Thermoplastic elastomers (TPEs) offer formulators a unique toolbox to meet critical customer requirements such as hardness, clarity, colorability, and balance of strength and toughness. They can also be used in overmolding applications to provide surface texture and feel that help consumer products like cell phone cases and hand tools stand out among the competition.
Despite the wide variety of TPE materials available, including SBC, TPV, TPU, TPO, COPE, and COPA, OEMs often continue to use over-engineered products simply because they have always done so. At Audia Elastomers, our experienced team has one goal: to help you identify the right material for your application. And that selection needs to achieve certain mechanical properties as well as a certain price point.
Two of the most commonly interchanged thermoplastic elastomer materials are styrenic block copolymers (SBCs) and thermoplastic vulcanizates (TPVs). Let’s review the similarities and differences between the two and when one might be preferred over the other.
Styrenic block copolymers (SBCs) are sometimes referred to as TPE in a generic sense, but in reality they are much more specific. SBCs are created via anionic polymerization to produce polymers with precisely molecular weights. This type of polymerization is characterized as “living,” due to its lack of termination and chain transfer agents.
SBCs are synthetic rubber copolymers of dissimilar materials that create a two phase system composed most commonly of styrenic (S) end blocks linked together by a rubber midblock of ethylene and butylene (EB). Styrene is the hard rigid phase and EB is the soft elastomeric phase. EB is produced by hydrogenating the butadiene midblock. These form a copolymer of S-EB-S where the styrene end block associates and forms a physical crosslink at room temperature, giving the TPE an elastic quality while melting and flowing easily at typical processing temperatures. Polypropylene (PP) is often used as the continuous phase but also use oils, fillers, stabilizers and other additives as part of the recipe. This category of TPEs is common in applications where the typical use temperature is between -40C and +90C, although this can be widened with the addition of additives.
In addition, hydrogenated SBCs offer the following unique characteristics:
- Oxygen, ozone and UV resistance
- Heat and chemical resistance
- Excellent oil absorption
- Balanced - toughness, compression set
- Easy of processability on injection molding, extrusion, and other common methods
- Compatible with polyolefins
- Excellent elasticity and hysteresis
- Stable processing at 250°C processing temperatures
Thermoplastic vulcanizates (TPVs) include many different types of chemistry; but, we will focus on TPVs consisting of crosslinked ethylene-proplyene-diene monomer (EPDM) and polypropylene (PP). In this system, the EPDM is dynamically vulcanized while being finely dispersed into PP. Other ingredients can include oils, fillers, stabilizers, and additives. Typical particle size of the EPDM is 1 to 5 microns. The PP is the continuous phase which melts upon being heated. The crosslinked EPDM is the elastomeric phase that can maintain its elastomeric properties even at very high temperatures depending on the level of unmeltable crosslinked rubber phase. TPVs of this chemistry are common in applications where the typical use temperature ranges between -40C to +125C, although again, this can be widened in specialized formulations.
Should you use a TPV or an SBC?
The elastomeric phase ultimately drives the decision about which one to use.
Benefits of TPV:
- Good compression set at a high in-use temperature.
- Oil resistance, melt strength and abrasion resistance.
- Well-suited for extrusion applications.
Benefits of SBCs:
- Increased design flexibility (because they are not fully crosslinked).
- Ability to achieve lower durometers in the 30 to 5 Shore A range (and perhaps even lower).
- High elongation and tear strength compared to TPVs.
Either TPV or SBC are suitable for applications that require good compression set resistance and tensile set resistance at temperatures up to +50C. In addition, they also offer similar performance with:
- Heat aging
- Weatherability/ozone resistance
- Aqueous fluid resistance
- Gas permeability
- Printability (after surface treatment)
When identifying the right material for your applications, Audia Elastomers can help. In addition to offering standard SBC based TPEs and TPVs, Audia Elastomers also offers custom grades that combine the properties of the various elastomers to meet the needs of your applications. Custom formulations allow for the best combination of properties and cost, which sets you up for success. Together, let’s Grasp What’s Possible.