SINOPEC Baling SEBS YH-506 is a linear styrene-ethylene/butylene-styrene block copolymer supplied as a white free-flowing powder. The product is manufactured by anionic solution polymerization of styrene and butadiene, followed by selective hydrogenation of the butadiene midblock to a saturated ethylene/butylene sequence. Manufacturer-published data list a nominal bound styrene content of 33 wt% and a diblock content not exceeding 1 wt%. The grade is not oil-extended and not maleic anhydride-grafted; formulator-controlled plasticizer and filler loadings are therefore possible. The absence of main-chain unsaturation distinguishes YH-506 from SBS and provides improved resistance to ultraviolet radiation, ozone, and thermal oxidation under equivalent conditions. This distinction is relevant in outdoor automotive and construction applications where SBS grades commonly fail by surface crazing and embrittlement. Because the ethylene/butylene midblock is saturated, the polymer is not curable by sulfur or peroxide systems; it relies on polystyrene endblock domains as physical crosslinks.

What Is the Property Envelope for Neat YH-506?

Table 1 lists manufacturer-published typical values for neat YH-506. These values are obtained on compression-molded specimens prepared according to the indicated test methods and should not be read as guaranteed specification limits; batch release values are provided in the certificate of analysis. The property envelope is relevant for neat polymer and for formulations containing moderate amounts of compatible plasticizer.

Solution viscosity is used as a quality-control proxy for molecular weight and batch consistency. A change in 25% toluene viscosity of more than 15% between batches may alter shear thinning behavior and final tensile strength even if melt flow rate remains within specification. Melt flow rate is measured on dried powder with a standard die according to ISO 1133-1:2022; moisture in undried powder can reduce the apparent MFR by promoting bubble formation. Storage should be in sealed containers below 40 °C, protected from ultraviolet light and moisture. Powder may compact under storage load; fluidization with dry air below 30% relative humidity is recommended before pneumatic conveying.

Under REACH, the polymer as such is exempt from registration, but monomers and additives used in production require registration. RoHS compliance for electrical and electronic applications is generally achieved if the compounded material does not contain restricted flame retardants or heavy metal stabilizers. FDA 21 CFR 177.2600 permits use in rubber articles intended for repeated food contact, subject to end-use extraction limits; migration testing on the finished article is required because the base polymer certificate alone does not establish food-contact compliance.

Before melt processing, YH-506 should be dried in a desiccant dryer at 70 °C for 2–3 h when surface moisture exceeds 0.1 wt%. On production-scale co-rotating twin-screw extruders with L/D ratios between 36:1 and 48:1, the most frequent powder-handling failure is feed-throat bridging caused by frictional heating. Feed-throat jacket temperature is held below 45 °C, and the first barrel section is cooled when ambient relative humidity exceeds 60%. Barrel setpoints from 150 to 190 °C are typical, with die temperature at 190–200 °C. Melt temperature should not exceed 220 °C when residence time is longer than 120 s; oxidative gel formation appears as specks and increases screen-pack pressure drop in filtration grades from 100 to 250 mesh. In injection molding, melt temperatures of 180–210 °C and mold temperatures of 20–40 °C are suitable; gate diameters below 1.5 mm can impose shear rates above 10,000 s⁻¹, producing melt fracture and reducing elongation by more than 20% in thin-walled parts.

Melt-mass-flow rate is a single-point index and is not a complete rheological model. Mold-flow simulation requires Cross-WLF viscosity coefficients obtained from capillary rheometry at 180, 200, and 220 °C and shear rates from 100 to 10,000 s⁻¹. Published continuous capillary viscosity data for this exact grade are limited; production-line viscosity data should be generated before tooling is cut.

Oil Extension Shifts the Mode of Mechanical Failure

In formulation practice, paraffinic white oil is used to lower hardness and reduce melt viscosity. At oil loadings from 30 to 120 phr, YH-506 remains processable on co-rotating twin-screw extruders, but the mechanical failure mode shifts from ductile yielding to lower-stress tearing. Tensile strength decreases monotonically with oil content; at 100 phr paraffinic oil, compression-molded tensile strength is typically below 12 MPa and may fall to 8 MPa or less when naphthenic oil is used. Elongation at break is less sensitive up to 70 phr, but softer formulations below 45 Shore A often show sticky surfaces and higher compression set. Naphthenic oil reduces compatibility with the saturated midblock; its use above 30 phr can produce surface bloom and lower tear resistance. Aromatic oil is not recommended for YH-506 because it plasticizes the polystyrene domains, lowers the upper service temperature, and increases compression set after exposure at 70 °C for 22 h.

Side-feed oil injection after the first kneading block maintains surface quality in extrusion compounding. Feeding oil too early reduces shear and produces undispersed oil pockets. As oil loading increases from 0 to 100 phr, Shore A hardness falls from about 75 to below 30, and the compound transitions from a structural elastomer to a sealant-like soft material. The trade-off between flow and mechanical strength must be resolved by end-use testing rather than by melt-flow data alone.

