Asahi Kasei S.O.E.™ SEBS L613 is a hydrogenated styrenic block copolymer in which polystyrene end blocks form thermally reversible physical crosslinks in a saturated ethylene/butylene midblock matrix. The material is supplied as pellets and can be processed on injection molding machines, single-screw extruders, and co-rotating twin-screw compounding lines without vulcanization. The absence of main-chain unsaturation differentiates it from unhydrogenated SBS by improving resistance to ozone, ultraviolet embrittlement, and oxidative chain scission. L613 is therefore considered for soft-touch overmolding, polyolefin modification, and elastomeric compounds that require melt reprocessability. Within the S.O.E.™ family, the L613 designation corresponds to a defined balance of styrene content, melt flow, and molecular architecture. The Asahi Kasei technical datasheet remains the controlling document for lot-specific physical properties; published data for the specific L613 configuration is limited in this document, so the values discussed below are standard test conditions or general ranges for hydrogenated SEBS architectures rather than guaranteed lot data.

Incoming quality checks should separate the neat resin properties from the final compound properties. For neat resin, melt mass-flow rate is measured at 230 °C under 2.16 kg load using ISO 1133-1:2022. Hardness is measured on a compression-molded plaque with Shore A durometer after 15 s per ASTM D2240-15 or ISO 48-4. Density is obtained at 23 °C by Method A of ISO 1183-1:2019. Tensile stress and elongation at break are determined on a 2.0 mm plaque or Type 5A dumbbell at 500 mm/min after conditioning for 40 h at 23 °C and 50 % relative humidity, using ASTM D638-14 or ISO 37:2017. Compression set is evaluated after 22 h at 70 °C under 25 % deflection with 30 min recovery, per ASTM D395-18 or ISO 815-1:2019. These methods do not replace the supplier’s certificate of analysis.

Material Composition and Specification Boundaries for S.O.E.™ L613

The specification boundary of L613 is governed by its phase-separated morphology. Polystyrene domains provide stiffness and recoverable elasticity below the styrenic glass transition temperature, while the saturated ethylene/butylene midblock contributes low-temperature flexibility and paraffinic-oil compatibility. Styrene content directly influences hardness, tensile strength, and melt viscosity. Commercial SEBS grades with comparable midblock architecture typically exhibit density between 0.90 g/cm³ and 0.94 g/cm³, Shore A hardness from 45 to 75, tensile strength from 18 MPa to 30 MPa, and elongation at break from 500 % to 800 %. These ranges reflect architectural variation and should not be interpreted as L613 specification limits.

For compounded L613 systems, the useful property window is strongly modified by oil concentration, polypropylene content, filler loading, and the presence of functionalized additives. Because the EB midblock is saturated, paraffinic and naphthenic oils are preferred; aromatic mineral oils are generally avoided due to phase incompatibility, which can cause surface exudation and loss of elastic recovery. The compound hardness and compression set should be re-measured on the final formula rather than estimated from the neat resin value. When L613 is the elastomeric phase in a polypropylene-rich blend, the polypropylene phase improves tensile strength and upper service temperature, while the SEBS phase improves impact toughness and softness. The exact balance is formulation-dependent and is normally established through design-of-experiments runs on production-scale equipment.

In terms of operational boundaries, L613 should not be exposed to melt temperatures above 250 °C for prolonged residence times. The saturated midblock is thermally stable compared with unsaturated elastomers, but the styrene domains and residual tertiary carbon sites can undergo thermo-oxidative degradation under high-shear hot spots. Degradation is typically indicated by a downward drift in melt pressure, yellowing of pellets or molded parts, and a reduction in tensile strength measured per ASTM D638-14. For this reason, melt-temperature sensors in the adapter and die zones are more useful than barrel set-point temperatures alone for detecting shear-induced temperature excursions.

What Processing Parameters Govern Oil-Extended Compounds Based on L613?

Pre-drying of neat L613 is not mandatory in all conditions. When relative humidity exceeds 60 % or when thin-wall molded surfaces must remain free of splay, a desiccant dryer at 60–80 °C for 2–4 h reduces moisture-related defects. The bulk of compounding, however, is performed on co-rotating twin-screw extruders with L/D ratios from 40:1 to 52:1. Barrel temperatures are normally set from 180 °C to 220 °C, with the die held between 190 °C and 210 °C. Oil injection after the initial polymer melting zone improves uptake and reduces screw slippage; paraffinic white oils with low aromatic content are preferred.

