Manufactured by Dynasol Elastómeros, the Calprene® SEBS H6420 grade is a linear hydrogenated triblock copolymer with the sequence polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene. The nominal bound styrene content is 18% by mass. The polystyrene endblocks form glassy domains at service temperatures below approximately 95 °C, while the ethylene-co-butylene midblock remains above its glass transition near −55 °C and provides elastomeric recovery. Typical neat-pellet values published by the manufacturer include a melt flow rate of 22 g/10 min at 230 °C under a 2.16 kg load according to ISO 1133-1:2022, a density of 0.91 g/cm³ according to ISO 1183-1:2019, a Shore A hardness of 42 after 15 s according to ASTM D2240-15e1, a tensile strength at break of 28 MPa according to ISO 37:2017, and an elongation at break of 700%. The hydrogenated midblock has a much lower double-bond content than unhydrogenated SBS, which reduces chain scission during melt processing and lowers UV-induced yellowing in dilute film applications.

The model designation H6420 identifies a high-flow, low-styrene SEBS intended for compounds that must combine softness with melt processability. Because the neat hardness is already 42 Shore A, formulations targeting 30 Shore A or lower require less mineral-oil plasticisation than higher-styrene grades, which reduces migration risk in skin-contact articles. The grade is not oil-extended as supplied; oil extension is a downstream compounding step performed by the processor or compounder.

What Distinguishes a 18% Bound Styrene SEBS from Higher-Styrene Hydrogenated Block Copolymers?

The structural distinction is the hard-block volume fraction. With 18% bound styrene, H6420 operates in the elastomer-dominated regime; room-temperature storage modulus and Shore A hardness are lower than those of grades containing 30% to 33% bound styrene because fewer polystyrene domains per unit volume are available to act as physical crosslinks. This composition reduces the 300% modulus and raises elongation at break, but it also lowers resistance to creep under continuous load and can increase compression set at 70 °C relative to a 33% styrene SEBS at equivalent molecular weight. In polypropylene modification, the lower styrene content shifts compatibility toward the propylene matrix, which is advantageous when the target is softness rather than heat distortion. Conversely, in oil-extended compounds intended for hardness below 30 Shore A, H6420 requires less extender oil than a higher-styrene grade to reach the same final hardness because the neat polymer hardness is already 42 Shore A.

Feed-throat behaviour on a corotating twin-screw extruder with an L/D ratio of 40:1 is generally stable without draft cooling at screw speeds up to 400 min⁻¹ when the barrel profile is held between 180 °C and 210 °C. Pellets may be introduced through the main hopper and no special drying is required below 60% relative humidity; however, condensation from cold storage should be removed by a desiccant dryer set at 70 °C to 80 °C for 2 h. If regrind use exceeds 20% by mass, the melt flow rate of the regrind fraction should be verified because repeated heat history can increase viscosity through chain extension and produce specks in translucent compounds. On a single-screw extruder with a 3:1 compression ratio and a Maddock mixing section, the low melt viscosity at 230 °C permits throughputs comparable to those of a 20 g/10 min polypropylene when a 20% to 30% H6420 masterbatch is used, but the screw should not generate melt temperatures above 240 °C for more than 10 min.

When a Melt Flow Rate of 22 g/10 min Expands Thin-Wall Injection Molding Capability

Injection molding is the primary route for cap liners, closures, and hygiene components. The melt flow rate of 22 g/10 min under ISO 1133-1:2022 is high enough to fill wall sections of 0.8 mm to 1.5 mm in multi-cavity tools when the nozzle temperature is set between 210 °C and 230 °C and the mold coolant inlet is held at 20 °C to 35 °C. Because the material is elastomeric, it is typically processed with a reverse temperature profile, from a cooler rear zone at 190 °C to a hotter front zone at 220 °C, to aid homogenisation while preventing premature softening of the feed pellets. Screw rotation should be set to complete plasticating within 60% to 70% of the overall cycle; hold pressure is lower than that used for semi-crystalline polypropylene because the compressibility of the melt is higher. Venting of the mould cavities should be at least 0.02 mm deep to avoid gas burn at the end of fill.

