1. The document discusses textile auxiliaries used in preparation and finishing processes like scouring and desizing. It focuses on the chemistry of products used rather than technology. 2. Scouring removes fats, waxes, oils and dirt using surfactants and builders like alkalis to improve absorbency. It is important for natural fibers which contain more impurities. 3. Desizing removes sizes which are applied during weaving to reduce breaks and aid weaving efficiency. The sizes must be removable for subsequent dyeing and finishing.

1. Submitted by: Muhammad Waseem
2022-NTU-MSTC-3044
Submitted to: Dr. Asif Javed
Assignment # 2
Textile Auxiliaries

3. PREPARATION OF SUBSTRATES
 ‘auxiliaries’ generally includes all chemicals used in preparation and finishing processes, even
though in these cases such chemicals often provide a primary rather than a secondary (auxiliary)
function as in coloration processes.
 chemistry of the products used rather than on the technology of processing is discussed
Scouring
• The purpose of scouring is to reduce to an acceptable level the amounts of fats, waxes, oils and dirt
present.
 major technical reason for scouring is to improve the extent and uniformity of absorbency for
subsequent processes, especially coloration. Usually the objective is the complete removal of all
extraneous matter but on occasion only partial removal is the aim, since a certain residue of oils, for
example, will aid such processes as spinning, weaving or knitting. Scouring is particularly important
with natural fibres, which obviously contain much more extraneous matter than do synthetic fibres.
 In scouring, surfactants function as primary, rather than auxiliary, agents. The basic requirements are
for good wetting power and detergency, the latter property generally including the ability to remove,
emulsify and suspend the extraneous matter in the liquo

5.  Detergency can be significantly improved by the use of additional compounds usually
referred to as ‘builders’,
 the chief of which is undoubtedly alkali in the form of sodium carbonate or hydroxide.
Alkalis function mainly through saponification of the waxes, fats and oils on the
substrate, thus. rendering them water-soluble and more amenable to removal and
suspension by detergents.
 The aminopolycarboxylates are generally preferred, both for their sequestering ability
and for their stability in warm to hot alkaline liquors. Polyphosphates are occasionally
used at lower temperatures but are less efficient in alkaline media. When incorporated
in the scouring medium certain organic solvents, such as pine oil, trichloroethylene,
perchloroethylene, triethanolamine or glycols, can greatly aid the removal of greasy
matter, particularly mineral oil which may be a component of any lubricating oils
present on the substrate. However, the use of these additives must be in accordance with
local environmental regulations.
 Soaps are occasionally still used for scouring, although anionic or nonionic
synthetic detergents are almost always preferred.

6.  Scouring is of crucial importance in wool processing: important, because the
raw fibre contains 20–60% of extraneous matter in the form of grease, suint,
dirt, sand and vegetable matter; and critical, because the fibre is so easily
damaged by hot alkaline treatments. There have been considerable changes in
wool scouring practice, evolving mainly from corresponding changes in the
types of lubricants used on the fibre, although environmental factors have also
played a part. It has been pointed out that the pollution load from a wool
scouring mill can be similar in magnitude to the average discharge from a
small town. Hence there are heavy environmental pressures on wool scourers.
 Soap and alkali were traditionally used and very greasy wools were scoured
with alkali alone, forming a soap in situ by saponification of the wool grease.

8.  The other major natural fibre, cotton, contains a significant proportion of extraneous
matter such as seeds, fats, waxes, coloring matter and dirt, as well as substances such as
sizes and lubricants applied during processing.
Unlike wool, however, it has outstanding stability in alkali and withstands strongly
alkaline treatments ranging from severe caustic kier boiling to milder treatments with soap
and soda [143,154]. It is difficult to detach the effect of scouring from the complete
sequence of desizing, scouring, mercerising and bleaching, since they all contribute to
improved absorbency and cleanliness. Traditional caustic treatment in kiers is carried out
at the boil or in some cases at up to 120 °C, using 1–2% o.w.f. alkali. This treatment bursts
the seed motes and saponifies fats and waxes, converting the fatty esters into sodium salts
and glycerol. This in situ formation of soaps naturally aids cleaning. Nevertheless, synthetic
detergents are often added to aid penetration through wetting and to increase detergency.

9.  The surfactants selected must be highly stable in the strongly alkaline conditions, as
well as in hard water. Anionic surfactants of the fatty alkyl and alkylaryl sulphate types
have been preferred, although the use of phosphate esters is increasing. A synergistic
mixture is beneficial, one component (C10–C13) to aid wetting, the other (C14–C16 )
as a detergent. The sulphosuccinates, often a first choice for wetting ability, cannot be
used here as they are hydrolysed under such strongly alkaline conditions. A
sequestering agent is usually added in order to remove metal ions that would create
problems in subsequent bleaching. Addition of a mild reducing agent guards against
alkaline oxidative tendering of the fibre through oxycellulose formation and also
promotes a degree of bleaching. The reducing agent will also reduce any iron(III)
contamination to iron(II) ions, which are easier to remove by the sequestering agent.

