Kraton™ G1642 H is a clear, linear SEBS triblock copolymer consisting of polystyrene terminal blocks and a hydrogenated ethylene/butylene midblock. The grade is supplied as dusted pellets, with a nominal polystyrene content of 20 wt%, a specific gravity of 0.91 g/cm³, and a melt mass-flow rate of 3.0 g/10 min at 230 °C under 5 kg load when tested according to ISO 1133-1:2022. The hydrogenation of the midblock eliminates the main-chain unsaturation present in SBS, thereby improving resistance to oxidative degradation and reducing UV-induced scission; however, neat SEBS still requires stabilization for prolonged outdoor exposure. Under ISO 1043-1, the material is classified as TPS-SEBS. The combination of high molecular weight, low styrene content, and moderate hardness makes G1642 H a base elastomer for highly oil-extended, soft-touch, and clear compounds where processing temperature is constrained by the end-block domain structure.

These values are typical and are not release limits. The dusted pellet surface may contribute minor inorganic residue; lot-specific certificates of analysis should be used when the material is converted into pharmaceutical or food-contact articles.

In soft-touch overmolding and consumer grips, G1642 H is often melt-blended with polypropylene homopolymer or random copolymer, paraffinic white oil, and calcium carbonate rather than processed neat. A polypropylene addition of 10–25 wt% raises the continuous-use stiffness, lowers compression set, and improves the melt strength of the SEBS; the penalty is increased hardness and reduced transparency if crystal size is not controlled by rapid cooling. Paraffinic oil loadings of 50–150 phr are common for translucent compounds, with the upper limit set by surface oil bloom and tensile strength retention. Compression set is normally determined at 70 °C for 22 h under 25% deflection according to ISO 815-1, and the result is highly dependent on oil content and plasticizer migration during the test. In filled compounds, calcium carbonate at 5–20 wt% reduces shrinkage but decreases tear strength, as measured by ISO 34-1, particularly when the filler is not fully wetted by the polymer-oil melt.

What Distinguishes G1642 H from Other Kraton SEBS Grades in Oil Extension?

Kraton™ G1641 H has a higher nominal polystyrene content of 33 wt%; the additional styrenic domains raise hardness, modulus, and tensile strength but reduce paraffinic oil uptake before surface tack develops. G1642 H, with its 20 wt% styrene content, produces softer, more rubbery compounds at equal oil loading and retains elongation better at low temperature. Kraton™ G1643 H has a similar styrene content but a lower molecular weight, which increases melt flow and improves filling of long, thin flow paths. The lower molecular weight also reduces tensile strength and oil-holding capacity; G1643 H may require higher addition levels of polypropylene or fillers to maintain creep resistance. Kraton™ G1650 H and G1651 H occupy the higher-styrene, higher-molecular-weight segment and are selected when toughness and high-temperature properties dominate over softness and melt flow. G1642 H therefore sits in an intermediate region: its melt flow is sufficient for injection moulding, while its molecular weight retains cohesive strength in extended formulations.

In twin-screw compounding of highly oil-filled G1642 H compounds, the process is constrained less by the barrel set points than by the heat history generated in high-shear kneading blocks. On a co-rotating twin-screw extruder with 40:1 L/D and segmented screw elements, barrel temperatures are typically set from 190 °C near the feed throat to 230 °C at the die, with a melt-temperature alarm at 260 °C. Paraffinic white oil is injected after the first melting section using a side stuffer or metering pump when the loading exceeds 50 phr; direct liquid addition to the feed throat above this value can cause screw slip, torque fluctuations, and variable pellet dimensions. The kneading elements downstream of the oil-injection port should be forward-conveying and low-shear, because excessive mechanical energy at high oil content can produce local melt temperatures above 260 °C, leading to chain scission, yellowing, and volatile emission. For high-clarity compounds, the base oil aromatic content should be kept below 5 wt%; higher aromaticity can soften the styrenic domains and reduce clarity through refractive index mismatch. Pelletizing through underwater or strand systems should be performed with melt temperature measured at the die rather than relying solely on barrel set points, because adiabatic heating in the screw can raise melt temperature by 10–20 °C above the last barrel zone.

Thermal Degradation Pathways and Stabilisation Requirements for G1642 H

Thermal degradation of G1642 H in air proceeds by chain scission and crosslinking in the ethylene/butylene midblock, with the styrenic domains losing physical crosslink density as the temperature approaches the styrene glass transition near 95 °C. The midblock glass transition is below −40 °C, which maintains elastomeric properties at low temperatures but also means that plasticizer migration and creep can occur above ambient temperature if the compound is not designed with sufficient end-block content or filler. A typical stabilizer package for oil-extended compounds includes a hindered phenolic primary antioxidant at 0.1–0.3 phr and a phosphite secondary antioxidant at 0.1–0.2 phr. For outdoor applications, a hindered amine light stabilizer should be added because the aromatic styrene phase can yellow under UV exposure even though the midblock is saturated. Continuous service temperature for load-bearing parts is commonly limited to 70 °C unless the formulation is specifically designed for higher heat through polypropylene modification and antioxidant selection. Thermogravimetric analysis under nitrogen indicates that significant thermal degradation begins above 250 °C; in air, oxidative mass loss is measurable at lower temperatures and processing atmosphere should be inert or well-ventilated.

