Rubber bands, as high-molecular polymer products made of natural or synthetic rubber, are subject to significantly accelerated oxidative degradation due to changes in temperature and humidity during storage, leading to loss of elasticity and deterioration of physical properties. This process involves the synergistic effect of chemical changes in the rubber molecular chain structure and external environmental factors, and its core mechanism can be analyzed from three dimensions: temperature, humidity, and their interaction.
Temperature is a key factor affecting the oxidative degradation of rubber bands. When the storage temperature rises, the thermal motion of the rubber molecular chains intensifies, intermolecular forces weaken, and the originally orderly helical structure gradually becomes disordered. At high temperatures, oxygen molecules become more active, more easily penetrating the rubber surface and reacting with double bonds in the molecular chains, initiating free radical chain oxidation. During this process, oxygen molecules combine with carbon-carbon and carbon-hydrogen bonds to form peroxides, which further decompose into oxidation products such as aldehydes and ketones, leading to molecular chain breakage and destruction of cross-linked structures. For example, in environments above 30°C, the oxidation reaction rate of rubber bands is significantly increased compared to room temperature, manifested as surface hardening, darkening of color, and difficulty in returning to its original shape after stretching.
Humidity has a dual effect on the degradation of rubber bands. On the one hand, high humidity promotes rubber's absorption of moisture, increasing the gaps between molecular chains, exposing more active sites, and accelerating oxygen penetration and oxidation reactions. Water molecules may also participate in hydrolysis, damaging oxygen-containing functional groups such as ester and ether groups in the rubber, further weakening the stability of the molecular chains. On the other hand, excessive humidity can induce mold growth, and the organic acids produced by microbial metabolism can corrode the rubber surface, forming microcracks that provide pathways for oxygen intrusion. Conversely, while low humidity can inhibit mold growth, excessive dryness can cause plasticizers in the rubber to volatilize, increasing the rigidity and brittleness of the molecular chains, thus accelerating the aging process.
The interaction of temperature and humidity amplifies the oxidative degradation effect. Under high temperature and high humidity conditions, the oxidation and hydrolysis reactions of rubber occur simultaneously, forming a "heat-humidity-oxygen" synergistic aging mechanism. High temperature accelerates moisture diffusion, and high humidity enhances the activity of thermo-oxidative reactions; both together lead to rapid breakage of rubber molecular chains and a decrease in cross-linking density. For example, placing a rubber band in an environment of 35°C and 85% relative humidity will significantly reduce its elongation at break within several weeks, and surface cracking will appear. Sudden temperature changes (such as frequent transitions from low to high temperatures) can cause stress concentration within the rubber, leading to the propagation of microcracks and further accelerating oxidative degradation.
The synergistic effect of light, temperature, and humidity cannot be ignored. Ultraviolet radiation can damage the double bond structure in rubber molecular chains, generating free radicals and initiating photo-oxidation reactions. Under high temperature and humidity conditions, photo-oxidation products react with moisture to produce acidic substances such as carboxylic acids, exacerbating the acidic hydrolysis of rubber. For example, rubber bands exposed to direct sunlight and humid environments for extended periods will rapidly pulverize due to the combined effects of photo-oxidation and hydrolysis, completely losing their elasticity.
To slow down the oxidative degradation of rubber bands, strict control of the storage environment is necessary. Ideally, the temperature should be maintained between 5°C and 25°C, and the relative humidity between 60% and 70%. Low temperatures inhibit molecular thermal motion and the rate of oxidation reactions, while moderate humidity prevents the rubber from becoming excessively dry or absorbing moisture. Simultaneously, storage locations should be far from heat sources, direct sunlight, and ozone sources, and sealed packaging should be used to isolate oxygen. For example, placing rubber bands in a dark, dry storage cabinet and adding talcum powder to prevent sticking can significantly extend their lifespan.
The oxidative degradation of rubber bands is the result of the combined effects of multiple factors, including temperature, humidity, light, and oxygen. Optimizing storage conditions can effectively slow down molecular chain breakage and cross-linking structure damage, maintaining their elasticity and physical properties. This process not only involves the polymer aging theory in materials science but also requires the integration of environmental control technologies to provide a scientific basis for the long-term preservation of rubber products.
