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A common formulation challenge in sealants is:
“The sealant no longer sags, but now it is too difficult to extrude.”
Fumed silica is widely used to control rheology and thixotropy, but increasing the amount of silica does not automatically improve the complete performance of a sealant.
The real objective is to find a balance between:
anti-sagging + extrusion + processing + application performance.
Fumed silica can form a three-dimensional particle network within a formulation.
This interaction helps increase structure when the material is at rest, which can improve resistance to sagging after application.
For vertical joints or sealant beads, this behavior can be particularly useful.
The same particle interactions that help build structure can also increase resistance to flow.
If the formulation becomes too structured, the customer may notice:
This is why simply increasing silica dosage is not always the correct solution.
If extrusion becomes difficult, reducing silica immediately may not always solve the underlying issue.
Other factors can include:
The complete formulation should therefore be reviewed.
Poorly dispersed silica can create local agglomerates and inconsistent rheological behavior.
A formulation may appear very thick without developing the balanced thixotropy needed for good application performance.
Therefore, silica selection and dispersion should be considered together.
Both hydrophilic and hydrophobic fumed silica can be used in formulated systems, depending on the chemistry and performance target.
For example, IOTA HL7200 is a hydrophilic fumed silica that can be evaluated for rheology control and reinforcement in applications including silicone materials, adhesives and sealants.
Hydrophobic grades can also be considered when surface treatment and compatibility provide advantages for the specific formulation.
The appropriate choice should be determined through formulation testing rather than assuming one type is universally better.
When evaluating a fumed silica grade for sealants, consider comparing:
A silica that gives the highest viscosity is not necessarily the best silica for the formulation.
Not necessarily. Increasing dosage can increase structure, but excessive loading may negatively affect extrusion and processing.
Possible reasons include silica dosage, grade, dispersion, base-polymer viscosity and formulation interactions.
It may help in some cases, but the full formulation and dispersion conditions should be reviewed before making a conclusion.
No. The appropriate surface type depends on the formulation chemistry and performance requirements.
Provide the sealant type, current silica grade and dosage, base polymer, viscosity or extrusion problem, mixing conditions and target performance.
For sealants, the objective is not maximum thickening. It is controlled rheology that provides both application stability and workable extrusion.
