Comparison of Aluminum Hydroxid for PVC vs. HFFR Cables
In the wire and cable industry, PVC (Polyvinyl Chloride) and HFFR (Halogen-Free Flame Retardant) materials have fundamentally different flame retardancy requirements. Aluminum hydroxide (Al(OH)₃), as a key flame retardant, must be precisely selected to match each system. Below is a detailed technical comparison:
1. Core Flame Retardant Standards Comparison
| Parameter | PVC Cables | HFFR Cables |
|---|---|---|
| Flame Rating | IEC 60332-1 (Single vertical flame) | IEC 60332-3 (Bundle A/B/C) |
| Oxygen Index (OI) | ≥28% | ≥35% |
| Smoke Density (4min) | ≤400 (GB/T 17651) | ≤150 (EN 61034) |
| Toxicity Index (CITG) | Not mandatory | ≤1.0 (EN 50305) |
| Temperature Rating | 70°C/90°C | 90°C/105°C/125°C |
Key Differences:
PVC relies on chlorine’s self-extinguishing properties, while HFFR achieves flame retardancy entirely through metal hydroxides.
HFFR’s smoke and toxicity requirements are >10× stricter than PVC’s.
2. Aluminum Hydroxide Grade Selection
For PVC Cables
| Parameter | Standard Grade | High-Performance Grade |
|---|---|---|
| D50 Particle Size | 5-10 μm | 3-5 μm |
| Whiteness | ≥85% | ≥90% |
| Oil Absorption | ≤25 ml/100g | ≤18 ml/100g |
| Typical Loading | 40-50% | 50-60% |
| Compliance | GB/T 18380.1 | UL 1581 (US Standard) |
Technical Notes:
Standard Grade: Used for building wires (BV/RV), meeting single-wire flame tests.
High-Performance Grade: For elevator/mining cables requiring UL VW-1 vertical flame tests.
For HFFR Cables
| Parameter | Basic Flame Retardant | Low-Smoke Enhanced |
|---|---|---|
| D50 Particle Size | 2-3 μm | 1-2 μm |
| Surface Area | 4-7 m²/g | 3-5 m²/g |
| Surface Treatment | Stearic acid coating | Silane + titanate hybrid |
| Typical Loading | 60-63% | 60-63% |
| Compliance | EN 50399 (EU Bundle Test) | IEC 60754-1 (LSZH) |
Technical Notes:
Basic Grade: For general power cables (e.g., WDZ-YJY), passing Bundle Flame Class B.
Low-Smoke Grade: For subways/nuclear plants (e.g., IE4), requiring IEC 61034 smoke tests.
3. Key Process Considerations
| Process Step | PVC System | HFFR System |
|---|---|---|
| Mixing Temperature | ≤110°C (avoid plasticizer loss) | ≤95°C (prevent Al(OH)₃ pre-decomposition) |
| Extrusion Temp. | Feed zone 150°C → Die 175°C | Feed zone 140°C → Die 160°C |
| Screw Design | Low shear (L/D=20:1) | High shear (L/D=25:1) |
| Die Configuration | Compression ratio 2.5:1 | Compression ratio 3:1 |
4. Future Technology Trends
Core-Shell Al(OH)₃:
Al(OH)₃@Mg(OH)₂ dual-layer coating: 25% higher efficiency at 50% loading.
In-Situ Polymerization:
Vinyl siloxane-grafted Al(OH)₃: 40% better polyolefin compatibility.
AI-Powered Optimization:
Machine learning for real-time grinding control (D50 ±0.2μm).
Conclusion
From PVC’s chlorine-based systems to HFFR’s metal hydroxide solutions, selecting the right Al(OH)₃ grade is a precision “flame retardant engineering” task. As EU CPR regulations tighten smoke toxicity limits, 1-3μm ultra-fine modified Al(OH)₃ will become the HFFR cable standard. Understanding these differences is the key for cable engineers to advance from compliance to excellence.
Key Terms:
OI (Oxygen Index): Minimum oxygen concentration to sustain combustion.
CITG (Corrosivity Index of Toxic Gases): Measures acidic gas emissions during burning.
LSZH (Low Smoke Zero Halogen): Halogen-free materials with limited smoke production.
