Look in your toolbox, and you might find a hammer with a soft grip that reduces shock and is less likely to slip out of your hand. You might also have a toothbrush or a hairbrush with a soft grip that is more comfortable to hold. These soft grips could be made out of a thermoplastic elastomer (TPE) compound. TPEs can be safe for food-contact applications, such as soft spoons for babies, and for healthcare applications, such as dental guards. TPEs also make good sealing materials, such as sealing rings in piping systems, or liners in bottle caps.
What are they?
A thermoplastic elastomer is a type of thermoplastic polymer. Thermoplastics melt when heated above the material's melting point and solidify when cooled. Because this melting process can be repeated many times, thermoplastics can be recycled. Thermoplastics include polyvinyl chloride (PVC), polyethylene (PE), and many others. Thermoset polymers, on the other hand, cannot be melted again once they are formed. Silicone and synthetic rubber (such as latex and ethylene propylene diene monomer or EPDM) are thermosets.
Thermoplastic elastomers are thermoplastics with an elastomeric component that makes them soft and flexible. Although they can have a rubbery feel and are sometimes called thermoplastic rubber, they are not made out of rubber. Unlike thermoset rubbers, these plastic compounds can be recycled. Thermoplastic elastomers can be formed into parts in the same way that other thermoplastics can be, so a "soft" TPE can be molded or extruded onto a "hard" thermoplastic in one process. This "co-molding" or "overmolding" creates design freedom that is not possible with thermoset rubbers. In addition, processing is much more efficient. For example, a thermoset part might take three minutes to mold, while a thermoplastic elastomer may take only 30 seconds.
Types of Thermoplastic Elastomers
Different types of polymers (“poly” = “many”) are made by connecting together various monomers (“mono” = “one”). For example, polypropylene is made by connecting propylene monomers. TPEs contain more than one type of polymer--an elastomer that gives the material its elastic or soft properties and another polymer that gives it strength. Styrenic block copolymer TPE compounds (sometimes called TPE-S), such as MSC’s EVOPRENE compounds, are made from styrene and an elastomeric part connected in alternating blocks. Styrene-butadiene-styrene (SBS) is a common type. A related polymer is styrene-ethylene butylene-styrene (SEBS), which is more resistant to oxidation and outdoor weathering.
Thermoplastic olefin TPO (or TPE-O) compounds are a special type of TPE that is made from a polyolefin (polypropylene) blended with an elastomer (EPDM). TPOs have many uses, including automotive parts and for wire and cable insulation. Thermoplastic elastomer vulcanizate TPV (or TPE-V) compounds are "vulcanized" or crosslinked, which gives them improved properties such as high compression set and resistance to heat deformation. MSC's GARAFLEX V TPV compounds are used in flexible cord, welding cable, pump cable, and automotive applications. Thermoplastic elastomer urethane (TPU or TPE-U) compounds are based on urethane monomers. TPUs, like MSC's GARATHANE compounds, are commonly used for footwear outer soles and wire & cable industrial jacket applications.
Sometimes a blend of PVC with an elastomer can be considered a TPE. But in most cases, a soft and flexible PVC is not a TPE. Flexible PVC is made soft and pliable using large amounts of plasticizers. Non-PVC TPEs, which do not contain plasticizers, can be a good alternative to PVC for some applications.
Great for soft-touch applications
These compounds are widely used as "soft touch" grips because the soft TPE can be easily molded or extruded onto a hard thermoplastic material using the same processing equipment. They also bond well to most rigid thermoplastic substrates, such as polypropylene (PP), polystyrene (PS), polyamide (PA), and acrylonitrile butadiene styrene (ABS). A thermoplastic elastomer supplier can give advice about which type of TPE bonds well to which type of substrate.
The softness of a TPE is measured by durometer on the Shore hardness scale. The lower the durometer, the softer the material. TPEs used for soft-touch grips typically have a durometer of around 60 to 75. MSC’s EVOPRENE 7050A, for example, is a TPE compound with a durometer of 75A made for injection molding of soft grips on tools.
Used for food applications.
Any plastic material--and all its ingredients--used in a product that comes into contact with food must have food-contact approval from the country where it will be used. Approval indicates that the material is safe for people in its intended use. Food-contact approved TPEs can be used to make soft baby spoons or toddler cup spouts, for example. MSC's EVOPRENE baby and toddler product line is formulated to be free from chemicals of concern, such as phthalate plasticizers, PVC, Bisphenol A, and latex.
Ideal for medical and healthcare applications.
TPEs for healthcare applications must meet the appropriate regulatory standards. TPEs can be sterilized using autoclaves, gamma irradiation, or ethylene oxide. TPEs can be designed to be biocompatible, have high purity, and have low levels of extractable and leachable substances. TPEs can be an alternative to latex, silicone, PVC, or rubber.
Perfect for sealing rings.
Sealing rings have traditionally been made out of thermoset rubbers, but TPE sealing rings can be colored (or white) and co-molded to make two-component seals. TPEs are more efficient to process—they use less energy and can be produced faster than thermoset rubbers.
Often found in cap and closure liners.
Bottle cap liners act as a seal between the bottle contents and the external environment for both metal crowns and plastic caps. Some cap and closure liners are made out of PVC. TPE liners, however, have some advantages over PVC, including better protection against oxygen transmission. Beer, for example, is particularly sensitive to oxygen. MSC created the ALPHASEAL 255 H TPE compound for a customer who needed a beer bottle cap liner that would allow a longer shelf life and better protect the beverage's taste. MSC’s ALPHASEAL TPEs are designed for cap and closure liners in carbonated soft drinks, hot fill, milk and retort applications.