Leather and Textile Uses

10Leather and Textile Uses

of Fats and Oils

Paul Kronick and Y.K. Kamath

1. GENERAL USE OF FATS AND OILS IN LEATHER

Although most of the 20-odd steps of leathermaking use fats and oils as detergents,

by far the majority of these materials are used as additives to soften leather. Oils are

usually applied in aqueous emulsions while the leather is still wet from tanning.

Several oils are conventionally used, often made self-emulsifying by partial sulfa-

tion or sulfonation by treating with sulfuric acid. These oils are called fatliquors.

Heavy grades of leather are also softened by the addition of neat melted fat after the

leather has been dried. This hot stuffing process involves softening the leather by

milling it in the presence of the warm molten fat. Although the milling by itself is

sufficient to soften the leather, the fat dispersed among the fibers allows the leather

to remain soft if it is dampened and dried again. The amount of these materials that

are used annually has not been compiled, but it is over 20 million pounds per year.

Aside from softening, a smaller amount of oils and fats as detergents are also

used in preliminary cleaning of the raw skins and hides; to suspend lime particles,

buffer the alkaline solution that removes the epidermis and hair, and suspend these

materials when they come off; to remove grease; to tan certain types of leather; and

to control the penetration of dyes.

Baileys Industrial Oil and Fat Products, Sixth Edition, Six Volume Set.Edited by Fereidoon Shahidi. Copyright # 2005 John Wiley & Sons, Inc.

353

2. SOFTENING OF LEATHER

2.1. Drying Skin or Hide

The skin or hide of an animal is an organ whose complex structure can be simplified

for purposes of analysis into two layers: a thin (

There are other drawbacks to conventionally fatliquored leather. When it is used

in automobile upholstery, it is often heated by sunlight in the unstirred air of the

parked vehicle to temperatures high enough to sublime or distill the fat or oil

onto the windows. This deposited material is troublesome to remove and causes

some lots of leather to be rejected by the automobile manufacturer. Another draw-

back is flammability, which can be obviated by a judicious choice of oil in the

emulsion. Further, the oil sometimes tends to migrate to the surface of the leather,

causing an unpleasant film, or spew, to form. Under some conditions it can cause

separation of the finish or coating from the leather substratum.

3. SOFTENING WITH FATLIQUOR

3.1. Physical Mechanism

It is not clear exactly why oil, added as a fatliquor emulsion when the leather is wet,

causes the leather to dry to a soft product. The most cogent hypothesis derives from

the observations of von Fuchs (1), who noticed that the oil could be removed from

the dried leather with solvent without causing it to become stiff. One concludes that

the fatliquor prevents the fibers from sticking together during the drying but after-

ward is not needed. There is uncertainty, however, about what comprises a fiber. We

have evidence that it is a bundle of the unitary 100-nm collagen fibrils, perhaps

10 mm in diameter (2) (Figure 1). The interaction of collagen and sulfated oilshas been studied (3).

The emulsion of a fatliquor should not be too stable. The leathermaker wants to

control its depth of penetration into the leather by the tendency of the surfactant to

adsorb to the protein of the hide. This adsorption depletes the micelles of surfactant,

causing the emulsion to break before it permeates the interior of the hide, releasing

the oil somewhat superficially. The untreated interior thereby retains its stiffness,

but with only a small mechanical moment. The product is then firm but resilient

(not like cardboard). The released oil, with the surfactant tightly bound to the fibers,

also resists being washed out of the leather by water. Suede leather, on the other

hand, requires full penetration of the fatliquor and, therefore, an emulsifier that

does not bind tightly to the protein.

