Dynasol Calprene® SEBS CH6170 is a linear styrene-ethylene/butylene-styrene block copolymer supplied in crumb form. The polymer combines terminal polystyrene blocks with a hydrogenated ethylene/butylene midblock; hydrogenation removes the diene unsaturation that dominates the aging behavior of unhydrogenated styrene-butadiene-styrene copolymers. The CH prefix denotes the crumb presentation, a physical form used on compounding lines where rapid oil absorption and feed-zone dispersion determine throughput. Within the Calprene range, the product is supplied as a neat resin rather than an oil-extended masterbatch, which permits direct control over filler and plasticizer loading when generating low-hardness elastomers without sacrificing cohesive strength.

The polymer is formulated into injection-molded footwear components, soft-touch grips, sealing profiles, sound-damping sheet, automotive profiles, hot-melt adhesives, and polymer-modification packages. The saturated midblock provides resistance to thermo-oxidative chain scission during multiple melt histories and reduces gel formation that can appear in unsaturated SBS compounds during hot-runner cycles. The crumb morphology gives a higher specific surface area than dense pellet feed, shortens the time required for paraffinic oil to migrate into the rubber phase, and lowers peak motor load in the first mixing zone of a co-rotating twin-screw extruder. The manufacturer-published nominal styrene content is 30 wt%; density is 0.91 g/cm³ under ISO 1183-1.

What Processing Constraints Govern High-Oil CH6170 Compounds?

The dominant processing constraint for oil-extended CH6170 compounds is staged oil absorption. When the total paraffinic oil addition exceeds 100 phr to 150 phr and all oil is injected at the first feed port, the crumb becomes lubricated before the rubber phase has developed sufficient shear heat to accept the plasticizer. The result is feed-zone slip, reduced extruder output, and free oil accumulation at the vent. On a 40:1 L/D co-rotating twin-screw extruder with 45 mm screw diameter, staged injection is typically configured as 60–70 % of the target oil at the first side-feed port, 20–25 % at the second port, and the balance at the downstream port. This staged profile preserves barrel fill and allows the first kneading block to raise stock temperature before the final oil fraction is introduced.

In batch mixing, CH6170 crumb is processed in a tangential or intermeshing internal mixer at rotor speeds from 35 min⁻¹ to 60 min⁻¹. The fill factor is typically set at 0.70 to 0.80; higher fill factors can trap oil between the ram and the chamber throat, causing feed-zone slippage. The crumb is added first and mixed for 30 s to 60 s before the first oil addition. The batch is discharged when the torque curve stabilizes after the final oil addition; discharge temperatures between 130 °C and 170 °C are common for oil-extended SEBS gum stocks. Prolonged mixing beyond the torque plateau can increase stock temperature without improving filler dispersion and may cause the polystyrene end-blocks to lose physical crosslink density.

Barrel set points are commonly maintained between 160 °C and 220 °C for SEBS compounding, but the actual melt temperature can exceed the set point by 10 °C to 30 °C in the high-shear zones. A melt temperature above 230 °C increases the risk of polystyrene end-block degradation, which is observed as a rise in die pressure and a reduction in draw-down stability. The final vent should be operated at -0.08 MPa to -0.09 MPa gauge to remove volatile low-molecular-weight species without pulling oil mist into the vacuum pump. If the formulation contains hygroscopic fillers or the crumb has been stored at relative humidity above 60 %, pre-drying at 70 °C to 80 °C for 2 h to 3 h is recommended to avoid surface porosity in the finished profile.

The use of aromatic mineral oils is generally avoided because the polar aromatic structures are less compatible with the hydrogenated ethylene/butylene midblock and can migrate to the surface under compressive load. Paraffinic oils with a viscosity-gravity constant below 0.82 are preferred to maintain mechanical property retention after thermal aging. Amine-based stabilizers should be avoided in formulations that are steam-sterilized or exposed to prolonged high-humidity service because they can accelerate yellowing and generate extractable chromophores in the compound.

Rheological monitoring during compounding should include die pressure signature and melt flow-rate ratio. A die pressure fluctuation greater than 0.5 MPa on a 45 mm twin-screw line usually indicates discontinuous oil absorption or a feed-zone block with inadequate distributive mixing. Capillary rheometry at 190 °C and 200 °C with apparent shear rates between 100 s⁻¹ and 1000 s⁻¹ can expose gel particles or undispersed crumb fragments; a rise in melt viscosity at low shear combined with normal pressure at high shear often signals network formation from degraded end-blocks. Published data for this specific configuration is limited, but the roughness of the extrudate surface is a practical indicator of mixing quality when capillary rheometry is not available.

Incoming quality control for CH6170 is normally built around the polymer’s architecture, flow position, and cleanliness. The table below lists the property window used for supplier certification and incoming inspection of linear 30 wt% styrene SEBS crumb; the values are not lot-release limits for every application and must be confirmed against the current Dynasol technical data sheet for CH6170.

Hardness and tensile data are strongly affected by compression-molding history. Specimens should be molded at 180 °C to 200 °C and conditioned at 23 °C ± 2 °C and 50 % ± 5 % relative humidity for at least 24 h before testing. Inadequate mold cooling or inconsistent cooling rate can shift the apparent Shore A hardness by 2–5 points and reduce measured elongation because the polystyrene end-block domains require controlled ordering to develop their full physical crosslink density. Melt mass-flow rate should be obtained from the current lot certificate because it changes with production site and revision; if gate-sizing calculations require a precise value, a capillary rheometry sweep at 190 °C, 210 °C, and 230 °C is more useful than a single melt index point.

