Manganese or copper alginate as catalytic charring agent for synergistic intumescent flame-retardant epoxy resins

In this study, two biomass-derived alginates (Copper alginate (Cu-A) and Manganese alginate (Mn-A)) were selected as high-quality carbon sources. They were respectively compounded with ammonium polyphosphate (APP) to form a synergistic intumescent flame retardant system for improving the flame retardancy of epoxy resin (EP). The flame retardancy and thermal stability of the composites were systematically investigated using limiting oxygen index (LOI), vertical burning test (UL-94), cone calorimetry (CCT), and thermogravimetric analysis (TGA). The results showed that the EP polymers both successfully passed the UL-94 V-0 rating when 0.05 wt% Cu-A/13.95 wt% APP or 0.10 wt% Mn-A/13.90 wt% APP was added, with the LOI values increased to 28.3% and 28.4%, respectively. TGA analysis showed that the composite system containing Cu-A or Mn-A possessed excellent thermal stability and exhibited a high residual char yield at the high-temperature stage. CCT results further demonstrated that the introduction of Cu-A or Mn-A effectively reduced the THR and PHRR values of the polymer, while significantly lowering the emissions of CO, CO 2 , and TSP. In addition, the char layer formed after combustion had a high degree of integrity and densification. Its inner and outer surfaces were smooth and continuous, and the degree of graphitization was significantly enhanced. Overall, the synergistic effect of Cu-A or Mn-A significantly improved the flame retardancy of EP/APP composites.