Fluorosilicone rubber is a high-molecular-weight poly(methyl trifluoropropyl) siloxane with vinyl groups at both the side and end positions. It belongs to a thermosetting fluorosilicone elastomer base rubber. It combines the high-temperature resistance of silicone rubber and the oil and solvent resistance of fluorosilicone rubber. Its operating temperature range typically extends from -50°C to 220°C, with some grades reaching as low as -60°C.
Can the same fluorosilicone rubber be directly replaced if the molecular weight and vinyl content are similar? One should not only look at the nominal values. When selecting, one should first confirm the vinyl content, the distribution of vinyl positions, the molecular weight/Mooney viscosity testing method, and the batch measured range. Then, in combination with actual applications such as sealing, oil resistance, solvent resistance, and high/low temperature conditions, evaluate the mixing processing performance, vulcanization performance, mechanical properties, and compressive permanent deformation. Ultimately, whether to adopt it should be confirmed through small-scale trials of the mixing formulation, pilot production, and product verification.
Place the key indicators in the same conditions for comparison
The typical indicators of this product are: colorless transparent gel-like appearance, molecular weight 80±20 0000 or 120±20 0000, vinyl content 0.1/0.3/1.0 mol%, Mooney viscosity ML1+4,100°C is 9–16, and volatile matter 150°C×3h < 2%. Product technical indicators
Before making inquiries and sending samples, both parties should clearly define the following information:
Vinyl content and distribution: Confirm the specific selection of 0.1/0.3/1.0 mol%, as well as whether the vinyl is at the end group or side chain, and whether it is vinyl end-capped. An increase in vinyl content will increase the crosslinking density, raising the hardness and tensile strength of the vulcanized rubber, while reducing the elongation and compressive permanent deformation.
Molecular weight/Mooney viscosity: Confirm the testing method, unit, and batch measured values. Molecular weight affects the mixing powder consumption speed, extrusion flowability, and mechanical properties of the vulcanized rubber.
Volatile matter: Confirm the weight loss limit at 150°C×3h, as it will affect the vulcanization quality and the reliability of the product.
Application and operating conditions: Clearly define the target application (such as fuel system sealing, oil seals, diaphragms, conduits, etc.), the contact medium, temperature range, hardness requirements, and unacceptable failure phenomena.
The procurement specifications should include the allowable range, testing methods, and acceptance conditions, rather than just a nominal interval. Typical values can be used to understand the product characteristics, but they cannot automatically be regarded as a commitment for each batch delivery.
In addition to molecular weight and vinyl content, which differences are worth checking
Checking items How to compare Relation to application
Checking items How to compare Relation to application
Vinyl content and position Confirm mol% values, proportion of end vinyl groups, and side chain distribution Effect on crosslinking density, hardness, tensile strength, elongation, and compressive permanent deformation
Molecular weight/Mooney viscosity Compare batch measured values under the same ML1+4,100°C conditions Effect on mixing processing performance, powder consumption speed, extrusion flowability, and product strength
Volatile matter Compare weight loss at 150°C×3h or the agreed condition Effect on molded bubbles, product appearance, sealing component reliability, and electrical properties
Batch consistency Combine COA, samples, and continuous batch records Judge whether supply fluctuations will affect vulcanization speed, hardness, and product stability
Mixing formulation compatibility Compare under the same fillers, vulcanizing agents, and processes Fluorosilicone rubber needs to be used in combination with reinforcing fillers and vulcanizing agents, and differences in the formulation will significantly change the product performance
Determine verification priorities based on application
Fuel and lubricant sealing applications
Compare the volume swelling rate, hardness change, tensile strength retention rate, and compressive permanent deformation under the target medium (such as aviation fuel, engine oil, hydraulic oil, solvents) and actual temperatures. Fluorosilicone rubber has excellent tolerance to non-polar solvents, but its tolerance to polar solvents is relatively poor. It should be verified separately for the actual contact medium.
High and low temperature application
Compare the low-temperature brittleness, low-temperature flexibility, mechanical performance retention rate after high-temperature aging, and compression permanent deformation within the actual temperature range. Fluorosilicone rubber can typically be used within the range of -50°C to 220°C, and some grades can be as low as -60°C. However, the specific applicable range should be confirmed through actual formulation and product structure verification.
Molded and extruded product applications
Maintain consistency in the filler system, vulcanizing agent, mixing process, vulcanization temperature and time, and observe the powder consumption rate, mixing uniformity, vulcanization speed, burning safety, tensile strength, tear strength, elongation rate, and appearance defects. An excessively high molecular weight may cause mixing difficulties, while an excessively low one may affect the mechanical properties.