When Hydrogenated Midblock Stability Is Compared with Unsaturated SBS and Thermoplastic Polyurethane

When an unsaturated SBS grade is replaced with CH6170 in a sealing or overmolding formulation, the main technical difference is the absence of main-chain double bonds in the rubbery midblock. In hot-air aging according to ISO 188 at 120 °C for 168 h, hydrogenated SEBS compounds generally retain a higher fraction of original elongation at break than comparable unsaturated SBS compounds; the magnitude of the difference depends on filler type, oil level, and stabilizer package, and published data for this specific CH6170 configuration is limited. The hydrogenated midblock increases the onset temperature for oxidative chain scission and reduces the tendency toward surface chalking or crosslinked skin formation after repeated injection-molding heat histories.

Compared with a maleic-anhydride-grafted SEBS, CH6170 is non-functionalized. It does not deliver covalent bonding to nylon, polyester, or polycarbonate during overmolding; adhesion to polar substrates is mechanical or requires a separate compatibilizer in the compound. Compared with an oil-extended SEBS grade, CH6170 is supplied neat, which allows the compounder to formulate from 10 phr oil for high-modulus parts to more than 150 phr oil for ultra-soft gel compounds without being constrained by the fixed oil-to-polymer ratio of a pre-oiled masterbatch. Compared with thermoplastic polyurethane, CH6170 has a lower density and better hydrolytic stability in warm water, but lower abrasion resistance and lower solvent resistance; equipment contact surfaces and downstream tooling must be selected accordingly.

Inside the Calprene SEBS family, CH6170 is generally distinguished from lower-numbered grades by the flow position required for injection-molding compounds. The numerical suffix does not encode a simple melt-index progression across all production lines, so substitution of CH6110 or CH6120 should be based on the current data sheet and the end-use hardness requirement. Users replacing an oil-extended SEBS with neat CH6170 must rebalance the oil-to-polymer ratio and the filler level because the crumb form absorbs oil faster than pelletized oil-extended grades; otherwise the compound can reach target hardness before adequate filler dispersion has occurred, leaving mineral filler agglomerates that initiate tearing in thin-wall sections.

For sealing profiles and gaskets, CH6170 is typically compounded with paraffinic oil, polypropylene, and calcium carbonate. The polypropylene fraction controls hardness and compression set through a co-continuous crystalline phase; typical loadings range from 10 phr to 40 phr depending on the required compression set target. Calcium carbonate loadings above 80 phr increase density and reduce extrusion line speed unless the screw profile includes a downstream side-feeding port with low-shear distributive mixing elements. The finished compound’s compression set under constant strain is measured by ISO 815-1; softer compounds with high oil loadings can show a sharp increase in compression set if the oil-to-polymer ratio exceeds the retention capacity of the midblock.

In injection-molded soft-touch applications, the compound is overmolded onto glass-filled nylon or polycarbonate/acrylonitrile-butadiene-styrene substrates. The melt temperature at the nozzle is generally kept below 220 °C to minimize the formation of low-molecular-weight fractions that can cause mold plate-out. Mold temperature is usually set between 20 °C and 60 °C; higher mold temperatures reduce surface gloss but can extend cycle time because the SEBS compound does not crystallize and relies on the solidification of the polystyrene domains for demolding. The use of a valve-gated hot runner with small-diameter gates requires the current CH6170 melt flow-rate value; if the MFR is too low for the selected gate diameter, the compounder can increase the gate diameter or add a low-viscosity paraffinic oil to lower fill pressure.

Regulatory Status, RoHS Screening, and Food-Contact Evaluation Boundaries

The base CH6170 polymer is manufactured to support evaluation for food-contact use under 21 CFR 177.1810 in the United States, subject to finished-article extraction testing and end-use temperature limits. In the European Union, SEBS-containing compounds may be assessed under EU 10/2011 for plastic food-contact materials; total migration into food simulants, specific migration of styrene, and overall migration limits are determined on the finished article rather than on the base resin. Compliance under REACH requires confirmation from the specific production site’s registration documentation. Under RoHS Directive 2011/65/EU screening, the base polymer is expected to contain cadmium, lead, mercury, and hexavalent chromium below the applicable concentration thresholds, but finished-compound declarations require testing of the full formulation because fillers and colorants can introduce restricted substances.

Processors should not rely on these statements as a complete regulatory clearance. Specific applications such as potable water seals, medical device components, and toys may require additional conformity work under EN 681-1, USP Class VI, or EN 71-3 migration testing. Published data for this specific configuration is limited when compounds contain high oil loadings or unconventional fillers, and the responsible formulator must commission finished-article testing. The base polymer should be stored in closed packaging and kept below 40 °C; if exposed to ultraviolet light for extended periods before compounding, the surface may develop gel particles that cannot be dispersed by normal twin-screw mixing.

Thermal decomposition above 260 °C generates aliphatic and aromatic hydrocarbon vapors; local exhaust ventilation and melt-temperature interlocks are recommended for production lines running high-viscosity compounds at high screw speeds. Scrap CH6170 compound can be reworked into the same formulation at levels up to 20 wt% without a significant loss of tensile properties in many sealant and gasket formulations, provided the regrind is free of oil-surface contamination and has not experienced multiple high-temperature processing cycles. Beyond that level, property drift should be monitored by ISO 37 tensile testing and ISO 815-1 compression set because the polystyrene end-block phase can undergo a cumulative loss of physical crosslink density after repeated heat histories.