Comprehensive Guide to Preparing a 105°C EVA and PE-Based Thermoplastic HFFR Compound for Cable Jackets

EVA (Ethylene Vinyl Acetate) and PE (Polyethylene) are commonly used together in thermoplastic halogen-free flame retardant (HFFR) compounds for cable jackets. Their combination ensures flexibility, flame retardancy, mechanical durability, and environmental compliance. This guide provides detailed instructions for preparing a 105°C-rated EVA and PE-based HFFR compound, along with strategies to achieve Shore 80 hardness.

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Introduction to EVA and PE-Based HFFR Compounds

Halogen-free flame retardant (HFFR) compounds are essential for modern cable applications due to their environmental and safety advantages. Combining EVA and PE leverages the properties of both polymers:
- EVA offers flexibility, processability, and compatibility with flame retardants.
- PE provides additional mechanical strength, rigidity, and cost efficiency.

Why Use EVA and PE in Cable Jackets?
1. EVA ensures excellent flexibility and thermal resistance.
2. PE increases tensile strength and rigidity.
3. The blend enhances flame retardancy and processability.
4. Complies with low-smoke zero-halogen (LSZH) standards, essential for safety-critical applications.

Applications of EVA and PE-Based HFFR Compounds
- Power cables for residential, industrial, and commercial use.
- Control cables in high-temperature environments.
- Data and communication cables with strict fire safety requirements.
- Public infrastructure cables for tunnels, airports, and railways.

Quote"The synergy of EVA and PE ensures a robust, flame-resistant, and environmentally friendly cable jacket material."

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Key Components of a 105°C EVA and PE-Based HFFR Compound

The performance of an EVA and PE-based HFFR compound relies on the careful selection of ingredients. Below are the key components and their roles:

1. EVA Resin
- **Function:** Provides flexibility, toughness, and compatibility with flame retardants.
- **Properties:**
  - Vinyl acetate (VA) content affects flexibility and filler compatibility.
    - 18–28% VA is typical for cable applications.
  - High melt flow index (MFI) for ease of processing.
- **Dosage:** 20–40 phr.

2. PE Resin (LDPE/HDPE)
- **Function:** Enhances tensile strength, rigidity, and dimensional stability.
- **Properties:**
  - Low-Density Polyethylene (LDPE): Improves flexibility and processability.
  - High-Density Polyethylene (HDPE): Provides stiffness and higher Shore hardness.
- **Dosage:** 20–40 phr.

3. Flame Retardants
- **Function:** Ensure compliance with flame retardancy standards while minimizing smoke and toxicity.
- **Types:**
  - Aluminum Hydroxide (ATH): Decomposes endothermically, releasing water to cool and suppress flames.
    - Dosage: 100–150 phr.
  - Magnesium Hydroxide (MDH): Secondary flame retardant with high thermal stability.
    - Dosage: 50–100 phr.

4. Compatibilizers
- **Function:** Improve the dispersion of flame retardants and fillers within the EVA/PE matrix.
- **Types:**
  - Maleic Anhydride-Grafted Polyethylene (MAH-PE).
  - Ethylene Butyl Acrylate (EBA) or Ethylene Methyl Acrylate (EMA).
- **Dosage:** 5–10 phr.

5. Plasticizers
- **Function:** Enhance flexibility and low-temperature performance.
- **Types:**
  - **Paraffinic Oils:** Commonly used for general flexibility improvement.
  - **Trimellitate Plasticizers (e.g., TOTM):** Provide long-term thermal stability.
- **Dosage:** 5–10 phr.

6. Fillers
- **Function:** Improve mechanical properties, stiffness, and flame retardancy.
- **Types:**
  - Talc: Improves stiffness and dimensional stability.
  - Calcium Carbonate (CaCO₃): Reduces cost and increases hardness.
- **Dosage:** 20–40 phr.

7. Stabilizers
- **Function:** Protect the compound from thermal degradation during processing and usage.
- **Types:**
  - Hindered phenolic antioxidants.
  - Phosphite-based heat stabilizers.
- **Dosage:** 1–2 phr.

8. Processing Aids
- **Function:** Enhance processability and ensure uniform extrusion.
- **Examples:**
  - Stearic Acid: Aids in the dispersion of fillers.
  - Silicone-based additives: Improve surface finish.
- **Dosage:** 1–3 phr.

