Technological development in wet processing technology
Department of Textile Engineering
Technological Development in Wet Processing
Department of Textile
Name: Rifad Hossain
Id: 2013000400011 Batch: 22, Sec:
Dyes and Chemicals ....................................................................................................................3
Preparation Innovations ..............................................................................................................5
Dyeing Innovations .....................................................................................................................5
Finishing Innovations ..................................................................................................................8
Recent developments in febric preparation process………………………………………………………9
Peracetic Acid (PAA) Bleaching an Eco-friendly Alternative……………..9
Implementation of Single Stage Preparatory Process………………………………………………….11
Application of Plasma Technology…………………………………………………………………………….13
Dyeing in Supercritical Fluids (DSF):…………………………………………………………………………17
Ultrasonic Assisted Textile Processing………………………………………………………………………19
The textile industry has been developing rapidly and newer technologies are introduced and the
only formula for survival is encapsulating those innovations into the manufacturing process
and making the best of use them for increasing the productivity and quality, says Chitra Siva
Textile industry is a traditional and a very old industry, and has been amidst almost all kinds of
culture around the world from the very beginning, which almost proves the point that the history
of human culture and the textiles are the same. A wide spectrum of processes is involved in the
textile industry. Starting from fibre manufacturing to the final processing and garmenting stage,
involves a lot of technologies and skills, which leads to a quality conversion of fibres into the
ultra-modern fashion or a high performance commodity in the case of technical textiles.
The first major change in the textile industry took place somewhere during the industrial
revolution which lead to the advent of the machines in to the manufacturing processes in the
textile industry. This major breakthrough lead to reduction in the work load of the labours and
pronounced the dawn of machines in the textile industry. After that there have been a lot of
developments in the various sectors of the textile industry, and the following would throw light
on the latest developments that have taken place in the major segments of textile industry,
namely spinning, weaving, knitting and processing
Textiles have undergone chemical wet processing since time immemorial.
Human ingenuity and imagination, craftsmanship and resourcefulness are
evident in textile products throughout the ages. We are to this day awed by
beauty and sophistication of textiles sometimes found in archeological
excavations. Developments in the wet processing of textile materials
introduce new techniques and methods to reduce the energy, chemicals,
time involved during various operations to obtain novel finishes. Application
of ultrasonic waves, microwave dyeing, plasma technology, supercritical
carbon dioxide, and electrochemical dyeing of textiles are some of the
revolutionary ways to advance the textile wet processing. Unable to
withstand the pressure generated on account of the pollution levels, eco-
friendly alternatives are also being developed continuously besides novel
The uniformity of dyed materials mainly depends on the efficiency of fabric
preparatory processes. The removal of natural and added impurities
thoroughly from the fabrics to achieve uniform whiteness throughout the
fabrics is most important for the production concern. Many factors exert
significant influences upon the path of technological developments in the wet
processing and many of the factors include comparable quality with existing
processes with or without value addition, chemical compatibility to provide
multi-functional process, cost reduction by minimizing the use of energy and
water, increased levels of process control, monitoring and automation, eco-
friendly application methods etc. Developments that occur in other branches
of engineering and technology are effectively utilized in various processes of
textile processing, also, to meet the best requirements for the production
The theme of ITMA 2015 held in Milan in November was “Master the Art of Sustainable
Innovation.” The exhibitors took this theme to heart as the materials and machinery seen all
focused on providing the textile industry with more sustainable wet processing. Although the
main emphasis was on water and energy savings through modifications to existing equipment, a
few truly innovative developments were on display.
Dyes and Chemicals
Cuyahoga Falls, Ohio-based Americhem, a supplier of additives for fiber producers, offered two
new products — mBrace™, a REACH compliant hydrophilic additive; and Nofia™, a non-
halogen flame retardant (FR) additive for polyester. Americhem also provides a new masterbatch
service; color trend reports; and has opened a new technical center in Manchester, England, for
customer product development.
The central component Archroma’s Inkpresso®
System is the Inkpresso Ink Formulation Unit.
Switzerland-based Archroma showed two non-fluorine water repellent finishes — Smartrepel®
Hydro CMD for cotton and cotton blend fabrics, and Smartrepel® Hydro PM for man-made
fabrics. Both products are based on microencapsulation technology. Archroma also introduced
Earthcolors, a line of dyes manufactured from nut shells, leaves and other agricultural waste. Six
dyes are available yielding brown, grey, and olive shades and are applied using a similar
processes to the process used with sulfur dyes. A key feature of the Earthcolors program is a
traceable supply chain from raw material to retailer, ensuring that sustainable processes were
carried out in the production of the dyed garment.
England-based Avocet Dye & Chemical Co. Ltd. exhibited several Oeko-Tex® approved flame
retardants. CETAFLAM® DB9 is a durable finish for polyester fabrics, Cetaflam PD 3300 is a
semi-durable finish for cotton fabrics, and Cetaflam PD 3MW is a non-durable finish suitable for
A variety of new textile chemicals were presented by Germany-based CHT/Bezema Group.
