SINOPEC Baling SEP YH-4010

Product designation SINOPEC Baling SEP YH-4010 identifies a hydrogenated styrenic block copolymer, commonly classified as SEPS, produced by selective hydrogenation of a styrene-isoprene-styrene triblock precursor. The molecular architecture consists of terminal polystyrene blocks and a saturated ethylene/propylene midblock. Main-chain unsaturation in the elastomer segment is essentially eliminated, which suppresses ozone cracking, ultraviolet chain scission, and thermo-oxidative degradation in comparison with unsaturated styrene-isoprene-styrene and styrene-butadiene-styrene products. The material is supplied as porous pellets; the porosity raises the oil absorption rate during compounding of soft TPEs, gels, and hot-melt adhesives. The saturated midblock also imparts resistance to polar solvents and improves re-processability relative to partially hydrogenated grades.

Because propylene repeat units interrupt crystallinity, the midblock remains amorphous at room temperature; the hard polystyrene domains provide physical crosslinks. The grade is produced by anionic polymerization followed by selective hydrogenation. Residual unsaturation is reduced to a low level, which is the structural basis for heat and ultraviolet resistance, but also increases raw material cost and reduces compatibility with unsaturated rubbers. In the Baling SEPS portfolio, YH-4010 is placed as a medium-to-high styrene-content grade. The styrene block fraction controls hardness, melt viscosity, and the upper service temperature of the physical network. Published lot-to-lot data from supplier technical bulletins list typical ranges rather than narrow specification windows.

What Melt Flow and Styrene Content Define YH-4010 Against the Baling SEPS Range?

The following table summarizes representative YH-4010 data reported with standard test methods. The values are typical production-lot ranges and do not constitute specification limits for every shipment.

For grade-to-grade comparison, the main variables are styrene content and melt flow. A lower-styrene SEPS product yields lower hardness and higher oil uptake, while YH-4010 provides higher tensile strength and geometric stability in molded articles. Differences from SEBS grades originate from the midblock chemistry: the ethylene/propylene segment contains propylene repeat units that improve thermodynamic compatibility with polypropylene and reduce melt viscosity at equivalent styrene content when compared with ethylene/butylene midblock grades. This distinction is most visible in polypropylene-rich TPE compounds, where YH-4010 disperses more easily and permits lower processing temperatures.

Molecular weight differences are not routinely specified as Mw or Mn on technical data sheets for this grade; instead, melt flow rate serves as the primary molecular weight surrogate. In production, lot-to-lot variation in melt flow rate is typically controlled within ±0.3 g/10 min around the nominal value. This variation affects feeding consistency and can require barrel temperature adjustment when running oil-extended compounds, because oil absorption capacity is inversely related to molecular weight. Compounds with high oil loadings are more sensitive to such variation, and feed-throat bridging has been observed on equipment using smooth feed sections when very low bulk-density regrind is introduced.

Capillary rheometry of YH-4010 at 200 °C shows pronounced shear thinning. Apparent viscosity declines by roughly one order of magnitude as shear rate increases from 100 s⁻¹ to 1000 s⁻¹. This response supports filling of thin-wall molds, but injection speed and gate dimensions must be matched to shear rate to avoid melt fracture. Gate shear rates above 10,000 s⁻¹ can produce sharkskin or jetting in unfilled SEPS, particularly when mold surface temperatures fall below 20 °C.

Thermal analysis of SEPS grades typically shows a midblock glass transition below -50 °C and a polystyrene glass transition near 95 °C. The resulting service temperature window permits flexibility at refrigeration temperatures and structural integrity in hot water up to 80–90 °C, provided the part is not under continuous load. Because the network is physical rather than covalent, creep accelerates as temperature approaches the polystyrene glass transition. This places an operational boundary on load-bearing applications such as hot-water seals and steam-exposed grips.

In production, YH-4010 pellets are dried before melt processing only when storage conditions allow moisture uptake. Desiccant dryers set at 70–80 °C for 2–3 h reduce surface moisture to below 0.1 % when ambient relative humidity exceeds 60 %. Residual moisture can produce splay, bubbles, or dimensional variation in profiles and films. Single-screw extrusion of neat YH-4010 is carried out with general-purpose screws of 24:1 to 30:1 L/D and barrel temperatures from 180 °C at the feed throat to 220 °C at the die. Co-rotating twin-screw compounding lines with 40:1 L/D are preferred for oil-extended or filled formulations because they allow staged addition of oil and filler and provide efficient devolatilization.

When Twin-Screw Compounding Demands Low Shear Heating in SEPS-Based TPEs

If YH-4010 is compounded on a co-rotating twin-screw extruder, the processing window is constrained by the thermal stability of the styrenic block copolymer and by the need to disperse high-viscosity additives without excessive chain scission. Barrel zones are normally set in a flat or slightly reverse profile, with feed-zone temperature near 160 °C and subsequent zones at 190–210 °C. Melt temperature measured at the strand die should remain under 230 °C. Extended residence at or above 240 °C can initiate yellowing and viscosity reduction, which appears on the production line as surging, strand rupture, or colour shift from white to pale yellow. Screw speeds on 40:1 L/D machines are typically restricted to 300–500 rpm to limit viscous heating. When white oil loadings exceed 100 phr, the oil should be injected in two or more mid-barrel positions. Single-port injection at high loading often creates screw slip, die pressure surges, and non-uniform oil distribution. A vacuum port downstream of the oil injection zone is operated at -0.08 MPa to remove volatiles and air entrained during oil addition. Strand die pressures are maintained between 2 MPa and 4 MPa; higher die pressures indicate insufficient devolatilization or excessive filler loading.

