Types of Fatliquors Saponification Value • Saponification value (or "saponification number"/"Koettstorfer number“ also referred to as "sap" in short) represents the number of milligrams of potassium hydroxide required to saponify 1g of fat under the conditions specified. • It is a measure of the average molecular weight (or chain length) of all the fatty acids present. • As most of the mass of a fat/tri-ester is in the fatty acids, it allows for comparison of the average fatty acid chain length. • The long chain fatty acids found in fats have a low saponification value because they have a relatively fewer number of carboxylic functional groups per unit mass of the fat as compared to short chain fatty acids. • If more moles of base are required to saponify N grams of fat then there are more moles of the fat and the chain lengths are relatively small, given the following relation: • Number of moles = mass of oil/relative atomic mass Iodine Value • The iodine value (or "iodine adsorption value" or "iodine number" or "iodine index") in chemistry is the mass of iodine in grams that is consumed by 100 grams of a chemical substance. • Iodine numbers are often used to determine the amount of unsaturation in fatty acids. • This unsaturation is in the form of double bonds, which react with iodine compounds. • The higher the iodine number, the more C=C bonds are present in the fat. • It can be seen from the table that coconut oil is very saturated, which means it is good for making soap. • On the other hand, linseed oil is highly unsaturated, which makes it a drying oil, well suited for making oil paints. Acid Value • Acid value (or "neutralization number" or "acid number" or "acidity") is the mass of potassium hydroxide (KOH) in milligrams that is required to neutralize one gram of chemical substance. • The acid number is a measure of the amount of carboxylic acid groups in a chemical compound, such as a fatty acid, or in a mixture of compounds. • In a typical procedure, a known amount of sample dissolved in organic solvent (often isopropanol), is titrated with a solution of potassium hydroxide(KOH) with known concentration and with phenolphthalein as a color indicator. Hydroxyl Value • Hydroxyl value is defined as the number of milligrams of potassium hydroxide required to neutralize the acetic acid taken up on acetylation of one gram of a chemical substance that contains free hydroxyl groups. • Hydroxyl value is a measure of the content of free hydroxyl groups in a chemical substance, usually expressed in units of the mass of potassium hydroxide (KOH) in milligrams equivalent to the hydroxyl content of one gram of the chemical substance. • The analytical method used to determine hydroxyl value traditionally involves acetylation of the free hydroxyl groups of the substance with acetic anhydride in pyridine solvent. • After completion of the reaction, water is added, and the remaining unreacted acetic anhydride is converted to acetic acid and measured by titration with potassium hydroxide. Objective of Fatliquoring • Softening • To prevent the fibre structure resticking during drying • Softening • Lubrication • Reduce the friction between the fibres The Concept of Fatliquoring • The charge on the leather (neutralization) can affect fatliquoring effectiveness (charge of the leather and fatliquor should be same for penetration) • Penetrating power depends on emulsion stability • Particle size distribution an emulsion is a variable that influences stability and penetration • Sulfonation (to make partially sulfited oils) imparts more stability than sulfation (to make partially sulfated oils) • Softness depends on the ratio of emulsifier fraction to neutral oil fractions • Softening is influenced by the viscosity and interfacial tension of oils Mechanism of Fatliquoring • The neutral oils is transported into the pelt as an oil-water emulsion • The emulsifying agent interacts with the leather, reducing or eliminating its emulsifying power • The neutral oil is deposited over the fibre structure- the level of hierarchy of structure depends on the degree of penetration • The water is removed by drying, allowing the neutral oil to follow over the fibre structure Factors Affecting Lubrication • Distribution • Diffusion • pH • Particle size • Viscosity (higher the viscous better the lubrication) Factors Affecting the Application of Fatliquor • High Temperature – Heating the fatliquor to the same temperature as the water, allows the oil to break up into small drops due to the decreased viscosity (practically 60°C-especially for vegetable tanned leathers) • Mechanical Action – For mixing the fatliquor into water, mechanical action must be maximised, because this the way the oil is dispersed into drops (motorised stirrer, broom handle) • Water – Formation of water in oil emulsion Particle Size • The particle size of the emulsion is determined by the degree to which the oil is converted into the sulfo derivative • The bigger the sulfo to neutral oil ratio the more solubilised the oil becomes and the particle size is reduced • Most fat liquor formulations contain about 50% neutral oil, 25% sulfo fraction and 25% water Difference between Sulfated and Sulfited Fatliquors Sulfated Sulfited Stability Less More Reactive More Less Penetration Less More Affinity More Less SO2-4 SO32- strength strength Stress softness Chemical softness softness softness Anionic Fatliquors-Sulfated • For sulfating the oil must be unsaturated with a minimum iodine value of 70 • The iodine values is defined as the number of grams of iodine absorbed by 100 g of oil or fat • Oils that have used are castor, neatsfoot, soya, groundnut, cod (sperm oil) Preparation of Sulfated fatliquors • Conc sulfuric acid 10-20% added slowly to the oil with constant stirring • The temperature of the exothermic reaction must be controlled to less than 28C (otherwise the oil can char results in darkening and the triglyceride oil may be hydrolysed to release the fatty acids • The release of fatty acids leads to the formation of “spue” when the long chain carboxylic acids migrate from the internal structure of the leather to the grain surface, visible as white efflorescence • Altenatively mixture of sulfuric and phosphoric acid (0.8:1.0)-this process is expensive but fast • Brine wash: Excess free acid is removed by washing the partially sulfate oil with brine, which also separated the oil fraction from the aqueous fraction • Brine is used to avoid creating an emulsion which would happen if only water is used • Alternatively, sodium sulfate, ammonium chloride or sulfate could be used • Neutralization: Bound and free acids are neutralised with alkali Sulfating Reactions Properties of Sulfation • Anionic charges increases, hence greater affinity for cationic leather • Lubrication decreases due to the lower concentration of neutral oil • Emulsion particle size decreases • Stability of the emulsion to coagulation by acid or metal salts increases • At high sulfation, the oil functions more like wetting agent than lubricant, hence the leather becomes more hyrophilic • The leather becomes looser in terms of break, possibly due to the damaging effect of the sulfate species on collagen • Hydrolysing the oil to create free fatty acids increases thereby creating the possibility of chrome soaps, fatty acid spue, poor wetting back, uneven dyeing and poor finish adhesion • Low level of sulfation: – Low stability of the emulsion to coagulating by acids or metal salts. – Typically used to lubricate the outer surfaces – Drum oiling of vegetable tanned leather • Medium level of sulfation – More stable to coagulation, therefore greater potential for penetration – Used for surface neutralized chrome leather • High level of sulfation – Used for complete neutralized chrome leather for gloving, clothing, softee leathers Sulfited Oils • The requirement for the oil is unsaturation for sulfating • Preparation • Sulfitation/oxidation – Air is blown through a mixture of 100 parts of oil (COD) and 50 parts of sodium bisulfite solution, with stirring at 60-80°C – Alternatively, hydrogen peroxide may be used instead of air • Brine wash: Washing with brine remove axcess sodium bisulfite – There is no pH adjsutment required, due to the use of bisulfite rather sulfur dioxide or sulfurous acid Properties of Sulfited Fatliquors • No charring or darkening • Higher emulsion stability to acids, hard water salts, metal ions (Al, Cr) due to the presence of sulfonate and hydroxysulfonate groups and the low level of free fatty acids or soaps, • The fatliquor may be formulated with non-ionic detergent, to increase emulsion stability, to promote better penetration, to make the leather softer and fuller • There is a danger of giving the leather loose break • Softness and strength for all leathers by deep penetration • Woolskins and furskins in mineral tanning baths • In shrunken grain production, to minimise loss of tensile strength in the acidic tanning bath Soap Fatliquors • Raw oil (neatsfoot oil) is emulsified with soft soap e.g. potassium oleate • The emulsions have a large particle size, due to their tendency to have low stability to water hardness and acid • The formulation typically has pH 8. • At pH less than 6, the soap is increasingly converted into free fatty acid which does not act as an emulsifier and so the emulsion coagulates • The uses of soap fatliquors are limited to the low emulsion stability • They have traditionally been used for surface fatliquoring calfskins for shoe upper and formaldehyde tanned sheepskins for gloving leather Cationic Fatliquors • Raw oil is emulsified with a cationic agent • The hydrophilic group is typically straight chain, aliphatic C10 to C18 • Low affinity for cationic charged leathers e.g. chrome tanned leather • High affinity for anionic charged leathers e.g. vegetable tanned for lubricating the outer layers • Incompatible with anionic reagents e.g. anionic dyes, fatliquors, retans • High stability to acid, but unstable to alkali • Good stability to metal • Poor shelf life • Emulsion stability can be improved by formulating with non-ionic detergents (e.g. alkyl ethylene oxide condensates) Non-ionic fatliquors • These fatliquors are emulsified with compounds made by condensing ethylene oxide in the presence of an aliphatic alcohol CnH2n+1-(OCH2CH2)x OH • The properties of the emulsifying agent depend on the value of n, the aliphatic carbon chain length and the value of x, the degree of polymerization of ethylene oxide • These compounds are not very good emulsifying agents because the hydrophilic end, the ethylene oxide chain, does not have a high affinity for water relying on hydrogen bonding via the ether oxygens Properties • High stability to metal ions, salts, hard water and wide pH tolerance • Miscible with cationic and anionic reagents • Little or no affinity for anionic or cationic charged leathers • The non-ionic emulsifier increases the hydrophobicity of leathers • Used for fatliquoring Zr and Al tanned leathers which are highly cationic charged • As a crusting fatliquor for suedes splits i.e. merely to prevent fibre resticking on drying to aid rewetting • May be formulated with anionic or cationic fatliquors to improve stability Multicharged Fatliquors • These fatliquors are formulations of non-ionic, anionic and cationic fatliquors in which the presence of the non-ionic species prevents precipitation of the anionic and cationic species • They are more stable to a wider pH range than singly charged fatliquors and hence more stable to variations in leather charge • The proportions of the constituents can be varied depending on the leather properties required – Depth of penetration – Surface lubrication – Ease removal from paste drying plates Amphoteric Fatliquors • Raw oil is emulsified with an amphoteric reagent i.e. one containing both acidic and basic groups • The point of neutrality, the isoelectric point, depends on the numbers of acidic and basic groups • A typical IEP for this type of structure is pH 5 • At pH>5, the emulsifier is negatively charged • At pH<5, the emulsifier is positively charged • The choice of pH of the fatliquors depends on the charge of the leather and the requirement of surface reaction or penetration Solvent Fatliquors • These are typically anionic fatliquors, containing a high boiling point, polar petroleum solvent with minimum flash point 60°C and preferably odorless • The function of the solvent is to replace the water as it is removed during drying • With lesser affinity for the leather than the polar triglyceride oils, it can spread further and deeper