Produced by selective hydrogenation of a butadiene–styrene triblock precursor, SINOPEC Baling SEBS YH-520 is a linear hydrogenated styrenic block copolymer. The saturated midblock is a random ethylene/butylene copolymer with a glass-transition temperature below −35 °C measured under ISO 11357-2. The polystyrene end-blocks have a glass-transition temperature near 95 °C and form the physical crosslink network responsible for thermoplastic elastomer behaviour. The product is supplied as a non-oil-extended neat SEBS for compounding, hot-melt adhesives, sealants, soft-touch injection moulded articles, wire and cable jacketing, and polymer modification.

The grade designation YH-520 does not encode the styrene mass fraction or melt flow rate; both values appear on the production certificate of analysis. A typical CofA for YH-520 lists melt flow rate under ISO 1133-1:2022, styrene mass fraction, solution viscosity, Shore A hardness under ASTM D2240-15, tensile strength and elongation at break under ASTM D638-14, bulk density under ASTM D1895, and volatile matter. Because public English-language datasheets for this specific grade currently provide limited lot-independent data, the following SEBS class-typical orientation ranges are not contractual acceptance limits for YH-520: density 0.90–0.94 g/cm³ tested under ASTM D792, Shore A hardness 60–80 under ASTM D2240-15, tensile strength 15–30 MPa under ASTM D638-14, and elongation at break 500–800 % under ASTM D638-14.

Applications that require guaranteed lot-specific values must refer to the current supplier CofA and request data under the same test conditions used for the finished article. The distinction between YH-520 and functionalized or oil-extended SEBS grades should be confirmed from the CofA and the supplier’s technical service document, not inferred from grade number alone.

What Are the Critical Storage and Drying Boundaries for YH-520?

In warehouses with relative humidity above 60 %, moisture uptake can exceed 0.3 % by mass within 24 h when measured by Karl Fischer titration under ISO 15512. A desiccant-bed dryer with a dew point no higher than −30 °C, a drying temperature of 70–80 °C, and a residence time of 2–4 h is required before twin-screw compounding or injection moulding. Air flow through the hopper should be maintained at approximately 0.5 m³/min per 100 kg/h of polymer throughput; lower air exchange rates allow moisture to re-condense in the return-air circuit.

Undried lot portions produce visible splay, nozzle drool, and shot-weight variation on injection moulding machines. The defect is not hydrolytic chain scission but rapid volatilization of surface water during plastication; in vented extrusion, the vacuum system can be overloaded and lose negative pressure. Production logs should record dryer dew point, return-air temperature, and hopper outlet temperature at intervals not exceeding 30 min.

On a co-rotating twin-screw extruder with L/D 40:1 to 52:1, YH-520 is typically fed at the main throat. A temperature profile from 150 °C in zone 1 to 190–220 °C at the die is common; the die melt pressure should remain between 5 MPa and 15 MPa. Screw speeds between 250 rpm and 450 rpm generate the shear required for filler dispersion but can produce melt temperatures above 240 °C if back pressure is high. Sustained melt temperatures above 240 °C initiate oxidative degradation of the thermoplastic elastomer. Specific mechanical energy input should be held between 0.15 kWh/kg and 0.25 kWh/kg. A vacuum vent downstream of the plastication zone, controlled between −0.07 MPa and −0.09 MPa, removes volatile residues and mineral filler moisture.

Mineral filler addition is preferably performed through a side stuffer after the polymer melting section. Side feeding of calcium carbonate or talc after the main plastication zone prevents filler accumulation on the screw root and reduces peak torque. In formulations with filler loading above 40 wt%, screw configuration should replace some kneading blocks with distributive mixing elements to prevent local temperature spikes. Melt-filter screen packs with 80–120 mesh are used for thin-wall or film-grade compounds; filter pressure rise above 3 MPa indicates filler agglomeration or gel formation and requires screen replacement.

Injection moulding of YH-520 compounds is performed on reciprocating-screw machines with clamp forces between 800 kN and 2,500 kN depending on part geometry. Barrel settings are generally 180–210 °C, and mould temperatures between 20 °C and 50 °C are sufficient for the physical crosslink network to form. Fill speed should be adjusted to keep gate shear rate below 10,000 s⁻¹; higher shear rates cause melt fracture and reduce surface smoothness. Gate land length of 0.5–1.5 mm and gate diameter not less than 0.8 mm are common for SEBS-based soft-touch components. Mould shrinkage of neat SEBS compounds commonly ranges from 1.0 % to 2.5 % depending on wall thickness and packing pressure; final dimensions should be validated under ISO 294-4.

