TPE vs. Silicone in Life Science Applications
Choosing the best fluid seal material for diagnostic or medical devices.
TPE or LSR for Fluid-Sealing Applications?
Thermoplastic elastomers (TPE) and silicone (especially liquid silicone rubber, or LSR) are both considered for fluid seals in diagnostic, medical, pharmaceutical, and other life science applications (e.g., microfluidic chip-based technologies). Both exhibit elastomeric/rubber characteristics, and both share a degree of reliability in sealing applications due to their material flexibility and resilience to fluid.
When it comes to identifying which material to use for your specific fluid seal component, the final application and production volume should be considered. It’s important to consider the material’s impact on manufacturability alongside other characteristics to make the right choice for your product.
The following comparison are, of course, generalities: life science applications are often full of uniquely specific requirements. The choice of sealing material is always dependent on each project’s specific conditions.
Manufacturability
TPE can be a fast and cost-effective material choice for high-volume manufacturing. Prototyping with TPE could be a smart move for a smooth transition to mass production. For consumables with large scale production requirements (e.g., disposables or cartridges), TPE may be a better option than silicone to optimize production costs and ensure sealing effectiveness. For projects eyeing eventual scale-up, identifying a TPE solution at the onset of your development stage could save effort and costs as opposed to starting with silicone and switching to TPE at a later stage.
The primary advantage of TPE is a simpler and more-robust manufacturing process when compared to silicone—one that brings long-term benefits such as fast, cost-effective production and stronger seals when overmolded.
TPE | Silicone/LSR | |
|---|---|---|
r | ||
Production Method | TPE fluid seals are commonly made by injection molding, where pellets of raw material are heated to melt, instantly injected into a mold cavity, and then subsequently cooled down to form a desired shape. This method shares the same generic equipment and processes used for standard thermoplastic injection molding, eliminating need to invest in additional equipment. | LSR can be injection molded for large volume production. Temperatures work the opposite from TPE injection molding. Two materials are constantly mixed in a cooled temperature, and then heated in the mold to solidify in desired form. A customized injection molding machine is required for different materials. |
Cycle Time“Cycle time” is the time it takes to complete one cycle of part production from raw materials to a solid part. Actual cycle time will depend on size, material, and complexity of each part. | In general, the process is simpler for TPE injection molding and ranges within the lower tens of seconds per cycle. “Multi-cavity” molds varying from two to more than sixteen cavities can produce copies of parts simultaneously, allowing the same cycle time to provide more parts. | LSR injection molding generally takes longer as there are additional steps to due to the different chemical reactions that take place. For example, the first cooling process for LSR is to mix two materials for the catalyst to cure the material. This is a more complex chemical reaction than the first heating process for TPE, which is simply melting pellets. Due to this complexity, cycle time could reach minutes. LSRs can be processed with multi-cavity molds as well. |
Assembly Process (Overmolding) | Certain TPEs are formulated to chemically bond to rigid plastic substrates, making it an ideal material for overmolding/two-shot molding. Having both chemical and mechanical bonding features could increase the seal strength. | There are limited silicone materials formulated to stick to plastic substrates. Overmolding with mechanical gripping features are still possible. However, since silicone molding process is done in high temperature, the other plastic component may be affected if it has low heat resistance. |
Assembly Process (Overmolding) | The raw materials of the TPE are stored at room temperature. | The raw material of the LSR requires refrigeration while in storage. |
Material Storage | The raw materials of the TPE are stored at room temperature. | The raw material of the LSR requires refrigeration while in storage. |
Production Cost | In addition to the above-mentioned production method, cycle time, and material storage requirements, TPEs have lower density / specific gravity per cm3 than LSR, producing more parts per same amount of material compared to silicone. Such elements make TPE’s production costs generally lower than LSR injection molding. | Due to the requirement of investment in customized equipment, longer cycle time, refrigeration facility, higher density/specific gravity per cm3 than TPE, and in some cases additional assembly process instead of overmolding, the overall production cost is usually higher than TPE injection molding. |
Material Characteristics
While silicone is resistant to extreme heat and constant pressure, TPE also meets many medical heat, pressure, and material benefits.
TPE | Silicone/LSR | |
|---|---|---|
r | ||
High Temperature Resistance | Medical grade TPEs can be heat resistant to a certain degree (e.g., TPEs are used in PCR applications where the temperature could temporarily reach above 90°C [194°F] or applications requiring autoclave sterilization at around 130°C [270°F]). Exposure to a higher temperature or for a longer time at a certain temperature could affect the sealing function. | LSR has a high heat resistance, not significantly changing its elasticity and sealing properties in temperatures kept constantly as high as around 200°C (400°F). |
Low Temperature Resistance | TPEs can typically withstand cold environments such as cryogenic storage at around -30°C [-22°F]. Morphologic change could begin around -60°C [-76°F] where TPEs could harden, which, depending on the structure of component and application, could either work better or less effective in terms of sealing. The hardness will be gradually restored to the original state as the temperature returns to room temperature. | For LSR, colder temperature does not generally affect its sealing performance down to around -50°C (-60°F). |
Compression Set |
Each variety of TPE has a certain compression set, meaning that exposure to pressure under certain temperatures for a long period could reduce its sealing function.
| Silicone tends to return to its original form even after long exposure to pressure, making it almost free from compression set. |
Recyclability | Just like rigid plastics , solid TPEs can return to liquid form upon heating. Thus, TPEs can also be recycled in general. | Once solidified, LSR does not return to a liquid state, making it impossible to recycle. |