Kraton™ G SEBS-Comp. G7820 GU-B is a hydrogenated styrenic block copolymer compound supplied as ready-to-process pellets. The base architecture is an A-B-A triblock in which styrenic end-blocks associate into glassy domains at ambient temperature while the hydrogenated ethylene/butylene midblock remains elastomeric. The hydrogenation step removes most residual olefinic unsaturation from the midblock, which distinguishes this grade from unsaturated styrene-butadiene-styrene products and improves thermo-oxidative and ultraviolet aging resistance. The “SEBS-Comp.” designation indicates that the material is not a neat SEBS crumb or powder but a formulated compound with stabilizers and processing modifiers incorporated before pelletization. This allows injection molders and extruders to feed the product directly without a separate oil-extension or polyolefin let-down step. Pellet geometry, bulk density, and fines content are controlled for vacuum conveying, hopper mass-flow, and gravimetric feeding on continuous production lines.

Compositional Markers and Specification Sheet Structure

The grade identifier G7820 positions the material within the Kraton G-series hydrogenated block copolymer portfolio; the exact styrene-to-rubber ratio, midblock molecular weight, and diblock content are defined by the manufacturing specification and reported on the certificate of analysis. Incoming quality control for this product generally includes melt mass-flow rate under 5 kg load at 230 °C according to ISO 1133-1:2022 or ASTM D1238, density by ISO 1183-1:2019 or ASTM D792, Shore A hardness by ISO 48-4 or ASTM D2240, tensile stress at break and elongation at break by ISO 37 or ASTM D638, and tear strength by ISO 34-1. Where the compound contains high-consistency additives or mineral fillers, ash content and pellet moisture are also specified. Published data for this specific configuration is limited, and converter validation should compare lot-specific certificate-of-analysis values against assigned critical-to-quality limits rather than relying on class-typical SEBS compound data.

What Differentiates This Compound from Unmodified SEBS and from Unsaturated SBS?

At the molecular level, the hydrogenated ethylene/butylene midblock gives G7820 GU-B a different degradation pathway profile than SBS. Unsaturated SBS grades are typically limited by oxidative chain scission and crosslinking under continuous heat above 80–90 °C; hydrogenated SEBS grades can sustain higher continuous service temperature, although creep and compression set still reduce the upper limit compared with crosslinked elastomers. Differences from unmodified SEBS base polymers such as G1652 or G1651 are equally significant. Neat SEBS crumb requires intensive oil absorption and polyolefin blending to reach processable hardness and cost targets, often on twin-screw equipment with liquid injection at precisely metered rates. In G7820 GU-B, the compounding step shifts that responsibility to the supplier, and the converter receives a pelletized material with reduced formulation sensitivity and improved lot-to-lot viscosity control. In comparison to olefinic TPVs, the SEBS compound generally offers lower density, better clarity when unfilled, and softer-touch surface character, but lower resistance to hot oil and permanent set.

On production-scale injection-molding machines with 20:1–25:1 L/D ratio and compression ratios of 2.0:1–3.0:1, barrel profiles for hydrogenated SBC compounds of this type are frequently set from 180 °C in the rear zone to 220 °C at the nozzle. Melt temperatures above 240 °C risk stabilizer decomposition and gel-particle formation; visible fisheyes in transparent parts are a common failure signal. Mold temperatures between 20 °C and 50 °C are used to improve surface gloss and reduce cycle time, but flow length in thin-wall sections may require higher mold temperatures at the expense of cycle. Pre-drying is required when pellet surface moisture exceeds 0.05% by weight or when storage has occurred at relative humidity above 60% RH; a dehumidifying dryer set at 70–80 °C for 2–4 h is typical. Vacuum conveying lines should be purged with dry air to avoid reintroducing moisture. For extrusion, single-screw machines with 24:1–30:1 L/D and barrier-flight screws designed for low-shear operation are acceptable. Batch-to-batch variation in pellet surface moisture remains a known bottleneck when material moves from cold storage to a warm production bay without sealed hopper conditioning.

Multi-cavity injection molds for soft-touch grips often run on hydraulic or electric toggle machines with 800–2,500 kN clamp force; the main process conflict is not clamping force but plasticating rate. Because SEBS compounds have high viscosity at low shear and low thermal diffusivity, screw recovery time can limit cycle time in high-cavitation tools. Screws with low compression ratios and deep flights are preferred to prevent melt overheating. Three-zone screws with compression ratio 2.0:1–2.5:1 and L/D 24:1–30:1 are generally suitable. Grooved feed sections are not necessary and can raise shear heating and pellet bridging. If a Maddock mixing section is used, the shear gap should be checked for excessive temperature increase at maximum screw speed. In hot-runner systems, the low thermal conductivity of SEBS compounds increases the risk of cold-stagnation layers in externally heated manifolds with low shear. Hot-runner nozzle tips should be profiled for amorphous styrenic block copolymers; sharp transition angles and dead spots generate black specks after color changes. If the material is processed on a machine previously running flexible PVC, purging with a styrenic or polyolefin cleaning compound is required because residual PVC decomposes and releases hydrogen chloride, which attacks the stabilizer package.

