Pickling: Pickling is the process of treating the pelt with a solution of acid and salt t bring them to acidic condition. The deliming and bating pelts have to a pH about 8 and by pickling the pH is brought down to ( 2.5- 3.5 ) depending on the amount of acid used.
Objectives of Pickling: Pickling has two main objects in leather manufacturing,
3. To remove all types of swelling and plumping.
4. To produce softer type white thin pelt.
5. To acidify the pelt, the pH brings down from 7.8 to 2.8
6. To reduce the astringency of chrome tanning agent
7. To modify the fibre structure.
8. To modify the water content of the pelt.
9. To stop enzymatic action
10. For quick penetration of the tannin and light and uniform color of leather.
Objectives of Pickling: Pickling has two main objects in leather manufacturing,
- Conditioning the pelt ready for tanning specially in chrome tanning.
- Preservation of pelt for longer period prior to tanning.
3. To remove all types of swelling and plumping.
4. To produce softer type white thin pelt.
5. To acidify the pelt, the pH brings down from 7.8 to 2.8
6. To reduce the astringency of chrome tanning agent
7. To modify the fibre structure.
8. To modify the water content of the pelt.
9. To stop enzymatic action
10. For quick penetration of the tannin and light and uniform color of leather.
Factors influence the pickling operation/ Parameters of pickling
(ⅰ) Float:
To save water, reduce pollution and enable quicker penetration of the pickling acids the pickling systems used today are mainly short floats of 40 - 80% and about 20 - 30% in the case of low salt or salt free pickling system. Non-swelling acids like sulphopthalic acids, glycolic acid, sulphuric acid etc. are used.
(ⅱ) Duration:
Depending on the skin materials thickness of the skins and desired penetration pickling takes about 45 minutes to 1 and half hours.
(ⅲ) Temperature:
The best temperature range is 20-30° C. The temperature below 20°C should be avoided because of the high risk of low temperature swelling and temperature exceeding 30°C because of possible damage to the grain.
(ⅳ) pH value:
In the value of pH is ＞3.2, penetration of the chrome tanning agent is quicker, however larger quantities of basifying agents have to be added. But if the pH value is ＞3.8 - 4.0, superficial precipitation may occur. Especially with unmasked tanning agents, which produce stains and make complete penetration of the tannin move difficult.
(ⅴ) Salt concentreation:
Usually 6.5 -10° Be.
(ⅵ) Additives:
Formaldehyde, glutaraldehyde are used for chrome free leather.
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