Four Factors Affecting the Aging of Silicone Products
Due to the excellent performance of silicone products, it has a wide range of applications. It is not only used as a special material in aviation, cutting-edge technology, and military technology sectors, but also in various economic sectors, and its application range has expanded to: construction, electrical and electronic, textile, automobile, machinery, leather and paper making, chemical light industry, metal and paint, medicine and medical treatment, etc.
1. Aging of silicone products in contact with media
Rubber materials used in exposure to natural environments will be affected by moisture in the air, or other conditions, such as external insulation materials for power systems, which are easily affected by salt spray in saline-alkaline areas, so aging studies are carried out to analyze such conditions Under aging performance becomes required. In addition, for some rubber products in contact with oil, testing their oil resistance and improving their oil resistance performance are also the research focus of practical applications. The aging behavior of rubber in different types of oil, the occurrence of wear and tear is due to the mechanical damage of aging on the one hand, and also due to the degradation of the cross-linking system of the material to produce low molecular weight substances. The presence of the fluid reduces the coefficient of friction, but it also accelerates the chemical degradation of the rubber, which accelerates wear.
2. Thermo-oxidative aging of rubber in silicone products
Natural rubber used for capacitor sealing, ethylene-propylene rubber, styrene-butadiene rubber, butyl rubber, silicone rubber, etc., all belong to this form of thermal-oxidative aging during use. Because it contains a large amount of unsaturated double bonds, under the joint action of heat and oxygen, the vulcanized rubber will undergo degradation reactions, and the molecular chains and crosslinks will be cracked and broken, resulting in aging. Thermal oxygen aging of silicone products is a free radical reaction and an oxidation reaction; under the condition of anaerobic thermal aging, free radical decomposition will occur, and the lower the bond cracking energy, the faster the decomposition; the polymer is ionized due to radiation. At the same time, excitation will be generated. At this time, the molecules will be cracked and free radicals will be generated, and then the main chain will be broken and cross-linked, and finally various gases will be generated; in ultraviolet aging, molecules will absorb ultraviolet rays and excite specific functional groups, and decompose or pass through Energy transfer etc. in other functional groups decomposes and reacts by generating active radicals.
Silicone rubber mainly undergoes oxidative decomposition reactions of side chain organic groups in an aerobic high-temperature open environment, resulting in hardening of silicone rubber; however, in an oxygen-free high-temperature airtight environment, the main chain scission reaction mainly occurs to generate volatile cyclic polysiloxane, which leads to the softening of silicone rubber. Silicone rubber mainly undergoes side chain methyl oxidation reaction and main chain degradation and cleavage reaction under high temperature conditions.
3. Fatigue and aging of silicone products
The fatigue aging of rubber refers to the aging phenomenon that occurs when the molecular structure of the rubber material changes under the action of a certain frequency and cyclic stress. It is the result of the activation of two main factors, namely force and heat. result. The anti-fatigue performance of natural rubber is an extremely important performance for vibration-damping elastic elements that are repeatedly subjected to stress. It is directly related to the failure of the damping function and the safe operation of locomotives and vehicles, and it is gradually attracting the attention of researchers.
4. Ozone aging of silicone products
The content of ozone in the atmosphere is extremely low. During the aging process of rubber, ozone attacks rubber molecules, causing the rubber to expand, causing cracks on the surface. Ozone reacts with the double bonds in the rubber molecules to generate moles of ozonide and peroxide, which in turn regenerate ozonide. This ozonide is decomposed into radicals under the action of light, heat, etc., resulting in a chain growth reaction. In addition, silica gel products will produce molecular breakage under the action of stress, instead of generating ozonide, and cracking and aging will occur.
Through the study of different types of tread rubber under the action of ozone, including natural rubber, oil-extended methyl styrene butadiene rubber, and polyisoprene rubber and butadiene rubber, it is shown that with the extension of the ozone action time, the rubber The service life decreases, and it drops rapidly in a short period of time under the action of ozone, which proves that the rubber is obviously degraded at the beginning of the action of ozone. With the prolongation of ozone exposure time, the lifespan decreased slowly, which may be caused by the slowing down of the degradation process in the deepening stage of polymer decomposition.