Horn meal hydrolysate–chromium complex as a high exhaust chrome tanning agent––pilot scale studies

Abstract

Acid hydrolysis of horn meal (obtained from raw horns of slaughtered cattle and buffaloes) yields a mixture of water soluble and low molecular weight peptides with average particle size of 3,838 nm (3.84 μm) and mean intensity of 5,243.7 nm (5.24 μm) and mean volume of 6,228.1 nm (6.23 μm). These peptides on reaction with Cr(III) yield a product that exhibits high exhaustion of chromium bath (above 92%) during tanning of hides and skins. To consolidate the results, the process was up-scaled in Central Leather Research Institute (CLRI) pilot plant for commercial trials. This material is applied directly to the pickled pelts at 8% w/w level and then the pelt is converted to wet blues and crust leathers. Control leathers were also processed concurrently using standard chrome tanning salts (8% w/w). Leathers showed the desired level of softness, fullness, shrinkage temperature and physical properties, and are comparable with control ones. Our results have indicated the use of Cr(III)–keratin complex could considerably reduce pollution load of Cr salts in leather processing.

Appendices

Appendix 1: Process details for making wet blue

Raw material: wet salted goat skins weighing 1–1.5 kg per skin.

Soaking: (% on raw weight)

• The skins were soaked for 6 h with 300% water and then washed with 2 changes of fresh water.

Liming: (% on soaked weight)

• Lime 15%

• Sodium sulphide (2%) made into a paste with 25% water and applied on flesh side and left overnight. Next day the skins were unhaired.

Reliming:

• Lime 10%

• Water 250%

• Kept in the reliming bath for 3 days. Next day they were fleshed and pelt weight was noted.

Deliming: (% on pelt weight)

• Water 150%

• Ammonium chloride 1.5%

• Run for 45 min, completion of deliming was checked, drained and washed with 200% water.

Pickling:

• Water 80%

• Salt 8%

• Run for 10 min

• Formic acid 0.5%

• Run for 20 min

• Sulphuric acid 0.75%

• Water 20%

• Given in four feeds at 10 min interval, finally run for 60 min. pH of the pelts was kept at 2.8.

Chrome Tanning:

• Pickled pelts at pH 2.8

• 50% pickle water

• 8% BCS (control lot) or 8% high exhaust chrome tanning agent (expt. lot)

• Run for 90 min

• 50% water

• Run for 30 min

• 1% sodium formate

• 10% water

• Run for 30 min

• 1% sodium bicarbonate

• Run for 4 × 10 min + 60 min, pH 3.8.

Appendix 2: Process details for making crust leather

Raw material: Shaved wet blue goat leathers at 1.0 mm thickness

Washing

• Water 250%

• Run for 10 minutes, drain.

Neutralization

• Neutralizing syntan 1.0%

• Run for 20 min

• Sodium formate 0.5%

• Sodium bicarbonate 0.5%

• Given in three feeds at 10 min interval, finally run for 20 min, pH should be 5.0. Then washed twice with 200% water for10 min.

Retanning, Dyeing and Fatliquoring

• Water100%

• Resin syntan 3%

• Run for 20 min

• Acid dye 2%, 30 min

• Synthetic fatliquor 4%

• Run for 30 min

• Melamine based syntan 8%

• Naphthalene based retanning syntan 8%

• Run for 40 min

• Fatliquor based on sulfochlorinated hydrocarbons 4%

• Polymeric fatliquor 3%

• Fatliquor based on synthetic and neutral oils 4%

• Run for 40 min.

Fixing

• Formic acid 2%

• Water 20%

• Given in three feeds at 10 min intervals and finally run for 30 min.

Then the leathers were piled overnight. Next day, they were set, conditioned, again set with reversible setting machine and hooked for drying. After drying, the leathers were staked and buffed using 400 grit emery paper.