SINOPEC Baling SEBS YH-604 is a linear triblock copolymer comprising polystyrene end blocks and a hydrogenated ethylene-butylene midblock. The saturated midblock differentiates the material from styrene-butadiene-styrene block copolymers by removing main-chain unsaturation, while the polystyrene domains remain physically crosslinked at service temperatures below approximately 95 °C. YH-604 is supplied as a low-dusting white powder or crumb without process oil, thereby allowing independent selection of plasticizer type and loading in thermoplastic elastomer compounds. Supplier literature positions the grade for general-purpose TPE compounding, polymer modification, adhesives, sealants, and soft-touch overmolding. The absence of grafted maleic anhydride functionality limits direct bond strength to polyamide, aluminum, and other polar substrates unless a functionalized coupling resin is incorporated. The product is not interchangeable with oil-extended SEBS grades because its melt flow rate is substantially lower and its oil absorption must be executed in a controlled compounding sequence rather than by simple dry blending.

Molecular Architecture and Specification Envelope

The styrene content in YH-604 is reported at 33 wt% ± 1 wt% in supplier technical documentation, with the balance as hydrogenated polybutadiene midblock. The polystyrene domains exhibit a glass transition temperature near 95 °C, and the ethylene-butylene midblock displays a sub-ambient glass transition below −40 °C. These transitions control the lower and upper service temperature limits. The polymer is not crosslinked and therefore reprocessable, but the same feature restricts compression set resistance in hot, loaded seals. The specification envelope places YH-604 in a low-to-medium hardness segment after compounding; plant-scale batches typically use within-lot consistency targets of ±2 Shore A for hardness and ±0.5 g/10 min for melt flow rate.

The low melt flow rate value should be interpreted as a neat-polymer indicator, not a compound specification. Once oil and fillers are introduced, compound melt flow can rise by more than two orders of magnitude depending on oil viscosity and polypropylene content. The styrene content governs the upper use temperature and hardness. At 33 wt% styrene, the polystyrene domains maintain network integrity up to about 85–95 °C under low stress; beyond this range, the domains soften and creep increases. The ethylene-butylene midblock contributes elastomeric recovery between −40 °C and 70 °C. Because YH-604 has no oil extension, its neat hardness is higher than oil-filled compounds but lower than some high-styrene SEBS grades with styrene contents above 40 wt%, which may be specified for sealing applications requiring higher moduli.

What Limits Processing Stability in High-Shear Compounding?

Thermal and shear stability limits are set by the polystyrene end blocks and the high molecular weight of the ethylene-butylene midblock. Barrel temperatures above 250 °C initiate depolymerization of the styrene blocks, producing low-molecular-weight fragments and a yellowing tendency. On a co-rotating twin-screw extruder with an L/D ratio of 40:1, a typical profile is 160 °C in the feed throat, 180 °C at the melt seal, 200 °C at the die, and 210 °C maximum at the mixing elements. Screw speeds of 250–400 rpm on a 40 mm machine balance dispersion and temperature rise; higher speeds above 500 rpm can produce melt temperatures above 240 °C and cause localized gel formation. A vacuum vent at −0.08 MPa absolute is recommended to reduce volatile content below 0.05 wt%. Residence time should not exceed 8 minutes at full output. Pre-drying of YH-604 at 80 °C for 2 hours is required when moisture content exceeds 0.1 wt%; otherwise extrudate porosity and melt viscosity variation may appear.

Rheologically, YH-604 exhibits pronounced shear thinning at processing temperatures. Capillary rheometry data show apparent viscosity decreasing from approximately 1500 Pa·s at 10 s⁻¹ to below 200 Pa·s at 1000 s⁻¹ at 200 °C. This behavior permits high-output extrusion once melt is formed but creates high start-up torque in cold screw sections. The first mixing zones should be designed with wider kneading-disc clearances to avoid excessive localized energy input. Batch-to-batch variation on production lines is generally observed as melt flow rate drift and die-pressure fluctuation when the polymer feedstock is not pre-dried or when regrind ratios exceed 20 %. Regrind from YH-604 compounds can be reincorporated up to 20 % without significant property loss if the regrind is dry and free of contamination; higher levels reduce tensile strength due to cumulative shear history.

