As a linear styrene-ethylene-butylene-styrene block copolymer, TSRC Vector® SEBS 8109 is supplied as a high-flow, non-oil-extended grade used where conventional SEBS types create excessive compounding torque or melt pressure. The bound styrene content is 30 wt% by ASTM D5775, and the density is 0.91 g/cm³ by ASTM D792. Melt flow rate is 18 g/10 min at 230 °C/2.16 kg by ASTM D1238. Typical mechanical values include Shore A hardness of 65 by ASTM D2240, tensile strength at break of 30 MPa, elongation at break of 550%, and 100% tensile modulus of 2.4 MPa by ISO 37. The saturated ethylene-butylene midblock provides thermo-oxidative stability not available from SBS, while the absence of extender oil means physical properties are not diluted.

The linear architecture and saturated midblock distinguish this material from SBS and from hydrogenated styrenic block copolymers with measurable diblock content. In SEBS 8109, the absence of midblock unsaturation raises the onset of thermal degradation relative to SBS and permits continuous melt processing at temperatures up to 240 °C when residence time is kept below 10 min. The grade is not oil-extended; therefore, tensile strength and hardness are determined by the styrene domain content and the ethylene-butylene midblock molecular weight. This avoids variable performance associated with extender oil migration in low-hardness compounds. Typical compression set after 22 h at 70 °C is 25% by ASTM D395. When compared with a lower-flow linear SEBS grade of the same styrene content, SEBS 8109 produces lower specific energy input during mixing and shorter injection-moulding fill times, but it may also exhibit lower tensile strength and higher compression set after extended loading. The material is supplied as porous pellets and requires pre-drying at 80 °C for 2 h when exposure to relative humidity above 60% is suspected.

What melt-flow threshold governs direct let-down in injection-moulded polypropylene?

In polypropylene impact modification, direct let-down of SEBS 8109 into injection-moulded articles avoids a separate masterbatch step only if the grade maintains sufficiently low melt viscosity at shear rates typical of thin-wall filling. At 230 °C and 100 s⁻¹, the melt viscosity of SEBS 8109 is substantially below that of linear SEBS 8101, permitting let-down ratios of 15 to 30 phr in PP homopolymer without exceeding a melt temperature of 240 °C. Production-scale data from co-rotating twin-screw lines with 40:1 L/D indicate that screw torque at 300 rpm is reduced by approximately 20 to 30% relative to a lower-melt-flow SEBS grade of equivalent styrene content. In injection moulding, a clamp force of 800 kN and barrel temperatures from 200 to 230 °C are sufficient for consistent cavity filling in 2.0 mm-thick test plaques. Notched Izod impact values determined by ASTM D256 typically increase from 3 kJ/m² to 12 kJ/m² at 20 phr loading in a PP homopolymer with an MFR of 12 g/10 min. The practical ceiling is governed by phase-rich morphology: above 35 phr, the co-continuous SEBS network can reduce modulus below 850 MPa in unfilled formulations.

At the microstructural level, the styrenic end blocks form physical crosslinks that persist through the melt state only within a limited residence time. Above 240 °C, domain dissolution can occur and the rheological signature changes from pseudoplastic to Newtonian. Processing trials confirm that a PP homopolymer with MFR of 12 g/10 min maintains a shear viscosity ratio between the PP continuous phase and the SEBS dispersed phase that prevents stringing and delamination at 20 phr loading. If the PP grade shifts to an MFR below 5 g/10 min, the viscosity mismatch increases and the dispersed SEBS phase may coalesce into elongated lamellae rather than fine domains, reducing impact efficiency by up to 40% in instrumented impact tests. Adding 5 phr of a maleic anhydride-grafted PP improves domain adhesion but raises die pressure; the formulation must balance adhesion against the pressure limit of the injection unit.

For hot-melt adhesive compounding, the relatively narrow molecular weight distribution of SEBS 8109 supports rapid dissolution in low-aromatic paraffinic oil and C5/C9 tackifier resins at mixing temperatures from 180 to 200 °C. A typical open-mix sequence begins with oil absorption into the elastomer crumb, followed by tackifier addition under high-shear dispersion. Melt viscosity measured by ASTM D3236 at 180 °C in a formulation containing 30 phr oil, 40 phr C5 resin, and 30 phr SEBS 8109 is typically below 6,000 mPa·s. This is low enough for gear-pump-driven slot-die coating without exceeding 60 bar at the die. In contrast, a lower-flow SEBS of identical styrene content under the same formulation yields values above 12,000 mPa·s, requiring wider die gaps and lower line speeds. Peel strength measured by ASTM D3330 increases with aromatic tackifier content, while shear adhesion failure temperature by ASTM D4498 decreases. The practical upper limit for tackifier loading is set by phase separation: above 45 phr of a fully hydrogenated C9 resin, the mixture displays two glass transition temperatures in dynamic mechanical analysis by ASTM D7028, indicating loss of compatibility. Gel formation is observed when the melt is held above 210 °C for more than 4 h in the presence of excess oxygen. A nitrogen blanket is therefore recommended for continuous mixing runs longer than one shift.

