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

Abstract

The key point in creating robust smoke- and heat-suppressing polymers lies in fabricating highly intumescent char layers with efficient radical quenching. However, the formation of radical capturers in the condensed phase during epoxy resin (EP) combustion remains unexplored, and the smoke released during the combustion process is at high levels. Herein, we investigated soluble carbohydrates white sugar (WS) as a heterogeneous char-forming agent with microencapsulated ammonium polyphosphate (MFAPP) to produce intumescent flame retardant EP (IFREP) with superexpanded char. Strikingly, the reductions in total smoke production and heat release of MFAPP/WS/EP (5/5/90) were 81.7% and 47.1%, respectively, achieving a UL-94 V-0 rating with an LOI of 28.3%, simultaneously. The improvements in fire safety of EP were assigned to the efficient radical quenching and physical barrier of the intumescent compact honeycomb-like char layer. The in situ-forming intumescent char could construct a semi-closed system (reduced O₂ concentration) to possess prominent diffusion limitation virtue to change EP pyrolysis behavior. Noteworthily, UV–vis analysis, EPR tests, XPS, and FTIR spectroscopy elucidated that IFREP char achieved improved radical quenching compared to EP-char, ascribed to the production of more aryloxy groups (as radical capturers) during the combustion process. Pyrolysis kinetic analysis demonstrated that the lower O₂ concentration could enhance EP thermal stability at high temperatures. Additionally, N₂ generated from C–N decomposition at 330–500 °C served as the gas source for harvesting the super-expansion intumescent char layer of EP. Summarily, this study offers a novel strategy for fabricating high-fire-safety IFREPs by forming expansion intumescent char with efficient radical quenching via soluble carbohydrates.