SINOPEC Baling Hunan SBS YH-792 is a linear styrene-butadiene-styrene block copolymer produced by anionic polymerization. The product has a nominal bound styrene content of 40 wt%, a polybutadiene midblock, and a predominantly linear chain architecture. It is supplied as a white porous pellet or crumb that is not sulfur-vulcanized during typical thermoplastic elastomer processing. The grade is manufactured at the Baling site in Hunan Province and is specified for general-purpose thermoplastic elastomer compounding, footwear soling, adhesive modification, and asphalt modification. Physical crosslinks are formed by phase separation of the polystyrene end blocks into glassy domains whose glass transition temperature exceeds ambient service conditions.

The designation YH-792 is differentiated within the producer’s SBS range by its linear chain topology and styrene mass fraction. Linear grades are produced without a multifunctional coupling agent, unlike radial grades such as YH-188. The linear topology reduces low-shear melt viscosity, die swell, and elastic memory relative to a radial polymer of equivalent molecular weight. However, cohesive strength and creep resistance of the final compound are also reduced, particularly at elevated temperature.

How does YH-792 compare with adjacent grades in the Baling SBS series?

For a manufacturer screening a footwear unit sole compound, the central variable is the styrene-to-butadiene mass ratio. YH-792 has a higher bound styrene content than softer grades such as YH-796, which increases hardness, abrasion resistance, and 300% modulus while reducing low-temperature flexibility and pressure-sensitive tack. In comparison with a radial SBS of similar bound styrene, YH-792 generally exhibits lower viscosity at low shear rates and a less pronounced shear-thinning response in a capillary viscometer. The practical consequence in an injection molding shop is that YH-792 fills a multi-cavity mold at lower injection pressure but may show higher linear shrinkage parallel to flow. Published single-point comparative data for the current production campaign are limited; the grade should not be selected as a direct substitute for radial SBS without running a full compound validation using ISO 37 tensile specimens and ISO 34 trouser-tear test pieces.

For specification-compliance testing, YH-792 is characterized under standard elastomer test methods. The supplier’s current technical bulletin records a nominal density of 0.94 g/cm³ when measured according to ISO 1183. Tensile strength and elongation at break are measured on 2 mm dumbbell specimens cut from compression-molded sheets per ISO 37; the grade is controlled to a minimum tensile strength of 20 MPa and a minimum elongation at break of 700%. The 300% modulus is specified at a minimum of 2.5 MPa, reflecting the reinforcing contribution of the polystyrene end-block domains. Hardness is typically within 85–90 Shore A under ISO 48-4 or ASTM D2240 after a 15 s reading. Melt flow rate under 200°C/5 kg load in ISO 1133-1:2022 is typically below 1.0 g/10 min, indicating a relatively high molecular weight and the need for adequate plastication energy in screw-fed processes. Volatile matter is held below 0.5 wt% and ash below 0.2 wt%, measured by methods aligned with ASTM D5668 and ISO 247 respectively. These values are acceptance limits or typical values from public supplier documents, not a certificate of analysis; incoming lots should be verified against the current production release report.

The solution viscosity of YH-792, measured as a 25 wt% solution in toluene at 25°C, is controlled within a supplier-specific band and is used to detect batch-to-batch variation in diene block length and molecular weight distribution. The linear architecture and 40 wt% bound styrene result in a more Newtonian steady-shear response than radial SBS of comparable styrene content. On production-scale compounding lines, the solution viscosity value is a more reliable predictor of dispersive mixing behavior than MFR alone, particularly when the product is dry-blended with fillers and oils before extrusion.

Processing window constraints for twin-screw compounding

In a co-rotating twin-screw extruder with an L/D ratio of 40:1 or greater, YH-792 is melted in the early barrel zones when barrel temperatures are set to 150–170°C in the feed section and 170–190°C downstream. The melt temperature should remain below 210°C; gel formation and chain scission accelerate above 230°C under high shear because the polybutadiene midblock contains residual unsaturation that is susceptible to thermal oxidation and radical recombination. Residence time should not exceed 4–5 min at these temperatures. The product can be pre-dried at 60–70°C for 2 h when storage relative humidity exceeds 60%, although moisture sensitivity is lower than that of condensation polymers. Addition of a hindered phenolic antioxidant at 0.1–0.3 phr and a phosphite secondary antioxidant at 0.1–0.2 phr is standard when the compound is intended for extended outdoor exposure or for multiple regrind cycles. The use of aromatic process oils should be limited because the polystyrene end-block domains are solvated by aromatic hydrocarbons, which lowers the upper service temperature and reduces tensile properties; naphthenic or paraffinic oils at 5–30 phr are preferred for viscosity reduction without excessive domain softening.

