SINOPEC Baling SEBS YH-502T is a linear styrene–ethylene/butylene–styrene block copolymer supplied as non-oil-extended pellets. The molecule consists of terminal polystyrene blocks connected by a saturated ethylene/butylene midblock. The midblock is produced by hydrogenation of the precursor polybutadiene, which removes main-chain unsaturation and gives higher oxidative resistance than unhydrogenated SBS triblock copolymers in accelerated aging evaluations conducted under ISO 188:2023. The nominal styrene mass fraction is 0.30. The polystyrene domains are immiscible in the ethylene/butylene phase and act as thermoreversible physical crosslinks; no vulcanization step is required. The grade can therefore be processed on thermoplastic equipment and reground within its thermal stability boundary. Typical pellet density is 0.91 g/cm³ when determined by ISO 1183-1:2022, and volatile matter after finishing is controlled below 0.5%.

Molecular Architecture, Specification Limits, and Incoming Inspection Parameters

The producer’s technical literature identifies the grade by styrene mass fraction, Shore A hardness, tensile strength, elongation at break, and melt mass-flow rate under a 5 kg load at 230°C. These properties are used for incoming inspection and compounding calculations. The following representative values are compiled from the supplier’s public datasheet and are not lot-release limits unless stated in a purchase agreement.

Property	Test method	Typical value or range
Styrene mass fraction	Producer NMR method, annealed cast film	0.30
Density	ISO 1183-1:2022	0.91 g/cm³
Hardness, Shore A, 15 s	ASTM D2240-15	65
Tensile strength, Die C, 500 mm/min	ASTM D412-16	18 MPa
Elongation at break	ASTM D412-16	500%
Melt mass-flow rate	ISO 1133-1:2022, 230°C/5 kg	10 g/10 min
Volatile matter	ISO 248-1:2011	≤0.5%
Ash	ISO 247-1:2018	≤0.1%

Because melt mass-flow rate does not fully describe shear-thinning behaviour, capillary or rotational rheometry is recommended before thin-wall mould filling simulation. Pellets stored at relative humidity above 60% are typically pre-dried in a desiccant-bed dryer at 70°C for 2 h before loading into a capillary rheometer conforming to ISO 11443:2021. The melt is pseudoplastic; apparent viscosity decreases with increasing shear rate, and the grade shows more shear sensitivity than a fully saturated polyolefin elastomer because of the styrene block domain persistence. Published shear-thinning coefficients for this specific configuration are limited, so spiral-flow mould trials on the production injection unit provide a more reliable gate-to-fill pressure estimate than an isolated melt index value.

What Limits the Upper Melt Temperature in Extrusion and Moulding?

Thermal degradation is the limiting boundary rather than melt viscosity. The producer’s technical handling information identifies 230°C as a practical maximum continuous melt-temperature setpoint. Above this threshold, the saturated midblock is not immediately unstable, but residence time in dead zones of hot-runner manifolds and screw flights can create gel particles and colour shift. On a co-rotating twin-screw extruder with a 40:1 L/D ratio, atmospheric and vacuum venting, and a strand pelletiser, a starting barrel profile of 160°C feed zone, 180°C compression zone, 200°C mixing zone, 210°C metering zone, and 200°C die is used. Screw speed is maintained between 250–450 min⁻¹. At screw speeds above 600 min⁻¹ with restrictive mixing elements, shear heating can increase melt temperature by more than 15°C above the barrel setpoint; the resulting melt temperature may exceed 245°C and produce visible gel specks in downstream cast film or injection plaques. The material should not be held at melt temperature longer than 10 minutes in a barrel or hot runner when the temperature exceeds 220°C.

Clamp force calculations for injection moulding use a melt pressure of 50–80 MPa at the gate, depending on flow length and wall thickness. Mould temperature is held at 30–50°C. Lower mould temperatures reduce cycle time but increase orientation and can produce weld-line weakness; the loss of weld-line strength can be evaluated by ISO 527-2:2012 on injection-welded plaques. On a 120-tonne hydraulic injection moulding machine with a general-purpose 20:1 L/D screw, shot size is limited to 60–70% of barrel capacity to avoid excessive residence time.

