UNIT-5

Class:II FD Subject Handle By N.Meenakshi

Wet Processing for Polyester Fabric:

In textile dyeing sector, different method applied for dyeing natural and man-made fibres
or fabrics. Here, the process varies from one to another. In the past I have discussed about
the process chart of wet processing for cotton fabric.The process sequence of wet processing for
synthetic fabric.

Process of Wet Processing for Synthetic Fabric (Printing Method):

Grey fabric
↓
Stitching the fabric
↓
Washing
↓
Drying
↓
Stentering
↓
Printing
↓
Polymerizing or curing
↓
Washing
↓
Calendaring
↓
Folding
↓
Poly packing

All the above processes have discussed in the below table:

SL Process Description
No.
01 Grey fabric The undyed and unfinished cloth is known as grey cloth.
02 Stitching the fabric It is the process to join up several grey cloth on to warpers beam to
produce a continuous fabric stand for quick wet processing action.
03 Washing The process to wash the textile material is known as washing.
04 Drying After washing the textile material is dried.
05 Stentering The process by which we can keep proper width of fabric in length
 and width wise and increases the smoothness, lusterness, evenness of
fabric is termed as stentering.
06 Printing Printing is one kinds of dyeing. When various types of color used to
make a particular design on the textile goods is termed as printing.
Normally printing is performed on the textile goods in dry condition.
07 Curing or polymerizing A process following application of a finish to textile fabrics in which
appropriate conditions are used to effect a chemical reaction is
known as curing. In the other words, the process used to link small
chemical molecules into a polymer is termed as polymerization.
08 Calendaring It is a temporary mechanical finishing process. It gives a smooth
surface of the cloth.
09 Folding It is defined as the process to fold one or more materials into the
desired configuration for weaving.
10 Poly packing To pack the textile materials treated by polyethylene bag.

Wet processing of silk

Wet processing includes the main processes of fabric preparation, namely desizing, bleaching,
mercerizing, dyeing, printing, and other specific treatments. These phases treat fabrics with
chemical and liquor baths and often require several washing, rinsing, and drying steps,
generating significant wastewater effluents. The recommended pollution prevention and control
techniques for the finishing pretreatment steps include the following:

 Selection of water soluble and biodegradable lubricants for knitted fabrics instead of mineral oil
and wash them with water;

 Use of organic solvent washing for non water soluble lubricants;

 The thermofixing step may be performed before the washing step. Air emissions generated from
the stenter should be treated by dry electrofiltration. The oil separated should be collected to
limit effluent contamination;

 Residual liquor should be minimized through reduced application, reduced tank volumes and
padding liquor recycling;
 Using mechanical dewatering equipment to reduce water content of the incoming fabric and
reduce energy consumption in stenter frame.

Desizing
Desizing operations may generate effluents with significant concentrations of organic
matters and solids. BOD and COD loads from desizing may be significant (35 to 50 percent of
 the total load), and COD concentrations up to 20,000 mg/I may be generated. Recommended
pollution prevention and control techniques include:

 Selection of raw material with low add-on techniques (e.g. pre-wetting of the warp yarn);

 Selection of more bio-eliminable sizing agents (e.g.-modified starches, certain galactomannans,

polyvinyl alcohol, and certain polyacrylates);

 Application of enzymatic or oxidative desizing with starch and modified starch sizing agents,
followed by washing systems;

 Integration of de-sizing / scouring and bleaching in a single step to reduce effluent generation
(e.g. reuse of bleach rinse water in desizing);

 Recovery and reuse of specific water-soluble synthetic sizing agents (e.g. PVA, poly-acrylates,
and carboxy-methyl cellulose) by ultra-filtration.

Bleaching
Common bleaching reagents include hydrogen peroxide, sodium hypochlorite, sodium
chlorite, and sulphur (European Commission, 2003). The degree of bio-elimination should be
>80 percent after 7 days. Hydrogen peroxide is the most commonly used bleaching agent for
cotton and is typically used with alkali solutions.
The use of chlorine-based bleaches may produce organic halogens (due to secondary
reactions) and cause significant concentrations of Adsorbable organic halogens (AOX),
particularly trichloromethane, in the wastewater. Sodium hypochlorite bleaching represents the
most significant concern, and lower AOX formation should result if sodium chlorite bleaching is
used. The wastewater is alkaline.

Mercecrising
During Mercerising, cotton fiber reacts with a solution of caustic soda, and a hot-water
wash treatment removes the caustic solution from the fiber. The caustic solution remaining on
the fiber is neutralized with acid, followed by a number of rinses to remove the acid. Wastewater
from Mercerising is highly alkaline, since it contains caustic soda.

