The document discusses developments in environmentally friendly functional finishes for cotton fabrics and garments. It provides an overview of finishes that are formaldehyde-free, as well as silicone softeners, bio-finishes, water repellent breathable finishes, and anti-microbial finishes. Emerging technologies discussed include plasma treatment, fiber coating, and genetically modifying cotton through biotechnology. The document then focuses on wrinkle-free finishes for cotton and methods for imparting these finishes through pre-cure, post-cure, dip, and tumble processes.

1. Developments in environment friendly functional finishes for cotton fabrics and
garments
R.B.Chavan
Department of Textile Technology
Indian Institute of Technology
Hauz-Khas, New Delhi 110016
Abstract
Global awareness for environment protection combined with stringent legislation on
industrial effluents had led to the search for environment friendly chemical processes for
textiles. In the present paper an overview of environment friendly functional finishes for
cotton fabrics and garments has been given. The developments in formaldehyde free wrinkle
free finishing, silicone softeners, bio-finishing, water repellent breathable finishes, anti-
microbial finishes, soil release finishes etc are critically discussed. Plasma treatment,
finishing through fibre coating, the use of biotechnology for genetic modification of cotton
are considered to be some of the emerging technologies for imparting functional finishes to
cotton.
Introduction
"The polluters must pay" is the concept, which has been emerged recently for
industrial production. There are stringent legislations particularly in developed countries on
eco-toxicological considerations, health and safety during storage, use and safe disposal of
chemicals in water, landfills or release in air during processing or during incineration. In
order to meet these requirements an integrated pollution control approach is essential. This
has necessitated having a re-look towards the entire textile production processes. As a result
of this some of the well-established chemicals, dyes, finishing agents and auxiliaries have
been replaced by environment friendly substitutes for the production of textiles.
Consumers particularly in developed countries prefer eco-friendly textiles. Therefore,
the manufacturing of textiles in developing countries for the export market in developed
countries is oriented towards achieving this goal, though the cost of production is high.
Among the various fibres used for apparels, cotton dominates the market due to its
several advantages. It is readily available at affordable price compared to silk and wool.
Being natural it is considered to be eco-friendly. In the present article an attempt has been
made to review critically the developments in functional finishes for cotton fabrics and
garments.
Eco-friendly cotton
Cotton is cultivated using pesticides, fertilizers and other crop related chemicals. The
residues of these chemicals remain on cotton bolls. These residues are removed during the
preparatory processes and enter into the wash liquor resulting in water pollution. Therefore in
true sense, cotton cultivated by using such chemicals is not considered to be eco-friendly. A
trend is started to cultivate cotton without the pesticides, fertilizers and other chemicals. Such
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2. cotton is considered to be eco-friendly and is known as natural cotton, green cotton or organic
cotton.
The use of biotechnology to introduce disease resistant cotton and organic farming
techniques may decrease the use of chemicals, pesticides, herbicides, fungicides, defoliants
and harvest aid chemicals used for cotton cultivation. This would help to decrease soil
pollution during cultivation and water pollution during preparatory processes.
Naturally coloured cotton
Naturally coloured cotton of various colours particularly green and brown varieties
were cultivated since ancient times in many countries. However, such cotton did not gain
commercial popularity due to low yield, short staple length, poor fibre strength, poor
spinnability and possible contamination due to pollination. The present environment
protection trends have given impetus to the revival of cultivation of naturally coloured cotton.
Such cotton is not subjected to dyeing and thus is free from pollution caused by dyeing
operations.
Finishing
Though attempts are being made to produce raw cotton itself as environment friendly
as possible. Nevertheless, to make salable consumer products, the fibre, yarn, fabric or
readymade garments have to go through various chemical-processing sequences such as
preparatory, dyeing, printing and finishing. Among these the finishing assumes considerable
significance because the value addition is realized through functional finishing of cotton in
fabric or garment form to impart desirable properties. Some of the most important finishes
are
1. Easy care/Durable press/Wrinkle free finishes
2. Softening
3. Enzyme/bio finishing
4. Water proof breathable finishes
5. Soil release and stain release finishes
6. Anti microbial finishes
Some of the recent developments related to eco-friendliness of the above finishes are
critically described in the present paper.
Easy care/wrinkle free finishes
The primary function of clothing is to prevent the loss of body heat to allow the sweat
to pass through it to the outside atmosphere. Cotton is good in each of these functions. These
properties together with its hydrophilicity, freedom from static charge generation and
pleasant natural feel makes it excellent fibre for tropical wear. However one of the major
shortcomings of cotton fabrics/garments is that, it is prone to creasing during wear and
washing. A treatment with cross linking agent is given to impart wrinkle free properties to
cotton. The process is traditionally known as resin finishing. This finish imparts crease
resistant properties to cotton and keeps shrinkage under control. However when the desirable
properties are imparted at attractive levels, the strength is reduced to unacceptable level. Of
the several technological attempts addressing this issue a few have been able to achieve a
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3. favourable balance of wrinkle resistance and mechanical properties and have become
commercially successful.
The development of all cotton wrinkle free apparel in 1990s has raised consumer's
expectations on the performance and appearance of cotton garments. The consumers expect
the wrinkle free performance to remain almost intact over at least 50 launderings. The rule of
thumb is that if the performance stands 10 washes (each of 10 minutes duration at 50-600 C in
presence of 1-5g/l detergent) it is likely to stand 50 washes.
