SEMISIL R272 Hydrophobic Fumed Silica (DDS-Treated)
SEMISIL R272 is a dimethyldichlorosilane (DDS)-treated hydrophobic fumed silica derived from a 200 m²/g hydrophilic base, providing moisture-stable thickening and rheology control that remains consistent under humid conditions and aqueous exposure. The hydrophobic surface prevents moisture uptake, making it the preferred reinforcing and rheology additive in silicone sealants, waterborne systems, and hydrophobic adhesives where hydrophilic silica would absorb water and lose its thickening effect.
Technical Specifications
| Properties and Test Methods | Unit | Typical Value | Standardization |
|---|---|---|---|
| Specific surface area (BET) | m²/g | 90 ~ 130 | GB/T 10722 |
| Carbon content | Wt% | 1.5 ~ 3.5 | GB/T 20020 |
| pH (1% in methanol/water 4:1) | – | 6.0 ~ 8.0 | Internal method |
| Loss on drying (2h @ 105°C) | Wt% | ≤ 0.5 | GB/T 5211.3 |
| Sieve residue (45 μm) | % | ≤ 0.05 | GB/T 5211.14 |
| Methanol wettability | % | ≥ 60 | Internal method |
| Silica content (ignited material) | Wt% | ≥ 99.0 | GB/T 20020 |
Application Suggestions
Silicone Sealants — Moisture-Barrier Enhancement
Acts as a moisture-resistant rheology modifier in RTV-1 silicone sealants. Unlike hydrophilic grades, SEMISIL R272 maintains its thickening efficiency in the presence of atmospheric moisture during production and shelf storage, reducing batch-to-batch viscosity variation and improving pot life consistency.
Waterborne Coatings
Provides stable anti-sag and anti-settling in waterborne epoxy, alkyd, and PU coatings without the water-swelling and viscosity spike observed with hydrophilic fumed silica. The hydrophobic surface creates a stable three-dimensional thixotropic network in water-based systems.
PDMS and Silicone Rubber Reinforcement
Functions as an in-situ reinforcing filler in polydimethylsiloxane compounds, delivering tensile strength improvement while maintaining optical clarity. The DDS surface treatment ensures good polymer-filler compatibility and prevents moisture-induced degradation of physical properties.
Specialty Adhesives and Sealants
Improves sag resistance and storage stability in polyurethane, MS-polymer, and hybrid adhesives/sealants. The hydrophobic surface prevents reaction with isocyanate groups in PU systems, extending pot life and improving thickening efficiency vs. hydrophilic alternatives.
Technical Support & FAQ: SEMISIL R272
+Q1: What are the key features and applications of SEMISIL R272?
SEMISIL R272 is the standard DDS-treated hydrophobic fumed silica for moisture-sensitive applications:
- Core Functions: Moisture-stable thickening, anti-sag, and PDMS reinforcement
- Key Features: Methanol wettability ≥60%; carbon content 1.5–3.5%; low moisture uptake
- Primary Applications: RTV silicone sealants, waterborne coatings, PDMS rubber, PU/MS adhesives
+Q2: How does SEMISIL R272 compare with other hydrophobic grades?
| Grade | Treatment | BET (m²/g) | Carbon (Wt%) | Best For |
|---|---|---|---|---|
| SEMISIL R272 | DDS | 90–130 | 1.5–3.5 | Silicone, waterborne, PU systems |
| SEMISIL R200 | HMDZ | 160–220 | 2.5–6.0 | HTV/LSR silicone rubber reinforcement |
Equivalent to: AEROSIL® R972 (Evonik), CAB-O-SIL® TS-530 (Cabot).
+Q3: What factors influence the pricing of SEMISIL R272?
- Production Costs: DDS surface treatment adds process steps vs. hydrophilic base; DDS reagent cost
- Quality Standards: Carbon content and methanol wettability are critical QC parameters
- Logistics: 10 kg PE-lined paper bags; moisture-sensitive packaging required
+Q4: What are the typical lead times and payment terms?
- Lead Time: Typically 7–14 days (Annual supply volume: 15,000 tons)
- Payment Terms: Flexible options including T/T, L/C at sight, and D/P
- Sample Support: Free samples (200g–1kg) available for R&D evaluation
Packing & Storage Information
Storage Conditions
SEMISIL® R272 must be stored in tightly sealed containers, protected from moisture and humidity. Do not store near water or steam lines. Use within 2 years of manufacture date. Once opened, reseal immediately.