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Performance evaluation of textile chemicals
By: Ashok Athalye
"Well prepared is half finished", the age old and universal adage probably has roots
in pretreatment of textile material. Ashok Athalye attempts to cover aspects related
to the evaluation of selection, application and performance (SAP) properties of
chemicals used in textile wet processing.
The aesthetic appeal and appearance, feel and comfort, fitment and shape retention
of the finished fabric are dependent on the effective preparation and colouration of
the textile substrate.
The final textile product, be it a ready-to-wear apparel, home textile item or a
technical performance material, undergoes many stages of processing. The steps
involved, depend on various factors, such as source of fibre - plant, animal or
synthetic; form of substrate - yarn, woven, knit, towel, garment or carpet; method of
processing - exhaust, semi-continuous or continuous; and use of machinery under
low/high turbulence or low/high temperature.
Fig 1. Processing of Cotton
The processing steps are aimed at optimising extraction of impurities, controlling
residual moisture content, achieving the desired extent of absorbency, maintaining
uniform standard of white, minimising the damage and loss of strength of the fibre,
and ensuring consistent pH from core to fibre surface.
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Irrespective of the textile material used, the pre-treatment process is highly
chemical-intensive and the desired result is possible only when adequate chemicals
are used. Apart from basic chemicals like caustic soda, soda ash, acetic acid and
hydrogen peroxide, many other specialised auxiliary chemicals are used during
textile wet processing and broadly categorised based on the intended purpose or
processing step for which they are used. A broad list of chemicals generally used
during cotton processing is given below
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Desizers and dispersants
Emulsifiers and detergents
Demineraliser and sequesterants
Bleach stabiliser and quenchers
Deaerators and defoamers
Acidic and alkaline pH controllers
Levelling and dispersing agents
Dye bath controllers and migration inhibitor
Dye accelerator and penetrants
Anti-crease lubricant and friction controllers
Dyefixers and wash-off improvers
Reducing and oxidising chemicals
Color fastness improvers
Abundant literature is available on each of these processing steps and the chemicals
used, depending on the machinery in use. Brief information is offered below on only
the critical parameters which govern selection, application performance evaluation of
these auxiliary chemicals.
The criteria for a specific chemical selection depends on its suitability for use under
intended thermo-mechanical conditions and the following end-use performance
evaluation indicators:
1. Physical characteristics
 Aspect: solid, paste, liquid
 Appearance: flakes, viscous
 Colou r: light or dark, shiny | duller
 Odour: ammoniacle, fishy, acrylic
2. Gravimetric analysis
 Non volatile matter, solid | active content
 Density and specific gravity
 Extent of impurity, insoluble matter
3. Chemical analysis
 pH of self and diluted solution
 Ionic nature: cationic, anionic, non-ionic, amphoteric
 UV-VIS spectroscopy: fluorescence, tint
 IR, FTIR nomenclature
 NMR molecular identification
 Atomic absorption for heavy metal ion identification and determination
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4. Ecological aspects
 Biodegradability and bio elimination
 COD, BOD and AOX level
 Toxicity to aquatic animals
 Presence or extent of components from restricted substance list
 Boiling, melting and flash point
 Storage conditions
 Disposal considerations
Apart from the basic and general qualitative chemical analysis, the efficacy of these
chemicals is determined and assessed by the functional performance evaluation.
Given below in brief are some of the most commonly used process chemicals and
their selection criteria and performance evaluation methods.
1. Desizers: Starch and its derivatives are the most widely used ingredient for
enhancing strength of cotton yarn during sizing process. After fabric weaving, such
temporarily applied sizing chemical needs to be removed to facilitate further
processing. Earlier, some simple but inaccurate methods, such as rot steeping or acid
steeping, were performed. However, with the advent of enzyme-based technology, a
simple, easy-to-use, accurate and eco-friendly process for starch based size removal
has gained popularity.
This process consists of use of a bacterial enzyme that has specific selectivity towards
starch and which effectively destroys starch without harming the cellulosic backbone
of cotton fibre. The selection, application and performance evaluation of such
enzymatic desizing chemical depends on
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Type and nature of size
Quantity of size
Fabric construction
Process and equipment used
Water conditions, water hardness
Compatibility with other chemical components
Enzyme activity | Assay
Weight loss estimation
Absorbency and wetting
TEGEWA scale rating of ? 7
Fig 2. TEGEWA Scale
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2. Emulsifiers and detergents: During the scouring and bleaching processes,
uniform extraction of impurities is desired. The basic criteria for selection of such
chemicals depends on how quickly it gets adsorbed and wets out the fibre surface.
