Synergistic effect between histidine phosphate complex and hazelnut shell for flammability reduction of low-smoke emission epoxy resin

Abstract A novel intumescent fire retardant (FR) system based on ground hazelnut shell (HS) and L-histidinium dihydrogen phosphate-phosphoric acid (LHP) was introduced into the epoxy resin (EP) in order to verify their effectiveness as fire retardants. The burning behaviour and smoke emission were assessed with cone calorimeter (CC) and UL-94 tests. Furthermore, the analysis of volatile products evolved during both the thermal decomposition and burning was conducted with the use of thermogravimetric analysis (TGA/FT-IR) and steady-state tube furnace (Purser/FT-IR), both combined with FT-IR with the use of a transfer line. It was found that the system containing 5 wt% of HS and 15 wt% of LHP lead to in the formation of a swollen char with numerous closed cells, which reduced the burning process as well as smoke emission. The obtained results confirm the occurrence of a synergistic effect between the components.