For polypropylene modification, YH-502T is compounded at 15–30 wt% with heterophasic PP copolymers in a twin-screw line to reduce low-temperature brittleness. Impact behaviour is reported as notched Charpy tested under ISO 179-1:2023 at -20°C, but the numerical improvement is formulation-specific and cannot be inferred from the SEBS datasheet alone. Injection moulding of appliance feet, power-tool soft grips, and toy components uses a melt temperature of 190–220°C. For these applications, the part is evaluated for abrasion resistance under ISO 4649:2021 and for hardness under ASTM D2240-15. Toy components require migration testing under EN 71-3:2019+A1:2021 or ASTM F963-23 depending on the target market. In sealants and hot-melt pressure-sensitive adhesives, YH-502T is dissolved in aliphatic or aromatic hydrocarbon solvents or compounded with tackifying resins. Final peel adhesion is tested under ASTM D3330/D3330M-24 and loop tack under ASTM D6195-22; test results depend on tackifier type and coating weight. Asphalt modification using YH-502T at 3–6 wt% is performed in low-shear mixing at 180°C; the resulting binder is evaluated for upper service temperature using AASHTO T315 and for storage stability with EN 13399.

When Substituting YH-502T for Other Baling SEBS Grades

Grade selection among Baling YH-501, YH-502T, and YH-503 depends on the balance of melt flow, hardness, and tensile strength. YH-503 contains a higher styrene mass fraction than YH-502T and therefore has a higher polystyrene domain fraction. This raises hardness and tensile strength but also raises melt viscosity at equivalent processing temperature. YH-502T is preferred where the part geometry is thin-walled or where the compounder needs a lower-viscosity SEBS ingredient to reduce power consumption on a given twin-screw line. YH-501, by contrast, is characterised by lower melt mass-flow rate and is used where higher molecular weight contributes to greater extensional viscosity and melt strength in sheet or profile extrusion. These distinctions are lot-dependent and should be verified by melt mass-flow rate under ISO 1133-1:2022 and by hardness under ASTM D2240-15 before a formal substitution.

Attribute	YH-502T	YH-503	YH-501
Styrene mass fraction	0.30 nominal	higher than YH-502T	similar to YH-502T
Hardness	65 Shore A	higher than YH-502T	similar to YH-502T
Melt mass-flow rate	10 g/10 min	lower than YH-502T	lower than YH-502T
Typical processing fit	thin-wall injection, PP modification, adhesives	higher-hardness articles, scratch-resistant surfaces	extrusion, high melt strength profiles

Compared with oil-extended SEBS grades, YH-502T contains no process oil in the pellet, so the compounder can control paraffinic white-oil addition independently. In formulations where 30–50 phr paraffinic oil is used to reduce hardness to 30–40 Shore A, the free-flowing pellet remains manageable because the oil is not pre-absorbed. Oil absorption capacity is finite and formulation-specific; excess oil can exude if the ethylene/butylene midblock is saturated. Migration is evaluated by weight change after contact with filter paper under ISO 177:2016 or by internal oven-aging methods.

Service contact with strong aromatic solvents, ketones, and esters should be avoided because the polystyrene domains can be solvated and the compound can soften. Aliphatic hydrocarbon oils above 50°C can plasticize the ethylene/butylene midblock. Continuous load-bearing service above 90°C is not recommended without a supplemental antioxidant package and creep testing under ISO 899-1:2017.

Regulatory evaluation for food-contact, medical, and electrical applications is article-specific. The base resin is generally evaluated under FDA 21 CFR 177.1810 for styrene block copolymers, but the final compound must meet extraction limits set out in that section. For medical devices, biocompatibility screening is performed under ISO 10993-1:2018, with cytotoxicity under ISO 10993-5:2009 and irritation testing under ISO 10993-10:2010. The base polymer does not substitute for finished-device biological evaluation. For electrical and electronic articles in the EU, compliance with Directive 2011/65/EU depends on the absence of restricted pigments and additives; the base polymer is not intentionally formulated with lead, cadmium, mercury, hexavalent chromium, PBB, or PBDE. REACH obligations are importer- and article-specific; users must verify with the safety data sheet and candidate-list declarations.