Deliming
Encyclopedia
The deliming operation in leather
processing is a drum/paddle or pit based operation where two main objectives are met:
Deliming operations of cattle hides usually last 2 hours and are generally associated with the alkaline phase of beamhouse operations. The progress of deliming in pelts is monitored by the checking of pH values of process liquors and in the cutting of a pelt cross-section. Phenolphthalein is used to monitor deliming pelt cross-sectional progress.
HI
and ammonium chloride
can be used as deliming agents and they follow the following chemistry:
SO4 → NH4+ (ammonium
) + SO42- (sulfate
)
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 to protonate
basic groups of the collagen and neutralize
solution alkali chemicals.
Other weak acids can be used such as boric acid. acetic, formic, lactic acid, Phosphoric Acid and carbonic acid. Carbonic acid is used in a deliming process called carbon dioxide deliming. Strong acids such as hydrochloric acid and sulfuric acid can also be used but their use is limited.
Leather
Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...
processing is a drum/paddle or pit based operation where two main objectives are met:
- Removal of alkaliAlkaliIn chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...
from the pelt and the consequent deswelling of the fibres. - Lowering of the liquor pH to the values used in the bating process.
Deliming operations of cattle hides usually last 2 hours and are generally associated with the alkaline phase of beamhouse operations. The progress of deliming in pelts is monitored by the checking of pH values of process liquors and in the cutting of a pelt cross-section. Phenolphthalein is used to monitor deliming pelt cross-sectional progress.
Removal of pelt alkali and deswelling
- As an acid is added it lowers the pH value of the internal pelt solution. This neutralizesNeutralizationIn chemistry, neutralization, or neutralisation is a chemical reaction in which an acid and a base react to form a salt. Water is frequently, but not necessarily, produced as well. Neutralizations with Arrhenius acids and bases always produce water:Y and X represent a monovalent cation and anion...
the solution alkalinity. The lowering of the pH results in rapid protonationProtonationIn chemistry, protonation is the addition of a proton to an atom, molecule, or ion. Some classic examples include*the protonation of water by sulfuric acid:*the protonation of isobutene in the formation of a carbocation:2C=CH2 + HBF4 → 3C+ + BF4−*the protonation of ammonia in the...
of the collagen basic groups.
HI
Lowering of liquor pH
- The acid present in the deliming agents neutralizes the process liquor pH. Typical values after effective, thorough deliming will range from 6 to 9. Ammonium salt deliming pH values should be pH 8 to 9.
Deliming types
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 sulfateAmmonium sulfate
Ammonium sulfate , 2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen as ammonium cations, and 24% sulfur as sulfate anions...
and ammonium chloride
Ammonium chloride
Ammonium chloride NH4Cl is an inorganic compound with the formula NH4Cl. It is a white crystalline salt that is highly soluble in water. Solutions of ammonium chloride are mildly acidic. Sal ammoniac is a name of natural, mineralogical form of ammonium chloride...
can be used as deliming agents and they follow the following chemistry:
SO4 → NH4+ (ammonium
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
) + SO42- (sulfate
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
)
The ammonium ion is then free to penetrate the pelt cross-section and further ionise to act as an acid:
- NH4+ (ammoniumAmmoniumThe ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
) + H2O → NH3 (ammoniaAmmoniaAmmonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
) + H3O+ (hydroniumHydroniumIn chemistry, a hydronium ion is the cation , a type of oxonium ion produced by protonation of water. This cation is often used to represent the nature of the proton in aqueous solution, where the proton is highly solvated...
)
The protons can then serve two functions, namely to protonate
Protonation
In chemistry, protonation is the addition of a proton to an atom, molecule, or ion. Some classic examples include*the protonation of water by sulfuric acid:*the protonation of isobutene in the formation of a carbocation:2C=CH2 + HBF4 → 3C+ + BF4−*the protonation of ammonia in the...
basic groups of the collagen and neutralize
Neutralization
In chemistry, neutralization, or neutralisation is a chemical reaction in which an acid and a base react to form a salt. Water is frequently, but not necessarily, produced as well. Neutralizations with Arrhenius acids and bases always produce water:Y and X represent a monovalent cation and anion...
solution alkali chemicals.
Other weak acids can be used such as boric acid. acetic, formic, lactic acid, Phosphoric Acid and carbonic acid. Carbonic acid is used in a deliming process called carbon dioxide deliming. Strong acids such as hydrochloric acid and sulfuric acid can also be used but their use is limited.