Flame Retardant Solutions for PET Sheet Films

Flame Retardant Solutions for PET Sheet Films

The customer produces transparent flame-retardant PET sheet films with thicknesses ranging from 0.3 to 1.6 mm, using hexaphenoxycyclotriphosphazene (HPCTP) and seeks cost reduction. Below are the recommended formulations and detailed analysis for transparent flame-retardant PET films:

1. Analysis of Flame Retardant Selection

Hexaphenoxycyclotriphosphazene (HPCTP)

• Advantages: Phosphazene-based flame retardants disperse well in PET, maintaining high transparency. The flame-retardant mechanism involves condensed-phase charring and gas-phase radical trapping, making it suitable for transparent films.
• Dosage: Recommended at 5%-10%. Excessive amounts may affect mechanical properties.
• Cost: Relatively high, but total cost remains manageable at lower loadings.

Aluminum Hypophosphite

• Disadvantages: Inorganic powders may cause haze, affecting transparency. Ultra-fine particle size or surface modification may be required for potential use.
• Applicability: Not recommended alone; can be blended with HPCTP to reduce overall cost (transparency testing required).

2. Recommended Formulation Options

Option 1: Single HPCTP System

• Formulation: 8%-12% HPCTP + PET base material.
• Advantages: Optimal transparency and high flame-retardant efficiency (can achieve UL94 VTM-2 or VTM-0).
• Cost Estimate: At 10% loading, the cost increase per kg of PET is approximately ¥10 (¥100/kg × 10%).

Option 2: HPCTP + Aluminum Hypophosphite Blend

• Formulation: 5% HPCTP + 5%-8% aluminum hypophosphite + PET base material.
• Advantages: Cost reduction, with aluminum hypophosphite assisting in gas-phase flame retardation, potentially reducing HPCTP usage.
• Note: Transparency must be tested (aluminum hypophosphite may cause slight haze).

3. Processing and Testing Recommendations

• Dispersion Process: Use a twin-screw extruder to ensure uniform dispersion of flame retardants and avoid agglomeration affecting transparency.
• Flame Retardancy Testing: Evaluate according to UL94 VTM or Oxygen Index (OI) standards, targeting OI > 28%.
• Transparency Testing: Measure haze using a haze meter, ensuring haze < 5% (film thickness: 0.3-1.6 mm).

4. Cost Comparison

Flame Retardant Loading and Cost Increase Table

5. Conclusion

• Preferred Option: HPCTP alone at 8%-10%, balancing transparency and flame retardancy.
• Alternative Option: Blend of HPCTP and aluminum hypophosphite, requiring verification of transparency and synergistic effects.

Recommendation: The customer should conduct small-scale trials first, focusing on flame retardancy (UL94/OI) and haze testing, then optimize the formulation and process. If further cost reduction is needed, explore surface-modified aluminum hypophosphite or novel phosphorus-based flame retardants.

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