SEBS YH-503, produced by SINOPEC Baling Petrochemical Co., is a linear styrene-ethylene/butylene-styrene block copolymer supplied as a non-oil-extended porous pellet. The saturated mid-block imparts oxidative stability and ultraviolet resistance relative to unsaturated SBS, while the linear triblock architecture produces lower melt elasticity and die swell than branched SEBS grades. Producer technical literature positions YH-503 at a styrene content near 30% by weight, Shore A hardness 72–75, tensile strength 22–26 MPa, and elongation at break 500–600%. Melt flow rate under 230 °C/5 kg is typically below 1.0 g/10 min when measured according to ISO 1133-1:2022. The material is therefore classed as a high-molecular-weight, linear SEBS for polyolefin modification, elastic films, extruded tubing, and high-strength thermoplastic elastomer compounds.

What Distinguishes YH-503 from Other Linear SEBS Grades in the Baling Portfolio?

Within the Baling SEBS range, YH-503 differs from lower-viscosity linear grades primarily by melt flow and tensile strength. A low-viscosity linear SEBS may provide melt flow rate above 5.0 g/10 min, but its tensile strength at equivalent hardness is frequently 8–12 MPa lower. YH-503 therefore suits applications requiring cohesive strength under extension, while a low-viscosity grade remains preferable for high-flow sprayable hot-melt adhesives. In comparison with oil-extended SEBS, YH-503 contains no pre-loaded paraffin or naphthenic oil; this reduces the risk of migration-induced hardness drift but moves the oil-absorption requirement entirely onto the compounding line. High-styrene linear grades yield greater Shore A hardness and modulus, but elongation at break and low-temperature flexibility tend to decrease. Branched or star-branched SEBS grades may offer higher extensional viscosity and creep resistance, but they can produce greater die swell and weaker knit-line strength in injection-moulded parts.

Table 1 lists representative specification parameters for YH-503 as given in producer technical bulletins. The values are single-point characterization data and do not replace end-use testing.

Melt Processing Parameters and Rheological Boundaries

On a production-scale compounding line using a 75 mm co-rotating twin-screw extruder with L/D 44:1, melt blending of YH-503 in a polypropylene/SEBS ratio of 60/40 typically requires barrel settings from 170 °C at the feed zone to 220–230 °C at the die. Screw speed is constrained by viscous heating; above 450 rpm, melt temperature can exceed 240 °C, raising the risk of gel formation and strand porosity in the water bath. Pelletizer strand breakage is a recurring failure mode when the water-bath temperature exceeds 20 °C or the strand draw ratio exceeds 3:1, because the linear mid-block does not provide the melt strength of branched SEBS. In feed sections without force feeding, bulk-density differences between SEBS and polyolefins can produce input-rate oscillation; a gravimetric feeder with agitating bin is specified to maintain feed stability below ±1.5%.

In injection moulding trials, the non-oil-extended character of YH-503 increases pressure drop relative to oil-extended SEBS of comparable hardness. Barrel temperatures below 210 °C can leave unmelted pellet fragments at the check ring; above 240 °C, surface splay and gel specks are aggravated. A clamping force of 1.5 kN/cm² of projected cavity area is commonly specified for thin-wall parts to prevent flash. Mould temperatures between 20 °C and 40 °C are adequate for demoulding, but gloss variation can occur when tool surface temperature varies by more than ±5 °C.

In polypropylene modification, addition of 20–30% by weight YH-503 shifts Izod notched impact strength from 4 kJ/m² to 15–25 kJ/m² when tested per ISO 180/A, but a steep property transition occurs above 35% by weight. Beyond that loading, tensile yield strength falls below 12 MPa and phase inversion becomes visually evident as surface delamination in moulded plaques. The processing window is therefore narrower than for oil-extended SEBS, which can tolerate higher SEBS loadings before gross tensile-yield loss.

When Formulating YH-503 for Hot-Melt and Medical TPE Applications

In hot-melt pressure-sensitive adhesive compounding, YH-503 is introduced at 15–25% by weight with a hydrogenated hydrocarbon tackifier and naphthenic process oil. The high molecular weight builds shear adhesion failure temperature but increases Brookfield viscosity beyond 20,000 mPa·s at 180 °C, which may favour slot-die coating over roll coating. Open-time performance depends on tackifier miscibility; a resin with softening point above 100 °C is generally required to maintain cohesive strength after 7-day thermal aging at 70 °C per ASTM D4498. Published data for this specific formulation configuration is limited; the cited viscosity range reflects typical bench-scale observations and must be confirmed on the target coating line.

For medical tubing and cushioning applications, YH-503 can be considered only where formulators demonstrate compliance with ISO 10993-1:2018 for biocompatibility and 21 CFR 177.2600 for food-contact elastomers. The grade is not supplied as a pharmaceutical-grade polymer, and batch-to-batch extractables may vary. A leachables assessment under ISO 10993-18:2020 is required for implant or mucosal contact. Pre-drying at 80 °C for 2 h is recommended when pellets have been stored at relative humidity above 60% or when melt temperature is below 200 °C, to reduce surface moisture effects on clarity.

In sealant and gasket compounds, YH-503 is combined with a paraffinic process oil at loadings of 30–50 phr. Above 50 phr, oil bleed-out becomes detectable after compression between absorbent paper sheets for 24 h at 70 °C, and hardness retention declines. The width of the safe oil-loading window is narrower than for oil-extended SEBS because the base polymer starts with zero extender oil. Formulators should avoid amine-based heat stabilizers and high-acid-number tackifiers, since acidic or amine species can catalyze mid-block oxidation and produce darkening during prolonged exposure above 200 °C.