Kraton™ G SEBS-Comp. G7720 GI-B is a pre-compounded thermoplastic elastomer based on a styrene-ethylene/butylene-styrene triblock architecture. The “Comp.” designation indicates that the product is supplied as a formulated compound rather than a neat SEBS polymer, and the GI-B suffix functions as a processing and market identifier rather than a molecular-weight specification. Publicly available grade-specific numeric data for G7720 GI-B is limited; therefore, the property and processing ranges presented below are drawn from the Kraton G-series SEBS compound class and standard injection-moulding documentation. These ranges must be replaced by the current manufacturer’s technical data sheet for G7720 GI-B before production qualification.

The saturated ethylene/butylene midblock differentiates this product from butadiene-based SBS grades. Unsaturated butadiene midblocks undergo oxidative crosslinking and embrittlement under ultraviolet and ozone exposure, whereas the EB midblock resists this pathway. Styrene endblocks form glassy domains with a glass transition near 95 °C in the neat base system. These domains serve as physical crosslinks below service temperature and melt out when heated, giving the material thermoplastic processing and regrind potential. The same domain softening creates a service limitation: under continuous load, mechanical integrity decreases as temperature approaches 70–80 °C.

Drying is not mandatory for SEBS in the absence of surface moisture, because the polymer backbone does not absorb significant water. Pellet surface condensation remains the main moisture risk when bins or octabins are moved from cold storage to a humid production area. A desiccant hopper-dryer operated at 70–80 °C for 2–4 h, with a drying-air dew point of ≤ −20 °C, is recommended when storage relative humidity exceeds 60 % RH. The drying interval should be confirmed on the production floor; surface moisture can vary with pellet shape, packaging, and warehouse cycling.

Incoming inspection should include melt flow rate testing under 230 °C/5.0 kg using ISO 1133-1:2022, Shore A hardness by ASTM D2240, density by ASTM D792, and visual clarity on a standard plaque. Variation in melt flow rate of ±1–2 g/10 min relative to the target is not unusual for oil-extended SEBS compounds and is often caused by shipment-to-shipment differences in oil content or stabilizer dispersion. If such variation appears, barrel temperatures or injection speed should be adjusted before changing tooling, because flow variation can alter pressure drop, gate freeze time, and part packing.

Why does the pre-compounded GI-B grade behave differently from neat SEBS pellets?

The difference is the viscosity-to-hardness balance. Neat high-molecular-weight SEBS polymers often require oil extension or blending with polypropylene before injection moulding because their melt viscosity is too high for thin-wall filling. The pre-compounded GI-B product is supplied with an internal additive package that lowers hardness and increases melt flow. Class-representative values for G-series injection-moulding compounds at this hardness band include a melt flow rate of 5–15 g/10 min under 230 °C/5.0 kg, density of 0.89–0.92 g/cm³, and Shore A hardness of 60–70 using ASTM D2240 with a 15 s dwell. These values are typical of the formulated product class and are not a substitute for the specific G7720 GI-B data sheet.

Mechanical evaluation follows elastomer protocols. Tensile strength and elongation at break are measured on ISO 37:2017 dumbbells at 500 mm/min, with tensile strengths in the 5–10 MPa range and elongation at break of 450–700 %. Tear strength by ASTM D624 die C typically falls at 25–40 kN/m. Compression set by ASTM D395-18, Method B, for 22 h at 70 °C is generally 25–40 %. The compression set result is the most critical property for sealing applications because it describes incomplete recovery after prolonged compressive strain.

The table illustrates why a processor selects a pre-compounded grade rather than a neat SEBS: the compound sacrifices some tensile strength to gain processability. The neat polymer reference has higher tensile strength, but its melt flow rate is too low for many injection-moulded parts without aggressive screw heating and high injection pressure. The pre-compound is therefore appropriate when softness, lower compounding-related conversion steps, and low-density elastomeric performance outweigh ultimate tensile resistance.

Capillary rheometry data at multiple shear rates should be used for mould-filling simulation, because single-point melt flow rate cannot adequately predict pressure drop across thin gates. The melt exhibits pronounced shear thinning. Published processing guidance for SEBS injection grades recommends gate shear rates below 100,000 s⁻¹ to avoid melt fracture and surface jetting. If high injection velocity is used to fill a thin-wall cavity, surface flow marks can appear even when moisture has been adequately removed. The cause in such cases is gate shear stress exceeding the melt’s elastic response; corrective action includes a larger gate cross-section or a lower fill speed.

On a co-rotating twin-screw extruder with 40:1 L/D, barrel temperatures should start at 180–190 °C in the feed zone and increase to 210–230 °C at the die. Screw speed should be set so that the melt temperature at the screw tip remains below 240 °C. Above this limit, styrene-domain degradation can produce gel particles, yellowing, and a measurable loss of elongation at break. Aggressive kneading blocks should be avoided or spaced after the melting zone, because high shear can raise local melt temperature by 10–20 °C above barrel setpoint and create stagnant regions. A dedicated SEBS purge or polypropylene purge is recommended after processing PVC, SBS, or other polar or unsaturated materials, because residual material can cause phase separation, silver streaking, and mould deposit formation.

