Kraton™ G SEBS-Comp. G7820 GU-N is a hydrogenated styrenic block copolymer compound supplied in pellet form. The polymer architecture consists of terminal polystyrene blocks that form a discrete glassy phase and a saturated poly(ethylene-co-butylene) midblock that provides elastomeric behavior without the residual backbone unsaturation present in styrene-butadiene-styrene block copolymers. The designation “SEBS-Comp.” indicates that the grade is a formulated compound rather than a neat SEBS resin; a polyolefin phase, paraffinic process oil, and stabilizer package are incorporated to control hardness, melt flow, surface friction, and compression set. The numeric model G7820 GU-N is supplier-specific ordering nomenclature; the suffix does not correspond to a standard polymer-class code. Because supplier-published grade-specific datasheet values are not available in this context, numerical ranges below are explicitly class-typical for compounded SEBS grades of similar segment and are not lot-release guarantees.

Density and hardness define the main specification boundaries. Class-typical compounded SEBS materials in this segment have density values between 0.88 g/cm³ and 0.95 g/cm³ when measured per ISO 1183-1 or ASTM D792. Hardness extends from 20 Shore A to 90 Shore A under ISO 868 or ASTM D2240; tensile strength as determined by ISO 37 Type 1A specimens commonly falls between 3 MPa and 12 MPa, while elongation at break spans 300% to 800%. Tear strength measured with ISO 34-1 Method B may range from 15 kN/m to 50 kN/m. Melt flow rate values are strongly formulation-dependent; processors should confirm the exact 230 °C/2.16 kg or 230 °C/5 kg ISO 1133-1 value from the certificate of analysis before tool trials.

The table separates the influence of compounding on hardness and tensile strength. Lower tensile strength relative to neat SEBS is expected because paraffinic oil expands the midblock free volume and dilutes the load-bearing polystyrene network. The practical effect is lower processing viscosity and higher flow length at equivalent wall thickness.

On production compounding lines, mineral filler and process oil are introduced downstream after the SEBS and polyolefin phases have achieved melt homogeneity. A corotating twin-screw extruder with L/D 40:1 to 48:1 and segmented conveying and kneading blocks prevents excessive shear heating. Typical zone temperatures are 150 °C at the feed throat, 180 °C in zones 2 and 3, 200 °C in zones 4 and 5, and 205 °C to 215 °C at the die plate. Melt temperature measured at the die should not exceed 230 °C; above 240 °C, gel bodies from degraded stabilizer or crosslinked polyolefin microdomains can appear in extruded strand. Residence time under melt state should be kept below 3 min when operating near the upper temperature limit. Strand pelletizing with a water slide at 25 °C to 35 °C produces cylindrical pellets; irregular pellet surfaces can indicate insufficient melt cooling or die buildup.

What processing constraints govern melt stability and phase integrity?

Shear heating in the metering zone and check ring, rather than barrel set points alone, determines local melt temperature. In reciprocating screw injection molding, a general-purpose screw with L/D 20:1 to 22:1 and a compression ratio of 2.2:1 to 2.8:1 is used. Barrel temperatures from feed zone to nozzle may be set at 170 °C, 185 °C, 200 °C, 210 °C, and 215 °C. Backpressure is held between 0.5 MPa and 1.5 MPa; backpressure above 3 MPa promotes melt temperature overshoot and visible color shift. Pre-drying at 80 °C for 2 h in a desiccant dryer is recommended when exposure to relative humidity above 60% is suspected, although SEBS compounds are less hygroscopic than thermoplastic polyurethane. Clamp force is calculated from projected area and cavity pressure; a 100 cm² projected area at 35 MPa cavity pressure requires approximately 350 kN clamp force. Processing at 70% to 80% of rated clamp force is standard to avoid flash while preserving venting.

Gate design affects anisotropy. For multi-cavity cold-runner tools, full-round runner diameters of 5 mm to 7 mm and subgates of 0.8 mm to 1.2 mm shear the compound less than point-gate configurations. Jetting in thick sections is reduced by locating gates adjacent to a flow-reducing rib or step; sequential valve gating is preferred for hot-runner systems when part mass exceeds 50 g. Weld-line tensile retention in SEBS compounds is normally lower than the bulk value; mold flow studies often show retention of 50% to 70% of tensile strength at weld lines. Published data for this specific configuration is limited for G7820 GU-N, so tool trials are required to confirm actual retention.

Mold shrinkage is anisotropic and depends on flow direction, wall thickness, and filler content. Unfilled soft grades can show shrinkage of 1.0% to 1.5% in the flow direction and 0.8% to 1.2% transverse to flow; filled SEBS compounds may exhibit lower absolute shrinkage. Shrinkage should be measured on plaques per ISO 294-4 after 24 h aging at 23 °C and 50% RH. Because the G7820 GU-N grade-specific shrinkage value is not provided here, a masterbatch-color trial plaque is recommended before cutting production tool steel.

