Eco – Friendly in Textile Wet Processing By

Aravin Prince Periyasamy., M.Tech (Textiles) Lecturer, Dept of Apparel Technology,

S.S.M. Institute of Textile Technology & Polytechnic College, Komarapalayam, Namakkal. Mobile #:+91-97 90 08 03 02

E-mail: aravinprince@gmail.com

ABSTRACT

Environmental considerations are now becoming vital factors during the selection of

consumer goods including textiles all over the world. However due to increased awareness of

the polluting nature of textiles effluents, social pressures are increasing on textile processing

units. Awareness about eco-friendliness in textiles is one of the important issues in recent

times since textiles are used next to skin and is called second skin. Owing to the demand of

global consumer the researchers are being carried out for new eco-friendly technology.

Plasma, biotechnology, ultrasonic, super critical carbon dioxide and laser is quite new

technology for the textile industry. It offers many advantages against wet techniques. There

are no harmful chemicals, wet processes, waste water and mechanical hazards to textiles, etc.

It has specific action on the all types of fibres and textiles.

INTRODUCTION:

Increasing environment consciousness in textile processing has forced research and

development efforts to search the safe methods for textile processing. The textile chemical

processing plays an important role in controlling the pollution load for environment. Because

the textile industry has long recognized that, for a large number of process and applications,

the surface properties are a key aspect of the product and often need to be quite different from

those of the fabric bulk. New applications and improved applicability of the many fibre used

for clothing, as industrial materials and for interior decoration requires the provisions of new

properties in such areas as dyeability, static resistance, and current control, stain resistance,

water absorption, hydrophilicity, water repellency, adhesive ability and so on. There are

surface treatment methods that additionally increase the value of textile materials.

The methods can be classified as chemical treatment (wet) methods and physical

treatment (dry) methods. Chemical treatment methods are most often used in actual practice.

Because of the large amount of energy involved and the high consumption of water and

consequently increase of pollution, these techniques are costly and not eco-friendly. In

addition, these processes treat the fabric in bulk, something which is unnecessary and may

adversely affect overall product performance. Problems related to toxicity and other health

hazards have resulted in the replacement of chemical processing by more eco-friendly

physical methods. The physical treatment processes are dry, which makes it possible to

preserve certain properties intrinsic to textile materials; they are likely to affect the surface of

the materials. Therefore the researchers are extensively studying the possibilities of physical

surface treatments as alternatives to the chemical treatments.

At the beginning, studies initially focused on electron beam irradiation and ultraviolet

light irradiation, but electron beam irradiation required too much energy and as a result,

properties deteriorated and graft polymerization sometimes occurred. In the latter case it was

necessary to find a means of reducing the efficiency of grafting. Ultraviolet light irradiation

was tried as a method of resin hardening, but never went beyond the scope of studies on

methods of treating fiber surface. In all probability, this was because it offered no specific

features superior to what could be obtained with chemical treatment. The industry is,

therefore, strongly motivated to seek alternative surface engineering processes which could

offer lower cost, environmentally-friendly manufacturing and routes to new products, with

improved lifetime, quality and performance. Research is going on worldwide with the focus

on new quality requirements that include maintaining the intrinsic functionality of the product

through an eco-friendly production process. Therefore, an attempt has been made to review

the physical methods for processing of textile materials by plasma, laser and supercritical

carbon dioxide to enhance the specific properties.

PLASMA TECHNOLOGY

The physical definition of plasma (glow-discharge) is an ionized gas with an

essentially equal density of positive and negatives charges. It can exist over an extremely

wide range of temperature and pressure. Plasma treatment usually practiced in textile industry

to enhance the functional finishing. High-pressure glow discharge plasma, modifying the

active surface characteristics of the polymer so it contains polar functional groups. A treated

fibre will comprise a hydrophobic core and a receptive pouter sheath which consists of

hydrophilic functional groups, resulting from the active species interacting with the surface of

polymer during treatment.

Fig 1 Plasma Technology

Plasma technology has been shown to improve fibre surface properties without

affecting desirable bulk properties. It also offers environmental advantages. Therefore, there

are increasing uses of plasma treatment of synthetic fibres such as polyethylene terephthalate,

nylon, and polypropylene. A general effect is in improvement in their hydrophilic properties.

