Kraton Kraton™G SEBS-Comp. G7705 GI-B is introduced as a pre-compounded styrenic block copolymer elastomer. The “SEBS-Comp.” designation separates it from a neat hydrogenated SEBS such as an unmodified Kraton G series polymer, while the GI-B suffix is a commercial marker commonly associated with a general injection-molding package and a black pigment load. The suffix should not be read as a compositional specification; the pigment, stabilizer, processing aid, and oil-extension content must be confirmed from the lot certificate of analysis. Chemically, the material is based on a styrene-(ethylene/butylene)-styrene architecture in which polystyrene endblocks form physical crosslink domains and the hydrogenated ethylene-butylene midblock provides elastomeric recovery. The material is supplied in pellet form, and its melt-state behaviour is governed by microphase separation until sufficient shear and temperature are imposed. Published datasheets for this exact GI-B subtype are limited; therefore, the following technical discussion distinguishes class-level industrial data from grade-specific release values and does not reproduce unverified single-point properties from secondary sources. Where a specification is required, the appropriate documents are the certificate of analysis, a product stewardship bulletin, and, if applicable, a food-contact or medical conformity statement.

What separates this grade from a blend-it-yourself SEBS compound in injection moulding economics?

A pre-compounded grade differs from a formulation assembled on the production floor from a neat SEBS polymer, paraffinic oil, polypropylene, stabilizer, and pigment. In the latter case, melt blending often requires oil loadings of 20–50 parts per hundred resin and polypropylene additions of 10–25 phr to reach useful injection moulding viscosity. Those dry-blend operations introduce feeder error and can produce wide batch-to-batch melt-flow variation. In contrast, the compounded pellet moves dispersive shear history from the molder to the compounder. On a 25 mm twin-screw extruder with an L/D of 40:1, the compounding step disperses hard polymer domains and consistency is built into the pellet. The practical trade-off is that the molder cannot reformulate at the press to correct a hardness or flow issue. Class-level measurements on pre-compounded SEBS grades show that a transition from dry blending to compounded pellets typically narrows melt mass-flow rate variability, often below ±0.5 g/10 min at 230 °C/5 kg when controlled by ISO 1133-1:2022. Capillary rheometry at 1000 s⁻¹ can also show lower entrance pressure drop in a compounded pellet compared with a dry-blended equivalent, because the dispersed oil and polypropylene domains are already distributed into the SEBS matrix. The difference against a neat high-molecular-weight SEBS such as Kraton G1651 is expected to be a lower melt viscosity and easier thin-wall fill for the compound, but this comes with modified tensile strength, surface tack, and compression set.

On production-scale injection lines, drying is required only when moisture exceeds 0.05 % by weight. A dehumidifying dryer set to 80 °C for 2–4 h is typical for SEBS compounds of this class; the exact moisture limit should be verified against the lot certificate because condensed water in the metering section can cause splay and reduce ultimate elongation without necessarily reducing melt temperature. Screw selection for a 40–80 t clamp machine should favour a compression ratio of 2.2:1 to 2.8:1 and an L/D of 20:1 to 24:1. High-shear barrier screws designed for glass-filled polypropylene can generate excessive viscous heating because the melt compressibility of a hydrogenated SEBS compound at 200 °C is lower than that of a glass-fiber-reinforced polypropylene. Barrel zone setpoints from feed to nozzle are commonly 190–230 °C, with the nozzle maintained in the lower half of the range to reduce drool and gate stringing. The upper temperature boundary is significant because residence above 240 °C for extended periods accelerates oxidation of the ethylene-butylene midblock and shifts appearance and mechanical retention. Hot-runner systems with external heating are preferred over internal hot-runner heaters in small-diameter channels, where adiabatic shear plus heater input can exceed the degradation threshold. Published data for this specific configuration are limited; the stated boundaries are class-level processing guidance rather than grade-specific warranty limits.

