Dynasol Calprene® SEBS CH6144 is a hydrogenated styrene-ethylene/butylene-styrene block copolymer supplied as low-dust porous pellets for melt-compounded thermoplastic elastomer applications. The polymer is obtained by sequential anionic polymerisation of styrene and butadiene, followed by selective hydrogenation of the butadiene midblock. Morphologically, the material consists of polystyrene domains dispersed in a saturated ethylene/butylene matrix; the domains act as physical crosslinks below the glass transition temperature of polystyrene and soften reversibly above approximately 95 °C. The CAS registry number for this saturated SBS family is 66070-58-4. Because lot-specific values for CH6144 are issued in the manufacturer’s certificate of analysis, the following content uses representative class data and processing boundaries published in elastomer compounding literature; finished-part qualification should be based on current supplier data and application-specific testing.

Compared with unhydrogenated SBS, CH6144 has reduced midblock unsaturation and therefore different ageing behaviour. Unsaturated SBS may contain 30–45 mol% double bonds in the butadiene block before hydrogenation, whereas hydrogenated SEBS grades are typically below 1 mol% residual unsaturation by iodine titration or FTIR. This structural difference shifts outdoor failure from ozone crack propagation to styrene domain ripening and stabiliser depletion. The saturated midblock also permits sustained processing at 190–230 °C without the rapid viscosity loss observed in unhydrogenated SBS.

In comparison with high-molecular-weight SEBS grades, CH6144 is positioned for applications requiring lower melt viscosity and shorter cycle times. The lower apparent viscosity reduces injection pressure in thin-wall tools, but the trade-off is a measurable decrease in tensile strength and creep resistance. Compared with EPDM, CH6144 does not require sulphur cure systems and can be reground and reprocessed in many formulations at addition levels up to 30 wt% without hardness shift exceeding 2–4 Shore A points. Compared with TPU, CH6144 compounds exhibit lower tensile strength but better low-temperature flexibility and reduced susceptibility to hydrolytic degradation.

How Does Selective Hydrogenation Alter Long-Term Ageing Kinetics?

Long-term ageing data generated according to ISO 188:2023 on compression-moulded SEBS compounds containing hindered phenolic antioxidants typically show tensile strength retention above 85% after 1000 h at 120 °C; published CH6144-specific values for this configuration are limited. The dominant failure mode at 140 °C is surface embrittlement from polystyrene domain coalescence, not midblock chain scission. Stabiliser packages containing amine-based additives should be avoided in systems subsequently exposed to strong oxidising agents, as nitroso oxidation products can accelerate discolouration.

For outdoor exposure, unstabilised SEBS may develop microcracks after 800–1200 h in QUV-A accelerated testing, so CH6144 compounds require carbon black or hindered amine light stabilisers in coloured articles. The saturated midblock does not eliminate photo-oxidative activity in the polystyrene domains or in mineral oil extenders. Thermo-oxidative degradation can be monitored by dynamic mechanical analysis according to ISO 6721-1:2019. A neat compression-moulded SEBS with 30 wt% styrene typically shows a storage modulus G′ at 1 Hz of 10–30 MPa at 25 °C; the loss tangent exhibits peaks near -40 °C for the ethylene/butylene phase and near 95 °C for the polystyrene phase. In a formulation containing 30 wt% paraffinic oil, the low-temperature loss peak may shift to -50 °C, while the upper service temperature declines by 10–15 °C.

Twin-Screw Compounding Windows and Oil Partitioning Limits

Compounding of CH6144 on a co-rotating twin-screw extruder with 36:1 to 48:1 L/D is performed at barrel temperatures from 160 °C to 220 °C. The feed zone is maintained below 170 °C to prevent pellet blocking before compaction; downstream zones may reach 210–220 °C. Specific energy input of 0.15–0.25 kWh/kg is typical for compounds containing 30–50 wt% paraffinic oil. A 58 mm diameter machine with 44:1 L/D permits oil injection through a side feeder at two-thirds of the barrel length without phase inversion. Torque should remain below 85% of drive capacity; if torque exceeds this value above 350 rpm screw speed, the formulation likely contains insufficient oil or excessive high-molecular-weight polypropylene.

Oil selection is critical. Paraffinic oil with aniline point above 80 °C partitions selectively into the ethylene/butylene midblock. Aromatic oil above 15 wt% of the compound plasticises polystyrene domains and can reduce Shore A hardness by 8–15 points. The oil uptake limit depends on diblock content and molecular weight; when oil is added too rapidly, torque fall exceeding 30% may generate slip on the screws and unmelted domains.

These data are class-typical and not lot-certification values. The higher melt flow range of CH6144 reduces injection pressure by approximately 15–25% relative to a high-molecular-weight SEBS at the same melt temperature and part wall thickness; actual pressure reduction depends on gate geometry and hot-runner design. Viscosity data for mould-filling simulation should be generated by capillary rheometry according to ISO 11443:2021 at 190 °C, 210 °C, and 230 °C. At shear rates from 100 s⁻¹ to 1000 s⁻¹, the melt exhibits shear-thinning with a power-law index in 0.30–0.45. Using only melt flow rate data underpredicts injection pressure in thin-walled tools by as much as 30%, because the power-law region controls gate shear heating and filling pressure.

When CH6144 Replaces a High-Molecular-Weight SEBS in Thin-Wall Injection Moulding

Thin-wall articles with a flow length-to-thickness ratio above 150:1 require low melt viscosity. On a 100-tonne injection moulding machine with 1.2 mm wall thickness, a CH6144-based compound at 210 °C melt temperature and 60 °C mould temperature may fill the cavity at 95% injection pressure; a high-molecular-weight SEBS comparison at identical hardness may require 230 °C to achieve complete filling. Moulded articles produced from CH6144 exhibit lower tensile strength and creep resistance because reduced entanglement density shortens the rubbery plateau. This can be partially offset by adding 10–20 phr polypropylene or by peroxide crosslinking.

Melt filtration is required before die extrusion. A screen pack of 80/120/80 mesh removes unmelted domains larger than 0.5 mm. Surface melt fracture can occur at shear rates above 1000 s⁻¹ if the die land length is less than 10 times the die gap; increasing die temperature to 220 °C and reducing screw speed below 40 rpm usually eliminates the defect. Pre-drying is recommended when pellets are stored at relative humidity above 80%: 2–4 h at 60 °C in a desiccant dryer with -40 °C dew point.

Which Compliance Obligations Apply to CH6144 in Food-Contact and Medical Articles?

CH6144 is subject to regional regulatory frameworks. For food-contact uses, the formulated article must be evaluated under 21 CFR 177.2600 for repeated-use rubber articles or 21 CFR 177.2200 when the polymer is used as an indirect component of olefin polymers. In the European Union, REACH Regulation (EC) No 1907/2006 requires safety data sheet communication and substance registration; RoHS Directive 2011/65/EU restricts lead, cadmium, mercury, hexavalent chromium, and restricted phthalates. Overall migration testing uses EN 1186-1:2002. Medical device compounds require cytotoxicity screening according to ISO 10993-5:2023, because downstream stabilisers and processing aids may alter biological response.

On industrial extrusion and injection moulding lines, pre-drying control at -40 °C dew point and avoidance of aromatic oil infiltration are necessary to prevent surface defects and hardness drift. Chlorinated solvents and strong oxidising agents should not be used for cleaning because they can attack the polystyrene domains. Formulations that include high-vinyl polybutadienes under high shear have shown tensile strength reductions exceeding 20% when tested to ISO 37:2017.