There are different routes for imparting wrinkle free/easy care properties to cotton
fabrics/garments. The most important routes are
1. Pre-cure and post-cure processes
2. Dip and tumbling processes
Pre-cure process
This is used for fabrics which do not require pleats. The advantages being uniform
distribution of chemicals and better process control. The steps involved are pad-dry-cure and
are carried out at mill level.
Post cure process
In this pad-dry application is done at mill level to produce sensitized fabric which is
then transported to garment manufacturing unit. Care during storage of sensitized fabric is
essential. Many ship the fabric by air and store under refrigeration. The time between
garment sensitization and garment making followed by curing is kept minimum (not more
than 3 months). The typical steps involved are
Pad with resin recipe (60-70% pick up).
Dry to 10-12% moisture content.
Sanforize without moisture spray.
Garment making
Garment pressing to introduce creases at desirable places
Garment curing at 150-1600C for 8-10 minutes.
Finishing in garment form
The principal benefits of wrinkle free processing in garment form are
1. Permanent fixing of creases in garment at desirable places
2. No risk of pre-mature cross linking during drying, storage and transportation.
3. Puckering of garment seams is minimized.
The following points must be considered.
1. Careful selection of sewing thread buttons zips etc. since these are exposed to corrosive
chemicals and heat during wrinkle free processing.
2. Resin finishing offers only one chance. If there is any thing wrong it can not be corrected.
This applies both to fabrics and garments. However the control may be more difficult in
case of garments than fabrics. Stripping of resin and re-finishing causes more damage.
There are two methods of garment finishing
1. Dip process
2. Tumbling process
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4. Dip process
1. Dip the garment inside out in the finishing chemicals keeping MLR 1:5. Suitable washing
machine may be used.
2. Rotate the garments for 20 minutes.
3. Hydro-extract to 70-80% pick up.
4. Tumble dry at 700 C to moisture content 10-12%.
5. Turn the garments right side out.
6. Iron/steam press the garments to set the creases at the desired places.
7. Cure at 150-1600C for 8-10 minutes.
The solution recovered from the hydro-extractor can be reused.
Tumble method
In this process the garments are placed (inside out) into a machine with sealed (not
perforated) drum and application of resin recipe by pumping or spraying. The drum is turned
for 20 minutes. There should not be excessive dripping of chemicals from the garments and
also there should not be dry spots on the garments. This method is being used more and more
due to the fact that there is no wastage of chemicals. After saturation the garments are hydro
extracted, tumble dry at 700C to 10-12% moisture content.
Iron/steam press the garment to set the creases.
Cure at 150-1600C for 8-10 minutes.
Important features
MLR should not be less than 1:0.85 for the garments weighing up to 600 gms/garment and
1:1 for those weighing more than 600 gms.
Minimum time of tumbling should be 20 minutes.
Tumble rotations speed 28-30 rpm.
Tumble drying temperature should not be more than 700C
Moisture retention after drying 10-12%. If it goes below 10% re-dip and dry.
Chemicals used
Cross linking agent Low formaldehyde modified glyoxal based (DMDHEU) with external
or built in catalyst and buffered. Various brand products are available in the market.
Catalyst Facilitates cross-linking reaction. Most commonly used is magnesuim
chloride:citric acid system
Wetting agent Helps to achieve quick wetting and even distribution of resin recipe.
High-density polyethylene emulsion Imparts hand, improve tear strength, abrasion
resistance and sewability.
Amino silicone or reactive silicone softener Impart soft hand and slick surface feel.
Improve wrinkle recovery and sewability.
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5. Silicone elastomer Impart springiness, improve strength.
Acrylates Improve soil release.
Typical application recipe
Cross linking agent 40-120 g/l
Magnesium chloride 10-25 g/l
Citric acid 0.3 g/l
Softeners combination (total) 40 g/l
Wetting agent 1 g/l
Acetic acid to pH 4-4.5
After resin application and drying turn the garments right side out. Steam press. Hung
from non-staining hanger. The assembly is then transferred to moving rails. The rail takes the
garments through curing oven and then to packing.
Important precautions
Pre finishing stage
1. Good water absorbency (<3seconds)
2. Free from size.
3. High tensile and tear strength (sufficiently high to remain acceptable even after 50% loss
after resin finishing).
4. Use mercerized cotton.
5. Fabric pH 5.
6. Fabric and garment should be free from softener.
Resin finishing stage
1. After drying the residual moisture content should not be <10%. Low moisture gives high
dry crease recovery at the cost of heavy loss in tensile and tear strength. For wrinkle free
performance both dry and wet crease recovery are important. Wet crease recovery is
achieved when moisture content in dry fabric is high.
2. Resin impregnated sulphur dyed fabric/garment deteriorates due to generation of acid
from sulphur dye. The generated acid may cause pre mature curing of resin. Sulphur dye
should be thoroughly oxidized.
3. Addition of 1-2% urea to the finishing bath is often useful to minimize the release of
formaldehyde from resin. Since urea would reduce the efficiency of the resin it may be
necessary to increase the resin concentration by 10%. However, it is best to use low
formaldehyde etherified DMDHEU.
Garment stage
1. Stone washing and other garment processes are done before wrinkle free finishes.
2. Lower curing temperature is required for white to prevent yellowing.
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6. 3. Pockets, belt loops, labels, sewing threads, buttons, zippers etc. should be resistant to
chemicals and heat. The resin recipe liberates acid during garment curing.
Quality control
Physical properties
Efficiency of wrinkle free finishing is tested by wet and dry crease recovery angle,
smooth appearance rating, resin add on, tear strength, tensile strength, abrasion resistance,
dimensional stability etc.
