Natural rubber (NR) exhibits superior performance and wide applications, but its inherent flammability limits its use. Due to its low thermal conductivity, NR products accumulate heat under dynamic conditions, accelerating aging and increasing fire risks. To address this, flame retardants like expandable graphite (EG) are incorporated. However, EG faces challenges such as poor hydrophilicity and weak interfacial adhesion with polymers, leading to uneven dispersion and aggregation.
Microencapsulation of EG improves its compatibility with polymers, but it may reduce thermal conductivity. To counteract this, high-thermal-conductivity materials like boron nitride (BN) and carbon nanotubes (CNTs) were introduced. This study prepared BN-enhanced microencapsulated EG (BN-EG) and CNT-enhanced microencapsulated EG (CNT-EG) via in-situ polymerization and incorporated them into NR composites.
Key Findings:
1. BN-EG/NR Composites:
- Flame retardancy: Peak heat release rate (pHRR) reduced by 45.06% (727.57 kW/m² vs. pure NR).
- Smoke suppression: Smoke production rate decreased by 40.42% (17.94 m²/s·m²).
- Thermal conductivity: Increased by 205% (0.451 W/m·K).
- Fire safety indices: Optimal fire performance index (FPI: 4.95×10⁻² m²s/kW) and low fire growth rate index (FGI: 13.72 kW/s·m²).
2. CNT-EG/NR Composites:
- Flame retardancy: pHRR reduced by 45.57% (723.52 kW/m²).
- Mechanical properties: Tensile strength improved by 118.8%, elongation at break by 23.7%.
- Thermal conductivity: Tripled NR’s baseline (0.46 W/m·K).
Conclusion:
Microencapsulated EG with BN or CNT significantly enhances NR’s flame retardancy, thermal management, and mechanical performance, making it ideal for high-safety applications like automotive, construction, and electrical insulation.
