Calprene® SEBS CH6110 is a linear styrene-ethylene/butylene-styrene triblock copolymer supplied by Dynasol as a non-oil-extended, high-molecular-weight grade. The polymer is produced by anionic polymerization of styrene and butadiene followed by selective hydrogenation of the polydiene midblock, which converts the unsaturated polybutadiene segment into a saturated ethylene/butylene elastomer. Bound styrene content in Dynasol technical documentation is reported in the range of 29–33% by mass, with a nominal value of 30%, when determined by ASTM D5775 or an equivalent calibrated method; the ethylene/butylene midblock comprises the remaining 70%. The diblock content is below 1.0%. Because the midblock is saturated, the base resin lacks the main-chain unsaturation that limits oxidative and UV stability in unhydrogenated SBS and SIS block copolymers. The triblock architecture produces physical crosslinking without vulcanization: polystyrene end blocks associate into glassy domains below the styrene glass transition, providing tensile strength, while the ethylene/butylene midblock remains flexible. CH6110 is supplied as a solid pellet and is intended for compounding rather than direct end-use injection moulding of neat resin. The high molecular weight, absence of extender oil, and linear architecture define its processing signature: high melt viscosity at standard styrenic block copolymer processing temperatures, high melt strength, and elevated tensile properties after oil extension during compounding.

What Limits Melt Flow in a Neat, High-Molecular-Weight SEBS?

The primary processing constraint for CH6110 is melt viscosity generated by its molecular weight and the absence of a process-oil phase. Melt flow rate measured at 230°C under a 5 kg load per ASTM D1238-20 is not a discriminating quality-control parameter; typical values are below 1.0 g/10 min. Solution viscosity in a high-boiling paraffinic solvent or toluene at 25°C is the more meaningful molecular-weight proxy in compounding operations. On co-rotating twin-screw lines with torque limitations, a barrel L/D ratio below 40:1 often requires throughput reduction when CH6110 replaces an oil-extended SEBS. In production practice on segmented twin-screw compounding lines, the first kneading block after the feed zone is configured to distribute the polystyrene domains while limiting peak melt temperature to 200–230°C. Barrel set points in the feed and melting zones are typically 150–170°C and 180–200°C. The feed throat is maintained below 40°C to prevent pellet agglomeration and hopper bridging. If melt temperature exceeds 250°C for extended periods, thermal shearing of the polystyrene end blocks can reduce tensile strength and increase diblock content, narrowing the service window of the final compound. The saturated ethylene/butylene midblock is thermally stable relative to unsaturated SBS, but the polystyrene domains remain the limiting thermal feature. Drying at 80°C for 2–4 h in a desiccant dryer is required when storage humidity has exceeded 60% RH because surface moisture on pellet surfaces promotes surface defects in extruded profiles and interferes with silane-treated fillers. The high melt viscosity is not a defect; it is the same property that permits high ultimate tensile strength and oil retention after the formulation is diluted with paraffinic extender oil. Oscillatory shear rheology of the neat polymer at 200°C displays a broad linear viscoelastic plateau and a low crossover frequency, reflecting high entanglement density. This rheological response translates into elevated die swell and the need for controlled downstream cooling in profile extrusion. In single-screw extruders, neat or lightly oiled CH6110 compounds require barrier screws with a compression ratio in the range of 2.5:1–3.5:1 and a grooved feed throat if high output is required. High screw speed can generate excessive shear heating, causing local melt temperature excursions beyond 240°C; underwater pelletising is therefore preferred over strand pelletising for high-hardness CH6110 compounds because the extrudate remains elastic and tacky at die exit.

Property Specifications, Test Designations, and Comparative Grade Positioning

Table 1 lists the typical physical property envelope for Calprene CH6110. The values are representative of Dynasol technical literature for compression-moulded plaques and are not batch release specifications.

The nominal 30% bound styrene level and high molecular weight place CH6110 in a segment of the SEBS class where tensile strength and hardness retention after oil loading are prioritised over melt flow. The 300% modulus of 4.5–5.5 MPa indicates that the polystyrene domains remain load-bearing at moderate extension; tensile strength above 28 MPa suggests that the failure mechanism transitions from chain slippage to styrene domain disordering as extension increases. The saturated midblock gives CH6110 a higher continuous compounding temperature than an unsaturated SBS with equivalent styrene content, which would undergo autocatalytic oxidation at allylic positions. In comparison with oil-extended SEBS grades, CH6110 carries no intrinsic process oil; this gives the compounder full control over oil type and loading but increases the melt viscosity penalty during let-down. In comparison with maleic anhydride-grafted SEBS, CH6110 has no pendant functional group. Adhesion to polar substrates is therefore based on mechanical interlocking and surface wetting rather than covalent coupling. Where primerless overmoulding onto polycarbonate, polyamide, or glass-reinforced engineering resins is required, a maleated grade or a separate tie-layer addition is necessary because CH6110 alone does not form interfacial covalent bonds.

