As a linear styrene–ethylene/butylene–styrene block copolymer supplied in pellet form, the material identified as Dynasol Calprene® SEBS CH6170 P contains a hydrogenated midblock of ethylene/butylene repeat units and terminal polystyrene blocks. The SEBS designation distinguishes the hydrogenated elastomer from unhydrogenated styrene–butadiene–styrene and styrene–isoprene–styrene grades because saturation of the midblock removes most main-chain unsaturation. The suffix P indicates pelletized supply form, not powder or crumb. Manufactured by Dynasol Elastomers, the grade is controlled under certificate-of-analysis parameters that include bound styrene content, total extractables, volatile matter, ash, and solution viscosity. Because the midblock is hydrogenated, the material resists thermo-oxidative chain scission and UV-induced crosslinking more effectively than unhydrogenated SBS and SIS; this chemical-structure difference is the primary distinction from conventional styrenic block copolymers, not a difference in hardness or styrene content alone. In melt-compounding operations, the grade functions as a high-viscosity base elastomer for filled TPE compounds, soft-touch injection-molded parts, seal and gasket profiles, automotive interior skins, and solvent-based or hot-melt adhesive systems. Not all formulations are suitable for all end uses; extender oil chemistry, polypropylene grade, filler particle size, and stabilizer loading determine the final property envelope.

How Does High Molecular Weight Translate Into Extrusion Back-Pressure and Torque Demand?

Because CH6170 P is positioned as a high-molecular-weight linear SEBS, it generates higher melt viscosity than low- and medium-viscosity SEBS grades having the same 30 wt% bound styrene. On a co-rotating twin-screw extruder with 40:1 L/D, screw diameter from 25 mm to 65 mm, and a segmented screw profile containing three kneading blocks, the grade is usually starve-fed at barrel set points of 180 °C in the feed zone, 200–220 °C in the mixing zones, and 230 °C at the die. Die pressure is typically 10–25 bar higher than for an otherwise identical compound using a low-viscosity SEBS at the same screw speed and feed rate; the exact rise depends on screw wear, die land length, and the oil injection point. To limit pressure spikes above 120 bar, processing trials on a 58 mm extruder have used die plate holes with land-length-to-diameter ratios between 5:1 and 10:1 and a screen pack of 60/120/60 mesh. Preheating pellets to 60–80 °C before forced feeding reduces viscosity at the first kneading block and improves wetting of naphthenic or paraffinic extender oil. If the extruder is to be shut down after a CH6170 P compound, purging with 2–5 kg of polypropylene or low-density polyethylene is required; residual high-molecular-weight SEBS can crosslink and char during reheating.

Within the manufacturer’s published technical data, the following typical values are used for initial compound design; lot-to-lot variation is controlled according to certificate-of-analysis limits. The values are not specification minima or maxima unless stated on the certificate of analysis.

Hardness is determined on compression-molded plaques after 24 h conditioning at 23±2 °C and 50±10% relative humidity. Tensile specimens are die-cut from 2 mm sheets. The melt mass-flow rate is not the primary molecular-weight control for this high-viscosity grade; solution viscosity is more sensitive to lot-to-lot variation and is therefore monitored as a release parameter.

Tensile Set, Oil Retention, and Soft-Touch Compound Response

When CH6170 P is compounded with 10–20 parts per hundred rubber extender oil and 30–50 parts per hundred rubber polypropylene, the high molecular weight of the SEBS phase allows higher oil loading before gross surface bloom. Oil retention is screened by visual surface bleed after 72 h at 70 °C and by volatile loss under ASTM D1203-22 activated-carbon methods. At equivalent oil content, the high-molecular-weight grade generally shows lower compression set after 22 h at 70 °C than low-viscosity SEBS; the longer midblock chain increases entanglement density and retards permanent flow. Soft-touch compounds based on 30 wt% CH6170 P and 70 wt% polypropylene are injection molded at melt temperatures of 190–220 °C and mold temperatures of 30–60 °C. Cycle time is governed by polypropylene crystallization rather than the SEBS phase; cooling time should be set from pressure-volume-temperature data, not from an arbitrary hold time. Shrinkage and warpage in thin-walled parts are controlled more strongly by the semicrystalline polypropylene matrix than by the hydrogenated midblock.

