Synthesis and characterization of non-ionic flame-retardant waterborne polyurethane

Area of Science:

• Materials Science
• Polymer Chemistry
• Flame Retardancy

Background:

• Waterborne polyurethane (WPU) is widely used but highly flammable, with existing flame retardants showing limitations in char formation and melt dripping suppression.
• Developing effective flame retardant solutions for WPU is crucial for enhancing safety in consumer products and industrial applications.

Purpose of the Study:

• To synthesize a novel phosphorus-containing flame retardant with dihydroxy groups, (6-((4-hydroxyphenyl)((4-hydroxyphenyl)amino)methyl) dibenzo[c,e][1,2]oxaphosphinine 6-oxide) (PHAD).
• To incorporate PHAD into WPU as a chain extender, creating non-ionic flame-retardant waterborne polyurethane (NFRWPU) emulsions.
• To evaluate the physical, mechanical, thermal stability, and flame retardant properties of the synthesized NFRWPU emulsions.

Main Methods:

• Synthesis of PHAD and its incorporation into WPU.
• Characterization of NFRWPU chemical structure using Fourier transform infrared spectroscopy and nuclear magnetic resonance.
• Evaluation of emulsion properties (particle size, viscosity) using dynamic light scattering and rheometry.
• Assessment of mechanical properties (tensile strength, elongation at break) via tensile testing.
• Investigation of thermal stability and flame retardancy using thermogravimetric analysis and limiting oxygen index measurements.

Main Results:

• NFRWPU emulsions with increasing PHAD content showed increased particle size and viscosity, reaching 106.6 nm and 89 mPa·s at 12% PHAD.
• Tensile strength initially increased with PHAD addition, reaching a maximum of 22.63 MPa, while elongation at break decreased to 1060%.
• Improved thermal stability and flame retardancy were observed, with the highest limiting oxygen index reaching 25.6% and maximum carbon residue increasing to 6.5%.

Conclusions:

• The synthesized PHAD effectively enhances the flame retardancy and thermal stability of WPU.
• NFRWPU emulsions exhibit promising comprehensive performance, making them suitable for applications requiring flame resistance.
• The developed NFRWPU represents a viable alternative to conventional WPU for enhanced safety applications.