Dr P Thanikaivelan Significiant Contributions

Siginificient Contribution

Leather processing involves cleaning of the skins or hides to remove unwanted materials, followed by preparing the stock for chrome tanning and subsequently tanning using basic chromium sulphate to stabilise the raw material against microbial degradation. The conventional cleaning processes (liming-reliming processes) lead to the generation of substantial amounts of sulphide, lime sludge and biological oxygen demand (BOD). The conventional preparatory process for chrome tanning namely pickling, which involves the use of sodium chloride and sulphuric acid, generates more amount of dissolved solids. The chrome tanning process by virtue of its poor exhaustion behavior emanates liquor containing chromium about 1000 fold more than the norm specified by the pollution control authorities.

Attempt into Enzyme Application for Dehairing

The researcher has developed an enzyme assisted dehairing process using sodium sulphide in an amount 85% lesser than that used in conventional lime-sulphide dehairing process. The process does not require lime for dehairing thereby ensuring not only 100% elimination of lime sludge formation, but also complete removal of hair at an unusual pH (8.0). However, the pelts require a reliming process, which in turn creates lime sludge and TDS problem. Hence, the researcher has developed a non-lime opening up method based on sodium hydroxide. An optimum concentration (1.0% offer at 350% float) of sodium hydroxide has been established for optimal opening up of fibre bundles. This has been substantiated through scanning electron microscopic, spent alkali liquor and pelt analysis, softness measurements and stratigraphic chrome distribution analysis. The pelt analysis shows that the opening up of fibre bundles has attained equilibrium and the pH of the cross-section is 8.5. Performance of the leathers is shown to be on par with conventionally treated leathers through physical and hand evaluation. Especially softness of the leathers is numerically proven to be comparable with that of control. The process also enjoys elimination of deliming process coupled with a 45% reduction in total solids load on environment.

Joy of Playing with Conventional Method of Liming

In an another attempt to combat the pollution from beam-house processes, the researcher has found an eco-friendly way of doing the conventional liming-reliming processes. An approach has been made to apply the beam-house chemicals with optimal requirement. This is based on the fact that swelling requires only 20 to 40% water (based on raw skin weight before soaking) for conventional opening up. This would, in principle, make possible the use of only one tenth of the chemicals conventionally used in liming-reliming processes maintaining the same concentration gradient. The process employs 40% water, 0.35% sodium sulphide and 1% lime for liming and 40% water and 1% lime for reliming, with conventional process time in a drum. It has been found that the dehairing is complete and the extent of 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 opened up leathers through physical and hand evaluation. Especially, softness of the leathers is proven to be numerically comparable with that of control. The process also enjoys reduction in chemical oxygen demand and total solids load on environment by 85 and 12%, respectively compared to the conventional process. The total dry sludge from the liming-reliming processes is brought down from 152 kg to 6 kg for processing 1 ton of raw skins, which has been demonstrated for the first time.

Success Story of Reduction in Chromium, TDS and Formaldehyde Emission

Conventional chrome tanning process does require pickling as a conditioning process. This process leads to substantial discharge of effluent containing sodium chloride and sulphates, which increases the TDS load. Hence, the researcher has developed a pickle-less chrome tanning process using a formaldehyde free chrome syntan instead of a conventional basic chromium sulphate salt. The process provides leathers having acceptable quality and reduces not only TDS but also chromium in the effluent. In an other attempt to reduce the chromium emission, the researcher has developed another tanning agent based on chromium and silica. The product exhibits more than 85% chromium exhaustion when used in tanning. The crust leathers exhibit excellent softness, suppleness, grain smoothness, stretch and strength.