Fig 2: Plasma Technology in Textiles

How does the Plasma treatment affects the textile material?

According to requirements the textile materials to be processed processing will be

treated for seconds or some minutes with the plasma. The following are the properties

improvements with plasma treatment:

1. The cleaning effect is mostly combined with changes in the wettability and the surface

texture. This leads to an increase of quality printing, dye-uptake, adhesion and so forth.

2. Increase of micro-roughness: this effect an anti-pilling finishing of wool.

3. Generation of radicals: The presence of free radicals induces secondary reactions such

as cross linking. Furthermore, graft polymerisation can be carried out as well as reaction

with oxygen to generate hydrophilic surfaces in hydrophobic fibres such as polyester or

polypropylene.

4. Plasma polymerization: It enables the deposition of solid polymeric materials with

desired properties onto the substrates.

The advantage of plasma treatment is that the modification is restricted to the

uppermost layers of the substrate, thus not affecting the overall desirable bulk properties of

the treated substrate.

Functional groups are introduced in the treated textile materials which would play

prominent role in improving the dyeability of hydrophobic fibres such as poly (tetraetylene)

(PET) and polypropylene (PP). The plasma treated PP and PET could be easily dyed by

water soluble acid dye which is more environmentally friendly plasma is advantageous in

formation of hydroxyl groups on the PET surfaces. To improve the deep colouring effect of

polyethylene terephthalate (PET) fabrics, anti-reflective coating layers have been deposited

on the surface of the fabrics with two different organo-silicon compounds such as HMDS,

TTMSVS using atmospheric pressure plasma. Oxygen promoted the decomposition of

organic monomers and contributed to the enhancement of the colour intensity on the PET

surface.

Plasma treatment can also be used for grafting of textile fiber with other polymer to

enhance specific properties. For example, Poly (ethylene terephthalate) (PET) would be

exposed to oxygen plasma glow discharge to produced peroxides on its surfaces. These

peroxides were then used as catalysts for the polymerization of acrylic acid (AA) in order to

prepare a PET introduced by a carboxylic acid group(PET-A). Chitosan and quaternized

chitosan (QC) were then coupled with the carboxyl groups and the PET-A to obtain chitosan

grafted PET (PET-A-C) and QC-grafted PET (PET-A-QC), respectively. After the laundering

the inhibition of the growth of the bacteria was maintained in the range of 48 – 58%, showing

the fastness of the grafted PET textures against laundering.

Not only the hydrophobic fibres but also the natural fibres treatment such as in wool

dyeing, plasma could be employed. The kinetics of dyeing of wool with acid dyes after

treatment with low temperature plasma was investigated researcher. It shown the plasma

treated wool can be dyed at 80‟c at high rates and dye fixing was improved. Modification of

the wool with low temperature plasma enables the dyeing temperature to be reduced, thus

helping to reduce fibre damage. Colour fastness of a wool fabric that was low-temperature

air-plasma treated and dyed with an acid dye has been evaluated. Colour fading of the plasma

treated fabric by carbon arc light irradiation was lesser at initial stage than that of the fabric

without plasma treatment. The oxidized substrate through the plasma treatment may inhibit

the photo reduction reaction of the dye. The colour fastness of the plasma treated fabric to

laundering was poorer than that of untreated fabric. The phenomena may be attributed to an

enhancement of dye diffusion in wool substrate by relaxation of inter cellular material of

wool by the plasma treatment.

Wool and nylon 6 fibres treated with oxygen low-temperature plasma were dyed with

acid and basic dyes. Despite the increase of electro negativity of the fibre surface caused by

the plasma treatment, the rate of the dyeing of wool was increased with both dyes, while that

of nylon 6 was decreased with the acid dye and increased with the basic dye. After a low

temperature glow discharge treatment on wool, reduced dyeing times are possible, reduced

cost of maintenance and possibilities of recycling are also possible due to reduced discharges

of toxic components. The process is also more environmentally friendly and introduces cost

savings by reducing the amount of dyestuffs and auxiliaries required.

