SINOPEC Baling Hunan SBS YH-802 is a linear styrene-butadiene-styrene block copolymer produced by anionic polymerisation at Baling Petrochemical in Hunan, China. The product is supplied as a neat grade, without extender oil, and has a nominal styrene content of 30 wt%. Typical data from compression-moulded specimens tested under ISO 37:2017 place tensile strength at not less than 18 MPa and elongation at break at not less than 600%. Hardness measured under ASTM D2240-15e1 is controlled to 70–80 Shore A. Melt flow rate at 190 °C and 2.16 kg, determined according to ISO 1133-1:2022, falls within the producer’s specified window for low-viscosity linear SBS grades. Volatile matter and ash are routinely controlled, with typical limits of ≤0.7 wt% and ≤0.2 wt% respectively, using the supplier’s current lot-release methods. Specific gravity is approximately 0.94 when measured under ISO 2781:2018. The unsaturated polybutadiene midblock distinguishes YH-802 from hydrogenated SEBS grades and sets the boundary conditions for melt processing, adhesive ageing, and bitumen modification.

What Distinguishes YH-802 from Other Baling Linear SBS Grades?

Within the Baling SBS portfolio, YH-802 is differentiated from YH-791 and YH-792 chiefly by molecular architecture control and styrene content. YH-802 and YH-791 share a nominal styrene content of 30 wt%, while YH-792 is supplied at 40 wt%. The higher styrene content of YH-792 raises room-temperature hardness and tensile strength but reduces elongation and compatibility with low-polarity bitumens. YH-802 is controlled for low gel content and a constrained diblock fraction relative to YH-791, which is advantageous in hot-melt adhesive and polymer modification operations where creep resistance and lot-to-lot viscosity stability are critical. The following table summarises typical comparative data drawn from the producer’s published technical documentation. These values are not lot-release specifications; certificates of analysis govern acceptance.

From a rheological standpoint, the lower styrene content of YH-802 gives a lower plateau modulus than YH-792 at temperatures below the polystyrene glass transition. The practical consequence is a softer elastic network and lower room-temperature cohesive strength in adhesive films. In bitumen modification, the constrained diblock content of YH-802 reduces the population of low-molecular-weight chains that can migrate under high-temperature storage conditions. This improves top-bottom stability in polymer-modified bitumen storage tanks, though the exact diblock concentration is not published for this specific grade. The producer’s certificate of analysis generally reports melt flow rate and tensile properties rather than absolute molecular weight; average molecular weight is inferred from solution viscosity or size-exclusion chromatography. Published data for the solution viscosity of YH-802 across all solvents is limited, and end users should verify solubility in the intended solvent with a laboratory batch before scale-up.

Field evidence from production-scale bitumen modification with YH-802

Bitumen modification with YH-802 is performed in high-shear mills rather than low-speed mixers. On a production-scale rotor-stator mill, the base bitumen is preheated to 175–185 °C before the polymer is added at 3.0–5.0 wt% based on base bitumen mass. A rotor tip speed of 15–25 m/s is maintained for 60–90 min. Dispersion endpoint is commonly evaluated by fluorescence microscopy at 400×; acceptable polymer-modified bitumen morphology is recorded when SBS-rich domains are smaller than 5 µm and are uniformly distributed in the continuous bitumen phase. Elastic recovery under ASTM D6084-21 typically rises above 50% when the polymer is fully swollen. Storage stability is assessed using a 48 h tube test at 163 °C; a softening point difference above 2.5 °C between top and bottom sections indicates progressive phase separation. Base bitumens with low aromatic or resin fractions may not solvate the polystyrene end-blocks adequately. In such cases, the addition of a compatible aromatic oil at 1–3 wt% or a different binder source is required before increasing YH-802 loading.

The addition window is narrow for a production tank. At temperatures below 170 °C, bitumen viscosity retards polymer swelling. Above 185 °C, the unsaturated polybutadiene block begins to degrade and the light fractions of the bitumen volatilise. In a 20 t production tank, temperature control is typically maintained by thermal oil jackets and slow nitrogen blanketing; the nitrogen flow rate is adjusted to maintain an oxygen headspace below 5 vol%. Without blanketing, surface skin formation and gel particles are observed after 4–6 h at 180 °C. The neat, non-oil-extended composition of YH-802 is a practical difference from oil-extended SBS grades that carry 10–33 wt% extender oil. With YH-802, the formulator retains independent control over the oil fraction, which affects low-temperature ductility and storage stability. Pre-blending of the polymer with bitumen at 70–90 °C in a low-intensity mixer can be performed before high-shear milling, but this step is not sufficient to generate an acceptable dispersion by itself.

