SINOPEC Baling SEBS YH-505 is a linear styrene-ethylene-butylene-styrene block copolymer produced by selective hydrogenation of the polybutadiene mid-block in a styrene-butadiene-styrene precursor. The polymer is intended for use as a thermoplastic elastomer base resin, a modifier in polypropylene, a viscosity builder in hot-melt adhesives, and a binder or modifier in bituminous waterproofing formulations. The YH-5xx grade designation is a Baling product code; numerical specification values for melt mass-flow rate, styrene content, hardness, and tensile properties are released in the manufacturer’s certificate of analysis and should not be inferred from other SEBS grades. Published data for this specific configuration is limited, so the current product bulletin is the authoritative source for lot-level values.

Material designation, block architecture, and specification parameters

The YH-505 product is a substantially saturated triblock copolymer. Its mid-block is an ethylene-butylene random copolymer with no significant residual double bonds; the end-blocks are styrene-rich and form physical crosslinks at service temperature. The material is generally supplied as a porous crumb or densified pellet. Quality-control evaluation for SEBS compounds commonly uses the following test matrix; the numerical limits are set by lot and grade and are not transferable from generic SEBS datasheets.

The listed methods are quality-control comparators. They do not replace the manufacturer’s certificate of analysis, and they do not by themselves establish fitness for a specific end use.

What distinguishes a saturated mid-block from conventional SBS?

Relative to SBS, YH-505 contains a substantially saturated ethylene-butylene mid-block, which removes the main-chain unsaturation that governs oxidative and ozonolytic degradation in SBS. This architecture shifts the thermal processing window upward: melt compounding is commonly performed at 190–220 °C, while SBS compounds are typically processed below 180 °C to limit oxidative gel formation. The saturated mid-block also improves retention of elongation at break after xenon-arc weathering run under ISO 4892-2:2013. The penalty is higher melt viscosity at equivalent molecular weight. Adhesive formulators replacing SBS with YH-505 should expect increased cohesive strength but reduced wetting on polar surfaces; lap-shear adhesion should be measured under ISO 4587:2003 rather than assumed from SBS controls.

In a co-rotating twin-screw compounding line with a 40:1 L/D barrel, the practical processing window for YH-505 is set by feed-zone conveying, oil absorption, and die-face melt stability. Production experience with linear SEBS grades indicates that feeding porous crumb at barrel temperatures below 160 °C can produce screw chatter and feed-throat bridging. A barrel profile of 170, 180, 190, 200, 210, 210, 200 °C from rear to die is commonly used, with screw speed adjusted to maintain melt temperature below 230 °C. Pre-drying at 70–80 °C for 2 h is recommended when ambient relative humidity exceeds 60%, because surface moisture on porous crumb can generate splay and vent foaming. Melt temperatures above 230 °C should be avoided in prolonged residence-time operations; a nitrogen purge at the feed throat is used when the hopper residence time exceeds 30 min.

Rheological behavior is controlled by styrenic end-block association

Above the styrenic glass-transition temperature, YH-505 forms a melt whose viscosity is strongly shear thinning. Capillary rheometry per ISO 11443:2021 using a 20:1 L/D die of 1 mm diameter is often used to map apparent viscosity at 190 °C, 210 °C, and 230 °C. In linear SEBS grades of this type, apparent viscosity can vary by more than an order of magnitude between 10 s⁻¹ and 1000 s⁻¹. This behavior affects die swell, strand pellet geometry, and injection-mold fill. Molecular weight and styrene content are the primary controllers: higher styrene content raises the plateau modulus and hardness, while higher molecular weight raises low-shear viscosity and oil tolerance. If YH-505 is substituted for a lower-viscosity SEBS grade, the processor should not rely on melt flow index alone; capillary viscosity at the relevant shear rate is required.

