Expanding the Practical Approach for Salt-Free Tanning A Chrome-free System

Abstract

Our research group previously established a practical approach for salt-free chromium tanning by changing the order of addition of masking salts (COAMS) for electrolyte-cum-masking effect. The present work deals with the modified COAMS process for developing a salt-chromium-free tanning system using aluminium. The tanning conditions such as Al to masking salt (cirtate) ratio, Al2O3 offer, the effect of phenolic syntan, and its order of addition on tanning performance have been studied in detail. It was found that the addition of 3% sodium carbonate (based on the weight of aluminium sulfate) along with aluminium sulfate reduces the acidity without affecting the tanning performance and leather quality. The ideal conditions for the pickle-free aluminium tanning were found to be 1.5% Al2O3 offer, 5% phenolic syntan offer, and an Al to citrate ratio of 1:0.2. It was also found that the order of addition of phenolic syntan did not affect the tanning performance. Furthermore, in comparison to leather produced without syntan, the combined effect of aluminum and phenolic syntan raises the shrinkage temperature by 6°C (Without syntan: 74°, with syntan80°) and decreases the rate of shrinkage by 74%. However, the addition of phenolic syntan did not improve Al exhaustion and leaching resistance to water. The physical characteristics and fiber compactness have been improved by the addition of phenolic syntan. SEX-EDAX study reveals that the aluminum is uniformly distributed throughout the cross-section.