Dyeing
Wastewater from dyeing may contain color pigments, Halogens (especially in vat,
disperse, and reactive dyes), metals. This agent should be considered only for flax and bast fibers
that cannot be bleached, with hydrogen peroxide. Consider use of a two-step process with a
Hydrogen peroxide stage to remove impurities, which would act as a precursor for AOX
formation, followed by elemental chlorine-free bleaching.
printing
Print paste components consist of color concentrates, solvents, and binder resins. Color
concentrates contain pigments (insoluble particles) or dyes. Organic solvents are used
exclusively with pigments. De-foamers and resins are aimed at increasing color fastness. Printing
blankets or back grays (fabric backing material that absorbs excess print paste)

Chemical processing of silk

The different ways of degumming silk are as follows:

a) Soap as a degumming agent

Soap is a good degumming agent and grey fabrics can be completely degummed by
treating with soap solution at close to boiling point for 1-2 hours. Neutral synthetic agents have
no degumming properties. After degumming the silk is thoroughly washed with water, with
weak solutions of ammonium chloride or soda ash at 40 -500C for 20mins.

b) Enzymatic degumming
Proteolytic enzymes like Trypsin and Papain may be used for degumming. All the sericin
is not removed by this treatment hence a subsequent treatment with soap solution is necessary.
The enzymes preferably hydrolyse peptide bonds formed by carboxyl groups of Lysine and
Arginine of silk to form low molecular weight water soluble products which can be easily
washed out.

c) Extraction with water

In order to remove sericin from raw silk the yarns must be autoclaved for long periods
with water at temperature over 1000C .The degradation of silk is minimum. There might be some
modification of the protein molecule.

Treatment with alkalis

Alkalis have severe destructive effect on proteins. Severity of the treatment required to
remove sericin from a given sample depends on the type of silk. Degumming with soaps in the
presence of alkalis is in practice since a long time. Here soap acts as the degumming agent and
the alkalis aid the process.

Bleaching Of Silk
Natural coloring matters present in silk are associated mainly with sericin and hence are
eliminated during degumming. The natural colouring matter of silk can be roughly divided into
 yellow, green and brown pigments. However the residual pigments are adsorbed by fibroin and
hence silk fabrics made from yellow raw silk after degumming are not white but have a cream
colour. The bleaching process may be based on reducing agents or oxidizing agents. But material
bleached with reducing agents tends to reoxidise and the original color may be restored. Hence
oxidizing bleaching is most preferred. Predominant reducing agents used are Sulphur dioxide,
sodium hydrosulphite and sodium or zinc sulphoxylate formaldehyde. While the oxidizing agents
used are potassium permanganate, sodium perborate, sodium peroxide or Hydrogen peroxide.
The hydrogen peroxide is the most preferred bleaching agent. The Chlorine based bleaching
agents are bleaching powder, sodium hypochlorite and sodium chlorite which are generally not
used since these agents tend to chlorinate the fibroin.

Optical Whitening
In order to enhance the whiteness of a fabric treatment is carried out with an optical
brightening agent. The optical brightening agent may be applied along with bleaching agent
during processing of silk.
Dyeing Of Silk
Since silk is a natural polyamide fibre it can be dyed with various classes of dyes as Acid, Basic,
Direct, Reactive, Metalcomplex and Solubilised vat dyes. The pH of the dyebath and the
temperature of dyeing should be adjusted in such a way that slow and even adsorption of the dye
takes place from the start.

Printing of Silk
Silk is mainly printed by handblock printing and screen printing methods. The handblock method
is a slow process. The different styles of printing are Direct, Discharge and Resist style. Hardly
any other fibre can be printed with so many different classes of dyes as silk.

The following classes of dyes can be used to print silk: Acid, Metal-complex, Direct, Reactive,
Basic, Vat and Indigosols. This wide variety is due to the fact that a high proportion of silk in the
market is always claimed by Discharge printing.

Finishing Of Silk
Silk being a noble fibre care must be taken during its finishing so as not to affect its classic feel,
scroopy handle and shimmering appearance. During finishing silk is treated for following
properties:-
 Crease resistance
 Antistatic effect
 Spot resistance( water and oil drops)
 Flame retardancy
 Dimensional stability ( with hand washing)
 Wash and wear properties.
WET PROCESSING OF NYLON:

1 .Scouring
Nylon woven graiges has acrylic and wax etc. added as a sizing agent to the warp. This is
a secondary contaminant applied in the process before weaving.In the scouring process, to
remove these secondary contaminants in the main continuous processing. In the scouring
process, secondary contaminants are removed by continuous treatment.polyurethane blend knit
removes secondary contaminants such as oils and moisture heat set by continuous scouring
process. Some woven fabrics scouring and desizing by continuous range then batch scouring
with relax.

2. Dyeing

Acid dyes and premetallized dye are used when dyeing nylon. Acidic dyestuffs and
premetallized dyestuff are water-soluble and dyeing by ionic bonding.In nylon dyeing, the
dyestuff used will change according to the desired shade densityLeveling agent are required to
obtain even dyeing, and the type of leveling agent used will also change depend on type of
dyestuff. Fiber-friendly anionic active agent is used for leveling dyestuff, and cationic nonionic
agent is used for milling and premetallized dyestuff.
Dyeing is generally done in batch processing, dyeing is done by running the fabric inside the
machine by looping the fabric. It is important for even dyeing that the runnability of the fabric is
stable, and if runnability is not stable, it leads color difference in batch and scraped and bruised.
If this kind of occurs, it is recommended to use a dye bath quality improver.

