Selective degradation of hemicellulose into oligosaccharides assisted by ZrOCl2 and their potential application as a tanning agent

Selective degradation of hemicellulose into value-added chemicals is promising for sustainable biorefinery, but the industrial application of these chemicals is limited. In this study, selective degradation of hemicellulose in pubescen was achieved with 97.3% conversion, and lower than 15% conversion of cellulose and lignin, via the assistance of ZrOCl2 at 120 °C. Oligosaccharides were predominant products after hemicellulose degradation, and the glycosidic bonds could be easily accessed and broken to obtain smaller molecules after ZrOCl2-assisted disruption of the hydrogen networks among the oligosaccharides. Moreover, ZrOCl2 inhibited the condensation of the dehydrated intermediates with xylo-oligosaccharides, preventing the repolymerization of xylo-oligosaccharides into macromolecules. The reaction liquid containing Zr-oligosaccharides was a complex tanning agent used for chrome-free tanning, where oligosaccharides acted as masking agents. By coordination in advance, the oxygen-rich oligosaccharides could help the penetration of Zr species into the leather matrix for further crosslinking with collagen fibers, thereby enlarging the tanning effect of Zr species and increasing the shrinkage temperature of the tanned leather to 13.8 °C. This work represented a step toward the application of biomass-derived chemicals to the sustainable leather industry.