Flame-Retardant Formulation Design Recommendations for Halogen-Free High-Impact Polystyrene (HIPS)
Customer Requirements: Flame-retardant HIPS for electrical appliance housings, impact strength ≥7 kJ/m², melt flow index (MFI) ≈6 g/10min, injection molding.
1. Phosphorus-Nitrogen Synergistic Flame-Retardant System
HIPS Flame-Retardant Formulation (Table 1)
| Component | Loading (phr) | Remarks |
| HIPS resin | 100 | Base material |
| Ammonium polyphosphate (APP) | 15-20 | Phosphorus source |
| Melamine cyanurate (MCA) | 5-10 | Nitrogen source, synergizes with APP |
| Expanded graphite (EG) | 3-5 | Enhances char formation |
| Anti-dripping agent (PTFE) | 0.3-0.5 | Prevents molten droplets |
| Compatibilizer (e.g., MAH-grafted HIPS) | 2-3 | Improves dispersion |
Features:
- Achieves UL94 V-0 via intumescent char formation from APP/MCA synergy.
- Halogen-free and eco-friendly, but may reduce mechanical properties; optimization required.
2. Metal Hydroxide Flame-Retardant System
HIPS Formulation (Table 2)
| Component | Loading (phr) | Remarks |
| HIPS resin | 100 | - |
| Aluminum hydroxide (ATH) | 40-60 | Primary flame retardant |
| Magnesium hydroxide (MH) | 10-20 | Synergizes with ATH |
| Silane coupling agent (e.g., KH-550) | 1-2 | Improves filler dispersion |
| Toughener (e.g., SEBS) | 5-8 | Compensates for impact strength loss |
Features:
- Requires >50% loading for UL94 V-0, but degrades impact strength and flow.
- Suitable for low-smoke/low-toxicity applications (e.g., rail transit).
3. Phosphorus-Nitrogen Synergistic System (Aluminum Hypophosphite + MCA)
Optimized HIPS Formulation
| Component | Loading (phr) | Function/Notes |
| HIPS (high-impact grade, e.g., PS-777) | 100 | Base material (impact ≥5 kJ/m²) |
| Aluminum hypophosphite (AHP) | 12-15 | Phosphorus source, thermal stability |
| Melamine cyanurate (MCA) | 6-8 | Nitrogen source, synergizes with AHP |
| SEBS/SBS | 8-10 | Critical toughener for impact ≥7 kJ/m² |
| Liquid paraffin/epoxidized soybean oil | 1-2 | Lubricant, improves flow/dispersion |
| PTFE | 0.3-0.5 | Anti-dripping agent |
| Antioxidant 1010 | 0.2 | Prevents degradation |
Key Design Considerations:
- Resin Selection:
- Use high-impact HIPS grades (e.g., Chimei PH-888, Taifa PG-33) with inherent impact strength of 5–6 kJ/m². SEBS further enhances toughness.
- Flowability Control:
- AHP/MCA reduce MFI; compensate with lubricants (e.g., liquid paraffin) or plasticizers (e.g., epoxidized soybean oil).
- If MFI remains low, add 2–3 phr TPU to improve flow and toughness.
- Flame Retardancy Validation:
- AHP can be reduced to 12 phr if combined with 2–3 phr EG to maintain UL94 V-0.
- For UL94 V-2, reduce flame retardant loadings to prioritize impact/flow.
- Injection Molding Parameters:
- Temperature: 180–220°C (avoid AHP/HIPS degradation).
- Injection speed: Medium-high to prevent incomplete filling.
Expected Performance:
| Property | Target Value | Test Standard |
| Impact strength | ≥7 kJ/m² | ISO 179/1eA |
| MFI (200°C/5 kg) | 5–7 g/10min | ASTM D1238 |
| Flame retardancy | UL94 V-0 (1.6 mm) | UL94 |
| Tensile strength | ≥25 MPa | ISO 527 |
4. Alternative Solutions
- Cost-Sensitive Option: Replace AHP partially with microencapsulated red phosphorus (3–5 phr), but note color limitation (reddish-brown).
- Validation: Conduct small-scale trials to balance impact vs. flame retardancy before optimizing flow.
More info. , pls contact lucy@taifeng-fr.com
Post time: Aug-15-2025
