SINOPEC Baling Hunan SBS YH-791E is a linear styrene-butadiene-styrene thermoplastic elastomer produced by sequential anionic polymerization. The product is supplied as non-oil-extended porous pellets and is used in polymer-modified bitumen, hot-melt pressure-sensitive adhesives, footwear compounds, and impact modification of polyolefins. The grade is identified by a nominal bound styrene content of 30 wt% and a polybutadiene continuous phase; the block structure forms physical crosslinks through polystyrene domains while retaining melt processability. Unlike random styrene-butadiene copolymers, YH-791E exhibits a distinct rubbery plateau between the polybutadiene glass transition and the polystyrene domain softening temperature. The CAS registry number is 9003-55-8, and the material is not oil-extended, allowing the formulator to control plasticizer type and level independently.

What Are the Specification Limits Reported on the Technical Data Sheet?

Published specification limits for YH-791E include a volatile matter requirement of 0.70% maximum according to ASTM D5668 and an ash content limit of 0.20% maximum under ISO 247-1. Tensile strength is controlled at 18 MPa minimum with elongation at break at 700% minimum when measured on compression-molded sheets according to ISO 37:2017. Hardness is specified at 70 Shore A with a permissible spread of ±5 units under ASTM D2240. Melt mass-flow rate is typically reported in the range of 0.1–1.0 g/10 min at 200°C and 5 kg load using ISO 1133-1:2022. Density is approximately 0.94 g/cm³ when determined according to ISO 1183-1:2019. The producer controls bound styrene at 30 wt% by spectrometric or refractometric methods. Solution viscosity data for this specific grade in toluene is limited; the linear architecture produces lower solution viscosity than star-branched SBS of identical styrene content.

Thermal processing limits are governed by the polybutadiene midblock rather than by styrene domain degradation. In twin-screw extruders with L/D ratios of 32:1 to 48:1, barrel profiles are typically set from 150°C in the feed zone to 180°C at the die, with melt-temperature alarms at 210°C. Residence time above 200°C should not exceed 20 min; oxidative gel formation begins as a gradual viscosity increase and then produces visible specks in extrudate. Capillary rheometry at 180°C shows shear-thinning behavior; apparent viscosity decreases by approximately 50–60% when apparent shear rate increases from 100 s⁻¹ to 1000 s⁻¹ under ISO 11443. Pre-drying at 60–70°C for 1–2 h in a dehumidified-air hopper dryer is required when pellets have been stored open at relative humidity above 60%. For hot-melt adhesives, mixing at 160–180°C under nitrogen blanket is typical; overheating beyond 190°C accelerates tackifier reaction and color shift. The product should not be processed with strong oxidizing acids or high concentrations of chlorinated solvents. Incompatible additives include certain amine-based curing agents that can react with residual double bonds and produce premature crosslinking.

The polystyrene domains exhibit a glass-transition temperature near 95°C, while the polybutadiene domains show a glass-transition temperature near −80°C when measured by dynamic mechanical analysis at 1 Hz. This architecture provides rubbery response between these transitions. The unsaturated butadiene midblock is sensitive to oxidative attack; the producer incorporates a hindered phenolic antioxidant and a secondary phosphite stabilizer. YH-791E is insoluble in water and polar solvents such as methanol and acetone, but dissolves readily in toluene, cyclohexane, and methyl ethyl ketone at concentrations up to 25 wt% under ambient conditions. Incoming quality-control laboratories typically monitor a 25 wt% solution in toluene at 25°C to detect molecular-weight drift; published data for this specific grade is limited, but linear SBS of this styrene content generally falls within 4,000–8,000 mPa·s under Brookfield viscometry.

Quality assurance on YH-791E uses in-process control of bound styrene, Mooney viscosity, and solution viscosity. Batch-release certificates report tensile strength, elongation, hardness, melt flow rate, volatile matter, and ash. Each lot is pressed into test sheets at 160°C for 10 min before tensile testing. Downstream incoming quality control often includes a 25 wt% toluene solution viscosity measurement to detect molecular-weight drift. Batches with solution viscosity below the lower control limit produce lower tensile strength and lower melt viscosity; batches above the upper control limit can create incomplete dispersion in bitumen and higher extruder torque. In hot-melt adhesive lines, excessively fragmented pellets can cause feed-throat bridging in gravimetric feeders; pellet integrity is therefore controlled by the producer. Moisture content above 0.1% in incoming pellets is a rejection criterion in processes with residence times above 5 min at 180°C, as degradation can occur.

Asphalt Modification, Polymer Network Formation, and Storage Stability

In paving-grade bitumen modification, YH-791E is typically added at 4–6 wt% based on bitumen mass. The mixing sequence uses a high-shear rotor-stator mill at 180–190°C for 60–120 min, followed by low-shear agitation to allow polystyrene domain formation. The resulting polymer network increases the softening point and elastic recovery of the binder. Storage stability is tested according to ASTM D7173 or EN 13399; separation temperature differences below 2.5°C between top and bottom samples are generally acceptable for many paving specifications. The linear structure of YH-791E usually requires less shearing energy than star-branched grades because of lower molecular weight. Field experience on production-scale asphalt blending units shows that inhomogeneous feeding of porous pellets into hot bitumen can create gel particles if local concentration exceeds 10 wt% before shear is applied. Therefore, pellets are added gradually under high shear, and stagnant zones in the tank are avoided. Elastic recovery measured at 25°C under ASTM D6084 typically shows values above 70% for well-digested binders at 5 wt% loading. At 5 wt% loading in a nominal 70/100 penetration-grade bitumen, rotational viscosity at 135°C by ASTM D4402 commonly reaches 1.5–3.0 Pa·s after complete digestion. Rutting factor G*/sin δ at 64°C may increase above 1.0 kPa after modification, measured by ASTM D7175; the failure temperature is often raised by 10–20°C relative to neat bitumen depending on base bitumen source. At polymer contents above 6 wt%, gelation can occur at 160°C, particularly with high-asphaltene bitumens, producing an elastic paste that cannot be pumped easily.

