Influencing factors of neutralization and Possible defects of neutralization

Typical method of Neutralization

Water - 100% at ntp

Napthaline based syntan (S. NG) - 2.5%

Sodium formate - 1%

Run 30 minutes

 pH - 4.5

Bi-Carb - 0.5%

Run 30 minutes

pH - 4.7 - 4.8

wash/Drain

Influencing factors of neutralization

• Intensity

The outer  zones are neutralized in the higher pH range but the inner zones are only slightly  neutralized. However, Leather which tend to develop a loose grain should always be  treated  in the lower pH range.

• Duration

About  30  min  to 2 hours depending on the thickness  of leather  and  texture, type of neutralization agent and type of leather to be produced.

• Float length:

With float coefficient of 0.5-2 depending on type of leather  thickness and type of vessel. A washing or rinsing bath should take place after deacidification  in order to remove the salts that have formed.

• Temperature

Carried out n a range of 30-40 ^o C < 38^o C if sodium hydrogen carbonate is used.

Possible defects of neutralization

• Inadequate deacidification

If the middle zone of thee cross section remains unneutralized problems may arise in subsequent processing.

1. Astringent (Tanning) retanning agents diffuse only with difficulty into this zone.
2. Fat emulsions crack in this zone and cause smudging (dirty) and fat stains.
3.  The free acid in the leather migrates into the outer zone, causing corrosion at metal parts of final products. And Fatty spew may also happen to a greater extent.

• Over neutralization

Over neutralization Results in detanning of the grain  zone and thus in loose grain, strawy, brittle grain or in the unfavorable cases even crankiness of the grain. Furthermore, may cause of uneven, pale and thin dying.