Two in One: Coloring Leathers Naturally While Reducing Chromium Emission Easily

All wastes containing chromium are considered hazardous by the US environmental protection agency (EPA). The researcher has been keenly involved in the development of new generation mineral tanning agents. One such development is the production of a novel chromium-iron tanning agent. The product ensures more than 90% exhaustion of chromium as against 60-70% exhaustion as in the case of conventional chrome tanning process. The product eliminates the drawbacks associated with solo iron tanned leather namely reduction in strength and discoloration on ageing. The product when used as a solo tanning agent produced leathers with increased softness and grain smoothness. Further, the chromium-iron tanned leathers exhibit comparable hydrothermal stability compared to that of chrome tanned leather. In view of environmental compatibility as well as protection, the product envisages another paramount advantage by eliminating the dyeing process. The conventional dyeing operation chiefly employs dyes having cancer-causing arylamines for coloring leathers. The intrinsic nature of the product lends itself to form variety of colors when treated with a variety of vegetable tannins, which are already used as retanning agents in post tanning operations. For instance, when chromium-iron tanned leathers are treated with myrobalan extract, a deep black color is imparted to the final leathers.

First Attempt in Narrow pH Leather Processing

The researcher has also developed a leather processing technique for tanning skins/hides without deliming and pickling processes. The process envisages the use of lyotropic agents for opening up the fibre bundles and employs a pickleless chrome tanning system in a narrow pH range (4.0-8.0). Thereby, the process claims an environmental benefit of reducing the chemical oxygen demand (COD) and total solids (TS) loads by 67 and 64 %, respectively. The developed process claims substantial reduction in water and time requirement as well.

Venturing into Biocatalytic Fibre Opening: Reviewed in Nature Science Update and Science & Technology, The Hindu

In an attempt to combat the pollution from beam-house processes, the researcher has found an enzyme based fibre opening process. An approach has been made to do the beam-house processes using bioproducts. This is based on the fact that the enzymes specifically act on the substrate. Suitable enzymes have been designed in order to target hair and cementing substances, separately. The approach leads to paradigm shift from chemical to bio processing. It has been found that the dehairing is complete and the extent of 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 opened up leathers through physical and hand evaluation. Especially, softness of the leathers is proven to be numerically comparable with that of control. The process also enjoys reduction in chemical oxygen demand and total solids load on environment by 45 and 35%, respectively compared to the conventional process. The total dry sludge from the liming-reliming processes is brought down from 152 kg to 12 kg for processing 1 ton of raw skins. However, the amylase-treated hides are further processed conventionally, soaking them first in a pickle bath consisting huge amount of salt and sulfuric acid and further chemically stop them from rotting by treating with chrome tanning salt. This results in significant increase of dissolved solids as well as chromium in the wastewater.

Marrying Pickle-free Chrome Tanning with Bioprocessing: A Successful Integration

Fortunately, this tailored pretanning process provides a clean collagen matrix having neutral pH. This provides a clue to tan the skins directly without deliming and pickling (acidification), if one has an effective tanning system without preacidification process. Recently, the researcher and his coworkers have developed a chrome tanning system without a pickling process for conventionally limed and delimed collagen matrix. Now, it is possible to integrate the bio-driven process with a pickle free chrome tanning process. This results in complete revamping of the conventional leather process sequence. Generally, conventional tanning process involves 'do-undo' processes like, curing (dehydration) - soaking (rehydration), liming (swelling) - deliming (deswelling), pickling (acidification) - depickling (basification). Further wide variation in pH has been limited to a very short pH profile. The net benefits of this approach are countless.

The researcher and his colleagues have now shown that this enzyme-driven three step tanning process is applicable not only to thin skins but also to heavy and thick hides. More excitingly, the processed leathers show similar or comparable physical and tactile properties to that of conventionally processed leathers. A scanning electron microscopic cross section view of tanned cowhides shows that the fibre bundles are not modified due to the change in a multistep process to an enzyme-driven three step tanning process. The researcher has also demonstrated that the bio-driven three-step tanning is economically viable and attractive, if commercial enzyme products are employed. Enzymatic processing when synergized with compact chrome tanning, results in reduction of chemical oxygen demand, total solids and chromium emissions into the environment by 80, 85 and 80% compared to traditional processing. It cuts the amount of solid sludge that dehairing and fibre-opening generate by an amazing 91%. It would further be interesting to note that the enzyme treatment softens the matrix thereby increases the area of the final leather. This results in nearly US$ 100 savings for processing 1 tonne skins/hides, since leather is sold on area basis.

	Dr. P Thanikaivelan Senior Scientist