Vario Bleach 3E is a bluesign®-approved bleaching agent for cotton fabric, which is effective at
70°C. Ecoperl Active is CHT’s non-fluorine water repellent offering, and Egasol Up is a unique
polyester dyebath additive that allows for very rapid dyebath heating — 5°C/minute — while
maintaining level dyeings.
Dyestuff producer Singapore-based Dystar offers Realan Black MF-PV, a new black dye for
wool as an alternative to Mordant Black 9. A fiber reactive dye series called Levafix® ECO,
which is not based on p-chloroaniline, was presented at ITMA. ECO Black, Navy, Forest
currently are available.
India-based Green Wave Global Ltd. showed a novel enzyme for bleaching cotton. Progen+ is
active under neutral conditions at 60°C and forms peracetic acid in-situ. Excellent whiteness,
minimum fabric degradation, and acceptable mote removal are achieved.
More non-fluorine water repellents were exhibited by Switzerland-based HeiQ Materials AG.
Barrier ECO-Dry for man-mades and Barrier ECO-Cel for cotton and cotton blends offer
Kyung-In Synthetic Corp. (Kisco), a Korea-based dyestuff supplier, presented Synozol Ultra
DS dyes, a series of seven dyes for medium and dark shades that can be used in exhaust,
continuous, and screen-printing applications.
Denmark-based enzyme supplier Novozymes, emphasized four concepts for processing textiles
with enzymes: denim processing; biopolishing at a neutral pH with a silicone softener;
processing Tencel®/cotton blends; and fully preparing cotton with only enzymes and natural
soaps. The latter process was demonstrated with the Geo towel, a soft, absorbent 100-percent
Novel chemical coatings containing graphene were shown by Italy-based Prochimica®
Novarese S.p.A. These coatings combined graphene — sheets of single layer carbon atoms —
with traditional coating materials to provide electrically conductive, antistatic and water-
repellent properties to textiles.
Germany-based Pulcra Chemicals focuses on active textile finishes. Highlights include
Silvadur®, a silver-based antimicrobial with a patented release mechanism; and Repellan®
ECO100, a non-fluorine water repellent with bluesign, GOTS, and Oeko-Tex approvals.
A new halogen-free FR product was presented by Germany-based Schill+Seilacher GmbH.
Flacavon FU3110 is intended for use with polyester technical textiles and home furnishings. The
company reports it anticipates commercializing a non-fluorine water repellent soon.
Switzerland-based Benninger AG exhibited the Trikoflex drum washer, which has been
completely redesigned for use with technical textiles. The washer now is available in widths up
to 5.5 meters. Benninger also showed the Tempacta, a low-tension steamer-washer designed for
Italy-based Lafer S.p.A. presented the liquid ammonia treatment range Permafix for knit goods.
Specially designed rollers control fabric shrinkage and 95-percent of the ammonia used during
processing can be recovered and recycled.
A singer designed for wide nonwovens was shown by Germany-based Karl Menzel
Maschinenfabrik GmbH & Co. The singer has enhanced process controls with improved fuel
efficiencies and higher production speeds, according to the company.
Italy-based MCS Group debuted the Starwash FS, an open-width drum washer designed for
efficient of washing digital prints under minimum tension. MCS also presented the Multiwash, a
combination J-box and spray rope washer that provides efficient washing with significant
savings of time and energy.
A dyeing machine with the capability to dye knit and woven fabrics at extremely low liquor
ratios was introduced by Acme Machinery Industry Co. Ltd., Taiwan. The AM-ICD
incorporates a conveyor belt system that allows polyester to be dyed at a liquor ratio of 1:2.5 and
cotton to be dyed at a liquor ratio of 1:3.5 under very low tension.
England-based Adaptive Control Solutions Inc. presented the Flow Book, a data storage
system that captures all relevant dyehouse data, which can be displayed on smart phones to allow
for rapid information transfer.
The design of the Rotora beam-dyeing machine from France-based Alliance Machines Textiles
has been improved to allow lower liquor ratios during dyeing. The Labojet from Alliance is a
laboratory dyeing machine for dyeing small accessories.
Italy-based Loris Bellini S.r.l. emphasized the Pulsar, a package dyeing machine designed to
dye yarns at a 1:3.8 liquor ratio. According to the company, the Pulsar operates with 25-percent
less steam, chemicals, and compressed air than traditional package dyeing machines as well as
uses 70-percent less energy for bath recirculation.
The Küsters DyePad from Benninger is designed for the cold pad batch dyeing of knits.
The Küsters DyePad from Benninger is designed for the cold pad batch dyeing of knits. The
DyePad is especially useful for short dye runs and operates under very low tension to minimize
Italy-based Brazzoli S.p.A. introduced the latest Ecologic jet-dyeing machine, which
incorporates a wash system that measures water consumption. The machine can process up to
750 kilograms of fabric at a liquor ratio of 1:4.
An improved hank dyeing machine was shown by Italy-based Cubotex S.r.l. The Unimat was
designed to combine the capabilities of both cabinet and spray machines into one and can operate
at temperatures of up to 100 °C with 30-percent less dye bath, according to the company.
