SINOPEC Baling SEBS YH-501 is a linear styrene-ethylene/butylene-styrene triblock copolymer supplied as a free-flowing powder or crumb. Manufacturer technical documentation lists a bound styrene mass fraction of approximately 30 wt%, a density of 0.91 g/cm³ per ISO 1183-1:2019, and volatile matter below 1.0 wt%. Unmodified cast-film tensile strength is reported above 20 MPa with elongation at break above 600% when tested per ISO 37:2017. Hardness is typically 68–72 Shore A per ISO 48-4. Melt mass-flow rate at 230°C/5 kg per ISO 1133-1:2022 is typically below 1.0 g/10 min because the grade is unextended and retains the full rheological resistance of the linear triblock. The absence of plasticizing oil and polar functional groups distinguishes YH-501 from oil-extended SEBS and maleic anhydride-grafted SEBS: oil-extended grades show lower hardness and viscosity but also lower tensile strength, while grafted grades improve polar adhesion but raise melt viscosity and require moisture control to avoid hydrolysis of the anhydride. The product is used in hot-melt adhesives, asphalt modification, polyolefin toughening, footwear foams, and soft-touch automotive or consumer goods. Published data for some specific service configurations is limited, particularly where the end-use formulation contains high filler loadings or reactive additives.

What Limits Mixing Torque and Thermal Degradation When YH-501 Is Compounded?

In twin-screw compounding of YH-501 with tackifier and paraffinic oil, the linear triblock first forms a high-viscosity melt before the oil diffuses into the EB midblock. A co-rotating twin-screw extruder with an L/D ratio of ≥ 40:1 and modular screw elements is typically used, with specific energy input commonly falling between 0.15 kWh/kg and 0.30 kWh/kg when oil is injected downstream. Barrel zones before oil injection are held at 180–200°C; downstream zones and die are limited to 200–210°C to reduce autoxidation. At melt temperatures above 230°C, the EB midblock undergoes chain scission at tertiary carbon sites, lowering solution viscosity and cohesive strength; residence time above 200°C should remain below 8 min. A phenolic primary antioxidant at 0.1–0.3 phr and a phosphite secondary antioxidant at 0.1–0.2 phr are typically added to stabilize the melt. On production-scale extruders, screw slip and feed restriction can occur if the feed throat is not cooled below 40°C, because the powder compacts into a cohesive plug; this is less severe in oil-extended grades. Published data for this specific grade under extremely high-shear mixing is limited, so pilot-scale torque calibration is recommended before scale-up.

Asphalt modification with YH-501 requires pre-swelling in hot maltenes for 30–60 min at 165°C before high-shear mixing in a rotor-stator mill with tip speeds of 15–25 m/s. Addition levels of 3–6 wt% on binder mass are commonly evaluated for rutting resistance; the saturated EB midblock retards oxidation during mixing compared with SBS. Softening point increases per ASTM D36, penetration decreases per ASTM D5, and separation is measured per ASTM D5976. Because YH-501 is unfunctionalized and linear, a base bitumen with low aromaticity can produce phase separation after 24 h at 160°C; the use of high aromatic process oil or a styrenated phenol compatibilizer improves storage stability. No vulcanization is required, and sulfur-free stabilization avoids gel formation that can block the rotor-stator mill. Published data for this specific grade in bituminous binders is limited; therefore, binder grade and polymer dosage must be validated by penetration index and temperature sweep rheology.

Tensile Set and Hardness Response in Oil-Extended SEBS Blends

When YH-501 is compounded with white paraffin oil at 50–100 phr, hardness decreases from approximately 70 Shore A to 30–40 Shore A, while tensile set increases because the linear EB midblock has fewer entanglements than a branched or coupled SEBS. Compression set per ISO 815-1:2019 at 23°C is often the limiting requirement for seals; compounds below 35% set after 22 h usually require oil loading below 50 phr and addition of a polypropylene or EPDM phase. The linear architecture also produces lower melt strength than branched SEBS, which aids flow but reduces oil retention; oil exudation can appear at oil loadings above 100 phr after ambient storage. Tensile stress-strain data per ISO 37:2017 show a non-linear decrease in tensile strength with increasing oil content, with tensile strength remaining above 10 MPa only when oil loading is below 50 phr. In thermoplastic vulcanizate formulations, YH-501 does not provide crosslinkable sites, so a second elastomer containing diene functionality is required for peroxide cure. The choice of oil is critical: high paraffin content reduces viscosity efficiently, while naphthenic oil improves compatibility but lowers UV stability.

