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A transparent silicone rubber sample looks acceptable in its normal state.
But after stretching, the customer notices:
The rubber becomes visibly whiter or loses transparency.
Is the silicone polymer necessarily the problem?
Not always.
The reinforcing filler, its dispersion and its interaction with the complete formulation should also be investigated.
A transparent rubber formulation requires good optical uniformity throughout the material.
When the rubber is stretched, differences related to filler dispersion, agglomeration and the filler-polymer system may become more visible.
For this reason, transparency should not be evaluated only on an unstretched laboratory sample.
The finished compound should also be checked under the deformation expected in the actual application.
No.
When evaluating silica for transparent silicone rubber, consider:
Changing the silica while changing several other formulation variables at the same time makes the result difficult to interpret.
IOTA FINE-SIL 7365 is a precipitated silica positioned for high-transparent reinforcing silicone rubber.
The current product information lists:
Particle size: 8 μm
BET surface area: 180–200 m²/g
pH, 5% suspension: 6–8
Moisture: 4–8%
The product series is specifically positioned for applications requiring reinforcement together with good color, transparency and appearance in silicone rubber. Iota Silica
No.
A silica specification alone cannot guarantee the appearance of the final silicone rubber.
The result still depends on:
polymer + silica loading + dispersion + additives + curing + finished-product deformation.
The correct approach is therefore a controlled comparison in the customer's actual formulation.
A practical first trial is:
Current silica → current formulation → current process
versus
IOTA FINE-SIL 7365 → same initial formulation → same process
Then compare:
Only after the controlled comparison should dosage or processing conditions be optimized.
Does whitening after stretching always come from silica?
No. The complete formulation and processing conditions should be investigated.
Is IOTA FINE-SIL 7365 fumed silica?
No. It is a precipitated silica.
What is its listed BET surface area?
180–200 m²/g. Iota Silica
Can precipitated silica be evaluated for transparent silicone rubber?
Yes. Suitable grades such as IOTA FINE-SIL 7365 are specifically positioned for transparent reinforcing silicone rubber.
Can it directly replace the customer's existing silica at the same dosage?
Use the same dosage as a controlled starting comparison, but the final optimized dosage may differ.
Related Product:
IOTA FINE-SIL 7365 Precipitated Silica
Application Boundary: Transparency, whitening after stretching and mechanical properties are properties of the complete cured formulation. Final suitability must be verified in the customer's actual compound and processing conditions.