The Netherlands-based DyeCoo Textile Systems BV has commercialized its super critical
carbon dioxide beam dyeing machine in Taiwan and Thailand. According to the company,
polyester fabric can be dyed to 98 percent dye exhaustion with no need for the usual reduction
clearing step with overall process savings of 40 to 50 percent realized. If preparation prior to
dyeing is required, conventional aqueous preparation should be carried out.
A ready for commercialization dyeing machine for dyeing polyester yarn packages with super
critical carbon dioxide was presented by eCO2dye, Allentown, Pa. Units with yarn capacities of
10, 50, and 100 kilograms (kg) are available with 50-percent reductions in energy and chemical
usage expected, according to the company.
Italy-based Flainox S.r.l. introduced an enhanced high-temperature garment dyeing machine.
The e3 machine is available in 10- and 30-kg capacities and features automated loading and
Hong Kong-based CHTC Fong’s Industries Co. Ltd. highlighted the Superwin, a package
dyeing machine with the capability of employing a unique single flow procedure with
appropriate yarns. Liquor ratios as low as 1:3 can be achieved.
Germany-based Fong’s Europe GmbH showed the Goller Economica Dye Pad, a heated dye
pad designed for open-width knit goods. The pad has been designed to minimize fabric
distortions on delicate fabrics.
Lab-Pro’s Dyewa machine features a rotating perforated beam whereby the dye bath is sprayed
from the interior of the beam onto the fabric wound on the beam.
An truly innovative beam dyeing machine was debuted by Switzerland-based Lab-Pro GmbH.
The Dyewa machine features a rotating perforated beam whereby the dye bath is sprayed from
the interior of the beam onto the fabric wound on the beam. Both cotton and polyester fabrics can
be dyed in 200 kg batches using up to 40-percent less water than conventional beam dyeings,
according to the company.
Italy-based Laip S.r.l. offered two low liquor ratio jet-dyeing machines. The Airjet 2000 can dye
fabric at a liquor ratio of 1:3, while the Jet 250HT is capable of operating at a liquor ratio of
The Dos-Chem dosing system was presented by Italy-based Lawer S.p.A. The system provides
automated dosing and dispensing of dyes and chemicals for laboratory and pilot plant dyeings
and includes automated weighing and dissolving of liquids and powders.
MCS introduced the Dynamica Sprint high-temperature jet-dyeing machine that allows five-hour
dye cycles at a liquor ratio of 1:3.5. The machine has a unique heat-recovery system that
provides for significantly lower energy requirements.
A new wash box design for indigo dye ranges was shown by Morrison Textile Machinery, Fort
Lawn, S.C. The Peak washer has a patented flow system that reduces water usage by 50 percent,
and also leads to increased rebeaming efficiency by minimizing yarns distortions, according to
Oasis® Dyeing Systems LLC, Leesville, S.C., presented the Oasis® process, a continuous
dyeing process for 100-percent cotton that incorporates a Gaston County foam dyeing system on
fabric that has previously been pretreated with the Oasis treatment. This treatment permits fiber
reactive dyeing with no salt, alkali, thickeners or afterwashing.
An automated package dyeing machine for lab and pilot plant was introduced by Obem S.p.A.,
Italy. The four-tube machine can accommodate up to 10 packages per tube in either a horizontal
or vertical configuration with automated loading and unloading.
France-based Rousselet Robatel displayed its continuous treatment line for fiber bleaching,
dyeing, and finishing applications. The conveyor belt system can accommodate production
speeds from 100 to 1,000 kg per hour.
A new approach to indigo dyeing called Smart-Indigo™ was shown by Switzerland-based Sedo
Engineering S.A. Leuco indigo is produced electrically under an argon atmosphere resulting in
reduced pollution and significantly reduced chemical costs, according to the company.
Italy-based Tecnorama exhibited Shakerama, a high-temperature laboratory dyeing system that
simulates the liquor ratios and mechanical action of production dyeing machines. Dyes and
chemicals are automatically measured and dispensed by the system.
An innovatively designed jet-dyeing machine was presented by Fong’s Europe. The Then
Supratec LTM features adjustable liquor ratios — ranging from 1:6 to 1:12 — and kier angles to
accommodate a wide range of fabrics. The Then Airflow® Synergy 8 jet-dyeing machine on
display at ITMA can operate at liquor ratios of 1:3.5 and consuming up to 25-percent less
energy, according to the company.
Thies GmbH & Co. KG, Germany, introduced the DyeControl dyebath monitoring system that
measures pH, salt, and dye concentrations, as well as total water consumption. This information
can lead to reduced cycle times and water usage, according to the company. Thies also
introduced the iMaster Mini, a lab and pilot plant version of its iMaster H2O production dyeing
Commercial scale atmospheric pressure plasma equipment was shown by APJeT® Inc.,
Morrisville, N.C. A variety of surface properties — including repellency, antimicrobial and
antistatic — can be achieved in a continuous process without heat or water. APJeT’s Morrisville
facility is available for pilot trials and proof of concept experiments.