Cuen (1 N cupriethylene diamine hydroxide) test
Pull the yarn from the backside of the finished garment. Fray the yarn. Put it on
microscope slide. Wet out the yarn with 1-2 drops of Cuen. Put the cover slide and observe
the swelling after15 minutes under the microscope. The Cuen rating is given by comparing
the standard photographs
Swelling Rating Remarks
None 5 Fully cross linked
Slight or none 4 Good cross-linked
Moderate 3 Moderately cross linked
Moderate to heavy 2 Partially cross-linked
Heavy, rapid 1 Low cross-linked
Rapid and dissolves 0 No cross linking
Rating 3-4 is normally taken as acceptable. Anything below 3 fails due to lack of resin
cure and anything above 4 fails due excessive loss of physical properties.
Eco-friendly cross linking agents
Majority of cross-linking agents used today is formaldehyde based including
DMDHEU and etherified DMDHEU, which has low formaldehyde level. Formaldehyde
based cross-linking agents are cost effective and efficient. However, the release of
formaldehyde vapours during finishing processes as well as during subsequent storage and
consumer use of finished products has caused world wide concern on its impact on human
health and environment because of the fears that it is carcinogenic and its well known
dermatitis effects. The release of formaldehyde is restricted to 20-ppm level.
Some of the approaches to limit the release of formaldehyde are
1. After wash of cured fabric/garment
2. Addition of formaldehyde acceptors or scavengers such as urea, carbohydrizide to the
finishing bath.
3. Application of 10-30% urea solution with 5-10% add on by atomized spray technique
using BASF fog chamber.
4. Modification of DMDHEU with alcohol to produce etherified DMDHEU to decrease
formaldehyde release e.g. treatment of DMDHEU with diethylene glycol or 2-
propanediol.
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7. Zero formaldehyde derivatives of DMDHEU are more expensive and less effective than
DMDHEU at the same add on levels. More active curing systems are also often required.
Polycarboxylic acids (PCA) as cross linking agents
An alternative approach has been based on the use of PCAs. In 1998 Welch reported
that cotton fabric treated with 1,2,3,4 butane tetra carboxylic acid (BTCA) in presence of
sodium hypo phosphite showed high level of wrinkle resistance and strength retention as well
as good durability to home launderings. However, exceedingly high cost has prevented the
use of BTCA on commercial scale. Citric acid (CA), a low priced tri-functional carboxylic
acid is less effective to home launderings than BTCA. It also causes yellowing of fabric
under curing conditions.
Mechanism of PCA cross linking
The crease resistance performance of cotton fabrics treated with traditional N-
methylol compounds is dependent on ether bond cross-linking with cellulose while BTCA
and other PCAs are based on ester-links. In general the esterification reaction takes place in
two steps.
Step 1 Two adjacent -COOH groups dehydrate and transfer in to cyclic acid and anhydride
under high temperature curing conditions.
Step 2 The acid and hydride undergoes esterification reaction with -OH groups of cellulose.
Requirement for step 1 is that two adjacent -COOH groups should be located at the same side
of the main chain which is responsible for easy dehydration and creating cyclic anhydride. If
O O
the two -COOH groups are located at the two sides of the main chain, cyclic anhydride will
not be generated and esterification of cellulose will not take place. Weakly basic alkali metal
salts of phosphorous containing mineral acids accelerate the formation of cyclic anhydride.
C
HC C OH HC
Among various phosphates sodium hypophosphite monohydrate (NaH2PO2.H2O) is found to
V V
- H2O
be excellent. The catalyst increases the rate of. anhydride formation as well as the rate of
O
cross linking through esterification.
HC C OH H C
V
C V
O O
Polycarboxylic aci Cyclic anhydride
O
O
HC C O R
HC C cellulose
HO – R V
V cellulose
O
Cellulose HC C
HC C O H
V V
O
O
7
Cyclic anhydride
Polycarboxylic acid bonded to
cellulose through an ester linkage

8. Fig. 1. Reaction of polycarboxylic acid with cellulose
Other carboxylic acids
Performance of various PCAs has been compared with conventional methylol derivatives as
wrinkle free finishing agents using sodium hypophosphite as catalyst. Most of these acids
imparted DP rating of 4.3-4.7, and crease recovery angle 285-300°. However, the resultant
finishes differed considerably in durability in alkaline laundering. The acids arranged in order
of decreasing durability in terms of maximum number of washings and tumble drying cycles
withstood were as follows:
BTCA>CA>Maleic acid.>Succinic acid.
Principle of PCA selection
The principles on which PCAs can be used as non-formaldehyde finishes are as
follows:
1. In terms of number of COOH groups, saturated Carboxylic acids should possess at
least three and unsaturated at least two COOH groups.
2. Regarding the position of COOH, the two COOH in aliphatic PCA should be in cis
configuration and two in aromatic PCA should be in adjacent position.
According to above principles it may be possible to develop new low cost PCA finishes
whose DP rating is as good as or greater than BTCA. It has been thought that polymaleic
anhydride (PMA) can be used as PCA finish but the reaction conditions should be strictly
controlled. The DP of polymerization of PMA should be within the range of 4-6.
CH CH
n
C C
O O
O
Fig 2. Polymaleic acid anhydride
Demerits of PCA finish
Eco-friendliness of catalysts
For cross linking of cotton with BTCA or CA the catalysts used are weakly basic alkali metal
salts of phosphorous containing mineral acids. Some of the salts which act as catalysts are
8

9. sodium hypophosphite, sodium dihydrogen phosphate, disodium hydrogen phosphate,
trisodium phosphate, tetrasodium pyrophosphate etc. mono di and tri sodium citrate are also
used in BTCA finishing. The most effective catalyst is sodium hypophosphite. But it has
serious disadvantages. For example:
1 High cost
2 Being reducing agent it brings about shade changes in most sulphur dyes and
reactive dyes.
