Hydroxyl-terminated silicone oil applied in silicone rubber mixing acts as a structural control agent, which prevents excessive bonding between fumed silica and raw rubber that causes structuring (hardened mixed rubber and poor reprocessing). The viscosity selection depends on specific application scenarios and requirements. Detailed specifications are as follows:
1. Mainstream Viscosity Ranges & Applicable Scenarios
| Viscosity Range (25℃, mPa·s/cst) | Hydroxyl Content | Applicable Scenarios | Features |
|---|---|---|---|
| 20~40 (25~30 as most common) | 6%~12% (8% commonly used) | General-purpose silicone rubber mixing, substitute for diphenylsilanediol | Good fluidity, easy dispersion, powerful anti-structuring effect, simplified process without heat treatment |
| 50~100 | 6%~12% | Most mixed rubber formulations | Balanced fluidity and performance, low oil bleeding, widely adopted |
| 10~30 (15~25 preferred) | 5%~10% | Silicone rubber requiring high transparency | Improves transparency and processability with minor impact on physical properties |
| 100~500 | 3.5%~8% | High-filler formulations requiring enhanced structuring control | Long-lasting performance, low migration, suitable for thick-walled products |
2. Core Selection Principles
- Function-oriented selection: For structural control, low-viscosity silicone oil with high hydroxyl content (6%~12%) is preferred. Abundant hydroxyl groups can effectively adsorb onto fumed silica surfaces and weaken filler interaction.
- Balance of processability: Viscosity below 10 cP tends to cause migration and oil bleeding; viscosity above 500 cP results in poor dispersion and compromised fluidity during processing.
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Performance requirements of finished products:
- Transparent products: 20~30 cst with around 8% hydroxyl content
- High-hardness products: Viscosity may be raised to 50~100 cst
- Low-hardness products: 20~40 cst to avoid interference with hardness adjustment
3. Dosage Reference
The addition amount of hydroxyl-terminated silicone oil is generally 3%~8% of fumed silica mass, or 0.5%~2% of raw rubber mass. Adjustments shall be made based on the specific surface area of fumed silica, formulation system and processing conditions.
Summary
Hydroxyl-terminated silicone oil with viscosity of 20~100 mPa·s (20~100 cst) is most commonly used for silicone rubber mixing, among which 25~30 cst and 50~100 cst are mainstream industrial grades. Viscosity selection shall comprehensively consider structuring control effect, processing fluidity and final product performance. Products with high hydroxyl content (6%~12%) are prioritized to guarantee optimal results.
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