Italy-based Biancalani S.r.l. exhibited the Brio® 24, a low-tension dryer for knit goods. A
combination of vibrating trays and hot air flow allows for high throughput with minimal fabric
distortions, according to the company.
Brückner’s Power-Frame Ecoline offers enhanced air flow and heat recovery.
A tenter frame with enhanced air flow and heat recovery was presented by Germany-based
Brückner Trockentechnik GmbH & Co. KG. The Power-Frame Ecoline is equipped with a
new control system to maximize productivity and minimize energy consumption. Brückner also
showed the Eco-Coat, a chemical applicator that minimizes wet pickup.
Switzerland-based Cavitec AG, a member of the Santex Rimar Group, introduced the Cavimelt
P+P, a hot melt coater/laminator designed for small production lots and startup companies.
Cavitec has incorporated the unwinding and rewinding sections into the compact unit to reduce
the machine’s overall footprint.
A vacuum plasma system was shown by Belgium-based Europlasma NV. The Plasma Guard
system currently offers seven different surface treatments for garments and small articles.
Spain-based Iberlaser exhibited equipment for the continuous laser treatment of denim. The
Delta machine is designed to treat full-width denim fabric, while the Zeta machine is intended
for treating denim garments.
Spain-based Icomatex S.A. presented an innovative approach to wash box design. The Icowash
incorporates submerged vacuum slots to enhance washing efficiency. Higher production speeds,
cleaner fabrics, and reduced water consumption are benefits reported by the company.
A new knit compactor was shown by Lafer. The Go-Rubber is an open-width knit compactor
that includes both rubber and felt belts to efficiently achieve high levels of compaction.
Germany-based Mahlo GmbH & Co. KG introduced the Orthomax RFMB-12, a fabric
straightener for woven fabrics. A combination of both pins and bow rollers provides for optimal
The Rotolabo Multi-600 coater was debuted by Italy-based Matex S.r.l. This machine is
equipped with multiple coating heads for lab, pilot plant, or small production lots and is capable
of reaching curing temperatures of 400°C.
Germany-based A. Monforts Textilmaschinen GmbH & Co. KG presented the Montex XXL
tenter designed especially for nonwovens. The Montex XXL can accommodate fabrics up to
seven meters wide. Monforts also showcased the Thermex Thermo, a denim finishing range with
production speeds of up to 80 meters per minute.
Two tubular knit processing machines were shown by Navis TubeTex, Lexington, N.C. The
SCS — Spirality Correction System — is a patented system that efficiently removes torque from
tubular knits. The company also highlighted the Pak-Nit e3+, which is a high-speed tubular knit
compactor that can process two strands simultaneously.
Switzerland-based Santex-Rimar AG, a member of the Santex Rimar Group, introduced the
SantaSynpact, an open-width-knit compactor. The SantaSynpact combines rubber and felt belts
and can reach production speeds of up to 60 meters per minute.
The Decofast 3.5 was exhibited by Italy-based Sperotto Rimar, also a member of the Santex
Rimar Group. This high-speed continuous pressure decator can process a variety of natural, man-
made, and blended fabrics.
Recent developments in febric preparation process:
Attempts have been made, in the past few decades, to optimize the
individual unit operations involved in wet processing to derive the
advantages in the respective unit operations1–3. New methods involving low
temperature, low pH and eco-friendly chemicals are also explored for
reducing the pollution and effluents generated during various operations in
industrial sectors. However, a logical approach to conserve energy and
materials in the preparatory processes is to shorten the sequence by
combining the three operations, desizing, scouring, bleaching, commonly
known as DSB process. Most of the combined preparation processes have
failed mainly due to inadequate removal of seed coats/mote. Various
combined processes have been developed in the past using different
chemicals and also using new formulations for scourant 1– 3.
Peracetic Acid (PAA) Bleaching an Eco-friendly Alternative: Any
substitute to the traditional bleaching agent NaOCl, should be a product with
comparable redox potential. In case of low temperature bleaching it has
been introduced peracids as stronger oxidizing agents than hydrogen
peroxide (Table- 1). Use of PAA as a bleaching agent has been discussed by
many authors for different fibres like cotton, flax, nylon 4 –9. The rate of
decomposition and consumption of PAA vary over a range of bleaching
temperature at different pH with varieties of alkalis. PAA consumption is slow
when sodium hydroxide (NaOH) is used as an activator, at different values
of pH and temperature, whereas consumption is quicker and rapid with
inclusion of magnesium carbonate. PAA is produced industrially by mixing
acetic acid with hydrogen peroxide in presence of an acid catalyst. At higher
pH and temperature, PAA decomposes spontaneously to produce acetic acid
and oxygen. The chemical reaction can be expressed as in mechanism -1.
Fabrics treated with PAA at neutral pH at room temperature for about an
hour followed by alkaline peroxide bleaching at 90°C have shown a
brightness of greater than 90 Berger units, significantly with less fibre
damage and crease marks. PAA is used for the removal of heat setting
discoloration from nylon, carried out at pH 6.0 –7.5 for about an hour at
80°C using 0.3% solution. The similar process also could be used for viscose
rayon, secondary acetate and triacetate materials.