3 Environment impact is also a major concern
Compounds containing phosphorous can consume large amount of oxygen in water,
deteriorate the quality of water and influence the reproduction of fishes. Recently attempts
have been made to replace sodium hypophosphite by trisodium citrate and a combination of
sodiun oxalate and sodium formate as catalysts. These catalysts do not have any effect on
sulphur or reactive-dyed fabrics.
Cost of BTCA
Due to extremely high price of BTCA, there are limitations in its industrial application. Two
alternative aspects may be taken in to consideration for cost reduction.
1. Cost of synthesis
The synthesis process of BTCA is extremely sophisticated, therefore, one should
strive to seek an optimum production to decrease its cost. Industrially used BTCA may be
manufactured without purification. The solution of BTCA can be decolorized and
concentrated in the paste form for the application.
2. Cost of Finishing
One can incorporate other PCAs or catalysts in to finishing formulation to reduce the
amount of BTCA in finish bath. Inexpensive citric acid may be used. Some auxiliary catalysts
such as triethanol amine (TEA) may be incorporated to lessen the finishing cost and to
enhance the strength of finished fabric.
Discoloration/yellowing effect of CA finished fabrics
When CA is applied, as cross-linking agent discoloration of finished fabric is observe The
reason for discolouration is that unsaturated poly carboxylic acids are produced during
curing, generating conjugated double bond system as a chromophore. Investigations showed
that major products formed during the curing process of CA treated fabrics are aconitic acid,
citraconic acid and etaconic acid.
H2C COOH
H2C COOH HC COOH
HO C COOH HC COOH
H2C COOH H2C COOH
Citric acid BTCA
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10. HC COOH CH2 CH3
HOOC C C COOH C COOH
H 2C COOH H2C COOH HC COOH
trans – Aconitic Itaconic acid Citraconic
Fig. 3. Formulae of PCAS used as crosslinking agents and of the unsaturated PCAS
formed during curing process of CA-treated fabrics
In order to minimize the yellowing, special additives such as triethanolamine (TEA),
N,N-bisHydroxy ethyl) glycine, boric acid and polyethylene glycol may be incorporated in
the finish bath. It has been observed that TEA can suppress the yellowing effect efficiently.
The mechanism of the yellowing suppression is suggested to be that, the OH in TEA can
react with OH in CA to form ester bonds which can block the OH in CA and prevents CA
from hydrating and decomposing to unsaturated polycarboxylic acid when it is exposed to
elevated temperature. As a result the formation chromophores responsible for discoloration
is prevented.
Poor wash fastness of finished fabrics
The difference in structure of CA and BTCA is that one OH group exist in structure of
CA. Accordingly, the difference in easy care effects between CA and BTCA is attributable
to the disturbance impact of the OH group in CA on esterification reaction between the
COOH in CA and OH in cellulose molecule. Due to this reason the hydrolysis rate of the
ester bonds formed by CA under alkaline conditions is greater, than those formed by BTCA.
Thus the OH group in CA is the origin of the low wash fastness of CA finished fabrics. In
order to improve the durability of the finish, OH group in CA must be modified.
Investigations indicate that when PMA is incorporated in to CA finish bath, the OH in
CA can undergo esterification reaction with the COOH in PMA to form extremely
complicated molecules under elevated temperature curing conditions. As a result the OH in
CA will he blocked and enhance the wash fastness of finished fabrics.
From the above-mentioned drawbacks it can be seen that there are many problems associated
with PCA based non-formaldehyde finishing. These include cost of the PCA, the
environmental problem of catalyst containing phosphorous, the yellowing effect and the low
wash fastness of CA finished fabrics. All these problems are under investigation and some of
which have been overcome satisfactorily. It is believed that it will not be too long before the
traditional N methylol amide finishes are substituted completely by PCA non-formaldehyde
finishes.
A new approach to the production, of formaldehyde free DP finishes has been the
10

11. recent work on the ester crosslinking of cotton by two polymers of maleic acid, namely
homopolymer (PMA) and a terpolymer (TPMA) based on maleic acid, acrylic acid and vinyl
alcohol. The terpolymer approach showed a significant improvement in DP performance of
cotton fabric and retention of physical properties compared to the DMDHEU.
Softeners
Fabrics and garments are usually comfortable to wear if they are soft to touch.
Chemical pretreatments remove natural cotton waxes rendering cotton harsh to handle. This
is usually made worst after wrinkle free finishing. To compensate this; softeners are widely
used. They also act as fibre lubricants decreasing both fibre-fibre and fibre-metal friction.
The draping and, cutting properties are also enhanced. The modem requirements are for
softeners of good durability to machine washing, and retain the wettability and absorbency as
well as properties against static charge under adverse conditions. The trend is towards the use
of silicone softener that provide a soft luxurious handle, thereby imparting a higher quality
and added value to the material.
Silicone softeners
Silicone is a general term that refers to class of man made polymers based on the
framework of alternate silicone and oxygen (Siloxane) bonds with organic substituents
attached to silicone. Methyl group (Me) is the most important of organic sustituents used in
commercial silicones.
The most dramatic changes in the field of softening have been the introduction of novel
Polysiloxane softeners in both macro and micro emulsion forms. Softeners and elastomers
based on Epoxy and amino functional polysiloxanes provide an ultra soft handle to cotton.