As noted, when a leather is dried without fatliquor, the fibrils adhere and form

irregular fiber bundles with a linear cross-sectional dimension of about 100 mm.When the leather is still wet in the fatliquoring step, however, the emulsion is dis-

tributed among the fibrils. As the fatliquored leather dries, the fibrils still tend to

adhere to each other but with weakened adhesive force because of the presence

of the oil. We believe that the lateral forces, due to shrinkage of the bundles of

fibrils as water evaporates, causes them to rupture into the 10-mm fibers. What isimportant is that the eventual softness of the leather would depend on the topology

of the fragments rather than directly on the rheological or chemical properties of the

oil. The same geometric effect should be achieved by mechanical milling of the

dried leather in the presence of grease or oil, as in hot stuffing.

SOFTENING WITH FATLIQUOR 355

Figure 1. Effect of fatliquor on the structure of fibers in leather after drying. (Top) The 100-mmfiber bundles in the leather dried without fatliquor are intact. (Bottom) They are broken into

fragments when dried with fatliquor, making the leather compliant. Bar 10 mm.

356 LEATHER AND TEXTILE USES OF FATS AND OILS

3.2. Components and Formulation

In formulating a fatliquor, one is concerned with the chemical interactions with the

substance of leather fibers, the dyes, and the tanning agent, mostly hydrated chro-

mic oxides. Mostly, these interact with the emulsifier. With the likely introduction

of substitutes for chromium, such as aluminum or vanadium, the reactions of the

emulsifiers will have to be adjusted. The surface charges of the new inorganic mate-

rials will be different from that of chromium, affecting the tendencies of various

emulsions to coalesce. This chemistry can be adjusted by changes in pH and

perhaps will lead to other requirements on lengths of the fatty chains.

The neutral portion of the fatliquor can be almost any oil. Triglycerides are most

common, but wool grease and mineral oil are also used. The oil is chosen to be

nonvolatile (for permanence and to prevent the fogging effect described above),

minimally soluble in water, and liquid at about 40C (and so emulsifiable). Longercarbon chains (above 14) are better. This has been attributed to retention of the oil

among, rather than within, the fibrils (4). Mixtures of different oils are usually used.

Esthetic properties are resistance to discoloration and hardening and lack of unplea-

sant odor. An important chemical property for an oil is that it should be easily sul-

fonated, sulfated, or oxidized so that it can be the starting material for its own

emulsifier. In fact, the most commonly used fatliquors are partially sulfonated

oils, adjusted to the correct degree of sulf(on)ate by addition of more base oil.

One of the most common oils is castor oil, which can be both sulfated and sulfo-

nated. Others commonly used are fish oils, especially from cod; neatsfoot oil,

rendered from the bones of cattle; rice bran oil; soy oil; coconut oil; linseed oil;

and rapeseed oil.

Sulf(on)ation is not the only method used to prepare fatliquor from oil. Simple

oxidation of fish oil with air or nitric acid is another, again causing a portion of the

oil to become amphipathic. The products are often referred to as moellons or

degras.

Leather softeners that are technically satisfactory can also be made from jojoba

oil (5) and even butadiene rubber (6). Waste animal fat obtained from scraping the

flesh from the fresh hide, before the leathermaking process is begun, can be used

after sulfation or ethoxylation.

Although neat fats and greases can be added to the leather after it has been dried,

oils must be emulsified if they are to be used during the wet end of the leathermak-

ing process. Fortunately, most oils can usually be sulf(on)ated or oxidized easily,

making them amphiphilic; the usual degree is 50% of the triglyceride molecules,

so that an oily emulsion can be prepared with excess neutral oil. By artful formula-

tion, the properties of the emulsion are carefully controlled with regard to the visc-

osity and size of the particles and their affinity for the leather fibers and the chromic

oxide tanning agent. These properties affect the ability of the emulsion particles to

penetrate the leather. Castor oil, unlike fish oil, yields the sulfated as well as the

sulfonated product when it is treated with sulfuric acid; its emulsions have a greater

tendency to break in the presence of electrolytes. When used as fatliquors, its emul-

sions tend to break in the superficial regions of the leather, releasing their oils there

SOFTENING WITH FATLIQUOR 357

rather than deeper inside. This allows the leathermaker a means to control deposi-

tion of oil stratigraphically. As already described, this permits adjustment of the

mechanical properties and leather esthetics.