Table- 1: Potential of oxidizing agents
Agents Potential (eV)
The main advantage of bleaching with PAA instead of hydrogen peroxide is
that satisfactory degree of whiteness can be obtained at 60°C, within 40 min
at neutral pH without addition of auxiliary agents. Optimum whiteness index
can be achieved at temperatures around 50°C and 90°C and bleaching time
over 60 min yields significantly higher brightness4. For a given degree of
whiteness, the percentage strength loss and the extent of chemical damage
are the least for PAA followed by hydrogen peroxide10. The absorbency time
and tearing strength decreases steadily up to a pH 7 value and the bleached
fabrics show comparable fastness properties with reactive dyes5.
Implementation of Single Stage Preparatory Process:
Single stage preparatory process using hydrogen peroxide has been
developed successfully for starch and acrylic-base sized textile materials
previously 11,12 . In such processes, caustic soda provides required
alkalinity for scouring and activation of hydrogen peroxide and when
activated, hydrogen peroxide degrades the sizing materials at lower
temperature and at higher temperature, bleaching occur along with
completion of desizing. Higher alkalinity at elevated temperature produces
efficient scouring action. A self-emulsifiable solvent system of bleaching has
been developed to combine the three different processes involved in the
preparatory process. The system uses a high proportion of water, very low
levels of solvents and hydrogen peroxide. The presence of hydrogen
peroxide helps both desizing and bleaching and the emulsified solvent
results in the scouring of cotton fabric11. Since the system involves very low
quantity of solvent content, need for a solvent recovery plant is obviated. In
the case of sodium chloride (NaCl)- hydrogen peroxide (H2O2) system, free
radical mechanism( Mechanism-2) is responsible for the bleaching action.
Various free radicals created during the treatment resulted in disintegration
and destruction of foreign matters present in the cotton. The bleaching effect
is more distinct with peroxide than sodium chlorite, even at the higher
concentrations. Presence of co-oxidants impedes the decomposition of each
other, especially at their lower concentrations. The reactions under alkaline
medium are initiated as chain reaction by the production of different free
radical in different steps. The different step of the reaction is shown below:
The HO· and HOO· radicals react with the chlorite ions and, as the result, a
reaction chain is perpetuated as suggested as:
These free radicals enhance the bleaching effect of NaCl by H2O2 when used
at their higher concentration. Thus created free radicals seem to disintegrate
the impurities and destroy the coloring matters of the cotton. Various recipes
that have been developed for the single stage preparatory process
summarized in Table -2. In case of the hypochlorite-solvent assisted single
stage preparatory process 13-15, the whiteness index and tensile strength
exhibit approximately a linear relationship with available chlorine in sodium
hypochlorite solution at various treatment at a time range from 45 to 225
min. Better wetting time is obtained at the scouring agent concentration of
8% at a temperature of 50°C – 55°C, which is closer to the cloud point of
the non-ionic emulsifier used in the recipe. In the peroxide-alkali process,
absence of either sodium hydroxide or hydrogen peroxide in the peroxide
based process results very low weight loss, indicating very low efficiency11.
Table- 2: Recommended recipes for single stage preparatory process
Process Name Recipes/Procedure Ref.
H2O2: 1.0 g/L, NaOH:10 g/L, Wetting
agent: 1.0 g/L, Temperature: 95° C,
Time: 120 min, pH = 10.5-11.5( using
Scouring agent : 4%, Peroxide: 2%,
Sodium silicate : 1%, Wetting agent :
0.1%, Temperature : 95°C, Time :180
min, pH = 10
Scouring agent : 4% , Peroxide :1%,
Sodium Silicate : 1%, Wetting agent :
0.1%, Temperature : 95°C, Time :180
min, pH = 10
Scouring agent : 4% o.w.f., H2O2:
1%, Na2SiO3 : 2%, Na3PO4 : 2%, or
tetra sodium pyrophosphate, pH =
11, Time :12 min – 16 min/24 h at
Solvent based scouring agent : 2%,
NaOCl : 6 g/L (avg. Cl2 ),
Temperature : 40°C, Time :180 min,
M : L –1: 20, pH = 11
NaClO2: 3 g/L, Na2HPO4: 10 g/L, NI
Wetting agent : 2 g/L, pH =10, Time :
90 min, Temperature : 95°C, M : l – 1
Sodium Chlorite : 0.8 – 1.95%,
Scouring Agent : 2%, (activators as
stated in the text), Temperature : 30
– 55°C, Time : 5 h – 14 h, pH = 4.6
(buffered) & 8 – 9(un-buffered)
Sodium Hydroxide : 20 g/L, Hydrogen
Peroxide : 30 ml/L -40 ml/L,
Peroxidisulphate : 5 g/L, Sodium
Silicate : 20 ml/ L, Surfactant : 10
g/L, Stabilizer : 5 ml/L
Ciba Tinoclarite FS :15 ml/kg – 30
ml/kg, NaOH(100%) : 30 gm/kg – 50
gm/kg, H2O2 (35%) : 49 ml/kg –
In the SSPP, an attempt has also been made to improve the efficiency by
carrying out the process using microwave of 600w for duration of 30sec to 3
min. The process involves steaming of the fabric with the simultaneous
exposure to the microwave energy. In another narrative approach, flash
steam procedure has been used to combine all the preparatory processes
into a single step.