Such softeners generally increase the tensile resiliency and decrease the bending rigidity.
Another aspect of elastomeric finishes is that they can be used to replace some of the cross
Linking agents used in typical easy care formulations.
When ethylene diamino functional siloxanes are cured for easy care finishing,
yellowing can occur through the formation of azo and azoxy compounds as a result of
oxidation of amine groups. Secondary amines such as cyclo hexyl amine and tertiary amines
such as piperazine have been studied for use in polysiloxane softeners. Yellowing is greatly
decreased but the finish is less hydrophilic and somewhat dryer than that obtained using
primary amino functional siloxanes.
Carboxy funtional, epoxy functional and amido funtional siloxanes have also been
developed. The Later is prone to yellowing and more hydrophilic than amino functional
siloxanes. Particularly, interesting is the research involving carboxy functional siloxanes
which may improve resistance to oily soiling.
The use of polysiloxane softeners modified to incorporate various organo functional groups
will increase in the next decade as cotton finishers strive to improve the strength retention of
easy care fabrics.
Silicones have been used as textile softeners since 1960. Initially, polydimethyle siloxane
(PDMS) were used but in late 70s the introduction of amino functional PDMS opened new
dimensions.
Currently available silicone softeners can be classified in to following classes:
1. non-reactive
2. Reactive
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12. 3. Organo reactive.
Non-reactive silicones These are based on polydimethyle siloxanes. They impart desirable
properties to fabrics due to their flexible polymer backbone, stable bonds and low
intermolecular forces. However, the softening effect is not very durable to washing due to
absence of reactive groups. -
2. Reactive silicones: these are PDMS polymers modified with silane hydrogen or
silanol functional groups. Conventional reactive silicones form a cross-linked siloxane
rework on the fabric surface in presence of water and Organo metallic catalyst. The
durability is better than non-reactive PDMS. Silanol functional polymers are also the basis
for silicone elastomers and textile finishes to improve hand and DP performance.
3. Organo functional silicones: In this amino functional groups, which are bound to PDMS
backbone improve the orientation and substantivity on fibre. The improved orientation of
amino functional silicone leads to extremely soft hand which if frequently described as
"super soft". In this Organo reactive groups such as amines epoxides and alcohols are
introduced in PDMS.
Me Me Me Me
Me3 SiO (SiO) Si Me3 Me3 SiO (-SiO) (-SiO) Si Me3 XMe3 SiO (-SiO) (-SiO)n Si Me2X
n a b
Me Me Me Me
Nonreactive silicon polymar Reactive silicone polymer
Me Me
Me3 SiO (-SiO) (-SiO) Si Me3 -HC CH2 - NR +Cl- , -COOH , NHCOR` , -O(EO) (PO) X
a b 3 a b
Me R
O
Y
X = -OH or RO- Y = - NH2
Organo functional reactive silicone polymar
Fig. 4. Examples of non-reactive, reactive and Organo functional reactive silicone
polymers
Eco-friendliness of silicone softeners
The textile processing operations produce an aqueous effluent, which is discharged to waste
water treatment plant for purification. Silicones are a minor part of that discharge. PDMS
becomes part of the plant wastewater stream in the form of tiny dispersed droplets and attach
to suspended solids. Because non-volatile PDMS fluid is essentially insoluble in water, these
materials become a minor component of the sludge in the treatment plant. The specific route
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13. of non-volatile silicones in the environment depends on how the individual wastewater
treatment plants handle the sludge. If the sludge is incinerated the silicone gets converted to
amorphous silica, water and CO2. Sludge, if used as a fertilizer it may introduce PDMS to
soil, where it is subjected to natural degradation processes. Similarly soil catalyzed
degradation is also expected to occur if sludge bound PDMS is land filled.
Though PDMS materials are highly resistant to biodegradation they break down in to lower
molecular weight silaxonols and silanols during soil contact. The degradation products are
susceptible to biological decomposition eventually oxidizing to natural silica.
Me
Me Soil HO (-SiO) H Me3 SiO H
y +
Me3 SiO (SiO) Si Me3 Water
x Me
Me y = mainly 1
Fig. 5 Degradation of PDMS
Effects
PDMS is ecologically inert and has no effect on aerobic or anaerobic bacteria. It does not
inhibit the biological process by which the waste water is treated. No adverse effects of
PDMS were seen on seed germination or survival percentage of plants. Studies found no
evidence that PDMS may inhibit the bacteria responsible for nitrogen fixation in some crops.
If PDMS enters the aquatic environment they do not bio concentrate. Their molecular size
prevents them from passing through the biological membrane of fish or other animals. PDMS
fluids attached to particulate matter and are effectively removed by the natural cleansing
process of sedimentation. They do not partition back in to water column. PDMS fluid exhibit
insignificant BOD. Testing on aquatic plants and animal life revealed no measurable adverse
effects even under highly exaggerated conditions of exposure. No significant change in the
growth of algae or other marine organisms has been found. PDMS has not been found to pose
threat to insect population and birds. While manufacturers across the world continue to seek
environment friendly alternatives for many performance additives and finish chemicals in the
textile industry, the inherent eco-friendly silicones and their low concentration usage indicate
the likelihood of there sustained presence in textile manufacturing.
Water resistant breathable finish
Present trend is to impart water repellency without affecting water vapour
permeability of fabrics and garments for use in out door activities, foul weather-clothing etc.