A balance of properties of the product can be obtained by formulations based on

natural oils to which sulf(on)ated oils are added. The mixtures can then be opti-

mized statistically with respect to the mechanical properties (7).

Aside from sulf(on)ates, carboxylates (soaps) and phosphates can also be used in

the surfactant. An emulsion based on alkyl phosphate emulsifier is reported to give

an especially soft leather (8). Phosphates are reviewed by Fricke and Haeussler (9).

There is also experience with sulfosuccinic acid amides (10) and other surfactant

formers.

Before the growth of organic chemistry and techniques for sulfonating fats and

oils, tanners emulsified oils for leather softeners with soap and protective colloids.

These mixtures were prepared as water-in-oil emulsions, called mayonnaise in

the trade and added to the water in the drum with the leather. They are still used

but not nearly as frequently as sulf(on)ated oils. On the other hand, salts of naphthe-

nic acid are used with hydrocarbon oils (e.g., 11) to make the reverse forms of

these.

Egg yolk was once commonly used, probably because of its lecithin, to emulsify

oils in leathermaking. Lecithin itself is effective as a fatliquor emulsifier (12). Non-

ionic emulsifiers have the advantage of forming emulsions that are stable to elec-

trolytes, so they do not interact electrostatically with the chromium or aluminum

tanning ions. Nonionicanionic combinations (e.g., 1% nonionic99% anionic)

are now used to suppress the accumulation of fatty deposits or extrusions at the

surface of the leather. These systems are under active development.

Cationic surfactants are used mainly to treat the surface of the leather, making it

waxy. These are typically C-16 to C-18 alkylbenzyl quaternary ammonium com-

pounds (e.g., 13). Also effective are cationic fatliquors from aminated and quater-

nized castor oil; other vegetable oils are also used (14).

Oils are frequently chlorinated in addition to being sulf(on)ated or oxidized. The

reaction is extended to both the neutral oil and the surfactant, to make them less

volatile and more flame resistant. Fish oil is the usual substrate for this treatment,

but it has been extended to fatliquor from mineral oil and paraffin wax (e.g., 15).

4. OTHER SOFTENING MATERIALS

Leather is also softened, after it is dried, by the addition of grease at temperatures at

which it is fluid. These stuffing compounds are made from wool grease or high-

melting (230266C, 110130F) mixtures of mineral waxes and fatty acids. Forreasons that are not understood, they must be used at much higher levels than fatli-

quorsusually about 30% of the weight of the leather, instead of 1015%.

The development of new softening materials is considered to be a high priority

by the international leather industry. Research to find materials that give softer

leather for garments without the drawbacks of greasy feel, odor, and cost that attend


increasing the amounts used is proceeding in many laboratories in many countries

(16). Research on leather softeners is driven by the same considerations every-

where: the need to find new sources of oils and greases that are of constant quality,

inexpensive, convertible to emulsifiers, color-fast, and preferably colorless, odor-

less, fixed well in the leather, and ecologically acceptable.

Examples of such developments are sulfation of transesterified rapeseed oil

phosphatides (17) and the use of bicontinuous microemulsions obtained by the

addition of aliphatic alcohols (18, 19). The stability of these systems promises to

be more reliable than those in present use. Oils from wood (tall oil) can be sulfo-

nated for self-emulsifying fatliquors (20). Polymerizable oils have been used in

fatliquors (21). We expect more progress on the use of high polymers, such as

the already commercial alkyl acrylate esters developed by Hodder et al. (2224),

and material based on elastomers (6). We anticipate the development of novel sys-

tems to be encouraged by the demand for leather in washable garments and auto-

mobile upholstery.

