Calprene® SBS 710 is a styrene-butadiene-styrene thermoplastic elastomer supplied by Dynasol Group under CAS registry number 9003-55-8. Manufacturer technical documentation identifies the grade as a radial or star-shaped SBS triblock with a nominal bound styrene content of 30 ± 1 wt% and a nominal butadiene content of 70 ± 1 wt%. The polymer is produced by sequential anionic polymerization followed by coupling with a multifunctional agent; the resulting architecture places polystyrene terminal blocks at each arm terminus and a continuous polybutadiene midblock phase between discontinuous polystyrene domains. At ambient temperature the polystyrene domains act as physical crosslinks. Thermoplastic re-melting occurs when the polystyrene domains soften above the glass transition temperature of approximately 95 °C, while the polybutadiene phase retains elastomeric character above its approximate glass transition of −85 °C, as measured by differential scanning calorimetry at 10 K/min. The product is supplied as solid pellets and is intended for compounding, bitumen modification, and adhesive manufacture. Unlike oil-extended SBS grades, Calprene® SBS 710 contains no extender oil at the point of sale; formulators therefore control the final oil loading directly. All rheological and mechanical values in the technical data sheet refer to the neat polymer, not to an oil-containing compound.

What Differentiates the Radial Architecture from Linear SBS Grades of Equal Nominal Styrene Content?

The radial coupling reaction yields a star-shaped molecule with three or more block copolymer arms joined at a central core. Compared with a linear triblock of the same bound styrene content, the radial grade exhibits lower melt mass-flow rate at equivalent arm molecular mass, higher coupling efficiency, and a broader molecular weight distribution. The presence of uncoupled diblock is controlled by the manufacturer; published certificate formats typically report total extractables below 1.0 wt% rather than a direct diblock value for this grade. In hot-melt compounding, the higher branching degree increases shear-thinning response and green strength after solvent evaporation. Oscillatory shear at 180 °C shows shear-thinning power-law indices between 0.3 and 0.6, which indicates pronounced pseudoplasticity; single-point melt flow data therefore cannot be extrapolated linearly across different shear rates. These differences become operationally significant in bitumen modification: radial SBS can raise softening point and elastic recovery at lower addition levels than a linear grade of equivalent styrene content, but the radial architecture also requires longer low-shear dispersion time under identical temperature and mixer speed.

Batch-certificate data for Calprene® SBS 710 commonly report the following control window. Values are manufacturer control limits rather than a fixed specification for any single production lot.

The tensile and hardness values are obtained from compression-moulded sheets conditioned at 23 ± 2 °C and 50 ± 5% relative humidity for 24 h. Because the grade is a neat SBS, the mechanical property envelope shifts when oil, polystyrene extender resin, or polyolefin is added; no single value should be applied to formulated compounds without re-testing under the intended end-use standard. The product does not carry a specified Mooney viscosity because Mooney measurement for SBS block copolymers at 100 °C is less sensitive to architectural differences than solution viscosity or melt flow. Users comparing viscosity across batches should use oscillation frequency sweeps from 0.1 rad/s to 100 rad/s rather than single-point capillary data.

Twin-Screw Extrusion Temperature Profiles and Shear-Thermal Limits in SBS 710 Compounding

In a co-rotating twin-screw extruder with L/D ratio of at least 36:1, a barrel profile from 150 °C at the feed throat to 190 °C at the die is specified for dispersion into styrenic or olefinic matrices. The melt temperature should not exceed 200 °C for more than 5 min because the polybutadiene midblock undergoes radical-mediated chain scission and crosslinking that shifts viscosity unpredictably. Vent port vacuum of −0.08 MPa or deeper is used to remove residual water and low-molecular-weight volatiles. When pellets are stored at relative humidity above 60%, pre-drying in a dehumidifying hopper at 65 ± 5 °C for 2–3 h is required before extrusion; otherwise surface moisture produces porosity in extruded profiles and reduces melt pressure stability.

On a 40 mm co-rotating twin-screw extruder with L/D 40:1, die pressure instability of more than ±0.3 MPa has been observed when pellet moisture exceeds 0.1 wt%, producing surging at the gravimetric feeder and inconsistent strand diameter. Screw configurations with high-shear kneading elements downstream of the feed zone generate local melt temperatures 10–15 K above barrel set point at screw speeds above 300 min⁻¹; production lines therefore use medium shear configurations with two or three kneading blocks and reverse elements to control residence time. For injection moulding of SBS 710 compounds, barrel temperatures from 160 °C to 205 °C and mould temperatures from 20 °C to 40 °C are used. Clamp force requirements are lower than for comparable polyamide or polypropylene compounds because shear-induced viscosity decay reduces injection pressure. However, knit-line strength can be affected by rapid re-solidification of the polystyrene domains; gate placement should avoid flow fronts meeting in thick, slow-filling regions.

