The refrigerant plays a crucial role in various cooling applications. Understanding the compatibility between silicone elastomers and refrigerants can help you provide suitable products to your customers and ensure the efficient and safe operation of the cooling system.
This article will introduce several refrigerants that are incompatible with silicone elastomers, helping you avoid purchasing errors.
Why Is Silicone Incompatible With Certain Refrigerants?
In refrigerant-related applications, you will find that silicone generally shows poorer refrigerant resistance than HNBR and EPDM in many refrigeration systems and therefore is not the preferred sealing material in direct refrigerant-contact applications. The reason is that silicone is not compatible with some refrigerants.
You should know that the greater the similarity in solubility parameters between polymers and solvents, the more obvious the material swelling will be. The flexible Si-O backbone and relatively high free volume of silicone allow certain refrigerant molecules to diffuse into the polymer network, causing swelling.
Silicone also has relatively high gas permeability compared with HNBR or FKM, making it less suitable for long-term refrigerant sealing. Therefore, refrigerants may cause your silicone seals and gaskets to swell, resulting in sealing failure.
Refrigerants Incompatible with Silicone Rubber
Incompatible refrigerants will reduce the sealing performance of your product, leading to leakage. Besides increasing your post-sale expenses, it will also affect your brand reputation and cause more difficult-to-recover consequences.
Therefore, choose the appropriate sealing material based on the specific refrigerant to ensure the good performance and reliability of your final product. There are mainly the following types, which you can refer to.
HFOs
Due to regulatory control over the use of refrigerants, the use of new low GWP (Global Warming Potential) refrigerants is the trend in your industry. However, if you choose to use these HFOs refrigerants in combination with silicone products, there will be an extremely high risk of material failure depending on formulation and operating conditions.
According to the test data from AHRI Project #8007, the R-1234yf model causes severe swelling of the certain silicone formulations, a 28.8% decrease in hardness, and cracks and white spots appear on the surface of the silicone under specific test conditions. If you use the R-1234ze (E) model, it will also cause severe swelling, although the hardness reduction is smaller than that of R-1234yf, reaching 23.8%.
The three-component mixed refrigerant composed of R-1234yf, R-1234ze (E), and R-32 will also weaken the performance of the silicone, causing a 22.2% decrease in hardness, and cracking and whitening after baking. Therefore, silicone is generally not the preferred sealing material for these refrigerant systems.
CFCs
Apart from the new refrigerants, the traditional refrigerants you use are also not suitable for products with silicone sealing.
If you use CFCs as the refrigerant during production, such as the R-12 model, there will be obvious swelling after coming into contact with silicone. The size and hardness of the silicone gaskets and sealing rings may continue to change, making it impossible to achieve stable sealing. Therefore, we do not recommend using them either.
And the R-114 model refrigerant causes more damage to silicone. In high-temperature environments, you will find that the silicone may experience severe swelling and loss of mechanical properties, become brittle and crack. Long-term operation is prone to equipment failures such as sealing leaks and component damage.
HFCs
If you are using certain HFCs refrigerants, you should also avoid using silicone material components.
In fact, earlier research conducted by the Technical University of Munich has shown that long-term exposure to R-134a may cause swelling in certain silicone formulations, making silicone less preferred than HNBR or EPDM for dynamic sealing applications.
The R-134a refrigerant will continuously penetrate the silicone polymer structure, causing swelling problems and gradually changing the original physical parameters of the silicone. After long-term operation, the elasticity and sealing performance of the silicone seal will continue to decline, unable to meet the stable operation requirements of your refrigeration equipment.
HCFCs
You might also use HCFCs refrigerants, but they are also incompatible with silicone products. Take the R-22 model as an example. When you use it for a short period of time in contact with silicone, you may find that the performance of the silicone changes little, unlike the HFOs type refrigerants which will cause a significant drop in the hardness of the silicone.
However, after long-term operation or under harsh high-temperature conditions, prolonged exposure combined with elevated temperature and lubricant interaction may gradually reduce sealing performance.
The compatibility of another HCFCs refrigerant, R-123 model is also not very good. This refrigerant can permeate silicone and may extract certain low-molecular-weight components from some formulations. After long-term use, you will gradually reduce the elasticity of the silicone sealing component, increasing the risk of leakage.
What Refrigeration Conditions Favor Silicone Elastomer Performance?
You might have doubts. The examples above show that many refrigerants are not compatible with silicone elastomers. So, does this mean that silicone elastomers cannot be used in refrigeration-related applications? In fact, silicone elastomers do not perform poorly in all refrigeration-related conditions.
Applications for Specific Refrigerants
In specific R-410A and R-407C refrigerant models, after 5 days of contact at 50°C, the weight and volume change rate of silicone is relatively small, not exceeding 5%, but long-term compatibility should still be validated under actual operating conditions.
Moreover, under the test condition of 60°C, silicone can be used together with refrigerant HFC-161. If your products mainly use these refrigerants, you can consider purchasing silicone sealing components.
Applications Without Direct Refrigerant Contact
In applications of cooling equipment where silicone is not directly exposed to refrigerants, such as HVAC electrical housing, cable sealing, some special silicone products have tolerance to coolant. Moreover, the weather resistance of silicone can enable it to maintain flexibility at temperatures ranging from -50°C to +200°C.
If you are in the home appliance industry, such as refrigerators and air conditioners, you can use silicone for general sealing in HVAC/R. Silicone is commonly used as electrical insulation, environmental sealing, and high-temperature gaskets.
FAQ
What Signs of Deterioration Mean Silicone Has Failed When Exposed to Refrigerants?
Silicone exposed to refrigerants may exhibit swelling and hardness reduction. This is generally regarded as a risk of failure for silicone seals. Significant volume swell may increase the risk of seal failure, although acceptable limits depend on the application and seal design.
Do Lubricants Impact Silicone Failure with Refrigerants?
Yes. Because in actual refrigeration systems, the refrigerant is often mixed with lubricants (such as POE oil, PVE oil or PAG oil) and circulated together. And silicone also showed severe swelling under the conditions containing POE or PVE oil, but there was almost no change in silicone in pure hydrocarbon lubricants.
How to Verify Silicone Material Compatibility with Refrigerants?
You can immerse the silicone elastomer samples in the refrigerant. Measure the relevant data at the specified temperature and time, such as 90°C for 21 days. The main measured data include: weight and volume change rate, hardness change, tensile strength and elongation at break according to ASTM D471.
Do Silicone Refrigerant Compatibility Data Apply to All Silicone Formulations?
No. Different formulations, such as different fillers, curing systems, and additives, can affect the final compatibility performance of silicone with refrigerants. You can ask the supplier to provide samples, and then conduct tests yourself before making a judgment.
What Is the Primary Risk of Silicone Seals in Refrigeration Systems?
The primary risk is not that the silicone seal will fail immediately, but that it will fail after a delay. Because the silicone seal does not immediately swell in certain types of refrigerants; instead, it only swells after prolonged contact. Therefore, you may not detect this during the factory quality inspection, but your customers may notice the problem after using it.
Final Thoughts
Legensilico is a manufacturer in China with over 20 years of experience in silicone production. We can provide you with a one-stop service. If you want to learn more about silicone-related knowledge, you can contact us at any time. We can offer customized silicone sealing component services, which can be adapted to your various compressors and valves.