Other important parameters are:
 It should not generate undesired foam.
 It should retain rewetting property.
 It should effectively clean and uniformly remove dirt and soil.
 It should be stable to varying temperature, pressure, turbulence and pH
conditions.
The important selection and performance evaluation criteria include:
 Ionic nature
 Shear stability
 Surfactancy: surface tension, cloud point
 Wetting efficiency: absorbency by Drave's test AATCC-17, wicking, detergency
 Foaming: turbulence, foam height, suppression time
 Density: auto dispensing, alkali stability
 Eco conformance: APEO free, bio degradability
Fig 3. Assessment of an Emulsifier
3. Chelating agent: Generally used for forming a complex with alkali earth metals
like Ca and Mg and heavy metal ions like Fe, Cu and Cr, this helps overcome metal
salt scale formation and deposition, thereby avoiding undesired contamination of
machine parts. It enhances dispersion stability, avoids tendering or tensile strength
loss of cotton yarn and minimizes risk of pin hole formation during continuous
bleaching process.
The commonly used terms are demineraliser (removal of metal ions from textile
fibre) and sequesterant (removal of metal ions from process water). The performance
evaluation criteria are chelation value by titration, stability under varying pH
conditions, hardness testing by Merck strips and dispersing effect by filteration or
spot test.
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4. Bleaching assistants: Generally, two types of auxiliary chemicals are used: one
at the beginning, for enhancing the bleaching efficiency and another at the end for
suppressing the residual bleaching agent. The chemical used during bleaching acts as
a stabiliser and helps control uniform decomposition of the main bleaching agent,
while the chemical used after the bleaching process helps neutralize the bleaching
component and ensure no residual component remains in the bath as well as on the
cotton substrate, which could affect subsequent dyeing process. The performance
assessment is usually carried out by using indicator paper strips, spotting with titanyl
chloride or volumetric titration.
5. Deaerator and Defoamer: Foam is a stable dispersion of gas bubbles in a
liquid. The atmospheric air can possibly enter water during the preparatory process
due to high speed agitation (package or soft flow machines), chemical mixing,
machine loading and bath filling, while some extent of air remains entrapped within
the interstices of the fibre which eventually entre into the process water. Generally,
the term deaeration is used for removing or expelling entrapped air from the fibre
while the term defoaming is used for removing foam in the form of air bubbles from
the liquid bath.
The chemicals used for deaeration work on the mechanism of rapid surface wetting
and diffusion inside the fibre, thereby releasing the entrapped air. While the
defoamers effectively block or hinder the air-water interface and help collapse air
bubbles formed inside the water. Both these types of chemicals help improve
uniformity and levelness of the intended process, whether bleaching or dyeing, avoid
usually encountered problems of dye specks or streak marks, and overcome
premature oxidation of vat and sulphur dyes.
The commonly used performance evaluation test methods involve
 Cylinder shake - extent of foam generation and time for foam suppression
 Foam rig agitation - measurement of foaming tendency
 Package immersion - dip yarn package in water and observe release of air
bubbles
Fig 4 Defoaming test
5. pH controllers: During various stages of pretreatment and coloration, use of
varying concentrations of acid and alkali is required. As certain specific pH
conditions are desired during various processing steps, it is necessary to adjust,
control and uniformly maintain the pH for effective processing. Various formulated
auxiliary chemicals are used for such purpose. Owing to the controlled buffering
capacity, these chemicals maintain specified pH under the treatment conditions.
Some of the actions expected are
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Remove surface and core alkali from the fibre
Ensure slightly acidic pH at the start of dyeing
Avoid premature dye hydrolysis of alkali sensitive reactive dyes
Release alkali during dye fixation stage
Impart adequate alkalinity required for fixation during CPB dyeing
Ensure adequate acidic pH to avoid disperse dye reduction
Avoid formation of disturbing neutralization salts
Minimise fibre damage
Avoid corrosion of machines parts
The performance assessment is done based on acid value, pH after drop-wise alkali
addition, estimated thermal stability, volatility, spot on filter paper and iron to check
degradation, observed precipitation of salts, foam formation and time of
suppression, chelation value using titration method, stability under varying
temperature conditions and impact on depth and tone of alkali-sensitive dyestuff.
