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 NH 3 , H 2 S, H 2 O, 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.