Improving the transpiration rate of perspiration through the textile materials is particularly
important in sports activities, where the relative metabolic rate is high. Water-resistant
breathable finishes are impermeable to water droplets but allow the escape of water vapour. It
is possible to achieve this property because of enormous size difference between liquid water
13

14. molecule (100 microns in diameter) and water vapour molecule (0.0004 microns) i.e. there is
factor of 2,50,000) between two sizes. Such type of garments is designed for sports wear,
skiwear, tracksuits, ram wear, clothing for mountaineering etc.
Lightweight fabrics coated with poly (vinyl chloride) and polyurethane have become
increasingly popular for foul weather clothing. Such fabrics provide exceptional protection
against rain but considerable build up of moisture vapour inside the clothing may cause
discomfort. This problem arises because of water vapour impermeability of the polymer
coating. To overcome this problem breathable polymer coatings are now available which
have greatly enhanced comfort properties of these clothing.
Classification of breathable fabrics
Breathable fabrics may be classified into three categories
High density woven fabrics
These are obtained by densely weaving fine smooth micro fibre yarns, this type of
weaving results in wind proof fabric with excellent water vapour permeability. However it is
not waterproof even after treating for water repellent finish. These fabrics are used for
fashionable ski clothing, where water vapour permeability and wind proofing is more
important than water impermeability.
Laminated fabrics
In this approach the fabric is coated with breathable adhesive with the help of rotary screen-
printing or spray coating. It is than laminated with micro porous breathable barrier film like
PTFE. The breathable films are made through biaxial stretching or by mechanical fibrillation
to produce microscopic tears through out the film. Manufacturers claim that such PTFE
membrane contains 9 billion pores per square inch with a maximum pore size of 0.2 microns.
Such PTFE membranes are used in Goretex two layer and three layer laminates of polyester
fabrics.
Other commercial micro porous polymeric membranes include
1. Sympatex(hydrphilic polyester): Akzo
2. Bion II (polyurethane): Toyo Cloth
3. Excepor U (Poly amino acid/PU): Mitsubishi-Kasei
4. Thintech (Poly olefin): 3M company
Coated fabrics
Micro porous coating
The most important techniques used to produce micro porous coatings for breathable textiles
are
1. Solvent exchange
2. Phase separation
3. Phase inversion
Solvent exchange
In this process the polymer is dissolved in water miscible solvent and then thinly coated onto
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15. the fabric. Passing through a coagulation bath develops the porous structure where the solvent
is displaced by water.
Phase separation
The coating polymer is applied from a mixture of relatively volatile solvent with a
proportion of higher boiling non-solvent. Precipitation of polymer as the micro porous layer
occurs as the true solvent evaporates faster during the subsequent drying process. e.g.
Ucecoat 2000, a polyurethane based coating Here a low temperature boiling solvent (methyl
ethyl ketone) evaporates preferentially as the fabric passes through oven, thereby increasing
the concentration of non solvent in the coating. When the concentration of the non solvent
reaches a critical level, the polyurethane precipitates out in a highly porous form and remains
in this form on complete drying
Phase inversion
A solution of polyurethane containing a non-solvent is coated on the fabric. In a selective
evaporation step, the solvent is eliminated first. The polyurethane then precipitates in a micro
porous way, the example is Ucecoat 2000 (S) of UCB specialty chemicals.
Bio finishing
Processing of cellulose fabrics and garments with cellulase enzymes is generally
referred as bio finishing or bio polishing. The concept was started in 1980's. Presently major
industrial application of cellulase enzymes is to produce wash down or worn out look (stone
wash) on indigo dyed denim. This is known as biostoning. Cellulases are multi component
enzyme system that is commonly produced by soil dwelling fungi and bacteria. The most
important cellulase producing organisms are fungi of Trichoderma, penicillium and
Fusarium. Cellulase consists of at least three enzyme systems working together
synergistically.
i. Endoglucanases or Endo cellulases hydrolyze cellulose randomly along with the
cellulose chains, preferentially the amorphous region.
ii. Cellobiohydrolase or Exo cellulase attack the chain ends and primarily produce cellobiose
iii. The cellobiose and the small chain oligomers produced by exocellulase are then
hydrolyzed by the third enzyme β-( 1,4 )-glucosidase into glucose
Depending on the pH of activity, there are three types of cellulase enzymes viz:
Acid stable (pH 4.5-5.5)
Neutral (pH 6.5-7)
Alkali stable (pH 9-10)
These enzymes can be used in the temperature range of 40-60° C. Biopolishing consists of
cellulase treatment so that there is partial hydrolysis of cellulose at the surface with a weight
loss of around 3-5% and loss of strength of 2-7%. Short fibre ends are hydrolyzed and are
removed by additional mechanical treatment to prevent pilling particularly in case of
PET/cotton blends.
Mercerization enhances the rate of enzymatic hydrolysis. Biostoning has achieved
considerable importance for treating casual wear garments to give them a wash down or worn
out look. Environmentally this is more acceptable because it replaces or decreases the
quantity of pumice or synthetic stones that cause damage to machine. It also avoids
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16. occurrence of pumice dust in the environment and in the garments creating a harsher handle.
Neutral cellulases are preferred for biostoning of indigo dyed denim trousers and other
garments. The bio finishing of cotton or PET/cotton blends reduces pilling, provides durable
soft handle, increased gloss or lustre.
The cellulase treatment of cotton is now well established. Further refinements in
process techniques would emerge. Developments such as the use of one or more specific
enzyme types rather than three types working synergistically will depend on commercial
separation of the enzymes.
