Thermoplastic elastomers (TPE) are made by combining hard and soft polymer segments into a single material that can be melted, shaped, and cooled like plastic but stretches and flexes like rubber. The production process varies depending on the type of TPE and the final product, but it generally involves compounding raw polymers, heating them to a specific melt temperature, and forming them through injection molding, extrusion, or a similar process. Here’s how each stage works.
What Makes TPE Different From Regular Rubber
Traditional rubber is “thermoset,” meaning once it’s cured, you can’t remelt or reshape it. TPE sidesteps this limitation through its molecular architecture. Every TPE is built from two types of polymer blocks: hard segments that give the material its structure and soft segments that provide elasticity. These blocks are arranged in an ABA pattern, where two hard terminal blocks (A) sandwich a soft central block (B). The hard blocks act like physical crosslinks, holding the material together at room temperature. When heated, those hard segments soften and allow the material to flow, which is what makes TPE processable on standard plastics equipment.
This dual nature means you can melt TPE, inject it into a mold, cool it, and end up with a rubber-like part. Scrap and runners can be reground and reprocessed, which cuts material waste significantly compared to thermoset rubber.
Main Types of TPE and How They’re Produced
Styrenic TPEs (TPE-S)
The most common TPE family uses styrene-based block copolymers. Two varieties dominate: SBS (which uses an unsaturated soft block) and SEBS (which uses a saturated, more heat-stable soft block). These are produced through sequential anionic polymerization, where the hard styrene blocks and soft rubber blocks are built up in controlled steps. The raw polymer is then compounded with oils, fillers, and additives in a twin-screw extruder to create pellets ready for molding. SEBS-based compounds tolerate higher processing temperatures (up to 260°C) because their saturated backbone resists degradation, while SBS compounds should not exceed 220°C.
Thermoplastic Vulcanizates (TPV)
TPVs are made through a process called dynamic vulcanization, which is fundamentally different from simple blending. Rubber (typically EPDM) and a thermoplastic (typically polypropylene) are mixed together in a heated extruder or internal mixer. While the two polymers are being sheared and blended, a curing agent is added that crosslinks the rubber phase. As vulcanization progresses, the rubber forms tiny crosslinked nanoparticles that agglomerate within the continuous polypropylene matrix. This phase inversion, where the rubber shifts from a continuous phase to a dispersed one, is what gives TPV its unique combination of rubber-like performance and plastic-like processability. The size of the rubber agglomerates increases during dynamic vulcanization and then stabilizes, locking in the material’s final properties.
Thermoplastic Polyolefin (TPE-O)
TPE-O is the simplest to produce. It’s a physical blend of polypropylene and an ethylene-based rubber, mixed in a twin-screw extruder without any chemical crosslinking. The lack of vulcanization makes it easier and cheaper to produce, though it generally offers lower elastic recovery than TPV.
Injection Molding: The Primary Forming Process
Most TPE parts are made by injection molding. The process starts with feeding TPE pellets into a heated barrel, where a rotating screw melts and homogenizes the material. The molten TPE is then injected into a cooled mold cavity under pressure.
Temperature control is critical. For SEBS-based compounds, the barrel temperature typically runs between 190°C and 245°C, with large parts requiring temperatures up to 260°C. SBS compounds process at lower temperatures, between 150°C and 205°C. If the melt temperature is too low, the part can develop “cold flow” defects that weaken it structurally.
Injection pressures range from 35 to 150 MPa depending on part size and geometry, but the goal is always to use the minimum pressure needed for smooth, uniform filling. Mold clamping pressure sits between 25 and 45 MPa, enough to keep the mold shut and prevent material from flashing out along the parting line. A material cushion of about 5mm in the barrel ensures consistent shot-to-shot filling, and a decompression stroke of 5 to 15mm prevents drooling from the nozzle.
Because TPE solidifies quickly, cycle times are short compared to many other polymers. Thin-walled parts (under 2mm) typically cycle in 15 to 25 seconds. Thicker sections between 2mm and 6mm need 30 to 60 seconds. Adequate cooling channels in the mold are essential for pulling heat out quickly and uniformly.
