Styrene-butadiene-styrene block copolymers are two-phase materials in which polystyrene end-blocks form glassy domains that anchor an elastomeric polybutadiene midblock network. Asahi Kasei Asaprene™ SBS T-411G is a linear, oil-extended SBS grade supplied with 50 parts by weight of paraffinic extender oil per 100 parts by weight of polymer. The bound styrene content is reported at 30 wt%. The oil extension lowers melt viscosity and permits direct compounding into soft injection-moulded items without the high mixing energy required for neat SBS. Typical downstream operations include footwear sidewalls, unit soles, moulded toys, anti-slip mats, and impact-modifier masterbatches for styrenic and polyolefinic matrices. The product is characterised by a specific gravity of 0.93 g/cm³ under ISO 1183-1:2019 and a Shore A hardness near 72 when injection-moulded or compression-moulded under standard conditions. The producer supplies T-411G in pellet form; because the extender oil is incorporated before pelletising, it functions as an internal plasticiser rather than as a cold post-added process oil. Published data for exact lot-dependent values should be confirmed against the current certificate of analysis.

When T-411G Replaces Neat SBS in Injection-Moulded Footwear Compounds

Replacement of a neat SBS with T-411G alters the processing envelope before the first compounding stage. The additional 33 wt% oil fraction in the pellet reduces the energy input required to reach homogeneous melt temperature. On a reciprocating-screw injection machine with a general-purpose screw of L/D 20:1 and compression ratio 2.5:1, melt-temperature set points of 160 °C to 190 °C are sufficient. The hydraulic clamp requirement is governed by projected area; for thin-wall soles less than 3 mm, typical injection pressures fall between 50 MPa and 80 MPa. Because T-411G is not hygroscopic, oven drying is unnecessary at indoor warehouse humidity below 60% RH. If bags have been stored outdoors or condensation is visible, tray drying at 60 °C for 2 h lowers surface moisture below 0.05 wt% and prevents splay in the gate area.

Mould temperature controls surface appearance and weld-line strength. A mould temperature of 20 °C to 40 °C yields rapid cycle times but can freeze flow fronts prematurely in multi-gated soles. Raising the tool surface to 50 °C improves knit-line integrity at the expense of cooling time. Because the butadiene midblock is unsaturated, hold pressure and back pressure should be selected to avoid shear heating above 200 °C; melt temperatures above 220 °C for more than 5 min initiate oxidation and gel formation, observable as black specks in translucent or light-coloured soles. A general recommendation is to place the gate in the thickest section and to use a cold or slightly warm runner; the oil-extended melt tends to jet when a small gate feeds a thin rib, so gate land lengths below 0.8 mm require reduced injection speed.

At a nominal 30 wt% bound styrene, T-411G retains a continuous polystyrene domain structure below the service temperature limit of the styrene glass transition. The paraffinic oil partitions preferentially into the polybutadiene phase, reducing the rubber-phase glass transition and lowering compound modulus. In tensile testing according to ISO 37:2017 using a 500 mm/min crosshead speed, representative values for a compression-moulded and conditioned sheet include tensile strength of 18 MPa, elongation at break of 750%, and 300% modulus of 2.0 MPa. Hardness by ISO 868:2003 is 72 Shore A. Melt flow rate under ISO 1133-1:2022 at 190 °C and 5 kg is reported in the range of 2.5 g/10 min to 4.5 g/10 min for typical production lots. Density by ISO 1183-1:2019 is 0.93 g/cm³. These values place T-411G in the low-viscosity segment of oil-extended SBS grades; they are not specification limits and do not replace lot-specific certificates.

Oil extension also alters filler acceptance. Because the extender oil is present before the compounding stage, talc, calcium carbonate, and silica can be incorporated at lower rotor temperatures than in neat SBS. In high-shear twin-screw compounding on a co-rotating line with L/D 40:1, a temperature profile from 160 °C in the feed zone to 190 °C at the die retains melt stability while dispersing filler agglomerates. Dispersion quality is assessed by sieve retention and by sheet tensile uniformity across three zones of a compression-moulded plaque. Published data for this specific configuration is limited; therefore, filler-specific processing windows must be verified by pilot trials rather than inferred from resin-only flow data.

What Are the Rheological and Compositional Boundaries of T-411G?

