Thedeliming operation inleather processing is a drum/paddle or pit based operation where two main objectives are met:[1]
Deliming operations of cattle hides usually last two hours and are generally associated with the alkaline phase ofbeamhouse operations. The progress of deliming in pelts is monitored by the checking ofpH values of process liquors and in the cutting of a pelt cross-section.Phenolphthalein is used to monitor deliming pelt cross-sectional progress.
The deliming process can be done with acids that can be rapid in their pH adjustment. Buffering salts like ammonium salts predominated the 20th century.Ammonium sulfate andammonium chloride can be used as deliming agents and they follow the following chemistry:
The ammonium ion is then free to penetrate the pelt cross-section and further ionise to act as an acid:
The protons can then serve two functions, namely toprotonate basic groups of the collagen andneutralize solution alkali chemicals.
Other weak acids can be used such asboric acid,acetic acid,formic acid,lactic acid,phosphoric acid andcarbonic acid. Carbonic acid is used in a deliming process calledcarbon dioxide deliming. Strong acids such ashydrochloric acid andsulfuric acid can also be used but their use is limited.