Marino wool can be treated with low temperature plasma based on

oxygen/helium/argon/tetrafluromethane for 30 – 180 sec before dyeing with acid or direct

dyes. The pretreatment not only increases the dyeing rate, but also the saturation of dye

exhaustion. The barrier effect is reduced by plasma treatment. The surface of the endocuticle

or the adhesive filler in the wool scales is relaxed by the plasma treatment, thereby improving

the dyeing of wool with direct dyes. Time of half-dyeing is reduced by oxygen and

tetrafluoromethane plasma treatment. Although the dyeing rate in short periods increased

independently of dyes and plasma gases, the helium/argon, plasma was especially effective. It

was found that there is no relationship to wettability with water and the dyeing rate of plasma

treated wool. Dye penetration is accelerated as a result of the plasma pretreatment.

LASER TREATMENT:

Another physical surface treatment method to create the hydrophilic groups on

hydrophobic fibres and enhance the dyeing process is laser treatment. Extensive research has

been carried out into the possibility of surface finishing of synthetic fibre fabrics by laser

irradiation. A laser type must be selected which irradiates in a strongly absorbing spectral

region of the high polymers. It is possible to obtain surface structuring without affecting the

thermal and mechanical properties of the body of the fibre. Surface properties affected

include particle adhesion, wettability and optical properties.

Poly (ethylene terephthalate)(PET)modified by a 248 nm KrF excimer laser with

high(above ablation threshold) and low (below ablation threshold)energy irradiation .The

PET surface develops a well-oriented periodic structure of hills and grooves or a “ripple

structure” with high energy treatment. However, the ripple size can be reduced to submicron

level by irradiation of the sample below the ablation threshold. Chemical surface changes of

the material can be characterized by X-ray photoelectron spectroscopy (XPS) and contact

angles. PET modified by high energy will normally exhibit the deposition of some yellow to

black ionized, carbon –rich debris on the treated surface, resulting in a reduction of the O/C

ratio. In contrast, a PET surface modified by low energy leads to oxidation and almost no

ablation. The increased oxygen concentration on low energy modified surfaces is probably

due to a subsequent reaction with atmospheric O2 during irradiation. Polar oxidized groups

like carboxyl are also included .Contact angle measurements are in good agreement with

these findings .Changes in surface morphology of PET fibres were found in relation to laser

energy applied . The mean roll to roll distance increased with increasing laser energy.

Merging of ripples was observed and believed to be a major reason of increased roll to roll

distance. With approximately 50 to 200 pulses, ripple almost approached parallelism. No

further change of PET surface was observed with more laser pulses applied since the fibre

has disintegrated into “ellipsoidal” segments.

In the study of morphological modification of laser-ablated PET fabrics, it was

observed that after laser treatment the ratio of carboxylic acid groups to ester groups

increased, the relative size if the amorphous regions increased and the ratio of oxygen to

carbon increased. A greater depth of shade was achieved on treated fabrics compared with

untreated fabrics dyed with the same amount of disperse dye. This is due to the scattering of

light caused by ripples on the fibre surface, and greater dye uptake by the amorphous regions

on the surface of laser irradiated PET fabrics. The same depth of shade can be obtained on

laser –treated fabric with less dye than is needed on untreated fabric.

Polyamide (nylon 6) fabrics were irradiated with a 193nm argon fluoride excimer

laser and the effects on the dyeing properties of the fabrics were investigated. Chemical

analysis indicated that carbonisation occurred in the laser irradiated samples. The laser

treatment breaks the long chain molecules of nylon, increasing the number of amine end

groups which change the dyeing properties with acid and disperse dyes. The results suggested

that laser treatment could be used to improve the dyeing properties of nylon fabric with a

disperse dye. Ablation products must be removed to achieve better bonding at laser treated

surfaces. Carboxyl group formation at surface of nylon or polyester is stimulated leading to

better dye ability. Anomalous surface structure of nylon and polyester fibres and yarns were

studied .ultraviolet laser radiation causes less damage to nylon yarn than to polyester yarn,

which absorbs more radiation and heats to higher temperatures. The higher temperatures are

produced in a pulse-like action in microscopic areas, resulting in a short-time pyrolysis which

generates changes in the surface structure.

