RAISING THE BAR FOR SUSTAINABLE TEXTILE DYEING S. Aishwariya and S. Thamima

Assistant Professor and PG Student, Department of Textiles and Clothing,

Avinashilingam Institute for Home Science and Higher Education for Women, Coimbatore, India.

aishu55@gmail.com

Abstract

Unprocessed raw textile has no market value. The grey cloth made through weaving and

knitting is expected to pass through stages of treatments with water and chemicals that

possibly improve their value. This processing involves synthetic and toxic materials that

are making the entire supply chain, non-sustainable. The industry, however, has tried on

replacing the conventional methods that use more energy and water resources to

techniques that result in lower carbon footprints This paper deals with the road map to

sustainable dyeing technologies and focuses on dyeing based on ultrasonic waves, critical

carbon dioxide, microwaves, and the inkjet printing technology. The process and benefits

of each are discussed in this paper.

Keywords: ultrasonic dyeing, critical CO2 dyeing, microwave-assisted dyeing, inkjet

printing technology, sustainable dyeing, eco-friendly dyeing, textile processing.

IntroductionTextile coloration is an integral part of the value addition of textile material. Dyeing

and printing increase visual beauty, aesthetic appeal, and uniqueness of the fabric. The

textile design and manufacturing are crafted with colors that help in fixing the brand image,

suit a particular season, age group, geographical positioning, and also the pricing. It is

obvious that dyed materials are more preferred and the application of chemicals to make a

fabric more appealing, costs human life and environment. Textiles is the second largest

polluting textile industry and this realization has paved the way to shift its entire supply

chain towards eco-friendly alternatives. Some of the core concepts like ultrasonic dyeing,

critical CO2 dyeing, microwave-assisted dyeing, inkjet printing technology are discussed in

this paper. Textile is one of the largest consumers of freshwater, which is used in dyeing

and cleaning. In this era of water scarcity and water pollution issues bombarding, textile

processing is aimed at waterless processing. Increased expense in sourcing water, the

complexity of the textile wastewater, strict legislation on expelling treated water into the

river bodies have been added factors for looking at alternatives.

1. Ultrasonic dyeing Sound can be defined as the vibrations that travel through the air or any medium

which on reaching human or animal ears is heard. Sound waves can be classified as

infrasound (16 kHz up to 106 kHz), audible sound (up to 16Hz), and ultrasound (20 Mhz -

500Mhz) (Figure 1). Among these, the oscillating waves with frequency bigger than the

maximum limit of human hearing, which makes them inaudible to the human ear is called

ultrasonic waves. The interesting property of these waves is its ability to reflect or refract

like light waves. They can travel through a vacuum, create vibrations in low viscosity

liquids, move with the speed of the sound, and travel with uniform velocity in a

homogenous medium. It can mold metal and plastic. The researchers have found that bats

and frogs use these waves to communicate between them, especially the bats emit high

pitch sound in low frequency, to migrate from one place to another. The ultrasonic

detectors which are employed in calculating distances use the same principle.

Figure 1. The spectrum of Sound Waves

Conventionally, ultrasonic waves a variety of applications in everyday life (Figure 2).

They are used for cleaning devices made of glass, metal, and ceramic to remove the dirt,

chips, oil, and grease. The aircraft sludge and lubricants are usually removed by the use of

ultrasonic waves. In the medical field, Sonography is a technique that helps in capturing

images of the body’s internal organs, which is done using ultrasonic waves. In textile

dyeing, the conventional methods used huge tones of water and energy which had various

allegations which made the way for sustainable solutions. Repeated dyeing to achieve the

better shade that consumes huge quantities of water and energy was a challenge.

In 1941, an alternative technology using ultrasonic waves was designed and textiles

were soaked, washed, and cleaned using these waves. There were studies conducted on

checking the effect of dyeing synthetic materials like polyester and acetate using direct

and reactive dyed with the help of ultrasonic waves. The experiment involved the use of air

bubbles in the dye bath along with the waves. It was observed that ultrasonic dyeing of

textiles helped in increasing the dye penetration on to the fibers, which resulted in better

fastness property. Besides, it does not harm the surface of the fibers, that was an added

advantage. Spectrophotometry was used in evaluating the dye penetration in the fabric.

