Chimei KIBITON® SBS PB-587 is a styrene-butadiene-styrene block copolymer extended with a hydrocarbon process oil. The grade is supplied in pellet form and is intended for downstream blending with polystyrene, hydrocarbon resins, asphalt, fillers, plasticisers, and oxidation stabilisers. The producer-published nominal styrene content is 33.5 wt%, and the nominal extender oil content is 32.5 wt%; these values should be confirmed against the lot certificate of analysis because production tolerances may affect compounding calculations.

Relative to non-oil-extended KIBITON SBS grades of similar styrene content, PB-587 exhibits lower melt viscosity, lower Shore A hardness, and lower tensile strength. The oil extension acts as an internal plasticiser that reduces the glass transition temperature of the polybutadiene midblock in the compounded state and increases melt flow length in injection moulding. Uses reported in producer literature include footwear soles, asphalt modification, hot-melt adhesives, sealants, and soft-touch overmoulding. The grade is not marketed as a food-contact material or medical resin; suitability for regulated applications must be established on the finished article.

The tabulated values are producer representative data, not specification limits. Mechanical properties are obtained on compression-moulded sheets prepared under specific thermal history and conditioning; ASTM D618 procedure A is commonly cited for conditioning at 23 °C and 50% RH. Injection-moulded specimens from compounds containing PB-587 may show higher or lower tensile strength depending on flow-induced orientation and skin-core morphology. Lot-to-lot variation in extender oil content of ±1 wt% can shift hardness by approximately 1–2 Shore A units and melt flow rate by 0.3–0.8 g/10 min; production trials should include a rapid melt flow measurement under ISO 1133-1:2022 before large-scale compounding.

What Differentiates PB-587 from Non-Oil-Extended SBS Grades in Melt Processing?

The extender oil level of 32.5 wt% reduces the apparent viscosity and shear heating during melt processing. The producer-published melt flow rate for PB-587 is 5.0 g/10 min under ISO 1133-1:2022 at 190 °C/5 kg. A non-oil-extended SBS triblock copolymer of comparable styrene content may show a melt flow rate below 1 g/10 min under the same conditions when tested as neat resin; the difference is attributable to the internal plasticiser effect of the extender oil rather than an increase in styrene content or molecular weight reduction alone. On a production-scale twin-screw extruder with an L/D ratio of 40:1, PB-587 can be compounded at barrel set temperatures from 150 °C at the feed throat to 190 °C at the die. Screw speeds in the range 200–350 min⁻¹ are sufficient for homogenisation; specific energy input is typically lower than for neat SBS. Melt temperature should be monitored by an infrared or immersion probe at the die entrance; sustained temperatures above 210 °C initiate thermal-oxidative attack at the polybutadiene unsaturation, producing gel particles, brown discolouration, and die-lip fouling. A nitrogen-flushed hopper or low-oxygen feed environment is used in some lines to reduce gel formation during long runs. Pre-drying is generally unnecessary below 60% RH; above this threshold pellets should be dried at 60 °C for 2 h in a desiccant dryer to avoid surface defects from steam.

Because the polybutadiene midblock is shear-sensitive, excessive backpressure in single-screw injection units or long residence times in hot runners can reduce melt viscosity by chain scission and produce inconsistent shot weight. The styrene domains remain physically crosslinked at service temperatures below approximately 70–80 °C; above this range the material softens and loses load-bearing capacity. This boundary is important when PB-587 is compared with vulcanised SBS compounds, which retain mechanical properties at higher short-term temperatures.

In footwear midsole and outsole compounding, PB-587 is typically blended with high-impact polystyrene, styrene-butadiene rubber, calcium carbonate, azodicarbonamide blowing agent, and paraffinic/naphthenic plasticiser. The PB-587 content in the polymer fraction often ranges from 30–70 wt%, depending on target density, abrasion resistance, and cycle time. Hardness is measured under ASTM D2240 on plaques conditioned at 23 °C and 50% RH for 24 h; midsole compounds containing 15–25 wt% high-impact polystyrene commonly fall between 55 Shore A and 65 Shore A. The upper limit is controlled by polystyrene content and filler; the lower limit is controlled by oil content and blowing agent efficiency. Tensile properties under ASTM D638 are less critical than abrasion and flex fatigue in footwear, but elongation at break of 400–600% is often specified to avoid crack initiation at flex grooves.