During polymer-modified bitumen production, Calprene® SBS 710 is dispersed into penetration-grade bitumen at 4.0–6.0 wt% using a high-shear mixer or colloid mill at 175–185 °C. High-shear rotor-stator devices with tip speeds above 15 m/s are used; lower-shear paddle mixers produce inhomogeneous swollen gel particles. The radial architecture produces a continuous elastomer network when the dosage exceeds the critical network concentration, typically 3.0–4.0 wt%; below that threshold the dispersed phase remains as discrete swollen particles and elastic recovery remains low. ASTM D6084 elastic recovery and ASTM D36 softening point are used to monitor network development. A dosage of 5.0 wt% in a paraffinic bitumen suitable for polymer modification has been reported to shift the performance grade from PG 64-22 to PG 76-22, with elastic recovery exceeding 70% at 25 °C. Storage stability testing per EN 13399 should be performed when the formulation contains aromatic process oils or synthetic waxes; radial SBS grades can exhibit greater phase separation than linear grades when the maltene aromatics content is below the solubility window. Oxidative aging per EN 14769 or ASTM D6521 should be evaluated because the unsaturated polybutadiene midblock is sensitive to prolonged storage at temperatures above 180 °C under air.

When Calprene® SBS 710 Is Substituted for Oil-Extended SBS in Hot-Melt Adhesive Formulations

In hot-melt pressure-sensitive adhesive formulations, substitution of an oil-extended SBS grade with Calprene® SBS 710 requires proportional adjustment of tackifier and plasticiser loadings. The radial grade has lower diluent tolerance before phase separation than a linear oil-extended equivalent, which constrains oil addition to 25–35 wt% for stable formulations. On a twin-screw adhesive line with melt temperature 160–170 °C, the radial architecture contributes higher cohesive strength and shear holding power but reduces tack at equivalent plasticiser content. ASTM D3654 loop tack and ASTM D4498 shear adhesion failure temperature are used to compare batches. Reported SAFT values for a 30 wt% polymer formulation are typically in the 70–90 °C range depending on C5/C9 tackifier ratio. Peel adhesion measured by ASTM D1876 at 23 °C is usually 2.0–4.0 N/25 mm for aluminium/polyethylene laminates; values below 2.0 N/25 mm indicate excessive plasticiser migration or incomplete polymer dispersion.

When the same formulation is run on a continuous kneader rather than a twin-screw extruder, the lower shear can leave undispersed gel particles with diameters above 50 µm. Filtration through a 150 µm mesh at the die has been used to detect dispersion breaks; pressure rise across the screen pack above 2.0 MPa indicates a change in polymer lot or insufficient tackifier wetting. Because specific publication of production-scale failure-rate statistics for this grade is limited, plant trials should establish lot-to-lot viscosity drift under the selected mixer.

In solvent-borne adhesives, Calprene® SBS 710 dissolves at 25–30 wt% solids in toluene, cyclohexane or methyl ethyl ketone/toluene blends using a high-speed disperser. Solution viscosity follows the table above; high-shear mixing is preferred because the radial architecture forms a transient gel network that can stall low-torque agitators at temperatures below 15 °C. Recovery of properties after solvent evaporation is influenced by drying rate; slow evaporation from 40–60 °C ovens permits greater polystyrene domain ordering and higher cohesive strength than flash drying at 90–100 °C.

In styrenic resin modification, Calprene® SBS 710 is not a drop-in replacement for high-styrene linear SBS or SBR latex grades. At 10 wt% addition to general-purpose polystyrene, notched Izod impact strength per ASTM D256 is reported in the 50–100 J/m range at 23 °C, while transparency drops because the polybutadiene domains create haze. Fusion processing in a single-screw extruder with barrier screw and L/D 30:1 requires melt temperature above the polystyrene domain glass transition; otherwise undispersed elastomer streaks appear in the extrudate. Published data for this specific PS/SBS blend configuration is limited, so material trials should verify the required impact-haze balance under the moulder’s gate and cooling conditions.

In footwear applications, the product can be blended with polystyrene and paraffinic oil for midsoles; the specific blend ratio is dictated by ISO 20345 sole abrasion requirements and ASTM D395 compression set testing at 70 °C for 24 h. The radial architecture retains compression set values below 30% when the polystyrene content is sufficient to maintain domain rigidity.

For REACH registration under EU Regulation 1907/2006, the polymer is manufactured within ISO 9001 quality systems and is not classified as hazardous in the supplied solid form under CLP criteria. Molten material above 180 °C can generate low-level decomposition products and requires local exhaust ventilation. Strong oxidising agents and copper-based materials should not be used in contact with molten SBS because transition-metal ions accelerate thermal oxidation of the polybutadiene midblock. Store at temperatures below 40 °C and protect from ultraviolet light.