KMT B3SL vs. B3V: Brucite Performance in PVC Cable Compounds

This study compares two brucite grades—KMT B3SL and KMT B3V—in a PVC-based formula: PVC SG3 (100%), DOP plasticizer (45%), Ca/Zn stabilizer (5%), aluminum hydroxide (35%), calcium carbonate (10%), and brucite (35%). Tested at 22.3–23.3°C and 48–51% humidity, results show B3V offers superior melt flow index (3.5 vs. 2.5), elongation at break (325–330% vs. 305%), and limiting oxygen index (31.2 vs. 27.7–28), while B3SL edges out in tensile strength (16.5 MPa vs. 16.2 MPa). These findings highlight B3V’s potential to enhance PVC cable compounds while reducing costs by lowering antimony trioxide (ATO) usage.

Introduction

Brucite, a natural form of magnesium hydroxide, is a high-filling flame retardant widely used in PVC cable compounds, including filling, bedding, and sheathing for low-smoke zero-halogen (LSZH) cables. This study evaluates KMT B3SL (established grade) against KMT B3V (newly developed) to assess mechanical and flame-retardant properties in a standard PVC formula. B3V’s improved performance allows manufacturers to reduce ATO content, maintaining key properties like elongation, tensile strength, and LOI, thus optimizing cost-efficiency.

Materials and Testing Methodology

Materials

• Formula: PVC SG3 (100%), DOP plasticizer (45%), Ca/Zn stabilizer (5%), calcium carbonate (10%), aluminum hydroxide (35%), brucite (35%).
• Brucite Grades:
  • KMT B3SL: 90% purity, 90% whiteness, 3.5–4.0 μm particle size (D50), uncoated.
  • KMT B3V: 90% purity, ≥90% whiteness, 2.5–3.0 μm particle size (D50), silane-coated.
• Source: KMT Industrial HK Limited.

Equipment

• Preparation: Banbury mixer, Plate Curing Press, mold, SY-6210-A Electronic Pulling Force Machine.
• Testing: Oxygen Index Meter, Melt Flow Index Tester, Electronic Tensile Machine.

Process

1. Preheat Banbury mixer to 100–120°C, mix for 30 minutes at 200 ± 10°C.
2. Transfer dough to a preheated mold (1 ± 0.1 mm thick).
3. Press with Plate Curing Press (prepress: 10 MPa, pressure: 10–15 MPa, 220°C, 2-minute preheat).
4. Cool samples to 40–50°C.

Test Conditions

• Temperature: 22.3–23.3°C
• Humidity: 48–51%
• Standards: Combustion performance per GB/T 2406.2-2009.

Results and Discussion

Brucite Specifications

1. Melt Flow Index (MFI)

Insight: B3V’s higher MFI (3.5 vs. 2.5) indicates better processing fluidity.

2. Elongation at Break

Insight: B3V improves flexibility by 20–25%.

3. Tensile Strength

Insight: B3SL slightly outperforms B3V (0.3 MPa difference).

4. Limiting Oxygen Index (LOI)

Insight: B3V enhances flame retardancy by ~3.5%.

Summary Table

Conclusion

KMT B3V outperforms B3SL in MFI (+1.0), elongation (+20–25%), and LOI (+3.5%), making it ideal for PVC cable compounds requiring enhanced processability and flame retardancy. B3SL retains a slight edge in tensile strength (+0.3 MPa). B3V’s silane coating and smaller particle size enable cost savings by reducing ATO reliance without compromising performance.

About KMT Industrial HK Limited

Headquartered in Gansu, China, KMT Industrial HK Limited specializes in magnesium hydroxide and natural brucite powder for flame-retardant applications. 

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