Green Approach for the Development of Novel Flame Retardant Waterborne Polyurethanes: Synthesis and its Characterizations

Abstract

Waterborne polyurethanes (WBPUs) are developed from water as a medium instead of solvent. Due to high volatile organic compounds (VOC) content in the solvents, the government has banned solvent based polyurethanes in few countries. Therefore, in present work attempts have been made to synthesize polyurethanes by the green approach in terms of utilizing water as a solvent medium. Waterborne polyurethane is one of the unique utmost quickly developing environmental friendly material. It has been found extensively useful in the field of applications like coatings, adhesives for automobiles and wood. Furthermore, extremely useful in flexible substrates such as leather, membranes, textiles and rubbers. These fields require a prominent flame retardancy of the materials, but the instant flammability is a major disadvantage of WBPU, which limits its use in further application in a rigorous situation of fire. Hence, flame retardancy has been improved in present work by incorporating phosphorous moiety in the polymeric chain in a reactive way. By the use of prepolymer mixing process and varying NCO:OH mole ratio, various flame retardant waterborne polyurethanes were synthesized. These synthesized WBPUs were coated on mild steel panels, glass panels and wood. Characterization was done through Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. Microtrac particle size analyzer was used to investigate the particle size. Scratch resistance, pencil hardness, adhesion (cross hatch), flexibility 1/4“ mandrel test, chemical resistance and solvent resistance test of the coated panels were also performed. Flame retardancy was inspected by limiting oxygen index (LOI) and UL-94 test methods.