Will High-Temperature Resistant Silicone Rubber Age and Harden with Long-Term Use?-Iota

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News > Dynamic industry > Will High-Temperature Resistant Silicone Rubber Age and Harden with Long-Term Use?

Will High-Temperature Resistant Silicone Rubber Age and Harden with Long-Term Use?

High-temperature resistant silicone rubber will indeed age and harden during long-term use, which is a physical inevitability determined by the "secondary crosslinking" reaction of the siloxane polymer chains. According to the GB/T 3512-2014 standard (Rubber, vulcanized or thermoplastic—Determination of heat resistance and acceleration ageing tests), under continuous high-temperature environments (e.g., above 200℃), the molecular chains of silicone will undergo accelerated decomposition and reorganization, forming a tighter rigid network. This leads to an increase in Shore hardness and a decrease in elongation at break, ultimately resulting in the loss of elastic sealing functions.

What is the "Secondary Curing" Phenomenon that Causes Silicone to Harden?
The core mechanism behind silicone hardening is the increase in internal crosslink density. Even for silicone that has been fully cured upon leaving the factory, when exposed to high-temperature environments beyond its design limits for a prolonged period, residual reactive groups will continue to undergo crosslinking reactions. This "secondary curing" makes the connections between molecular chains tighter, manifesting macroscopically as the material losing its softness and becoming hard and brittle.

How Do Environmental Factors Accelerate the Aging Process of Silicone?
Besides temperature, ozone and chemical media are also key drivers accelerating aging. Ozone attacks the double bonds in the molecular chains of silicone rubber, causing surface cracking; meanwhile, acidic and alkaline corrosive environments can destroy the stability of siloxane bonds. According to the IEC 60068-2-2:2007 environmental testing standard, the coupling effect of high temperatures and chemical stress will significantly shorten the service life of silicone seals.

What Specific Hazards Does Silicone Aging and Hardening Pose to Equipment?
After silicone hardens, changes in its physical properties will directly compromise the integrity of the sealing interface. First, the hardened material cannot accommodate the thermal expansion and contraction of the equipment, leading to seal failure and leakage. Second, the tear strength of hardened silicone drops drastically; it easily powders and falls off in vibrating environments, losing its insulation and protective effects on electronic components, and may even cause short-circuit risks.

How to Predict the Service Life of Silicone Using Experimental Data?
In engineering, hot air ovens are typically used for accelerated aging tests to estimate lifespan. Following the ASTM D573-2014 standard, samples are baked at specific high temperatures (e.g., 150℃ or 200℃) for 72 to 168 hours. The evaluation is based on comparing the rate of change in physical properties before and after aging. If the retention rate of tensile strength after aging is below 80%, or the retention rate of elongation at break is below 60%, the material is deemed unable to meet the expected requirements for long-term use.

What Role Does Low-Field NMR Technology Play in Silicone Aging Detection?
Low-field nuclear magnetic resonance (NMR) technology is a cutting-edge method for evaluating the degree of silicone aging. By measuring the transverse relaxation time (T2) of hydrogen protons in the sample, this technology can highly sensitively reflect changes in the crosslinked system. As aging progresses and the internal crosslink density increases, the T2 time shows a regular shortening, allowing for the precise quantification of aging characteristics without destroying the sample.

Is There Any Way to Restore Softness to Aged and Hardened Silicone?
For industrial silicone that has already undergone chemical crosslinking aging, there is currently no reliable chemical method to restore its original elasticity. Although physical methods such as soaking in hot water or wiping with vegetable oil might temporarily alter the surface feel, they cannot reverse the rigidified structure of the internal polymer chains. Therefore, in critical sealing applications, once obvious hardening of the silicone is detected, it must be replaced immediately to eliminate safety hazards.

Information Source: This article is compiled based on general testing standards such as GB/T 3512-2014 and ASTM D573-2014, as well as the mechanisms of material aging. For the specific service life of products, please refer to the manufacturer's Technical Data Sheet (TDS). Contact Email: zyf@siliconeoil.cn

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