The following manufacturer-published neat-resin data provide a starting specification. Values are typical and not batch-release limits.

Regulatory Assumptions, Sterilization Compatibility, and Migration Constraints

For food-contact and medical applications, the base hydrogenated block copolymer may be referenced against FDA 21 CFR 177.1810 for styrenic block copolymers in contact with food, and against Regulation (EU) No 10/2011 for plastic materials and articles intended to come into contact with food. These references apply only to the neat polymer and do not transfer automatically to finished compounds containing oils, fillers, or colorants. Overall migration compliance for a finished seal should be verified according to EN 1186-1:2002 using the intended simulant and contact time. For medical uses, the supplier may provide statements based on ISO 10993-5 for cytotoxicity and ISO 10993-10 for irritation, but the grade is not sterilizable by all modalities: gamma irradiation above 25 kGy can induce a measurable increase in yellowness index, while electron-beam sterilization at similar doses produces lower chromophore development. Steam autoclaving at 121 °C is usually not recommended for SEBS compounds intended for dimensionally stable parts because the styrenic domains soften near 95 °C and can leave permanent set under load.

Compared with EPDM, H6420 requires no vulcanization and can be processed on conventional thermoplastic equipment; the absence of a cure system removes scorch time constraints, but the softening of the styrenic domains above 95 °C limits continuous service temperature under load more severely than a peroxide-cured EPDM. Compared with a thermoplastic vulcanizate of Shore A 40, H6420 typically exhibits lower compression set resistance after 22 h at 70 °C when the TPV contains a crosslinked rubber phase; however, H6420 offers higher melt flow and easier reprocessing of regrind. Published data for the specific compression set of H6420 at 70 °C is limited; compounders should request current manufacturer data before specifying seals for hot-water service. Compared with lower-molecular-weight SEBS grades with melt flow rates above 40 g/10 min, H6420 retains higher tensile strength and puncture resistance because the endblock molecular weight is not reduced to the same degree; however, it may require higher injection pressures in long-flow closures.

A Processing Window Narrower Than the Bulk Stability Limit

Although the fully hydrogenated midblock tolerates temperatures above 250 °C for short periods, the practical melt-processing window for H6420 is narrower. Residence times above 240 °C should be limited to less than 10 min to avoid viscosity build-up; oxygen exclusion is more important than nitrogen blanket purity, and vacuum venting at −0.08 MPa during compounding reduces volatile content and improves surface quality. Processing temperatures below 170 °C are insufficient to generate a homogeneous melt in high-shear compounds; therefore, the feed zone should not be held below 170 °C when the formulation contains more than 20% by mass of mineral oil. In oil-extended compounds, oil injection downstream of the first kneading block is preferred, and the barrel temperature should be reduced by 10 °C after oil injection to restore viscosity and prevent oil slip on the screw.

High-oil extension of H6420 follows a saturation threshold. Because the ethylene-co-butylene midblock is highly compatible with paraffinic white mineral oil, oil plasticises the rubber phase and lowers hardness. At oil loadings below 30 phr, the reduction in tensile strength is roughly linear; above 50 phr, the compound transitions toward a soft gel and surface tack increases. The exact saturation point depends on oil viscosity and aniline point; naphthenic oils with low aniline point are more aggressive and can disrupt styrene domains if the melt temperature exceeds 220 °C. For low migration in skin-contact foams, compounders should select paraffinic oils with kinematic viscosity above 40 mm²/s at 40 °C.

The grade is also used as a modifier for polystyrene and poly(phenylene ether), where the hydrogenated midblock reduces brittle failure. In these blends, addition of 5% to 10% by mass H6420 increases notched impact strength, but the effect saturates because the dispersed SEBS phase reaches a critical particle size; published data for this specific configuration is limited. In cast film and sheet extrusion for medical packaging and hygiene films, H6420 can be dry-blended with a polypropylene random copolymer at a let-down ratio of 20% to 50% by mass. The low bound styrene content produces a lower coefficient of friction than high-styrene SEBS in cast film, but the exact value depends on antiblock addition and die geometry. Published data for this specific configuration is limited; line trials on a chill-roll stack should be used to fix draw ratio and roll temperature.