The process was fast, simple, and safe which suggests its sustainable nature. The

benefits in the processing were less quantity of dye, increased dye absorption, uniform

distribution of dyes on the material, quick processing time, less power consumption, less

pollution with dyed water. This makes it economically and ecologically the best alternative

solution. Less dye, less dyeing time, and low dyeing temperature are advantages of

ultrasonic dyeing. The effect is more in hydrophobic, fibers dyed with insoluble dyes than

hydrophilic with ionic dyes. It is also observed that the rate of dyeing, increased dye

uptake, the effect is more on coated textiles. Ultrasonic cavitation speeds up the rate of

dye diffusion and allows dye penetration more rapid, the sonication speeds the reaction

between dye and fiber. Dispersing is uniform due to the sonic waves and the uniform

dyeing was possible even at a low temperature of 30ºC, which is 230% more than color

strength compared to conventional dyeing.

Figure 2. Application of Ultrasonic waves

Methods of producing ultrasonic waves a. Formation of cavitation: Ultrasound energy is sound waves with frequencies above

20,000 oscillations per second. In liquid, these high-frequency waves cause the formation

of cavitation (microscopic bubbles) and insignificant heating of the liquid. In textile dyeing,

ultrasonic waves are absorbed in the liquid system and the cavitation/bubbles are created.

This can liberate entrapped gases from liquid or materials like textiles, dye bath.

b. Compression or rarefaction: There is a compression/ rarefaction during each cycle of

a wave. When ultrasonic waves are absorbed in the liquid system, the phenomenon of

cavitation takes place, which is an alternative wave formation, the oscillation of tiny

bubbles/ cavities. When the bubbles collapse, they generate tiny but powerful shock

waves into the liquid. In a dye bath, the vibration of waves makes compressions or

rarefactions. This creates minute vapor bubbles of 500 nanometer in size, which can

collapse and cause shock waves throughout the bath

c. Streaming: The waves push the 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 the microscopic level. If the bubbles collapse in textile materials, it will

result in the formation of high-velocity micro-jet particles with high velocities directed

towards the solid surface. These microjets 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.

Textile processing using Ultrasonic wavesVarious studies have reported the use of ultrasonic waves in dyeing natural,

synthetic, and regenerated textile fibers. The studies on using ultrasonic waves for dyeing

of wool is quite interesting. They have shown positive effects on the dyeing behavior and

increased dye exhaustion rate on dyeing woolen fibers with acid dyes. It could be due to

the reduced boundary in liquor surrounding the fiber which is the characteristic feature in

the ultrasonic irradiated environment. Low dyeing temperature for wool can be more

effective using ultrasonic waves, the resultant fiber has a good wash and fastness

property. In textile finishing, the herbs are coated on textile materials for its medicinal and

novel properties. In this scenario, the herbal extraction can be done by the use of

ultrasonic waves. Cavitation in the liquid is good with the use of these ultrasonic waves

however the pH, salt concentration, time, pressure, and power of ultrasonic waves will

affect the finishing process. In another study, natural dye lac with varying percentages of

dye, temperature, and power resulted in a different amount of dyeing material. A dried and

grounded sample mixed with methanol and placed in an ultrasonic bath for 30 minutes.

The temperature was increased from 20- 60 °C after an hour. The process was repeated a

few times to get the required amount of extract. This process is based on producing colors

by addition and subtractions of textile materials by ultrasonic waves. Unlike gases and

liquid, in solids both longitudinal and transverse waves are transmitted. The effects of

ultrasonic arise when sound is circulated through the medium. In liquids, longitudinal

vibrations of molecules generate compressions and rarefactions, 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 throughout the

medium.

