Rubber bands are common items whose utility stems from elasticity. They are composed of polymers, which are long chains of repeating molecular units, typically derived from natural latex or synthetic compounds. When stretched, these coiled polymer chains uncoil, storing elastic potential energy. The ability of the material to snap back to its original shape makes the rubber band useful, but this polymer structure is also susceptible to degradation and failure. Breaking is the result of chemical and physical forces breaking down the polymer structure over time and use.
Environmental Accelerants of Material Breakdown
The polymer chains that make up a rubber band are under constant chemical attack from the surrounding environment. Exposure to ultraviolet (UV) light from the sun or artificial sources provides enough energy to directly break the chemical bonds within the rubber’s polymer chains, a process called photodegradation. This bond-breaking generates highly reactive molecules known as free radicals, which accelerate the decay and cause the material to become brittle and discolored.
Oxygen in the air initiates oxidation, a slow chemical reaction that attacks the double bonds in the polymer structure. This reaction forms weak points along the chains, reducing elasticity and causing the material to crack. A particularly aggressive form of oxygen, ozone, is present in trace amounts in the atmosphere, often near electric motors or high-voltage equipment. Ozone causes ozonolysis, which creates deep surface cracks perpendicular to the direction of stress, quickly compromising the band’s structural integrity.
Elevated temperatures significantly increase the rate of all these chemical reactions, accelerating the breakdown of the polymer chains. Storing rubber bands in a hot attic or near a heat source dramatically shortens their lifespan because the heat provides the activation energy needed for oxidation and chain scission to occur faster. Conversely, storing rubber bands in a cool, dark environment can substantially slow these environmental degradation processes, helping them maintain their flexibility for a longer period.
Material Quality and Shelf Life
Composition
The inherent composition of a rubber band determines its baseline resistance to failure. Many bands are made from natural rubber (latex), which offers superior elasticity but is more vulnerable to heat and ozone degradation. Synthetic rubbers, which are petroleum-based, can be formulated with greater resistance to specific environmental threats like heat or oil, often at the expense of maximum stretch.
Vulcanization
Vulcanization stabilizes the rubber by creating chemical cross-links, often using sulfur, between the polymer chains. This process transforms raw, sticky rubber into a strong, durable, and elastic material. If vulcanization is poorly controlled (under-curing or over-curing), the band will have a compromised network structure, making it prone to premature failure and brittleness.
Shelf Life and Fillers
Even when stored perfectly, rubber bands have a limited shelf life due to continuous, slow chemical aging. This natural aging involves chain scission (polymer chains breaking) and the formation of new cross-links, which causes the rubber to harden and lose its snap. Lower-quality rubber bands often contain excessive inert fillers to reduce production costs, which inherently weakens the polymer network and makes the final product more susceptible to cracking and failure.
Physical Stress and Application Limits
Beyond chemical degradation, rubber bands fail because of physical stress that exceeds the material’s mechanical limits during use. Every rubber band has an elastic limit, and stretching it beyond this point causes the polymer chains to undergo permanent deformation. When stretched too far, micro-tears develop, and the chains cannot fully return to their original state, resulting in a permanently weakened band.
Repeated stretching and relaxing cycles, even if they remain within the elastic limit, lead to material fatigue over time. Each cycle slightly weakens the molecular bonds and introduces subtle structural imperfections that accumulate until the band can no longer withstand the tension. This cyclical stress eventually leads to a sudden break without any apparent overstretching.
Friction and contact with rough or sharp surfaces also initiate mechanical failure. The act of sliding a rubber band over a stack of paper or a metal corner causes abrasion that creates stress concentration points. These minor cuts or nicks act as starting points for a tear, and when the band is next stretched, the force concentrates at the weak point, leading to a catastrophic and instant break.