5. EVALUATING EFFECTS OF FAT IN LEATHER

The amount of residual natural fat and added fatliquor is usually determined by

chemically analyzing hexane extracts, following ASTM Standard D-3495 (25).

The leather is extracted in a Soxhlet apparatus and the amount dissolved in the

hexane is determined gravimetrically. Analyses for specific fatty components are

described in (26).

Fatliquor affects mostly the mechanical properties, measured also by a collection

of ASTM methods given in (25). In addition, the sounds emitted by leather when it

is deformed are greatly suppressed by the presence of fat, supporting a method of

assay by means of the acoustic emission test (27).

6. GENERAL USE OF FATS AND OIL FOR TEXTILES

Consumer textiles are produced from natural and synthetic fibers. To be converted

into useful goods, such as apparel and home furnishings, fibers have to go through a

series of processes such as spinning, weaving, and dyeing. The economics of pro-

duction of these materials demand relatively high speeds of processing. Under these

conditions, fibers and yarns coming into contact with other surfaces undergo fric-

tional heating and abrasive damage and often break, impairing the efficiency of the

process. Sticking of the abraded material to the processing machinery makes this

situation worse.

In addition to abrasion, triboelectric charging is a serious problem in the produc-

tion and processing of synthetic fibers. Charged fibers, because of interfiber repul-

sion, do not form a coherent yarn, and it is difficult to wind such yarns on bobbins to

be transferred to other locations for further processing. To overcome these

problems, combinations of oils, fats, and their derivatives are used extensively as

GENERAL USE OF FATS AND OIL FOR TEXTILES 359

lubricants and antistatic agents, known in the trade as spin finishes. Mechanisms of

their action in the fiber and yarn-forming processes are discussed. Oils and fats in

the form of their surface-active derivatives are also used in scouring, dyeing, and

softening. It is important to note that synthetic oils have replaced most of the nat-

ural oils in the processing of textiles. Natural oils are used mainly as their fatty acid

derivatives.

7. COMMON TEXTILE FIBERS

With the exception of silk, which is extruded as a continuous filament by the silk

worm, most natural fibers, such as cotton, occur in the form of short filaments called

staple fibers. Synthetic fibers like nylon, polyester, and poly(propylene), are melt

spun (28) in the form of continuous filaments. High-melting acrylic fibers, on the

other hand, are produced by a process known as wet spinning (29) in which fibers

are regenerated by precipitating the polymer in the fiber form in a suitable nonsol-

vent. Some of the less common fibers are sometimes produced by solution spinning,

in which fibers are regenerated by evaporating the solvent. All manufactured fibers

can be converted into the staple form by cutting the continuous filaments to the

required length.

8. PROCESSING OF FIBERS

8.1. Spinning

In the textile trade, spinning refers to the production of yearns by twisting staple

fibers, as well as the production of yarns from synthetic polymers by the extrusion

of continuous filaments through spinnerettes. In the spinning of staple fibers, yarns

are produced at relatively high speeds by the alignment, drawing, and twisting of

fibers in automatic machines. Stout (30) has studied the role of lubrication in spin-

ning of staple fibers. Open-end spinning (31), used mainly for short staple fibers, is

a more recent spinning method that eliminates the intermediate step of fiber align-

ment. In open-end spinning, fibers are brought to a twisting location in a chamber

by air turbulence. The stability and the efficiency of this process depends on good

fiber cohesion, which prevents yarn breakage. Treating the staple fiber with an oil

promotes fiber cohesion, in addition to lubrication against hard surfaces of the

processing machines to prevent abrasive damage.

Melt or solution spinning of synthetic fibers is a marvel of modern technology.

