Rubber aging and protection methods

Although various polymer materials have their own excellent characteristics, they also have common shortcomings, that is to say, they all have a certain service life, the reason is that they will age to different degrees. 1. The concept of rubber aging During the process of processing, storage and use of rubber or rubber seals products, due to the combined effects of internal and external factors (such as heat, oxygen, ozone, metal ions, ionizing radiation, light, mechanical force, etc.) The performance gradually declines, and finally loses its use value. This phenomenon is called the aging of rubber. There are various phenomena of rubber aging, such as: raw rubber will become hard, brittle or sticky when stored for a long time; rubber film products (such as raincoats, raincloths, etc.) will change color, become brittle and even rupture after being exposed to sunlight and rain; Wires and cables erected outdoors will become hardened and ruptured due to the action of the atmosphere, and even affect the insulation; those stored in warehouses or other products will crack; hoses in the laboratory will become hard or sticky, etc. In addition, some products will be broken by hydrolysis or damaged by mold.……All of these are aging phenomena of rubber. The aging process is an irreversible chemical reaction that, like other chemical reactions, is accompanied by changes in appearance, structure and performance. 2. Changes in the aging process of rubber 1. Appearance changes Different types of rubber and different use conditions have different changes. Soft and sticky: thermal oxidation of natural rubber, aging of chlorohydrin rubber. Hardening and brittle: thermo-oxidative aging of cis-butadiene rubber, aging of nitrile rubber and styrene-butadiene rubber. Cracking: Ozone aging of unsaturated rubber, photo-oxidative aging of most rubbers, but the shape of cracks is different. Mildew: Bio-microbial aging of rubber. In addition, there are: spots, cracks, frosting, chalking and whitening. 2. Changes in properties (the most critical changes) Changes in physical and chemical properties: specific gravity, thermal conductivity, glass transition temperature, melting point, refractive index, solubility, swelling, rheology, molecular weight, molecular weight distribution; heat resistance, cold resistance, Changes in properties such as air permeability, water permeability, and light transmission. Changes in physical and mechanical properties: tensile strength, elongation, impact strength, bending strength, shear strength, fatigue strength, elasticity, and wear resistance all decrease. Changes in electrical properties: changes in electrical properties such as insulation resistance, dielectric constant, dielectric loss, breakdown voltage, and decrease in electrical insulation. Appearance changes and performance changes are caused by structural changes. 3. Structural changes Cross-linking occurs between molecules, and the molecular weight increases; the appearance becomes hard and brittle. The molecular chain is degraded (broken), the molecular weight is reduced, and the appearance becomes soft and sticky. Other changes in the molecular structure: modification of the main chain or side chain, the shedding of the side group and the breaking of weak bonds (occurs in special rubber). 3. Reasons for rubber aging: 1. Internal factors: ① Molecular structure and chemical structure of rubber (or chain link structure): The basic structure of rubber, such as the unit isoprene of natural rubber, has double bonds and active hydrogen atoms, so it is easy to participate in reaction. Molecular chain structure: The weak bond of the rubber macromolecular chain, the more weak links, the easier it is to age. Unsaturated carbon chain rubber is prone to aging, and the oxidation reaction ability of saturated carbon chain rubber is related to its chemical structure. For example, branched macromolecules are easier to oxidize than linear macromolecules. In terms of oxidative stability, various substituent groups are arranged in the following order: CH Vulcanizate cross-linking structure: The cross-linking bonds are -S-, -S2-, -Sx-, -C-C-, and the cross-linking bond structure is different. Vulcanizates have different aging resistance, -Sx- is the worst. ②Rubber compounding components and impurities: There are often variable valence metals in rubber, such as Ca, Fe, Co, Ni, etc. If it exceeds 3ppm, the aging of the rubber will be greatly accelerated. 2. External factors: Physical factors: thermoelectric, opto-mechanical force, high-energy radiation, etc. Chemical factors: oxygen and ozone, water vapor in the air, acid-base salts, etc. Biological factors: Microorganisms: Bacteria and fungi Insects: Termites and cockroaches eat polymer materials. Sea creatures: oysters, lime worms, seaweeds, seaweeds, etc. In practice, the above factors often play a role at the same time. The effects of these factors are also different in different use conditions and regions, so the aging of rubber is a complex process. Among them, the most common, most influential, and most destructive factors are: heat, oxygen, photo-oxygen, mechanical force, and ozone. It boils down to thermal-oxidative aging, photo-oxidative aging, ozone aging, and fatigue aging. 4. Protection of rubber aging aging and iron rusting, people want to aging as naturally, we can only use the law to delay the aging of rubber through the study of aging law, but can not be absolutely prevented. Commonly used protection methods are: Physical protection method: try to avoid the interaction between rubber and aging factors. Such as: adding paraffin to rubber, rubber-plastic blending, electroplating, coating, etc. Chemical protection method: The aging reaction of rubber is delayed by chemical reaction to continue. Such as: adding chemical antioxidants. Company website: https://www.orksealing.com/
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