains, allowing them to contract.
Allow the rubber band to remain submerged for 30 seconds to one minute, depending on the band’s thickness. Exceeding this time risks damaging the material, while too little time will not provide enough energy for sufficient shrinkage. Immediately use the tongs to quickly transfer the band from the boiling water directly into the bowl of cold water.
This rapid cooling step is important to quickly “lock in” the new, smaller size by reducing the molecular motion. The combination of thermal energy followed by rapid cooling helps the polymer chains retain their more coiled structure. Once cooled, the rubber band can be removed and tested for its restored tension.
Recognizing When a Rubber Band Cannot Be Saved
While heat can restore elasticity lost due to stretching, it cannot repair physical or chemical damage. The most common forms of irreversible damage are brittleness, cracking, and a sticky or gummy texture.
Exposure to ultraviolet (UV) light, like from the sun, breaks the chemical bonds in the polymer chains, leading to a hard, brittle material. Chemical degradation from oxygen and ozone also causes the polymer network to break down, which heat cannot reverse. If a band snaps easily or has visible cracks, the internal molecular structure is too compromised for heat treatment to be effective.