SINOPEC Baling SEBS YH-604T is a hydrogenated styrene-ethylene-butylene-styrene triblock copolymer produced by Baling Petrochemical Company, Sinopec. The polymer consists of two terminal polystyrene blocks and a saturated poly(ethylene-co-butylene) midblock. The saturated midblock differentiates YH-604T from unsaturated SBS elastomers such as Baling YH-792 by reducing the concentration of reactive double bonds in the rubber phase, which improves resistance to ultraviolet irradiation, ozone, and thermal-oxidative chain scission during processing. Producer technical documentation positions YH-604T as a compounding grade for elastomeric articles requiring a balance of tensile strength, filler acceptance, and controlled melt flow. The typical styrene content is reported near 32 wt%, and the diblock content is controlled to ≤1.0 wt%. A low diblock concentration is significant because diblock chains possess only one styrenic terminal block and therefore do not contribute to the glassy styrenic network; excessive diblock reduces tensile strength and increases compression set. YH-604T is supplied as free-flowing porous crumb with low dust, and it may be pelletized after oil extension. The grade is not intended as a neat injection-molding resin; industrial use typically proceeds through a separate compounding operation.

Product Definition and Specification Framework

The specification framework for YH-604T is defined by medium styrene content, linear molecular architecture, and controlled gel content. Linear SEBS grades exhibit lower die swell and lower melt elasticity than radial grades, which allows higher filler loadings before the torque limit on a co-rotating twin-screw extruder is reached. Producer-reported typical values are summarized in Table 1. The values are not contractual quality limits and should be verified against the lot-specific certificate of analysis. In food-contact or medical applications, grade-specific compliance must be established under FDA 21 CFR 177.2600, EU Regulation (EU) No 10/2011, or similar national legislation; the polymer supplier’s declaration does not cover the finished compounded article.

When YH-604T is used in soft-touch automotive interior skins and grip layers, the usual processing route is melt blending with polypropylene homopolymer and white oil on a co-rotating twin-screw extruder. A representative starting formulation contains 100 parts YH-604T, 25 parts isotactic polypropylene homopolymer, 80 parts hydrotreated paraffinic oil, and 0.2 parts hindered phenolic antioxidant. Oil is introduced through a downstream liquid-injection port rather than at the main feed throat to maintain solids conveying and dispersive mixing in the melting zone. On a production line with 40:1 L/D and side-feeding capability, the first barrel zones are held between 160 °C and 190 °C, and the final zones are held at 220–230 °C. Higher final zone temperatures produce fuming from low-molecular-weight oil fractions and a measurable broadening of molecular weight distribution in subsequent gel-permeation chromatography. Batch-to-batch variation in YH-604T crumb bulk density can shift gravimetric feeder output by 5–10%; processors compensate by densifying the crumb or by using an agitated hopper. The compounded pellets are then injection molded into thin-wall grip surfaces, where the SEBS domains reduce stress whitening and improve scratch resistance relative to neat polypropylene. Scratch resistance is evaluated according to VW PV3952 or an equivalent automotive manufacturer standard; published data for this specific YH-604T compound configuration is limited, and target values depend on surface grain depth and mold texture.

The use level of YH-604T is constrained by the desired hardness and fogging performance. At oil loadings above 100 phr, hardness falls below 60 Shore A and the polypropylene phase must be increased to restore mar resistance. Fogging measurements according to ISO 6452 are influenced by the oil’s volatility and by antioxidant migration, not only by the SEBS base resin. Therefore a grade change from a high-flow SEBS to YH-604T without adjusting the oil package can fail cockpit interior limits. In such cases, oil with a flash point above 250 °C and a volatility after 16 h at 100 °C below 0.5% is typically required.

What Limits the Processing Window in High-Shear Injection Molding of YH-604T?

The principal processing limit for YH-604T compounds in injection molding is not the melting of the styrenic end blocks but the shear-induced temperature rise at the screw check ring and gate. Neat YH-604T exhibits high low-shear melt viscosity; consequently, it is usually processed as a compounded pellet with melt flow rate adjusted by oil or polypropylene. For a compound containing 30–40% YH-604T, a melt temperature of 200–230 °C and a mold temperature of 30–50 °C are adequate for thin-wall sections down to 1.0 mm. Filling times are maintained at 0.5–1.5 s to prevent premature freeze-off. The critical threshold is localized melt temperature above 240 °C at the gate. At this temperature, chain scission in the EB midblock can begin, and the resulting melt flow drift after molding may exceed 15% relative to the original pellet. The failure signature on the production floor is a combination of gate blush, splay, and reduced weld-line elongation, often accompanied by a drop in hardness after annealing.

To control shear heating, molders use a general-purpose screw with a compression ratio of 2.5:1 and a check-ring clearance below 0.2 mm at the molding temperature. When the clearance exceeds 0.3 mm, backflow raises melt residence time near the screw tip and produces gel particles visible as hard specks in transparent or unpigmented compounds. A shot size below 25% of barrel capacity should be avoided because the long residence time in the barrel will cause the melt flow rate to drift even when barrel temperatures are held at 220 °C. In these conditions, a decrement of 5 °C in metering-zone set point often reduces splay without sacrificing filling. Pre-drying of YH-604T is not required when the storage bag has remained sealed below 60% relative humidity. If the crumb has been exposed to humid air, drying for 2 h at 80 °C in a desiccant hopper dryer is recommended to prevent steam bubbles and surface roughness in molded parts.