For mold filling, capillary rheometry provides more useful data than a single melt flow rate value. Compounded SEBS melts are pseudoplastic; apparent viscosity may decrease from 300 Pa·s at 100 s⁻¹ to 80 Pa·s at 1000 s⁻¹ at 230 °C. This shear-thinning behavior supports thin-wall filling, but pressure loss in long cold runners can be higher than expected when the flow front cools. Flow length-to-thickness ratios above 300:1 are attainable only with high-flow formulations and fast injection speeds; published data for this specific configuration is limited.

Thermogravimetric analysis under nitrogen typically shows degradation onset above 300 °C for SEBS compounds, but this is not a processing target. Isothermal aging at 150 °C in air can cause oxidative embrittlement after 500 h to 1000 h, depending on antioxidant package. In dark interior parts, UV exposure is less critical than sustained heat; in exterior parts, carbon black or hindered amine stabilizers are used. The G7820 GU-N grade should be stored below 40 °C to prevent pellet blocking; storage in direct sunlight can raise pellet core temperature above 50 °C and cause tackiness.

Regrind use in molding is common. Because SEBS does not crosslink, sprues and rejected parts can be re-pelletized and blended with virgin material at 10% to 20% by weight without the property loss observed in thermoset rubber. However, repeated heat histories above 230 °C reduce elongation and increase the MFR; lot-to-lot regrind fraction should be controlled by weight and melt flow after 3 or more passes. Dryer residence time should not exceed 4 h to avoid thermal yellowing.

Performance boundaries versus unsaturated SBS and olefinic TPVs

The hydrogenated midblock in G7820 GU-N provides greater resistance to oxygen and ozone attack than unsaturated SBS in outdoor seals and automotive exterior parts. However, the styrenic glass domains limit high-temperature compression set; a typical compounded SEBS may reach compression set values of 25% to 50% after 22 h at 70 °C per ISO 815, while a peroxide-cured EPDM or a PP/EPDM TPV can show lower set at 100 °C or 125 °C. EPDM, however, requires irreversible crosslinking and does not enter melt-reprocessing loops; SEBS compounds re-melt and recover regrind into molding streams. Relative to thermoplastic polyurethane, the SEBS compound class exhibits lower tensile strength, lower abrasion resistance, and lower maximum service temperature, but it has lower moisture absorption, lower density, and generally higher flow-length for a given hardness. Olefinic TPVs may offer better oil resistance and compression set, but SEBS compounds usually provide lower density and softer feel at comparable hardness. These are class-level differences; published data for this specific configuration is limited.

Sealing components, soft-touch grips, and automotive interior parts are candidate application spaces for a compounded SEBS of this type. In automotive interior parts, VOC and fogging expectations require testing per VDA 278 and ISO 6452; SEBS compounds can be formulated with low-volatility white oils to reduce fogging, but higher oil loadings increase the risk of condensable emissions. Medical device applications require grade-specific biocompatibility testing according to ISO 10993-1; a material does not carry a USP Class VI claim by virtue of being SEBS. Food-contact status must be confirmed under 21 CFR 177.1810 or 21 CFR 177.2600 depending on end use and formulated composition. Published data for this specific configuration is limited for each application; therefore, end-product qualification remains mandatory.

Oil migration is a critical defect in two-component assemblies. When a soft SEBS compound is overmolded onto a rigid substrate, low-molecular-weight paraffinic oil can migrate into the substrate or into a mating surface, causing loss of softness and environmental stress cracking in polycarbonate. To assess emission or migration tendency, extraction or fogging methods such as VDA 278 and ISO 6452 are used. Published data for this specific configuration is limited.

When material selection requires documentation of regulatory conformity

Compliance statements cannot be reduced to a polymer class. The compounded SEBS grade may require supplier documentation covering REACH SVHC content under EC 1907/2006, heavy metals under RoHS 2011/65/EU Annex II, and residual solvent or monomer limits. For food-contact repeat-use articles, 21 CFR 177.1810 applies to styrene block copolymers subject to end-use migration testing; for potable water seals, NSF/ANSI 61 or KTW/BWGL documents are required. A request for the G7820 GU-N certificate of compliance should specify the regulatory annex, test method, and article surface-to-volume ratio; generic statements of “FDA approved” are not technically sufficient.

Incompatibilities include aromatic oils and solvents that plasticize the polystyrene domains, causing hardness loss and surface tack. Ketones, esters, and chlorinated solvents can swell or dissolve the midblock. Strong oxidizing agents attack the ethylene-butylene midblock under prolonged exposure. Amine-based slip agents or certain phenolic antioxidants should be avoided if interactions with the hydrogenated midblock are not screened; the specific stabilizer system in this grade is supplier-controlled.