Kuraray SEPTON™ SEBS 8006 is a linear hydrogenated styrene-butadiene block copolymer supplied as pelletised feedstock for thermoplastic elastomer compounding. The grade has a nominal styrene content of 20 mass% and a typical specific gravity of 0.91 as determined by ASTM D792. Its elastic recovery, low hardness, and hydrogenated ethylene-butylene midblock distinguish it from styrene-butadiene-styrene block copolymers that lack midblock saturation. The material is used in soft-touch grips, sealing profiles, flexible tubing, sheet, and compounded TPE formulations where a Shore hardness below approximately 70 A and good long-term ageing are required. The product is differentiated from higher-styrene SEBS grades by its lower modulus and from lower-molecular-weight grades by its higher melt viscosity and tensile strength. Representative mechanical data for neat pressed film include a tensile strength at break of 30 MPa, elongation at break of 500%, and a 100% modulus of 2.5 MPa when tested according to ASTM D638-14.

Because the styrene end-blocks form physical crosslinks at service temperature, the 20 mass% styrene content provides a balance between softness and strength. At processing temperatures above the styrene glass transition, these domains soften, allowing melt processing. On cooling, the domains re-form and restore elastomeric integrity. This behaviour allows the use of conventional thermoplastic equipment without vulcanisation. The material is often blended with polypropylene, high-density polyethylene, or polystyrene to raise hardness and improve processability; however, blend morphology affects oil retention and tear strength.

What distinguishes the 20 mass% styrene architecture of SEPTON 8006 from higher-styrene SEBS grades?

In higher-styrene SEBS grades such as SEPTON 8076, the styrene content is specified at 30 mass%, which raises the volume fraction of the hard domain phase and produces a harder, higher-modulus material. The corresponding increase in styrene domain continuity improves resistance to creep and reduces compression set at room temperature, but it also reduces the rubbery character and may require higher melt processing temperatures. SEPTON 8006, at 20 mass% styrene, has a typical Shore hardness of 64 A and an elongation at break near 500%; it is therefore better suited to applications requiring high elongation, low hardness, and low flexural modulus. Compared with SEPTON 8004, a lower-viscosity grade with the same nominal styrene content, SEPTON 8006 exhibits lower melt flow and higher cohesive strength. Published datasheets list SEPTON 8006 melt mass-flow rate at 0.5 g/10 min under 230 °C and 2.16 kg load according to ASTM D1238-20, whereas moulding grades with higher MFR are preferred for long flow paths and thin walls.

The following representative values apply to compression-moulded film; lot-specific values should be confirmed from the certificate of analysis.

The values in the table are not to be interpreted as specification limits. Neat resin data do not predict final compound properties when oil, filler, or polyolefin are added; formulation-specific testing under ASTM D638-14 and ASTM D2240-15 is required. The difference between neat resin hardness and final compound hardness is a function of oil loading and filler surface area.

Compounding: torque, dispersion, and oil uptake

On a co-rotating twin-screw extruder with an L/D ratio of 40:1, SEPTON 8006 is typically processed with barrel set temperatures from 170 °C to 230 °C across the profile. Because the grade has a comparatively low melt flow, initial melting generates high torque in the plastification zone. Side-feed of paraffinic oil after the polymer melting section is used to reduce screw slip and to prevent oil from coating pellets before melting. When oil is injected too early, torque can fall sharply, melt pressure instability increases, and strand pelletisation becomes inconsistent. Published data for this specific configuration is limited to processor reports; however, the phenomenon is consistent with the reduction in melt viscosity produced by oil plasticisation. Processors typically pre-dry regrind or materials stored above 60% relative humidity at 60–80 °C for 2–4 h in a desiccant dryer to maintain pellet moisture below 0.05 mass%.

For injection moulding, melt temperatures of 190–230 °C and mould temperatures of 10–40 °C are commonly used for SEBS-based compounds. Because SEPTON 8006 has a high molecular weight, thin-wall filling may require higher injection pressures than using higher-MFR grades. Gates should be sized for shear-thinning melt fronts; excessive shear at the gate can introduce frictional heating and surface defects. Clamp force requirements are formulation-dependent and are normally calculated per projected part area, but published data for a single universal clamp-force value is not meaningful.

Grade selection between SEPTON 8004, 8006, and 8076 is primarily driven by hardness, melt flow, and oil tolerance. SEPTON 8004 provides higher melt flow for complex moulds and high-speed extrusion, but lower ultimate tensile strength. SEPTON 8076 shifts compound hardness upward and improves mar resistance, but it can increase modulus and reduce elastic recovery in very soft compounds. SEPTON 8006 occupies a middle position that favours high elongation and low hardness retention after oil extension. For a given oil loading, lower styrene content increases the distance between styrene domains, which can increase oil uptake but also increases the risk of oil bleed at high loadings.

