Dynasol Calprene® SEBS CH6140 is a linear hydrogenated styrenic block copolymer comprising two terminal polystyrene segments separated by a saturated ethylene-co-butylene midblock. The material is supplied as low-dust pellets and is intended for thermoplastic elastomer compounding, impact modification, soft-touch articles, appliance seals, and hot-melt adhesives. Bound styrene content is typically 30 wt%, with release ranges generally confined to 29–31 wt%. Melt mass-flow rate according to ASTM D1238-20 at 230 °C under 5.0 kg load is typically 8 g/10 min, with lot-dependent variation between 6 g/10 min and 10 g/10 min. The density is 0.91 g/cm³ by ISO 1183-1:2019. The polymer is registered under EC 1907/2006 (REACH) and is not formulated with phthalate plasticisers or intentionally added bisphenol A. The hydrogenated midblock imparts resistance to ozonolysis and ultraviolet degradation, but the polymer remains thermoplastic and is not vulcanised; continuous service above 100 °C is therefore limited.

These values are representative for compression-moulded specimens conditioned at 23 ± 2 °C and 50 ± 5 % RH for 40 h. Lot-specific certificates of analysis govern release decisions, because moulding temperature, cooling rate, and additive package alter phase mixing and final hardness. For injection moulding, thin-wall soft-touch parts with gate thickness of 1.0 mm are feasible when melt front temperature is held above 200 °C and mould temperature is maintained at 15–30 °C. A single-screw extruder with 24:1 L/D and 3:1 compression ratio is sufficient for profile extrusion if die temperature is kept 10–20 °C above melt temperature. The saturated midblock does not require vulcanisation, and regrind can be added up to 20 wt% in most compounds without severe loss of puncture resistance.

What Restricts Continuous Extrusion Output When CH6140 Is Extended with Paraffinic Oil?

Oil extension lowers compound hardness and increases melt index, but the continuous extrusion ceiling is determined by phase continuity rather than specific energy input alone. White mineral oil with kinematic viscosity of 70–100 cSt at 40 °C is dispersed into CH6140 on a co-rotating intermeshing twin-screw extruder with 40:1 L/D and atmospheric plus vacuum venting. Stable strand geometry and pellet integrity are generally retained to 50 phr oil; at 60 phr, Shore A hardness measured by ASTM D2240-15e1 drops below 30, and the compound becomes sensitive to strand waviness at the pelletiser intake. Screw fill and die pressure decrease as oil concentration increases, but the wall shear stress threshold for sharkskin does not shift; capillary rheometry shows melt fracture onset at wall shear stress near 0.2 MPa for compounds containing 50–70 phr oil. The processing window narrows because the polystyrene end blocks must remain below their order–disorder transition. When melt temperature exceeds 230 °C, the physical crosslink network is insufficient to maintain strand integrity, regardless of screw speed.

Paraffinic oil with a pour point below −20 °C and viscosity index above 90 is preferred; naphthenic oil reduces compatibility with the ethylene/butylene midblock and may exude after 72 h at 70 °C. Aromatic process oils should be limited in applications where light colour and food-contact migration are constrained. Oil exudation is not governed solely by total addition; it is accelerated by cooling-rate gradients across the strand cross-section. A strand cooling water temperature of 25–35 °C produces a near-equilibrium surface morphology and reduces surface tack. In a 40:1 L/D co-rotating twin-screw extruder, a typical barrel profile is 170 °C at the feed throat, 190–210 °C in the mixing zones, and 190 °C at the die. Screw speeds of 300–600 rpm are used with a specific energy of 0.15–0.25 kWh/kg. Vacuum venting at −0.08 MPa is applied after the first melt seal to remove low-molecular-weight volatiles. Torque increases sharply when oil is injected after the mid-extruder feed port rather than at the main feed, because pre-wetting of pellets reduces frictional heating in partially filled zones.

Compounding with calcium stearate at 0.05–0.1 phr and a hindered phenolic antioxidant at 0.1–0.3 phr reduces thermo-oxidative chain scission during hot-runner dwell. Nitrogen blanketing of the feed hopper and screw flights lowers yellowness index drift to below 2.0 units after 24 h at 180 °C. Injection-moulded plaques of 2 mm thickness exhibit tensile strength of 28 MPa and elongation at break of 750 % when tested according to ASTM D638-14 Type IV. The polymer itself absorbs less than 0.5 wt% moisture at 23 °C and 50 % RH; however, surface condensation on chilled pellets can generate splay and surface defects in filled or hygroscopic compounds. Pre-drying at 70 °C for 2 h is therefore required when pellets have been stored or transported at relative humidity above 60 %.

