Fluorescent Tracing of Dialdehyde Sodium Alginate Tanning Agent in Leather Matrix

Dialdehyde polysaccharides possess a sustainable nature and good tanning performance. However, the lack of specific detectable groups in their molecular structure results in the difficulty in the determination of the location of dialdehyde polysaccharides in leather fiber networks. In this study, dialdehyde sodium alginate (DSA) tanning agent was fluorescent labeled by 5-(4,6-dichlorotriazinyl) aminofluorescein (DTAF). The purified DTAF–DSA showed high and stable fluorescent intensity at emission wavelength of 515.2 nm when the pH was over 6.0, and the temperature was in the range of 20°C to 50°C. DTAF–DSA was used in tanning and tracked using fluorescence microscopy. Its penetration in the fiber network could be clearly visualized, and its distribution in leather differed with the molecular weight of DSA. As a result, this fluorescence tracing technique could display the mass transfer behavior of dialdehyde polysaccharide tanning agents in leather matrix, which will provide underlying data for tanning mechanism exploration.