SINOPEC Baling SEBS YH-561T is a linear poly(styrene-b-ethylene-co-butylene-b-styrene) triblock copolymer obtained from sequential anionic polymerisation of styrene and butadiene followed by selective hydrogenation of the polybutadiene midblock. The grade is supplied as white or off-white porous pellets or powder. The producer’s specification envelope places bound styrene content at 30–33 wt%, volatile matter at ≤1.0 wt%, and ash at ≤0.2 wt%. Melt flow rate determined under ISO 1133-1:2022 at 230 °C with a 5 kg piston load is reported in the range of 1.0–3.0 g/10 min. Compression-moulded plaques tested under ASTM D638-14 exhibit tensile strength not less than 18 MPa and elongation at break not less than 500%; Shore A hardness of the neat polymer is typically 60–70 after conditioning at 23 °C and 50% RH for 24 h. Lot-specific certificates of analysis should govern production release because plant campaigns may narrow the released value envelope. Published English-language application data for YH-561T under specific end-use configurations is limited; pilot-scale verification is therefore required before high-volume commercial conversion.

Molecular-weight characterisation by gel permeation chromatography with refractive-index detection should confirm residual diblock content below 5 wt% because diblock concentration controls paraffinic oil uptake, oil bleed, surface tack and compression set in monolayered film and injection-moulded parts. The hydrogenated ethylene-co-butylene midblock eliminates backbone unsaturation, so compounds exhibit better oxidative and UV stability than unhydrogenated SBS grades under ISO 188 ageing at 70 °C for 168 h; stabilised compounds typically retain at least 80% of original elongation at break when a hindered phenolic primary antioxidant and a phosphite processing stabiliser are present at a combined loading of 0.2–0.5 wt%. The linear architecture produces lower concentrated-solution viscosity than radial grades of similar styrene content; this is observed on L/D 40:1 co-rotating twin-screw compounding lines as reduced backpressure and melt pump energy below 0.25 kWh/kg during pelletising.

What Distinguishes YH-561T from High-Molecular-Weight SEBS Grades?

Relative to high-molecular-weight linear SEBS grades in the Baling product slate, YH-561T occupies the lower melt viscosity segment. In injection moulding trials using a 250-tonne clamp force machine and a thin-wall cold-runner tool with 1.0–1.5 mm wall thickness, YH-561T at 25–35 wt% in polypropylene filled the cavity at melt temperatures of 190–210 °C, while a high-molecular-weight linear reference grade required 220–235 °C and a higher injection velocity to prevent short shot. This melt-viscosity advantage is balanced by lower cohesive strength in unfilled polymer; tensile strength may be 10–15% lower than high-molecular-weight linear SEBS, and cyclic tension testing under ASTM D412 is required where load-bearing behaviour governs end use. The absence of reactive grafting separates YH-561T from maleic-anhydride-grafted SEBS grades: polar adhesion to polyamide, aluminium or glass fibre cannot be assumed, and peel adhesion to polar substrates must be generated by an external adhesion promoter or by surface activation.

When YH-561T Is Melt-Compounded into Polypropylene for Injection Overmoulding

In polypropylene modification, YH-561T is fed in the main throat of a 25 mm co-rotating twin-screw extruder with L/D 40:1 at barrel set temperatures of 170–200 °C, screw speed 250–400 min⁻¹, and specific mechanical energy input of 0.15–0.25 kWh/kg. Paraffinic extender oil is injected downstream after melt seal formation to prevent screw slip; oil additions of 20–60 phr relative to SEBS shift compound hardness from 35 Shore A to 75 Shore A. Melt temperature at the die is maintained below 220 °C and residence time below 5 min. Above 240 °C, chain scission in the ethylene-co-butylene midblock is observed as a 5–10% drop in capillary viscosity at 200 s⁻¹ and as loss of elongation at break after injection moulding. On a 250-tonne injection moulding machine with a 0.8 mm-thick cold-runner overmoulding tool, a hold pressure of 40–60 MPa packs the YH-561T-softened polypropylene; high-molecular-weight SEBS under identical conditions requires 60–80 MPa. Melt temperature entering the nozzle is set at 190–210 °C to balance weld-line strength and surface gloss, and mould temperature is maintained at 30–50 °C for untextured surfaces.

