STUDY OF THE COMPOSITION AND PROPERTIES OF COMBINED CHROME-ZINC TANNING AGENTS

Abstract

In this work, the combined tanning agents Cichrome C (with zinc sulfate) and Cichrome A (with zinc acetate) were obtained by the reduction of potassium dichromate in an acidic medium in the presence of zinc salts. Glucose was used as a reducing agent. The completeness of the reduction of hexavalent chromium was determined by reaction with diphenylcarbazide. The ratios of components in the synthesis of tanning agents were selected based on the results of a study of complex formation in solutions of chromium tanning agent and zinc salts, performed earlier. The resulting tanning agents were dried to a powder state and the content of chromium oxide and zinc oxide in them was analyzed. The solubility of dry tanning agents in water was determined by pH and electrical conductivity values. The properties and fractional composition of combined tanning agents were studied using derivatography and column ion-exchange chromatography methods. Thermal tests confirmed the presence of chromium and zinc in the tanning agents, and also made it possible to determine the effect of the zinc salt anion on the decomposition process of the combined tanning agents. Using the method of ion exchange chromatography, supplemented by spectrophotometry at wavelengths of 420 and 580 nm characteristic of chromium compounds, the fractional composition of the synthesized tanning agents was established. It has been shown that all tanning agents contain six fractions, differing in the amount of charge of the complex and the ratio of chromium and zinc atoms. The absence of zinc atoms in cationic complexes with a charge of 4+ and 5+ has been established, and the structural formulas of such compounds are presented. The percentage content of each fraction in the tanning agent was calculated and the effect of zinc salt on the ratio between neutral, anionic and cationic complexes was shown. The spectral characteristics of individual tanning agent fractions are presented. The prospects for using combined chromium-zinc tanning agents in leather technology and the influence of the fractional composition on their penetrating and tanning ability are assessed.