Interaction between retanning agents and wet white tanned by a novel bimetal complex tanning agent

Abstract

A promising and practical chrome-free tanning system has been developed based on a novel Al-Zr bimetal complex tanning agent. However, to achieve satisfactory resultant leather, the retanning process that is compatible with this emerging tannage needs to be investigated systematically. This paper aims to explore the interaction between the bimetal complex tanned wet white and retanning agents. The isoelectric point (pI) of wet white was 7.2, which was nearly the same as wet blue. The electropositivity of wet white was even higher than that of wet blue during post-tanning processes, resulting in higher uptake rate of retanning agents. The distribution of various retanning agents in wet white was analyzed by pI measurement of layered leather and fluorescent tracing technique. The retanning agents were unevenly distributed throughout the cross-section, which might be an important restriction factor in obtaining satisfactory organoleptic properties of the crust leather. This fact is mainly due to the strong electrostatic interaction between anionic retanning agents and wet white. Applying a high dosage of multiple retanning agents in a proper sequence of addition benefited the full penetration of retanning agents in leather matrix and thus improved the organoleptic properties of crust leather. This work provides guidance for optimizing retanning process of the wet white leather.

Essential role of isoelectric point of skin/leather in leather processing

“…Thus, the pI of leather shows gradual decline through the posttanning. This system is also suitable for non-chrome mineral tanned leathers [8]. However, the post-tanning system for organic tanned leathers should be redesigned since the pIs of organic tanned leathers are much lower than that of chrome tanned leather.…”

Tannery wastewater treatment: conventional and promising processes, an updated 20-year review

“…Therefore, cleaner production strategy in tanning processes has been proposed as one more promising way as it could reduce even eradicate Cr discharge to effluent so that a series of tough problems concerning Cr disposal in subsequent wastewater treatment processes could be solved. Cleaner production strategy such as enhancing Cr uptake in tanning process or "Cr exhaustion" [184], novel Cr tanning agent carriers [185], Cr-free syntans [186], nonchrome metal tanning agents and chrome free organic tanning agents [187][188][189], etc. are good examples, and these low-risk strategies could relieve the pressure from Cr segregation in wastewater treatment processes even eliminate Cr pollution from root cause.…”

Effect of cationic monomer structure on the aggregation behavior of amphoteric acrylic polymer around isoelectric point

“…In particular, the isoelectric point (pI) of chrome-free tanned semi-finished leather (wet white) is significantly different from that of chrome tanned one [6], which leads to poor fixation of conventional anionic post-tanning chemicals in the chrome-free leather [7]. It has been reported that amphoteric polymer retanning agents with appropriate pI could adjust the charge properties of wet white leather to improve penetration and fixation of post-tanning chemicals, so as to result in satisfactory physical and organoleptic properties of chrome-free leathers [8][9][10].…”