Anti microbial finish
Clothing and textile materials carriers of microorganisms such as pathogenic bacteria,
odour generating bacteria and fungi. Because of the growth of micro organisms on the fabric
surface, anti microbial / anti bacterial / anti fungal fabrics gained significant importance in
the recent years due to its wide acceptance as surgical apparels, baby clothing, under
garments etc. There is growing concern all over the world on the dangers of microbial
contamination. Recent outbreak in diseases such as AIDS, Hepatitis B has increased the
awareness of these health hazards and the need for protection against them. Anti microbial
finished fabrics for surgical apparel play an important role in reducing diseases transmitted in
operation theatre, as the bacterial and viral diseases are spread through air and blood. Anti
microbial agents in these fabrics prevent the proliferation of disease causing microbes or
reduce their number by the action upon them by destroying their cell membrane. Anti
microbial surgical apparels act as physical barrier against the transfer of micro organisms. A
surgical patient is at greater risk because the wound created during the operation is open and
easily accessible to microorganisms and hence may become septic. For this reason the
surgical gowns used by patients should be free from microbes. The doctors and nurses are
also to be protected from the blood and other body fluids of the patients, which may contain
microorganisms spreading the disease to doctors and nurses. Anti microbial under garments
is also useful in preventing skin related diseases, urinary track infection etc. Baby's clothing
are advised to be anti microbial and their thin skin may be permeable to microbes. Since the
internal intake of anti biotic for the infants is not desirable so protective action against
microorganisms should be taken through clothing. Taking all these factors into consideration
development of anti microbial fabrics/clothing is important.
Requirements in anti microbial finshing
1. Durability to multiple launderings and dry cleaning.
2. No toxic effects on wearer.
3. Acceptable moisture transfer properties.
4. Compatibility with dyes, auxiliaries and other finishing agents.
5. Ready availability at reasonable price.
6. Should not affect the fastness properties of dyes.
Mechanism of protection
There are three mechanisms by which treated fabrics are made resistant to disease
causing bacteria Viz. Controlled release, regeneration model and barrier or blocking action.
Controlled release
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17. This finish is considered effective when in the presence of sufficient moisture, the anti
bacterial agent is released from fabrics at a rate sufficient to kill or inhibit the growth of
bacteria.
Regeneration model
This model is based on subjecting the fabric to agency that would destroy the bacteria e.g.
addition of bleaching agent during laundering or exposure to UV light
Barrier or blocking mechanism
This include
a) insertion of physical barrier films or coatings that are simply impervious to transmission
of micro organisms through fabric ..
b) Films or coatings that have direct surface contact activity against bacterial growth.
Finishing techniques
Following processes can be used for imparting anti bacterial finish to cotton or PET/cotton
blends
Pad-dry-cure process for fixation of anti bacterial additive onto fabric with the help of cross
linking agent
Grafting
Incorporation of anti bacterial agent during fibre finish
Pad-dry-cure method
Various chemicals, which can impart antimicrobial property to cotton, are shown in Table
Table 2. Anitibacterial chemicals
Name Chemical Nature Effective
Concentration (g/l)
Afrotin LC Na salt of heterocyclic compound 20
Mysotox ELN Pentachlorophenyl laurate and
Non-ionic emulsifying agent 2.5
Mystox WFE Aqueous solution of Sodium
Ortho phenylphenate 1
Antibac MF An organic compound containing
Nitrogen with no halogen 40
Antibac MFB Combination of hetrocyclic
Organic compound 80
Fungitex OP Derivatives of bezimidazole 100
Above agents can be applied along with cross linking agent by pad-dry-cure technique.
However the wash fastness of the finish is not satisfactory.
Chitosan and citric acid
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18. Chitosan and citric acid are used as durable press anti microbial finish cotton when applied
by pad-dry-cure process CA reacts with OH group of cellulose and NH2 of chitosan to form
ester cross links and inter ionic attraction
Poly(hexamethylene-biguanide hydrochloride, PHMB)
A new anti microbial finish called Ruptex 20 has been found to give durable finish to cotton
and cotton blends. It is based on the active agent PHMB. It is applied by padding or
exhaustion technique. The Finish can withstand 25-50 wash cycles depending on wash
conditions.
Tulsi leaves (Ocium santum)
One bath process for dyeing and simultaneous anti microbial finish by methanolic
extract (1-5%) of Tulsi leaves on cotton has been investigated. It is believed that Urosolic
acid (C30H48O3) is the active ingredient, which inhibits the growth of bacteria.
Grafting
Poly-(2-methyl-5-vinyl pyridine) was grafted onto cellulose followed by immersion in
aqueous Kl solution. Such a technique produces idophor, a material that slowly releases
iodine to impart anti bacterial and anti fungal activity.
Barrier coating
Organo silicone
The anti bacterial finish based on the concept of barrier coating (direct surface contact
activity) is Dow Corning 5700 (3-trimethoxy silyl propyl dimethyl octa decyl ammonium
chloride) Organo silicone polymer. Containing pendant quaternary ammonium group that
forms a bio barrier onto fabric. This finish is effective in inhibiting the growth of odour
causing bacteria and is durable to atleast 40 laundry washes.
Soil release and stain release finishes
Soil release and stain release finishes are particularly
important where leisure or sports wear activities may lead to
greater incidence of soiling or staining. This type of finish
would become more important as standards of easy care
increase and consumer expectations become greater Another
factor is the trend towards lower temperature washing of
garments where removal of persistent soil and stain removal
becomes more problematic. In general, the approach in textile
finishing has been to ensure that any soil that is deposited is
less strongly bound to facilitate the removal of soil during
domestic washing. Because most persistent soils are
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19. hydrophobic, the major trend has been to use finishes that
render the fibre surface more hydrophilic. On this principle
three major groups of finishes are developed.
