Four SSBR Grades in High-Performance Tire Tread: Comparative Study

Four SSBR Grades in High-Performance Tire Tread Compounds: A Comparative Study

This study compares four solution styrene-butadiene rubber (SSBR) grades (SOL5251H, SOL5360H, SOL5271H, SOL6440H from Kumho Petrochemical) in high-dispersible silica-filled tread compounds, evaluating processing, cure, mechanical properties, wet grip, rolling resistance, and wear.

Keywords: SSBR; solution SBR; high-performance tire; tread compound; wet grip; rolling resistance; silica; Payne effect

Introduction

Modern high-performance tires are judged on three core metrics: wet grip, rolling resistance, and wear. Each wet grip grade improvement shortens braking distance by 3–5 m; each rolling resistance grade improvement saves ~17 L gasoline per tire per 50,000 km (~68 L per vehicle). BR has low hysteresis and good wear but poor wet grip; NR has high strength but inadequate wet grip. SSBR offers controllable microstructure — styrene and vinyl content can be tuned independently. Higher vinyl content raises Tg for better wet grip without the heat buildup caused by high styrene. Narrow molecular weight distribution means fewer low-molecular-weight chains and lower hysteresis, making SSBR the preferred matrix for high-performance treads.

Experimental

Materials

Formulation (phr): SSBR 100; silica 80; silane coupling agent 12.8; naphthenic oil 37.5; activator 5; antioxidant 3; sulfur 1.5; accelerator 4.

Mixing: Two-stage. First stage: 90 rpm, 60°C cooling, dump at 150°C. Second stage: 40 rpm, add sulfur + accelerator, dump ≤105°C. Cure: 161°C, 20 min (2 mm sheets / DIN abrasion), 30 min (mechanical specimens).

Results and Discussion

Raw Polymer Properties

5360H has elevated styrene (higher Tg). 5271H keeps styrene at 5251H level but greatly increases vinyl. 6440H has the highest styrene and lowest vinyl, with very high Mw (1.1 million) and broader PDI — high green strength but harder processing. 5251H/5360H/5271H have narrow PDI, favoring low hysteresis.

Cure Characteristics

6440H has the highest Mooney viscosity (from massive molecular chain entanglement), shortest scorch time (narrower processing window), and highest crosslink density.

Physical Mechanical Properties

6440H has the highest hardness, tensile, and tear strength due to ultra-high molecular weight. Compared to 5251H, 5360H and 5271H show higher M300 but lower rebound and wear — chain stiffness increases. 6440H’s single-end modification gives weaker filler-rubber interaction (lower M300 than 5271H) but its massive Mw delivers the best strength.

Dynamic Mechanical Properties

Wet grip ranking: 5360H > 5271H > 6440H > 5251H. Styrene content contributes more to 0°C tanδ than vinyl at similar Tg.

Rolling resistance: 5251H is best (lowest 60°C tanδ). Both higher styrene and higher vinyl slightly increase 60°C tanδ. Despite same raw Tg, 6440H has significantly higher RR than 5271H due to its strong filler network (Payne effect ΔG’ = 1152 kPa, more than double the others).

Conclusions

1. SSBR5251H: Lowest Mooney, best processability; highest rebound and DIN wear; lowest rolling resistance; lowest Tg means weaker wet grip. Best for low-RR-oriented tread compounds.
2. SSBR5360H: High styrene; processability similar to 5251H; higher M300, slightly lower wear; dramatically higher 0°C tanδ (best wet grip), with only modest RR penalty. Best for high-wet-grip treads.
3. SSBR5271H: High-vinyl dual-end modified; higher M300, slightly lower wear; combines good wet grip with low rolling resistance — the balanced all-rounder.
4. SSBR6440H: Ultra-high molecular weight, highest Mooney, shortest scorch, narrowest processing window; best tensile and tear strength, decent wear; same raw Tg as 5271H but strong Payne effect (poor silica dispersion) means higher RR and heat buildup.