In injection molding, the recommended melt temperature is 190–220 °C, and the mold temperature should be 20–50 °C. Clamp force requirements are typically 2–4 kN/cm² of projected area. High injection speeds reduce gate blush but increase frictional heating; nozzle melt temperature should not exceed 240 °C. Shrinkage is anisotropic: 1.2–1.6 % in the flow direction and 0.8–1.2 % transverse, as determined on 110 mm × 110 mm × 2 mm plaques. This anisotropy should be accounted for in tooling for multi-cavity molds.

No single formulation window controls all uses of YH-604. In polypropylene-based TPE compounds, the grade is typically used at 30–60 wt% with polypropylene as the continuous phase. Addition of 10–20 wt% high-density polyethylene reduces die swell and improves surface smoothness in profile extrusion; elongation at break is sacrificed by approximately 5–10 % absolute. Paraffinic white oils with kinematic viscosity of 30–100 mm²/s at 40 °C are absorbed at loadings from 20 phr to 120 phr. When oil loading exceeds 120 phr, surface exudation develops unless enough polypropylene is present to generate a co-continuous network; the critical oil retention threshold can be evaluated by measuring Shore A hardness after 7 days at 23 °C. Calcium carbonate with median particle size 2–5 µm is tolerated up to 30 wt%, but tensile strength measured under ASTM D638-14 decreases by roughly 0.5 MPa per 10 wt% filler addition. The addition of 0.1 wt% hindered phenolic antioxidant plus 0.1 wt% phosphite stabilizer is standard for long-term heat aging above 80 °C.

For adhesives and sealants, YH-604 is dissolved in aliphatic or cycloaliphatic solvents or hot-melt compounded with tackifier resins. Aliphatic tackifier resins with softening points above 100 °C are preferred because aromatic tackifiers plasticize the polystyrene end blocks and lower the shear adhesion failure temperature. Hot-melt formulations based on YH-604, a mid-block compatible tackifier, and a small amount of polypropylene wax show open times of 30–60 seconds and viscosity suitable for bead application at 180 °C. In cable-filling compounds, YH-604 is used with high-viscosity white oil to produce gels with cone penetration values controlled between 200 and 300 tenths of a millimetre under ISO 2137; published data for specific YH-604 cable gel formulations is limited.

When a Non-Hydrogenated SBS or Maleated SEBS Is Considered

Differences between YH-604 and other block copolymer products become significant in weathering, adhesion, and processing. Compared with a non-hydrogenated SBS of similar styrene content, YH-604 retains a higher fraction of original elongation under artificial weathering because the ethylene-butylene midblock has no allylic hydrogen sites that accelerate autoxidation. In unfilled compounds exposed under ASTM G154-16 Cycle 2 using UVA-340 lamps, SEBS often retains more than 70 % of initial elongation after 1000 h, while general-purpose SBS may embrittle within 300–500 h. The saturated midblock also gives better thermal stability during hot-melt compounding, but it raises raw material cost and reduces compatibility with high-polarity plasticizers. YH-604 differs from oil-extended SEBS grades by having higher neat viscosity and requiring separate oil absorption; this creates wider formulation latitude but demands more controlled mixing than pre-extended grades. Compared with maleic anhydride grafted SEBS, YH-604 has negligible inherent polar adhesion; lap shear adhesion to polycarbonate under ISO 4587 is generally below 0.2 MPa, whereas maleated SEBS can exceed 1.5 MPa after 24 h moisture annealing. The lower reactivity of YH-604 is advantageous where low residual acidity and high volume resistivity are required.

Operational boundaries of YH-604 are defined by solvent exposure, thermal aging, and compression set. The grade is not recommended for dynamic seals in hot air above 100 °C unless a crosslinking package or high-crystallinity polypropylene is added. Compression set after 22 h at 70 °C under ASTM D395-18 Method B typically remains in the range of 25–45 %. Aromatic hydrocarbons, ketones, and chlorinated solvents dissolve the polystyrene domains or swell the ethylene-butylene midblock; toluene volume swell at 23 °C can exceed 300 %. Strong oxidizing acids and high-aromatic process oils should be avoided. In adhesive service above 120 °C, published data for YH-604-specific formulations is limited; performance must be validated by the end user under the relevant ISO or ASTM exposure protocol. The product is not intended for biomedical implant applications unless separately qualified under ISO 10993. Material stored above 60 % RH requires pre-drying before melt processing to prevent extrudate porosity and melt viscosity variation.