Injection moulding of PB-587-based footwear compounds is performed on machines with clamp forces from 800–1,600 kN and screw diameters from 35–55 mm. Melt temperature at the nozzle is maintained between 160 °C and 190 °C; higher temperatures reduce viscosity but increase the risk of oil volatilisation and surface tack. Injection speed is set to fill the cavity within 1–2 s; packing pressure is held at 30–50% of peak injection pressure. Mould release is generally acceptable without external release agents because the extender oil in PB-587 migrates toward the melt-metal interface; however, excessive migration can reduce adhesion to textile or leather upper materials. Peel adhesion is evaluated under ASTM D903 or a purchaser-specific test; a minimum peel strength of 2–4 N/mm is common for footwear bonds, but the value depends on the adhesive primer and surface treatment. Abrasion resistance of outsole compounds is tested under DIN 53516; compounds containing PB-587 with filler and high-styrene resin may exhibit mass loss values in the range 150–250 mm³, although specific results depend on filler type and cure state. Flex fatigue is evaluated by repeated bending under ASTM D1052; crack growth through the polybutadiene phase is retarded by the low glass transition temperature of the midblock, but resistance to cut growth is lower than that of vulcanised SBS compounds containing crosslinked butadiene networks.

Asphalt Modification Behaviour and Storage Stability Parameters

Addition of PB-587 to paving-grade bitumen at polymer loadings of 3–5 wt% by mass of asphalt is a typical starting point. After correction for the 32.5 wt% extender oil, the effective neat SBS loading is 2.0–3.4 wt%; substitution on a one-to-one basis will under-deliver polymer and may compromise high-temperature rutting resistance. Dispersion is carried out in a rotor-stator high-shear mill at 170–190 °C for 1–3 h depending on bitumen source and compatibility. The oil-extended polymer wets and disperses more rapidly than neat SBS pellets under low-shear initial mixing, which can reduce the time required to reach a continuous polymer-rich phase. Completion of dispersion is evaluated by ultraviolet fluorescence microscopy; a fine, continuous polymer network without discrete pellet remnants is the usual criterion.

Rotational viscosity under ASTM D4402 is measured at 135 °C and 190 °C; the lower-temperature value is relevant for pumping and laydown. At the above polymer loadings, 135 °C viscosity may remain below 3 Pa·s; however, published PB-587-specific viscosity curves are limited, and the asymptotic viscosity at high polymer loadings depends on bitumen aromaticity. Softening point under ASTM D36 increases by 10–25 °C relative to the base bitumen, depending on base bitumen source and extender oil contribution; penetration at 25 °C under ASTM D5 is reduced by 20–40 dmm relative to the neat bitumen. Storage stability under EN 13399 after 48 h at 163 °C should show a top-bottom softening point difference of less than 2.5 °C for tank-stable formulations. Formulations that fail this limit may require crosslinking additives or a higher-vinyl homopolymer, but PB-587 itself is not sulphur-crosslinked in asphalt; any added sulphur or vulcanisation package must be evaluated for gelation and loss of workability.

Low-temperature performance of PB-587-modified asphalt is influenced by the polybutadiene midblock. Bending beam rheometer tests under ASTM D6648 and direct tension tests under ASTM D6723 are used to assess low-temperature cracking; the oil-extended grade may improve low-temperature flexibility relative to a neat SBS of the same polymer loading because the extender oil contributes to bitumen-phase flexibility, but the exact performance depends on base bitumen stiffness and ageing under ASTM D2872. Rutting resistance is evaluated under AASHTO T 340 or an equivalent repeated load axial test.