SUPER CRITICAL CARBON DIOXIDE:

Hydrophobic textile materials require creating pores, so that the non-ionic dye

particles would be entered into the textile materials at high temperature and pressure during

dyeing process. After dyeing when the temperature of the dyed materials goes down to the

room temperature, the dye particles would entrapped by the dyed textile materials. Therefore

the hydrophobic textiles are normally dyed from aqueous dye liquors. In such dyeing, a

complete bath exhaustion never occurs, i.e. the dye does not exhaust quantitatively onto the

respective substrate, with the further result that, after the dyeing process, the residual dye

liquor still contains more or less amount of dye depending on the particular dyes and

substrates. For this reason, dyeing results in the formation of this reason, dyeing results in the

formation of relatively large amount of coloured effluents which have to be purified at

considerable trouble and expense.

The process of the invention has a number of advantages as they claimed such as:

1. The supercritical carbon dioxide used in the process does not pass into the effluent,

but is reused after the dyeing process. Therefore no contamination of the effluent

occurs.

2. Further, compared with the aqueous system, the mass transfer reactions necessary for

dyeing the textile substrate proceed substantially faster, so that in turn the textile

substrate to be dyed can be penetrated particularly well and rapidly by the dye liquor.

3. When dyeing would carried out in wound packages by the process of the invention,

no unlevelness would occurs with respect to penetration of the packages, which

unlevelness is regarded as responsible for causing listing defects in the conventional

process for the beam dyeing of flat goods.

4. Also the novel process does not give rise to the undesirable agglomeration of disperse

dyes which from time to time occurs in conventional dyeing with disperse dyes. Thus

the know lightening of disperse dyes and hence the spotting which may occur in the

conventional dyeing processes carried out in aqueous systems are avoided by using

the process of the invention.

Fig 3 phase diagram of CO2

Carbon dioxide, as pressurized liquid in super critical conditions was used with

success as a solvent in the dyeing polyester fibres at pressures up to 30 MPa and temperature

to 423k.The solubility of the dyes is of the order 10 mg/litre of carbon dioxide at 293.15k and

a pressure of 25MPa.

Not only the dyeing process but also the other chemical process could be carried out

by the super critical carbon dioxide. Hydrophobic textile materials are usually whitened from

aqueous liquors. This never results in complete exhaustion of the bath, i.e. the fluorescent

whitening agents do not show quantitative exhaustion onto the textile material. This in turn

has the effect that the whitening liquor remaining after whitening still contains, depending on

the particular fluorescent whitening agents and substrates, certain amounts of fluorescent

whitening agent. Their invention relates to a process for the fluorescent whitening of

hydrophobic textile material with fluorescent whitening agents, wherein the textile material is

treated with a fluorescent whitening agent in super critical carbon dioxide. The process

according to the invention has a number of advantages same as in dyeing with super critical

carbon dioxide, such as no water pollution, much higher mass transfer rate than in aqueous

systems, no non-uniformities with respect to the flow through the wound package, no

unwanted agglomerations on the fibre material. A further advantage of the process according

to the invention is that it is possible to use disperse fluorescent whitening agents which

exclusively consist of the actual whitening agent and do not contain the customary

dispersants and diluends.

The fluorescent whitening agents used in the process according to the invention are

water insoluble compounds two identical or different radicals selected from the group of

consisting styryl, stilbenyl, naphthotriazolyl, benzoxazolyl, coumarin, naphthalimide, pyrene,

and trizinyl which are linked to one another directly or via a bridging member selected from

the group consisting of vinylene, styrylene, stilbenylene, thienylene, phenylene, napthylene

and oxadiazolylene.

ULTRASONIC ASSISTED WET PROCESSING

Ultrasonic represents a special branch of general acoustics, the science of mechanical

oscillations of solids, liquids and gaseous media. With reference to the properties of human

ear, high frequency inaudible oscillations are ultrasonic or supersonic. In other words, while

the normal range of human hearing is in between 16Hz & 16 kHz. Ultrasonic frequencies lie

between 20 kHz and 500 MHz. Expressed in physical terms, sound produced by mechanical

oscillation of elastic media. The occurrence of sound presupposes the existence of material it

can present itself in solid, liquid or gaseous media. Wet processing of textiles uses large

quantities of water, and electrical and thermal energy. Most of these processes involves the

use of chemicals for assisting, accelerating or retarding their rates and carried out at elevated

temperatures to transfer mass from processing liquid medium across the surface of the textile

material in a reasonable time. Scaling up from lab scale trials to pilot plant trials have been

difficult. In order for ultrasound to provide its beneficial results during dyeing, high

intensities are required. Producing high intensity, uniform ultrasound in a large vessel is

difficult.

