Synthesis and synergistic effect of cuprous(I) oxide nanoparticles and polyethyleneimine modified ammonium polyphosphate on enhancing the flame resistance of epoxy resin

Abstract

Abstract In this study, cuprous(I) oxide nanoparticles (Cu2ONPs) and APP@PEI (polyethyleneimine-modified ammonium polyphosphate) materials were successfully synthesized and combined to create a flame-retardant system for the fabrication of epoxy (EP) resin with high flame resistance. The characteristic results revealed that the synthesized Cu2ONPs exhibited a particle shape with a size below 200 nm. The synthesized APP@PEI material possessed dimensions ranging from 10–20 micrometers, featuring a core–shell structure. The combination of Cu2ONPs and APP@PEI has proven to be an effective flame-retardant system, significantly enhancing the flame resistance of EP resin. The epoxy-based composite prepared with 2 wt% Cu2ONPs and 18 wt% APP@PEI demonstrated high flame resistance, achieving a V-0 rating (the highest rating according to the UL-94 method for evaluating the flame retardancy of materials) and a limiting oxygen index value of 36% (indicating the material’s self-extinguishing ability). This limiting oxygen index value was significantly higher than that of neat EP resin, which only reached 19%. The characteristic results of the flame-retardant epoxy-based composite demonstrated that both APP@PEI and Cu2ONPs were well dispersed in the EP resin and did not undergo structural transformation during the material preparation process. APP@PEI and Cu2ONPs enhanced the thermal degradation of EP-based composite materials at lower temperatures, exhibiting a faster degradation rate compared to EP resin. This augmentation facilitates the formation of a protective char layer on the surface of composite, thereby shielding it from direct flame exposure during combustion. Cu2ONPs played a role as oxidative catalysts, acting as Lewis acids. In addition to enhancing fire resistance, APP@PEI and Cu2ONPs have increased thermal conductivity, reduced impact strength, maintained tensile strength, and improved flexural strength of the composite material based on EP compared to neat EP resin.