The tanning processes

How the Zeology tanning processes work

Although the processing conditions are very similar to those of wet blue and GDA wet white tanning, the chemistry of Zeology tanning is different. For its execution, conventional wet blue and wet white processes can be used as a basis, both for structure and duration. However, to successfully convert pelts into Zeo White, you will have to take some specifics into consideration.

The suggested processes below are a general advice on how to prepare the hides for Zeology tanning and how to perform the tanning itself. For suggestions specific to your situation, taking all the variables into account (e.g. hide source, the use of auxiliaries, target leather articles), please consult our team of Zeology experts.

Soaking

It is imperative to properly prepare collagen for an even liming operation and the production of clean and flat pelts. While removal of salt or other preservatives is, of course, the primary objective, further far-reaching benefits can be derived from a well-structured soaking regimen.

As is the case with all leathers, Zeology tanning requires a controlled and complete rehydration or wetting back of salt-cured stock and wetting-through of green or fresh material, to support the removal of non-leather making components. Efficient soaking to rehydrate and transport these unwanted constituents from within the hide, will yield a solid foundation for the unhairing and liming operations.

The use of mild alkalis, selected enzymatic preparations and suitable surfactants assists with the removal of these strongly hydrophobic soluble proteins, native fats and oils.

Liming

Hides to be tanned with Zeology benefit greatly from well-opened fiber bundles, especially in the thickest and more densely structured areas of the pelt. Fully penetrated, well let-out and relaxed pelts strongly support successful tanning with Zeology.

Hair saving or semi-hair saving systems yield particularly good results. Here, lime is typically added before alkaline swelling occurs from subsequent additions of sodium sulphide and sodium hydrosulphide. This enables the lime to penetrate and diffuse evenly through the pelts, for optimal fibre splitting and separation.

The use of selected enzymatic auxiliaries can support pre-keratinous digestion and ensures the epidermis and hair are removed quickly and evenly. This further promotes a deeper, more uniform penetration of calcium and other liming chemicals.

In the case of hair burning systems, where sulphides are added before lime, you need to allow sufficient time for the lime to fully penetrate the pelts, before swelling occurs on the addition of fresh water. Similarly, when working in paddles, you should take care to promote good lime solubility and diffusion, while balancing the simultaneous removal of hair and epidermis in more dilute conditions.

This is best achieved through the incorporation of auxiliary organic compounds and other liming auxiliaries which further assist with lime solubility, pH buffering and swell regulation, especially on sensitive grained material.

De-liming

After the pelts have been well opened and through-limed in the beamhouse, Zeology tanning requires an efficient and complete removal of lime and the neutralization of residual alkalinity, after fleshing and/or splitting.

For both full substance and lime-split material, this is done most effectively using proprietary organic acids and acid-salts which form highly soluble lime complexes. If necessary, you can employ small quantities of ammonium salts and other auxiliaries to quickly de-swell the grain and enhance the rate of penetration of the main de-liming agents.

Additional care must be taken to adequately buffer the de-liming bath and avoid the precipitation of soluble proteins through a rapid drop in float pH. These precipitates may adversely impact Zeology penetration through the grain.

It should be noted that any residual alkalinity or bound calcium, which is not removed during de-liming, can be carried over into the pickling system and may interfere with pickling and later Zeology distribution and uptake.

Complete de-liming and thorough washing to remove the de-lime reaction products and organic detritus from the beamhouse processes, are essential for creating optimal conditions for Zeology.

Bating

Zeology fiber stabilization comes with a specifically compact, tight and firm-grained leather. Therefore, we recommend an extended, more intense bating operation than would typically be employed for other tanning agents.

The network of elastin fibers, which are insoluble in the highly alkaline conditions of liming, should now be evenly relaxed through the extended action of suitable enzyme preparations. By carefully selecting the type and quantity of detergents and emulsifiers used during bating, we can effectively manage both grease removal, as well as the bate’s efficiency in elastin digestion.

By the end of bating, it is important to have effectively emulsified and dispersed any residual native fats and oils and mobilized unbound proteins or residues. These are best removed from the collagen network by thorough washing and complete draining, before proceeding to the pickle stage.

Once into the pickle, a higher electrolyte concentration and lower pH value will negatively impact the solubility of these unwanted by-products, a quantity of which will always remain trapped within the hides themselves. Adequate washing and the measured application of surfactants will prove critical in producing white, unblemished Zeo White.

Pickling

The right choice of acids and the respective amounts applied are crucial to Zeology tanning. Deviating from the advised pickle composition strongly affects the quality of tanning and leather. The presence of organic and inorganic acids aid the Zeology tanning agent’s dispersion into the pickle float. The original powder structure is crystalline and the particles are aggregated. In the pickle float, they disperse into smaller structures. This is a dispersion and not a solubilization into the separate elements. The main acid applied is formic acid. The use of formic acid is the key factor for creating the right degree of zeolite dispersion. Sulphate ions, on the other hand, can dissolve the Zeology tanning agent. Therefore, you should avoid higher concentrations, or the zeolite structure will no longer be intact. Sulphuric acid is used in relatively small amounts only and mainly serves to ensure that acidity of float and pelt are at the required level for optimum tanning.

In addition, a small amount of citric acid can be added to slacken the pelt and enhance penetration of the tanning agent. The amounts offered should not exceed 0,18% of the pelt weight.

Penetration/diffusion

The specific pickle composition provides the control necessary for the penetration of Zeology. The organic acids have a threefold function:

• to shield collagen from the tanning agent’s latent reactivity
• to support the optimum dispersion
• to stabilize the structure of the tanning agent and prevent it from dissolving

The addition of zeolite raises the float pH considerably. Proper pickling is required to ensure that the float pH does not exceed 3,8 during the penetration phase. The float pH typically levels out at around 3,6 once the zeolite is fully penetrated. The penetration time of the Zeology is comparable to conventional tanning.
As the zeolite penetrates the pelt, the tanning agent gradually begins to interact with collagen. Even though near full stabilization is reached after the initial 90-120 minutes (as measured by the shrinkage temperature of the Zeo White), a major part of Zeology is still in dispersion and remains unbound.

Activation

Zeology possesses no basicity either, since it is not a metal tanning agent. The reaction between collagen and zeolite comes about by the activation of the dispersed tanning agent forming a sheath-like network around the fibers.

Once pH stability or equilibrium between float and hide has been achieved, during the first two hours of the tanning process, additions of alkalis are required to initiate the formation of these sheaths from the dispersed tanning agent. Depending on the overall process conditions and desired end pH of the tanning, which varies between 4.2 to 5.2 depending on the article, we recommend using between 3.0 – 3.5% sodium bicarbonate or 1.8 – 2.0% sodium carbonate to activate the zeolite. Activation is carried out in 4 to 5 equal steps and run for 4-6 hours.

It is recommended to rest the Zeo White overnight before sammying and shaving.

Read more about Zeo White