Expandable graphite for halogen-free flame-retardant of high-density rigid polyurethane foams

We obtained the high-density rigid polyurethane foam (RPUF) filled with expandable graphite (EG) by airtight cast molding, and its fire performance was evaluated. The results show that the LOI values increase linearly with EG content, especially the LOI value of the 20 wt% EG-filled RPUF composites increases rapidly to 39.5% from 22.5% of pure RPUF. When the pure RPUF was burned, no clear transition process between burning spots and virgin material is observed. But when the EG/RPUF composite was burned, EG produced high-volume expanded graphite and covered the surfaces of the materials, which can prevent combustible gases from feeding the flame, and it also separates oxygen from the burning material efficiently. The thermal degradation of foam was investigated using thermogravimetric analysis (TGA). The result shows that the thermo-oxidative degradation of pure RPUF takes place in the range of 220-350 degrees C and 450-650 degrees C, respectively. The thermal stability of RPUF composites increased slightly when it contained 20wt% EG. The mechanical and electrical properties of EG/RPUF were also discussed. Generally, addition of EG resulted in a slight decrease in the mechanical properties and no influence on the electrical conductivity.