Fiber lubrication, which is of the utmost importance in this high-speed process, is

achieved by the application of spin finisha combination of oils and surfactants. A

typical spin line for the production of polyester staple fiber is shown schematically

in Figure 2. The number of filaments, which can vary from tens to thousands, come

into contact with various parts of the machinery, some of which are heated for prop-

er fiber modification. To replenish the lost finish and to ensure adequate lubrication,


the finish is applied more than once at strategic locations along the spin line. Spin

finishes are also applied to solution spun fibers, after the regeneration step. As these

finishes protect the fibers in subsequent processing, an even distribution at low add-

on is an important requirement. Methods of determining the distribution of finishes

on fibers and yarns have been developed (32).

8.2. Texturing

As a result of crimp, natural fibers form relatively bulky yarns. These produce soft

fabrics that are preferred by the consumer. Texturing is a process that imparts bulk

to melt-spun continuous filament yarns, by introducing crimp in the individual fila-

ments. False-twist friction texturing is one such process (33). The heated yarn is

passed between ceramic friction discs rotating in opposite directions, which intro-

duces a temporary twist in the yarn. The twist is undone as the yarn leaves the discs,

leaving a permanent crimp in the individual filaments. The mechanism of texturing

has been presented (34). Application of a proper finish is critical for the success of

this process in which the interfiber friction should be low and the fiberdisc friction

should be high. Formulating a finish that achieves these two opposing requirements

at a high temperature without degradation is a challenge (35). The effect of

volatilization of a lubricant on yarn friction has been investigated (36). The nature

of the finish plays an important role in the uniformity of the textured yarn and con-

sequently in the quality of the fabric.

8.3. Weaving and Knitting

Solid fats, like tallow, are sometimes used as lubricants on sized warp yarns in shut-

tle looms. Without such lubricants, warp yarns can unravel and break as a result of

the abrasion of the size by the shuttle and the heddle. This would introduce defects

in the fabric and will also affect the efficiency of the weaving process. In knitting,

the lubrication of the yarns is also important. Lack of lubrication results in nonuni-

form yarn movements that affect the quality of the fabric.

Figure 2. Schematic of a typical spin line for the production of staple fibers.

PROCESSING OF FIBERS 361

9. PHYSICAL EFFECTS OF OILS AND FATS ON FIBERSAND YARNS

9.1. Fiber Lubrication

Surfaces of materials possess different degrees of roughness depending on the way

they are produced. When two solid surfaces are pressed together with a force acting

normal to them, they make contact at the tips of the asperities in the two surfaces. In

the case of soft metals and polymers, because of yielding, these points of contact

form adhesive junctions. The minimum force required to slide one surface over the

other is the force of friction F and is given by (37)

F As; 1

where A is the area of real contact (much smaller than the geometrical area) at the

asperities and s is the shear strength of the junctions. This is shown schematically in

Figure 3. When a liquid film of a low-shear strength material is introduced at the

interface, some of the solidsolid junctions are replaced by the liquid film. The new

friction force is given by (38)

F0 Aas 1 asl; 2

where a is the fraction of the surface with solidsolid junctions and sl is the shearstrength of the liquid. It should be noted that F0 F because a 1 and sl s.

Adhesion of the lubricant film to the solid surface is an important requirement.

Lack of adhesion will lead to the squeezing of the lubricant film out of the interface

and the re-establishment of the solidsolid junctions (39, 40). This will render the

lubricant less effective. The work of adhesion W between a liquid lubricant andthe solid surface is given by (41)

W s1 cos y; 3

where s is the surface tension of the liquid and y is the contact angle, which is ameasure of the interaction between the liquid and the solid. As, for a given solid

Figure 3. Schematic of the effect of a lubricant film on the formation of adhesive junctions at a

solidsolid interface.


surface, cos y is inversely related to the surface tension of the liquid (42), properformulation of a lubricant to maximize W by adjusting s and cos y is important.The solidliquid interaction parameter, cos y, also plays an important role in thespreading and penetration of the liquid lubricant into the yarn (43). This type of

friction at low sliding speed is known as boundary friction, and lubrication in

this regime is known as boundary lubrication (38).

