Sustainable metal-free leather manufacture via synergistic effects of triazine derivative and vegetable tannins

Restrictions on heavy metals,especially chromium,have encouraged alternative tanning systems that can reduce environmental and human health risks from conventional chrome-based tanning.In this work,metal-free combination tanning was developed by using vegetable tannins and a triazine-based syntan containing active chlorine groups(SACC).Specifically,the relationship between leather performance(e.g.,hydrothermal stability and organoleptic properties)and technical protocols(e.g.,types and dose of tannins)was systematically established.The optimized protocol involving a unique procedure(i.e.,10%SACC pre-tanning,shaving,and 25%wattle tanning)endowed the leather with high shrinkage temperature(~92℃)and met the Chinese standards for shoe upper leather(QB/T 1873-2010).Our method not only produces zero chrome-containing solid wastes,but also uses~75%less tannin for leather manufacture.The excellent leather performance was ascribed to the synergistic effects,where SACC and wattle diffused into collagen fibrils and may bind to collagen via covalent,hydrogen and ionic bonding,locking the hierarchical structure of collagen from microfibrils to fiber bundles.Moreover,we summarized these findings and proposed a diffusion-binding-locking mechanism,providing new insights for current tanning theory.Together with the biodegradable spent tanning liquor,this approach will underpin the development of sustainable leather manufacture.

Covalent and Ionic Bonding between Tannin and Collagen in Leather Making and Shrinking:A MALDI-ToF Study

Collagen powder hydrolysates were reacted with a solution of commercial mimosa bark tannin extract.The mixture was prepared at ambient temperature and prepared at 80°C to determine what reactions,if any,did occur between the collagen protein through its amino acids and the polyphenolic condensed tannin.The reaction products obtained were analyzed by matrix assisted laser desorption ionization time-of-flight(MALDI ToF)mass spectrometry.Reactions between the two materials did appear to occur,with the formation of a relatively small proportion of covalent and ionic linkages at ambient temperature but a considerable proportion of covalent linkages tannin-protein amino acids and the disappearance of ionic bonds.The linkages between the two materials appeared to be by amination of the phenolic–OHs of the tannin by the amino groups of the non-skeletal side chains of arginine,and by esterification by the–COOH groups of glutamic and aspartic acid of the aliphatic alcohol-OH on the C3 site of the flavonoid units heterocycle of the tannin.The proportion of covalent linkages increases markedly and predominate with increasing temperatures.This tightening of the tannin-protein covalent network formed may be an additional contributing factor both to leather wear resistance and performance as well to leather shrinking when this is subjected to excessive temperatures.

Combination tanning mechanism inspired environmentally benign catalyst for efficient degradation of tetracycline

The utilization of chelation reaction between metals and tannins is a common tanning method in leather chemistry.Herein,a novel combination tanning mechanism inspired environmentally benign catalyst(CMBT-Fe^(0))was synthesized by immobilizing Fe nanoparticles onto bayberry tannin(BT)grafted chitosan microfibers(CM).The obtained catalyst featured a well-defined microfibrous structure,on which Fe^(0)nanoparticles were highly dispersed to exhibit exceptional catalytic activity for the degradation of tetracycline(TC).The catalytic activity of CMBT-Fe^(0)was 1.72 times higher than that of the commercial Fe^(0)nanoparticles without immobilization,with 95.03%of TC degraded within 90.0 min.The CMBT-Fe^(0)catalysts were recycled 6 times,with the removal rate of TC maintained at 82.56%.Furthermore,a possible mechanism responsible for the catalytic removal of TC was provided by analyzing the catalytic degradation products via liquid chromatography-mass spectrometry.Therefore,our investigation successfully developed efficient catalysts to address the concerned environmental issue of antibiotic pollution.