Calprene® CH6170 PH is a linear styrene–ethylene/butylene–styrene block copolymer supplied in powder form. The producer’s published specification identifies a styrene content of 30% by mass and a fully hydrogenated ethylene/butylene midblock. The absence of butadiene unsaturation differentiates the grade from unsaturated SBS and reduces the rate of thermo-oxidative chain scission during high-temperature melt processing. The material is specified by its 10% by mass toluene solution viscosity at 25 °C; the representative value is 6500 mPa·s. This viscosity class corresponds to a high molecular mass relative to general-purpose SEBS grades and is selected when compounds require high tensile retention, high tear resistance, and controlled elastic recovery after oil extension.

The powder presentation influences bulk handling. Lot certificates for pour density and fines content are reviewed before feeder stroke and screw speed are set. In production-scale operations, a twin-screw gravimetric feeder with a vertical hopper agitator and a 2 mm mesh protecting the feed throat is often specified. Bridging at high ambient humidity is managed by pre-drying at 80 °C for 2 h when moisture uptake exceeds 0.1%. Compared with pelletized SEBS grades, the powder form dissolves faster in oil and solvent systems but requires dust control at feed stations and static-discharge management.

Relative to lower-molecular-weight SEBS grades with toluene solution viscosities of 75–1200 mPa·s, CH6170 PH requires higher processing torque and generates higher melt viscosity at a given temperature. This difference is deliberate: the longer midblock and higher entanglement density improve tensile strength, tear strength, and compression set after oil extension. Lower-molecular-weight grades are easier to injection mold in thin sections, but they often require lower oil addition or higher styrene content to match tensile properties. The trade-off is visible in melt flow: high-molecular-weight SEBS typically shows a melt flow rate below 1 g/10 min under ISO 1133-1:2022 at 230 °C and 2.16 kg, whereas low-viscosity grades may exceed 5 g/10 min.

How Does High Midblock Molecular Mass Affect Twin-Screw Compounding and Melt Temperature Control?

Compounding of this viscosity class on a co-rotating twin-screw extruder with an L/D ratio of 40:1 is typically conducted with barrel set points between 180 °C and 220 °C. Because the high molecular mass generates shear heating, actual melt temperatures can exceed the barrel set point by 10–20 °C when screw speeds rise from 250 min⁻¹ to 450 min⁻¹. Melt temperature is therefore monitored with an immersion thermocouple at the die rather than by barrel-zone sensors alone. The recommended maximum melt temperature is 240 °C; excursions above 260 °C initiate chain scission and produce gel particles in the final compound.

The grade is introduced at the main feed throat, while paraffinic white oil is injected downstream after the polymer has formed a melt seal. Splitting oil addition into 2 or 3 injection ports reduces torque instability and prevents phase inversion in oil-extended compounds. A vacuum vent with a pressure of -0.08 MPa is positioned after the final oil injection zone to remove volatiles. Screw configuration should favor distributive mixing elements over reverse kneading blocks; excessive shear can raise melt temperature and reduce compound viscosity non-reversibly.

Barrel temperature profiling in high-molecular-mass SEBS compounding is constrained by two process conflicts. The first conflict is the need for sufficient melt temperature to incorporate fillers and to lower viscosity for downstream molding; the second is the thermal sensitivity of the hydrogenated midblock. On production-scale lines with co-rotating twin-screw extruders of 40–58 mm screw diameter, rear-zone temperatures below 170 °C can lead to unmolten powder at the feed seal, while front zones above 230 °C can produce local melt-temperature spikes. Torque fluctuations of 5–10% are observed when bulk density varies between lots or when moisture absorption increases; feeder trim adjustments and vacuum vent pressure are corrected accordingly. Published data for this specific configuration is limited, and line-specific thermal profiling should be validated by short-shot residence-time distribution tests.

When Continuous Gravimetric Dosing Requires Control of Powder Flow and Segregation

When the powder grade is used in continuous compounding lines, feeder accuracy and hopper flow are controlled to avoid segregation. Powder segregation can occur if the material is transferred pneumatically over long distances; dense-phase conveying at low velocity or mechanical conveying is preferred. Feeder setpoints are calibrated with the actual bulk density lot value, and loss-in-weight feeder control is adjusted to maintain dosing variability below ±0.5% at the main feed throat. A nitrogen purge in the hopper and feed throat is applied when ambient relative humidity exceeds 60% to reduce moisture pickup.