Polypropylene toughening with YH-501 typically uses addition levels of 20–30 wt% to shift the ductile-to-brittle transition below −20°C in notched Charpy testing per ISO 179-1. The linear SEBS phase forms a dispersed domain with a typical particle size of 0.5–2.0 µm when processed in a co-rotating twin-screw extruder at 220°C. Impact strength improvement depends on inter-particle distance; below 15 wt% addition, the brittle-to-ductile transition remains above 0°C in many PP grades. Because YH-501 is unextended, melt viscosity of the PP matrix is not reduced as much as with oil-extended SEBS; this is useful when balancing impact modification with stiffness retention. The tensile modulus of the compound per ISO 527-2 declines by approximately 30–50% at 30 wt% SEBS, so the grade is often combined with short glass fiber or talc to maintain flexural modulus per ISO 178.

Footwear midsole compounds containing YH-501 are typically prepared by blending with polyolefin elastomer and a chemical blowing agent. The compound is processed in an injection molding machine with a clamping force of 1,800–3,000 kN and a screw L/D ratio of 20:1–24:1. Melt temperature at the nozzle is held at 190–210°C; barrel residence time above 200°C is limited to 8 min. Because YH-501 has linear architecture, its melt strength is lower than branched SEBS, so closed-cell foam requires 0.5–1.0 wt% talc or 2–3 wt% organoclay as a nucleation agent to prevent cell coalescence. Abrasion resistance of the foamed part is assessed per DIN 53516; values for expanded SEBS systems are typically measured in the 200–300 mm³ range, but published data for this specific grade in footwear microcellular foams is limited. The unextended nature of YH-501 allows the formulator to add oil separately at the mixer, which gives leaner control of softness than a pre-oil-extended grade.

When YH-501 Replaces Oil-Extended or Maleic Anhydride-Grafted SEBS in Compounded Formulations

Direct substitution of YH-501 into a formula designed for oil-extended SEBS without adjusting the free oil addition will produce a compound with higher hardness and higher tensile strength but significantly higher mixing torque. Conversely, using YH-501 in place of maleic anhydride-grafted SEBS removes reactive coupling to glass, metal, or polyamide; peel adhesion in insert-moulded assemblies will fall unless a separate primer or tackifier is introduced. The following matrix compares the main structural and processing variables.

These differences allocate YH-501 to unextended general-purpose compounding where high oil absorption capacity is needed. In adhesive formulations requiring cohesive strength after plasticizer migration, YH-501 shows less cohesive dilution than oil-extended grades because the oil is introduced during compounding rather than pre-absorbed into the polymer. The linear chain also yields lower gel strength in high-temperature shear than branched SEBS; hot-melt viscosity at 180°C may be lower than branched grades at equal styrene content.

Hot-melt pressure-sensitive adhesive formulations use YH-501 at a polymer loading of 20–30 wt%. Loop tack per ASTM D6195 and shear adhesion failure temperature per ASTM D4498 define the application window. The unfunctionalized EB midblock yields lower specific adhesion to low-energy polyethylene films; corona treatment to a surface energy above 32 mN/m or a separate primer is required. Because the grade is linear, it dissolves more rapidly in the tackifier melt than coupled SEBS, but it also exhibits lower static shear resistance at 50°C. Formulations containing 20 wt% YH-501 and 60 wt% tackifier may maintain cohesion in cardboard packaging, while recycled board with high humectant content requires additional styrenic block copolymer or wax. Melt viscosity at 180°C is typically in the range that permits slot-die coating without solvent; however, published data for this specific grade in pressure-sensitive adhesives is limited and should be verified by thermosel viscosity per ASTM D3236.

The Unmodified Backbone Imposes Specific Limits in Wire and Cable Insulation Compounds

YH-501 can be used as an impact modifier and flexibility additive in polyolefin wire and cable jackets, but it is not a crosslinkable base polymer. In a moisture-curable polyethylene system, silane grafting is not effective on the saturated EB midblock, so YH-501 remains a dispersed phase that softens the jacket. Volume resistivity of the compound is evaluated per IEC 60093, and heat deformation is evaluated per IEC 60811-507. Because YH-501 has no polar groups, water treeing resistance is generally better than EVA-filled systems, but the grade must not be used as the sole insulation polymer at operating temperatures above 105°C unless stabilized with hindered amine light stabilizers and phenolic antioxidants. The product does not contain halogen, antimony trioxide, or lead stabilizers, but compliance with RoHS Directive 2011/65/EU still requires validation of the final compound because additive components can carry restricted substances.