Metal Organic Based Syntan for Multi-stage Leather Processing

Abstract

The leather industry in India and elsewhere have adopted a two stage processing methodology wherein hides/skins are processed up to wet blue in stage one, and subsequently converted to value added products in stage two. The process of rechroming carried out when wet blue leathers are sourced from various vendors thus attains significance. Many tanners prefer to employ chromium based synthetic tanning agents for rechroming, as against basic chromium sulfate, so as to provide for a tanning at higher pH values of above 3.5 – 4.0. Chromium based synthetic tanning agents in addition to employing masked chromium salts also provide for increased fullness to the leather. A significantly large number of these synthetic tanning agents are based on formaldehyde condensed aromatic intermediates, the use of which could result in the presence of free formaldehyde in the crust leathers. Instances of poorer raw material quality also call for the use of melamine-based syntans for preferential filling of the belly regions. In this work, the application of a chromium based melamine syntan devoid of the use of formaldehyde for condensation is reported. The product has been evaluated in tanning, rechroming and post tanning (as a retanning agent). In tanning, the product provides for a shrinkage temperature of 106oC, 3.25-3.75% Cr2O3 content (dry weight) alongside good belly filling. On use in rechroming or post tanning, the product provides for fuller leathers complete with physical properties meeting standard norms. The results indicate that the newly developed product has a significant scope in increasing the cutting value of the leathers by way of providing uniform substance alongside good tanning properties.