Hot-melt adhesive use of YH-561T is carried out by dissolving the polymer in a hydrocarbon tackifier and paraffinic/naphthenic oil melt at 160–180 °C in a jacketed high-shear mixer. Brookfield viscosity at 180 °C is adjusted to 1.5–3.0 Pa·s for spiral spray application on carton-sealing lines. The low residual diblock content of YH-561T reduces low-temperature tack drift relative to SIS block copolymers, but adhesion to untreated polyethylene is limited. T-peel strength on steel surfaces reaches above 2 N/mm under ASTM D1876 only after addition of a chlorinated polyolefin or polar adhesion promoter; open time on a 23 °C steel substrate is below 10 s for that bond level, which restricts manual positioning while benefiting high-speed packaging lines. Publicly available adhesive-specific spray trial data for YH-561T is limited; pilot-line validation with the intended tackifier and oil ratio is required before specification for pressure-sensitive assembly.

Within cast film and sheet extrusion, YH-561T at 20–30 wt% in low-density polyethylene or polypropylene produces elastic films with tensile set below 20% after 200% elongation when tested under ASTM D412. Slot die temperature is held at 190–205 °C and chill-roll temperature at 15–25 °C; melt fracture occurs if die gap is below 0.4 mm or if residual resin moisture exceeds 0.08%. Film surfaces are heat-sealable at 130–150 °C under seal pressure of 0.3–0.5 MPa, but seal strength is lower than EVA-based films and must be measured under ASTM F88 for the final laminate. For vacuum-formed trays and elastic closure liners, the polymer is typically pre-mixed with polypropylene and a hydrocarbon oil in a high-speed mixer before compounding.

Thermoplastic elastomer compounds for footwear expandable microcellular midsoles use YH-561T with blowing agents such as azodicarbonamide at 0.5–1.5 wt%. Foaming is carried out on a 120-tonne injection moulding machine at melt temperatures of 180–200 °C with mould temperature of 40–50 °C; expansion ratio of 1.2–1.6 and density of 0.55–0.75 g/cm³ are achievable, but cell uniformity depends on gate diameter above 1.0 mm and on gas counter-pressure control. The grade provides better flex-crack resistance than EVA at densities below 0.70 g/cm³ when tested at -10 °C under ASTM D1052; however, adhesion to chlorinated polyethylene midsoles is limited and requires a mechanical buffing step.

Why Low Residual Diblock Content Governs Compression Set and Gel Formation

Compression set in YH-561T compounds is tested on 13 mm cylindrical buttons under ASTM D395 Method B at 70 °C for 22 h. Formulations based on YH-561T with residual diblock below 5 wt% and paraffinic oil at 30 phr typically show compression set values of 35–45%; compounds with higher diblock or aromatic oil show higher set and surface tack. Gel formation, observed as undispersed translucent specks in cast film, is sensitive to processing shear history and residual moisture. If granules are stored at relative humidity above 60%, pre-drying at 70–80 °C for 2 h is required before extrusion to keep residual moisture below 0.1% and avoid splay. The grade is not recommended for continuous contact with ketone solvents, strongly aromatic mineral spirits, or concentrated ozone; swelling under ISO 1817 in IRM 903 oil is higher than in polar elastomers, and seal compatibility should be confirmed by immersion testing.

For bitumen modification, YH-561T is mixed into paving-grade bitumen at 4–8 wt% using a high-shear mixer at 170–180 °C for 45–90 min. Softening point and penetration are evaluated under ASTM D36 and ASTM D5; the grade raises softening point by 10–20 °C depending on bitumen source, but published data for this specific configuration is limited and tank blending requires a well-maintained high-shear rotor to avoid gel lumps. The addition of YH-561T may increase storage stability only when a suitable compatibiliser is present; otherwise, phase separation can occur after 72 h static storage at 160 °C.

Medical tubing and drip chamber compounds based on YH-561T are formulated at 20–40 phr into polypropylene or SEBS/oil precompounds at hardnesses of 35–65 Shore A. Finished devices are evaluated under ISO 10993-5 and ISO 10993-10; the base polymer alone does not provide medical biocompatibility approval. Autoclave resistance at 121 °C for 30 min requires a stabilised compound and should be validated by measuring hardness and tensile retention after 30 cycles. The material is not supplied sterile and is not intended for direct long-term implantation without further testing.

Regulatory Compliance and Lot-to-Lot Control Boundaries

Compliance statements are issued by the manufacturer against current raw-material regulations. The matrix below lists the standard designations most often requested for SEBS elastomers; a specific lot certificate should be referenced before use in food-contact or electrical applications. Raw-material variability in bound styrene and melt flow rate can shift compound hardness by 2–4 Shore A; inline rheometric control on the compounding line is therefore recommended when the downstream process operates within a narrow hardness window.