Seserbia
Sesotho
TargetSe-Slovak
Base RubberSesomali
Flame Retardants:
- Se-Scots Gaelic: 15 phr
- Sesindhi
- SesundaneseSeswahili
- Se-Tajik
- Zinc borate (ZnB): 5 phr
- Sethai
- Aluminum hydroxide (ATH, chemical method, 1.6–2.3 μm)Se-Urdu
- Se-Uzbek
Additives:
- Sewelshe
- Sexhosa
- Seyiddish
Features:
- Sezulu
- Sekinyarwanda
Se-Tatar
TargetMaTurkmen
Base Rubber: VMQ (100 phr)
Flame Retardants:
- Ammonium polyphosphate (APP, phosphorus-nitrogen-based): 12 phr
- Core of intumescent char formation, with good compatibility with silicone rubber.
- Aluminum hypophosphite (AHP): 8 phr
- Supplementary phosphorus source, reduces APP hygroscopicity.
- Zinc borate (ZnB): 5 phr
- Synergistic char catalysis and drip suppression.
- Aluminum hydroxide (ground, 3–20 μm): 15 phr
- Low-cost auxiliary flame retardant, reduces APP loading.
Additives:
- Vinyl silicone oil (3 phr, plasticization)
- Precipitated silica (15 phr, reinforcement)
- Platinum curing system (0.1% Pt)
Features:
- Total flame retardant loading ~40 phr, effective for thin products due to intumescent mechanism.
- APP requires surface treatment (e.g., silane coupling agent) to prevent migration.
3. High-Loading Aluminum Hydroxide Optimized System (Cost-Effective Type)
Target: UL94 V-0, suitable for thick products or cables
Base Rubber: VMQ (100 phr)
Flame Retardants:
- Aluminum hydroxide (ATH, chemical method, 1.6–2.3 μm): 50 phr
- Primary flame retardant, endothermic decomposition, small particle size for better dispersion.
- Aluminum hypophosphite (AHP): 5 phr
- Enhances char formation efficiency, reduces ATH loading.
- Zinc borate (ZnB): 3 phr
- Smoke suppression and anti-glowing.
Additives:
- Silane coupling agent (KH-550, 1 phr, improves ATH interface)
- Fumed silica (8 phr, reinforcement)
- Peroxide curing (DCP, 1 phr)
Features:
- Total flame retardant loading ~58 phr, but ATH dominates for cost efficiency.
- Small ATH particle size minimizes tensile strength loss.
4. Standalone Aluminum Hypophosphite (AHP) System
Application: UL94 V-1/V-2, or where nitrogen sources are undesirable (e.g., avoiding MCA foaming affecting appearance).
Recommended Formulation:
- Base Rubber: VMQ (100 phr)
- Aluminum hypophosphite (AHP): 20–30 phr
- High phosphorus content (40%); 20 phr provides ~8% phosphorus for basic flame retardancy.
- For UL94 V-0, increase to 30 phr (may impair mechanical properties).
- Reinforcing Filler: Silica (10–15 phr, maintains strength)
- Additives: Hydroxyl silicone oil (2 phr, processability) + curing agent (Diperoxide or platinum system).
Features:
- Relies on condensed-phase flame retardancy (char formation), significantly improves LOI but has limited smoke suppression.
- High loading (>25 phr) may stiffen the material; recommend adding 3–5 phr ZnB to improve char quality.
5. Aluminum Hypophosphite (AHP) + MCA Blend
Application: UL94 V-0, low loading with gas-phase flame retardant synergy.
Recommended Formulation:
- Base Rubber: VMQ (100 phr)
- Aluminum hypophosphite (AHP): 12–15 phr
- Phosphorus source for char formation.
- MCA: 8–10 phr
- Nitrogen source for P-N synergy, releases inert gases (e.g., NH₃) to suppress flame propagation.
- Reinforcing Filler: Silica (10 phr)
- Additives: Silane coupling agent (1 phr, dispersion aid) + curing agent.
Features:
- Total flame retardant loading ~20–25 phr, significantly lower than standalone AHP.
- MCA reduces AHP requirement but may slightly affect transparency (use nano-MCA if clarity is needed).
Flame Retardant Formulation Summary
| Formulation | Expected UL94 Rating | Total Flame Retardant Loading | Pros & Cons |
| AHP alone (20 phr) | V-1 | 20 phr | Simple, low cost; V-0 requires ≥30 phr with performance trade-offs. |
| AHP alone (30 phr) | V-0 | 30 phr | High flame retardancy but increased hardness and reduced elongation. |
| AHP 15 + MCA 10 | V-0 | 25 phr | Synergistic effect, balanced performance (recommended for initial trials). |
Experimental Recommendations
- Priority Testing: AHP + MCA (15+10 phr). If V-0 is achieved, gradually reduce AHP (e.g., 12+10 phr).
- Standalone AHP Test: Start at 20 phr, increment by 5 phr to evaluate LOI and UL94, monitoring mechanical properties.
- Smoke Suppression: Add 3–5 phr ZnB to any formulation without compromising flame retardancy.
- Cost Optimization: Incorporate 10–15 phr ATH to reduce cost, though total filler loading increases.
Recommended Mixing Process
(For two-part addition-cure silicone rubber)
- Base Rubber Pre-Treatment:
- Load silicone rubber (e.g., 107 gum, vinyl silicone oil) into a planetary mixer, degas under vacuum if needed.
- Flame Retardant Addition:
- Powdered flame retardants (e.g., ATH, MH):
- Add in batches, pre-mix with base rubber (low-speed mixing, 10–15 min) to avoid agglomeration.
- Dry at 80–120°C if hygroscopic.
- Liquid flame retardants (e.g., phosphates):
- Blend directly with silicone oil, crosslinker, etc., under high shear (20–30 min).
- Other Additives:
- Sequentially add fillers (e.g., silica), crosslinker (hydrosilane), catalyst (platinum), and inhibitors.
- Homogenization:
- Further refine dispersion using a three-roll mill or high-shear emulsifier (critical for nano-additives like CNTs).
- Degassing & Filtration:
- Vacuum degas (-0.095 MPa, 30 min), filter for high-purity requirements.
Key Considerations
- Flame Retardant Selection:
- Halogen-free retardants (e.g., ATH) require fine particle size (1–5 μm); excessive loading harms mechanical properties.
- Silicone-based retardants (e.g., phenyl silicone resins) offer better compatibility but at higher cost.
- Process Control:
- Temperature ≤ 60°C (prevents platinum catalyst poisoning or premature curing).
- Humidity ≤ 50% RH (avoids reactions between hydroxyl silicone oil and flame retardants).
Conclusion
- Mass Production: Pre-mix flame retardants with base rubber for efficiency.
- High-Stability Requirements: Blend during compounding to minimize storage risks.
- Nano-Flame Retardant Systems: Mandatory high-shear dispersion to prevent agglomeration.
More info., pls contact lucy@taifeng-fr.com
Post time: Jul-25-2025