Capillary rheometry of SEBS compounds at 200 °C shows shear thinning from 10 s⁻¹ to 1,000 s⁻¹; the power-law index for YH-520 compounds is typically between 0.3 and 0.5. A high shear-thinning response reduces viscosity at cavity-filling shear rates but also requires careful gate design to avoid jetting. In filled YH-520 compounds, tensile strength under ASTM D638-14 may decline by 10–30 % at high mineral filler fractions, while Shore A hardness under ASTM D2240-15 can remain relatively stable until the filler loading exceeds the polymer’s wetting capacity. Fillers with median particle size above 10 µm generate visible surface roughness on gloss soft-touch parts.

When YH-520 Replaces Unhydrogenated SBS in Weatherable Compounded Goods

Compared with an unhydrogenated SBS grade, the structural differentiator in YH-520 is the removal of residual midblock double bonds. In unhydrogenated SBS, the trans-1,4 double bond absorbs near 966 cm⁻¹ in transmission FTIR; in YH-520, the corresponding absorption is weak or absent. This chemical saturation changes thermo-oxidative stability and long-term weathering. Accelerated weathering of SBS compounds under ASTM G154-16 commonly shows surface cracking and hardness rise due to crosslink densification, whereas hydrogenated SEBS compounds retain better elongation. However, published data for this specific YH-520 configuration under outdoor exposure is limited; end-use qualification should include the intended radiation cycle, temperature, and sample thickness.

Direct substitution of YH-520 into an SBS formulation without adjusting tackifier and oil selection can reduce cohesive strength because the solubility parameter of the saturated midblock is lower and less compatible with aromatic oils and aromatic tackifiers. In SBS, aromatic resins associate with the styrenic domains and modify upper service temperature. In YH-520, aromatic resin loading above 20–30 phr can produce a non-equilibrium multiphase system with lower tensile strength under ASTM D638-14 and increased creep. Paraffinic or cycloaliphatic tackifiers are preferred; hydrogenated rosin esters are commonly used in adhesive formulations where colour stability is required.

Compression-set testing under ASTM D395-18, method B, at 70 °C for 168 h is commonly applied for weatherable seals. Hot-air ageing under ASTM D573-04 at 70 °C for 168 h provides retained tensile and elongation values. These tests are release criteria rather than universal selection criteria; the exact pass/fail thresholds depend on part geometry and service load.

For paraffinic oil extension in a batch mixer, the melt temperature is normally held at 150–170 °C with incremental oil addition after the polymer forms a coherent melt. The neat grade accepts between 50 phr and 200 phr of paraffinic oil in standard compounding practice. Above 200 phr, the continuous polystyrene domain network becomes discontinuous, and tensile strength measured under ASTM D638-14 falls steeply; elongation may remain high, but permanent set rises. This is a phase-cliff edge, not a linear dilution effect. Oil penetration time is used as a quality-control marker; extended oil absorption times can indicate residual moisture or insufficient mixing shear.

The difference from oil-extended SEBS grades is operational. Oil-extended grades are supplied with a fixed extender fraction, such as 50 phr or 100 phr depending on the grade, and therefore report lower as-packed Shore A hardness but reduce formulation freedom. YH-520, by contrast, enables dry handling and custom oil extension at the compounder’s plant. In hot-melt adhesives, YH-520 is compounded with hydrogenated tackifier and wax at 160–180 °C; viscosity is monitored with a Brookfield viscometer at 177 °C. Typical SEBS-based hot-melt viscosity at application temperature ranges from 5 Pa·s to 50 Pa·s; formulations outside this range require nozzle or pump adjustment.

In solvent-borne adhesive systems, YH-520 is dissolved in aliphatic or cycloaliphatic solvents. Aromatic solvents are less compatible with the saturated midblock and can produce phase separation. Solution viscosity at 25 °C is determined by polymer molecular weight, solvent composition, and concentration; adhesive formulations commonly use solids between 20 wt% and 40 wt%. Peel adhesion on polypropylene substrates is evaluated under ASTM D3330; exact adhesion values are application-dependent, and published data for YH-520 in solvent-borne adhesives is limited.

YH-520 should not be substituted for maleic anhydride-grafted SEBS in glass-reinforced polypropylene or polyamide impact modification; the absence of anhydride functionality prevents covalent adhesion at the polar interface. For those applications, a dedicated functionalized grade is required.

Compliance Verification Under Standard Test Conditions

Before lot acceptance is completed, test methods and regulatory documentation must be aligned with the finished article’s end-use standard. The table below lists the most commonly used standard designations in material release and regulatory compliance. The table is not a certificate of analysis and does not establish compliance for a particular shipment; a supplier statement and lot-specific CofA must be obtained.

For applications that require medical or food-contact compliance, the specific regulatory status of YH-520 must be confirmed in writing. No blanket FDA or USP class statement is made in this document because such status depends on formulation, downstream processing, and the final article’s conditions of use. For heavy-metal and brominated-flame-retardant restrictions, the supplier’s RoHS compliance statement under RoHS Directive 2011/65/EU Annex II is the controlling document.