Extrusion for Continuous Profiles
When the product is a tube, seal, gasket, or continuous profile rather than a discrete molded part, extrusion is the go-to process. TPE pellets are fed into a single-screw extruder that melts and pushes the material through a shaped die. For SEBS compounds, a typical starting temperature profile runs from 170°C at the feed zone up to 210°C at the die, then gets fine-tuned based on the specific grade and product. Softer compounds generally process at the lower end of the range. SBS extrusion temperatures stay between 150°C and 205°C and should not exceed that upper limit to avoid thermal degradation.
Overmolding TPE Onto Rigid Substrates
One of the most commercially valuable TPE techniques is overmolding, where a soft TPE layer is molded directly onto a rigid plastic substrate like polypropylene or ABS. This is how soft-grip tool handles, toothbrush grips, and many medical device housings are made.
The bond between TPE and substrate depends on three factors: chemical compatibility between the two materials, the TPE’s melt temperature (which determines how easily it flows over and bonds to the substrate), and surface cleanliness. The substrate insert must be completely free of dirt, dust, moisture, and skin oil. Handling with gloves is standard practice, because any contamination on the surface will compromise bond strength or cause outright failure.
There are two main approaches. Insert molding involves placing a pre-molded rigid part into a second mold and injecting TPE around it. Multi-shot molding uses a specialized machine that molds both the substrate and TPE in sequence without manual handling. Some TPEs behave quite differently depending on which method is used, so material selection and process selection go hand in hand.
How Cooling Shapes Final Properties
The rate at which TPE cools after forming has a direct effect on its crystalline structure and, by extension, its mechanical properties. In semicrystalline TPEs, slower cooling gives the hard segments more time to organize into crystals, producing higher stiffness and better heat resistance. Faster cooling limits crystal formation, resulting in a softer, more transparent material. Manufacturers can tune these properties by adjusting mold temperature and cooling time. A great variety of microstructures can be developed simply by changing crystallization conditions, including crystal size, volume fraction, and orientation.
Shrinkage is another cooling-dependent variable. Crystalline regions are denser than amorphous ones, so parts with higher crystallinity shrink more as they cool. Consistent mold cooling, with well-placed channels that pull heat out uniformly, prevents warping and dimensional variation from part to part.
Processing for Specialized Applications
Medical-grade TPE production adds layers of control that go beyond standard manufacturing. Parts that contact the body must meet biocompatibility standards defined by ISO 10993, which assesses how device materials interact with biological tissues based on the type of contact and how long it lasts. This means the raw TPE compound must be formulated with biocompatible additives, processed in controlled environments to prevent contamination, and tested for biological safety as part of a broader risk management process. The specific testing required depends on whether the part touches only skin, contacts mucosal tissue, or enters the bloodstream.
On the sustainability front, bio-based TPEs are an emerging category. Researchers have developed biodegradable thermoplastic elastomers from renewable feedstocks like plant-derived sugars and organic acids. One example uses a soft central block made from a common diol and glutaric acid, capped with hard polylactic acid (PLA) blocks. The mechanical and biodegradation properties can be tuned by adjusting the block lengths. Bio-based plastics overall still represent only about 0.5% of global production (roughly 2.3 million tonnes out of over 431 million), but capacity is projected to roughly double to 4.7 million tonnes by 2030.
Minimizing Defects During Production
The most common TPE processing problems come from getting the shear and temperature balance wrong. High shear during injection can orient the polymer chains, creating parts with uneven properties that are stronger in one direction and weaker in another. Using lower injection pressure, slower velocity, and higher melt temperature reduces this orientation effect. Short holding times and low holding pressures after the mold fills prevent the gate area from over-packing, which can cause internal stress and warping.
Flash, where thin films of material squeeze out along the mold parting line, happens when clamping pressure is insufficient or when the melt is too fluid. Proper mold maintenance and keeping the melt temperature within the recommended range for your specific TPE grade are the simplest preventive measures. Since TPE grades vary widely in viscosity and melt behavior, starting with the material supplier’s recommended processing window and adjusting from there is standard practice.