53 / 2023-08-14 22:01:45

Synthesis of a novel phosphaphenanthrene-based flame retardant with pyrimidine and its application in epoxy resin

Phosphaphenanthrene; Flame retardant; Epoxy resin

Phosphorus Material Chemistry and Applied Science > 1) Phosphorus chemistry in material science

Epoxy resin is an important polymer material, but its limiting oxygen index (LOI) value is only 20%^[1], limiting its application in many fields with fire prevention requirements. Phosphaphenanthrene-based flame retardants have the advantages of low toxicity, migration resistance and flame retarding durability. ^[2] In particular, P-N synergistic flame retardants constructed with phosphaphenanthrene and nitrogen containing  units such as triazine ^[3] and triazine trione ^[4] show excellent flame retardancy. In this paper, a phosphorus-nitrogen compound DPSN containing phosphaphenanthrene and pyrimidine was synthesized by the addition reaction of P-H bond with -C=N-. DPSN was applied as a flame retardant to bisphenol A type epoxy resin (DGEBA), after curing with 4,4'-diaminodiphenyl sulfone (DDS). The results showed that DPSN could increase the carbon residue generation of DGEBA/DDS, and inhibit its droplet during the combustion process. When the phosphorus content reached 1.0 wt%, DPSN could increase the LOI value of DGEBA/DDS from 22.5% to 32.2%, and enhance vertical combustion (UL-94) from no grade to the highest flame retardant grade of V-0 rating. Meanwhile, DPSN could reduce the maximum heat release rate (PHRR) of DGEBA/DDS by 40.5% and the total heat release rate (THR) by 27.9% when the phosphorus content of the system reached 1.5wt%, which could effectively reduce the risk of fire spread during the combustion of epoxy thermosets. The results of flame retardant mechanism study showed that the phosphaphenanthrene in DPSN could promote the formation of more carbon residue during the thermal degradation process, and the pyrimidine could produce nitrogen containing non-flammable gases to promote the expansion of char layer. The expanded char layer formed on the surface of the material effectively blocked the transfer of oxygen and heat to the interior of the material and inhibited combustion. DPSN shows excellent phosphorus-nitrogen synergistic flame retardancy and has further development and application value as an efficient and environmentally friendly flame retardant.