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A grease manufacturer completes a production batch.
The product initially appears uniform, but after storage, a layer of oil becomes visible on the surface.
The first question may be:
Is the thickener dosage too low?
Not necessarily.
Oil separation, often called oil bleeding, can be influenced by the thickener system, base oil, processing conditions and storage environment.
Increasing the amount of thickener without identifying the cause may create additional processing or application problems.
Grease is a structured material in which a thickener network holds a lubricating fluid.
Under certain conditions, some oil may separate from that structure.
The extent and significance of oil separation depend on the grease type and application.
Possible contributing factors include:
Thickener type and concentration
Base oil properties
Thickener dispersion
Mixing and processing history
Storage temperature
Storage duration
Compatibility with other additives
Some controlled oil release may be part of the lubrication mechanism, but excessive or unintended separation can create quality concerns.
Therefore, oil bleeding should be evaluated against the required grease specification.
Fumed silica can be used as a rheology modifier or structuring component in selected grease formulations.
Its high-surface-area structure can influence the flow and consistency of a formulation.
However, the result depends on the silica surface treatment, base oil and complete additive package.
Hydrophobic fumed silica may be considered where compatibility with nonaqueous systems is important.
This does not mean every hydrophobic silica grade will provide the same thickening or oil-retention behavior.
IOTA HB7139 Hydrophobic Fumed Silica is a surface-treated fumed silica grade.
According to its published product information, it is produced from a hydrophilic fumed silica base followed by treatment with polydimethylsiloxane (PDMS).
Selected published specifications include:
| Property | IOTA HB7139 |
|---|---|
| BET surface area | 110 m²/g |
| Surface treatment | PDMS |
| pH, 4% dispersion | 5.5–7.5 |
| Loss on drying | ≤1.5% |
| Carbon content | 4.5–6.5% |
Published application areas include silicone rubber, coatings, adhesives, sealants, greases and cable gels.
For grease manufacturers, IOTA HB7139 can be evaluated as a candidate structuring or rheology-control material.
However, the product specifications alone cannot guarantee a reduction in oil bleeding.
First: Check the base oil.
Different base oils may interact differently with the thickener system.
Second: Check dispersion.
Poor incorporation or uneven distribution may affect the consistency of the finished product.
Third: Review processing conditions.
Mixing time, temperature and shear history can influence the resulting structure.
Fourth: Review storage conditions.
Compare samples under controlled storage temperatures and periods.
Fifth: Evaluate application performance.
A change that reduces visible oil separation may also affect pumpability, consistency or lubrication behavior.
The target should be balanced grease performance, not simply maximum thickening.
A useful evaluation should begin with a controlled base formulation.
Compare the existing thickener system with the candidate grade while recording:
Silica loading
Mixing conditions
Finished grease consistency
Oil separation under a defined test
Storage stability
Application-related performance
If the initial results are promising, the formulation and processing conditions can be optimized further.
The appropriate test methods should be selected according to the grease type and customer requirements.
Does visible oil separation always mean the grease is defective?
Not necessarily. The amount and significance of oil release depend on the grease specification and application.
Can hydrophobic fumed silica be used in grease formulations?
Yes. Selected hydrophobic fumed silica grades can be evaluated for structuring and rheology control.
Is IOTA HB7139 treated with PDMS?
Yes. Its published product information identifies polydimethylsiloxane surface treatment.
What is the BET surface area of IOTA HB7139?
The published value is 110 m²/g.
Will adding more IOTA HB7139 automatically prevent oil bleeding?
No. Performance depends on loading, dispersion, base oil compatibility, processing and storage conditions.
IOTA HB7139 Hydrophobic Fumed Silica
Application Boundary: Oil separation and grease consistency depend on the complete formulation, processing conditions and test method. Final suitability should be confirmed through controlled formulation and storage trials.
