Fabrication of a transparent, flame retardant, and antimicrobial epoxy resin by a novel phosphorus-containing Schiff base molecule

A flame retardant DPPVA was synthesized through a Schiff-base reaction of vanillin, 3,5-diamino-1,2,4-triazole, and diphenylphosphinyl chloride, which was used to improve the thermal stability, flame retardancy, and antibacterial activity of the cured epoxy resin (EP). The EP/4% DPPVA sample looked yellow, but it was still transparent, and it passed the V-0 rating with a limit oxygen index (LOI) of 34.5%. The presence of 4wt% DPPVA in EP decreased the peak heat release rate (pHRR), total heat release (THR), and total smoke production (TSP) by 32.5%, 25.2%, and 29.3%, respectively. Compared with that of the control EP, the char residue was increased to 14.9wt% from 9.6wt%. In TGA the max mass loss rate of the EP/4% DPPVA sample was reduced to 0.86%/ °C from 1.75%/ °C of the control sample, which means the pyrolysis of EP was slowed down by DPPVA. The EP/4% DPPVA sample exhibited effective repellence to E. coli and S. aureus. The addition of 4% DPPVA to EP decreased the impact strength to 8.5 kJ/m2 from 9.9 kJ/m2, which was acceptable for many industrial scenarios. This work provided a potential strategy with an easy process for manufacturing flame retardant, antibacterial and transparent EP composites.