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• Mn 3 CoO x was prepared to enhance the fire safety of epoxy resins (EP). • Mn 3 CoO x impressively reduced pHRR and pSPR by 47.5 % and 34.6 %, respectively. • Mn 3 CoO x can effectively catalyze the transformation of hazardous gases. • Recovery of Mn 3 CoO x to 90.0 % in EP composite. The development of metal oxide flame retardants that are easy to synthesize, efficient, and recyclable would be more beneficial to circular economy. In this work, a porous core-shell Mn 3 CoO x was developed to efficiently reduce heat, smoke as well as hazardous gas during the combustion of epoxy resin (EP). Compared with pure EP, the peak heat release rate (pHRR), total heat release (THR), peak smoke production rate (pSPR), total smoke production (TSP), peak CO production rate (pCOPR), and peak CO 2 production rate (pCO 2 PR) of EP/Mn 3 CoO x are reduced by 47.5 %, 21.5 %, 34.6 %, 17.6 %, 58.6 %, and 55.4 %, respectively. It has been shown that Mn 3 CoO x not only catalyzes the formation of high-quality char layer but also effectively catalyzes the conversion of hazardous gas products into CO 2. Recovery experiments of Mn 3 CoO x filler in EP composites show that the recovery of Mn 3 CoO x can reach 90.0 %. This work provides insights into the design of efficient metal oxide flame retardants and ideas for the development of recycled flame retardants. [Display omitted] [ABSTRACT FROM AUTHOR]

• The strength of chars was heightened significantly by the bi-component flame retardant (PODSE/APP). • 20 wt% PODSE/APP led to an 88.1 % and 87.0 % reduction in pSPR and TSP. • The char residue was substantially increased by 89.2 % with 20 wt% PODSE/APP. • PODSE/APP changed the internal structure of chars into honeycomb with higher expanded ratio. The intrinsic flammability and high smoke production are two major defects that epoxy resin (EP) must overcome during the practical application. However, few current studies have acknowledged in both fire resistance and smoke suppression performance, which is vitally interrelated with quality of char layers. Herein, a P/S-containing compounds (PODSE) was prepared via esterification and then supplemented with ammonium polyphosphate (APP) to develop an intumescent flame retardant for heightening the strength of char. With 20 wt% PODSE/APP, the peak of smoke produce rate (pSPR) and total smoke production (TSP) of EP3 reduced by 88.1 % and 87.0 %, respectively, indicative of superior smoke suppression performance. It attained a limited oxygen index (LOI) value of 40.0 % with V-0 rating during vertical burning test (UL-94) and the char residues at 700 °C increased from 15.8 % to 29.9 % compared with pure EP. More importantly, in order to figure out the reason for such highly-improved performance, the residual chars after cone calorimeter (CC) test were comprehensively investigated. The result showed that the internal chars of the samples modified by PODSE/APP exhibited honeycomb-like structure instead of irregular network structure of the one modified with single PODSE, endowing the char layers with higher expanded ratio and strength, which responded to excellent insulation effect. This finding provided theoretical and experimental basis for further exploration of P/S synergistic intumescent flame retardant. [ABSTRACT FROM AUTHOR]