Figure 3. Ultrasonic waves in washing textiles

Ultrasonic waves are used in the washing of fabrics using ultrasonic vibration,

cavitations, and transducer working on the surface of the material (Figure 3). The

advantages are deep and effective cleaning, low energy requirement, less water, less

detergent, fewer accessories and does not harm the fabric. The merits of ultrasonic dyeing

are its ability to save energy by dyeing a low temperature which enables in power

consumption. The reduction in consumption of dyes and synthetics contributes less load to

the effluents. Reduced processing time, reduced usage of auxiliary chemicals,

enhancement of color shade, reduced processing cost, improvement in quality, and easier

process control. The demerits of ultrasonic dyeing are the difficulty in producing high-

intensity ultrasound waves in the chamber. To conclude, the major idea of using the

ultrasonic dyeing is to improve dye productivity, washing fastness, reducing both energy

cost and water usage.

2. Supercritical Carbon dioxide Dyeing (SC-CO2 Dyeing)Carbon dioxide is available in abundance, ecologically harmless, non -toxic, and

non-explosive. A supercritical fluid has both the gaseous property of being able to

penetrate anything and the liquid property of being able to dissolve materials into their

components. Supercritical fluid (SCF) denotes highly compressed gases that combine

properties of gases and liquids intriguingly. It is a substance that can either be liquid or

gas, used in a state above the critical temperature and pressure where gases and liquids

can coexist. This shows unique properties that are different from those of either gases or

liquids under standard conditions (Figure 4). Supercritical fluid carbon dioxide (SCF) is

obtained by heating carbon dioxide above 31º C (88° F) and pressurizing it. In this stage, it

becomes supercritical which is an expanded liquid or a heavily compressed gas. Carbon

dioxide is the most commonly used supercritical solvent, which is made in excess by

industry with high purity. It is inexpensive, non-toxic, non-flammable and has a near

ambient critical temperature (31°C). The high density and good diffusivity make

supercritical CO2 a very good and popular solvent. High performance, economic,

sustainable, ecofriendly is its added merits. The SC-CO2 dyeing is mainly used for

synthetic dyes but also proved effective for natural dyes.

Figure 4. Properties of Supercritical fluid

The process eliminates water consumption, effluent generation, reduced energy

consumption, fewer air pollutants, faster dyeing, no need for surfactants and chemicals

with the ultimatum, which is 95 percent of the CO2 used in the process can be recycled for

repeated use. The demerits are high cost of installation and process is done as batches.

The dye solubility requires high temperature and pressure. The entire process is now

focused on synthetic textiles however it is found to be working best on polyester.

Figure 5. Advertisement of DyeCoo promoting Waterless campaign

Supercritical carbon dioxide is used in various industries like Food and

Nutraceuticals, Perfumes and Cosmetics, Pharmaceuticals, Electronics, Aerogels,

Ceramic and innovative Materials, Oil and gas, Waste treatment, and Waste valorization.

The decaffeination of coffee, extraction of natural flavors, isolation of compounds for

fragrances is some examples. In textiles, a Netherlands based DyeCoo Textile Systems,

was the first in the world to have made a commercial success in treating synthetic textiles

with CO2 and without water (Figure 5). At the end of research for more than eight years,

Nike has adopted to use recycled carbon dioxide to color synthetic textiles that have

proved to reduce effluent to a great extent. Energy consumption is found to be reduced by

40% and color consistency is 98%. Statistics quote by 2015, 39 million tons of polyester

will be dyed, whereas processing one kilogram of textile consumes 100-150 liters of water.

When the goal of the company is to conserve water, energy, and chemical consumption

such techniques are handy.

Figure 6. Steps involved in Supercritical Carbon dioxide Dyeing

Textile Dyeing using SCF-CO2The textiles to be dyed are wrapped on a dyeing beam to achieve an equal dyeing

result. The dyeing beam is placed in the dyeing autoclave and the dyestuff is filled into the

receiver. When the pressure vessels are closed, carbon dioxide is fed in several stages

which are explained in Figures 6 & 7.

a. Pretreatment: In the first step the textiles are cleaned from pollutants and sticking

auxiliary materials from the production because materials like wax, oils, and other

hydrophobic substances can disturb the dyeing process. With the pressurization pump

liquid CO2 from the buffer tank is compressed to supercritical pressure and heated up in

the heat exchanger to supercritical temperature. The supercritical CO2 flows through the

textiles in the dyeing autoclave and, besides, solves carefully all sticking pollutions from

the fibers. The loaded CO2 flows via an expansion valve and becomes by the pressure

decrease gaseous. Thereby the solution power is reduced and the extracted pollutions

precipitate and are collected in the separator. The purified CO2 is liquefied in the

condenser and is led via the buffer vessel back into the circulation.

