UV-curable behavior of phosphorus- and nitrogen-based reactive diluent for epoxy acrylate oligomer used for flame-retardant wood coating

Multifunctional phosphorus and nitrogen containing tris-diethanolamine spirocyclic pentaerythritol bisphosphorate reactive diluent (TDSPBRD) for epoxy acrylate oligomer was synthesized from spirocyclic pentaerythritol bisphosphorate diphosphoryl chloride, diethanolamine, and allyl chloroformate. The synthesized reactive diluent was utilized to formulate ultraviolet (UV)-curable wood coating. The weight fraction of reactive diluent in the coating formulation was varied from 5 to 25 wt% with constant photoinitiator concentration. The molecular structure of the reactive flame retardant was confirmed by Fourier transform infrared (FTIR), ¹H nuclear magnetic resonance (NMR) and ³¹P NMR spectral analysis and energy dispersive spectroscopy (EDAX). Further, the effectiveness of the flame retardant behavior of the coatings was evaluated using the limiting oxygen index and UL-94 vertical burning test. Thermal stability was estimated from thermogravimetric analysis and differential scanning calorimetry. The effects of varying the concentration of TDSPBRD on the viscosity of the coating formulation along with the optical, mechanical and chemical resistance properties of the coatings were evaluated. The coatings gel content, water absorption behavior, and stain resistance were also studied.