Injection moulding should use a general-purpose screw with a compression ratio of 2.2:1 to 3.0:1 and a shot capacity that uses 40–70 % of the barrel volume. Nozzle melt temperature is maintained at 200–220 °C; mould temperature between 20–40 °C is adequate for most unfilled soft-touch parts, although polished surfaces may require mould temperatures up to 50 °C. Because the compound freezes quickly in thin sections, gate thickness should be at least 1.0 mm for edge gates and at least 0.8 mm for subgates. Thin gates create premature freeze-off, prevent sufficient packing, and increase sink marks in thicker sections. Hot-runner manifolds should use full-round channels and avoid dead spots; manifold temperatures are held at 200–230 °C. Residence time should not exceed 8–10 min at processing temperature, and longer interruptions require purging or temperature setback.

Production failure modes for this compound class include gate blush and surface haze when the gate land is too short or the gate is overheated. Sink marks occur in thick sections when packing pressure is insufficient. Voids can form when the core temperature is too high or the shot volume is not properly buffered. Warpage arises from non-uniform melt orientation and differential shrinkage; reducing hold pressure and moving the gate to a thicker section is generally more effective than increasing cooling time alone. These failure modes define the practical design limits for G7720 GI-B components.

Overmoulding onto polypropylene is possible because the olefinic midblock can bond to polypropylene under sufficient melt temperature and mould pressure. The polypropylene substrate should be pre-heated to at least 40–60 °C before overmoulding to promote interfacial adhesion. In high-volume two-shot moulding cells, melt temperatures of 200–230 °C and substrate surface temperatures above 50 °C are generally used. Adhesion should be verified by a fixture peel method agreed between moulding and end-use parties, because bond strength is sensitive to mould-release residues, surface contamination, and substrate crystallinity.

If the part must survive hot-air ageing above 70 °C, which design changes are required?

The first change is to eliminate continuous compressive load or to reinforce the component with a rigid polypropylene or engineering-polymer insert. A gasket exposed to 80 °C can lose sealing force because compression set increases and the styrene domains soften. If the application is a static soft-touch grip over a rigid core, retained stress is lower and functional life may be longer. For dynamic seals, a TPV based on crosslinked EPDM generally has lower compression set at 100 °C and better resistance to hot hydrocarbon oils. The SEBS compound is preferred where clarity, low density, styrenic overmoulding, and low-temperature flexibility are valued more than hot-oil resistance.

Chemical resistance for G7720 GI-B must be evaluated for the formulated compound, not only the SEBS base polymer. Dilute aqueous acids and bases are generally less aggressive to the saturated olefinic backbone, but the internal process oil and stabilizer package may migrate. Aromatic solvents, chlorinated solvents, ketones, and strong oxidizing acids should be avoided because these fluids swell or degrade the styrenic and olefinic phases. Aliphatic hydrocarbon contact may produce reversible swelling and a temporary decrease in hardness; volume change under ISO 1817 should be measured for each service fluid. If the application involves intermittent contact with isopropanol or disinfectants, extraction testing and visual stress-cracking evaluation should be performed because solvents can extract low-molecular-weight additives and alter surface tack.

Regulatory assessment requires grade-specific documentation. The neat SEBS class is often evaluated under FDA 21 CFR 177.1810, EU 10/2011, USP Class VI, and ISO 10993-5. Because G7720 GI-B is a pre-compound, the addition of oils, antioxidants, or processing stabilizers can change the regulatory status. Published evidence for this specific configuration is limited; therefore, a grade-specific regulatory declaration from the manufacturer or compounder is mandatory before use in food-contact, medical, or toy applications. The same restriction applies to RoHS Directive 2011/65/EU and REACH SVHC compliance, which depend on the full compound formulation.

Compared with an SBS compound, the EB midblock gives improved resistance to ultraviolet radiation and ozone cracking, making G7720 GI-B more suitable for outdoor handled parts. Compared with a thermoplastic polyurethane of similar hardness, the SEBS compound has a lower density, typically 0.92 g/cm³ versus 1.10–1.20 g/cm³ for TPU, and generally lower abrasion resistance. Compared with a neat SEBS polymer, the pre-compound reduces converter-side mixing and increases melt flow, but it also reduces tensile strength and may increase additive migration. The product’s position is therefore best understood as an injection-moulding SEBS compound for soft-touch grips, overmoulded housings, gaskets, seals, flexible connectors, and consumer devices where upper service temperature remains below 70 °C and where end-use regulatory declarations support the application.

Batch-to-batch variation in a pre-compounded SEBS product is normally controlled by the compounder, but oil content and stabilizer dispersion can influence melt flow rate, hardness, and surface tack. Incoming inspection should track melt flow rate by ISO 1133-1:2022, Shore A hardness by ASTM D2240, density by ASTM D792, and compression set by ASTM D395-18. Regrind use should be limited to 20–30 % by weight without validation, because repeated heat history increases yellowness and lowers elongation at break measured by ISO 37:2017. The operational boundary is clear: continuous load at temperatures above 80 °C, hot hydrocarbon oil contact, aromatic solvent exposure, or strong oxidizing conditions should be avoided. For intermittent exposure to 100 °C, such as short sterilization cycles, parts should be fixtured to maintain shape and validated for dimensional stability and compression set.

Published grade-specific data for G7720 GI-B is limited in open-source repositories. The processing, property, and application statements above are therefore structured around the Kraton G-series SEBS compound class and standard injection-moulding practice. The current manufacturer’s technical data sheet and regulatory documentation remain the controlling references for any commercial part qualification or production release decision.