Have ever wondered how your favorite leather wallet and bags looks so great and long-lasting? there must be some sort of chemicals used in the process of its making. This article will talk about the list of chemicals used in the tanning process.
The Tanning Process
The leather industry itself is an industry that focuses on the leather goods and its modification. one of the biggest leather tanning industry, also the one which uses the most chemicals, is the leather-tanning industry. The leather-tanning industry is an industry that processes raw skin (hides or skins) into finished skin or leather with a tanner. In the tanning process, all non-colagenic raw skin parts may react with the tanners. The skin becomes so different from the raw skin in organoleptic, physical, and chemical properties.
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In this leather industry, there are three basic stages, namely:
- Wet Processing. (Beam house).
- Tanning Process (tanning).
- Finishing.
Each of these stages consists of several kinds of processes, each process requires additional chemicals and generally requires a lot of water, depending on the type of raw skin used and the desired type of skin. In principle, in terms of the tanner used, then there are several kinds of tanning:
1. Vegetable Tanning
Tanning with vegetable tanning materials derived from plants containing tanning materials eg: acacia bark and sagawe. Finished leather such as leather luggage bag, sole leather, horse saddle leather, leather tire machine, leather belt etc.
2. Mineral tanning
Tanning with mineral tanning materials such as chrome tanning materials. Leather produced eg: leather box, leather jacket, glase leather, suede leather,
3. Tanning oil
Tanner tanner substance derived from shark oil or other fish, usually called crude oil. Leather produced for example: hairy skin tanned, leather chamois (skin to wipe the glass).
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Thus, here are some of the chemicals used in the tanning process:
1. Water (H 2 O)
Although water is only a supporting material, but the role of water is very important. It works as an intermediate or medium to deliver other chemicals into the skin.
2. Salt (NaCl)
It can absorb the liquid contained in the skin, so that moisture and salinity become balanced. Salt makes the bacteria become dry and eventually die, so there is no breeding bacteria that cause the skin to be damaged
3. Sodium Sulfide (Na2S)
Sodium sulfide serves to remove the hair. This can happen because the sulphide compound can break the sulphide bridge from the keratin or feather compounds so that the feathers fall out.
4. Chalk (Ca(OH) 2)
Lime function is to store oil or fat in the skin, lime duty can transport the remaining protein in the skin.
5. Formic acid and Sodium bisulfate
Formic acid and sodium bisulfate are used in the lime residue removal process that is still present in the skin during the feather removal process.
6. Sulfate oil
Fish oil with concentrated sulfuric acid sulfate will produce oil, its usefulness for liquoring or anointment in the process of tanning leather.
7. Sulfuric acid
The acidification process is used to stop the activation of the enzymes used in the erosion process.
8. Formaldehide (CH2O)
Formaldehyde reactions with amino acids that occur in skin proteins are able to change the properties of proteins so that the skin becomes more durable.
10. Cromosal B
Cromosal B is derived from Bayer patent product, cromosal B is used in the process of chrome tanning.
11. Compound SB
Compound SB comes from Hadson’s product, its usefulness is to increase the basis of the chrome tanning process.
12. Mimosa
Mimosas are derived from herbs and produced by hadson and bayer, their use as an ingredient for vegetable tannins containing tannin active substances. Indeed, that’s all chemicals used in the tanning process.
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The phases and process of the leather tanning
below are the different phases and process that the industry do to achieve the best quality leather and to know how the chemicals used in the tanning process works.
Phases of the wet process (Beam House):
1. Immersion
The purpose of this immersion is to restore the properties of raw skin to be like, soft, soft and so on. Raw skin is dried after weighing, then soaked in 800- 1000% water containing 1 gram / litre of wetting agent and antiseptic, molescal, cysmolan and so forth for 1- 2 days. Leather scraped on the inside and then rotated with waterless drum for 1/5 hours, so that the skin fibers become loose so easily enter the water and skin quickly become wet again.
Soaking work is sufficient if the skin becomes weak, soft, does not provide resistance in the handle or when the skin weight has become 220- 250% of the dry raw skin weight, which means the water content is near the fresh skin (60-65%). In the immersion process, the cause of contamination is residual disinfectant and impurities from the skin.
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2. Liming
The purpose of the calcification process is to.
- Eliminates the epidermis and feathers.
- Eliminates the sweat glands and the fat glands.
- Eliminate all substances that are not collagen active facing tanners.
In this calcification process causing pollution that remains of Ca (OH) 2, Na2S, substances that dissolve the skin and fur.
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3. Splitting
For the manufacture of rawhide leather tops thick (buffalo-cow) skin should be thinned according to the desired thickness with the skin split into multiple sheets and be machined sides (splinting Machine). For the manufacture of sole skin, not done the process of cleavage because it takes the entire thick skin.
4. Deliming
Since all tanning processes can be said to take place in an acidic environment the lime in the skin should be cleaned altogether. The remaining lime will disrupt the tanning process. For example:
- For vegetable tanned leather, lime will react with substances Calcium Tannat tanner become dark and hard to break easily lead to skin.
- For skin to be tanned chromium, it may even lead to chronic deposition of chromium hydroxide.
- Lime removal will use acid or salt asm, for example H2SO4, HCOOH, (NH4) 2SO4, Dekaltal etc.
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5. Erosion Protein (bating)
This process uses a protese enzyme to continue the removal of all non-collagen non-toxic substances in the limiting process, among others:
- The remains of root hairs and pigment.
- Remnants of unsaturated fat.