In compounding, a separate degradation route is oxidative loss of the EB midblock when process oil is injected into a high-shear zone without sufficient antioxidant. In twin-screw lines with downstream oil injection, the antioxidant is preferably added with the YH-604T crumb at the main feed throat. If the antioxidant is pre-dispersed in the oil, uneven oil flow at turndown ratios below 50% can create antioxidant-poor regions and reduce hot-air aging stability. The resulting compound exhibits lower retention of elongation after aging according to ASTM D573-04 or ISO 188:2011. The pelletized output should be screened with a 40-mesh screen pack to detect gel bodies before injection molding; an increase in screen backpressure of more than 10% within a production shift is an early indicator of thermal degradation.

When Oil-Extended YH-604T Replaces Low-Styrene SEBS in Wire and Cable Jacketing

When YH-604T is selected for flame-retardant wire and cable jacket compounds, the grade is combined with high loadings of magnesium hydroxide or aluminum trihydrate to meet vertical flame propagation tests such as IEC 60332-1-2 or UL 1581. The styrenic end blocks provide a higher tensile plateau than low-styrene SEBS grades, which helps preserve mechanical integrity when filler loading reaches 100–150 phr. A representative formulation contains 100 parts YH-604T, 120 parts magnesium hydroxide, 15 parts polypropylene, 60 parts naphthenic or paraffinic oil, and 1–2 parts processing stabilizer. The magnesium hydroxide grade is selected for a surface coating that reduces water uptake and improves dispersion; uncoated filler can produce viscosity instability and surface roughness. The melt temperature in jacket extrusion is maintained between 210 °C and 230 °C, and the die is heated only to the level required to avoid melt fracture. A die temperature above 240 °C increases oil volatilization and deposits on the die lip.

Long-term heat resistance is evaluated by hot-air aging of the jacket for 168 h at 136 °C according to UL 1581 or EN 50363-0. A compound based on YH-604T must retain at least 70% of original elongation to meet common cable specifications; this is achievable only if a compatible antioxidant system is retained during compounding and if the styrene domains are not plasticized by aromatic oil. Aromatic oils are generally excluded because they can lower the glass transition temperature of the polystyrene end blocks and reduce tensile retention after aging. Low-temperature flexibility is evaluated by a cold-bend test at −40 °C according to IEC 60811-504; the saturated EB midblock retains flexibility at this temperature, but filler and oil selection can have a larger effect than the SEBS grade alone.

In this application, YH-604T differs from low-styrene SEBS grades in that the higher styrene content increases modulus and dimensional stability but reduces melt flow. A line originally designed for a low-styrene high-flow SEBS may require barrel temperature increases of 5–10 °C or a screw rotation speed reduction of 10–15% to stay below torque limits. Failure to adjust the profile can produce melt fracture at the die lip, which appears as a rough jacket surface with longitudinal ridges. If the jacket is produced on a single-screw extruder with L/D below 24:1, melt homogeneity may be insufficient for 100–150 phr filler; a twin-screw compounding step is normally required before jacket extrusion. Published data for this specific YH-604T cable compound configuration is limited, so downselection trials must include filler dispersion microscopy and aged tensile elongation.

Direct substitution of YH-604T for other SEBS grades without reformulation is technically risky because the rheological and mechanical balance differs by styrene content, diblock level, and molecular architecture. Against a low-styrene grade such as Baling YH-602, YH-604T is higher in tensile strength and modulus but lower in melt flow; this means an existing extrusion line may experience higher head pressure. Against a radial SEBS, YH-604T has lower melt tension and lower die swell, which is advantageous in thin-wall injection molding but unfavorable in blow molding and calendering where sag resistance is required. Against Baling YH-688, which is positioned for adhesive and sealant applications, YH-604T has lower tack and higher network strength, making it less suitable for pressure-sensitive hot melts but more suitable for molded or extruded elastomeric goods. In comparison with Kraton G1650, a linear SEBS with a styrene content near 30%, YH-604T has comparable styrenic phase separation but the producer-controlled diblock content is specified more tightly in typical Baling documentation; however, published data for this specific comparison is limited.

The operational boundaries of YH-604T include sensitivity to aromatic oils, certain amine-based stabilizers, and long residence time above 230 °C. Aromatic process oils can plasticize the polystyrene end blocks and reduce the upper service temperature. Amine-based additives should be avoided in formulations where they can generate color bodies or interfere with hindered phenolic antioxidants. Long residence time above 230 °C can produce gel particles and a decrease in tensile elongation after aging. When the compounded part is intended for consumer goods sold in the EU, the downstream formulator is responsible for demonstrating compliance with REACH and RoHS Directive 2011/65/EU; the polymer producer supplies composition declarations but does not certify the finished article. For medical tubing or food-contact devices, migration testing according to ISO 177:2016 and the applicable national regulation must be performed on the final compound because oil and filler additives dominate extractables.