When to Select YH-506 Over YH-503 or YH-502

YH-506 is positioned in the Baling SEBS range as a medium-styrene, higher-flow grade. The higher melt flow relative to YH-503 allows thin-wall injection molding and lower clamp force requirements; however, the tensile strength is slightly lower than that of lower-MFR grades. Table 2 compares representative manufacturer-published values. Users should verify the exact comparison against the certificate of analysis because batch-to-batch variation and test specimen preparation influence the values.

Compared with YH-501, YH-506 has higher bound styrene and therefore higher hardness and modulus; it is selected when a stiffer, more heat-resistant compound is required. Compared with YH-503, YH-506 has higher melt flow and lower solution viscosity, which reduces injection pressure and permits longer flow paths. In profile extrusion, YH-503 may be preferred because its higher melt strength reduces die swell; in injection molding of multi-cavity footwear parts, YH-506 is preferred because of fill pressure limitations. The tensile strength penalty relative to YH-503 is usually 2–4 MPa in neat compression-molded sheets, but in filled formulations the difference may be smaller than batch variation.

Aging, Compression Set, and Fluid Resistance

Oven aging according to ISO 188:2011 at 100 °C for 168 h typically retains more than 70% of tensile strength when the antioxidant package remains intact. Without additional stabilizers, continuous service above 100 °C in air is not recommended for neat YH-506. Compression set measured by ISO 815-1:2019, method A, after 22 h at 70 °C is typically below 35%; after 24 h at 100 °C, the set may exceed 50%. This occurs because the polystyrene endblock domains soften near their glass-transition region, reducing the physical crosslink density. Sustained sealing applications above 100 °C should use a crosslinked SEBS or an alternative thermoset material.

Fluid resistance is dominated by the saturated midblock. YH-506 swells in aliphatic and naphthenic oils; mass uptake in ASTM No. 3 oil at 70 °C for 70 h can reach 50–150%. It is not recommended for seals continuously immersed in hydrocarbon oils unless the compound is designed for high oil swell. The product shows low water absorption; immersion in distilled water at 23 °C for 7 days generally yields less than 1% mass increase. Continuous contact with aromatic hydrocarbons, chlorinated solvents, and strong oxidizing acids should be avoided because these fluids attack the polystyrene domains or degrade the rubber midblock.

In footwear compounding, YH-506 is blended with polypropylene, paraffinic oil, and calcium carbonate. Starting formulations often contain 100 phr YH-506, 30–50 phr paraffinic oil, 20–40 phr polypropylene, and 20–60 phr calcium carbonate. Hardness is adjusted to 55–65 Shore A for foamed midsoles and 70–80 Shore A for outsole skins. Density reduction from 0.90 to 0.45 g/cm³ is obtained by chemical foaming or gas-counterpressure injection molding. Abrasion resistance is not an intrinsic property of neat YH-506; finished-sole wear performance is evaluated according to DIN 53516 or ISO 4649.

In polypropylene impact modification, YH-506 is used at 5–20 wt%. Notched Izod impact measured by ISO 180/A improves from 3–5 kJ/m² to 15–40 kJ/m² depending on the matrix and phase dispersion. The dispersed SEBS particle size should remain below 2 µm; poor dispersion leads to macroscale delamination and inconsistent impact values. Above 20 wt%, the compound enters thermoplastic elastomer behavior and tensile modulus falls below 800 MPa.

Hot-melt adhesives can be formulated with YH-506, hydrogenated hydrocarbon tackifiers, and paraffinic wax. The styrenic domains provide elevated-temperature cohesive strength, while the ethylene/butylene midblock contributes tack and flexibility. Viscosity stability at 180 °C for 24 h is generally below 10% change when 0.3–0.5 phr of a hindered phenolic antioxidant is present. Bond performance depends on substrate and should be tested by ISO 4587 or ASTM D1002.

Wire-and-cable jacketing containing YH-506 requires high loadings of mineral flame retardants to achieve cable flame ratings. Magnesium hydroxide or aluminum trihydrate levels often exceed 60 wt%; elongation may drop below 150% unless a compatibilizer is used. Volume resistivity after conditioning at 20 °C and 50% relative humidity is evaluated according to IEC 62631-3-1; typical values exceed 1 × 10¹⁰ Ω·m for clean, dry compounds.

Polymer-modified bitumen can be produced with YH-506 at 4–6 wt%. Softening point and low-temperature flexibility improve, but storage stability under EN 14023 often requires a chemical stabilizer because phase separation may occur after 72 h at 180 °C in unstabilized blends. Published data for this specific configuration is limited; plant trials are required to set stabilizer dosage.