We will explain the high-temperature aging process of silicone foam materials to you from the core principle of high-temperature aging and how the five major factors affect the aging process
一,Two Core Aging Mechanisms of Silicone Sponge
The aging of silicone foam board under thermal conditions fundamentally results from the combined effects of the two parallel pathways illustrated in the figure above.
Chemical pathway (thermal-oxygen aging): High temperature and oxygen attack the siloxane backbone (-Si-O-) and methyl side chains (-CH₃), causing molecular chain breakage (depolymerization) or increased crosslinking. This is the chemical root cause of material brittleness or hardening.
Physical path (thermal stress failure): The porous structure of foam is inherently mechanically weak. The mismatched thermal expansion coefficients of its components generate localized stresses during thermal cycling, which propagate from the most vulnerable pores to initiate microcracks and ultimately cause structural collapse.
二. In-depth analysis of specific influencing factors
1. Polymer molecular structure (determining factor)
The type of raw rubber and the vinyl content: Vinyl is the key point of crosslinking reaction. The content of vinyl directly determines the density and stability of the network structure after vulcanization. The raw rubber with specific vinyl content is usually used for high-temperature silicone foam board.
Low volatile content (critical): As previously discussed, residual D4/D5 cyclides and moisture act as "aging catalysts". These components tend to accumulate in foam cells, rapidly accelerating the disengagement degradation of the main chain at elevated temperatures. Controlling this is the primary task to ensure longevity from the source.
2. Strengthening the system (skeleton support)
The type of filler and dispersion: The gas phase silica is the main reinforcing filler. Its specific surface area, surface treatment process and dispersion uniformity in silica gel directly determine the reinforcing effect. Uneven dispersion will form stress concentration points and become the starting point of aging and cracking.
3. Additives and Formulations (Stability and Protection)
Heat-resistant additives: The addition of heat-resistant additives such as iron oxide (iron red) and cerium oxide can effectively capture free radicals and inhibit the thermal oxygen aging process, which is the key to improving long-term temperature resistance.
Sulfurization system: the type and dosage of peroxide vulcanizing agent will affect the type and density of crosslinking bond. The more stable and dense crosslinking network has better anti-aging ability.
4. Production Process (Structural Implementation)
Uniformity of foaming: The size and distribution of bubbles are critical. Uneven bubble structure will cause uneven stress distribution when heated, and the large bubbles or weak areas will be destroyed first.
Sulfur content: Insufficient sulfur may cause incomplete network structure, reduced mechanical strength, and accelerated aging. Excessive sulfur may result in over-tightened network, decreased elasticity, and increased brittleness.
Post-processing: Sufficient two-stage vulcanization (baking) is essential to completely remove residual volatiles and small molecules, which is necessary for stabilizing product performance and improving heat resistance.
5. External application environment (final test)
Operating temperature and duration: The aging rate roughly doubles for every 10-15℃ increase in temperature. Prolonged operation at the rated temperature limit will significantly shorten the lifespan.
Temperature cycling: The thermal fatigue stress caused by frequent alternation of hot and cold is much more destructive to the porous structure than that in constant temperature environment.
Environmental medium: Contact with oil, acid, alkali or continuous exposure to ultraviolet light and ozone will have synergistic effect with heat and accelerate aging.
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