When CH6110 Replaces Oil-Extended SEBS in Soft-Touch Compounding

In soft-touch compounds, CH6110 is typically dry-blended with polypropylene homopolymer or impact copolymer, paraffinic white oil, and mineral filler. A starting formulation for a 60–70 Shore A compound may contain 25–35 phr CH6110, 10–20 phr polypropylene, 30–50 phr paraffinic extender oil, and 0–20 phr mineral filler. Oil is injected downstream after the first kneading block to prevent lubricated pellet conveying and screw slip; early oil injection before the polymer is sufficiently plasticated produces an inhomogeneous melt and visible gel-like defects in extruded profiles. Paraffinic extender oil with an aromatic content below 1% is recommended because aromatic oil plasticises the polystyrene domains, causing a disproportionate reduction in hardness and tensile strength at oil loadings above 50 phr. The high molecular weight of CH6110 permits higher oil loadings than lower-molecular-weight SEBS grades before tensile strength falls below 8 MPa, but at oil loadings above 120 phr the compound approaches a property cliff-edge where compression set at 70°C deteriorates rapidly and oil exudation increases. Published data for CH6110-specific energy consumption in this formulation window is limited; the actual torque demand depends on screw geometry, fill level, filler particle size, and injection point configuration.

For extrusion-grade compounds, the screw profile should include forward conveying elements after oil injection to homogenise the oil-polymer-filler mixture, followed by vacuum devolatilisation to remove volatiles. If mineral fillers are side-fed, a downstream atmospheric vent before the vacuum port reduces wet filler-related steam pressure. In injection moulding, the high viscosity of CH6110-based compounds requires a slow-to-moderate injection speed to prevent jetting and gate blush, while holding pressure is maintained until gate freeze. Mould surface temperatures of 20–40°C are usually sufficient for ejection because the saturated midblock does not require crystalline solidification. Mineral fillers such as calcium carbonate with a median particle size of 2–5 µm and stearic acid surface treatment are used to reduce tack and cost. The high molecular weight CH6110 can accept up to 150 phr calcium carbonate in low-performance applications, but tensile strength and elongation fall rapidly beyond 100 phr. Surface-treated talc with lamellar structure increases stiffness and heat deflection temperature but reduces weld-line strength. Amino-silane coupling agents are generally avoided in polypropylene-containing CH6110 compounds because they can promote oxidative degradation of the polypropylene phase under hot-air ageing.

In automotive interior applications, the odour and fogging characteristics of the final compound depend on the extender oil volatility and antioxidant package rather than on the base polymer alone. Compounds based on CH6110 are evaluated according to VDA 270 and VDA 278 for odour and volatile organic compound emissions, with fogging measured under DIN 75201. The base SEBS itself contributes low odour relative to unsaturated SBS, but the complete formulation must be tested because process oil and stabiliser packages dominate emission behaviour. Overmoulding adhesion to polypropylene cores is achieved when the polypropylene fraction in the TPE compound is in the range of 10–25 phr, allowing co-crystallisation at the interface; above this range, hardness increases and elongation at break decreases. Adhesion to polyamide or glass-reinforced polycarbonate is generally poor without a functionalised tie-layer, because the saturated ethylene/butylene midblock and non-polar polystyrene domains do not participate in dipole-dipole or covalent bonding with condensation polymers. For medical and pharmaceutical compounds, CH6110 can be investigated as a candidate raw material for formulations designed to meet USP <88> Class VI and ISO 10993-5:2009 cytotoxicity requirements after gamma or ethylene oxide sterilisation validation. Food-contact formulation can be designed around 21 CFR 177.1810 and EU Regulation 10/2011, but migration testing is formulation-dependent because plasticiser, antioxidant, and filler choices dominate the final extractable profile. In wire and cable jacketing, the saturated midblock offers low tension set and high dielectric strength after electron-beam crosslinking or silane grafting; CH6110 itself is not per-oxidically crosslinkable without co-agents because the midblock lacks carbon-carbon unsaturation. For outdoor weatherseal profiles, UV stabiliser packages are necessary because the polyolefin fraction and mineral oil still degrade under prolonged UV exposure, even though the SEBS midblock is saturated.