Quantitative Determinations of Isoelectric Point of Retanned Leather and Distribution of Retanning Agent

Abstract

Neutralized chrome leathers (pH 6.3) were retanned with typicalanionic retanning agents acrylic resin (AC), amino resin (AR)and mimosa extract (ME) alone or together. The isoelectricpoints (pIs) of the retanned leathers were determined using azeta potential analyzer for solid-state materials, and thepenetration as well as the uptake of the retanning agents in theleathers was analyzed using a fluorescent tracing technique. Itwas found that the pIs of the surface layers of the leathersretanned with 3% of AC, AR or ME alone became below 5.4,while the pIs of their middle layers were still around 7.4. The pIsof the upper, the middle and the lower layers of the leatherretanned with 3% AC, 3% AR and 3% ME together were veryclose and below 3.6. Additionally, greater penetrations anduptakes of the retanning agents were obtained after retanningwith AC, AR and ME together compared to alone. These resultsindicate that retanning with more and various anionic retanningagents is very useful for a more thorough decrease in the pI ofthe chrome-tanned leather and favors the penetration and theuptake of the retanning agents in the leather.