Novel 3D-networked melamine–naphthalene–polyamic acid nanofillers doped in vinyl ester resin for higher flame retardancy

In this study, melamine–naphthalene covalent polyamic acid and its metal carboxylate salts were synthesized as building blocks of nanofillers (Nt–Mn–PA–COOM, M = H, Li, Na, and K). The Nt–Mn–PA–COOM nanofillers were added as a dopant to vinyl ester resin at 1–5 wt% and their flame retardancy and thermal properties were evaluated. The flame retardancies of 5 wt% of Nt–Mn–PA–COOK–VE and Nt–Mn–PA–COONa–VE were found to improve the heat release rate by up to 95% and 90%, respectively, in comparison with the pristine vinyl ester (VE) composite. These results demonstrated significant progress in the fireproofing performance of VE composites. The burning times of Nt–Mn–PA–COONa–VE and Nt–Mn–PA–COOK–VE composites were shown to be higher 10.6 min, and 12.1 min, respectively, when compared with the pure VE composite (6.28 min). Also, the burning rates of Nt–Mn–PA–COONa–VE and Nt–Mn–PA–COOK–VE concerning flame retardancies were decreased from 11.92 min to 7.07 and 6.19 min, respectively. The delay in burning time, and the reduction of burning rate clearly refer to the enhancement of flame retardancy behavior of the Nt–Mn–PA–COOM–VE composites. It was found that 5 wt% of nanofiller dopants Nt–Mn–PA–COOM–VE (M = Na, and K) in VE was the ideal loading for considering the integrated perspective for flame retardancy applications. The excellent flame retardancy and thermal performance of the Nt–Mn–PA–COOM–VE (M = Na, and K) composites made them promising candidates for developing novel flame retardancy nanofiller dopants.