Chimei KIBITON® SBS PB-575 is a linear styrene–butadiene–styrene block copolymer supplied as compacted porous pellets. The grade is targeted at high-styrene-content applications in which modulus, abrasion resistance, and melt strength act as primary performance variables. Manufacturer-published typical values for compression-moulded test plaques are summarised in Table 1.

Dynamic mechanical analysis of PB-575 shows a polybutadiene-phase glass transition at -50 °C and a styrene-domain softening transition above 95 °C. The tensile set after 300% extension under ISO 2285 is 20–30%; this value is higher than for PB-585 but lower than for oil-extended SBS grades. Compression set after 24 h at 70 °C under ISO 815 is 35–45% when tested on 6 mm moulded buttons.

The grade is compounded into footwear units, hot-melt adhesives, bituminous waterproofing membranes, and injection-moulded thermoplastic elastomer articles. Compared with a lower-styrene SBS such as KIBITON PB-520, PB-575 produces higher room-temperature hardness and tensile strength because the higher styrene endblock fraction increases the volume fraction of hard microdomains. The trade-off is a reduction in low-temperature flexibility and a narrower processing window above the melt order-disorder transition. Compared with PB-585, PB-575 has lower melt viscosity at typical processing shear rates, allowing thinner wall filling but producing slightly lower cohesive strength.

What Processing Limits Emerge During Twin-Screw Compounding of PB-575 at Production Scale?

On a co-rotating twin-screw extruder with 40:1 L/D and segmented screws, PB-575 is processed with barrel settings of 160 °C, 170 °C, 180 °C, 190 °C, and 190 °C from feed throat to die. The feed zone is maintained below 40 °C to prevent pellet surface sintering. Pellets exposed to ambient relative humidity above 60% are pre-dried at 80 °C for 2 h in a desiccant dryer with a dew point below -20 °C; skip drying at high moisture loads reduces melt viscosity by hydrolysis-related chain scission and creates surface pitting on extruded profiles.

Torque increases sharply when the melt temperature falls below 160 °C because the styrene endblock domains have not fully dissociated. Typical screw speeds are 250–350 rpm, with specific mechanical energy limited to 0.18 kWh/kg. Above this mechanical energy input, die-face temperature can exceed 240 °C, initiating thermal-oxidative scission of the polybutadiene midblock. Vacuum venting at -0.08 MPa gauge in the terminal barrel segment reduces volatile content to below 0.3%. When the compound contains 5 phr titanium dioxide, die-lip deposit accumulation has been observed after 4 h continuous extrusion; die wiping periods of 90 min are used to control surface defects.

The apparent melt viscosity at 190 °C and shear rate 1000 s⁻¹ is typically 350–450 Pa·s using capillary rheometry under ISO 11443. Die swell ratio from a 1 mm capillary at shear rate 500 s⁻¹ is 1.4–1.7, requiring downstream calibration on profile dies by 5–10% drawdown. The onset of melt fracture in unfilled PB-575 occurs above 10⁴ s⁻¹; this shear rate is not exceeded in film extrusion but may be reached in small-gate injection moulds.

High-shear dispersion of 10–20 phr calcium carbonate is possible without melting torque instability if the carbonate is predried and added via side stuffing after the polymer has reached 170 °C. The same formulation can show a reduction of tensile strength by 8–12% when tested under ISO 37 after 72 h at 23 °C, because filler-particle aggregation increases flaw density. Application of 0.2–0.5 phr erucamide reduces die pressure by 5–8% without exceeding a 2% loss in tensile strength.

Asphalt Modification, Storage Stability, and Low-Temperature Ductility

PB-575 is dispersed into penetration-grade bitumen at loadings of 3–6 wt% using a rotor-stator high-shear mixer with a tip speed of 20–25 m/s and a mixing temperature of 180–190 °C. After 45–60 min, a continuous polymer network develops, and the softening point of a 50/70 base bitumen increases from approximately 46 °C to 58–65 °C under ASTM D36. The phase morphology remains stable only if the formulation includes 0.1–0.3 wt% elemental sulphur or a sulphur donor; otherwise sealed-tube storage at 163 °C for 72 h under ASTM D7173 yields a top-bottom softening-point difference greater than 5 °C. With sulphur addition the separation drops below 2.5 °C, indicating dynamic vulcanization of the polybutadiene midblock at the polymer–bitumen interface.

Fourier-transform infrared spectroscopy of sulphur-crosslinked PB-575/bitumen shows a reduction in the 966 cm⁻¹ trans-butadiene absorption relative to unmodified bitumen after 4 h at 180 °C, indicating consumption of unsaturation in the vulcanization network. Gel content increase to 15–20% is typical; above 25% gel content the modified binder becomes non-homogeneous and loses low-temperature ductility. The processing window for sulphur addition is therefore approximately ±0.1 wt% around the optimum loading in a 50/70 base bitumen.