For hot-melt pressure-sensitive adhesive formulations, PB-587 is combined with hydrocarbon tackifier resins and liquid plasticisers in sigma-blade mixers or continuous twin-screw hot-melt lines. Starting formulations often use a tackifier-to-polymer ratio from 1.5:1 to 3.0:1 and a plasticiser content of 10–30 wt% of the adhesive. Brookfield viscosity under ASTM D3236 can be adjusted from 5,000–50,000 mPa·s at 177 °C; high-tackifier formulations in the upper range may require higher application temperatures. The oil-extended SBS dissolves more rapidly than neat SBS at mixing temperatures of 150–170 °C, reducing batch time and local hot spots. Loop tack under ASTM D6195 and shear adhesion failure temperature under ASTM D4498 are used to balance pressure-sensitive tack against cohesive strength. The styrene end-blocks provide physical crosslinks that resist shear flow, while the polybutadiene midblock imparts tack and low-temperature adhesion; increasing styrene content in the SBS would increase SAFT and melt viscosity, which is why PB-587 at 33.5 wt% styrene is positioned for pressure-sensitive applications rather than structural adhesives.

Compatibility with C5 aliphatic tackifiers is generally better than with highly aromatic C9 resins in terms of low-temperature tack, but aromatic resins may be used to improve adhesion to polar substrates. Highly aromatic process oils and amine-based viscosity modifiers should be evaluated for oxidative degradation and phase separation; the polybutadiene segment is sensitive to radical-initiated chain scission. Antioxidants such as hindered phenolics at 0.1–0.3 wt% of the adhesive compound are commonly added to stabilise melt viscosity during hot-melt holding at 177 °C for 24 h; colour change is monitored under ASTM E313.

When PB-587 Replaces Higher-Styrene Grades in Injection-Moulded Overmoulding

When PB-587 is substituted for a higher-styrene non-oil-extended SBS in a soft-touch overmoulding tool, the first measurable change is a reduction in Shore A hardness from the typical 70–80 Shore A range of neat higher-styrene SBS grades to the producer-published 65 Shore A of PB-587 under ASTM D2240. Tensile strength at break decreases from values above 10 MPa for many neat SBS grades to approximately 4.9 MPa under ASTM D638. The same substitution lowers injection pressure and improves flow length in thin-wall sections. On a 1,200 kN injection moulding machine, transfer pressure may decrease by 5–15% relative to a neat SBS of equivalent hardness, although actual values depend on gate geometry, wall thickness, and melt temperature setpoint. Because PB-587 contains 32.5 wt% extender oil, the volumetric shrinkage can differ from a neat grade; mould dimension corrections of 0.5–1.5% may be required depending on filler loading and packing pressure.

The lower styrene content reduces tensile set after repeated extension and improves elastic recovery. Compression set at 70 °C for 22 h under ISO 815 may be higher than that of sulphur-vulcanised or radiation-crosslinked SBS compounds; PB-587 is physically crosslinked by styrene domains at service temperature and is not supplied as a pre-vulcanised SBS. Sulphur vulcanisation of the polybutadiene midblock is possible only in formulated compounds where curatives are added, but the extender oil can alter cure kinetics and scorch time. For load-bearing or elevated-temperature applications above 60 °C, the designer should compare creep data under ISO 899 for the final compound rather than relying on Shore A hardness alone. Surface migration of the extender oil at 70 °C can produce fogging on interior automotive glazing; fogging tests under ISO 6452 are recommended for automotive interior components. The product is also incompatible with strong oxidising acids and ketones; these solvents can extract the oil and swell the polybutadiene midblock, causing dimensional instability and loss of styrenic physical crosslinks.

Storage of PB-587 pellets should avoid temperatures above 40 °C and direct UV exposure. Polybutadiene unsaturation is oxidatively sensitive; prolonged storage beyond 6 months should be conducted under nitrogen or in sealed moisture-proof packaging with an antioxidant package. The material is not recommended for direct food-contact applications unless the finished article complies with the applicable migration limits in EU Regulation 10/2011 or FDA 21 CFR 177.2600 for rubber articles, and the extender oil must be assessed independently for purity and regulatory status. REACH and RoHS compliance is available in the producer’s supply chain documentation but must be re-validated for each lot. Use of amine-based antidegradants can discolour and gel the polymer; small-scale torque rheometer trials in a 60 cm³ mixing chamber at 170 °C for 15 min are recommended before production scale-up.