Rubber products refer to natural and synthetic rubber as raw materials. Using rubber products produces many of them. This also includes using waste rubber to make new products. Rubber aging refers to changes in rubber and rubber products. These changes happen during their processing, storage, and use. A mix of internal and external factors causes them. The structure of the rubber and its usage cause these factors. Its performance for cracking, sticky, hardening, softening, chalking, discoloration, mold, etc.
1。Rubber Aging Test Scope
The rubber aging test covers all vulcanized and thermoplastic rubber. It also includes vulcanized rubber and thermoplastic rubber products. It also includes raw rubber.
2.Rubber Aging Test Items
Rubber aging test items include (wet) heat aging (hot air aging performance), (resistance) ozone aging, ultraviolet aging, salt spray aging, xenon aging, carbon arc lamp aging, halogen aging, weather aging performance, artificial climate aging test, high-temperature aging test, low-temperature aging test, high and low temperature alternating aging, aging in liquid medium, liquid medium aging, aging in liquid medium, natural climate sun exposure test, storage of materials, life projection, salt spray test, humidity heat test, and so on. Life projection, salt spray test, humidity and heat test, sulfur dioxide – ozone test, thermal oxygen aging test, user-specific conditions aging test, and low-temperature embrittlement temperature.
3.Rubber aging symptoms
Rubber aging is often marked by significant signs. For example, stored natural rubber softens, gets sticky, and gets spots. Rubber products deform. They become brittle, harden, and crack. They grow mold, lose shine, and change color. The physical properties of rubber include swelling, rheological properties, and other changes. The tensile strength, elongation at break, and impact strength drop. So do the bending strength, compression rate, elasticity, and other properties.
4.Rubber aging reasons
Heat, oxygen, light, force, radiation, and chemicals all age rubber. So do air ozone and other outside factors. This exposure causes chemical changes in the rubber’s chain. It destroys the rubber’s original structure. This change leads to the rubber going bad. External factors cause rubber to age. They are mainly physical, chemical, and biological. Physical factors include heat, light, electricity, stress, etc.; chemical factors include oxygen, ozone, acid, alkali, salt, and metal ions, etc.; biological factors include microorganisms (molds, bacteria), insects (termites, etc.). These external factors in rubber aging often do not act alone. They interact with each other to speed up rubber aging. For example, heat, light, and strain affect tire sidewalls. They also face oxygen, ozone, and other factors during use.
5.Factors of Rubber Aging
The main factors that cause rubber aging are oxygen, ozone, heat, and moisture. Also, light and mechanical stress.
(1) Oxygen
Oxygen in rubber and rubber molecules causes free radical chain reactions. These break molecular chains or create excessive crosslinks. These changes rubber properties. Oxidation is one of the important causes of rubber aging.
(2) Ozone
Ozone is much more chemically active than oxygen and more destructive. It causes the same kind of molecular chain break. But, its effect on rubber is different depending on whether the rubber is deformed. When applied to deformed unsaturated rubber, cracks appear across the stress direction. This is called ‘ozone cracking’. When applied to deformed rubber, only the surface cracks. It makes an oxide film.
(3）Heat
Increasing the temperature can cause thermal cracking or thermal crosslinking of rubber. But the basic role of heat or activation. This will improve the oxygen diffusion rate. It will activate the oxidation reaction, speeding up the rubber oxidation rate. This is a common type of aging called thermal oxygen aging.
(4) Light
The shorter the light wave, the greater the energy. The destructive effect on rubber is the ultraviolet light with higher energy. Also, UV light can break rubber molecules and cross-link them. The rubber absorbs light and makes free radicals. They trigger and speed up oxidation. UV light acts as a heating agent. Light action is also different from heat action. It is mainly generated on the rubber’s surface. The rubber has many specimens. Both sides will get network cracks, the ‘light outside the crack’.
(5) Mechanical stress
Under the repeated action of mechanical stress, it will make the rubber molecular chain break to generate free radicals, triggering the oxidation chain reaction, and the formation of a force chemical process. Mechanical breakage of molecular chains and mechanical activation of the oxidation process. Which can prevail, depending on the conditions under which they are located. In addition, it is easy to cause ozone cracking under stress.
(6) Moisture
The role of moisture has two aspects: rubber in the humid air drenching or immersed in water, is easy to destroy, which is due to the rubber in the water-soluble substances and components such as clear water groups are dissolved by water extraction. Hydrolysis or absorption and other causes. Especially under the alternating action of water immersion and atmospheric exposure, the destruction of rubber is accelerated. But in some cases, moisture on the rubber is not destructive and even has the role of slowing down aging.
(7) Oil
Oil and rubber contact for a long time, infiltration will produce analysis of mutual diffusion, change the structure, and swelling, so that the strength of rubber and other mechanical properties decline.
(8) Other
Chemical media, variable metal ions, high-energy radiation, electricity, and biological factors will also play a rubber role in aging.