10.  Compared with wool and cotton, the scouring procedures for synthetic fibres are
relatively simple since these fibres contain fewer impurities. Most of these have at least
some degree of water solubility; the most important are sizes and lubricants. The major
sizes used are poly(vinyl alcohol), carboxymethylcellulose and poly(acrylic acid), all of
which are completely or partially water-soluble. Sometimes aliphatic polyesters are
used.
 When scouring synthetic fibres that are to be dyed with disperse dyes, nonionic
scouring agents are best avoided unless they are formulated to have a high cloud point
and are known not to adversely affect the dispersion properties of the dyes. Conversely,
when scouring acrylic fibres, anionic surfactants should be avoided because they are
liable to interfere with the subsequent application of basic dyes. These fibres are usually
scoured with an ethoxylated alcohol, either alone or with a mild alkali such as sodium
carbonate or a phosphate. Polyamide and polyester fibres are generally scoured using an
alkyl poly(oxyethylene) sulphate and sodium carbonate

11. Desizing
Desizing is an essential part of the purification process for woven fabrics. Sizes perform an
adhesive and lubricating function.
After drying, the size forms a protective film on the surface of the warp yarns, bonding the
protruding fibrils to produce a smoother yarn with improved tensile strength and abrasion
resistance.
The objective of sizing is to improve weaving efficiency by reducing the number of yarn
breakages, reducing frictional wear of loom parts and allowing increased running speeds.
 Individual size polymers may be used alone or in combination with one another and
their performance may be further improved by the addition of other components such as
waxes and lubricants. Depending on the type of size and the dyes used, dye uptake may
be increased or resisted hence uneven distribution of size may lead to unlevel
coloration.

13. Chemistry of size polymers
Sometimes a distinction is made between primary sizes, secondary sizes and binders. This
distinction appears to be an arbitrary one depending mainly on the proportions present in a
mixture, although other factors may also be pertinent. There is a great deal of similarity in
essential chemistry between typical size polymers, thickening agents used in printing and
migration inhibitors used in continuous dyeing.
It is important to recognise that the molecular characteristics (average molecular mass and
distribution, possible degree of substitution) of such polymers can be varied quite widely,
with attendant changes in properties. Thus polyacrylic acids and their salts may be
described as either sizes or binders.
 A product marketed specifically as a binder may have molecular characteristics that
provide properties different from those of a similar product marketed as a size
component. For example, an acrylic size may be engineered specifically for adhesion
and film-forming properties whereas an acrylic binder may be designed to enhance film
elasticity when added in smaller quantities (about 10%) to a size formulation. It is
therefore important to bear in mind that different polymers based on similar chemistry
can be engineered to provide suitability for specific uses.

15.  Animal glue is a complex colloidal mixture of proteins. The related gelatins are also
complex heterogeneous mixtures of proteins. They are strongly hydrophilic and rich in
the amino acids glycine, proline, lysine, hydroxyproline and hydroxylysine. Casein is a
phosphoprotein obtained from the milk of mammals. Poly(vinyl alcohol) has the
structure. Poly(vinyl acetate) is the fully esterified derivative of poly(vinyl alcohol), in
which the –OH groups are replaced by –OCOCH3 groups. These products may
comprise 100% of either polymer, or combinations of the two monomers in any
proportions. Crotonic acid (2-butenoic acid), widely used in the preparation of resins,
may also be a component. This compound exhibits cis–trans isomerism. The solid trans
form is produced readily by catalysed rearrangement of the liquid cis isomer.
 The polyester sizes used have a much lower average molecular mass than polyester
fibres. These structures (10.69) contain sulphonic acid groups and may be water-soluble
or water dispersible types. The degree of sulphonation is low. If these resins are
subjected to a high pH, the sulphonate groups can be hydrolysed, giving an insoluble
resin that is very difficult to remove from the fibres.

17. The application and properties of sizes:
the essential aim of sizing is to increase productivity in weaving. This is achieved through a
reduction in yarn breakages that permits increased running speeds. Indeed, the high speeds
of modern weaving processes could not have been realised without corresponding
improvements in sizing technology.
The most important requirements of a size formulation can be summarised as follows
• – high adhesion and good film-forming properties on the yarn, together with good
elasticity of the applied film
• – low tendency to foam in the application liquor
• – freedom from skin formation in the application liquor
• – good storage stability
• – good compatibility of wash-off liquors containing different size components
• – appropriate compatibility with alkalis and bleaching agents if desizing is not carried
out separately from scouring and bleaching

18.  The adhesive strength of a size film is an important consideration as it has a bearing
on stability during weaving . Adhesive strength depends on such factors as type of size
polymer, additives present (e.g. wetting agent), sizing liquor temperature, yarn
characteristics, viscosity index of the size formulation and degree of saponification of
poly(vinyl acetate) sizes.
 The similarity in molecular structure between polyester sizes and synthetic fibres
facilitates hydrophobic bonding between hydrocarbon segments of the polymer
chains.
 Economic factors play a major part in the selection of sizes. For this reason, starch
sizes and their mixtures continue to be the most widely used, particularly on cellulosic
substrates. Nevertheless, more costly size polymers may be economically justifiable if
this can be offset by higher productivity in weaving. High productivity generally
demands high elasticity and strong adhesion, provided mostly, if not exclusively, by
synthetic sizes. Water-jet weaving machines require water-resistant sizes. Some sizes
are adversely affected by high temperatures (as in heat setting) or by treatment at
inappropriate pH values and these effects can make their removal more difficult.

19.  The choice and combinations of different size components must take account of
many factors if optimum results are to be obtained.
 Cotton warp yarns sized with starch are normally woven at high humidity (80% and
above) to keep yarn breakages low, as the starch film is brittle at low humidity.
 The incorporation of waxes or lubricants components exert a significant influence on
weavability and on the conditions and efficiency of desizing. The lubricant may be
added as a component of the size formulation, or applied separately by kiss-roll after
sizing. Lubricants may themselves be used as sizing agents, particularly on synthetic
warp yarns.