“Structurally modified functional N, P-Based flame-retardant precursors for covalent incorporation into epoxy thermosetting networks”

Abstract

Growing need of halogen free advance coating systems demands novel approach to develop sustainable materials that contain components like phosphorous and nitrogen. The present research study provides a two-step synthesis route to fabricate a newly structured phosphorous containing Schiff-base derivative. Firstly, an imine intermediate (SAEA) was synthesized by condensing salicylaldehyde with ethylenediamine, which was then treated with phosphorous moiety to obtain final product (SAEAP). Structures of intermediate and final product were confirmed by FTIR, NMR and hydroxyl value analysis. The synthesized SAEAP was loaded in epoxy matrix with varying quantities of commercial crosslinker and coated on mild steel panels. XRD analysis showed a decrease in crystallinity and an increase in d-spacing, suggesting formation of a more amorphous and expanded polymer structure. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used for evaluating the thermal behaviour of the cured coatings, and the results showed that the addition of phosphorus improved thermal stability. UL-94 vertical burning tests and the limiting oxygen index (LOI) were used to evaluate flammability performance. The phosphorus-modified epoxy coatings fulfilled the criteria for advanced flame-resistant materials since they demonstrated remarkable flame-retardant characteristics, with LOI reaching 30 at 10% SAEAP loading. Overall, by employing phosphorus-capped Schiff-base derivatives, the study presents a novel halogen-free approach for flame-retardant epoxy coatings. In addition to improving thermal stability and flammability resistance, the novel SAEAP structure shows significant potential for next-generation protective coatings that need higher fire safety requirements.