Functional nanocomposite based on waterborne polyurethane and layered double hydroxide as a flame retardant for leather

Incorporation of multifunctional nanomaterials into collagen fibers is considered as a promising approach to fabrication of multifunctional leather. In this study, an effective approach for improving the flame retardancy of leather and promoting absorption of anionic dyes and fatliquoring agents on leather through introduction of layered double hydroxide (LDH) into waterborne polyurethane (WPU) by physical blending method to prepare WPU/LDH nanocomposite as leather retanning agent has been reported. The results indicate that the original form and intercalated form of LDH both coexist in the WPU/LDH composites, and the LDH is evenly dispersed in WPU. Moreover, hydrogen bond and electrostatic interaction exist between LDH and WPU. The penetration and dispersion of LDH in collagen fibers improves the thickening rate, dye uptake, softness and mechanical properties of leather. Moreover, the introduction of LDH also improves the flame retardancy of the resulting leather. Compared to the leather treated with WPU, the ignition time, the length of charring, and the mass loss rate of the leather treated with WPU/LDH-8% are reduced by 74.2%, 58.6% and 46.2%, respectively, and the limiting oxygen index (LOI) value increases from 23.6% to 26.0%. The peak heat release rate (PHRR) and total heat release (THR) of the leather treated with WPU/LDH-8% decreased by 34.4% and 28.7% compared to that of the leather treated with WPU. The excellent flame retardancy of leather can attributed to the barrier effect of highly reinforced carbonaceous char, retarding the escaping of flammable volatiles in the leather and shielding the further damage of the leather by external heat irradiation. The high performance nanocomposites are promising for applications in the manufacture of flame-retardant leather. In addition, the reduction of BOD and COD of the WPU/LDH post-tanning systems is beneficial to reduce the impact of retanning agents on the environment, which is of great significance to "cleaner production".