Rubber products refer to natural and synthetic rubber as raw materials to produce a variety of rubber products activities, but also include the use of waste rubber reproduction of rubber products. Rubber aging refers to rubber and products in the processing, storage, and use of the process, due to a combination of internal and external factors caused by the structure of the performance of the phenomenon caused by changes in the use of value. Its performance for cracking, sticky, hardening, softening, chalking, discoloration, mold, etc.
1。Rubber Aging Test Scope
The rubber aging test scope includes all kinds of vulcanized rubber, thermoplastic rubber, vulcanized rubber products, thermoplastic rubber products raw rubber, and so on.
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
The rubber aging process is often accompanied by some significant phenomena, such as the appearance of natural rubber can be found in the long-term storage of softening, sticky, spots; rubber products have deformation, brittle, hardness, cracked, mildew, loss of light, and color change. The physical properties of rubber include swelling, rheological properties, and other changes. Mechanical properties in the tensile strength, elongation at break, impact strength, bending strength, compression rate, elasticity, and other indicators of decline.
4.Rubber aging reasons
Rubber aging phenomenon occurs from its long-term heat, oxygen, light, mechanical force, radiation, chemical media, air ozone, and other external factors, so that its macromolecular chain of chemical changes, destroying the original chemical structure of the rubber, which leads to the deterioration of rubber properties. External factors that lead to the rubber aging phenomenon are mainly physical factors, chemical factors, and biological factors. 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 the rubber aging process, are often not alone, but interact with each other to accelerate the rubber aging process. For example, tire sidewalls are affected by heat, light, alternating stress and strain, oxygen, ozone, and other forms of factors during use.
5.Factors of Rubber Aging
The main factors that cause rubber aging are oxygen, ozone, heat, moisture, light, mechanical stress, and so on.
(1) Oxygen
Oxygen in rubber and rubber molecules occurs in free radical chain reaction, molecular chain breakage, or excessive crosslinking, causing changes in rubber properties. Oxidation is one of the important causes of rubber aging.
(2) Ozone
The chemical activity of ozone is much higher than that of oxygen and more destructive, it is the same molecular chain fracture, but the role of ozone on the rubber with the rubber deformation with or without is different. When applied to deformed rubber (mainly unsaturated rubber), cracks appear perpendicular to the direction of stress, the so-called ‘ozone cracking’; when applied to deformed rubber, only the surface generates an oxide film without cracking.
(3）Heat
Increasing the temperature can cause thermal cracking or thermal crosslinking of rubber. But the basic role of heat or activation. Improve the oxygen diffusion rate and activate the oxidation reaction, thus accelerating the rubber oxidation reaction rate, which is a widespread aging phenomenon – 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. In addition to the ultraviolet light can directly cause the breakage of rubber molecular chain and cross-linking, the rubber absorbs light energy and produces free radicals, triggering and accelerating the oxidation chain reaction process. UV light acts as a heating agent. Another characteristic of light action (different from heat action) is that it is mainly generated on the surface of the rubber. Containing a high rate of rubber specimens, both sides will appear network cracks, the so-called ‘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 placed in the atmosphere for some time, there will be different problems, such as changes in appearance, including cracking, spotting, chalking, or color changes, and even a decline in performance, which may be due to the loss of molecules in the resin resulting in changes in the chemical bonds in the molecular structure, the main reason for the sunlight, the industrial exclusion of exhaust gases, bacteria, etc. caused. The aging performance of the product directly affects the use of the product time, so the aging test is of great significance.
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. Both types of carbon arc lamps were used in early equipment, the former was originally used for textile light resistance testing, and the latter was originally used for coating light resistance testing. The luminous body of the enclosed carbon arc lamp is a set of carbon rods, through which an electric current emits an arc of light.
But the spectral energy distribution of the arc light emitted by the carbon rods and the spectral energy distribution of natural light is a big difference, neither the short-wave ultraviolet radiation of natural light, in the 400-800nm between the high-intensity energy is not sunlight. Sunlight-type carbon arc lamps and daylight spectral energy distribution of the match have improved, but the two between 50-350nm spectral energy distribution is still very different.
What are the protection methods for rubber aging?
As the aging of rubber is a complex integrated chemical reaction process, and to prevent rubber aging is impossible, appropriate measures can be taken to slow down the speed of rubber aging, to achieve the purpose of extending the service life of rubber. Anti-aging measures are mainly physical protection and chemical protection methods.
The physical protection method refers to trying to avoid rubber and various aging factors interacting, such as the use of surface layer or treatment, plus light shielding agent, plus paraffin, etc.
The chemical protection method refers to the addition of certain substances to prevent or delay rubber aging, such as the addition of amine or phenolic chemical antioxidants.
7.Summary
With different products in different conditions of use, and the role of various factors in different degrees, the aging situation is not the same. Even the same product, due to the use of different seasons and regions, the aging situation is also different. Therefore, the aging of rubber is a comprehensive chemical reaction caused by a variety of factors. Among these factors, the most common and important chemical factors are oxygen and ozone; physical factors are heat, light, and mechanical stress. The general aging of rubber products is caused by one or more of these factors together, the most common thermal oxygen aging, followed by ozone aging, fatigue aging, and light oxygen aging.
Rubber aging refers to the rubber in the storage and use of the process of natural and artificial environments by the combined effects of various conditions, performance, and appearance over time, and the phenomenon of deterioration. Rubber products are often due to heat, oxygen, and ozone in the air, sunlight, wind, rain, snow, moisture, and the use of a variety of mechanical stress or chemical solvent erosion, so that the chemical structure of rubber is damaged, become soft or hard brittle cracking, surface roughness, mechanical properties decline over time and gradually lose the value of use. To prevent or delay the aging tendency of rubber must pay attention to the protection, try to avoid the influence of the above factors, and in the preparation of rubber material to add antioxidants.
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