Synthesis of acrylated cardanol diphenyl phosphate for UV curable flame-retardant coating application

Acrylated cardanol diphenyl phosphate (ACP) was synthesized via epoxidation of unsaturation in long side chains of cardanol, followed by acrylation of epoxidized cardanol and, phosphorylation of acrylated cardanol. The chemical structure of synthesized products was confirmed using Fourier transform infrared spectroscopy (FTIR), Nuclear magnetic resonance spectroscopy (H-1 NMR, C-13 NMR and, P-31 NMR) and gel permeation chromatography technique (GPC) respectively. The effect of increasing content of ACP into UA oligomer on viscosity of coating formulations was studied using rheometer analysis. The properties of UV curable coatings were determined by differential scanning calorimetry (DSC), X-ray diffraction analysis (XRD) and, thermogravimetric analysis (TGA). The flammability of UV cured coatings were analyzed by limiting oxygen index (LOI) and UL-94 vertical burning test. TGA result shows that the introduction of ACP into UA oligomer promotes degradation of UA oligomer and enhances the char formation. The structure of obtained char residues was further investigated from scanning electron microscopy (SEM), FTIR and Raman spectroscopy analysis. These cardanol based reactive diluent is promising candidates for UV flame retardant UV curable coatings because of their unique structure contains rigid benzene rings, phosphate moiety, polar hydroxyl groups, and long aliphatic chains.