Sandwich structure composite with expandable graphite filled or coated: evaluation of flame retardancy and mechanical performances

Sandwich composites are increasingly used in high-performance application due to their high specific stiffness, strength and thermal insulation. The sandwich composites were developed using honeycomb and carbon fibre reinforced composite face sheet in this study. Expandable graphite (EG) weighting 5 wt% and 10 wt% were filled in honeycomb or coated on face sheet to improve the fireproof performance. The vertical burning test, cone calorimetry test, thermal insulation analysis, scanning electron microscopy and mechanical test were taken into account. With the increase of EG in the sandwich composites, a significant improvement on flame retardancy with better thermal insulation, lower values of peak heat release rate and MAHRE were confirmed for sandwich composite with EG both coated and filled. In addition, the sandwich with EG coated on face sheet presented better fire resistivity and thermal insulation properties when compared to that with EG filled in honeycomb. However, more total smoke release was also observed for EG coated composites due to partial combustion of resin within sufficient heat and oxygen. Furthermore, no significant effect on the mechanical properties of composites was confirmed from both fireproof approaches.