Rheological boundaries are set by both viscosity and temperature-sensitive degradation. The melt flow rate under 190 °C/5 kg does not capture high-shear injection behaviour; capillary rheometry at 180 °C and shear rates from 100 s⁻¹ to 10,000 s⁻¹ is required for gate and runner design. At low shear rates the oil-extended melt remains pseudoplastic; at shear rates above 5,000 s⁻¹, melt fracture can occur when the melt temperature falls below 160 °C. This defect is a die-surface phenomenon that can be mitigated by raising the die temperature to 190 °C or by using a wider land length. Because the grade contains a high oil fraction, melt compressibility is greater than in neat SBS; injection machines without check-ring seals may show cushion instability when shot size exceeds 70% of barrel capacity.

Thermal-oxidative degradation of the unsaturated polybutadiene segment is the principal processing constraint. Under air exposure, the oxidation rate increases rapidly above 200 °C. Processing should therefore avoid melt temperatures above 220 °C, hot-runner dead spots, or residence times beyond 5 min. In moulded parts, gel particles appear first at the melt-cushion boundary because oxygen ingress into the screw check ring is highest there. On a production line, the onset is detected by an increase in injection pressure and a simultaneous reduction in melt flow rate of purged material. These failure modes are not corrected by increasing back pressure; they require barrel cleanout and a reduction in the rear-zone temperature to 150 °C. Aromatic process oils should be avoided because they plasticise the polystyrene end-blocks and reduce tensile strength. Strong oxidising agents and unsaturated drying oils are also incompatible with the polybutadiene segment.

Where T-411G is used in consumer goods, the final compound, not the raw polymer, determines regulatory status. REACH Regulation (EC) No 1907/2006 applies to the imported polymer as a substance or mixture; a Safety Data Sheet should confirm the registration status of the oil-extended form. Restriction of hazardous substances under 2011/65/EU is formulation-dependent: the SBS and paraffinic oil fraction normally do not introduce lead, cadmium, mercury, hexavalent chromium, PBB, or PBDE, but pigments, flame retardants, and stabilisers must be evaluated separately. No food-contact status is claimed for T-411G; if the compound is intended for repeated food-contact use, migration testing under Regulation (EU) 10/2011 or 21 CFR 177.1810 is required. The base polymer is not crosslinked, so regrind from runners and rejects can be re-pelletised, but total regrind levels above 20 wt% reduce tensile strength in proportion to thermal history. For outdoor applications, UV stabilisation is mandatory because the unsaturated midblock is susceptible to ozone and photo-oxidative chain scission.

Comparative Position Against Neat SBS, SEBS, and Vulcanised Rubber

The principal differences between T-411G and a neat SBS of equivalent styrene content are oil content, melt viscosity, hardness, and tensile strength. A neat SBS with 30 wt% styrene typically requires higher processing temperatures or lower molecular weight to reach an equivalent melt flow. After injection moulding, the neat grade yields a harder compound, often above 80 Shore A, while T-411G produces 72 Shore A without additional plasticiser. Consequently, T-411G is selected where reduced hardness and improved flow must be achieved without post-polymerisation oil addition. Because the oil is already distributed in the pellet, lot-to-lot oil variation is generally lower than in dry-blend oil-extension processes, although extrusion shear is still required to fully homogenise the melt.

Compared with hydrogenated SEBS grades, T-411G retains an unsaturated polybutadiene midblock. The saturated midblock of SEBS provides superior resistance to ozone, UV, and long-term heat ageing; under ISO 188:2011 hot-air ageing at 70 °C for 168 h, SEBS compounds typically show smaller hardness and tensile retention than SBS compounds. T-411G compensates for that limitation by offering lower melt viscosity, lower compound cost, and easier adhesion to styrenic substrates. It is not recommended for exterior parts exposed to UV without carbon black or stabiliser packages. For overmoulding onto polyamide or polyester, a maleic anhydride-functionalised SEBS is required because T-411G is not reactive and does not develop comparable polar-substrate adhesion.

Against vulcanised rubber compounds based on SBR or EPDM, T-411G is melt-processable without a cure system. Injection moulding cycle time is therefore shorter, and sprues and runners can be reground. However, resistance to compression set, hot-oil swell, and continuous service temperature above 70 °C is lower than for a sulphur-cured EPDM compound. Where the service environment includes ozone, hot grease, or continuous deformation, T-411G requires reformulation with a hydrogenated grade or replacement with a thermoset elastomer. This boundary defines the product’s most consistent industrial role: a low-viscosity, oil-extended SBS for high-flow moulding and cost-sensitive compounding where the unsaturated butadiene midblock is not exposed to sustained oxidative attack.