Filler addition modifies rheology. Calcium carbonate loadings above 30 wt% raise melt viscosity and die pressure, while silica loadings beyond 10 wt% can produce discontinuous strand surfaces. In oil-gel compounds based on YH-4010, paraffinic white oil is favoured over naphthenic or aromatic oils because the saturated ethylene/propylene midblock absorbs high paraffinic oil volume with lower bleed-out. However, at oil loadings above 100 phr, the compound may become pressure-sensitive, and exudation tests at 70 °C for 72 h are used to qualify the formulation.

Injection molding of YH-4010-based TPEs uses barrel zone settings of 180 °C in the rear, 200 °C in the centre, and 220 °C at the nozzle. Mold coolant is maintained at 20–40 °C. Because SEPS is a physical network rather than a vulcanized elastomer, remelting and re-processing are possible, but regrind addition beyond 30 % can reduce tensile strength and shift hardness. In thin-wall parts below 1 mm, gate freeze-off becomes the limiting factor because the styrene domains reform quickly below 100 °C. Slow cooling increases the degree of physical crosslinking and raises stiffness; fast cooling preserves a finer styrene domain structure and produces lower tension set.

In-line quality checks on production lines commonly include melt flow measurement every 2 h, Shore A hardness on conditioned plaques, and moisture analysis by Karl Fischer titration. For transparent films, melt filter packs with 100 mesh screens are installed upstream of the die to remove gel particles. Gel counts above 10 particles per 100 cm² can produce visual defects in thin film; the screen pack is replaced when die pressure increases by more than 20 % from the initial value.

Property Cliff-Edges at Polystyrene Content Above 30 wt% in SEPS Compounds

When YH-4010 is used in polypropylene-based TPEs, total polystyrene content in the formulation has a threshold effect. At total polystyrene content above 30 wt%, hardness and tensile strength rise sharply, while elongation at break and low-temperature impact decline. In blends with polypropylene homopolymers, the dispersed hard phase can become co-continuous when YH-4010 addition exceeds 40 wt%; this morphological shift changes failure mode from ductile drawing to brittle fracture at room temperature. The effect is measurable in notched Izod impact testing according to ISO 180:2023 and in tensile elongation according to ISO 527-2:2012.

The practical consequence of this architecture is that YH-4010 can be formulated with polypropylene at lower melt temperatures than SEBS grades, yet it retains cohesive strength in hot-melt adhesive bonds. In hot-melt adhesive formulations, YH-4010 is combined with hydrogenated tackifier resins and paraffinic oil at resin loadings of 40–120 phr. Viscosity control for pneumatic application is obtained at 180 °C, and adhesive thermal stability is monitored by viscosity retention after 72 h at 180 °C. Compared with SBS-based hot melts, YH-4010 exhibits lower colour development and less odour because the saturated midblock produces fewer volatile degradation by-products.

Unlike EPDM, YH-4010 does not require vulcanization, can be re-melted and re-processed, and is suited to high-speed injection molding and extrusion. However, SEPS compounds do not match EPDM in hot-water compression set or resistance to strong oxidizing acids. The choice between SEPS and EPDM in seals and soft-touch parts typically depends on whether recyclability and fast cycle times or permanent-set resistance under hot-water immersion is the primary requirement.

YH-4010 is processed into transparent flexible tubing, films, and molded grips where resistance to ultraviolet light, ozone, and hot water is required. Compounds can be evaluated for food-contact suitability under 21 CFR 177.1810, which covers styrene block copolymers as components of articles intended for food contact under defined conditions. Biocompatibility of final devices is assessed by extraction and cytotoxicity test methods described in USP <88>; compliance depends on the complete formulation and sterilization method. Sterilization by ethylene oxide at 55 °C or gamma irradiation at 25–40 kGy is common for SEPS-based medical disposables. Steam autoclaving at 121 °C can cause dimensional recovery of oriented films and should be validated for each part. Ozone cracking resistance is evaluated according to ISO 1431-1:2022, and compression set testing is typically performed under ISO 815-1:2019 for thermoplastic elastomers. For pharmaceutical and food-contact applications, raw material compliance must be confirmed against the specific article condition. FDA 21 CFR 177.1810 permits styrene block copolymers in contact with food only under defined conditions of use and extraction, and the final compound must also satisfy overall migration limits under EU Regulation EU 10/2011 when applicable. REACH registration under EC 1907/2006 is required for EU supply. Published data for the specific configuration of YH-4010 in all end-use devices is limited; validation on finished articles is required.