Reference Formulation for V-0 Flame-Retardant PVC Thermoplastic Plastics
To achieve a V-0 flame retardancy rating (according to UL-94 standards) in PVC thermoplastic plastics, aluminum hypophosphite and boric acid are two commonly used flame retardants. Their addition levels need to be optimized based on the specific formulation, processing conditions, and performance requirements. Below are some recommendations and reference ranges:
1. Addition Level of Aluminum Hypophosphite
Aluminum hypophosphite is an efficient phosphorus-based flame retardant suitable for PVC materials. It inhibits combustion by forming a protective phosphate layer and releasing phosphoric acid gas.
- Recommended addition level: 15–25 phr (parts per hundred parts of resin)
- For standard PVC, adding around 20 phr of aluminum hypophosphite typically achieves a V-0 flame retardancy rating.
- For higher flame retardancy, the dosage can be increased, but the impact on mechanical properties should be considered.
- Precautions:
- Excessive aluminum hypophosphite may reduce processing performance (e.g., poorer flowability).
- It is recommended to combine with other flame retardants (e.g., boric acid, aluminum hydroxide) for synergistic effects.
2. Addition Level of Boric Acid
Boric acid is a low-cost flame retardant that works primarily through endothermic decomposition and the formation of a glass-like protective layer.
- Recommended addition level: 5–15 phr
- Boric acid is usually used as a secondary flame retardant, and excessive amounts may impair mechanical and processing properties.
- In PVC, adding around 10 phr of boric acid can synergize with aluminum hypophosphite to enhance flame retardancy.
- Precautions:
- Boric acid is hygroscopic, so storage and handling should avoid moisture absorption.
- Its flame-retardant effect is limited when used alone; it is typically combined with other flame retardants (e.g., aluminum hypophosphite, aluminum hydroxide).
3. Synergistic Formulation of Aluminum Hypophosphite and Boric Acid
To achieve a V-0 rating, aluminum hypophosphite and boric acid can be combined for synergistic effects. Below is a reference formulation:
- Aluminum hypophosphite: 15–20 phr
- Boric acid: 5–10 phr
- Other additives:
- Plasticizer (e.g., DOP): As needed (adjusted based on PVC hardness requirements)
- Stabilizer: 2–5 phr (e.g., lead salts, calcium-zinc stabilizers)
- Lubricant: 0.5–1 phr (e.g., stearic acid)
Example Formulation:
- PVC resin: 100 phr
- Aluminum hypophosphite: 18 phr
- Zinc borate: 8 phr
- Plasticizer (DOP): 40 phr
- Stabilizer: 3 phr
- Lubricant: 0.8 phr
4. Testing and Optimization
In practical applications, the following steps are recommended for testing and optimization:
- Pilot formulation: Prepare a small-scale trial based on the reference ranges.
- UL-94 test: Conduct vertical burning tests to evaluate the flame retardancy rating.
- Performance testing: Assess mechanical properties (e.g., tensile strength, impact strength) and processing performance (e.g., flowability, thermal stability).
- Optimization: Adjust the addition levels of aluminum hypophosphite and boric acid or introduce other flame retardants (e.g., aluminum hydroxide, antimony trioxide) to further enhance performance.
5. Key Considerations
- Processing temperature: The decomposition temperatures of aluminum hypophosphite and boric acid are relatively high; ensure processing temperatures do not exceed these limits to avoid degradation.
- Dispersion: Ensure uniform dispersion of flame retardants in PVC to prevent localized concentration issues.
- Environmental impact: Both aluminum hypophosphite and boric acid are eco-friendly flame retardants, but compatibility with other additives should be verified.
6. Conclusion
To achieve a V-0 flame retardancy rating in PVC thermoplastic plastics, the recommended addition levels are 15–25 phr for aluminum hypophosphite and 5–15 phr for boric acid. Synergistic use of these flame retardants can enhance performance. In practice, optimization based on specific formulations and performance requirements is essential, and UL-94 testing should be conducted to verify the flame retardancy rating.
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Post time: Jun-23-2025
