PBT Halogen-Free Flame Retardant Reference Formulation
To optimize the formulation of halogen-free flame retardants for PBT, it is essential to balance flame retardancy efficiency, thermal stability, processing temperature compatibility, and mechanical properties. Below is an optimized compounding strategy with key analyses:
1. Core Flame Retardant Combinations
Option 1: Aluminum Hypophosphite + MCA (Melamine Cyanurate) + Zinc Borate
Mechanism:
- Aluminum Hypophosphite (Thermal stability > 300°C): Promotes char formation in the condensed phase and releases PO· radicals in the gas phase to interrupt combustion chain reactions.
- MCA (Decomposition at ~300°C): Endothermic decomposition releases inert gases (NH₃, H₂O), diluting flammable gases and suppressing melt dripping.
- Zinc Borate (Decomposition > 300°C): Enhances glassy char formation, reducing smoke and afterglow.
Recommended Ratio:
- Aluminum Hypophosphite (10-15%) + MCA (5-8%) + Zinc Borate (3-5%).
Option 2: Surface-Modified Magnesium Hydroxide + Aluminum Hypophosphite + Organic Phosphinate (e.g., ADP)
Mechanism:
- Modified Magnesium Hydroxide (Decomposition ~300°C): Surface treatment (silane/titanate) improves dispersion and thermal stability; endothermic cooling lowers material temperature.
- Organic Phosphinate (e.g., ADP, thermal stability > 300°C): Highly effective gas-phase flame retardant, synergizing with phosphorus-nitrogen systems.
Recommended Ratio:
- Magnesium Hydroxide (15-20%) + Aluminum Hypophosphite (8-12%) + ADP (5-8%).
2. Optional Synergists
- Nano-clay/Talc (2-3%): Improves char quality and mechanical properties while reducing flame retardant loading.
- PTFE (0.2-0.5%): Anti-dripping agent to prevent burning droplets.
- Silicone Powder (2-4%): Promotes dense char formation, enhancing flame retardancy and surface gloss.
3. Combinations to Avoid
- Aluminum Hydroxide: Decomposes at 180-200°C (below PBT processing temperature of 220-250°C), leading to premature degradation.
- Unmodified Magnesium Hydroxide: Requires surface treatment to prevent agglomeration and thermal decomposition during processing.
4. Performance Optimization Tips
- Surface Treatment: Use silane coupling agents on Mg(OH)₂ and zinc borate to enhance dispersion and interfacial bonding.
- Processing Temperature Control: Ensure flame retardant decomposition temperature > 250°C to avoid degradation.
- Mechanical Property Balance: Compensate for strength loss using nano-fillers (e.g., SiO₂) or tougheners (e.g., POE-g-MAH).
5. Example Formulation
| Flame Retardant | Loading (wt%) | Function |
|---|---|---|
| Aluminum Hypophosphite | 12% | Main flame retardant (condensed + gas phase) |
| MCA | 6% | Gas-phase flame retardant, smoke suppression |
| Zinc Borate | 4% | Synergistic char formation, smoke reduction |
| Nano Talc | 3% | Char reinforcement, mechanical enhancement |
| PTFE | 0.3% | Anti-dripping |
6. Key Testing Metrics
- Flame Retardancy: UL94 V-0 (1.6mm), LOI > 35%.
- Thermal Stability: TGA residue > 25% (600°C).
- Mechanical Properties: Tensile strength > 45 MPa, notched impact > 4 kJ/m².
By fine-tuning the ratios, high-efficiency halogen-free flame retardancy can be achieved while maintaining PBT’s overall performance.
More info., pls send email to lucy@taifeng-fr.com
Post time: Jul-08-2025