If a soft-touch part must meet Shore A 30 without plasticiser migration, how should 8006 be compounded with paraffinic oil?

Low hardness in SEBS compounds is commonly achieved by addition of white paraffinic oil or hydrotreated mineral oil. With SEPTON 8006, oil loadings between 30 phr and 80 phr can depress Shore hardness to approximately 25–50 A depending on oil molecular weight and any polypropylene content. Oils with a low pour point and narrow molecular weight distribution are preferred because they lower glass transition temperatures without increasing bleed. Oil retention is governed by the styrene endblock domains and the rubber midblock; if the oil molecular weight is too low, migration to the surface occurs after compression moulding. A hardness of 30 A may require an oil loading near 70 phr, but this should be confirmed by compounding trials because the neat tensile strength drops as oil content increases. ASTM D2240 hardness and ASTM D638 tensile tests should be performed on final plaques, and the compound should be examined for surface exudation after 7 days at room temperature and after accelerated ageing at 60 °C for 24 h. Compression set under ASTM D395-18 at 70 °C may increase as oil loading increases, and formulations requiring low compression set may require partial oil replacement with low-density polyethylene or polypropylene.

For dynamic seals, the low styrene content of SEPTON 8006 reduces stress relaxation at room temperature, but compression set after ageing at 100 °C is inferior to crosslinked rubber. In automotive sealing systems, the compound must be selected according to ASTM D395-18 compression set under service-specific temperatures and the part must be validated for low-temperature recovery using ASTM D1054-19 rebound resilience or ISO 4662. Because the grade is thermoplastic, repeated reprocessing can shift the styrene domain morphology and reduce tensile strength; the amount of recycled regrind is typically limited to 20–30 mass% unless incoming lot-specific MFR and Shore hardness are monitored.

In extruded sealing profiles and automotive interior skins, SEPTON 8006 is often blended with polypropylene and a phenolic or phosphite stabiliser to maintain melt stability during repeated reprocessing. The hydrogenated midblock provides better resistance to ozone and ultraviolet ageing than unsaturated SBS, but long-term outdoor exposure still requires UV absorbers and hindered amine light stabilisers. ASTM D1149-18 ozone testing and ISO 4892-2 xenon-arc weathering are used to qualify compounding packages. Without stabilisation, surface tack and oxidative embrittlement can occur at elevated service temperatures.

Limitations in oxidative and UV environments

The oxidation resistance of the hydrogenated midblock is superior to that of unsaturated SBS, but the material is not intrinsically immune to oxidative degradation. Processing at melt temperatures above 280 °C can initiate chain scission and discolouration; the recommended melt temperature range is 190–230 °C. In hot-air ageing, antioxidants based on hindered phenols and secondary phosphites are used at addition levels of 0.1–0.3 mass%; published data for specific stabiliser combinations is limited. For flame-retardant grades, halogenated additives may be avoided because they can promote acid-catalysed degradation at high processing temperatures. The grade is not recommended for continuous immersion in aliphatic or aromatic hydrocarbon solvents because the ethylene-butylene midblock swells. Food-contact status is only valid when the final article is formulated with appropriate food-contact additives under FDA 21 CFR 177.1810 or equivalent regional regulation. The European REACH Regulation (EC) No 1907/2006 and RoHS Directive 2011/65/EU requirements are commonly addressed through the material safety data sheet and supplier declarations.

Chemical compatibility should be assessed by immersion testing according to ASTM D471-16. In aliphatic hydrocarbons, the ethylene-butylene midblock exhibits swelling; in polar solvents such as water and dilute acids, the material is relatively stable. Use of the hydrogenated midblock improves resistance to ozone attack compared with SBS, but ozone testing under ASTM D1149-18 is still recommended for outdoor profiles.

In coextrusion of a soft-touch grip over a rigid polypropylene core, SEPTON 8006-based compounds are selected because the low styrene content reduces interfacial hardness mismatch. Adhesion to polypropylene can be improved by using a tie layer or by blending the compound with polypropylene, typically 10–30 mass%, because the polypropylene domains co-crystallise with the substrate. The final peel adhesion should be measured according to ASTM D903-98 or a relevant internal peel test, because published data for specific part geometries is limited. Under cyclic loading, the compound’s elastic recovery reduces permanent set when the typical service temperature is below 70 °C; above this limit, thermal softening of the styrene domains accelerates creep and compression set.