Application of Plasma Technology:
The plasma technology is considered to be very interesting future oriented
process owing to its environmental acceptability and wide range of
applications. Plasma is the fourth state of matter besides solid, liquid and
gas which contains ionized gas comprising of ions, electrons, atoms and
molecules. Presence of free electrons and other charged particles converts
plasma as electrically conducting and responsive to electricity. The plasma
modifies the fabric surface by the bombardment with high energy electrons
and ions shown in Figure- 1. The classification systems of plasmas is often
based on temperature, pressure, type of current used, and the types of
gaseous matters used in the plasma processes, types of substrates used and
the results appear to vary depending upon the effects targeted.
Figure -1: Plasma (a) A mixture of reactive species, (b) Principle of plasma
Reactive gases, inert gases, water vapor and combination of these are used
on all types of textile materials depending upon the applications16. The
mean free path of gas particles, typical distances in the fabric structures like
inter-fibre distance and inter-yarn distances have to be considered in the
plasma processing17, 18. Plasma treatment causes ablation (Figure -2) of
fibres surface by introducing different kinds of surface roughness such as
cracks and fissures.
Figure- 2: Effect of plasma treatment on fabrics surface.
The structure and construction of yarn play major roles in deciding the
efficiency of plasma processing. The presence of impurities in the raw fibres,
additives present in the yarn and fabrics also intervene during the plasma
processing. The free radicals produced in the treatments can undergo
reactions depending upon the gases present in the atmosphere. The
acidification of raw cotton increases with increase in purity of cotton fibres
and the change in pH was to the extent of about 1.0 for raw cotton whereas
it increases to above 2.0 for bleached fibres. Even very high power supply
with prolonged treatment results in no significant change in tenacity and
elongation at break values for both PET and cotton fabrics.
The voids and cracks developed in PET also aid penetration of moisture.
Plasma treatment offers effect which are often decaying in nature, i.e.,
ageing or durability effect. Grafting of flame retardant monomers has been
successfully carried out on the cotton fabrics to obtain durable effects than
that is possible with conventional surface deposits. Development of self -
cleaning cotton textiles through RF-plasma, MW-plasma and UV -radiation to
introduce functional groups to anchor TiO2 on textile surface shows the
formation of TiO2 crystallites with 5 - 7 nm size immediately, from the
precursor 19. Plasma processing has been attempted in desizing of PVA
sized viscose rayon, starch sized cotton yarns, scouring of cotton and wool
fibres using cold plasma20. These reactions occurred mainly due to ablation
of surface, removal of starch and hydrophobic substances. The subsequent
washing reduces the wetting time to less than1 sec.
The percent desizing ratio21 reaches up to 97%, air-oxygen-helium plasma
yields better weight loss (up to 2.8%) compared to air-helium plasma 2.3%.
The contact angle decreases considerably after oxygen plasma treatment
compared to untreated samples and the plasma treatment followed by
scouring results in the residual wax content to 8.0% in cotton and wool.
Surface modification of textile materials to create a reactive surface suitable
for dyeing and finishing treatments has been attempted by many
researchers17, 19,. The effect of plasma treatment on fabrics made of
various fibres and the relevant results are summarized in Table-3.
Table- 3: Effect of plasma finishing on various fabrics.
Fibre Process Name Procedure Effects Result
Air – O2 plasma,
low pressure 0.6-8
Air-O2 plasma, low
temperature at 9
pa pressure, 70w
– 120w CF4 ,C3F6
300w, 50 m & 75
m, Torr for CF4
m – 150 m
Torr for C3F6
C = O,
Linen Wicking (RF-
Ar – O2 plasma,
pressure 15 pa
with power 100w,
Ar- O2 plasma,
power, 100w and
pressure 1– 10pa.
– OH, –
changes due to
Nylon Water repellency
power, 100w &
of F atoms
Dyeing in Supercritical Fluids (DSF):
Any gas above its critical temperature retains the free mobility of the
gaseous state but with increasing pressure its density will increase towards
that of a liquid (Figure- 3).
Supercritical fluids are highly compressed gases and combine valuable
properties of both liquid and gas21. Supercritical fluids have solvent power
similar to a light hydrocarbon for most solutes. Solubility increases with
increasing density (i.e., with increasing pressure). However, fluorinated
compounds are often more soluble in CO2 than in hydrocarbons, which
increased solubility, is important for polymerization. A liquid can be
converted to a supercritical fluid by increasing the temperature and
consequently its vapor pressure and simultaneously with increasing
pressure. A closed system thus reaches the supercritical state, where no
boundary between the liquid and gaseous state can be distinguished.
Figure- 3: Temperature- pressure relationship of substances.
