Manufactured as a linear styrene-butadiene-styrene block copolymer, Dynasol Calprene® SBS 401 is supplied as a non-oil-extended thermoplastic elastomer with a typical styrene content of 30 wt% and a butadiene content of 70 wt%. The polymer consists of two terminal polystyrene blocks separated by a polybutadiene midblock, producing a microphase-separated morphology in which the styrene domains act as physical crosslinks. The model designation 401 places the material in the medium-styrene range of the Calprene SBS series. In neat form the product is typically pelletised with a specific gravity near 0.94 when measured according to ISO 2781. The polymer is identified under CAS 9003-55-8.

That composition supports use in bitumen modification, footwear compounds, technical goods, and solvent-borne adhesives. Compared with SEBS grades, the unsaturated butadiene midblock of Calprene SBS 401 provides lower resistance to oxidative attack but higher elastomeric recovery at ambient temperature. Compared with SIS grades, the styrene-butadiene-styrene sequence exhibits a different tackifier resin compatibility envelope and generally lower hot-melt viscosity at equivalent block length. The product is not oil-extended; formulations requiring reduced hardness must add processing oil during compounding rather than relying on a pre-plasticised carrier.

Specification values are anchored to standardised test methods

Supplier technical literature lists the following typical properties for the neat polymer. These values should not be read as batch-release minima because lot-to-lot variation in block length, styrene distribution, and stabiliser package can shift melt viscosity and tensile response. Incoming inspection should verify melt flow behaviour on a calibrated melt indexer and confirm mechanical properties on compression-moulded plaques conditioned at 23 °C and 50% relative humidity.

Published data for this specific configuration is limited with respect to solution viscosity and molecular weight distribution. The unsaturated midblock imposes a thermal-oxidative ceiling that is more restrictive than that of saturated midblock grades. Consequently, melt processing parameters should be validated on production-scale equipment rather than extrapolated from capillary rheometry alone.

How does melt viscosity influence compounding and injection moulding?

The melt mass-flow rate of 10 g/10 min at 190 °C/5 kg indicates a medium-viscosity grade within the Calprene SBS range. In compounding, this viscosity is low enough for corotating twin-screw extrusion with oil injection but high enough to retain mixing intensity at the die. A corotating twin-screw extruder with an L/D ratio of 40:1 and segmented kneading blocks is commonly used for filler and oil incorporation. Barrel set temperatures from 160 °C to 190 °C are maintained to avoid excessive viscosity rise at the feed throat and thermal degradation in the metering zone.

Degradation of the butadiene segment becomes measurable above 220 °C when oxygen is not excluded. Residence times above 6 min at the upper set-point can raise melt flow rate and reduce tensile strength through chain scission. Screw speed and feed rate should therefore be balanced to limit melt temperature to 200 °C maximum. For injection moulding, a general-purpose screw with a compression ratio between 2.5:1 and 3.5:1 is adequate. Clamp force requirements depend on part geometry but are typically below 150 t for mouldings up to 500 g. The polymer contains no intentionally added processing oil, so mould release and flow length can be adjusted with external lubricants or compound-level plasticisers.

Because the unmodified polymer absorbs little water under ambient storage, pre-drying is not mandatory below 60% relative humidity. If surface condensation occurs or vacuum-packed bags are opened in high-humidity environments, drying for 2 h at 70 °C in a dehumidifying air dryer is sufficient to prevent extrudate splay and surface defects.

In bituminous binder modification, Calprene SBS 401 is typically incorporated at 3–7 wt% of total binder using a high-shear rotor-stator mill. The linear architecture of this grade yields a lower tendency for gel formation during milling than some radial SBS grades, but it develops elasticity more slowly at equivalent polymer content. The modified binder should be evaluated by softening point ring-and-ball EN 1427, elastic recovery EN 13398, and storage stability by the cigar-tube segregation test under EN 13399. In laboratory formulations, a softening point increase of 10–20 °C is observed at 4–5 wt% polymer, with elastic recovery values above 70% at 5 wt% when the binder and polymer are milled for 60–90 min at 180 °C.

Low-temperature behaviour depends on base-bitumen composition. SBS modification alone does not guarantee a specific Fraass breaking point or bending beam rheometer stiffness. Published data for this specific configuration is limited, particularly for high-wax binders. Laboratory ageing under EN 12607-1 and dynamic shear rheometry under EN 14770 should be performed before field use.