Melt Rheology, Gate Freeze-Off, and Barrel Temperature Boundaries

Gate freeze-off controls packing and dimensional stability in thin-wall, low-hardness components. In SEBS compounds, the solidification front does not show the sharp crystallization exotherm associated with semi-crystalline polypropylene; effective freeze-off is better measured by pressure decay at the gate after transfer to hold pressure. If the gate diameter is below 0.8 mm for a nominal wall thickness of 2.0 mm, premature freeze-off can occur before cavity pressure reaches 30–40 MPa, producing sink marks and low knit-line strength. Injection velocity should be profiled so that flow-front shear rate does not exceed 20,000 s⁻¹ in the gate region; beyond that, polystyrene endblock orientation and uneven relaxation can create visible flow marks. Melt cushion should be maintained at 4–8 mm on a 40 mm screw. If the cushion falls below 4 mm, shot-weight variation can exceed 0.3 % on hot-runner tools, and short shots may occur without an alarm-level cushion drop. For black pigmented grades, a thermal processing window of ±5 °C across barrel zones is often required for colour consistency because the pigment package can be sensitive to local overheating, and the black colour can mask early thermal degradation until a mechanical property drop is measured.

The pseudoplastic response of the compound can be evaluated by capillary rheometry to ISO 11443:2021 at 200 °C and 230 °C. Class-level curves for pre-compounded SEBS elastomers show a power-law index below 0.4 at shear rates of 500–2000 s⁻¹, with the exact value dependent on oil content and polypropylene addition. This shear-thinning behaviour permits long thin-wall flow, but it also means that a reduction in screw rotation speed can raise apparent viscosity and increase cycle-to-cycle fill variation. Apparent viscosity at 1000 s⁻¹ and 230 °C for this material class can be in the range of 60–120 Pa·s; the range is not a grade-specific release value but provides a comparison with a TPU of equal hardness, which often exhibits higher low-shear viscosity and a more pronounced shear-thinning region. Direct gates with diameters below 0.8 mm can induce melt fracture at volumetric flow rates above 20 cm³/s in a cold-runner tool; a fan gate or tab gate is preferred for thin-wall parts with flow length-to-wall thickness ratios above 150:1. Multi-cavity tools with unbalanced runners can show flash at the cavity nearest the sprue while the farthest cavity shorts. A runner-balancing trial or pressure-loss simulation should be performed such that runner pressure loss does not exceed 15 % of total injection pressure; otherwise cavity-to-cavity shot variance can exceed 0.5 %.

Post-mould shrinkage in soft SEBS compounds can continue for 24 h after ejection. Dimensional checks should therefore be conditioned and measured according to ISO 294-3 rather than immediately after demoulding. The saturated ethylene-butylene midblock provides better oxidation resistance than an unsaturated styrene-butadiene-styrene midblock during melt processing, but the polystyrene terminal blocks can still undergo chain scission when residence time exceeds 5–8 min at 230 °C in a 40 mm screw. Degraded material may appear as a yellow shift in natural grades; in black grades the colour shift is masked, so weld-line tensile testing is necessary to detect retention loss. The practical processing window is therefore bounded by flow-induced shear heating at the lower end of throughput and oxidative degradation at the upper end of residence time.

The following table identifies the standard methods commonly applied to lot release and application qualification. The table lists standard codes, not measured values. Grade-specific values for G7705 GI-B must be read from the supplier certificate of analysis under the same specimen geometry and conditioning specified in the method.

Regulatory status must be confirmed on the final article, not inferred from the product name. For food-contact applications in the United States, the applicable citation for styrene block polymers is 21 CFR 177.1810, subject to the extraction limits and end-use restrictions in paragraph (c). In the European Union, a finished overmoulded article must comply with REACH Article 33 communication duties if any substance of very high concern is present above 0.1 % w/w. Under the RoHS Directive 2015/863, a black pigmented electrical or electronic component would be expected to meet the cadmium and lead thresholds of 100 mg/kg and 1000 mg/kg, respectively, but this must be confirmed on the final article because the GI-B pigment package can vary by lot. Medical device applications require a medical-grade lot and evidence generated under ISO 10993-5 for cytotoxicity and, where relevant, ISO 10993-10 for irritation and sensitization. No independent food-contact or medical conclusion can be drawn from the trade name alone.