On a production-scale 40:1 L/D twin-screw line, closed-loop gravimetric feeding of L613 and mass-flow oil injection reduce lot-to-lot variation in compound hardness. Pelletizing stability is sensitive to strand temperature. Strand water bath temperature is typically maintained below 40 °C; higher temperatures can produce tacky strands and pellet agglomeration. If the melt temperature at the die face exceeds 230 °C, strand cutting may generate fines and irregular pellet geometry. In such cases, the screw speed, feed rate, and barrel temperature profile are rebalanced before adjusting the die plate.

Injection molding of L613-based compounds usually employs melt temperatures from 190 °C to 230 °C and mold temperatures from 20 °C to 50 °C. A general-purpose polyolefin screw with compression ratio from 2.0:1 to 2.5:1 is commonly used. Because the melt is shear-thinning, filling thin-walled cavities is improved by higher injection velocity, but excessive velocity can cause gate blush and flow-front instability. Packing pressure is set to minimize sink without inducing overpacking at the gate. If a lot-to-lot melt mass-flow rate shift greater than ±10 % from the supplier’s nominal value is observed by ISO 1133-1:2022, fill pressure and cushion position should be re-qualified before production continuation.

Overmolding onto polypropylene relies on interdiffusion between the EB midblock and the polypropylene surface, not on covalent adhesion. Melt temperature at the upper recommended range and a substrate surface temperature of 60–100 °C improve weld-line integrity. Polyamide, polyester, and other polar engineering substrates typically require plasma, corona, or a functionalized tie layer because L613 does not inherently develop structural adhesion with those materials. Molding trials should include cross-cut adhesion testing and, where relevant, peel testing per recognized test methods agreed between supplier and molder.

Thermal degradation in L613 processing is best controlled by monitoring melt-temperature uniformity. Local viscous heating in high-shear kneading blocks can raise the material above the indicated barrel set point. When the local melt approaches 250 °C, molecular-weight redistribution and styrene-domain degradation become measurable as lower viscosity, reduced tensile strength, and increased yellowing. The practical melt-temperature window is not critically narrow, but the avoidance of prolonged residence time at high melt temperature is important for maintaining batch-to-batch consistency in pellet color and mechanical properties.

Because L613 is a hydrogenated SEBS rather than a crosslinked rubber, replacement of EPDM or SBS in an existing compound requires rebalancing the additive package. The hydrogenated midblock has higher thermal and ozone resistance than SBS, but the final ozone resistance of a compound should be confirmed by ISO 1431-1 or equivalent accelerated testing. The fatigue resistance and crack-growth behavior of L613-based compounds differ from those of vulcanized rubber; dynamic testing on the final part is required before substitution in cyclic-loading applications. Compared with EPDM, L613 compounds can be reprocessed, but they may exhibit higher compression set at service temperatures above 100 °C and may swell in non-polar solvents until fluid resistance is documented per ASTM D471-16a.

Compared with lower melt flow SEBS grades in the same family, L613 is positioned for higher flow and easier thin-wall mold filling. This flow advantage is commonly accompanied by a trade-off in tensile strength and compression set. The exact balance should be measured on molded plaques using ASTM D638-14 and ASTM D395-18 rather than inferred from melt flow alone. Selection between L613 and a lower-MFR SEBS grade therefore depends on the maximum flow length, the required surface appearance, and the allowable loss in mechanical recovery. Compounds that must retain elastic recovery after repeated loading may require a harder or higher-molecular-weight SEBS grade; compounds that prioritize complex-part filling may favor L613.

For medical, food-contact, or electrical applications, the final compound is assessed under the relevant end-use standards. A compliance checklist for the final formulated material may include the following designations:

Because L613 is supplied as a compounding raw material, these regulatory assessments apply to the finished article rather than to the neat polymer. The final compound’s oil, filler, pigment, and stabilizer package determines whether the article meets the applicable threshold. A supplier regulatory statement for L613 should be obtained for REACH, RoHS, and any food-contact or medical-grade claims before commercial specification.