Kuraray SEPTON™ SEEPS 4030S is a hydrogenated styrenic block copolymer in which a saturated ethylene-ethylene/propylene random mid-block is terminated by polystyrene domains. The SEEPS architecture is a styrene-[ethylene-ethylene/propylene]-styrene block copolymer, and the 4030S grade carries a nominal styrene content of 30 wt% with a specific gravity of approximately 0.91 g/cm³ when characterized according to ISO 1183-1. The saturated mid-block removes the main-chain unsaturation present in unhydrogenated SBS and SIS copolymers, which is the primary structural difference governing oxidative, thermal, and ultraviolet resistance.

Published data for this specific configuration is limited in the open literature. Where manufacturer lot certificates are unavailable, the compounder should treat the numerical values in the following sections as representative of the 30 wt% styrene SEEPS class rather than as guaranteed specification limits. The product is supplied in pellet form and is intended for melt-compounded thermoplastic elastomer formulations, polymer modification, and selective adhesive systems requiring a styrenic hard phase with a saturated rubber mid-block.

Why Does Mid-Block Saturation Control Performance in SEEPS 4030S?

The saturated mid-block is not a minor structural detail. In unhydrogenated styrenic block copolymers, allylic hydrogen positions adjacent to main-chain double bonds provide initiation sites for oxidative chain scission, crosslinking, and ozone attack. The SEEPS structure eliminates most of those sites, shifting the degradation pathway toward slower radical oxidation of the saturated chain. This is why compounds based on SEEPS 4030S are specified for sealing profiles, automotive interior skins, and other applications in which retention of tensile behavior after long-term heat exposure is evaluated under protocols such as ISO 188 or ASTM D573. The ethylene-ethylene/propylene mid-block also raises the upper service temperature of the neat polymer relative to SBS, though the exact performance limit in a compounded system depends on plasticizer type, filler loading, and antioxidant package.

Because the polystyrene end-blocks remain physically crosslinked rather than covalently crosslinked, the material retains thermoplastic processability. The styrene domains provide tensile strength and hardness, while the saturated mid-block contributes elastic recovery and low-temperature flexibility. This combination is particularly relevant when a formulation must pass both high-temperature compression set testing and low-temperature flexibility testing in the same component.

Specification Profile for SEEPS 4030S

The specification profile in Table 1 is expressed as test-conditioned data. The property ranges reflect the 30 wt% styrene SEEPS class and should be confirmed against the current Kuraray lot certificate for 4030S before final specification setting.

Because the melt flow rate is below 1.0 g/10 min under the stated conditions, 4030S is a medium-to-high melt viscosity SEEPS grade. This viscosity influences oil acceptance, filler wetting, and the practical upper dilution limit in soft compounds. Hardness values above 70 Shore A in the neat polymer mean that plasticizer addition is normally required for soft-touch or low-hardness seal applications. The tensile values apply to compression-molded test specimens, not to final injection-molded or extruded parts, because weld-line integrity, orientation, and frozen-in stress reduce component tensile values.

When Twin-Screw Extrusion Requires Pre-Drying and Zone Temperature Control

Compounding of 4030S is carried out on equipment capable of controlling both shear and residence time. At storage relative humidity above 60%, pellets should be dried at 80°C for 2–4 h before extrusion to reduce surface splay and hydrolytic elimination at the feed throat. In production-scale co-rotating twin-screw extruders with 40:1 to 48:1 L/D, barrel temperatures from 190°C to 230°C are typical. Melt temperature should remain below 240°C during normal operation; extended residence above 240°C can degrade gel strength and increase discoloration in unfilled formulations.

Plasticizer oil should be injected after the polymer has begun to melt, commonly at zone 4 or zone 5 of a 10-zone barrel, rather than at the feed throat. Early oil addition reduces solids conveying and can produce screw slippage or torque instability. In filled compounds, side feeding of mineral filler or glass fiber should be followed by distributive mixing elements to reduce filler agglomerates without excessive shear heating. Production operators commonly observe that the highest injection-molded tensile retention is achieved when the extrudate is pelletized at a water-bath temperature below 40°C to prevent pellet blocking.

Injection molding of formulated compounds based on 4030S generally uses melt temperatures of 200°C to 230°C and mold temperatures of 30°C to 60°C. Gate freeze time and hold pressure should be established from part weight studies rather than fixed transfer pressure tables. Thin-wall parts below 1.5 mm wall thickness may require melt temperatures near the upper end of the range, but residence time must then be minimized.

Compounds based on 4030S are used in automotive interior skins, soft-touch grips, seals, gaskets, and impact modification of polypropylene. In automotive interior skin formulations, fogging and volatile organic compound requirements are evaluated according to ISO 6452 and VDA 278. The saturated mid-block lowers the generation of low-molecular-weight volatile species compared with unhydrogenated styrenic block copolymers, but the final formulation still requires low-volatility oil, antioxidant, and release agent selection to pass OEM fogging thresholds. Sealing profiles and gaskets are typically tested for compression set under ISO 815-1 after aging at temperatures from 100°C to 120°C, depending on the service requirement.

4030S Sits Between 4033 and 4044 in the Kuraray SEEPS Range

The 4030S designation places it within the 30 wt% styrene SEEPS family alongside 4033 and 4044. Published data for this specific configuration suggests that it is neither the highest-flow nor the highest-melt-strength member of that range. The S suffix is a manufacturer-specific grade designation; it does not necessarily denote a change in styrene content, and users should confirm the exact specification from the current technical data sheet.

Table 2 is assembled from multiple public datasheets and technical bulletins. Test methods differ by laboratory, so cross-grade comparison requires normalization to the same testing protocol. Under identical processing conditions, 4033 has higher tensile strength and a slightly lower practical flow than 4030S. Grade 4044 provides significantly higher melt flow for thin-wall or high-speed injection molding but yields lower hardness and tensile strength. Grade 4055 has a much higher melt viscosity and is used where oil extension is high or where a softer, highly elastic final compound is required. 4030S is therefore selected when 4033 has insufficient melt flow for a given mold configuration but 4044 produces a hardness or tensile value below the component requirement.

Regulatory Boundaries and Incompatibility Limits for 4030S

Food-contact use is not automatic for 4030S. Formulations intended for food-contact sealing or processing equipment must be evaluated under 21 CFR 177.1810 for styrene block copolymers and the relevant European Union migration requirements under EU 10/2011. Compliance is determined on the finished compound, not on the raw polymer alone. Medical and pharmaceutical components require additional validation of the final compound under applicable ISO 10993 or USP protocols.

The melt should not be exposed to free-radical-generating organic peroxides above 150°C unless a controlled reactive processing step is specifically intended, because chain scission or crosslinking can occur and destabilize the viscosity envelope. Strong oxidizing acids, aromatic hydrocarbon solvents, and ketones should be avoided in service and in cleaning operations. For solution processing, aromatic solvents such as toluene and cyclohexane can swell or dissolve the polymer at room temperature; solvent selection and evaporation profiles must be controlled to avoid gel formation. The saturated mid-block does not eliminate all oxidative degradation. A formulated antioxidant package is still required for prolonged aging, and the final part should be tested under the relevant aging standard rather than assuming neat-polymer stability.