Vanillin-derived phosphorus-containing aromatic imine for flame-retardant polyurethane coating

Present work reports the synthesis of phosphorus-containing imine derivative of vanillin for application in the flame-retardant (FR) polyurethane (PU) coatings. The multifunctional vanillin-imine-phosphorus (VEDAP) compound involved a two-stage synthesis in which the first stage contained the imine formation by the reaction of vanillin (a biobased compound) and ethylenediamine (EDA). The latter stage continued with the incorporation of phosphorus moiety into the compound. The synthesized compound was incorporated into a commercial PU 2-pack formulation with different concentrations and coated onto the mild steel panels. The chemical structures of the intermediates were confirmed using Fourier-transform infrared (FTIR) spectroscopy, determination of the hydroxyl values, and nuclear magnetic resonance (NMR) spectroscopy. The thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) results revealed an increase in the degradation temperatures of the VEDAP containing coatings and the char yield. The heat resistance index temperatures (T-HRI) showed significant improvement in thermal stability with increasing concentration of VEDAP. The change in the coating formulations' crystallinity was studied using X-ray diffraction (XRD) method. The mechanical properties almost retained even for higher loading of VEDAP while biobased content apparently increased with increasing concentrations of VEDAP. The flame-retardant properties were checked using the limiting oxygen index (LOI) and UL-94 vertical burning test. The VEDAP has remarkably imparted flame retardancy with the highest LOT value of 29 with no dripping and self-extinguishing behavior within 10 s. [GRAPHICS] .

Automated summary

This study presents the synthesis of a phosphorus-containing imine derivative of vanillin and its application in flame-retardant polyurethane coatings. The synthesized compound significantly improves the flame retardancy and thermal stability of the coatings without compromising mechanical properties.