PBT Halogen-Free Flame Retardant Formulation
To develop a halogen-free flame retardant (FR) system for PBT, it is essential to balance flame retardancy efficiency, thermal stability, processing temperature compatibility, and mechanical properties.
I. Core Flame Retardant Combinations
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 temp. ~300°C): Endothermic decomposition releases inert gases (NH₃, H₂O), diluting flammable gases and suppressing melt dripping.
- Zinc Borate (Decomposition temp. > 300°C): Enhances glassy char formation, reducing smoke and afterglow.
Recommended Ratio:
Aluminum Hypophosphite (10-15%) + MCA (5-8%) + Zinc Borate (3-5%).
2. Surface-Modified Magnesium Hydroxide + Aluminum Hypophosphite + Organic Phosphinate (e.g., ADP)
Mechanism:
- Modified Magnesium Hydroxide (Decomposition temp. ~300°C): Surface treatment (silane/titanate) improves dispersion and thermal stability while absorbing heat to lower 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%).
II. Optional Synergists
- Nano Clay/Talc (2-3%): Improves char quality and mechanical properties while reducing FR dosage.
- PTFE (Polytetrafluoroethylene, 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.
III. Combinations to Avoid
- Aluminum Hydroxide: Decomposes at 180-200°C (below PBT processing temp. of 220-250°C), leading to premature degradation.
- Unmodified Magnesium Hydroxide: Requires surface treatment to prevent agglomeration and thermal decomposition during processing.
IV. Performance Optimization Recommendations
- Surface Treatment: Use silane coupling agents on magnesium hydroxide and zinc borate to enhance dispersion and interfacial bonding.
- Processing Temperature Control: Ensure FR decomposition temperature > 250°C to avoid degradation during processing.
- Mechanical Property Balance: Incorporate nano-fillers (e.g., SiO₂) or tougheners (e.g., POE-g-MAH) to compensate for strength loss.
V. Typical Formulation Example
| Flame Retardant | Loading (wt%) | Function |
|---|---|---|
| Aluminum Hypophosphite | 12% | Primary FR (condensed + gas phase) |
| MCA | 6% | Gas-phase FR, smoke suppression |
| Zinc Borate | 4% | Synergistic char formation, smoke suppression |
| Nano Talc | 3% | Char reinforcement, mechanical enhancement |
| PTFE | 0.3% | Anti-dripping |
VI. Key Testing Parameters
- 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 optimizing the ratios, an efficient halogen-free flame retardant system can be achieved while maintaining PBT’s overall performance.
More info., pls contact lucy@taifeng-fr.com
Post time: Jul-01-2025