Compared with lower-styrene KIBITON PB-520, PB-575 attains a target softening point at a lower polymer loading because the higher aromatic segment content contributes more to high-temperature stiffness. The same structural change reduces low-temperature ductility: force-ductility curves at 5 °C under ASTM D113 show a shorter post-peak plateau before fracture. This performance cross-over limits the use of PB-575 in cold-region paving asphalts where binder strain tolerance at -10 °C is mandatory. Published data for this specific paving configuration is limited.

Substitution of PB-585 with PB-575 in a 12-cavity hot-runner injection mould for overmoulded polypropylene handles illustrates the grade-specific flow difference. At a melt temperature of 190 °C and a hot-runner manifold set point of 200 °C, fill pressure decreases by 10–15% compared with PB-585, while the required clamp force declines from 3.2 kN/cm² to 2.7 kN/cm² of projected area. The trade-off is a 6% lower tensile strength and a 4 Shore A lower hardness after 24 h annealing at 80 °C. Cycle time is controlled by the solidification of styrene endblock domains; mould cooling water at 20–30 °C is recommended, and ejection should occur below 45 °C to prevent dimensional distortion. Published data for this specific tooling configuration are limited, but plant-scale observations indicate that PB-575 is preferred when the design contains wall thickness below 1.2 mm.

Short-shot studies in a spiral mould of 2 mm depth show PB-575 flow length at 190 °C injection temperature is 110–130 cm at 80 MPa injection pressure; PB-585 under identical conditions gives 85–100 cm. This supports selection of PB-575 for high-cavitation and thin-wall tools. Hold pressure is set at 60–70% of peak injection pressure for 3–5 s to avoid sink marks without overpacking.

For adhesive compounding, PB-575 is dissolved in aliphatic/aromatic tackifier blends at 30–50% solids. Brookfield viscosity at 25 °C for a 40% solids solution in toluene is reported in the range 2000–4000 mPa·s under ISO 2555; this range permits roll coating and slot-die application without excessive shear thinning. Peel strength on stainless steel after 24 h dwell under ASTM D903 is typically 4–7 N/25 mm, but the exact value depends on tackifier softening point, oil content, and substrate surface energy.

When PB-575 Is Compounded with Stabilizers for Outdoor TPE Profiles

Outdoor exposure of PB-575 compounds requires addition of a hindered amine light stabilizer at 0.5–1.0 phr and a benzotriazole UV absorber at 0.2–0.5 phr. Without these stabilizers, accelerated QUV weathering under ISO 4892-3 produces surface cracking after 300–400 h and the tensile strength retention falls below 70%. The polybutadiene midblock is the oxidation-sensitive site; carbonyl index measured by FTIR at 1720 cm⁻¹ increases as the absorbed dose accumulates. Paraffinic process oil reduces hardness but increases UV sensitivity; therefore oil-extended PB-575 compounds for outdoor use are limited to 20 phr of paraffinic oil unless additional antioxidant is placed at 0.3 phr of a phenolic and phosphite binary system.

Thermal-oxidative stabilizers should be selected for compatibility with the butadiene midblock; a binary phenolic/phosphite system at 0.2–0.3 phr total is more effective than a single antioxidant at the same loading. Prolonged heat aging at 100 °C for 168 h under ISO 188 retains approximately 85% tensile strength in stabilised PB-575, whereas an unstabilised control retains below 60%.

Incompatibility boundaries should be observed during compounding. PB-575 is soluble in toluene, cyclohexane, and methyl ethyl ketone blends, but swells or dissolves in strong aromatic and chlorinated solvents with solubility parameter below 7.5 (cal/cm³)^0.5. The grade should not be melt-compounded with polyvinyl chloride containing high phthalate levels because plasticizer migration into the SBS phase produces surface tack and dimensional change after warehouse storage at 40 °C for 28 days.

Regulatory Compliance Boundaries and Material Incompatibilities Are Displayed in Table 2

Compliance status is supplied under standard declarations for the base polymer. End-use verification is required for food-contact, medical, or toy applications because compound-specific migration data are limited.

Batch-to-batch variance in melt flow rate is controlled within ±0.5 g/10 min according to supplier certificate of analysis. Warehousing of pellets in high-temperature containers above 40 °C may cause pellet agglomeration; bulk silo storage should include hopper blowback and anti-segregation cones to preserve uniform styrene content. Extended storage beyond 12 months from production date should be re-tested for melt flow rate and volatile content before use.