3 .Soaping
When dyeing is finished, it removes unexhausted dyestuff on fibers and dispersant
by soaping after cold water rinse.

4. Fixing

In general, fixatives are used medium to dark shade, however fixatives effect to hand
feeling. Sometime, fixatives are used for lighter shade, due to minimalize to hand feeling
changed by shade. Adjust the amount of fixative is used according to the color concentration

5. Finishing

It is the process of adding to hand feeling and functional performance for the final
product.Continuous pad process is common, required of finishing process is pad bath stability.
Functional property, such as add soft feelling, water repellent and quick dry (moisture
management).

WET PROCESSING OF WOOL

Wool processing is the multi step process. The basic steps
• Scouring
• Drying
• Carding or Combing
• Spinning
• Felting
• Dyeing

Scouring

 Scouring, the technical term for washing, is the first step in wool processing. This
involves washing the wool in hot soapy water to remove dirt, grease and dry plant matter
from the fleece. The preferred water temperature for washing wool is 60 degrees C.
 Soaps of various natures have been tried with much success. For those washing wool in
their home, Dawn dishwashing soap seems to be a favorite. Use a mild soap, nothing
harsh. Commercial processors may use a slight alkaline solution (by adding sodium
carbonate) to aid in the scouring process.
 The key is to keep the water temperature and the volume of soap used as low as possible
while still being able to wash out the grease and dirt. Wool that is very greasy will require
hotter and stronger solutions to remove the grease.

Drying
After washing and thorough rinsing the wool is dried. On a commercial scale large
mechanical dryers are used. The wool is set on screen tables with hot air circulation. On a
individual scale the wool can be placed on a sheet and set in the sun.

Carding or Combing
 In researching wool processing information there was some confusion between these two
terms. Many recent sources do not mention combing at all and older sources talk of it as
something entirely different from carding. Nowadays, the terms combing and carding are
often used interchangeably and the more common term of carding prevails.
 As far as we can discern, carding is gently spreading washed and dried wool in
preparation for further processing.
 Combing is straightening and stretching the fibers to obtain maximum spinning capacity.
  For carding the shorter wools are preferred and for combing the longer wools are
preferred. The shorter carded wools are generally the ones that will be processed into
clothing.

Carding
 Carding is a hand or mechanical process. Individuals can purchase hand carders while
commercial processors will use mechanical machines. Either way, steel fingers seperate
and straighten the fibres and then twist them back into one another again thus forming
strings of wool. These strings are again twisted into one another to produce longer
continuous ropes of wool called rovings
 . Any dry plant material still in the wool will fall out or should get picked out during the
carding process.
 At this stage of the wool processing the paths can diverge. Dependent on the quality and
type, wool will either be used for the purpose of spinning or will make its way to the
felting table.

Spinning
 Spinning is the process where the wool rovings produced during carding, are turned into
yarns. On a commercial wool processing scale the rovings pass through a spinning
machine. On an individual scale a spinning wheel or a hand spindle is used. During
spinning the wool rovings are gently stretched again. Through a series of twisting and
spinning and twisting again the wool is spun into batches of similar quality and strength.
 The spun wool is formed into and stored as skeins of yarn, what you see and buy in the
store. These are small bundles of yarn that can now be dyed if warranted.

Felting
 Felting can occur after carding and instead of spinning
 Felting is a feature of wool that enables it to form mats of fabric because the fibers can
interlock with each other. How much it can felt is dependent on the fineness or
coarseness of the fibers. The finer wools felt better due to the finer crimp which results in
more ridges and a tighter lock or joining.
 In the process of felting the wool is subjected to moisture, pressure and gentle beating
action. Layers of wool are laid at right angles to one another to establish fibers that run
lengthwise and then crosswise and then lengthwise again. The felting machine applies
steam moisture and pressure along with a back and forth action to felt the wool. As the
fibers shrink they become entangled together and form a strong, durable felted mat of
material.
  Wool can be felted to the point where it is impossible to distinguish the fibres in the
material or to pull it apart as the fibers have become so entangled and tightly meshed.
Felting done to this extent is then called fulling.

Dyeing
 As wool readily accepts dye colors, dyeing can occur at almost any stage of the wool
processing. The two common stages for wool dyeing is right after washing or after
spinning wool into skeins of yarn.
 If the dyeing occurs after the wool is washed then it is referred to as stock dyed wool. If
the wool is dyed after it is spun into yarn then it is referred to as yarn dyed.
 Many subtle dye colors can be extracted from various plants for a natural dye process. On
a large commercial scale the use of chemical dyes is more convenient and thus more
common.