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.

Insight into the structural transformation of tetraphenylethylene acids at liquid–solid interface induced by linear aminofunctionalized triazine derivatives and annealing treatment

The interaction between organic photoelectric molecules leads to the formation of a certain aggregation structure,which plays a pivotal role in the charge transport at the intermolecular interface.In view of this,we investigated the mechanism and law of intermolecular interaction by detecting the self-assembled behaviors between organic photoelectric molecules at the interface by scanning tunneling microscopy(STM).In this work,the structural transformations of tetraphenylethylene acids(H_(4)ETTCs)on graphite surface induced by temperature and triazine derivatives(zcy-19,zcy-27,and zcy-38 molecules)were studied by STM technology and density functional theory(DFT)calculations.At room temperature,zcy-19 and H_(4)ETTC molecules formed a small range of ordered co-assembled nanostructure,while for zcy-27 or zcy-38 molecules,no co-assembled nanostructures were observed and only their own self-assembled structures existed on graphite surface,individually.In the thermal annealing trials,the original co-assembled H_(4)ETTC/zcy-19 structure disappeared,and only zcy-19 and H_(4)ETTC self-assembled in separate domains.Nevertheless,new well-ordered H_(4)ETTC/zcy-27 or H_(4)ETTC/zcy-38 co-assembled structures appeared at different annealing temperatures,respectively.Combined with DFT calculations,we further analyzed the mechanism of such structural transformations by triazine derivatives and temperature.Results reveal that triazine derivatives could interact with H_(4)ETTC by N–H···O and O–H···N hydrogen bondings,and whether temperature or zcy series compounds could achieve successful regulation of H_(4)ETTC assembly behavior is closely associated with the conjugated skeleton length of zcy series compounds.