In hot-melt adhesive manufacturing, the powder can be charged directly into a high-shear mixer or a Banbury-type internal mixer. Dissolution is faster than dense pellets because of the higher specific surface area, but dust extraction systems must be designed for thermoplastic elastomer powders because airborne fines can accumulate on static discharge points. The powder feed is not recommended in processes where only single-screw flood feeding is available without a controlled feed throat.

Oxidative Stability and Solubility Differences from Unsaturated SBS and SEPS

Calprene CH6170 PH is differentiated from unsaturated SBS by the fully hydrogenated ethylene/butylene midblock. SBS grades undergo free-radical attack at the butadiene double bond during heat aging, leading to crosslinking, embrittlement, and melt-flow loss. The SEBS structure tolerates continuous melt processing at 230 °C without the same rate of oxidation, and its UV resistance is higher in thin-film applications. In comparison with SEPS grades, the ethylene/butylene midblock provides a different lower glass-transition temperature and solubility parameter; SEPS may provide lower low-temperature modulus, while the high-molecular-mass SEBS generally exhibits higher ambient tensile strength and tear resistance under ASTM D624-00.

Because the midblock is saturated, additive packages are restricted to non-staining phenolic or phosphite antioxidants. Avoid combination with amine-based antioxidants that can produce discoloration in white or transparent compounds. Maleic anhydride grafting is technically possible, but excessive peroxide initiator can cause chain scission in the saturated midblock rather than the crosslinking pathway observed with unsaturated SBS; grafting efficiency should be measured by acid number titration and FTIR before scale-up.

Oil-extended elastomer gels based on Calprene CH6170 PH are processed in vertical mixers or co-rotating twin-screw extruders with paraffinic white oil. The high molecular mass permits higher oil loading before loss of cohesive strength; at oil loadings above 150 phr, phase separation becomes dependent on oil aromatic content and cooling rate. Tear strength of compression-molded plaques is measured according to ASTM D624-00, and hardness is measured according to ISO 868:2003. Oil retention is assessed by weight loss after 72 h at 70 °C in a forced-air oven, but published data for this specific configuration is limited and application-specific aging should be conducted under the end-use heat history.

Calcium carbonate and silica fillers can be added at 10–30% by mass, but filler surface chemistry affects oil absorption and melt viscosity. The high molecular mass of CH6170 PH provides enough melt strength to encapsulate filler particles during mixing; however, high filler loadings require increased extruder torque and can reduce low-temperature flexibility. The filler effect on tensile strength is measured under ASTM D638-14, and filler/matrix adhesion is confirmed by scanning electron microscopy of cryofractured surfaces.

For injection molding of SEBS-based compounds containing Calprene CH6170 PH, clamp force requirements depend on projected area and flow length. High-molecular-mass SEBS compounds exhibit pseudoplastic flow; apparent viscosity decreases with increasing shear rate. Molds with cold-runner systems are used with nozzle temperatures of 200–230 °C and mold temperatures of 30–50 °C. Injection speeds are set in the medium-to-high range to prevent surface melt fracture. Published data for this specific configuration is limited.

Elastomeric recovery is quantified by compression set testing under ISO 815-1:2019 or ASTM D395-18. High-molecular-mass SEBS compounds typically show lower compression set than lower-molecular-weight grades at equal oil loading, but stabilizer migration and post-curing of the compound can alter values. For compounds requiring repeated flexural cycles, Ross flex resistance or de Mattia flex testing is used; the test method should be selected according to end-use strain amplitude.

In polymer modification, the grade is added to polypropylene or polyethylene at 5–20% by mass to improve impact resistance and reduce low-temperature brittleness. Twin-screw compounding uses the same downstream melt temperatures as unfilled polyolefin, but torque rises with addition level; addition above 25% by mass may require a side feeder and a gear pump to stabilize die pressure. The concentration dependence of impact strength should be measured under ISO 179-1:2010 or ASTM D256-10e1 because published data for this specific configuration is limited.

In bitumen modification, SEBS addition rates of 3–7% by mass are used in modified binders requiring elevated storage stability, and high-shear mixing at 180–190 °C is used to disperse the powder. Storage stability is assessed by the difference in softening point between top and bottom samples after 72 h at 163 °C, tested according to EN 13399 or ASTM D7173. The powder form shortens dissolution time relative to dense pellets, but the rate depends on bitumen composition and impeller tip speed.