When the vinyl content in silicone rubber is too low, it will have a significant impact on its vulcanization properties, mechanical properties, processing properties and final application. The specific performance and countermeasures are as follows：


1. The impact of low vinyl content
Decreased vulcanization performance
Insufficient crosslinking: Vinyl is the active crosslinking point in the vulcanization process of silicone rubber. If the content is too low, the crosslinking density will be insufficient, the vulcanization rate will slow down, and even the vulcanization will not be complete.
Uneven vulcanization: Insufficient local crosslinking may cause defects such as air bubbles and lack of glue, which affect the appearance and performance of the product.
Deterioration of mechanical properties
Reduced strength: The tear strength and tensile strength are significantly reduced, and the material is easy to break.For example, when the molar fraction of vinyl drops from 0.15% to 0.06%, the tear strength may drop by more than 50%.
Insufficient elasticity: the elongation and resilience deteriorate, the material becomes brittle, and it is difficult to meet the needs of flexible applications.
Poor processing performance
Abnormal fluidity: The vinyl content is too low, which may cause the fluidity of the rubber to be too poor (difficult to fill the mold) or too good (sticky mold, overflow), which increases the difficulty of processing.
Difficulty in mold release: After vulcanization, the product sticks to the mold, and additional mold release agents need to be used to increase production costs.
Changes in heat resistance and aging resistance
Improved thermal stability: The low vinyl content can reduce the risk of fracture of crosslinked bonds at high temperatures, but the performance degradation caused by incomplete vulcanization needs to be weighed.
Stable aging resistance: the resistance to ultraviolet rays, ozone and other aging factors has not changed much, but the performance attenuation may be accelerated due to insufficient crosslinking in long-term use.
2. Problems in typical application scenarios
Seals: Insufficient crosslinking leads to poor sealing and easy leakage.
Thermally conductive materials: Low vinyl content may improve thermal conductivity, but insufficient mechanical properties cause the material to be easily damaged.
Medical products: incomplete vulcanization may leave unreacted monomers, which affects biocompatibility.
Electronic packaging: Insufficient strength causes the packaging layer to crack and cannot protect the internal components.
3. Solutions and optimization suggestions
Adjust the formula
Increase vinyl content: Increase the overall crosslinking density by adding silicone rubber with high vinyl content (such as vinyl molar fraction 0.15%~0.25%) or vinyl silicone oil.
Optimize the vulcanization system: adjust the amount of vulcanizing agent (such as peroxide), or use a two-component vulcanization system (such as platinum catalyst + hydrogen-containing silicone oil) to improve the vulcanization efficiency.
Improved processing technology
Extend the vulcanization time: compensate for insufficient crosslinking and ensure complete vulcanization.
Increase the vulcanization temperature: heat up appropriately within the allowable range of the equipment to accelerate the vulcanization reaction.
Segmented vulcanization: The process of low temperature pre-vulcanization + high temperature post-vulcanization is used to reduce internal stress and improve the uniformity of crosslinking.
Material substitution and compounding
Blending modification: Mix low-vinyl silicone rubber with high-vinyl silicone rubber proportionally (such as 50/50) to balance performance and cost.
Filling enhancement: Add fillers such as fumed silica and carbon nanotubes to improve strength and wear resistance.
Surface treatment: The mold is polished or coated with a mold release agent to improve the mold release.
Application scenario adaptation
Low-stress scenarios: If the strength requirements are not high (such as temporary sealing), a low vinyl content can be accepted to reduce costs.
High thermal conductivity requirements: In situations where thermal conductivity is required but mechanical properties are low (such as heat dissipation gaskets), low-vinyl silicone rubber can be preferred.
4. Case reference
A seal production case: The molar fraction of vinyl in the original formula is 0.06%, and the tear strength of the product is only 20kN/m, which is easy to crack.By adding 20% vinyl silicone rubber with a molar fraction of 0.15%, the tear strength is increased to 35kN/m and the vulcanization time is shortened by 30%.
A case of a thermally conductive silicone gasket: Silicone rubber with a vinyl molar fraction of 0.04% is used, with a thermal conductivity of 3.0W/(m·K), but the tensile strength is only 1.5MPa.By filling with 5% fumed silica, the tensile strength is increased to 3.0MPa to meet the needs of electronic packaging.
summary
The vinyl content is too low, which will significantly weaken the vulcanization properties and mechanical properties of silicone rubber, but through formula adjustment, process optimization or material compounding, the defects can be effectively compensated.In practical applications, comprehensive decisions need to be made based on specific performance requirements (such as strength, thermal conductivity, cost) and processing conditions (such as vulcanization equipment, mold design) to achieve a balance between performance and cost.