STEPPING INTO THIRD MILLENNIUM: THIRD GENERATION LEATHER PROCESSING - A THREE STEP TANNING TECHNIQUE

摘要

The do-undo methods adopted in conventional leather processing generate huge amounts of pollutants. In other words, conventional methods employed in leather processing subject the skin/hide to wide variations in pH. Pre-tanning and tanning processes alone contribute more than 90% of the total pollution from leather processing. Apart from this, a great deal of solid wastes like lime and chrome sludge is being generated. In the approach described here, the hair and flesh removal as well as fibre opening have been achieved using biocatalysts and sodium hydroxide at pH 8.5 for cow hides. This was followed by a pickle free chrome tanning, which does not require a basification step. Hence, this tanning technique involves primarily three steps namely dehairing, fibre opening and tanning. It has been found that the extent of hair removal and opening up of fibre bundles is comparable to that of the control. This has been substantiated through scanning electron microscopic, stratigraphic chrome distribution analysis and softness measurements. Performance of the leathers is shown to be on par with conventionally processed leathers through physical and hand evaluation. Importantly, softness of the leathers is quantitatively found to be comparable with that of control. The process also demonstrates reduction in chemical oxygen demand (COD) load by 71%, total solids load by 72% and chromium load by 84% compared to the conventional process. The total dry sludge from the beam house processes is brought down from 149 to 14 kg for processing 1 ton of raw hides. The input-output audit shows that the biocatalytic three step tanning process employs very low amount of chemicals thereby reducing the discharge by 84% compared to the conventional multi step processing. Further, it has also been demonstrated that the process is techno-economically viable.