Selection of Fumed Silica Dosage and Type

In PU adhesive systems, the dosage and type of fumed silica are key factors affecting thixotropy and adhesion:
Dosage Control:
Recommended dosage is 5-20% (by mass). Too low a dosage has little effect, while too high a dosage may affect processing performance.
Low content (5-10%): Moderate viscosity, good flowability.
Medium content (10-20%): Significant thixotropy, viscosity decreases during application, facilitating handling.
High content (>20%): Viscosity increases sharply, potentially affecting processing performance.

Type Selection:
Hydrophobic fumed silica is more suitable for PU adhesive systems than hydrophilic fumed silica.
It is recommended to choose products with a specific surface area below 200 m²/g to balance thixotropy and application performance. Products treated with silane coupling agents maintain adhesion better.

Dispersion Process Optimization
1. 1. Dispersion Equipment Selection
A high-speed shear disperser (linear speed 10-20 m/s) is recommended.
For high-viscosity systems, a kneader or open mill can be selected.
The dispersing equipment should have speed adjustment and cooling/heating functions.

2. Process Parameter Control
Parameter | Recommended Range | Function
Temperature | 40-60℃ | Optimal dispersion temperature
Shear Rate | 3000-21000 rpm | Select according to viscosity
Time | 30-60 minutes | Ensure thorough dispersion
Dispersion Method | "Donut" dispersion method | Achieve optimal dispersion effect

3. Dispersing Agent Usage:
Add 0.5-2% superdispersant to improve dispersion.
Avoid using different types of fumed silica; choose a single type.
Consider using resin homogenizers to improve dispersibility.
Thixotropy and Adhesion Balancing Strategy:

Interfacial Bond Enhancement:
Treat the fumed silica surface with silane coupling agents.
Choose hydrophobic products to reduce agglomeration and improve dispersion uniformity.

Rheological Property Control:
Adjust thixotropy by fumed silica content; choose low-viscosity formulations for electronic seals; choose high-thixotropic formulations for building seals.

Formulation Design Optimization:
Balance reinforcement and processability; control the addition amount to 10-20%.
Use wetting agents, thickeners, and other additives to extend open time.