Application usage of Kraton Kraton™G SEBS-Comp. G7705 GI-B is concentrated in injection-moulded components that require low hardness, elastic recovery, and reduced moisture uptake. These include device housing grips, protective corner bumpers, appliance seals, medical device handpieces, and footwear components. In load-bearing soft-touch components, the material selection does not rely solely on Shore A hardness because cut growth resistance, surface tack, and oil migration control the part lifetime. Class-level continuous use temperature for unfilled SEBS compounds is commonly 90–110 °C in air, but long-term heat ageing must be assessed to ISO 188 because oxidative degradation of the polystyrene endblocks and the ethylene-butylene midblock reduces ultimate elongation before visible embrittlement occurs. If the grade contains an oil-extension package, contact with mineral oil or low-polarity solvents can extract low-molecular-weight process oil. Immersion testing based on ISO 1817:2015 can quantify volume change; for dynamic seals, many processors limit volume change to ±10 % in the relevant service fluid, but the exact limit depends on seal geometry, compression ratio, and temperature. In applications requiring overmoulding onto polycarbonate or ABS, oil migration and the non-polar surface of the SEBS compound can contribute to environmental stress cracking or weak interfacial bonding; prototype parts should be cycled from -20 °C to 60 °C at 90 % RH before production release.

When surface polarity and adhesive overmoulding impose application limits

Overmoulding of a non-polar SEBS compound onto polar engineering thermoplastics can fail at the interface unless mechanical interlocking or surface activation is introduced. Plasma or corona treatment raises surface energy, but bond durability under temperature cycling from -20 °C to 60 °C must be verified with a cyclic adhesion protocol because no universal cyanoacrylate or epoxy primer exists for SEBS-to-polycarbonate bonding. In load-bearing or safety-critical joints, a TPU or a SEBS-polyurethane alloy is often selected instead because the urethane domains provide higher surface energy and better adhesion to polar adhesives. The GI-B grade retains the inherently non-polar surface of the ethylene-butylene midblock and has lower moisture uptake than thermoplastic polyurethane, but its abrasion resistance is typically below that of an ether-based TPU of equal Shore A hardness when measured by ISO 4649 mass loss. Under repeated dynamic flexing, the SEBS compound does not rely on covalent crosslinks, so permanent set can be higher than a peroxide-cured TPV. This same absence of covalent crosslinks permits regrind reincorporation; regrind levels of 10–20 wt% are common for non-appearance components, but weld-line tensile strength should be validated on weld-line specimens to ISO 37. The grade differs from a TPV not by melting temperature but by reprocessing reversibility and lower initial compression set after 22 h at 23 °C compared with some TPVs; conversely, at 70 °C, a TPV can show lower compression set because of its covalent EPDM crosslinks. Compared with a silicone elastomer, the SEBS compound is melt-reprocessable and can be reground, but it generally has a lower continuous use temperature and lower resistance to sterilisation by superheated steam.

Footwear and cold-climate components exploit the low-temperature flexibility of the ethylene-butylene midblock. The glass transition temperature of the EB midblock in SEBS architectures is commonly below -50 °C, which preserves flexibility without external plasticizer migration. When processed with a physical blowing agent or a chemical foaming agent, cell growth is governed by pressure decay at the gate and melt strength at the blowing temperature. The combination of high melt strength and shear-thinning behaviour supports microcellular foam densities in the range 0.7–0.9 g/cm³ when measured by ISO 1183-1, but the exact range for this GI-B grade is controlled by the supplier’s additive package and the injection unit’s gas dosing capability. Published data for this specific configuration are limited; a tool trial is required to establish the foaming window, gas dosing profile, and post-foam dimensional recovery before production release.