The silicone has many excellent characteristics and functions. But silicone belongs to the production of synthetic raw materials, the different proportion of ingredients in the materials will have a different functional effect, and what reasons for the aging in silicone rubber products? Following are some reasons for aging in silicone cases.
Contact medium aging
Exposure to moisture in the air, or other conditions, such as the external insulation of electrical power systems, in salt-contaminated areas, is extremely susceptible to salt spray, therefore, it is necessary to study the aging performance under this condition. In addition, some silicone rubber products which come into contact with oil are tested to improve their oil resistance.
The aging of silicone rubber under different kinds of oil is due to the mechanical damage of aging on one hand, and on the other is the degradation of cross-linking system, which results in low molecular weight materials. The presence of fluid can reduce the coefficient of friction, but it can also accelerate the chemical degradation of the silicone rubber, thus accelerating wear.
Thermal oxidative aging
Natural rubber (NR) for capacitor seals, EPM, EPDM, Styrene-butadiene, butyl rubber, silicone rubber (NVQ), and so on, are all of these forms of thermal-oxidative aging during use. NR containing a lot of unsaturated double bonds, under the combined action of heat and oxygen, the VULCANIZATE will degrade, the molecular chain and cross-linking bond will be cracked and broken, resulting in aging.
Thermal oxidative aging is both a radical and an oxidation reaction. Under anaerobic thermal aging conditions, free radical decomposition occurs, and the lower the bond cleavage energy, the faster the decomposition, when molecules break down and form free radicals, then the main chain breaks and forms cross-links, producing all kinds of gases. In ultraviolet aging, molecules absorb ultraviolet light and activate certain functional groups, and decomposition or through the energy transfer in other functional groups, such as decomposition, through the formation of active groups and reaction.
The oxidative decomposition of side-chain organic groups in silicone rubber occurs mainly in the anaerobic high-temperature open environment, which leads to the hardening of silicone rubber, while in an oxygen-free high temperature closed environment, the main chain fracture reaction occurs mainly, the formation of volatile cyclic polysiloxane, resulting in softening of silica gel products. The oxidation of side-chain methyl and the degradation and fracture of the main chain are the main reactions of silicone rubber at high temperatures.
The fatigue aging of silicone rubber case is that the aging phenomenon of silicone rubber products under the action of a certain frequency and periodic stress, which is caused by the change of the molecular structure of silicone rubber material, that is, force and heat effect. (due to the rubber in a number of deformation, hysteresis phenomenon, so that the internal silicone causing heat )
Ozone content in the atmosphere is very low, in the aging process of silica gel, ozone attack silica gel molecules, silica gel expansion and dispersion resulting in surface cracks. Ozone reacts with double bonds in silica molecules to form Ozonide and peroxide, which in turn regenerates ozonide. The Ozonide is broken down into free radicals by the action of heat and light, leading to a chain growth reaction. In addition, the silicone rubber under stress will produce molecular fracture, but not the formation of Ozonide, the phenomenon of cracking and aging.
By studying the effect of ozone on different kinds of tread rubber, including natural rubber, oil-filled methyl-styrene-butadiene rubber, and the blend of isoprene rubber and cis-1,4-polybutadiene rubber, etc., the service life of silicone rubber decreased and decreased rapidly in the short time of ozone action, which proved that silicone rubber had obvious degradation at the beginning of ozone action. Along with the Ozone Action Time extension, the service life drops slowly. This may be due to the degradation process slowing down during the deepening phase of polymer decomposition.