Any increase in pressure subsequently results, increase in dielectric constant
and the dissolving power to a greater extent. Carbon dioxide is frequently
used as a solvent because of some inherent advantages associated with the
system like, non-toxic, non-corrosive and non-hazardous nature; CO2 is
produced commercially and can be transported easily. The critical points of
the CO2 can be achieved easily compared to other gases. The dissolved
dyestuff available for diffusion into the boundary layers in the supercritical
fluid is absorbed and diffuses into the fibres. The state of the dyestuff in a
super critical solution can virtually be described as gaseous. Supercritical
CO2 has almost a plasticizing effect which accelerates the diffusion
processes by increasing the chain mobility of the polymeric molecules. This
means that it will be absorbed by the fiber at a rate comparable to the high
diffusion rates corresponding to that of a gas. The distribution dyestuff-fluid
can be continuously shifted in favor of the polymer until after expansion of
the gas to standard pressure the solubility in the fluid will be equal to zero,
where a theoretical exhaustion level of 100% is achieved.
The wet processing of textile materials includes highly energy consuming
operations, approximately to 80% of total energy requirement of all the
operations. Out of this, about 66% of the energy is consumed in heating and
evaporation of water from the fibres. Invariably, the liquor retained in the
fabric is distributed 22 within and between the fibres in the form of capillary
liquid in the available spaces between the yarns and also on the surface of
the textile material, i.e., surface bound water. Squeezing the fabric between
the nips eliminate the excess liquor available on the surface of the fabric and
the interstices of the yarns, which depends on the nip pressure, hardness of
rubber, roller diameter and machine speed or fabric speed. The concept of
low add-on is based on the controlled transfer of a reduced quantity of liquor
from a dipping roller to the fabrics. Moreover foam application is different
from the low add-on technique since air is used to dilute the liquor, which is
not the case in the earlier ones. In the foam process the liquor is diluted
using the air instead of water that is normally used to apply the chemicals
over the textile materials.
In foam finishing, most of the water is replaced by air, which leads to a
reduction of energy requirements in the drying processes resulting in
substantial savings in energy cost. Foam is a colloidal system comprising of
mass of gas bubbles dispersed in the liquid continuum23, 24. Foam can be
generated by mechanical air blowing, through excess agitation or chemically
by introduction of foaming agents or combination of these methods. The
relative proportions of air and liquid phases in the foam are designated by
blow ratio. Foam stability, density and diameters are the important
parameters that need constant attention25. A varying bubble size represents
an unbalanced bath density. Foam density in general, varies between 0.14
g/cc – 0.07 g/cc for the foam finishing and 0.33 g/cc – 0.20 g/cc in the foam
printing. The selection of the density of the foam depends on the fabric
weight and needs to be increased with increasing fabric weight. Foam
viscosity depends on the foam density and viscosity of the un-foamed liquor.
Increase in foam viscosity results increased foam stability. Bubbles with
smaller size are more stable than bigger bubble size and the bubble
diameter ranges, generally, from 0.001 mm – 2.0 mm depending on the
generation systems. Bubbles or foams, inherently, do not thrive in higher
energy environment since higher energy levels results in the destability of
the foam25. Destabilization of the foam is also caused by creation of the
faults in the foam structure at the air/liquid/air interface. The destruction of
foam after application on to the fabrics can be achieved by conventional
padding or vacuum application or combination of both.
Foam application technique can be used23, 24 in the fabric preparation,
dyeing and printing, DP finish, softening, soil-release finish, water, oil
repellant finish, FR finish, anti-static finish, mercerization, etc. The foam can
be applied either on one or both sides of the fabrics. Horizontal padder, kiss
roller coating, knife over the roller coating, knife on air system and slot
applicator system are commonly employed in foam applications.
Conservation of water and energy has been the centre of research during
the past and today also 26,27 and foam finishing process can be used to
achieve 80% of water consumption28, the energy consumption by 60% –
65% in the form of gas, electricity depending upon the type of finishing
treatment used, obnoxious gases and their related pollution can be
minimized29. The chief advantages of foam application techniques with foam
finishing treatment reduces the payback period to as low as six months to
two years 24, 25, 9, 10, 11.
Ultrasonic Assisted Textile Processing:
Sound waves have been classified into infra-sound (up to 16Hz), audible
sound (16 Hz –16000 Hz) and ultrasound which include sound waves higher
than audible sound with a frequency above approximately 16 kHz up to 106
kHz. Unlike gases and liquid, in solids both longitudinal and transverse
waves are transmitted. The effects of ultrasonics actually arise from the way
in which sound is propagated through the medium. In liquids, longitudinal
vibrations of molecules generate compressions and rare factions, i.e., areas
of high and low local pressure. The latter results in the formation of cavities,
i.e., very small vapor bubbles of 500nm in size, which can collapse and
cause shock waves through out the medium. The formation of cavitations
depends on the frequency and intensity of waves, temperature and vapor
pressure of the liquid 30. Cavitation is the principal physical phenomenon
behind all the effects of ultrasound in most of the treatments. Cavitations
refer to the formation, growth and collapse of vapor or gas bubbles under
the influence of ultrasound. If the bubbles collapse in the vicinity of a solid
surface such as a textile material, it results in the formation of a high
velocity micro jet with the velocities as high as 100 m/s –150 m/s directed
towards the solid surface31. These micro jets can give rise to intra yarn
flow, increase in the rate of the mass transfer between the intra-yarn and
inter yarn pores. On the other hand, they may be carried along with the
sound waves if they do not collapse immediately. This, in turn, pushes water
along with the bubbles producing a flow of water called streaming away from
the sound source. The two phenomena attributed to ultrasound are the rapid
movement of liquids caused by variation of sonic pressure which subjects
the solvent to compression and rarefaction and micro streaming.