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Typical Formulation for a 105°C EVA and PE-Based HFFR Cable Jacket

| Ingredient              | Dosage (phr)       | Function                                |
|--------------------------|--------------------|-----------------------------------------|
| EVA Resin (18–28% VA)    | 20–40              | Provides flexibility                   |
| PE (LDPE/HDPE)           | 20–40              | Adds rigidity and strength             |
| Aluminum Hydroxide (ATH) | 100–150            | Primary flame retardant                |
| Magnesium Hydroxide (MDH)| 50–100             | Secondary flame retardant              |
| Paraffinic Oil           | 5–10               | Plasticizer for flexibility            |
| Talc                    | 10–20              | Improves stiffness and stability       |
| Calcium Carbonate        | 20–30              | Cost reduction and hardness            |
| Compatibilizer (MAH-PE)  | 5–10               | Improves dispersion                    |
| Hindered Phenolic Antioxidant | 1–2          | Thermal stabilizer                     |
| Processing Aids (Stearic Acid) | 1–3          | Enhances extrusion                     |


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Steps to Prepare the EVA and PE-Based HFFR Compound

1. Mixing
- Use an internal mixer (e.g., Banbury) or twin-screw extruder.
- Add EVA and PE resins, followed by flame retardants (ATH, MDH) in stages to ensure uniform mixing.
- Gradually introduce fillers, plasticizers, compatibilizers, and stabilizers.

2. Extrusion
- Pass the compound through an extrusion line to shape it into a cable jacket.
- Maintain processing temperatures between 160°C and 180°C to prevent the decomposition of flame retardants.

3. Testing
- Perform quality control tests for:
  - Flame retardancy (UL 94 or IEC 60332-1).
  - Shore hardness.
  - Tensile strength and elongation.
  - Thermal aging performance.

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How to Adjust Formulation for Shore 80 Hardness

To achieve Shore 80 hardness, the formulation needs to balance increased rigidity and retained flexibility. Here's how to modify the compound:

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1. Increase Filler Content
- Add rigid fillers like talc and calcium carbonate.
  - Talc improves stiffness and maintains dimensional stability.
  - Calcium carbonate increases hardness while reducing cost.

2. Adjust EVA and PE Ratios
- Increase the proportion of HDPE relative to LDPE or EVA.
  - HDPE provides greater rigidity and hardness.

3. Reduce Plasticizer Dosage
- Lower plasticizer content to decrease flexibility.
- Replace with a more stable plasticizer like TOTM to maintain thermal performance.

4. Optimize Flame Retardants
- Ensure the ratio of ATH to MDH is maintained to avoid compromising flame retardancy while modifying hardness.

Example Adjusted Formulation for Shore 80 Hardness:

| Ingredient              | Dosage (phr)       | Function                                |
|--------------------------|--------------------|-----------------------------------------|
| EVA Resin (18% VA)       | 20–30              | Flexibility and filler compatibility   |
| PE (HDPE/LDPE)           | 30–40              | Rigidity and Shore hardness            |
| Aluminum Hydroxide (ATH) | 120–150            | Primary flame retardant                |
| Magnesium Hydroxide (MDH)| 50–80              | Secondary flame retardant              |
| Paraffinic Oil           | 5–10               | Reduced plasticizer content            |
| Talc                    | 20–30              | Increased for stiffness                |
| Calcium Carbonate        | 20–30              | Increased for hardness                 |
| Compatibilizer (MAH-PE)  | 5–10               | Improves dispersion                    |
| Hindered Phenolic Antioxidant | 1–2          | Thermal stabilizer                     |
| Processing Aids (Stearic Acid) | 1–3          | Enhances extrusion                     |


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Final Considerations

1. **Balancing Hardness and Flexibility:** Ensure filler and plasticizer levels are adjusted carefully to avoid brittle behavior while achieving Shore 80.
2. **Environmental Compliance:** Verify all components comply with RoHS, REACH, and LSZH standards.
3. **Testing and Validation:** Perform extensive tests to ensure mechanical, thermal, and flame-retardant properties meet application requirements.

This guide provides detailed instructions for preparing a 105°C EVA and PE-based HFFR compound and achieving Shore 80 hardness. Let us know if you need additional assistance or clarification!