When CH6140 Replaces Unsaturated SBS in Low-Hardness Overmoulding Compounds

Replacement of solution-polymerised SBS with CH6140 is technically justified only when midblock oxidation is the controlling failure mode. In overmoulds with Shore A 40–60, CH6140 retains a higher proportion of tensile elongation after accelerated weathering under ISO 4892-2:2013 cycle 1 for 500 h. A conventional 30 wt% styrene SBS loses more than 40 % of elongation under the same exposure, whereas the saturated ethylene/butylene midblock of CH6140 develops negligible ozone cracks. The molecular weight distribution of CH6140 is narrower than many SBS grades, which reduces die lip build-up but increases sensitivity to shear-induced melt fracture at the same apparent shear rate. In twin-screw compounding with polypropylene at 20 wt%, the co-continuous phase morphology generated by CH6140 shifts the brittle–tough transition to approximately −35 °C under ISO 6603-2:2000 instrumented puncture. Published data for this specific formulation are limited; the −35 °C value is an interpolated class result for linear SEBS with 30 wt% bound styrene and must be verified on production lots.

Compared with non-hydrogenated SBS, CH6140 requires higher processing temperatures because capillary rheometry at 100 s⁻¹ shows melt viscosity approximately 3–5 times higher at 200 °C. Unlike SEPS, the ethylene/butylene midblock has no pendant methyl groups along the saturated chain, giving lower entanglement molecular weight and higher tensile strength at equal bound styrene content. Against plasticised EVA, CH6140 retains tensile properties better after oil extraction in olive oil for 72 h at 50 °C; mass loss is below 1 wt%, whereas EVA compounds may lose 5–10 wt% plasticiser. The product is not a substitute for crosslinked rubber in compression-set-critical applications above 100 °C, where compression set can exceed 50 %.

Thermal stabilisation and olefinic midblock degradation thresholds

Differential scanning calorimetry of CH6140 shows the polystyrene end-block glass transition at 95 °C and the ethylene/butylene midblock glass transition at −54 °C at heating rate 10 K/min under ISO 11357-2:2020. The broad endothermic signal from the saturated midblock is absent in unsaturated SBS, which confirms the hydrogenated architecture. Thermo-oxidative degradation proceeds by hydrogen abstraction from tertiary carbon atoms in the midblock followed by chain scission and carboxylic acid formation. During open-mill mixing, compound temperatures above 180 °C generate measurable melt discoloration within 15 min unless a phosphite co-stabiliser is included. The material should not be held above 240 °C for longer than 10 min because polystyrene domain degradation leads to permanent tensile strength loss and gel formation. Compatibilisation with ethylene-octene copolymers lowers modulus but does not eliminate the need for secondary antioxidants in thin-film extrusion.

On an injection moulding machine with shot size of 50 % of barrel capacity and clamp force of 800–1200 kN, a melt temperature of 190–210 °C, mould temperature of 15–30 °C, and holding pressure of 20–40 MPa are typical. Rapid cooling from the melt freezes the polystyrene domains, yielding hardness near 68 Shore A. In polyolefin modification, CH6140 at 15–30 wt% in polypropylene random copolymer reduces notched impact sensitivity at 0 °C without reducing heat deflection temperature by more than 5 °C. Blown film extrusion of such compounds requires a die gap of 0.5–0.8 mm and blow-up ratio of 2.0–2.5 to maintain bubble stability. The saturated midblock preserves melt strength during film bubble formation, reducing bubble instability compared with EPDM-modified polypropylene at equivalent melt index.

Adhesion and Substrate Wetting Limits in Ester-Free Hot-Melt Systems

CH6140 is incorporated into hot-melt adhesive formulations in a vertical sigma-blade mixer with jacket oil at 170–180 °C. Aromatic-modified aliphatic tackifiers with ring-and-ball softening point of 85–105 °C under ASTM E28-18 produce lower plateau modulus than fully aromatic C9 resins, which reduces low-strain peel on low-energy substrates. Peel adhesion on untreated polyethylene according to ASTM D903-98(2017) is 2–5 N/25 mm for a representative system containing 40 wt% CH6140, 40 wt% tackifier, and 20 wt% oil. Hot-melt viscosity measured by ASTM D3236-88(2014) at 180 °C remains below 15 Pa·s when mixer residence time is kept below 90 min. Sustained exposure to ester-based plasticisers is not recommended because the plasticiser can migrate into the ethylene/butylene midblock and reduce cohesive strength.

Food-contact suitability is formulation-dependent and cannot be established by polymer selection alone. Compounds based on CH6140 may be evaluated under 21 CFR 177.1810 for styrene block copolymers when the finished article meets all extraction and end-use requirements. Electrical and electronic applications require verification of heavy-metal concentrations under the IEC 62321 series and compliance with RoHS Directive 2011/65/EU. Incompatibility with strong aromatic or chlorinated solvents should be assumed; the midblock swells in toluene, and the polystyrene domains dissolve above 60 °C. The material should not be specified as a sole fuel-contact seal because continuous contact with high-aromatic oils produces dimensional failure. Published data for this specific configuration are limited for cyclic compression at 90 °C in the presence of automotive greases; long-term sealing applications require part-specific testing under ISO 815-1:2014.