Visualization of Penetration and Reaction of Aldehyde Tanning Agent in Leather using Fluorescence Technique

Penetration and reaction of tanning agents in leather greatly influence tanning performance and leather quality. Aldehyde tanning agents are widely used in leather manufacture, but their penetration and reaction in leather cannot be detected easily. Considering the fact that aldehyde can form a fluorescent Schiff base with amino groups of collagen, we visualized the distribution and reactivity of typical aldehyde tanning agents in leather during tanning process using a fluorescence microscope. The results showed that glutaraldehyde in leather was easily observed under the fluorescein isothiocyanate (FITC) filter system. The fluorescence intensity of pelt/leather gradually increased with penetrating of glutaraldehyde, basifying and heating, which was consistent with the formation of Schiff base and the increase in Ts of pelt/leather. Oxidized sodium alginate and dialdehyde sodium carboxymethyl cellulose in leathers were also detected using a fluorescence microscope because the aldehyde group of the two tanning agents formed a fluorescent Schiff base with amino groups of collagen. The oxazolidine tanned leather and the tetrakis hydroxymethyl phosphonium tanned leather emitted little fluorescence because they crosslinked collagen with hydroxymethyl group. These results indicate the fluorescent technique is useful to visualize the penetration and reaction of aldehyde tanning agents that crosslink collagen with aldehyde groups.