Aging test, used to simulate the sunlight, temperature, and humidity environment on the material of the broken role, reasonable prediction of the service life of the product; material aging, including fading, loss of light, strength reduction, cracking, peeling, chalking, and oxidation. Mainly for all kinds of polymer materials.
6.Rubber aging test methods
Aging tests include artificial climate aging tests (xenon arc lamp, carbon arc lamp, ultraviolet lamp), natural climate exposure tests, material storage life projection, salt spray tests, humidity, and heat tests, high and low-temperature tests, ozone tests, sulfur dioxide – ozone test, thermal oxygen aging test, liquid medium aging test, aging test under user-specific conditions and so on. General test items will be done as needed.
01 Artificial accelerated aging
Aging test in the laboratory using the aging box to simulate the natural environmental conditions of certain aging factors.
Heat aging test: It is a simple artificial simulation experiment method to evaluate the adaptability of materials to high temperatures, which is to put the materials at a higher temperature than the relative use temperature to make them subjected to thermal effects, and evaluate the heat resistance of materials by testing the changes in performance before and after exposure.
02 Xenon Light Ageing
The xenon arc radiation source is subjected to one of two different light filtration systems to alter the spectral distribution of the radiation it produces, simulating the spectral distribution of ultraviolet (UV) and visible (VIS) light from solar radiation, and simulating the spectral distribution of UV and VIS light from light radiation filtered through 3mm thick window glass, respectively.
Xenon aging testing is the evaluation of the ability of equipment used and stored outdoors without shelter to withstand the thermal and optical effects of solar radiation. The range of effects includes whether the electrical function of the object to be tested is normal, whether the material structure is deformed or damaged, and verifying the color degradation of the surface material of the object to be tested after prolonged exposure to sunlight, a color difference meter is usually used to test the degree of color variation both before and after the test.
This is a test performed on products and their manufacturing materials that are exposed to sunlight. Solar radiation can cause both photochemical and thermal effects. In most cases, this test can replace the high-temperature test. The sunlight test examines the effects of solar radiation on the use or open storage of products or related materials.
03 Ultraviolet light aging
The UV aging test is an accelerated weathering test using a fluorescent UV lamp as a light source to accelerate the weathering of materials by simulating UV radiation and condensation in natural sunlight, to obtain the results of the material’s weather resistance. UV aging test is widely used in non-metallic materials, and organic materials (such as coatings, paints, rubber, plastic, and its products) by the sunlight, humidity, temperature, condensation, and other climatic conditions under the changes in the inspection of the products and materials aging phenomenon degree and situation.
Purpose: Products left in the atmosphere for some time will have different problems. These include changes in appearance, like cracking, spotting, chalking, or color changes. There may also be a decline in performance. This decline may happen because molecules in the resin are lost. This loss causes changes in the chemical bonds in the resin’s molecular structure. Sunlight and industrial exhaust gases, bacteria, etc. are the main causes. The product’s durability directly determines its usability duration. So, the aging test is very important.
04 Carbon arc lamp aging
Carbon arc lamp is divided into two kinds, a closed carbon arc lamp, and a sunlight-type carbon arc lamp. Early equipment used both types of carbon arc lamps. The first tested textile light resistance. The second tested coating light resistance. The lamp’s luminous body is a set of carbon rods. An electric current emits an arc of light through them.
But the arc light from the carbon rods and natural light have very different energy levels. Spectral distributions call them. Natural light lacks the high-energy 400-800nm ultraviolet radiation of arc light. Sunlight-type carbon arc lamps and daylight have improved. But, their light’s 50-350nm spectral energy is still very different.
What are the protection methods for rubber aging?
Rubber aging is a complex chemical process. It is impossible to prevent. But, we can take steps to slow it. This will extend the service life of rubber. Anti-aging measures are mainly physical protection and chemical protection methods.
This method is about avoiding rubber and aging factors from interacting. It involves using a surface layer or treatment, plus a light shield, plus paraffin, etc.
Chemical protection means adding substances to prevent or delay rubber aging. For example, adding amine or phenolic antioxidants.
7.Summary
Products vary. They are in different conditions. Various factors play a role to different degrees. So, aging is not the same for all. Even the same product ages differently. This is due to the use of different seasons and regions. So, the aging of rubber is a full chemical reaction. Many factors cause it. The most common and important chemical factors are oxygen and ozone. Physical factors are heat, light, and stress. Rubber products age due to one or more of these factors. The most common are thermal oxygen aging. Ozone aging, fatigue aging, and light oxygen aging follow it.
Rubber aging refers to the rubber in the storage and use. It happens because many things add up. These include conditions, performance, and appearance over time. It happens in natural and artificial environments. And, it causes the rubber to deteriorate. The air contains heat, oxygen, and ozone. Sunlight, wind, rain, snow, and moisture also damage rubber. Stress or chemicals also harm it. They harm the rubber’s chemical structure. This makes it soft or hard, brittle, rough, and weak over time. It loses value. To prevent or delay rubber aging, pay attention to protection. Try to avoid the above factors. Also, add antioxidants when preparing rubber.
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