Simultaneous formation and collapsing of tiny air bubbles result in a large
increase in pressure and temperature at microscopic level. Heat induced by
the ultrasonic process is adequate for dyeing process and thus eliminates the
need for external heating in many cases. Advantages of ultrasonics in textile
wet processing include energy saving by reduced processing temperature,
time, and lower consumptions of auxiliary chemicals and further processing
enhancement by overall cost control33. Ultrasonic method has been
effectively utilized in various fabric preparation processes including desizing,
scouring, bleaching, mercerization and auxiliary processes, like washing and
laundering31, 34-36. Desizing of cotton and nylon fabrics under ultrasonic
treatment results complete removal of oils used in the size recipe while the
treatment without ultrasound shows residual oil stains. Effect of ultrasonic in
enzymatic scouring has been tested using both acidic pectinases and alkaline
pectinases and found to have increased wettability of all treated samples
both tests compared to the conventionally treated samples. Ultrasonic
treatments help to reduce the processing and temperature required for a
result comparable to the normal bleaching and subsequent dyeing processes
in terms of absorbency and fastness properties. Ultrasound is used for
mercerizing 100% cotton fabrics in the after treatment and speeds up the
process up to 2 – 3 times. Ultrasonic also has been used for evaluating its
impact on washing the fabrics and garments under the simulated stain
conditions on 100% PES and P/C (65/35) blends using the detergent of 1
g/L. Attempts have been made to analyze the effect of ultrasonic in dyeing
processes on almost all types of fibres using direct, reactive, acid and
disperse dyes. Ultrasonic waves accelerate the rate of diffusion of the dye
inside the fibre with enhanced wetting of fibres. Acoustic irradiation of the
liquor results in a higher and more uniform concentration of dyestuff on the
fibre surface, making it available for ready diffusion into the fibre interior(
Figure - 4: Liquid flow through and around a textile yarn. The dots
represent the fibres in yarn.
The influence of ultrasonic on the dyeing system has threefold effects
namely, dispersion effect, i.e., breaking up of micelles and high molecular
weight aggregates into uniform dispersion in the dye bath, degassing by the
removal of dissolved or entrapped gas molecules or air from fibre capillaries
and interstices at the cross over points of the fabric into liquid thereby
facilitating a dye-fibre contact and accelerating the rate of diffusion of the
dye inside the fibre by breaking the boundary layers covering the fibre and
accelerating the interaction between dye and fibre. These above mechanisms
may be in effect individually or in combination of the above. Extracts
obtained various natural plants sources like Cassia fistula, Impatiens
balsamina, Al root bark, barks of eucalyptus, which grow abundantly in
tropical and sub-tropical forests have been obtained to the cellulose fibres
and their blends using ultrasonicators for both extraction as well as for the
application purposes 37,38. An attempt has been made to compare the
dyeability of both PET and PBT in presence of ultrasound using disperse
dyes. The effect of carrier and ultrasound together was significantly larger
than either individually. Table- 4 shows various frequencies and power
output required for various textile wet processing operations including
Table - 4: Frequency and power output for wet processing.
30,47 230 Laundering of
20,24 600 Desizing 4
20 ….. Natural dyes on
cotton and blends
26 120 Disperse dye on
20 180, 600 Dyeing with
acid, basic dyes
520 ……. Effluent treatment16
The development of unique textile wet processing technology comes with a
host of challenges. Finishes must be durable during the finishing process;
stable in the presence of other chemicals; wash-fast; and evenly and
consistently applied. Finishes also need to be financially feasible and
environmentally friendly. The typical dyeing process involved the use of
chemicals and thermal energy, which can be reduced, by using ultrasound
energy. Among the wet processes, application to dyeing seems to be most
advantageous, followed by finishing and preparation processes. There may
be a possibility of reducing the pollution load on effluent water. Since
recently, however, the plasma Technology is being introduced in textile
industry as well. The processes the methods are economical and reduce the
environmental impacts caused by the chemical textile industry. Dyeing with
super critical CO2 is still at its infancy. It has been proved time and again
that it’s successful at laboratory scale. Large amount of research input is
needed for system integration.
3. Editor’s Note: William Oxenham, Ph.D., is associate dean for academic programs at
North Carolina State University’s
4. Department of Textile and Apparel Technology and Management, Raleigh, N.C.
Oxenham received both a B.Sc.