What is rubber aging? What is this manifestation on the surface?

Answer: During the processing, storage, and use of rubber and its products, the physical, chemical, and mechanical properties of rubber gradually deteriorate due to the combined effects of internal and external factors, ultimately losing its value for use. This change is called rubber aging.

On the surface, it manifests as cracking, sticking, hardening, softening, powdering, discoloration, and mold growth.

What are the factors that affect rubber aging?

The factors that cause rubber aging include:

A) Oxygen and oxygen undergo free radical chain reaction with rubber molecules in rubber, causing molecular chains to break or over crosslink, resulting in changes in rubber properties. Oxidation is one of the important causes of rubber aging.

B) Ozone and its chemical reactive oxygen species are much higher and more destructive. It also causes molecular chain breakage, but the effect of ozone on rubber varies depending on whether the rubber deforms or not. When used as rubber for deformation (mainly unsaturated rubber), cracks appear in the direction of stress, known as "ozone cracking"; When applied to deformed rubber, only an oxide film is formed on the surface without cracking.

C) Heat: Increasing the temperature can cause thermal cracking or cross-linking of rubber. But the basic function of heat is still activation. Improving oxygen diffusion rate and activating oxidation reaction to accelerate rubber oxidation reaction rate is a common aging phenomenon - thermal oxidative aging.

D) Light: The shorter the light wave, the greater the energy. The high-energy ultraviolet radiation has a destructive effect on rubber. Ultraviolet radiation can not only directly cause the breakage and cross-linking of rubber molecular chains, but also generate free radicals in rubber due to the absorption of light energy, triggering and accelerating the oxidation chain reaction process. External light plays a heating role. Another characteristic of light action (different from heat action) is that it mainly occurs on the surface of rubber. Samples with high adhesive content will exhibit network cracks on both sides, known as "outer layer cracks".

E) Mechanical stress: Under repeated mechanical stress, rubber molecular chains will break and generate free radicals, triggering oxidative chain reactions and forming a mechanochemical process. Mechanical breakage of molecular chains and mechanical activation of oxidation processes. Which one can have an advantage depends on the conditions they are in. In addition, it is easy to cause ozone cracking under stress.

F) Moisture: Moisture has two functions: rubber is easily damaged when exposed to humid air, rain, or water immersion, due to the water-soluble substances and components such as water droplets in rubber being extracted and dissolved by water. Caused by hydrolysis or absorption. Especially under the alternating action of water immersion and atmospheric exposure, it will accelerate the damage of rubber. But in some cases, moisture does not have a destructive effect on rubber, and even has a delaying effect on aging.

G) Other factors that affect rubber include chemical media, valence metal ions, high-energy radiation, electricity, and biology.