Die pressure, screw fill, and vent port stability during compounding

Compounding SEBS 8109 with polypropylene, calcium carbonate, and paraffinic extender oil on a co-rotating twin-screw extruder requires attention to screw fill and vent stability. A typical screw configuration uses two sets of kneading blocks after the feed zone, a distributive mixing section before vacuum venting, and a gear pump for pellet pressure control. Specific energy input values between 0.18 and 0.26 kWh/kg are recorded when the barrel profile is set from 190 to 220 °C, the die temperature is held at 200 °C, and throughput is maintained at 300 to 450 kg/h. Under these conditions, die pressure typically remains below 80 bar. When throughput is raised above 600 kg/h, unmelts can appear at the vent port due to insufficient residence time in the restrictive elements, producing strand breaks downstream. This is the key difference from lower-flow SEBS grades: those grades enter the die at higher pressure and torque, whereas SEBS 8109 tends to show feed-zone slip if the throat is overheated above 80 °C. Correct setup requires a chilled feed throat at 40 to 50 °C and vacuum level below -0.6 bar.

When calcium carbonate is introduced at 20 to 40 phr, the high-flow SEBS 8109 wets filler surfaces faster than a low-flow SEBS, but this faster wetting can create a transient torque peak in the first kneading block unless oil is injected before the filler feed port. Field observations from production lines show that reversing the addition sequence—filler first, oil second—raises melt temperature by 8 to 12 °C and causes vent flooding. The recommended sequence is SEBS plus PP, then oil injection at 40 to 50% of axial length, then filler, then vacuum venting at 30 kPa absolute pressure to maintain pellet brittleness.

Compared with oil-extended SEBS grades, SEBS 8109 provides a higher Shore A hardness and better tensile strength at equivalent flow because no paraffinic oil is present to plasticise the ethylene-butylene midblock. When a formulation demands Shore A hardness below 50, an oil-extended grade is preferred. The current grade is therefore not a direct drop-in for soft gel applications unless paraffinic oil is added during compounding. The absence of oil also reduces extraction mass loss under ISO 6427 plasticiser extraction testing and avoids oil bloom after thermal ageing.

In halogen-free flame-retardant cable jacketing, SEBS 8109 is used as an impact modifier and processing aid for highly filled polyolefin formulations containing 50 to 60 phr of magnesium hydroxide or aluminium trihydroxide. The high melt flow allows filler loadings that would be unprocessable with lower-flow SEBS without excessive torque in a 90 mm single-screw compounder. Limiting oxygen index by ASTM D2863 and heat release rate by ASTM E1354 depend on the hydrated filler loading rather than on the elastomer grade, but the incorporation of SEBS 8109 reduces low-temperature embrittlement because the ethylene-butylene midblock retains flexibility below -40 °C. Processing trials show screw amperage remains under 90% of motor rating when the barrel profile is capped at 190 °C, which is necessary to prevent premature release of water from the filler. Release of water at temperatures above 200 °C produces surface porosity in the extruded jacket.

In extruded medical pump tubing and flexible packaging compounds, the selection of SEBS 8109 instead of a lower-melt-flow SEBS reduces melt pressure during single-screw extrusion with a 30 mm screw and 24:1 L/D. Barrel zones of 180, 195, 205, and 210 °C provide a smooth surface without plastisol-derived plasticizers. Compounds containing SEBS 8109 can be submitted for cytotoxicity testing according to ISO 10993-5 and for food-contact migration testing under EU 10/2011 or FDA 21 CFR 177.2600, but the raw grade itself does not carry a regulatory opinion; each formulated compound must be evaluated. Gas transmission in thin films is governed by the ethylene-butylene midblock volume fraction and must be measured by ASTM D3985 for oxygen and ASTM F1249 for water vapour rather than inferred from the SEBS grade alone. Published data for this specific configuration is limited for exact permeability coefficients.

For pump tubing, kink resistance and pump life are determined by compression set and tensile recovery. The formulation can be adjusted with high-density polyethylene or PP to raise Shore A hardness to 70 to 80 while retaining the softness provided by the ethylene-butylene midblock. Sterilization resistance is evaluated by ISO 11135 for ethylene oxide and ISO 11137 for gamma irradiation; post-sterilization tensile retention of 90% or greater is typically achieved with stabilizer packages free of amine-based antioxidants. Amine-based stabilizers are not recommended in SEBS 8109 compounds intended for oxidative environments because they can form chromophore species at the styrene-ethylene interface during autoclave cycling at 121 °C.

When SEBS 8109 is substituted for lower-flow SEBS grades in oxygenated medical films

When SEBS 8109 is substituted for a lower-melt-flow SEBS in a medical film formulation containing 20 phr of a high-clarity PP random copolymer, the extrusion melt temperature can be reduced by 10 to 15 °C without increasing die pressure. On a 75 mm single-screw cast-film line with chill-roll temperatures of 20 to 25 °C, this substitution lowers screw amperage and reduces gel-building at the die lip. The trade-off is a measurable reduction in tensile strength at break from 28 to 22 MPa when the same formulation is tested by ISO 527-3; tear strength by ASTM D1004 may also decline. Film formulations therefore require rebalancing of the PP continuous phase and re-optimisation of the draw ratio to retain puncture resistance. The absence of extender oil in SEBS 8109 avoids oil bloom after sterilisation, while lower-melt-flow oil-extended SEBS grades can show surface exudation after gamma irradiation at 25 kGy. This distinction is critical for medical device packaging where visual clarity and seal integrity are specified by ASTM F88.