Ultrasound reduces processing time and energy consumption, maintain or improve

product quality, and reduce the use of auxiliary chemicals. In essence, the use of ultrasound

for dyeing will use electricity to replace expensive thermal energy and chemicals, which have

to be treated in wastewater

BUBBLING PHENOMENON

Ultrasound energy is sound waves with frequencies above 20,000 oscillations per second,

which is above the upper limit of human hearing. In liquid, these high-frequency waves cause

the formation of microscopic bubbles, or cavitations. They also cause insignificant heating of

the liquid.” Ultrasound causes cavitational bubbles to form in liquid. When the bubbles

collapse, they generate tiny but powerful shock waves. we needed to agitate the border layer

of liquid to get the liquor through the barrier more quickly, and these shock waves seemed

like the perfect stirring mechanism.

BASIC PRINCIPLE

In a solid both longitudinal and transverse waves can be transmitted whereas in gas and

liquids only longitudinal waves can be transmitted. In liquids, longitudinal vibrations of

molecules generate compression and refractions, i.e., areas of high pressure and low local

pressure. The latter gives rise to cavities or bubbles, which expand and finally during the

compression phase, collapse violently generating shock waves. The phenomena of bubble

formation and collapse (known as cavitations) are generally responsible for most of ultrasonic

effects observed in solid/liquid or liquid/liquid systems. Here Fig below shows the waves

produced by ultrasound .

Figure 4: Representation of Some Typical Characteristics of an Ultrasonic Wave

GENERATION OF ULTRASONIC WAVES

The ultrasonic waves can be generated by variety of ways. Most generally known are the

different configurations of whistles, Hooters and sirens as well as piezo-electric and

magnatostrictive transducers. The working mechanism of sirens and whistles allow an

optimal transfer of the ultrasonic sound to the ambient air. In the case of magnatostrictive and

or piezo-electric transducers of ultrasonic waves, the generators as such will only produce

low oscillation amplitudes, which are difficult to transfer to gases. The occurrence of

cavities depends upon several factors such as the frequency and intensity of waves,

temperature and vapor pressure of liquids.

ULTRASOUND IN TEXTILE APPLICATIONS

The effect of ultrasound on textile substrates and polymers has started after the

introduction of the synthetic materials and their blends to the industry. These include

application in mechanical processes (weaving, finishing and making up for cutting and

welding woven, non-woven and knitted fabrics) and wet processes (sizing, scouring

bleaching, dyeing, etc) .It deals with the application of ultrasound in the mechanical

processes of industrial as well as apparel textiles. Ultrasonic equipment for cutting and

welding has gained increase acceptance in all sectors of the international textile industry from

weaving, through finishing to the making-up operation.

Mass transfer in textile materials and ultrasound waves

A piece of textile is a non-homogeneous porous medium. A textile comprises of yarns,

and the yarns are made up of fibers. A woven textile fabric often has dual porosity: inter-yarn

porosity and intra-yarn porosity. As mentioned earlier, diffusion and convection in the inter-

yarn and intra-yarn pores of the fabric form the dominant mechanisms of mass transfer in wet

textile processes. The major steps in mass transfer in textile materials are:

Mass transfer from intra-yarn pores to inter-yarn pores,

Mass transfer from the inter-yarn pores to the liquid boundary layer between the textile

and the bulk liquid,

Mass transfer from the liquid boundary layer to the bulk liquid.

The relative contribution of each of these steps to the overall mass transfer in the textile

materials can be determined by the hydrodynamics of the flow through the textile material.

BIO-TECHNOLOGY:

One of the most negative environment impacts from textile production is the

traditional process used to prepare cotton fiber, yarn, and fabric. Before cotton fabric or yarn

can be dyed, it goes through a number of processes in a textile mill. One important step is

scoring is the complete or partial removal of the non-cellulosic components found in native

cotton as well as impurities such as machinery and size lubricants. Traditionally it is

achieved through a series of chemical treatments and subsequently rinsing in water. This

treatment generates large amounts of salts, acids, and alkali and requires huge amount of

water.