Dye bath chemicals: The colouration of textile material involves dyeing as well as
printing using various application methods. The performance in terms of uniformity
and levelness, depth and shade achievability, coverage and sharpness of motifs and
attainment of desired fastness levels depends on the optimum performance of
auxiliary chemicals apart from the dye in use.
Different textile substrates need different types of colorants and accordingly, the
chemicals involved also vary. The major application areas involve pH control by
buffering, levelling aids, dye dispersion enhancers, washing off agents, dye fixators,
migration inhibitors, metal ion sequesters, rheology modifiers, diffusion accelerators
and crease preventers.
Further, the use of chemicals depends on the type of textile material being used,
whether in self or in blends, machinery in use, process sequence followed and the
end use fastness expectations.
6. Levelling, dispersing and anti-migrating agents: For ensuring and
maintaining adequate dispersion of water insoluble dyes and achieving uniform level
dyeing, certain chemicals are added during dyeing. These chemicals help achieve
optimum dye diffusion inside the fibre, avoid dye agglomeration or precipitation and
attain the desired shade brilliance. Further, the success of the dye being evenly
exhausted and uniformly applied depends on
 Rate of liquor flow through the package
 Consistency of flow rate through all packages
 Rate of temperature rise
 Time and temperature of migration phase
 Exhaustion rate and migration properties of the dye
 The dispersion stability of the dye
 Preventing dye migration during continuous dyeing
 No gelling or agglomeration in hard water
 No sticky film on rolls
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Some methods of performance assessment include filter paper spot test, flow test,
suction filter test, separating funnel test, speck test and sandwich filter test.
7. Anti-crease lubricants: These help minimise fibre-to-fibre and fibre-to-metal
or -machine part friction during the high turbulent movement of the textile material
over machine parts, especially fabric processing on Jet or soft-flow machines,
thereby avoiding risk of crease mark or chafe mark during dyeing. These also help
avoid the Moire effect in beam and pad-batch dyeing.
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The performance efficiency of such chemicals is assessed by visual inspection of the
dyed fabric or instrumental analysis of coefficient of friction.
8. Dye clearing and fixing agents: The desired shade and depth is achieved only
when the unfixed superficial dye is thoroughly washed off and removed from the
fibre surface. Similarly, the desired wet fastness properties are achieved when there
is no bleeding or extraction of dye in aqueous medium under thermo-mechanical
conditions and color staining on adjacent surface. This is achieved by use of a
suitable chemical for efficient washing off of superficial dye and subsequent
treatment with another chemical for not allowing any dye molecule to break away
from the fibre and come out during end use application.
The performance evaluation of these chemicals is conducted by testing various wash
fastness properties, dispersing and chelating power, foaming behavior, effect of color
depth and hue, effect on absorbency and handle of the textile material and
compatibility and stability under varying pH conditions.
Further, such auxiliary chemicals are expected to be stored in closed containers
under cool and dry conditions (a temperature of 20+/-20C) and at relative humidity
of 65 per cent so as to maintain shelf life of about a year. However, the shelf life may
vary depending on the chemical constituents and their concentration. Therefore, it is
expected that the chemical supplier specifies shelf life for their product. Some of the
assessment methods are
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Freeze-Thaw test: Should pass at least five cycles of storage at 500C for 8
hours, followed by refrigerator for 8 hours
Centrifuge test: No layer separation after centrifuging at 20,000 RPM for 30
minutes
Foam-rig test: No layer separation after 30 minutes circulation
Accelerated storage stability or ASS test: Keep at 600C for a week and
reevaluate its performance
At the end of textile processing, these chemicals need to be removed and drained into
the effluent stream. This necessitates understanding of their disposal as well as effect
on solid, liquid and gaseous effluent.
The selection of adequate chemicals is key to the success of optimum textile
preparation and colouration. The criteria for performance evaluation, storage
conditions and disposal properties of these chemicals vary based on their chemical
composition as well as concentration in use.
About the author: Dr Ashok Athalye is from the technical service, Atul Ltd, Colors
Business, Valsad, Gujarat.