In waterproofing membranes and bitumen sheets, YH-791E is used at 8–12 wt% in combination with fillers and flame-retardant additives. The grade provides low-temperature flexibility measured by cold flexibility tests according to EN 1109; compounds typically achieve a cold bending temperature of −20°C or lower depending on formulation. At these loadings, melt viscosity is influenced strongly by filler surface area; shear mixing under vacuum is required to remove entrapped air. Because the butadiene segmer is unsaturated, heat-aged sheets must be protected with antioxidants. Accelerated aging per ASTM D5721 should show less than 10% change in ring-and-ball softening point for a properly stabilized formulation.

Hot-melt pressure-sensitive adhesive compounds based on YH-791E use tackifier resins, typically C5 aliphatic or hydrogenated rosin ester, and plasticizing oil, typically naphthenic or paraffinic. A starting formulation may contain 100 phr YH-791E, 120 phr tackifier, and 50 phr oil, with 1.0 phr antioxidant. The blend is mixed at 170–180°C until homogeneous; viscosity measured by ASTM D3236 at 180°C after 4 h thermal aging should not increase by more than 20% to ensure pot stability. Because YH-791E is not oil-extended, the formulator controls oil type and content independently; this differs from oil-extended SBS grades where the fixed oil level limits formulation flexibility. Melt viscosity at 180°C is lower than radial SBS types, which permits slot-die coating on standard hot-melt lines without gear-pump pressures above 80 bar. Slot-die lines may operate at 20–100 m/min; coat weights of 18–25 g/m² are common for label stocks. However, the lower molecular weight also reduces high-temperature cohesive strength; creep resistance at 60°C may be lower than star-branched SBS unless the formulation is reinforced with end-block reinforcing resin. Shear adhesion failure temperature measured by ASTM D4498 may range from 55°C to 70°C depending on tackifier softening point and oil level. Loop tack depends on coating weight and substrate; validation is performed according to ASTM D6195 on polyester film. For food-contact adhesive applications, the final adhesive formulation must be evaluated under 21 CFR 175.105 or applicable regional regulations; the raw YH-791E polymer does not carry independent food-contact clearance.

When YH-791E Is Evaluated Against YH-792 and Star-Branched SBS

In direct comparison with SINOPEC Baling YH-792, a linear SBS with a nominal bound styrene content of 40 wt%, YH-791E has lower hardness, lower tensile strength, and higher elongation. The higher butadiene content of YH-791E provides greater low-temperature flexibility in modified asphalt and lower modulus in adhesive films. YH-792 is preferred where higher tensile strength and higher service temperature are needed, such as rigid polymer modification and certain footwear sole compounds. Compared with star-branched SBS grades, YH-791E has a narrower molecular-weight distribution and lower melt viscosity; this translates to lower compounding torque on twin-screw extruders and easier mixing into bitumen. On production-scale bitumen units with rotor-stator mixers below 50 kW, YH-791E is often fully dispersed in 60 min, whereas radial grades may require 120 min or more, depending on bitumen source and tip speed. However, star-branched grades generally show higher tensile strength, better elastic recovery at elevated temperature, and greater resistance to permanent set. In adhesive applications requiring low creep at 70°C, YH-791E may require a higher polystyrene end-block resin level; a star-branched grade may meet the same creep specification without modification. Published data for direct comparative creep testing of YH-791E against star grades in identical adhesive formulations is limited; selection should be confirmed on production-scale coating equipment with the intended tackifier package.

Compounding of YH-791E into footwear microcellular sole formulations is carried out in internal mixers or twin-screw lines with EVA or polypropylene. Typical addition levels range from 10–30 phr in compounds where the SBS contributes impact modification and soft-touch properties. In polypropylene impact modification at 5–20 wt%, the notched Izod impact at −30°C is improved relative to unmodified material; testing is conducted according to ISO 180/A on specimens conditioned for 24 h. Melt mixing is performed in twin-screw extruders at 190–220°C with distributive mixing elements to avoid phase coalescence. Compression set of YH-791E compounds measured per ISO 815-1 at 70°C for 24 h is typically below 40% for high-styrene-end-block formulations, but compound-specific validation is required. Published data for the specific YH-791E grade in polypropylene is limited, but the response follows linear SBS impact-modifier behavior. Because the butadiene segment is unsaturated, outdoor exposure requires antioxidants, antiozonants, or carbon black loading above 2 phr.

YH-791E is packaged in 25 kg polyethylene bags, which should be stacked no more than 5 layers to prevent agglomeration. Storage below 40°C and away from direct sunlight is required. Under these conditions, a shelf life of 24 months from date of manufacture is stated by the producer. Opened bags should be reclosed and consumed within 30 days if ambient relative humidity exceeds 70%.