THE GREEN ALTERNATIVE:

With bio-preparation using the enzyme the cotton fibers can be treated under very

mild condition. The environmental impact is reduced since there is less chemical waste and

a lower volume of water is needed for the procedure. The bio preparation process decreases

both effluent load and water usage to the extent that the new technology becomes an

economically viable alternative. Instead of using hot sodium hydroxide to remove the

impurities and damaging parts of the fiber enzymes do the same job leaving the cotton fiber

intact. It is believed that the replacement of caustic scouring of cotton substrates by bio

preparation with selected enzymes will result in the following quantifiable improvements:

lower, BOD, COD, TDS, and Alkalinity. Process time, Cotton weight loss, and harshness of

hand.

An extremely powerful alkaline pectinase recently has been isolated. This new

enzyme is now being produced in volume and is being reduced to commercial use in bio

preparation on a worldwide basis. The major benefit of this enzyme in bio preparation is that

the enzyme does not destroy the cellulose of the cotton fiber. The enzyme is a pectate lyase,

and as such very rapidly catalyses hydrolysis of salts of polygalacturonic acids (pectin‟s) in

the primary wall matrix. The term alkaline pectinase is used to describe the enzyme because

the biological catalyst is used under mildly alkaline conditions which are very beneficial in

preparation process.

ENZYMES:

Enzyme is a Greek word „Enzymos‟ meaning „in the cell‟ or „from the cell‟. They are

the protein substances made up of more than 250 amino acids. Based on the medium for

their preparation, they are classified as bacterial, pancreatic (blood, lever etc) malt

(germinated barely) etc. their major functions are fails on hydrolysis, oxidation, reduction

coagulation and decomposition. Grouped under the following groups :

ENZYME IN TEXTILES

Enzymes are used to remove lubricants and sizes. Enzymatic desizing has achieved

industry-wide adoption as a particularly cost-effective treatment, with savings in both

processing costs and wastewater treatments. Sticky insect secretions from silk fibres can be

removed using enzymes. Wool and Cotton can be scoured effectively using enzyme rather

than harsh chemicals. Enzymes rather than caustic chemicals can be used to fade fabrics

without the wastewater treatment cost of ordinary bleaches. Bio-stoning has been widely

adopted as the standard method of achieving “stone –washed” denim.

Enzymes are used to fade the denim rather than the abrasive action of pumice

stones. Substantial savings result from reduced water usage and less damage to the fabric.

Enzymes has been used effectively in shrink proofing of wool, giving improved quality and

significantly reduced effluent costs as opposed to using chemical treatments.

Bio polishing involves the use of enzymes to shear off the micro fibres of cotton

and other cellulose materials to produce fabrics with superior softness, drape and resistance

to pilling. This mode has been specially developed to achieve a cleaner pile on terry towels.

A treatment with “ultrazyme LF conc.”- A powerful composition gives a clear look to the

pile, improved softness and absorbency. Fabrics containing regenerated cellulosic fiber

often show fuzzy surface due to chafing during wet processing. A smooth and clear finish

can be achieved by bio singing.

CONCLUSIONS:

Due to the increasing requirements on the dyeing and finishing of textile fibres

/fabrics, the society demand for textiles that have been processed by eco-friendly sound

methods, therefore, new innovative production techniques are demanded. In this field, the

plasma technology, laser treatment and supercritical fluids treatment shows distinct

advantages because, these are environmentally friendly, and even surface properties of inert

materials can be changed easily. It is thus expected that in future, many of the physical

processes would help in solving the environmental problems possessed by dyeing and

finishing plant of textile industry. Therefore these physical processes need to be explored at

the bulk processing level.The result of bio-preparation with enzymes is that the cellulose is

not degraded, resulting in less weight or strength loss than occurs with either caustic scouring

or cellulose treatment.

REFERENCE

1. Aravin Prince Periyasamy- Application of Nano Technology In Textile Finishing –

Textile Magazine Dec 2006

2. Aravin Prince Periyasamy - Bio Processing in Textile Application / Textile

magazine-July 07

3. Aravin Prince Periyasamy- Ultrasonic assisted textile wet processing – Indian

Textile Journal May 2009

4. Dr Bhaarathi dhurai Application of enzyme in textile processing – National

Conference held in PSG Tech Coimbatore

5. www.resil.com

6. www.mapsenzyme.com

7. www.bharattextile.com