A different frictional behavior is observed in the lubrication of fibers and yarns at

high speeds (44). Friction appears to increase with the sliding speed. Hydrodynamic

origin of this behavior was first explained by Reynolds (45) based on the lubrication

of bearings rotating at high speeds. According to this theory, at high rates of shear,

hydrodynamic pressure is generated in the lubricant film, which supports the

normal load at the interface. The friction coefficient is found to be a function of

the product of viscosity (Z) and the sliding speed V. This relationship betweenthe friction coefficient (m) and ZV is seen in the hydrodynamic region ofFigure 4, at high values of ZV=W (44). In the boundary friction regime, at lowvalues of ZV=W , high friction results from the solidsolid junctions. Under theseconditions, abrasive wear is the result. As the formation of adhesive junctions is a

time-dependent phenomenon, at high sliding speeds, fewer adhesive junctions are

formed, and therefore, friction decreases with an increase in sliding speed.

Stick-slip phenomenon, which is characteristic of boundary friction, disappears

(46). In the hydrodynamic region, on the other hand, high coefficients of friction

need not be indicative of abrasive wear. In this friction regime, under the conditions

of good adhesion, a lubricating finish film is always present at the solidsolid

interface.

Figure 4. Schematic of the effect of viscosity and sliding speed on hydrodynamic friction. W is

the normal load (44).

PHYSICAL EFFECTS OF OILS AND FATS ON FIBERS 363

9.2. Fiber Adhesion

Adhesion between the filaments of a yarn is an important requirement in processing

of fibers. Twist contributes significantly to yarn cohesion. In the case of low-twist

continuous filament yarns, filament adhesion can be improved considerably by the

application of a liquid finish. Liquid bridges are formed by the applied finish, and

the capillary pressure of these liquid bridges is responsible for the increase in

cohesion. This is shown schematically in Figure 5 (47). The force per unit length

of the fibers is given by

F 2s sinj y 2Rs sinj cosj yR1 cosj d ; 4

where R is the fiber radius, 2d is the distance between the fibers, j is the half-anglesubtended by the liquid bridge at the center of the fibers, y is the contact angle, ands is the liquid surface tension. The first term on the right-hand side is the attractiondue to the component of surface tension parallel to the line joining the fiber centers.

The second term is the Laplace pressure of the liquid bridge, whose magnitude

depends on y. It is at a maximum when y 0, and is negative when y > p=2.Therefore, repulsion between the fibers is possible if the second term in Equation 4

becomes negative and is numerically larger than the first. Physically, this means

liquidair interface of the bridge is convex rather than concave. It is important to

note that the presence of liquid bridges in the yarn makes a small but significant

contribution to the strength of the yarn (47).

Figure 5. Geometry of a liquid bridge between two filaments.


10. OILS AND FATS IN TEXTILE PROCESSING

10.1. Natural vs. Synthetic Oils

Although natural oils can be used as lubricants and processing aids in textiles, they

have some serious drawbacks. As a result of unsaturation, these molecules adsorb

strongly on fiber surfaces and are not completely washed off the finished goods. The

residues form resinous products by autoxidation in the presence of oxygen leading

to yellowing (48). Oils with conjugated double bonds in the fatty acids are even

worse in this regard. Storage stability of these goods is poor in warehouses and in

the presence of ultraviolet light. As a result of this, in modern textile processing,

synthetic oils are preferred over their natural counterparts. Saturated fatty acids

from natural oils and fats find their way into surfactants in scouring and dyeing

and as antistatic agents in spin-finish formulations. Uses of these surfactants in

the textile industry have been reviewed extensively (49,50).