Finishes containing carboxyl groups
Finishes containing oxy ethylene and /or hydroxyl groups
Fluorocarbon finishes
Finishes that contain carboxyl, oxy ethylene or hydroxyl
groups may be incorporated within zero formaldehyde based
chemical cross-linking systems for cotton. Easy care finishes
make cotton more hydrophobic and can increase oily soiling.
Whereas the introduction of hydrophilic carboxyl groups can
improve the release of oily soil dramatically. It is known that
hydrophilicity, anti soiling and soil release properties are not
usually associated with silicone softeners, and silicone based water repellent finishes do not
provide oil repellency.
Fluorochemicals
Fluoro chemicals or fluorocarbons are increasing in use because of greater ability to engineer
the chemical structure to provide good water repellency and soil and stain release properties.
Hybrid flouro chemical finishes have been introduced that contain per-fluoro alkyl containing
polymer segments and also hydrophilic segments. In air the fibre-air interface is dominated
by closely packed per fluoro alkyl moieties which promote soil repellency. In aqueous wash
liquor, molecular reorientation occurs, leading to. the hydrophilic segments being oriented
towards fibre-liquid interface, thereby promoting soil release. The use of perfluoralkyl
acrylate and methacrylate based copolymers modified to suit particular end uses is well
established.
Emerging technologies
Traditionally chemical finishes are applied by padding or low wet pick up techniques such as
lick roll, porous bowls, vacuum extraction or foam. Alternative methods include coating and
lamination technologies. New application technologies are emerging. Some of these are
briefly mentioned.
Nextec Process
It is patented by Nextec Applications Inc. USA. It is a novel process by means of which
individual fibres within the fabric are encapsulated or wrapped with an ultra thin film of
polymer. This can be utilized to provide a breathable barrier film within the fabric, preventing
liquid water from penetrating while allowing moisture vapour to pass through at as close to
the same as original fabric. The handle of the fabric is relatively unaffected. It is also possible
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20. to introduce chemicals for imparting wrinkle resistance, soil release, stain resistance.
Chemical and biochemical additives may be positioned on the fabric in order to provide water
repellency, UV protection, flame resistance or viral barriers. So far this unique fibre
encapsulation process has been applied using silicone-based polymers, polyurethane,
polyacrylate and other polymers. This process would open up many opportunities for
providing multi functional finishes on cotton fabrics.
Plasma treatment
The plasma treatment is based on ionized gases produced by electrical discharges.
The plasma treatment is highly surface specific and does not affect the bulk properties. The
surface properties enhanced include wettability, adhesion, cross-linking, bio- compatibility,
chemical affinity or inertness. Relative free radical intensity of the plasma treated fibres
measured by ESR, increases in the following order
Cotton > wool > silk > Nylon = PET
Plasma treatment may enable to avoid pre-coating and pre-lamination preparation of the
substrate, replacing some costly and environmentally polluting processes. The dry treatment
and environment friendliness for improved wetting, adhesion and bondability offer scope for
improvement in functional finishes for cotton.
Use of biotechnology
The use of biotechnology for the modification of cotton is at an exciting stage and the greater
applicability of enzyme treatments as chemical pre treatments and finishing treatments is
worth exploiting. The next decade should bring forward some interesting developments in
this field and the genetic manipulation of cotton gene may usher in new cotton varieties with
improved properties and performance that can be further exploited in chemical finishing to
produce innovative effects.
UV protection
The problems of ozone depletion in the upper atmosphere have led to increased
problems of exposure of skin to UV radiations. The size and depth of Antarctic ozone hole
has caused concerned, particularly in Australia. It has been suggested that a decrease of 1%
ozone would lead to increase UV radiation at the earth's surface and may eventually lead to a
2-3% increase in skin cancer. Hats, sun screens, sunglasses and clothing can be used to
decrease the exposure to UV radiation by a factor of 10 or more. The term UV protection
factor (UPF) has been introduced such that a garment of UPF 15 will provide the same
amount of protection against solar UV radiation as a sun screen of SPF 15 (Sun protection
factor). Garments with UPF value of 20-29 offer high protection (UVR transmission 5-3.3%).
A UPF value of 30-40 (UVR transmission 3.3-2.5%) offers very high protection and UPF
value of >40 offers maximum protection with UVR transmission of <2.5%
This opens up another area of opportunity for cotton fabric and garment producers to
manufacture comfortable ranges of clothing for leisure and for out door work wear that offer
significant enhanced protection against UV radiation. The appropriate selection of dyes,
fluorescent brightening agents and particularly UV absorbers should enable cotton finisher to
provide high level of UV protection.
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21. Conclusions
Desirable properties can be imparted to cotton by the application of functional finishes. This
not only would improve the quality of cotton but also give value addition. Innovations
through R&D in chemical finishing will be necessary to stimulate the more demanding
consumer and to develop specialty and niche markets for cotton fabrics and garments. The
development of finishes with multi-functionality will be particularly interesting field
especially with regard to easy care finishing.
Novel methods that minimize water and energy costs may be based upon plasma
treatments, but such treatments for cotton are still in the development stage. Enzyme
treatments also offer many promises. In general many innovative ideas are being explored in
the field of functional finishes for cotton and in the next decade quite a few new concepts
may be introduced for imparting desirable properties to cotton fabrics and garments.
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