Medical or hygiene-related applications
While meeting the application performance requirements, it is necessary to verify the material's physiological inertness, cleanliness, volatiles, extractables, and compliance with target market requirements. Medical-related applications cannot be judged for suitability solely based on the raw rubber indicators; verification should be conducted according to the finished product regulations and actual contact conditions.
How to verify from samples to mass production
First, agree on the acceptance items
Keep the current raw rubber's COA, batch records, normal production data, and historical anomalies, and convert them into checkable items, such as vinyl content, Mooney viscosity, volatile matter, mixing processability, vulcanization curve, hardness, tensile strength, compression permanent deformation, and media resistance.
Perform small-scale tests under the same conditions
Keep the current material as a control, and test the candidate materials under the same filler, vulcanizing agent, mixing process, vulcanization temperature and time. When the formula needs to be adjusted, another test group should be listed and the reasons recorded.
Test production under real conditions
After the small-scale test meets the requirements, then verify the mass mixing, mold pressing/extrusion, actual molds, stability of continuous production, and consistency of the finished product. The aging time, temperature range, media immersion time, and cycle number should be determined based on the product lifespan and application risks, and not use uniform qualified values.
Write the results in the purchase and change requirements
Record the approved vinyl content range, molecular weight/Mooney viscosity range, volatile matter limit, testing methods, applicable processes, and restrictions, and agree on COA, retention samples, batch traceability, and change notification. After the sample passes, continuous observation of subsequent delivery batches is still required.
The basis for judgment should be the pre-agreed acceptance criteria, rather than "appearance transparency" or "molecular weight close". If the candidate material only passes a certain test, the conclusion should also be limited to that test and corresponding conditions.
What information to prepare before inquiring from the supplier
You can first provide a non-confidential application summary: material usage, target vinyl content (0.1/0.3/1.0 mol% selected), molecular weight specification (800,000 or 1,200,000), Mooney viscosity requirements, volatile matter limit, filler system, vulcanizing system, molding process, operating temperature, contact medium, current problems, target market, and expected purchase quantity. When there are requirements for oil resistance, solvent resistance, high/low temperature resistance or medical compliance, the testing methods and acceptance criteria should also be specified.
As a solution provider for the entire organic silicon industry chain, Aijota can discuss candidate specifications around the material range of fluorosilicone raw rubber and customer conditions. After the initial selection, then verify the corresponding technical materials, safety materials and batch inspection documents, and the specific applicability is confirmed by actual application verification.
FAQ
1. How to choose the vinyl content: 0.1/0.3/1.0 mol%. The vinyl content directly affects the crosslinking density and the performance of the vulcanized rubber. When the content is low, the hardness and strength are lower, and the elongation and compression permanent deformation are larger; when the content increases, the hardness and strength rise, but if it is too high, it may affect the thermal stability. Generally, within the range of 0.10%–0.25% mol%, the comprehensive performance is better. The specific choice should be based on the formula and application.
2. Is there a big difference between molecular weights of 800,000 and 1,200,000?
The difference mainly lies in the mixing processing properties and mechanical properties. The higher the molecular weight, the usually better the mechanical properties of the vulcanized rubber, but the mixing powder consumption speed slows down and the processing difficulty increases. Extruded products may need to be combined with lower molecular weight raw rubber to improve fluidity.
3. Does the Minitest viscosity range of 9–16 represent good processing performance?
This range only reflects the viscosity level under the ML1+4,100℃ conditions. The actual processing performance is also related to the type and amount of fillers, structure control agents, and mixing process, and should be verified under the actual formula and process conditions.
4. Can fluorosilicone rubber and ordinary silicone rubber rubber be interchanged?
No. The fluorosilicone rubber contains trifluoropropyl side chains and has excellent oil resistance and solvent resistance, which are not possessed by ordinary silicone rubber. However, fluorosilicone rubber has a higher cost and greater processing difficulty, and the selection should be based on the actual working conditions.
5. Can it still be used after the shelf life exceeds 12 months?
The information indicates that the shelf life is 12 months and it should be stored in a cool and dry environment. This product has cold flow properties, and during transportation and use, the packaging bag should be avoided from being damaged. Whether it can be used after the storage period has passed should be rechecked for appearance, vinyl content, Mooney viscosity, volatile matter, and the performance of mixing and vulcanization, and confirmed through small-scale tests.
6. How to start the selection when there is no complete data for the currently in-use raw rubber?
One can first use the normal production samples and the current working conditions to establish a baseline, and then confirm the vinyl content, molecular weight/Mooney viscosity, volatile matter limits, and batch inspection documents with the supplier. Any data gaps should be recorded, and speculation should not be regarded as the established specifications.