10.2. Spinning

The commercial importance of spin finishes can be realized from the sheer volume

of synthetic fibers produced. For the year 2000, the production figures of the three

major synthetic fibers, e.g., polyester, polyamide (nylon), and poly(acrylonitrile)

were approximately 18, 4, and 3 million tons, respectively (51). If spin finishes

are applied at 0.250.5% level, the annual requirement of these finishes will be

in the range of 70140 thousand tons. This has given rise to industries that supply

spin-finish components and completely formulated spin finishes for specific

applications (52). An experimental nonproprietory spin finish formulation supplied

to TRI/Princeton by Henkel Corp. follows:

UCON 50 HB 660 (lubricant), 66.0%

Butyl stearate, 8.5

Oleic acid, 8.5

KOH (45% aqueous), 2.8

POE (6) nonyl phenol, 10.0

POE (2) ethyl hexyl K salt, 4.2

UCON is a random copolymer of ethylene oxide (EO) and propylene oxide (PO)

and can be considered as a synthetic oil. POE is poly(oxyethylene), which is a

homopolymer of EO. Random EO-PO copolymers are typical of synthetic oils

used as lubricants in textile processing (53, 54). PLURONICS (BASF) are block

copolymers of EO and PO. Both of these copolymers can be produced with visc-

osities ranging from that of a thin oil to that of a thick paste. Oils of appropriate

viscosity give hydrodynamic lubrication in the high-speed spinning of synthetic

fibers. The hydrophilelipophile balance (HLB) in these polymers can be varied,

by changing the EOPO composition, to suit the aqueous solubility requirements.

The other major synthetic oils used in textile processing are the silicone oils, based on

the polymers of dimethyl siloxane, (CH3)3SiO(Si(CH3)2O)nSi (CH3)3 (55).

OILS AND FATS IN TEXTILE PROCESSING 365

Similar to the copolymers of EO/PO, these polymers can also be produced with a

range of molecular weights and varying viscosities. In contrast to the EOPO copo-

lymers, these have much lower surface energies and spread easily on a surface to

give very thin films. Therefore, they make rather poor boundary lubricants. How-

ever, because of the low surface tension and high wettability with other surfaces,

they make good hydrodynamic lubricants (42). For the same reasons, these oils

are often used in soil and water-repellent treatments of fabrics (56, 57). More

recently silicone oils have been combined with POEs and EOPO copolymers to

produce surfactants with varying HLB numbers and are used as lubricants and

emulsifying and spreading agents (58). In general, silicones are known to be better

lubricants than the EOPO-based copolymers. The brief nature of this review

precludes detailed discussion of the rather voluminous literature available in this

area.

Mineral oils of different viscosity are used in the spinning of natural and syn-

thetic fibers (59). These are paraffins of varying molecular weights, byproducts

of the petroleum industry.

Apart from lubricants, spin finishes contain antistatic and spreading and emulsi-

fying agents. These are generally alkyl sulfates, alkylbenzene sulfonates, sulfonated

fats and oils and poly(ethylene glycol)-modified fatty acids, fatty acid amides, fatty

alcohols, and fatty amines. Potassium alkyl phosphates are extensively used in the

production of polyester staple fibers.

10.3. Scouring

Here oils and fats are used principally as detergents and wetting agents in the clean-

ing of natural fibers, to remove, for example, fats and waxes from cotton and wool

(60) and in removing finishes used as processing aids in the manufacture of syn-

thetics. Generally, anionic surfactants are used in this process. As most natural

and synthetic fibers have negative charges on the surfaces, anionics will not adsorb

strongly and therefore can be rinsed out easily. Among the nonionic surfactants,

alkyl, alkylphenol, fatty acid, and fatty-acid-amide-modified POEs are more com-

mon. The pH of the bath is an important consideration in the selection of the proper

surfactants.

10.4. Dyeing

In dyeing, surfactants are used as wetting agents. They are also used in the formu-

lation of disperse dyes. A stable suspension of the dye is prepared with the help of

an anionic surfactant, such as alkyl or aryl alkyl sulfonate. It has been shown that

dyeing takes place through the aqueous phase by the slow dissolution of the solid

dye particles (61, 62). The presence of the surfactant helps the dissolution of

the dye.

