Precipitated Silica BET 220 m²/g HD Grade

What Is BET 220 m²/g HD Precipitated Silica?

Precipitated silica BET 220 m²/g HD (highly dispersible) represents the highest surface area commercial grade in the precipitated silica product range. It is engineered specifically for ultra-high performance (UHP) and sport tire tread compounds where every fraction of a percent of rolling resistance reduction contributes to fuel efficiency ratings, and where the EU tire label A grade is a mandatory target.

The "HD" designation is not just a marketing term — it represents a fundamental modification of the silica particle surface and granule structure. At 220 m²/g, a conventional powder grade would be nearly impossible to fully disperse in rubber, producing unacceptable compound variability and agglomerate streaks in tire tread cross-sections. HD technology solves this by:

1. Surface modification: Selected surface treatment (partially silanized surface or surface-active agents) to pre-passivate highly reactive silanols, reducing silica-silica aggregation tendency during mixing.
2. Controlled granulation: Spray granulation or roller compaction produces porous granules that break apart readily in the mixer's shear field, releasing individual aggregates without energy-intensive agglomerate destruction steps.
3. Specific CTAB surface area targeting: HD grades are characterized by CTAB surface area more carefully controlled than conventional grades, with tighter tolerances of ±8 m²/g vs ±15 m²/g for powder.

Dispersibility Technology Explained

The dispersibility index (DI), measured by methods equivalent to ASTM D3053, quantifies the completeness of silica dispersion in a standard rubber compound. Values range from 0 (completely undispersed) to 100 (fully dispersed, no agglomerates detected).

• Conventional powder BET 220 m²/g: DI typically 50–65
• HD granule BET 220 m²/g: DI typically 90–96

This difference translates directly to tire uniformity. Undispersed silica agglomerates act as stress concentrators, reducing fatigue life and creating non-uniform rolling resistance across the tire tread width. HD grades eliminate this variability.

The HD granulation technology also delivers an important practical benefit: granules are significantly less dusty than powder. In large-scale tire mixing operations, handling precipitated silica powder creates respirable dust that requires engineering controls and PPE. HD granules dramatically reduce this exposure, simplifying plant hygiene and compliance.

Performance in UHP Tire Compounds

Rolling resistance: BET 220 HD achieves a rolling resistance index of 108–112 relative to BET 175 HD (set at 100). This 8–12% improvement is the primary driver for UHP tire OEM selection of this grade. In SSBR/BR compounds optimized for this surface area, tan δ at 60°C values of 0.07–0.10 are achievable.

Wet grip: BET 220 HD also improves wet grip index by 4–7% relative to BET 175 HD. Higher surface area silica creates a denser bound rubber layer, improving the 0°C tan δ that correlates with wet braking performance.

Wear resistance: Properly dispersed BET 220 HD maintains equivalent or slightly better wear resistance compared to 175 HD in SSBR/BR compounds. The key is complete dispersion — undispersed agglomerates reduce wear resistance.

Mixing time reduction: Despite the higher surface area, HD granulation enables 15–20% shorter mixing cycles compared to equivalent-surface-area powder grades. The granule structure wets out quickly without requiring extended mastication time to break down agglomerates.

Compound Design for BET 220 m²/g HD

Silane selection: Si-75 (TESPD) at 10–12 phr per 100 phr silica is the standard silane for BET 220 HD. The lower sulfur content of Si-75 (disulfide) compared to Si-69 (tetrasulfide) is important at this surface area level — higher silanol surface density means more sulfur input per unit mass with Si-69, which can affect compound crosslink density and mechanical properties. Some formulators use blocked mercaptosilane (NXT/Si-363 type) for improved processability.

Rubber polymer selection: The highest performance compounds for BET 220 HD use functionalized SSBR — solution SBR with amine, silanol, or siloxy end-group modification that interacts directly with silica surface silanols, improving bound rubber content and filler-polymer coupling efficiency. Non-functionalized SSBR requires full reliance on silane coupling and typically gives 5–8% lower rolling resistance performance than functionalized grades.

DPG and accelerator system: DPG at 2–2.5 phr is standard. Some OEM specifications require DPG-free compounds (due to amine release concerns in tire recycling) — in this case, alternative secondary accelerators such as MBTS or TBZTD are used at adjusted dosages.

Recommended compound (UHP sport tire):

• Functionalized SSBR (30% styrene, 50% vinyl): 80 phr
• High-vinyl BR: 20 phr
• Precipitated silica BET 220 HD: 70 phr
• Si-75 silane: 7 phr (per 100 phr rubber)
• TDAE oil: 25 phr
• ZnO: 2 phr, Stearic acid: 1.5 phr
• 6PPD: 2 phr, TMQ: 1 phr
• Sulfur: 1.5 phr, CBS: 2.5 phr, DPG: 2 phr

Expected: tan δ 60°C ≈ 0.07–0.10, tan δ 0°C ≈ 0.42–0.50, Akron abrasion ≤1.1 index.

Comparison with Evonik Ultrasil 9000GR and Solvay Zeosil Premium 200MP

Chinese BET 220 HD grades match the Evonik Ultrasil 9000GR performance class in compound trials. The dispersibility index ≥90 meets the threshold for production-scale tire tread mixing. At 30–40% lower price than Evonik equivalents, Chinese HD grades represent significant cost reduction opportunity for tire manufacturers who qualify them through their supplier approval process.

FAQ

Q: Is BET 220 HD always better than BET 175 HD for tire performance? A: Better rolling resistance and wet grip, yes — but the gap narrows when comparing optimized 175 vs 220 compounds with the correct silane, polymer, and mixing protocols. For most PCR replacement tire applications targeting EU label B, BET 175 HD is sufficient and more cost-effective. BET 220 HD is justified for label A UHP applications, sport tires, and premium OEM specifications.

Q: How does BET 220 HD compare in compound Mooney viscosity vs 175 HD? A: Surprisingly similar when both are in HD granule form. The HD technology for 220 m²/g reduces the viscosity penalty vs conventional 220 powder substantially — the granule form wet-out is efficient enough that compound Mooney viscosity is typically only 5–10 ML(1+4) units above the 175 HD compound at equivalent silane loading.

Q: What mixing equipment is needed for BET 220 HD? A: Standard Banbury-type internal mixers with temperature control are sufficient. No specialized equipment is needed beyond what is required for BET 175 HD. The key requirements are: reliable temperature measurement at dump, consistent fill factor control (70–75%), and a two-pass mixing protocol with cooling between passes.