Compounding for footwear unit soles begins with dry-blending YH-792 with general-purpose polystyrene at 10–30 phr to increase hardness and abrasion resistance. The blend is injection molded on a reciprocating-screw machine with a mold temperature of 30–50°C, which is sufficient because the styrenic domains vitrify rapidly and provide green strength without crosslinking. Abrasion loss testing under DIN 53516 shows that the higher styrene content of YH-792 produces lower mass loss than lower-styrene SBS grades in solid microcellular formulations. The main processing bottleneck is gate blush and melt fracture at high shear rates; reducing injection velocity and increasing nozzle temperature to 190°C mitigates surface defects. Batch-to-batch variance in solution viscosity has been observed on production-scale lines; incoming inspection should compare lot values to the supplier’s control chart before setting screw speed and back pressure.

For hot-melt pressure-sensitive adhesive applications, YH-792 is combined with a tackifier resin, typically a hydrogenated glycerol ester of rosin or a C5/C9 aliphatic-aromatic hydrocarbon resin, at tackifier loadings of 80–120 phr relative to polymer. The linear architecture provides lower cohesive strength than radial SBS at equal coating weight, but the lower melt viscosity enables more uniform slot-die coating at 160–180°C. The styrenic domains confer creep resistance at ambient temperature, while the polybutadiene midblock provides pressure-sensitive tack. Open time and shear adhesion failure temperature are functions of tackifier selection and resin-to-polymer ratio; formulation with a tackifier having a ring-and-ball softening point of 100 ± 5°C yields a shear adhesion failure temperature above ambient but below the polystyrene domain glass transition. Avoid amine-based adhesion promoters because residual amine can catalyze oxidative degradation of the unsaturated midblock at processing temperatures.

When YH-792 is selected for hot-melt adhesives instead of a radial SBS

Selection of YH-792 over radial SBS for a hot-melt formulation should be based on a comparison of melt viscosity, die swell, and cohesive strength after coating. The linear YH-792 grade generally produces a lower die swell in the molten state because the linear chains relax more uniformly through the slot die, which reduces neck-in and coating width variation. In contrast, a radial SBS of similar bound styrene content may provide higher low-shear viscosity and greater elastic recovery, improving sag resistance in vertical applications. For a manufacturer running a slot-die coater at 170°C, the linear grade is less likely to exceed the pressure limit of a gear pump, but the resulting adhesive film may show slightly lower peel adhesion on low-energy substrates. The difference is measurable with ASTM D3330 loop tack and ASTM D3654 shear adhesion tests, but the direction and magnitude of the difference depend on tackifier solvation and film thickness. Because published data for this specific configuration are limited, a side-by-side compound validation is required.

In comparison with styrene-isoprene-styrene block copolymers, YH-792 exhibits a higher tensile strength and better abrasion resistance due to the butadiene midblock, but lower tack and low-temperature flexibility. In comparison with hydrogenated styrenic block copolymers such as SEBS, YH-792 has higher flowability at a given molecular weight and stronger interaction with hydrocarbon tackifiers, but lacks the oxidative stability of a saturated midblock. In comparison with ethylene-vinyl acetate copolymers used in foam midsole compounds, YH-792 has a lower density and requires no crosslinking agent, but has lower ozone resistance and lower compression set resistance at elevated temperature.

In asphalt modification, YH-792 is dispersed into paving-grade bitumen at 4–6 wt% through a high-shear mill operated at 180–190°C for 30–60 min. The higher styrene content increases the softening point and elastic recovery compared with lower-styrene SBS, but requires longer digestion time to achieve a continuous polymer network. A storage stability test under EN 13399 is used to measure phase separation after 72 h at 180°C; high-shear dispersion must minimize SBS particle size to avoid settling. The modified binder should be evaluated for penetration at 25°C per EN 1426 and ring-and-ball softening point per EN 1427, with values depending on base bitumen and polymer content rather than on polymer grade alone.

Storage and handling practice follows standard thermoplastic elastomer guidelines. The product should be kept below 40°C, away from direct sunlight, and in an area free of ozone-generating electrical equipment. Under these conditions the supplier’s shelf life for SBS grades is typically 24 months from the date of production. When the product is transferred from cold storage to a warm processing hall, condensation must be avoided by leaving the packaging sealed until temperature equilibration is complete. Under the European REACH regulation, SBS polymers are notified substances, and the grade is generally outside the scope of hazardous classification; users should confirm the latest safety data sheet and verify RoHS applicability for compounded formulations containing additional pigments or flame retardants.

YH-792 should not be used in continuous service above 80°C under load unless the compound is crosslinked or blended with a continuous high-temperature phase. It is not recommended for immersion in aromatic or chlorinated solvents, which plasticize the polystyrene domains and can induce gross swelling. Ultraviolet exposure causes surface embrittlement; compounds intended for outdoor use require carbon black at 2–5 wt% or a hindered amine light stabilizer package. Because the polybutadiene midblock is unsaturated, ozone resistance is poor compared with hydrogenated SEBS grades; the material should not be specified for dynamic seals in ozone-rich environments.