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What is rubber aging? What is the performance on the surface?

time:2018-09-08 |  source:WEIHAI RONGHUA TAPE CO., LTD. |  clicks 558

a) What is rubber aging? What is the performance on the surface?
Answer: During the processing, storage and use of rubber and its products, the physical and chemical properties and mechanical properties of rubber are gradually deteriorated due to the combined effects of internal and external factors, and finally the use value is lost. This change is called rubber aging.
On the surface, it is characterized by cracking, stickiness, hardening, softening, chalking, discoloration, and mildew.
What are the factors that affect rubber aging?
The factors that cause rubber aging are:
a) Oxygen and oxygen undergo a free radical chain reaction with rubber molecules in the rubber, and the molecular chain is broken or excessively crosslinked, causing a change in rubber properties. Oxidation is one of the important reasons for rubber aging.
B. Ozone and ozone have much higher chemically active oxygen and are more destructive. It also breaks the molecular chain, but the effect of ozone on rubber is different depending on whether the rubber is deformed or not. When it is used as a rubber for deformation (mainly unsaturated rubber), a crack which is straight in the direction of stress is generated, that is, "ozone cracking"; when it acts on a deformed rubber, only an oxide film is formed on the surface without cracking.
C) Heat: Increasing the temperature can cause thermal cracking or thermal crosslinking of the rubber. But the basic role of heat is activation. Increasing the rate of oxygen diffusion and activating the oxidation reaction, thereby accelerating the oxidation rate of the rubber, is a ubiquitous phenomenon of aging - thermal aging.
D) Light: The shorter the light wave, the greater the energy. What is damaging to rubber is the higher energy of ultraviolet light. In addition to ultraviolet rays directly causing the breakage and cross-linking of rubber molecular chains, rubber generates free radicals by absorbing light energy, which initiates and accelerates the oxidation chain reaction process. The external light acts as a heating. Another characteristic of light action (unlike heat) is that it mainly grows on the surface of the oak. For samples with high gel content, there will be reticular cracks on both sides, the so-called "light outer crack".
E) Mechanical stress: Under the repeated action of mechanical stress, the rubber molecular chain will be broken to form free enthalpy, which will initiate the oxidative chain reaction and form a force chemical process. Mechanically broken molecular chains and mechanically activated oxidation processes. Which one can prevail depends on the conditions in which it is located. In addition, it is easy to cause ozone cracking under stress.
F) Moisture: There are two aspects to the effect of moisture: when the rubber is exposed to humid air or immersed in water, it is easily destroyed. This is because the water-soluble substance in the rubber and the components such as water sputum are dissolved by water. Caused by hydrolysis or absorption. Especially in the alternating action of water immersion and atmospheric exposure, it will accelerate the destruction of rubber. However, under certain circumstances, moisture does not have a destructive effect on rubber, and even has the effect of delaying aging.
G) Others: The factors affecting rubber are chemical media, variable metal ions, high energy radiation, electricity and biology.
(2) What types of rubber aging test methods can be divided into?
A: It can be divided into two categories:
1) Natural aging test method: It is divided into atmospheric 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 heat aging, ozone aging, photoaging, artificial weathering, photo-ozone aging, biological aging, high-energy radiation and electrical aging, and chemical media aging.
Hot air aging test What temperature grade should be selected for various rubber compounds?
For natural rubber, the test temperature is usually 50~100 °C, the synthetic rubber is usually 50~150 °C, and some special rubber test temperatures are higher. For example, nitrile rubber is used at 70~150°C, and silicon fluoride rubber is generally used at 200~300°C. In short, it should be determined according to the test.
(5) What is vulcanization?

The term “vulcanization” has its history. It was named after the initial natural rubber products were cross-linked with sulfur as a crosslinking agent. With the development of the rubber industry, it is now possible to crosslink with a variety of non-sulfur crosslinkers. Therefore, the more scientific significance of vulcanization should be "cross-linking" or "bridge", that is, the process of forming a network polymer by linear polymer crosslinking. From the physical property, it is the process of converting plastic rubber into elastic rubber or hard rubber. The meaning of "vulcanization" includes not only the process of actual cross-linking, but also the method of producing cross-linking.

(6) Which four stages can the vulcanization process be divided into? What are the characteristics?

Answer: It can be seen from the measurement of the tensile strength of the rubber (or vulcanizer) that the entire vulcanization process can be divided into four stages: vulcanization induction, pre-sulfurization, normal vulcanization and persulfurization (reversion to natural rubber).

During the vulcanization induction period (scorch time), the cross-linking has not yet started, and the rubber compound has good fluidity. This stage determines the scorch and processing safety of the compound. At the end of this phase, the compound begins to crosslink and loses fluidity. The length of the vulcanization induction period is related to the nature of the raw rubber itself, mainly depending on the additives used, such as the use of a retardation accelerator to obtain a longer scorch time and a higher processing safety.

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