Waterborne polyurethanes: A three step synthetic approach towards environmental friendly flame retardant coatings

Flame retardant waterborne polyurethanes (WBPU) were synthesized by reacting a phosphorous based polyester polyol with isophorone diisocyanate (IPDI) in different mole ratios of NCO:OH in three steps. In first step, the polyester polyol was synthesized by reacting tris(bisphenol-A)mono phosphate (TBAMP), sebacic acid, polyethylene glycol which was characterised by measuring acid value and hydroxyl value. Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy and gel-permeation chromatographic techniques were used for the characterization of polyester polyol. In second step, the polyurethanes were synthesized by reacting polyester polyol with diisocyanate in different proportions. In third step, the polyurethane was neutralised using tertiaryamine. A calculated amount of water was then added at this stage followed by addition of a chain extender at controlled pH. This resulted into waterborne polyurethanes. By varying the proportion of NCO/OH, four WBPUs have been prepared. These WBPUs were subjected for coating and casting purposes. Physico-chemical properties such as particle size, dispersion stability, viscosity were measured. The flame retardency of casted films were studied by LOI (limiting oxygen index) and UL-94 test methods. Thermal properties were determined using thermogravimatric analysis (TGA) technique of casted film. Chemical resistance and Mechanical properties of the coated samples have been found out.