What is rubber aging?

Answer: Rubber and its products in the process of processing, storage and use, due to the comprehensive effect of internal and external factors caused by rubber physical and chemical properties and mechanical properties gradually deteriorate, and finally lose the use value, this change is called rubber aging.

On the surface, it is cracked, sticky, hardening, softening, powdery, discoloration, mildew and so on.

What are the factors affecting rubber aging?

Answer: The factors causing rubber aging are:

A) Oxygen and oxygen in rubber occur free radical chain locking reaction with rubber molecules, molecular chain fracture or excessive cross-linking, resulting in changes in rubber properties. Oxidation is one of the important reasons of rubber aging.

B) ozone, ozone chemical activity is much higher than oxygen, more destructive, it is also to make molecular chain fracture, but the effect of ozone on rubber is different with rubber deformation or not. When used for deformation of rubber (mainly unsaturated rubber), there is a vertical crack with the direction of stress action, that is, the so-called "ozone cracking"; When acting on deformed rubber, only oxide film is formed on the surface without cracking.

C) Heat: increasing the temperature can cause thermal cracking or thermal crosslinking of rubber. But the basic function of heat is activation. Increase the oxygen diffusion rate and activation oxidation reaction, so as to accelerate the rubber oxidation reaction rate, which is a universal aging phenomenon? Thermal oxygen aging.

D) Light: The shorter the light wave, the greater the energy. The damage to rubber is caused by higher energy ultraviolet light. In addition to directly causing the fracture and crosslinking of rubber molecular chain, ultraviolet radiation can produce free radicals by absorbing light energy, which can trigger and accelerate the oxidation chain reaction process. Ultraviolet light acts as heating. Another characteristic of photogenesis (as opposed to thermal) is that it mainly develops on the surface of rubber. The sample with high gel content will have network cracks on both sides, which is called "optical outer crack".

E) Mechanical stress: under the repeated action of mechanical stress, the rubber molecular chain will break and generate free radicals, trigger oxidation chain reaction and form mechanochemical process. Mechanical fracture of molecular chains and mechanical activation of oxidation processes. Which prevails depends on the conditions under which it is placed. In addition, it is easy to cause ozone cracking under stress.

F) water: the role of water has two aspects: rubber in the wet air rain or soaked in water, easy to damage, this is because the water-soluble substances in rubber and water groups and other components are extracted and dissolved by water. Caused by hydrolysis or absorption. Especially in the alternating action of water immersion and atmospheric exposure, can accelerate the destruction of rubber. But in some cases, water does not destroy rubber, and even has the effect of delaying aging.

G) Other factors: chemical media, variable metal ions, high-energy radiation, electricity and biology, etc.

Rubber aging test methods can be divided into what categories?

A: It can be divided into two categories:

1) Natural aging test method: it is divided into atmospheric aging test, atmospheric accelerated aging test, natural storage aging test, natural medium (including buried ground, etc.) and biological aging test.

2) Artificial accelerated aging test method. For thermal aging, ozone aging, light aging, artificial climate aging, photoozone aging, biological aging, high-energy radiation and electrical aging and chemical media aging.

What temperature grade should be selected for the hot air aging test for various adhesives?

A: For natural rubber, the test temperature is usually 50 ~ 100℃, synthetic rubber is usually 50 ~ 150℃, some special rubber test temperature is higher. Such as nitrile rubber with 70 ~ 150℃, silicone fluorine glue generally with 200 ~ 300℃. In short, it should be determined according to the test.