A P/N/S containing flame retardant for epoxy resins with excellent optical, mechanical and flame retardant properties

A highly efficient flame retardant TFD was synthesized based on 2-thenaldehyde, furfurylamine and DOPO. When 4% of TFD is incorporated into EP, EP/TFD-4 exhibits 38.9 % of LOI value and UL-94 V-0 rating. In cone calorimeter test, the peak of heat release rate, total heat release, total smoke production are dropped by 20%, 9% and 65% respectively, and the char residue is increased by 67% as compared with the pure EP. The P/N/S elements in TFD play important roles both in gas phase and condensed phase. The decomposition of 2-thenaldehyde and furfurylamine moieties produces NH3, H2S, H2O, etc., which partly leak and dilute flammable gases, but majorly participate into structural reorganization in the char layer. The degradation of DOPO group releases phosphorus-containing free radicals and phosphate-like compounds. The former quenches the chain combustion reaction, and the later promotes the formation of a stable carbon layer as a barrier effect. Benefited from the good compatability between TFD and EP, and the fine balance between the increased rigidity and the declined cross-linking density, the EP/TFDs exhibit the strikingly similar transmittance to pure EP in the range of 200–800 nm, and the improved mechanical performance in tensile, flexural, and impact tests.