In the copolymerization system of acrylic emulsion and vinyl silicone oil, the selection of vinyl silicone oil viscosity must be core-matched with three key factors: polymerization compatibility, process operability, and target product performance. Silicone oils with different viscosity ranges correspond to different application scenarios, and the specific selection scheme is as follows:
1. Viscosity Classification of Vinyl Silicone Oil and Suitable Application Scenarios
The viscosity of vinyl silicone oil is usually measured in mPa·s (25℃). Combined with the actual requirements of acrylic emulsion polymerization, it is divided into three core ranges:
| Viscosity Range | Suitable Application Scenarios | Core Advantages | Notes |
|---|---|---|---|
| Low viscosity (10~100 mPa·s) | High-transparency emulsions, coating film-forming aids, textile hydrophilic finishing agents |
1. Excellent compatibility with acrylic monomers/emulsions, achieving uniform dispersion without agglomeration;
|
1. Weak hydrophobicity, not suitable for scenarios requiring high water resistance;
|
| Medium viscosity (100~1000 mPa·s) | General-purpose modified acrylic emulsions (architectural coatings, leather finishing agents, adhesives) |
1. Optimal balance between compatibility and functionality, taking into account both dispersibility and performance improvement;
|
1. It is necessary to add a small amount of silane coupling agent (e.g., KH-570) to improve the grafting rate;
|
| High viscosity (1000~5000 mPa·s) | High-end weather-resistant anti-corrosion coatings, wear-resistant coatings, high-temperature sealants |
1. Long molecular chain structure, which greatly improves the wear resistance, aging resistance, and high/low temperature resistance of the polymer after grafting;
|
1. Poor compatibility, direct addition is prone to delamination, pre-emulsification is mandatory;
|
2. Key Selection Principles
-
Prioritize matching target performance
- If transparency and film-forming property are pursued → select low viscosity (10~50 mPa·s);
- If general modification effects (hydrophobicity + weather resistance) are required → select medium viscosity (200~500 mPa·s), which is the most commonly used viscosity range for acrylic emulsion copolymerization;
- If high weather resistance and wear resistance are needed → select high viscosity (1000~3000 mPa·s), and a pre-emulsification process must be used in conjunction.
-
Adjust according to polymerization process
- Emulsion polymerization (semi-continuous dropping method) : Prioritize low to medium viscosity, no complicated pretreatment is required, and the process stability is high;
- Bulk/solution polymerization : High viscosity can be selected, and the system viscosity is reduced by solvent dilution to improve dispersibility;
- Soap-free emulsion polymerization : Only low viscosity (<50 mPa·s) can be used to avoid agglomeration caused by the lack of emulsifiers.
-
Control the correlation between addition amount and viscosity
- Silicone oil addition amount 1%~5% (based on the total mass of acrylic monomers): Both low and medium viscosity are applicable, with little impact on the emulsion system;
- Silicone oil addition amount 5%~15%: Prioritize low viscosity to prevent a sharp increase in system viscosity and avoid gelation.
3. Optimization Suggestions
- Regardless of the viscosity selected, adding a silane coupling agent (e.g., KH-570, dosage: 2%~5% of the silicone oil mass) can significantly improve the grafting rate between vinyl silicone oil and acrylic chains, and reduce performance degradation caused by free silicone oil.
- High viscosity silicone oil must undergo pre-emulsification treatment : Mix silicone oil, emulsifier, and deionized water in proportion, perform high-speed shearing (8000~10000 r/min) for 10~15 min to prepare silicone oil emulsion, and then add it to the polymerization system.
Links