Injection moulding of G1642 H compounds can use a barrel temperature profile from 190 °C to 230 °C with a mould temperature of 20–40 °C as a practical starting point for neat G1642 H and its oil-extended compounds. A general-purpose screw with a compression ratio of 2.2:1 to 3.0:1 is adequate, but a shut-off nozzle is recommended to prevent drool from low-viscosity oil-extended formulations. The hydrophobic midblock means that the polymer does not require drying under normal dry indoor storage; however, cold pellets moved into a humid plant can pick up surface moisture, and a desiccant dryer at 80 °C for 2 h should be used when pellet surface moisture is suspected above 0.1 wt%. Shrinkage of neat SEBS is anisotropic and lower than that of semi-crystalline polyolefins; tooling dimensions should be confirmed using ISO 294-4 shrinkage plaques from the actual formulated compound rather than neat virgin data. For thick sections, melt temperature should be kept below 240 °C to avoid long residence time degradation, and the screw back-pressure should be limited to 0.5–1.0 MPa to reduce shear heating.

Profile extrusion of the same oil-extended compounds requires attention to die pressure and extrudate surface quality. A gradual transition screw with a compression ratio of 2.5:1 to 3.5:1 and a barrel length of at least 24:1 L/D is sufficient. When running frosted or clear tubing, the melt filter pack should not exceed 60 µm mesh size because finer filtration increases shear heating and can reduce output. The extrudate may exhibit sharkskin at high shear rates; raising the die temperature by 5–10 °C or reducing line speed typically restores a smooth surface. The use of a monofilament die with a draw ratio above 3:1 is not recommended for unfilled G1642 H because the low crystalline fraction produces low melt strength and unstable bubble or filament geometry.

Assessing Tackification and Resin Compatibility Limits

G1642 H can be tackified with hydrogenated hydrocarbon resins, hydrogenated rosin esters, or aliphatic hydrocarbon resins to generate pressure-sensitive adhesives and assembly adhesives. Resin loadings from 20–60 phr shift the glass transition of the styrenic phase and increase peel strength, but excessive tackifier levels lower shear holding power and can produce adhesive transfer. The formulation should be evaluated for loop tack by ASTM D6195 or ISO 8510 and for shear adhesion failure temperature by ASTM D4498. Polar resins such as unhydrogenated rosin esters and aromatic hydrocarbon resins are less compatible with the hydrogenated midblock and can phase-separate, causing haze and loss of cohesive strength. Because G1642 H has a saturated midblock, it does not require sulfur or peroxide vulcanization; the physical crosslinks from the styrenic domains are reversible and can be disrupted by excessive processing temperature or by exposure to aromatic and chlorinated solvents.

When Higher Styrene Content or Higher Melt Flow Is Required

If the end-use specification requires a Shore hardness above 70 Shore A without adding polypropylene, or if the application imposes rapid die cutting and demands higher tensile modulus, Kraton™ G1641 H with its 33 wt% styrene content should be evaluated. That substitution increases hardness and modulus but reduces the amount of paraffinic oil that can be added before oil bloom appears, and the compound becomes stiffer at low temperature. If the processing constraint is a long flow-length-to-wall-thickness ratio in injection moulding, Kraton™ G1643 H provides a lower melt viscosity at equivalent temperature and may allow lower filling pressure; however, the tensile strength and oil-holding capacity of G1643 H compounds are lower. In applications requiring both high temperature resistance and high toughness, G1650 H or G1651 H may be substituted, but melt processing becomes more difficult and the resulting compounds are harder. G1642 H is selected when a single SEBS must satisfy both a moderate hardness after oil extension and sufficient melt flow for high-speed injection or extrusion lines, without the property compromises of extreme molecular weight or styrene content.

Because G1642 H is delivered as dusted pellets, the dusting agent can be amorphous silica or calcium carbonate depending on the production lot. This inorganic surface layer must be quantified in clean-room or food-contact operations, and it may influence hot-melt adhesive clarity if not wetted by the formulation. Food-contact status under 21 CFR 177.2600 or European Union harmonized legislation is not automatic for the finished product; the formulator must obtain a manufacturer compliance letter for the specific SEBS grade and validate migration for the final compound, including plasticizer and antioxidant contributions. REACH registration and RoHS heavy-metal restrictions are typically addressed at the polymer-supply stage, but the downstream converter remains responsible for documentation of the final article. Storage should be in dry, covered conditions below 50 °C, and contact with ketones, chlorinated hydrocarbons, and aromatic oils should be avoided because these solvents swell or dissolve the styrenic domains. Unstabilized or lightly stabilized compounds exposed to direct sunlight for prolonged periods may yellow and lose surface tack due to styrenic photo-oxidation. The product is supplied as a combustible solid; processing vents should be exhausted because thermal decomposition above 250 °C can release low-level hydrocarbon volatiles.