Kuraray SEPTON™ 8007L is a hydrogenated styrene-ethylene/butylene-styrene block copolymer supplied in pellet form for thermoplastic compounding. The molecular structure contains polystyrene end-blocks that form physical crosslinks on cooling and a hydrogenated poly(ethylene/butylene) midblock that provides elastomeric recovery without requiring vulcanisation. The grade belongs to the 8000 series, which is positioned at the lower-hardness end of the SEPTON portfolio. In unfilled compression-moulded specimens, the material exhibits a density of 0.88 g/cm³, a melt mass-flow rate of 0.7 g/10 min at 230 °C under 2.16 kg load, and a Shore A hardness of 62. The polystyrene content is approximately 30 wt%. Because the midblock is saturated, the thermo-oxidative stability of the polymer is higher than that of unmodified styrene-butadiene-styrene block copolymers, while the absence of carbon-carbon double bonds improves resistance to ultraviolet embrittlement.

Mechanical values reported for unfilled moulded sheets include a tensile strength of approximately 20 MPa, elongation at break of approximately 800%, and a 300% modulus of approximately 1.5 MPa when evaluated according to ISO 37:2017. Hardness is determined at 15 s using ISO 868:2003, and melt-flow behaviour is characterised under ISO 1133-1:2022. These properties place 8007L at the softer, higher-elongation side of the 8000 series. Compared with grades 8004 and 8006, which contain higher polystyrene block concentrations and develop greater tensile strength and hardness, 8007L provides lower modulus and higher flow. The trade-off is relevant in injection moulding of thin-wall components and in film processes where reduced melt pressure and greater drawability are required. Published data for specific film-grade formulations containing this polymer is limited.

When Hydrogenation of the Midblock Alters Thermo-oxidative Stability and Melt Processing

Substitution of 8007L into existing SBS production lines requires an upward shift of the thermal profile. Barrel temperatures for a co-rotating twin-screw extruder with an L/D ratio of 40:1 are typically set from 180 °C in the feed zone to 220 °C at the die. Melt temperatures above 260 °C should be avoided because chain scission and gel formation increase sharply. The saturated midblock does not consume stabilisers through unsaturation-driven degradation, which reduces the tendency toward black specks or viscosity drift during residence time. However, the low polystyrene content reduces melt strength, which can narrow the stable bubble window in blown film and can produce strand breakage during compounding if vacuum venting is insufficient. Purge with polypropylene or low-density polyethylene is used to remove the grade from production equipment.

Oil extension with paraffinic white oil at loadings between 50 phr and 150 phr lowers hardness and modifies tensile set. On production-scale twin-screw lines, staged oil injection after the first melt seal is required above approximately 100 phr; direct injection in the feed throat causes screw slippage and torque instability. The hydrogenated midblock absorbs paraffinic oil effectively, allowing formulations below 30 Shore A without phthalate ester plasticisers. High-shear distributive mixing is preferred over elongational mixing to maintain uniform polystyrene domain size at lower barrel temperatures. Laboratory mixing trials should record torque, melt temperature, and specific energy input to detect batch-to-batch variance in oil uptake. Pre-drying at 70–80 °C for 2–4 h is recommended when the resin has been exposed to relative humidity above 60%, as residual moisture produces surface defects at the die lip.

What Distinguishes the Low-Hardness 8000 Series Grades from Conventional SEBS and SBS Materials?

Three structural variables separate 8007L from higher-hardness grades: overall polystyrene content, molecular weight distribution, and melt-flow response. The 30 wt% polystyrene end-block content produces fewer hard domains per unit volume than grade 8006, which is reported with 33 wt% polystyrene and develops higher tensile strength and lower elongation. The 8007L grade exhibits higher melt flow than 8004 and 8006, which reduces filling pressure in thin-wall injection moulds and lowers shear heating. Against an unmodified SBS of similar styrene content, the hydrogenated midblock removes most reactive double bonds, improving resistance to thermo-oxidative breakdown and permitting use in air at continuous temperatures near 100 °C in static applications. Unsaturated SBS without intensive stabilisation is more susceptible to viscosity drift during processing and to surface cracking after prolonged UV exposure. This difference is the main reason 8007L is selected for exterior soft-touch parts, elastic films, and components exposed to repeated flexing.

Film Extrusion Conditions for Low-Styrene SEBS Compounds

Cast film production with chill-roll temperatures held at 20–40 °C is used to control blocking and tensile set; rapid cooling affects the physical crosslink density developed by the polystyrene domains. Blown film operation typically requires a blow-up ratio below 3:1 and a frost-line height sufficient for stress relaxation. The lower melt strength of 8007L relative to higher-styrene SEBS narrows the stable bubble window, especially when oil loadings exceed 100 phr. Film formulations containing 50–100 phr paraffinic oil retain elastic recovery after 300% elongation, but antiblock addition is required for roll winding. The material is not a barrier polymer; oxygen and moisture vapour transmission rates depend on thickness and filler content rather than on the hydrogenated midblock. Pre-drying before film extrusion is mandatory when ambient humidity exceeds 60%; otherwise moisture vapour at the die lip produces melt fracture and surface roughness.

Soft-touch grips, overmoulded handles, and non-slip inserts are produced by injection moulding compounds based on 8007L over glass-filled polypropylene or polycarbonate substrates. Adhesion in overmoulding is process-dependent; substrate surface temperature is often maintained above 80 °C at the interface to promote wetting without excessive cooling of the SEBS melt. For toys and consumer articles, compounds are formulated without phthalate plasticisers, and migration of elements is evaluated under EN 71-3 where applicable. Elastic hygiene films and medical film applications require formulation-specific validation of biocompatibility; the base polymer does not eliminate the need for testing under ISO 10993-5 for cytotoxicity and ISO 10993-10 for skin sensitisation. Published data for specific film configurations of 8007L is limited.

Handling and storage limits are governed by moisture uptake and thermal degradation. Bulk storage in sealed containers is recommended below 40 °C and at relative humidity below 60%. Extended exposure to strong oxidising agents, aromatic solvents, or high-shear conditions above 260 °C can degrade the polymer and should be avoided. When regrind is incorporated, the maximum recommended regrind level depends on the end-use standard; process consistency requires routine melt-flow and Shore A hardness checks after reprocessing.