Tanning the skin for making leathers

Tanning is a crucial process in the production of leather, and it involves several steps:

 

1. Preparation: Animal hides go through several stages before they are ready for tanning. These stages may include fleshing (removal of flesh), preservation or curing (preventing bacterial growth), soaking, liming (removal of natural grease, fats, keratin, and hair), unhairing, splitting, de liming, bating, degreasing, bleaching, pickling, and de pickling.

 

2. Curing: The hides are cured with salt to prevent putrefaction by preventing bacterial growth on the hide between procurement and processing. It greatly reduces the moisture content of the hide.

          

3. Soaking: The salts left over from the curing are removed in a process called soaking. This process involves soaking the skins in water which has certain chemicals added to prevent bacterial and fungal growth.

 

4. Liming: The hides and skins go for liming, which means soaking the hides in a drum or pit filled with milk of lime, an alkaline solution. Liming results in the removal of natural grease and fats as well as keratin and hair.

 

5. Fleshing: After liming, the pelt goes through a machine to remove fleshy tissue from the flesh side. This process, fleshing, involves removing connective tissue and meat residue from the flesh side of the skin. It uses rotating scraping rolls.

 

6. Unhairing: Unhairing follows fleshing, which involves the removal of hair from the hides. After applying unhairing agents like sodium hydroxide and calcium hydrosulfide, most of the hair is then removed, first with a machine and then by hand using a dull knife to shed it out.

The hides can then be bated, depending on the intended use of the leather. Bating involves the addition of enzymes to the hides to soften them.

         

         

7. Tanning:

 What exactly is leather tanning the next question we need to as is “why”. Why do we need to tan leather? The simplest answer would be “to make leather.”

 

It is to keep the animal skin or hide from rotting, decomposing, and putrefying. Once the animal is dead, the skin will take its natural course and begin to break down. There are many elements that usually break down and decompose the animal skin. It may be because of bacteria that eats away the flesh or the elements which will try to harden the skin or both. Tanning, therefore, prevents all of this from happening.

Tanning will permanently alter the protein structure of the animal skin. It will make the skin more durable and less likely to decompose. Different solutions offer different changes to the skin. Changes such as the change in color, flexibility, softness, or strength. However, whatever method or technique you use, the primary purpose of tanning is to preserve the skin. Tanning, therefore, preserves the animal skin and likewise creates leather in the process. Additionally, tanning will not only preserve the skin but also protect it from the elements. Protecting it from decomposing when it gets wet.

 

The hides are then prepared to receive a tanning agent, typically eggs, brain, fat, or chemical/mineral. They are then soaked, stretched, dried, and sometimes smoked. A tanning solution, made by mixing warm water and the mashed-up animal brain, is applied by rubbing it onto the hide.

 

The tanning process stabilizes the protein of the raw hide or skin, preventing putrefaction, and preparing it for a wide variety of end applications. The main difference between tanned and untanned dry hides is that untanned hides will putrefy after getting wet, while tanned leather will not. Tanning also changes the appearance of the hide.

 

1. Chrome Tanning: This is the most common method of tanning used today. It involves using chromium salts, which results in soft and flexible leather that’s highly resistant to water, heat, and scratches. This type of leather is often used in clothing and footwear.

 

2. Vegetable Tanning: This is a traditional method that uses tannin-rich plant extracts derived chiefly from tree bark, trunks, and leaves. The resulting leather is firm and durable, making it ideal for belts, saddles, and other heavy-duty items.

 

3. Chrome-Free Tanning: Also known as aldehyde tanning, this method uses glutaraldehyde or oxazolidine compounds instead of chromium salts. It’s an alternative for those who are allergic to chrome-tanned leather or for applications where chrome is undesirable.

 

4. Zeolite-Based Tanning: This is a newer method that uses zeolites, a type of microporous mineral. It’s an environmentally friendly alternative to chrome tanning.

 

Oxazolidine Means in nature:

1. Oxazolidine is a five-membered heterocycle ring with the formula (CH2)3(NH)O. The oxygen atom and NH groups are not mutually bonded, in contrast to isoxazolidine. Oxazolidines are derivatives of the parent oxazolidine owing to the presence of substituents on carbon and/or nitrogen.
2. Oxazolidines are traditionally prepared by condensation of 2-aminoalcohols with aldehydes and ketones. The ready availability of chiral amino alcohols by reduction of amino acids enables the synthesis of chiral oxazolidines. Oxazolidines are prone to hydrolysis, the reverse of their syntheses.
3. Several oxazolidine derivatives occur naturally. Some occur as post-translational modifications of proteins. Others are components of alkaloids, a few of which are highly active against some tumors. Oxazolidines are used as moisture scavengers in polyurethane and other systems. Oxazolidines have even been researched and used as fuel additives.
4. In the context of leather tanning, oxazolidine compounds are used in chrome-free tanning methods as an alternative for those who are allergic to chrome-tanned leather or for applications where chrome is undesirable.