Study of different-sized sulfur-free expandable graphite on morphology and properties of water-blown semi-rigid polyurethane foams

In this paper, EG with different nominal particle sizes (70 mu m, 430 mu m and 960 mu m) and different loadings from 0 to 50 pphp were considered to investigate the effect of expandable graphite on the morphology and properties of water-blown semi-rigid polyurethane foams (SPFs). Experimental results showed that a higher content of EG in the SPF was more conducive to the formation of a barrier layer after expansion and exhibited better flame retardancy. Horizontal burning test confirmed the conclusion that the EG-430 mu m and EG-960 mu m with various loadings could effectively enhance the flame retardant properties of the SPFs. However, EG-70 mu m could not improve the fire behavior of the composite due to a weak ability to form an efficient char layer on the surface of the SPF. Thermo gravimetric analysis (TGA) indicated that EG had a positive effect on the thermal stability of SPFs. In addition to the flame retardant behavior, effects of EG on the density, pore structure, thermal properties, mechanical properties and damping properties of the SPFs were also investigated.