- A little or a lot of unnecessary skin substances means that a lighter boss’s skin requires a longer bating process.
6. Pickling
This process is done for the leather and chrome leather or synthetic and is not done for the leather or leather vegetable oil. The intention of acidification process to acidify the skin at pH 3-3 but skin skin in a state not swollen, so that the skin can adjust to the pH of tanning material that will be used later.
Besides acidification is also useful for:
- Removes the remaining lime.
- Eliminate the iron stains caused by Na2gS, in calcification to make the skin clean white.
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Phases of Treatment (Tanning)
At this stage of tanning there are several ways that can be done, namely:
1. Tanning Process
How to Tanning with Materials Vegetable Tanning
- How to Counter Current
Leather tanning immersed in a bath that contains a solution of vegetable extracts + 0.5 0. For hard and good sol leather usually after cooking skin with extract solution, tanning is continued with the way skin is planted and given concentrated extract solution for 2-5 weeks.
- The system is fast
Preceded by early tanning using 200% water, 3% extract of mimosa (Sintan) rotary drum 4 hour dive. Rotate and add the peyamak substance until cook to let stand 1 night in the drum.
How to Tannery with Mineral Tannery
- Using chrome tanner
The commonly used chrome tanner is the basic chromium sulphate form. The most widely used commercial tanners have a base of 33.33%. If the chrome tanner is to be fixed in the skin substance, then the base of the chromium fluid should be increased so as to increase the size of the chrome tanner particles.
- How to tanning with aluminium tanner (white alum).
The acidified skin is rotated by:
– 40-50% water.
– 10% of white alum.
– 1- 2% salt, rotate for 2-3 hours lu stacked for 1 night.
– The next day the skin is rotated again for ½ – 1 hour, then gigantung and dried in the humid air for 2-3 days. The skin is stretched by hand or machine until it is sufficiently weak.
How to Tanning with Tannery Oil
The skin to be oiled is usually pre-tanned with formalin. The skin is washed to remove excess formaldehyde then transform and reduce the water, playing with 20-30% fish oil, for 2-3 hours, stacked one next night dive hung and aired for around 7-10 days.
Signs of skin when ripe skin is quite elastic and also appear white. Skin that has been cooked washed with 1% Na2CO3 solution.
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2. Shaving
The cooked skin is stacked for 1-2 days then milked by machine or hand to remove most of the water, then plucked with a crude machine on the meat to adjust the thickness of the skin to flat. The skin is weighed to determine the amount of chemicals that will be required for subsequent processes, followed by washing with ½ hour running water.
3. Bleaching
Only worked for vegetable tanned leather and organic acids normally used with the aim of:
- Eliminate bsixek from engine.
- Lowering the pH of the skin, which means ease klit color.
How to do the bleaching process, skin rotated with 150-2005 water warm (36- 40 0 C). 0.5-1.0% oxalic acid for ½- 1 hour.
4. Neutralization (Neutralizing)
Only done for chrome leather. in its surrounding, chrome leather is very acidic (pH 3-4) skin should be neutralized again so as not to interfere in the next process. Neutralization usually uses alkali salts such as NaHCO3, Neutrigan etc.
5. Dyeing
The purpose of basic dyeing is to give the basic colour on the skin so that the use of paint cap will not be too thick so that the paint is not easily broken.
Basic paint used for skin there are 3 kinds:
- Cat direct, for skin chrome tanned.
- Cat acid, for chrome and vegetable tanned leather.
- Cat base, for vegetable leather.
6. Massage
The purpose of the petroleum process on the skin, among others, as follows:
- For lubricating skin ag leather fibers become resistant pull and hold shakes.
- Keep skin fibers from sticking to one another.
- Make skin waterproof.
How do anointment, the skin after painted base, played for ½ – 1 hour by 150% – 200% water 40 to 60 0 C, 4-15% oil emulsion. Added 0.2- 0.5% formic acid to break the oil emulsion. Oil is left in the skin and the water is removed. Leather stacked on the horses for 1 night.
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7. Lubrication (oiling)
Lubrication is only done for vegetable leather sole leather. The purpose of lubrication is to keep the tanning material is not out of the skin surface before the skin becomes dry, resulting in the skin to darken and break easily when bent nerfnya ..
How to lubrication, sole skin part of the water is milked then the skin is treated with a mixture:
- 1 part paraffin oil.
- 1 part oil of sulphonir.
- 3 parts water.
The skin is thin but flattened both surfaces, then dried.
8. Drying
The skin is watered with a machine or hand then dried. This process aims to stop all chemical reactions in the skin. Water content in the skin to be 3-14%.
9. Humidity
The skin after being dried is allowed to be 1-3 days in regular air so that the skin adjusts to the humidity of the surrounding air. Skin then moistened sawdust grown in water containing 50 to 55% during the first night, skin will take water and get wet evenly. The skin is then removed and cleaned powder.
10. Stretching and Time
Skin stretched by hand or stretch machine. The purpose of this stretch is to pull the skin until it reaches the limit of its elongation, so that if made craft items are not too elastic, do not change the shape of the size.
11. Final Stage of Completion (Finishing)
The final solution aims to beautify the appearance of the finished skin, strengthen the base colour of the skin, polish, smooth the appearance of the surface and cover the defects or uneven basic paint colour.
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This article has covered all you need to know about the leather-tanning industry. It also talks about the list of chemicals used in the tanning process, which hopefully will come handy if some of you would like to start your own leather business. remember to always put extra care to your leather goods for its a very delicate and sensitive material.