A green chemistry approach to leather tanning process: Cage-like octa(aminosilsesquioxane) combined with Tetrakis(hydroxymethyl)phosphonium sulfate

The octa(aminopropylsilsesquioxane) (POSS–NH2) was synthesized by hydrolytic and condensation of γ-aminopropyltriethoxysilane in isopropyl alcohol solvent with tetraethylammonium hydroxide as catalyst. The structure and morphology of products was characterized by Nuclear magnetic resonance (1H, 13C-NMR), fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). A novel chrome-free tanning process based on combination tanning with cage-like octa(aminosilsesquioxane) and tetrakis(hydroxymethyl) phosphonium sulfate (THPS) has been proposed. Hygrothermal stability test showed that the shrinkage temperature (Ts) of THPS tanned leather was obviously increased with the introduction of POSS-NH2, implying that THPS and POSS nanoparticles had synergistic effect in the combination tanning process. The tanning process is optimized as 6.0% POSS-NH2 combination with 2.5% THPS, endowing the leather with Ts above 83.0 °C and thickness rate 44.6%. FT-IR analysis showed that hydrogen bond were formed between amino groups of POSS and hydroxyl groups of collagen during tanning process. The results of scanning electron microscope and energy dispersive X-ray spectroscopy (SEM-EDX) results reveal that POSS and THPS tanning agents could penetrate and bind evenly in the leather matrix, thus promoting the weaving of collagen fibers into a tight network structure.