What factors affect rubber aging in rubber bands?
Rubber aging occurs when it is exposed to external factors such as heat, oxygen, light, mechanical forces, radiation, chemical media, and ozone in the air. These factors cause chemical changes in the macromolecular chains, disrupting the rubber's original chemical structure and leading to deterioration of rubber properties. External factors that cause rubber aging include physical, chemical, and biological factors.
Physical factors include heat, light, electricity, and stress;
Chemical factors include oxygen, ozone, acids, alkalis, salts, and metal ions;
Biological factors include microorganisms (mold and bacteria) and insects (termites).
These external factors often do not act alone during the aging process of rubber, but rather interact with each other, accelerating the aging process. For example, the tire sidewall is affected by heat, light, alternating stress and strain, oxygen, ozone and other factors during use.
Oxygen in rubber undergoes a free radical chain reaction with rubber molecules, causing molecular chain breakage or excessive crosslinking, which alters rubber properties. Oxidation is a major cause of rubber aging. Oxygen aging increases with increasing oxygen partial pressure.
During the aging process, temperature accelerates rubber aging by increasing the oxygen diffusion rate and activating oxidation reactions, thereby accelerating the oxidation reaction rate and sometimes affecting the aging mechanism.
The time it takes for various rubbers to develop cracks after ozone aging significantly decreases with increasing ozone concentration. The degree of cracking varies depending on the rubber type. Ozone concentration also affects the crack growth rate, increasing with increasing ozone concentration.
Ozone is much more chemically active than oxygen and is more destructive. While it also breaks molecular chains, its effect on rubber varies depending on whether the rubber is deformed or not. When acting on deformed rubber (mainly unsaturated rubber), cracks perpendicular to the direction of stress appear, which is the so-called "ozone cracking"; when acting on non-deformed rubber, only an oxide film is formed on the surface without cracking.
Different products, under varying usage conditions, experience varying degrees of influence from various factors, leading to varying degrees of aging. Even the same product can experience varying aging patterns depending on the season and region of use. Therefore, rubber aging is a complex chemical reaction caused by multiple factors. Among these factors, the most common and important chemical factors are oxygen and ozone; the physical factors are heat, light, and mechanical stress. Generally, rubber product aging is the result of the combined effects of one or more of these factors, with thermal oxidative aging being the most common, followed by ozone aging, fatigue aging, and photooxidative aging.
