Synthesis and application of self-crosslinking and flame retardant waterborne polyurethane as fabric coating agent

A series of self-crosslinking and flame retardant modified waterborne polyurethanes (SFR-WPU) were synthesized and the chemical structure of SFR-WPU was characterized by FT-IR. Particle size, particle size distribution and zeta potential were tested to evaluate the emulsion stability. Afterwards, SFR-WPU as a finishing agent was coated on polyester fabric. The experimental results of limiting oxygen index (LOI) and vertical burning test (VBT) indicated that when the content of FRC-6 was 9.07 wt% in SFR-WPU, the LOI, afterflame time, afterglow time and damaged length values of the coated polyester fabric were 27.5%, 4.7 s, 0.0 s and 10.9 cm, respectively, but the LOI, afterflame time, afterglow time and damaged length values of the pristine polyester fabric were only 20.1%, 62.0 s, 0.0 s and 30.0 cm, respectively. Even after AATCC standard washing process, the LOI, afterflame time, afterglow time and damaged length values of the coated polyester fabric changed slightly to be 26.8%, 5.0 s, 0.0 s and 12.3 cm, respectively. Then, the flame retardant mechanism was explored by testing thermal property and char residue of polyester fabrics with thermogravimetry (TG), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). It was found that SFR-WPU obviously reduced the initial decomposition temperature of the fabric, but significantly improved the residual carbon content, which was contributed by the synergistic flame retardant effect of P and N elements in SFR-WPU from both condensed-phase and gas-phase, respectively.