Effect of two-dimensional layered material/zinc borate compounds on flame retardancy of expandable polystyrene foams

Flame retardant expandable polystyrene foams were prepared by coating with melamine modified urea formaldehyde resin. The flame retardant system was based on ammonium polyphosphate, and the combination of three kinds of two-dimensional layered material and zinc borate was used as synergist. The influence of different flame retardants on fire resistance, smoke suppression and thermal stability was discussed. The experimental results show that the flame retardancy is significantly improved by the presence of expandable graphite and zinc borate with mass ratio of 2:1 and total additive amount of 24 phr. The limiting oxygen index of EPS foams is increased to 32.6%, with V-0 rating in UL-94 vertical burning test. The smoke density grade is decreased to 27.31. Compared with the sample containing only expandable graphite, the introduction of zinc borate enhances the strength of residue char from 14.3 to 86.1. Thermal analysis suggests that the thermal stability and char formation are improved by the presence of synergist. The residual char observation reveals that zinc borate is beneficial to form complete and integrated char layers with less crack and breakage