A facile technique to investigate the char strength and fire retardant performance towards intumescent epoxy nanocomposites containing different synergists

• X-ray tomography and DMA together are applied for mechanical property of char study. • Nanomaterials reinforce the strength of char and improve the fire safety of epoxy. • A step function curve exists in stress-strain curve due to multi-scale porous char. Construction of fire retardant performance for polymer via protection from intumescent char is an efficient approach. In this work, the mechanical strength and effectiveness of the char barrier to provide fire retardancy towards epoxy resin were investigated. The compression tests under controlled force mode were carried out by dynamic mechanical analysis (DMA). Together with the non-destructive technology X-ray tomography (X-CT) analysis for epoxy nanocomposites containing intumescent fire retardant, and metal-organic framework and graphene oxide hybrid (MOF@GO), the inner structure of carbonaceous char was studied. The minimum strength and modulus of EP/MOF@GO-IFR samples significantly improved by more than double, which quantitatively demonstrated that the MOF@GO hybrid reinforced the strength of the char. Moreover, a step function curve appeared in the stress-strain curve resulting from the existence of the multi-scale porous structure within carbonaceous char in terms of enhanced strength. The results revealed that the robustness of char, foaming, viscosity and thermal insultation governed the fire retardant performance. Simultaneously applying layered double hydroxide (LDH) and nano clay as synergists further verified the applicability of the proposed char reinforced mechanism.