Ultralow-Smoke-Release Epoxy Resin with Efficient\nRadical Quenching Fabricated via Soluble Carbohydrates

The\nkey point in creating robust smoke- and heat-suppressing polymers\nlies in fabricating highly intumescent char layers with efficient\nradical quenching. However, the formation of radical capturers in\nthe condensed phase during epoxy resin (EP) combustion remains unexplored,\nand the smoke released during the combustion process is at high levels.\nHerein, we investigated soluble carbohydrates white sugar (WS) as\na heterogeneous char-forming agent with microencapsulated ammonium\npolyphosphate (MFAPP) to produce intumescent flame retardant EP (IFREP)\nwith superexpanded char. Strikingly, the reductions in total smoke\nproduction and heat release of MFAPP/WS/EP (5/5/90) were 81.7% and\n47.1%, respectively, achieving a UL-94 V-0 rating with an LOI of 28.3%,\nsimultaneously. The improvements in fire safety of EP were assigned\nto the efficient radical quenching and physical barrier of the intumescent\ncompact honeycomb-like char layer. The in situ-forming intumescent\nchar could construct a semi-closed system (reduced O<sub>2</sub> concentration)\nto possess prominent diffusion limitation virtue to change EP pyrolysis\nbehavior. Noteworthily, UV–vis analysis, EPR tests, XPS, and\nFTIR spectroscopy elucidated that IFREP char achieved improved radical\nquenching compared to EP-char, ascribed to the production of more\naryloxy groups (as radical capturers) during the combustion process.\nPyrolysis kinetic analysis demonstrated that the lower O<sub>2</sub> concentration could enhance EP thermal stability at high temperatures.\nAdditionally, N<sub>2</sub> generated from C–N decomposition\nat 330–500 °C served as the gas source for harvesting\nthe super-expansion intumescent char layer of EP. Summarily, this\nstudy offers a novel strategy for fabricating high-fire-safety IFREPs\nby forming expansion intumescent char with efficient radical quenching\nvia soluble carbohydrates.