In special cases, cationic surfactants are used as dye-leveling agents (63, 64).

Cationic dyes with temperature-sensitive diffusion coefficients often yield non-uni-

form shades, because of the difficulty of maintaining constant temperatures in large


industrial dye baths. Cationic surfactants used in these dye baths diffuse into the

fiber ahead of the dye molecules and occupy some of the sites. This, in general,

reduces the rate of dyeing, but improves uniformity. Overall dye uptake is not affected

because at the end of the process the surfactant molecules are displayed by the dye mole-

cules. Quaternized long-chain surfactants are generally used for this purpose.

10.5. Softening

Fabrics often feel rough after scouring and washing. Ionic as well as nonionic sur-

factants are used to soften such fabrics (65). Several mechanisms have been sug-

gested for the softening effect. In the case of low-molecular-weight ionic and

nonionic surfactants, softening has been attributed to the moisturizing and lubrica-

tion of the fibers in the fabric. When the interfiber friction is low, the fabric deforms

easily by the slippage of fibers over one another. This results in a softer hand. As

a result of low molecular weight and lack of substantivity, these effects tend to be

temporary, and the fabric needs to be treated after every wash. A more permanent

softening is achieved by the surface deposition of an elastomeric polymer, which

forms interfiber bonds. Surface-deposited silicones (66) are known to be superior

in this respect. A principal drawback of these polymeric softeners is that they inter-

fere with the water absorbency of the fabric because of their hydrophobic nature. A

rather unusual application of silicones is in the shrink proofing of wool garments

(67). In this instance, the interfiber bridges prevent unidirectional fiber migrations

that otherwise would lead to the felting of the fabric.

11. CONCLUDING REMARKS

The foregoing discussion shows the importance of oils and fats in the processing of

textiles. As a result of oxidative stability, synthetic oils have superseded their nat-

ural counterparts. However, fatty acids from natural oils still play an important role

in the processing of textiles. There is considerable pressure on the textile industry to

reduce the amounts of these additives, or to eliminate them completely, because of

the environmental implications of the effluents (68). In response to this, consider-

able effort is being made in the industry to develop additive-free processes.

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Front MatterTable of ContentsVolume 1. Edible Oil and Fat Products: Chemistry, Properties, and Health EffectsVolume 2. Edible Oil and Fat Products: Edible OilsVolume 3. Edible Oil and Fat Products: Specialty Oils and Oil ProductsVolume 4. Edible Oil and Fat Products: Products and ApplicationsVolume 5. Edible Oil and Fat Products: Processing TechnologiesVolume 6. Industrial and Nonedible Products from Oils and Fats6.1 Fatty Acids and Derivatives from Coconut Oil6.2 Rendering6.3 Soaps6.4 Detergents and Detergency6.5 Glycerine6.6 Vegetable Oils as Biodiesel6.7 Vegetable Oils as Lubricants, Hydraulic Fluids, and Inks6.8 Vegetable Oils in Production of Polymers and Plastics6.9 Paints, Varnishes, and Related Products6.10 Leather and Textile Uses of Fats and Oils6.10.1 General Use of Fats and Oils in Leather6.10.2 Softening of Leather6.10.3 Softening with Fatliquor6.10.4 Other Softening Materials6.10.5 Evaluating Effects of Fat in Leather6.10.6 General Use of Fats and Oil for Textiles6.10.7 Common Textile Fibers6.10.8 Processing of Fibers6.10.9 Physical Effects of Oils and Fats on Fibers and Yarns6.10.10 Oils and Fats in Textile Processing6.10.11 Concluding RemarksReferences

6.11 Edible Films and Coatings from Soybean and Other Protein Sources6.12 Pharmaceutical and Cosmetic Use of Lipids

Index

Documents

Leather and Textile Uses