Dynasol Solprene® SBS 416 is a non-oil-extended styrene-butadiene-styrene thermoplastic elastomer supplied as a radial, star-branched block copolymer with a typical bound styrene content of 30 wt% determined by ISO 2453. The grade is manufactured via anionic block copolymerization, yielding a two-phase morphology in which polystyrene domains act as physical crosslinks and the butadiene continuous phase controls low-temperature flexibility. In the as-supplied crumb form, specific gravity is typically 0.94 under ISO 2781, bulk density measured by ASTM D1895 procedure A is commonly 0.35–0.45 g/cm³, and residual volatile matter is controlled to ≤ 0.5 wt% under ISO 248. Ash content is specified at ≤ 0.5 wt% under ISO 247. The stabiliser package is non-staining and protects against oxidative chain scission during storage and melt processing at temperatures up to 200°C; sustained exposure above 230°C in oxygen-rich atmospheres produces viscosity loss, discoloration, and gel formation. The butadiene phase exhibits a glass transition below −80°C and the polystyrene domains a glass transition near 95°C when measured by dynamic mechanical analysis under ISO 6721-11. Melt mass-flow rate at 190°C under 5 kg load using ISO 1133-1 is reported below 1 g/10 min, positioning the product in the low-flow radial SBS class. Solution viscosity for a 25 wt% solution in toluene at 25°C is typically 1000–3000 mPa·s when measured with a rotational viscometer per ISO 2555.

Specification Boundaries and Representative Properties

Table 1 consolidates representative quality parameters for lot screening. The values are not contractual limits; the certificate of analysis for the specific lot takes precedence. Compression-moulded test sheets of 2 mm thickness are prepared at 150–160°C for 5–10 min and conditioned at 23°C ± 2°C and 50% ± 5% relative humidity for 24 h before testing. Moisture on the crumb above 0.1 wt% causes porosity, surface defects, and elongation loss of 10–25% under tensile loading.

The tensile strength range assumes void-free moulded sheets and adequate polymer fusion. Incomplete fusion at temperatures below 150°C produces brittle failure and reduces elongation to 300–500%. Oven aging at 100°C for 168 h under ISO 188 typically shifts hardness by less than 5 Shore A units. The product retains the general styrenic block copolymer profile of high tensile integrity before oil extension and pronounced strain softening after repeated cycling; hysteresis data should be generated on the finished compound because compound oil content and filler surface area control energy dissipation more strongly than the neat polymer hardness.

Why Does the Radial Branching Pattern Control High-Shear Bitumen Modification?

When Solprene SBS 416 is dispersed into penetration-grade bitumen, the radial star architecture swells in the maltene phase and then undergoes phase inversion from a bitumen-continuous system to a polymer-continuous network at polymer loadings above approximately 5 wt%. The high-shear field is typically generated in a rotor-stator mill with tip speeds of 20–30 m/s and a stator gap of 0.5–1.0 mm. Polymer addition at 3–7 wt% into 50/70 or 70/100 penetration bitumen at 175–185°C for 60–120 min produces a homogeneous elastomeric network. The temperature window is narrow: below 170°C the swelling rate declines and mixing torque rises, while above 190°C bitumen oxidation accelerates and the polymer degrades at local hot spots. Fluorescence microscopy of stable dispersions typically shows polymer-rich domains below 10 µm; larger domains indicate insufficient shear or premature cooling. Softening point by ASTM D36 rises from 45–50°C to 75–90°C, and elastic recovery by ASTM D6084 commonly exceeds 70% at 25°C. Storage stability by ASTM D7173 is generally considered acceptable when the softening point difference after 72 h at 163°C remains below 2.5°C. Published formulation-specific data for Solprene SBS 416 in high-viscosity asphalt cements is limited; however, the above ranges are consistent with radial SBS grades of equivalent styrene content processed on production-scale high-shear mills.

In solution adhesive formulations, Solprene SBS 416 is typically applied at 25–35 wt% solids in toluene, cyclohexane, or methyl ethyl ketone/toluene blends. Brookfield viscosity under ISO 2555 at 25°C is commonly 1000–3000 mPa·s at 20 rpm, depending on solvent composition and polymer grade. Shear adhesion failure temperature after compounding with endblock-compatible resins is generally raised to 60–80°C when tested at 500 g load under ASTM D4498. For footwear soling and microcellular compounds, batch mixing in an internal mixer with a ram pressure of 0.4–0.6 MPa and drop temperatures of 120–140°C permits incorporation of 30–50 phr naphthenic oil, 20–40 phr polystyrene, and 10–30 phr silica or calcium carbonate. Compounds of this type typically display hardness of 50–65 Shore A, tensile strength of 12–20 MPa, and tear strength of 25–40 kN/m under ISO 34-1. Abrasion loss under ISO 4649 is commonly 200–400 mm³, although the value depends on filler dispersion and oil type. The radial architecture imparts lower solution viscosity than a linear SBS of similar molecular mass, but the finished compound requires sufficient distributive mixing to prevent oil-rich domains and gloss variation.

When Solprene SBS 416 Is Benchmarked Against Linear and Oil-Extended SBS Products

The product differs from linear SBS grades of equivalent styrene content principally in shear-thinning behaviour and elastic recovery. Under capillary rheometry per ISO 11443 at 190°C, the radial architecture produces a power-law index n in the range 0.2–0.4 across 10–1000 s⁻¹. Linear SBS grades with similar bound styrene often exhibit n values of 0.4–0.6. This difference lowers high-shear dispersion torque in bitumen modification and reduces extruder backpressure in compounding, but the radial grade also generates higher die swell and melt elasticity. Compared with oil-extended radial SBS products containing 30–50 phr naphthenic or paraffinic oil, neat Solprene SBS 416 provides higher hardness and tensile strength immediately after moulding but requires separate oil addition during formulation, which increases mixing energy and requires exact oil injection control. In a twin-screw extruder with L/D 40:1, barrel temperatures from 160°C to 200°C and screw speeds of 200–400 rpm are typical for oil extension. Oil injection at 30–50 phr reduces melt temperature by 5–10°C and lowers die pressure by 15–30% when the feed rate and screw fill are held constant. Excessive oil addition without sufficient distributive mixing creates surface gloss heterogeneity and lowers tensile integrity to 8–12 MPa at 50 phr oil. Reported lot-to-lot variation in crumb bulk density can affect gravimetric feeder accuracy; values below 0.30 g/cm³ increase the risk of hopper bridging and require an agitated feed hopper or crammer.

In thermoplastic modification, Solprene SBS 416 is compounded with polypropylene or polystyrene at 10–30 wt% to improve low-temperature impact behaviour. Notched Izod impact by ISO 180 commonly increases from 2–3 kJ/m² to 8–15 kJ/m² in brittle matrices, but the measured gain depends on matrix melt flow, compatibiliser level, and moulded part thickness. The styrenic endblock content is sufficient to maintain interfacial adhesion with polystyrene domains, whereas the butadiene midblock contributes impact energy absorption at temperatures above the polybutadiene glass transition. The grade is not inherently compatible with strongly polar polymers such as polyamide or polyester without an appropriate compatibiliser; without interfacial modification, delamination occurs at tensile strain below 5%. Processors should verify the residual styrene monomer and total extractables against the relevant regulatory limits under EU REACH and 21 CFR 177.1810 where food-contact use is proposed. Pneumatic conveying of the crumb requires grounding and inerting if dust concentrations exceed 30 g/m³ to avoid static charge accumulation.