Thermoplastic Elastomer vs Liquid Silicone Rubber
The ambiguity around the choice of plastics for particular purposes frequently causes misunderstandings regarding the proper application of bespoke injection molding. As a result, original equipment manufacturers (OEMs) could overlook the benefits that plastics provide in terms of product design.
Despite the fact that the phrases “thermoplastic” and “thermoset” have similar sounds, both categories offer viable solutions for challenging applications in a variety of markets. However, the best option for your injection molding project will ultimately depend on the distinct features and processing behaviors of the materials within these categories.
Let’s compare one plastic from each group in order to better grasp the similarities and differences.
What is Thermoplastic Elastomer and Liquid Silicone Rubber?
Thermoplastic elastomer (TPE), is a synthetic plastic that undergoes melting when heated and solidifies upon cooling, while maintaining its chemical composition. On the other hand, LSR, or liquid silicone rubber, is a synthetic plastic composed of polymers bonded together through chemical processes, resulting in permanent hardening after a single application of heat.
The primary distinction between the two lies in their reaction to heat. TPE can be reprocessed after heating, allowing for modifications and alterations. In contrast, LSR cannot be changed once it has been subjected to heat.
The moldability of thermoplastic elastomer and liquid silicone rubber is influenced by the properties and behaviors of these materials during the heating process. Let’s examine the moldability processes for each:
To mold thermoplastic elastomer, plastic pellets are subjected to heat, which causes them to liquefy. The molten thermoplastic elastomer is then injected under pressure into a mold, where it takes the desired shape. Upon curing, the thermoplastic elastomer solidifies and gains strength, maintaining its shape without the need for a chemical bond. One notable advantage of thermoplastic elastomer is that the molding process can be reversed. Defective or excess molded components can be reground and melted down for reprocessing. This allows for corrections and adjustments to be made, and the plastic can be reused multiple times.
The moldability process for LSR involves working with a highly viscous liquid plastic. The LSR material is heated, and during this heating process, polymer cross-linking occurs. Cross-linking refers to the formation of chemical bonds between polymer chains, resulting in a three-dimensional network structure. This cross-linking provides the LSR with irreversible strength and shape after the curing process. In some cases, a catalyst is mixed with another component before injection into the mold to initiate the cross-linking reaction. This method allows for greater control over the curing process and ensures the desired properties in the final LSR product.
Pros and Cons: TPE vs. LSR
Advantages and disadvantages play a significant role in the selection between thermoplastic elastomer and liquid silicone rubber, influencing moldability and project outcomes. It is crucial to understand the strengths and weaknesses of each plastic:
Pros of TPE include:
- Recyclability and lower energy consumption during production.
- Ability to be re-molded without undergoing a chemical change.
- Easier molding process compared to thermoset LSR.
- Shorter molding cycles.
- Lower cost of the molding process.
- Heat sealability.
- Easy coloration using most dyes.
- Greater number of options for two-shot molding.
Cons of TPE include:
- Potential for post-cure melting if exposed to high temperatures.
- “Creeping” and deformation under sustained pressure or other stressors.
- Costly tooling.
Pros of LSR include:
- Better resistance to high temperatures compared to thermoplastics.
- Design flexibility, including the ability to create thick-to-thin wall constructions.
- High tear strength.
- High chemical resistance.
- Superior compression set.
Cons of LSR include:
- Lack of recyclability.
- Inability to be re-molded after curing.
- Possibility of burning if heated after curing.
- Lengthy curing period, which increases production time and cost.
- Potential for production delays as equipment must be disassembled and cleaned if early curing occurs.
- Handling difficulties with liquid plastic.
- Bulky or thick appearance.
Common Applications:TPE vs. LSR
When considering the suitability of thermoplastic elastomer and liquid silicone rubber for complex applications, such as overmolding or metal-to-plastic conversion, the decision-making process can be challenging. However, reliable injection molders like Sungplastic assess each project based on its unique requirements. Here are some typical examples of projects that are well-suited for Thermoplastic Elastomer and LSR:
TPE is well-suited for:
- Soft-touch grips, seals, impact-resistant devices, and component housings
Thermoplastic elastomer’s flexibility and durability make it an excellent choice for providing a comfortable and secure grip, as well as protecting components from impacts.
- Sealing rings
Thermoplastic elastomer’s ability to create a tight seal makes it suitable for applications requiring effective sealing, such as in industrial equipment or consumer products.
- Food-contact-approved applications
Certain thermoplastic elastomer formulations can meet FDA regulations, making them suitable for use in bottle cap and closure liners, baby bottles, and toddler cup spouts.
- Medical/healthcare applications
Thermoplastic elastomer can be used as an alternative to latex, silicone, PVC, or rubber in medical and healthcare applications. It is commonly used in gloves and non-invasive equipment components.
LSR is well-suited for:
- Medical implantables
LSR’s biocompatibility, high tear strength, and resistance to high temperatures make it an excellent choice for medical devices that come into contact with the human body for extended periods.
- Gaskets and hardware in consumer appliances
LSR’s ability to withstand high temperatures and provide excellent sealing properties makes it suitable for applications in consumer appliances like microwaves, where gaskets and hardware are exposed to heat and require reliable performance.
- Electronic interfaces on device keyboards or touchpads
LSR’s durability, resistance to high temperatures, and excellent electrical insulation properties make it ideal for creating precise and reliable electronic interfaces in various devices.
- O-rings, wire harnesses, coverings, stoppers, and other automotive parts
LSR’s resistance to harsh chemicals and high temperatures makes it well-suited for automotive applications where exposure to chemicals and heat is common.
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