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A silicone sealant manufacturer increases the amount of hydrophobic fumed silica to meet a formulation target.
The result is unexpected: the compound becomes harder to mix, the extrusion force increases, and production becomes less efficient.
Should the manufacturer simply reduce the silica loading?
Not necessarily.
The first step is to determine whether the problem is related to the silica grade, filler loading, dispersion or the overall formulation.
IOTA HB7135 Hydrophobic Fumed Silica is a candidate worth evaluating when a formulation requires a low thickening effect and good processability.
Fumed silica can influence the rheology of a formulation.
The final effect depends on several factors:
Silica surface treatment.
Specific surface area.
Filler loading.
Base polymer and other ingredients.
Dispersion quality.
Mixing equipment and processing conditions.
Adding more silica does not always produce a better result.
Excessive thickening may increase mixing difficulty and extrusion force, while reducing the filler loading without testing may affect the desired performance of the finished sealant.
The objective is to balance processing behavior with the required properties of the cured material.
Hydrophobic fumed silica is produced by modifying the surface of hydrophilic fumed silica.
The surface treatment changes how the silica interacts with the surrounding formulation.
Different grades can produce different effects on viscosity, dispersion and processing.
For manufacturers experiencing excessive thickening, a grade with a lower thickening effect may be worth evaluating, particularly when the formulation requires relatively high filler loading.
However, a lower thickening effect does not automatically mean better anti-sag performance in every sealant. The complete rheological profile must be tested against the application requirements.
IOTA HB7135 is a hydrophobic fumed silica produced by post-treating IOTA HL7380 with HMDS, or hexamethyldisilazane.
Its published specifications include:
| Property | IOTA HB7135 |
|---|---|
| BET specific surface area | 210 m²/g |
| Surface treatment | HMDS |
| pH in 4% dispersion | 7.0–8.5 |
| Loss on drying | ≤0.5% |
| Silica content, based on ignited material | ≥99.8% |
| Carbon content | 3.5–6.5% |
Published applications include silicone rubber, adhesives and sealants, defoamers and toner.
The product information highlights low thickening effect, good processability, the ability to support high loading in polymers and reinforcement in silicone rubber.
These characteristics make HB7135 a candidate for formulation evaluation, not a guarantee of a particular extrusion force or finished-product performance.
A useful comparison should isolate the effect of the silica grade.
Reference formulation
Record the existing silica grade, loading, mixing procedure and extrusion behavior.
Candidate formulation
Evaluate IOTA HB7135 while keeping other ingredients and processing conditions as consistent as practical.
Performance comparison
Measure the properties relevant to the application, such as:
Mixing time and processing behavior.
Extrusion force or extrusion rate.
Viscosity or rheological response.
Sag resistance, where required.
Adhesion and cured-sealant properties.
Do not change the silica grade, loading and mixing procedure simultaneously in the first trial. Otherwise, it becomes difficult to identify the cause of any change.
No.
A sealant must meet both processing and end-use requirements.
A formulation that is easier to extrude may still require adjustment to meet its required sag resistance, application behavior, adhesion or cured properties.
For this reason, HB7135 should be evaluated against the manufacturer's actual formulation targets rather than selected on one property alone.
If the main problem is excessive extrusion force, the evaluation should prioritize processing behavior while confirming that the finished sealant still meets its specifications.
When requesting a recommendation, provide:
Application: silicone sealant, adhesive or silicone rubber.
Base polymer and curing system, where available.
Current silica grade and loading.
The specific problem: excessive thickening, difficult dispersion or poor extrusion.
Mixing equipment and processing conditions.
Required cured-product properties.
Even when the full formulation is confidential, these non-confidential details help narrow down suitable candidates.
1. Why does a sealant become harder to extrude after adding hydrophobic fumed silica?
Possible factors include the silica grade, loading, surface treatment, dispersion and the overall formulation.
2. What is IOTA HB7135?
It is an HMDS-treated hydrophobic fumed silica with a published BET surface area of 210 m²/g.
3. Can HB7135 help when excessive thickening makes processing difficult?
Its published low thickening effect and good processability make it a candidate for evaluation. Actual results depend on the formulation and processing conditions.
4. Does low thickening effect guarantee anti-sag performance?
No. Extrusion behavior and sag resistance are different requirements and should be tested separately.
5. Can HB7135 directly replace an existing silica grade?
Direct replacement should not be assumed. A controlled comparison is recommended.
IOTA HB7135 Hydrophobic Fumed Silica
Contact the IOTA team with your application, current silica grade and processing problem to discuss a suitable candidate for testing.
