The flame retardant and thermal conductivity properties of high thermal conductivity expandable graphite microcapsule filled natural rubber composites.

• Boron nitride-doped expandable graphite (EG) microcapsule (BN-PMEG) was prepared. • BN improves the thermal conductivity of microcapsule. • BN and EG form an expressway network for heat transfer. • High thermal conductivity BN -PMEG reduces the risk of combustion of natural rubber. The flammable feature limits the application of natural rubber in building fields. Although expandable graphite (EG) microcapsule has good compatibility with natural rubber (NR), the organic wall material of microcapsule has the disadvantage of low thermal conductivity and increases the risk of combustion of NR. In this study, EG microcapsule was prepared via in-situ polymerization (BN-PMEG) whilst its organic shell with high compatibility and thermal conductivity was developed by boron nitride (BN)-doped. The composite structure and thermal performances were analyzed via scanning electron microscope test (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TG). Following this, the cone calorimeter test, limiting oxygen index test, vertical burning test, time to ignition test, tensile strength and fracture test were used to describe the fire behavior and mechanical properties. The results indicate that the BN is embedded in the PMMA shell and the diameter of BN-PMEG is 20–50 μm. According to the mechanical property and thermal conductivity test, BN-PMEG have better compatibility with NR than expansible graphite and increases the thermal conductivity of NR composites. Our work provides a new choice for designing and applying rubber composite materials in buildings. [ABSTRACT FROM AUTHOR]