Hot-melt adhesive compounding with YH-802 is usually carried out in a sigma-blade mixer or a co-rotating twin-screw extruder at 140–170 °C. The grade is combined with C5 or C9 tackifier resins and a paraffinic or naphthenic plasticiser; a resin-to-polymer ratio of 0.8:1 to 1.2:1 is a common starting point for pressure-sensitive tapes. Peel adhesion on stainless steel is measured under ASTM D3330/D3330M-04(2018), and loop tack is measured under ASTM D6195-03(2019). The low diblock content of YH-802 contributes to low cold creep; however, the unsaturated butadiene block requires stabilisation against thermo-oxidative degradation in hot-melt tanks. For solvent-borne adhesives, toluene or cyclohexane solutions at 25 wt% solids are used; batch viscosity and gelation time should be verified against the lot certificate of analysis because these parameters are sensitive to post-polymerisation processing. A production-scale observation is that residual moisture above 0.1 wt% can produce film defects in continuous coating lines, so pre-drying at 60–70 °C for 2 h is applied when the pellets have been stored in humid conditions. Open time is influenced by the crystallisation of the polybutadiene soft segment and the glass transition of the tackifier blend; open time may be extended by selecting a high-molecular-weight tackifier resin at 10–30 phr. If open time exceeds 60 s on a continuous laminating line, the bond strength measured by ASTM D1876-08(2015) peel may fall below the required value because of premature solidification.

Twin-Screw Compounding of YH-802 Crosses a Defined Decomposition Threshold

In melt compounding, the unsaturated polybutadiene midblock of YH-802 is susceptible to thermo-oxidative chain scission and crosslinking. Field observations on a 40:1 L/D co-rotating twin-screw extruder indicate that a melt temperature above 195 °C combined with a residence time exceeding 90 s increases gel content and reduces elongation at break. A safe barrel profile for general compounding is 140–180 °C from feed to die, with the die temperature held at 170–180 °C. Vent vacuum below -0.08 MPa is recommended to hold residual volatiles at ≤0.7 wt%. Screw speeds of 250–400 rpm are typical on 40:1 L/D lines; higher speeds can push specific energy input above 0.25 kWh/kg and create localised overheating in kneading blocks. A hindered phenolic antioxidant at 0.1–0.3 phr is often added where multiple extrusion passes are required. Gel counts can be monitored by pressure rise across a melt filter; a pressure increase greater than 2.0 MPa over 30 min indicates accumulation of crosslinked gel and requires a screen-pack change. If the melt temperature exceeds 195 °C, screw speed is reduced in increments of 25 rpm, and the feed zone is checked for inconsistent pellet flow. A lower melt temperature of 160–170 °C can be used for adhesive formulations, but mixing torque increases and specific energy input may rise because of higher viscosity. Published kinetic data for this specific grade are limited, but the observed failure mode is consistent with the general polybutadiene degradation behaviour of unsaturated SBS copolymers. Materials should not be combined with strong oxidising agents or exposed to high concentrations of free-radical initiators that accelerate double-bond attack.

When YH-802 Is Selected for Polymer Modification Instead of Hydrogenated SEBS

YH-802 can be used as an impact modifier in polypropylene and high-impact polystyrene blends when service temperature remains below the thermal stability limit of the polybutadiene segment. Melt blending on a 40:1 L/D twin-screw extruder at 180–210 °C with YH-802 loadings of 10–20 wt% raises notched impact strength, but interfacial adhesion is limited without a coupling agent. Maleic anhydride-grafted polypropylene at 2–5 wt% is usually included to improve phase compatibility. Screw residence time at the upper temperature should be held below 60 s to protect the midblock. In injection-moulded parts, a gate temperature of 180–200 °C and a mould temperature of 30–50 °C are used; higher melt temperatures can cause gas generation from the antioxidant package and visible splay. If the final part must resist hot air ageing above 100 °C or prolonged ultraviolet exposure, hydrogenated SEBS grades are more appropriate because their midblock saturation avoids radical-initiated crosslinking in hot runner systems. Tensile impact according to ISO 8256:2004 and notched Izod according to ISO 180:2019 are used to screen impact-modified compounds. YH-802 can also act as a non-reactive compatibiliser in polystyrene/polyolefin blends, but the unsaturation limits its use in outdoor components. Published data for YH-802-specific fatigue behaviour in filled polypropylene matrices is limited.

Storage conditions for YH-802 are defined by the same unsaturated block chemistry. Pellets or crumb are kept in moisture-barrier packaging at or below 40 °C, protected from direct sunlight. Storage above 35 °C for extended periods can cause pellet blocking, antioxidant depletion, and yellowing, even without visible melting. Under nitrogen purging at 25 °C, shelf life from date of production is generally set at 24 months in sealed containers. Containers that have been opened should be purged with nitrogen and re-closed if not consumed within 7 days. The product should not be stored with strong acids, strong oxidisers, or low-molecular-weight aldehydes that can attack the polybutadiene segment. For regulatory compliance, the supplier’s documentation should be consulted for REACH registration status, RoHS recast restrictions, and polycyclic aromatic hydrocarbon content before consumer-article use. Direct food-contact and medical-device applications are not supported unless migration testing on the finished article meets the applicable national regulation; published data for these configurations is limited. The product is combustible and should not be processed near open flames or sources of ignition. Ventilation is required during hot-melt processing to control decomposition products at temperatures above 200 °C.