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During silicone sealant production, a manufacturer may notice that more air bubbles appear after adding fumed silica.
The immediate assumption may be that the silica grade is responsible.
However, visible bubbles after powder addition do not automatically mean that the fumed silica is defective or incompatible.
Powder incorporation, mixing equipment, vacuum conditions and formulation chemistry can all influence the result.
Fumed silica is a lightweight, high-surface-area powder.
During powder handling and incorporation, air can become entrained in the material being mixed.
The extent of air incorporation may depend on:
Powder addition rate
Mixing equipment
Mixing speed and circulation
Formulation viscosity
Powder wetting and dispersion
Timing and effectiveness of vacuum degassing
A formulation that becomes more viscous during mixing may also release trapped air less readily.
No.
It is important to distinguish mechanically entrained air from gas generated by a chemical reaction or contamination.
For example, depending on the curing system, moisture contamination or unwanted reactions may contribute to gas formation.
Therefore, manufacturers should check when the bubbles first appear.
Do they appear during powder addition?
During vacuum mixing?
After the curing package is introduced?
Or only after the finished sealant has been packaged?
The timing can help identify the likely cause.
Hydrophobic fumed silica is used in silicone formulations for functions including reinforcement and rheological control.
Its surface treatment can influence interaction with the silicone polymer and other formulation components.
IOTA HB7620 Hydrophobic Fumed Silica is an HMDS-treated grade with the following published specifications:
| Property | Specification |
|---|---|
| BET surface area | 170 m²/g |
| pH, 4% dispersion | 5.5–8.0 |
| Loss on drying | ≤0.5% |
| Carbon content | 1.5–2.5% |
| Surface treatment | HMDS |
Its published applications include silicone rubber, adhesives and sealants, coatings and printing inks.
However, using a hydrophobic grade does not automatically prevent air entrainment or eliminate the need for degassing.
Step 1: Identify when bubbles appear
Record the process stage where bubbles first become visible.
Step 2: Review powder addition
Check whether the silica is being incorporated uniformly or too rapidly for the equipment.
Step 3: Review mixing conditions
Compare mixing speed, circulation, viscosity development and temperature.
Step 4: Review vacuum degassing
Confirm that the equipment and process provide suitable conditions for removing entrained air.
Step 5: Check formulation chemistry
If bubbles appear after introducing curing components, investigate moisture, compatibility and possible reaction-related gas formation.
Avoid changing multiple processing variables at the same time.
IOTA HB7620 can be considered when a silicone sealant manufacturer is reviewing hydrophobic fumed silica grades for reinforcement and rheological control.
A meaningful trial should compare:
Powder incorporation behavior
Dispersion quality
Air entrainment and degassing
Extrusion behavior
Sag resistance
Curing and final mechanical properties
The goal is to establish whether the candidate grade meets the requirements of the actual formulation.
Does fumed silica itself always cause bubbles in silicone sealant?
No. Bubbles may result from air incorporation, mixing conditions, degassing or formulation-related reactions.
Can vacuum mixing remove all bubbles?
Not necessarily. Results depend on viscosity, equipment and the process conditions.
Is IOTA HB7620 hydrophobic?
Yes. It is an HMDS-treated hydrophobic fumed silica.
What is the published BET surface area of IOTA HB7620?
170 m²/g.
Can IOTA HB7620 directly replace another hydrophobic silica grade?
A direct replacement should not be assumed. Side-by-side formulation and processing trials are recommended.
IOTA HB7620 Hydrophobic Fumed Silica
Application Boundary: Bubble formation, dispersion, degassing and final sealant performance depend on the complete formulation and production process. Final suitability must be confirmed through controlled trials.