When compounding footwear and moulded goods, phase morphology dictates hardness and set

When Calprene SBS 401 is used in footwear and technical compounds, the balance between styrene domain reinforcement and butadiene phase deformation controls Shore hardness and compression set. In a general-purpose footwear formulation containing 100 phr SBS 401, 30–50 phr naphthenic oil, and 20–40 phr polystyrene or mineral filler, hardness can be targeted between 55 and 70 Shore A. The 300% modulus of the neat polymer is low enough to permit high oil loading without oil bleed, provided the oil aromaticity is matched to the butadiene phase. Aromatic or high-solvency oils soften the polystyrene domains excessively and reduce abrasion resistance; paraffinic oils have limited compatibility and may exude above 50 phr.

Compression set measured by ASTM D395 Method B after 22 h at 70 °C typically rises above 50% in oil-filled compounds, reflecting the thermoplastic nature of the physical crosslinks. For applications requiring set below 35%, compounders usually add a separate crosslinkable phase or select an SEBS grade with a saturated midblock, because SBS 401 does not develop a covalent network under normal melt processing.

Tensile response of the neat polymer is strain-history dependent. Initial extension produces yielding of the styrene domains; subsequent cycles to the same strain exhibit lower stress, a response commonly described as the Mullins effect. First-cycle hysteresis at 100% strain in unfilled films compression-moulded at 150 °C is typically 20–30%, depending on domain annealing. Cyclic hysteresis is better characterised using ISO 6943 or custom strain-controlled tensile testing than by single-point modulus values.

Footwear soles are typically injection moulded on rotary machines with clamp force between 80 and 250 t. Mould temperatures from 20 °C to 40 °C and melt temperatures from 170 °C to 190 °C are typical. Rapid cooling at the mould surface can freeze partially ordered styrene domains, so post-mould annealing at 60 °C for 30 min is sometimes used to stabilise hardness and reduce immediate set.

In solvent-borne adhesive manufacturing, Calprene SBS 401 is used as the elastomeric component in contact adhesives and pressure-sensitive adhesive bases. A starting formulation contains 15–20 wt% SBS 401, 60–70 wt% solvent blend of toluene and hexane, and 10–20 wt% tackifier resin. Resin choice controls adhesive performance: rosin esters with softening points between 90 °C and 110 °C are compatible with the polybutadiene midblock, whereas high-polarity resins associate with the polystyrene domains and can reduce cohesive strength. Initial T-peel adhesion on stainless steel tested under ASTM D1876 is influenced more by resin loading than by polymer type; cohesive failure requires molecular weight integrity and polystyrene domain formation.

Unlike SIS-based adhesives, the SBS midblock provides lower tack at low peel rates but greater shear resistance at ambient temperature. For solvent-free hot-melt pressure-sensitive adhesives, SBS 401 can be mixed with styrenated terpene resins and mineral oil at 160–180 °C in an anchor stirred mixer. Pot life is governed by antioxidant content and temperature. Published data for this specific adhesive configuration is limited, so peel, loop tack, and shear adhesion failure temperature should be measured on production-coated film because coating thickness and drying rate alter domain morphology.

Differentiation from SEBS, SIS and oil-extended SBS grades

The product is differentiated from other thermoplastic elastomers by midblock chemistry, block length, and extender-oil content. The following comparison summarises qualitative differences that affect selection in industrial compounds.

For asphalt modification, linear grades such as SBS 401 are often preferred when storage stability and low gel formation are critical. Radial grades may generate higher elastic recovery at equivalent polymer content but can be more difficult to disperse uniformly. The absence of extender oil in SBS 401 permits formulation flexibility in rubber goods and adhesives, whereas oil-extended grades reduce hardness and melt viscosity at the expense of final compound control.

Storage and regulatory boundaries are set by oxidative stability

Warehouse storage should be maintained below 40 °C and away from direct sunlight. Pallets should not be stacked more than 3 high to avoid pellet deformation. The polymer is not classified as hazardous under CLP Regulation (EC) No 1272/2008, but compliance with REACH registration and RoHS Directive 2011/65/EU for electrical and electronic applications should be verified through the safety data sheet. Food-contact status must be confirmed for the specific additive package; the neat polymer is not certified for direct food contact. Dust formation from pellet abrasion should be controlled with local exhaust ventilation, and the material should not be processed in the presence of strong oxidisers or open flame above the melt ceiling because the unsaturated butadiene block is combustible under sustained thermal load.