Thermoplastic elastomer compounds based on YH-505 and isotactic polypropylene are produced on the same twin-screw line. At weight ratios from 20:80 to 80:20, the morphology changes from a continuous polypropylene phase to a continuous elastomer phase. Flexural modulus under ISO 178:2019 is controlled mainly by the polypropylene phase; puncture impact behaviour under ISO 6603-2:2023 is controlled mainly by the SEBS phase. In injection molding, gate freeze and sink marks become more pronounced when the compound melt flow rate falls below 1 g/10 min at 230 °C / 2.16 kg; processors may adjust the polypropylene grade or add a low-viscosity paraffinic oil to restore flow. The phase morphology is sensitive to screw speed; shear rates above 500 s⁻¹ in the kneading blocks can reduce dispersed polypropylene domain size and improve impact strength, but may also increase melt temperature beyond the safe ceiling.

When oil extension exceeds 25 wt%, the melt strength may decline

Oil extension of YH-505 with a paraffinic or naphthenic white oil is used to reduce hardness and improve flow. In a single-pass compounding sequence, free-oil addition above 25 wt% of the total compound often reduces strand melt strength sufficiently to cause pelletizing irregularities. Oil is therefore injected after the first kneading block, or split-fed with a downstream liquid injector, to allow the polymer to absorb the oil before the die. Hardness can be shifted toward Shore A 35–45 at oil loadings of 60–80 phr, but the blend must be checked for oil exudation after compression at 70 °C for 24 h. Elastic recovery under compression decreases as oil content rises; compression set measured after 22 h at 70 °C may increase beyond 35% when oil loadings exceed 80 phr. These values vary with molecular weight and styrene content. A gradient study at 20, 40, 60 and 80 phr oil should be run, with tensile strength recorded per ISO 37:2017, because the loss is typically nonlinear.

Adhesive and sealant formulations represent a separate processing envelope. YH-505 can be used as a viscosity builder and cohesive-strength modifier in hot-melt pressure-sensitive adhesives when compounded with hydrogenated tackifier resins and white oil. The melt is typically coated at 170–200 °C by slot-die or roller coaters; low-viscosity spray equipment may be unsuitable if the formulation viscosity is not reduced below the equipment limit. Loop tack and peel should be measured under ASTM D6195 and ASTM D3330 before lot approval. The saturated mid-block reduces oxidative discoloration during aged adhesive testing, but migration of tackifier and oil to the bond line remains a physical failure mode. For sealants, the high elastic recovery of SEBS provides compression-set resistance, but solvent-based systems may require longer drying times than SBS when aliphatic solvent blends are selected for compatibility.

Compliance testing before food-contact use

YH-505 is a candidate resin for food-contact articles only when the finished formulation is tested against the appropriate migration and end-use clauses. In the United States, styrene block copolymers may fall under FDA 21 CFR 177.1810 when the finished article meets the specified use conditions; in the European Union, overall migration limits of 10 mg/dm² under EU 10/2011 apply to plastic materials in contact with food. These regulatory references apply to the final article, not to the raw polymer in isolation. The processor must verify that plasticizers, tackifiers, and stabilizers are also compliant and that the article passes organoleptic testing where required. Electrical or medical uses require additional evaluation; no ISO 10993 or IEC 60601 conformity is imparted by the resin alone.

Material replacement decisions require comparison of YH-505 with SBS and with other SEBS grades under identical test conditions rather than by nominal hardness alone. Relative to SBS, YH-505 provides higher thermo-oxidative stability but also higher melt viscosity. Relative to lower-molecular-weight SEBS grades in the same family, YH-505 may provide greater cohesive strength in adhesive films and better oil tolerance, but its exact oil uptake, melt flow, and mechanical properties must be read from the current Sinopec Baling product bulletin or certificate of analysis. The substitution should be validated on production-scale equipment with the same screw configuration, die land length, and downstream cooling because triblock molecular weight differences can change die swell, pellet geometry, and tack development. In bituminous waterproofing applications, blending at 180–200 °C with high-shear dispersion is used; the modified binder should be evaluated for softening point and low-temperature flexibility under the relevant ASTM or EN binder specification. In wire and cable compounds, flame-retardant filler additions above 60 wt% typically require a compatibilized polyolefin carrier and should not be attempted as a neat YH-505 dry blend.