Department of Biomass Science and Engineering, Sichuan University, Chengdu 610065, PR China; National Engineering Research Center of Clean Technology in Leather Industry, Sichuan University, Chengdu 610065, PR China.
Instituto de Carboquímica, CSIC, Zaragoza 50018, Spain.
Sci Total Environ. 2022 Sep 1;837:155570. doi: 10.1016/j.scitotenv.2022.155570. Epub 2022 Apr 30.
Developing chrome-free and sustainable tanning agents is extremely important to the sustainability of the leather industry. Herein, we have synthesized an Al-Zr-oligosaccharides tanning agent via a simultaneous degradation and oxidation of cellulose in waste paper. The influence of the temperature and the concentrations of AlCl and HO during the synthesis were thoroughly investigated on the properties of the tanning agent and the leather produced. The synthesis temperature and the concentration of AlCl were the factors primarily affecting the effective depolymerization of cellulose. They controlled the conversion of waste paper into oligosaccharides with an appropriate molecular weight to efficiently penetrate the leather matrix. In parallel, the HO concentration substantially influenced the tanning performance of the Al-Zr-oligosaccharides, diminishing the chromaticity of the tanning liquid via oxidation and promoting the conversion of C2/C3/C6-OH moieties into -CHO/-COOH. These functional groups increased the surface charge of the oligosaccharides allowing more effective coordination with Al/Zr, which facilitated the penetration of Al/Zr species into the leather matrix. Once inside the leather matrix, Al and Zr were released and reacted with the collagen fibers in leather, which resulted in effective leather tanning. The process optimization revealed that up to 57% of waste paper could be converted into a low-chromaticity (4350 AU) liquid hydrolysate with the synthesis conducted at 177 °C in a system comprising 47 mM AlCl and 5 vol% HO. The application of this liquid for tanning provided leather with a shrinkage temperature (86.5 °C) sufficiently high for commercial applications. These excellent results, combined with the intrinsic green nature of our approach, exemplify a step forward to simultaneously reduce pollution and hazards in leather industries giving a second life to waste paper.
开发无铬且可持续的鞣剂对于皮革工业的可持续发展至关重要。在此，我们通过废纸中纤维素的同步降解和氧化合成了一种 Al-Zr-低聚糖鞣剂。详细研究了合成过程中温度以及 AlCl 和 HO 浓度对鞣剂性质和鞣制皮革的影响。合成温度和 AlCl 浓度是影响纤维素有效解聚的主要因素。它们控制着废纸转化为具有适当分子量的低聚糖，以有效地渗透皮革基质。同时，HO 浓度极大地影响了 Al-Zr-低聚糖的鞣制性能，通过氧化降低鞣液的色度，并促进 C2/C3/C6-OH 部分转化为 -CHO/-COOH。这些官能团增加了低聚糖的表面电荷，使其与 Al/Zr 更有效地配位，从而促进 Al/Zr 物种渗透到皮革基质中。一旦进入皮革基质，Al 和 Zr 就会释放出来，并与皮革中的胶原纤维反应，从而实现有效的皮革鞣制。通过过程优化，在 177°C 的温度下，在包含 47mM AlCl 和 5 体积%HO 的体系中进行合成，57%的废纸可以转化为低色度（4350AU）的液体水解产物。该液体用于鞣制可提供收缩温度（86.5°C）足够高的皮革，适用于商业应用。这些优异的结果，加上我们方法固有的绿色性质，体现了朝着同时减少皮革工业污染和危害、赋予废纸第二次生命的方向迈出的一步。