Failure modes observed on production lines include gate blush, flow marks, and brown specks after color change. Gate blush in SEBS compounds is often caused by excessive injection velocity through a restricted gate, which induces local shear heating and surface stretching. Reducing velocity and increasing gate land length tends to reduce blush. Brown or black specks after color change frequently arise from degraded stagnant material in hot-runner manifolds; color changes from black to natural require a dedicated screw and barrel purge sequence. The compound’s elastic nature also affects gate freeze time; premature holding-pressure switchover can cause gate wash and dimensional variation. Processing-window studies using a design-of-experiments matrix with injection velocity, packing pressure, and mold temperature are recommended because the failure boundaries are not symmetrical around the optimum.

Melt viscosity of hydrogenated SBC compounds is shear-thinning but less temperature-sensitive than that of semicrystalline polyolefins. Increasing barrel temperature does not reduce viscosity as rapidly as raising injection speed or decreasing part thickness; as a result, filling imbalances are better corrected by gate and runner design than by raising melt temperature. Spiral flow testing under fixed injection pressure is used to compare batch-to-batch lot fluidity. The melt mass-flow rate under 5 kg load at 230 °C is a quality-control parameter, but it does not capture high-shear behavior; a capillary rheometer or Moldflow viscosity model using ISO 11443 data is needed for scientific mold-filling analysis. For lot acceptance, tensile specimens are often die-cut from 2 mm compression-molded sheets or injection-molded plaques. The orientation effect in injection-molded specimens can produce tensile strength differences depending on flow direction; specimens should be cut parallel and perpendicular to flow to quantify anisotropy. Because the compound is soft, load at 100% elongation is less reproducible than tensile stress at break unless test speed is tightly controlled.

When Hydrogenated SBC Compounds Replace Plasticized PVC in Medical Device Housings

G7820 GU-B is evaluated in applications where soft-touch grip, clarity, processability, and regulatory simplicity outweigh the lower set resistance of SEBS compounds. Typical uses include overmolding onto polyolefin substrates, clear appliance seals, protective medical device components, and extruded tubing. The compound is not a thermoset vulcanizate; continuous exposure above 90 °C or repeated steam sterilization at 121 °C requires creep and compression-set evaluation per ISO 815-1. In flexible PVC replacement, the product avoids ortho-phthalate plasticizer management, but oil retention and permanent set are generally poorer than those of olefinic TPVs. Dynamic seals with tight permanent-set limits are not the first selection. For medical applications, USP Class VI and FDA food-contact suitability must be confirmed against the exact lot; published data for this specific configuration is limited, and biological reactivity testing under the final sterilization cycle is mandatory.

Unlike plasticized PVC, G7820 GU-B does not rely on a low-molecular-weight plasticizer for softness. Softness is built into the molecular architecture through the rubbery ethylene/butylene midblock. Consequently, plasticizer migration into adjacent polyolefin, ABS, or polycarbonate parts is not the primary concern. However, the compounded stabilizer package and any processing oil used by the formulator can exude under high-temperature storage; a fogging test per DIN 75201 or ISO 6452 may be specified for automotive interior applications. For medical tubing, extractables testing per ISO 10993-12 is required, and the compound should be characterized for mineral oil or silicone-based additive migration before final qualification. UV stabilization of the compound is achieved through hindered-amine or benzotriazole-type stabilizers; the exact package is supplier-defined. QUV exposure under ISO 4892-2 or ASTM G154 should be used to set replacement intervals.

One critical threshold in SEBS compound selection is additive loading. Addition of polypropylene or mineral fillers to increase hardness and modulus can create a property cliff-edge between 15% and 25% addition by weight, where elongation at break and elastic recovery change rapidly. Converter-specific dilution of G7820 GU-B with regrind or additional polyolefin should be limited to the supplier’s recommended maximum; repeated regrind levels above 20% can reduce tensile strength and increase hardness drift. If the converter dry-blends oil or filler to reach a lower durometer, the resulting mixture is no longer the original compound and should be revalidated for consistency, extractables, and long-term aging.

Regulatory Documentation and Compliance Matrix

The following documentation should be requested from the supplier for each production lot or supply agreement. Compliance statements must cover the final compounded pellet and not only the base SEBS polymer, because additive packages can affect migration, extractables, and regional regulatory status.

Pellet moisture uptake is slow because the compound is hydrophobic, but condensation on cold pellets during warehouse-to-production transfer is the principal moisture source. If the material is stored at 5 °C and opened in a 25 °C, 60% RH production bay, surface condensation can form within minutes. Sealed gaylord liners or hopper dryers with desiccant beds are considered baseline controls. Conveying air should be dried to a dew point below -30 °C. High humidity increases the risk of surface voids in thick extruded cross-sections, not only from water vapor but also from entrained air carried by irregular pellets. For incoming inspection, pellet moisture, bulk density, and melt flow rate should be trended together; a shift in bulk density without a corresponding melt flow change often indicates pellet geometry variation or fines accumulation, which can disturb gravimetric feeder accuracy on continuous extrusion lines.