Processed through sigma-blade mixers or heated horizontal kneaders, CH6170 P must be combined with tackifying resins and process oils under conditions that limit both thermal degradation and premature gel formation. Because the grade is high molecular weight, dissolution in toluene, cyclohexane, or blends of methyl ethyl ketone and n-heptane is slower than for low-viscosity SEBS. Solvation is usually carried out in closed reactors with condensing capacity and jacket temperature at 40–60 °C under agitation. The resulting solution viscosity at 25 wt% solids can exceed 20,000 mPa·s; solvent-adhesive formulations may require a co-solvent such as n-hexane to reduce application viscosity. Pressure-sensitive adhesive formulations using CH6170 P with C5 or C9 tackifiers typically require tackifier loadings of 40–60 parts per hundred rubber to achieve loop tack values measurable by ASTM D6195-22. The hydrogenated midblock swells in aliphatic and aromatic hydrocarbons; therefore, the grade is not recommended for immersion in strong solvents or motor fuels unless crosslinked or protected by a barrier compound. Maximum continuous service temperature under load should be verified by thermomechanical analysis according to ISO 11359-2:2021.

When a 30 wt% Polypropylene Let-Down Reaches High Shear Rates

At shear rates representative of injection molding—10³ s^-1 to 10⁵ s^-1—SEBS/polypropylene blends exhibit shear thinning. The high molecular weight of CH6170 P extends the power-law index toward shear-thinning behavior and can reduce jetting if gate geometry is correctly specified. Capillary rheometry per ISO 11443:2021 is used to collect shear viscosity data at 210 °C, 220 °C, and 230 °C over die lengths of 10 mm and 20 mm with diameter 1 mm; Bagley corrections are required for accurate values. Typical shear viscosity at 1,000 s^-1 and 220 °C for a 30 wt% polypropylene compound is reported between 150 Pa·s and 350 Pa·s, but published data for this specific configuration is limited. In injection molding, gate freeze time must be calibrated with pressure-volume-temperature data to avoid premature gate freeze; hot-runner systems should maintain manifold temperatures below 240 °C to limit residence-time degradation. Shrinkage in soft-touch parts depends more on the semicrystalline polypropylene phase than on the SEBS phase, and mold-flow analysis should use measured PVT coefficients rather than generic TPE values.

Because the hydrogenated midblock reduces pendant unsaturation, outdoor weathering programs under ASTM G154-23 usually show less crosslinking and discoloration than unhydrogenated styrenic block copolymers. Compounds pigmented with carbon black at 2.0 wt% and stabilized with a hindered amine light stabilizer at 0.2 wt% are reported to retain more than 80% of initial tensile strength after 1,500 h of UV-A exposure; however, this value is formulation-dependent and must be confirmed by actual compound testing. The polymer is not inherently flame-retardant; halogen-free flame-retardant packages based on magnesium hydroxide at 50–60 wt% reduce tensile properties and require high-torque compounding because of filler surface area. When CH6170 P is used in wire insulation or jacketing, tensile retention after 168 h in hot air at 100 °C should be verified by IEC 60811-401:2012 rather than by unaged tensile alone.

Thermal Degradation Thresholds in High-Shear Compounding

When melt temperature exceeds 250 °C for residence times longer than 5 min, measurable chain scission and gel formation occur in CH6170 P. The extruder should be purged with a 2–5 kg charge of polypropylene or low-density polyethylene before shutdown; residual SEBS in a hot barrel can form crosslinked deposits on kneading blocks. Predrying is not always required, but pellets stored above 60% relative humidity can produce surface splay in injection molding. Under such conditions, drying in a desiccant dryer at 80 °C for 2 h with a dew point of -20 °C or lower is recommended. The grade should not be combined with strong Lewis acid catalysts or amine-based additives that accelerate midblock degradation. In twin-screw compounding, the maximum barrel setpoint should remain at 230 °C; only short die-temperature excursions to 240 °C are tolerated for thin-wall filling.

For end-use qualification, the following regulatory references are commonly applied to SEBS grades. Acceptance depends on migration testing of the finished formulation, not solely on base-polymer composition.