Inspiration for a greener tanning industry from the Arzignano tanning district.

Developments in the enzymatic depilation

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by Marco Nogarole, Ikem

The project aims to the substantial replacement of the most common depilatory based sulfides for reductive action, to remove hair from the hide through an innovative use of enzymes.
Although sulphides have long been used as the most effective reagents for removal and destruction of the hair, they are nevertheless highly pollutants in waste waters and contribute greatly to the evolution of toxic and malodorous gases.
In this project we are searching a new enzymatic depilation process using a new generation of enzymes suitable to overcome the above mentioned problems and capable of achieving complete and controlled depilatory action.

The research

The experimentation is mainly focused on depilation with hair recovery. The preliminary tests carried out on hide samples in a lab scale drums were subsequently carried out in testing drums containing from 1 to 3 entire hides (pilot test).
The depilation efficacy evaluation tests were done on the quantity of hair removed (partial or complete removal) and on the organoleptic quality of the hides at the end of the process (integrity of the grain, leather deterioration, distention, bloating). Also the quality of waste water collected was evaluated (chemical analysis such as COD on the filtered material, total Nitrogen TN, chlorides, total suspended solids, total sulfur etc.) and quantity and quality of the removed hair.

First results of depilation with hair recovery

The action temperature of the enzyme was 26-27 ° C for all tests, while the enzyme input was 0.1% or 0:13% depending on the type of enzyme used. A first analysis of the results reveals the considerable difficulty of an effective depilation with a quantity of reducing agents (hydrogen sulphate and sulphide) not greater than 1:25%. Enzymatic hybrid hair removal and sulfide, still unsatisfactory, has made it necessary to progress through the completion of the test application recipe and the use of new, more effective, depilatory enzymes.
The following experimentation has led to the selection of three competitive and efficient enzymes called PU, TF and BU while the application recipe has evolved at last to make it more effective and practicable.
The conservative depilation with 1.5% of sodium sulfide, always followed by an enzymatic soaking, have shown the best performance for the TF type about:
• degree of depilation
• swelling
• hide tightening
• grain preservation
The successive test phases have been conducted with the use of only TF enzyme.

Second phase of the enzyme depilation: the oxidative contribution

In the second phase, there was a combination of enzymatic treatment and a subsequent completion of depilation using hydrogen peroxide (oxidative).

In the case of a destructive depilation without recovery of hair, tests highlighted the possibility to remove hair with only 1:25% post enzymatic treatment of sodium sulfide, while 1% of Na2S in the conservative.

Destructive enzymatic removal + oxidative

  • depilation with hair destruction
  • France bulls 37+
  • green fleshing
  • enzymatic soaking
  • hair removal using TF enzyme
  • sodium sulfide 1% vs. hydrogen peroxide 5% + 4% NaOH 30%
  • degree of hair removal = ok
  • swelling = ok
  • relaxation = discreet
  • grain preservation = better with the oxidative

Destructive enzymatic hair removal; half of the hide on the right was treated by a further process of oxidation with hydrogen peroxide (5% on pelt weight), the second half of the same hide was treated with 1% of sodium sulfide and 1.5% of hydrated lime both after enzyme treatment.

ikem 1

The degree of hair removal for both was satisfactory (95%)

ikem 2ikem 3

Microscope images of the hide grain treated with hydrogen peroxide (left) and with sulfide (right).

 

Results

Reduction in the sodium sulfide in the conservative treatment of 66%, compared to a traditional process that uses the 3% of Na2S; in the destructive treatment there is a 58% reduction.

Depilated hides have a good technically and organoleptic quality.

Excellent quality of the recovered hair.

Future perspectives

  1. Soaking Enzyme without surfactants and baths recovery
  2. Green fleshing
  3. Enzymatic and oxidative depilation with the addition of new specific catalyst enabling to achieve a complete depilation with a lower working temperature, and a reduction in the use of caustic soda that might produce an excessive and undesired swelling.
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