Figure 7. The schematic diagram for Dyeing using Supercritical Carbon dioxide

b. Dyeing: After the pre-treatment the actual dyeing process begins by switching off the

dyestuff receiver into the CO2 circulation. The supercritical CO2 solves the dyestuff in the

dyestuff receiver and flows through the dyeing autoclave. The CO2 loaded with dyestuff is

delivered through the textiles and the dyestuff is adsorbed in the fibers. After the dyeing

autoclave the CO2 flows through a filter to the circulating pump and afterward is fortified in

the dyestuff receiver with fresh dyestuff and is led as long as in the circulation, until the

desired dyeing intensity of the textiles is achieved.

c. After Treatment: After finishing the dyeing step the CO2 circuit and dyed Material are

cleaned from excess dyestuff. Therefore, the dyestuff receiver is taken out of the CO2

circuit and the loaded CO2 is expanded via the expansion valve into the separator. The

excess dyestuff precipitates fall out and are collected in the separator. The CO2 is

circulated as long as the plant and the textiles are cleaned from the excess dyestuff

leftovers. After finishing the complete dyeing process the CO2 circulation is stopped and

the dyeing autoclave is depressurized to atmospheric conditions. The dyed textiles are

taken out of the autoclave.

In a nutshell:

The test begins in a given condition, the gas-like diffusion of supercritical CO2

happens where the dye is evenly dispersed into the pores and crevices of the fiber.

The dyestuff is fed in the autoclave, and the dyeing instrument is flushed with liquid

CO2.

The preheated liquefied CO2 absorbs the dye and performs dyeing operation (like

solvent dyeing). With the increase of pressure CO2 becomes gaseous and loses its

dissolving capacity. The residues of dye are then separated after liquefication.

Carbon dioxide which is free from dye goes back into the collecting tank after the

dyeing process. The circulation of CO2 is stopped and the dyeing autoclave is

depressurized.

The unused dye powder is seen to have deposited at the bottom of the machine.

The technique does not produce any drainage and is considered a sustainable

solution for conventional dyeing.

3. Microwave-Assisted DyeingMicrowaves are of 3 and 300 GHz frequency with a corresponding electrical

wavelength between λ = c/f = 10 cm and λ = 1 mm, respectively. They were popular during

the Second World war as an important part of radar systems. The use of radiofrequency

heating using microwaves was discovered in 1946 and today more than 60 million homes

have a microwave oven in their houses. Microwave radiation spreads inside a matter

similar to the light waves. They are reflected by metals, absorbed by a dielectric material,

and implemented through other materials without any loss of energy. The organic solvent

can absorb microwave radiation, while ceramic, quartz and most thermoplastic material

absorb microwave irradiation to moderate levels.

Figure 8. Microwaves in the electromagnetic spectrum

The use of microwaves, in dye extraction and application, is termed as microwave-

assisted textile dyeing. This is done using the dielectric and thermal properties of the

solution. The dielectric property refers to the intrinsic electrical properties that affect the

dyeing by dipolar rotation of the dye and influences the microwave field upon the dipoles.

The aqueous solution of dye has two polar components, in the high-frequency microwave

field oscillating at 2450MHz. It influences the vibrational energy in the water molecules and

the dye molecules. The thermal (heating) mechanism is through ionic conduction, which is

a type of resistance heating. Depending on the acceleration of the ions through the dye

solution, the collision of dye molecules occurs within the molecules of the fiber. The

mordant helps in the penetration of the dye resulting in superior dyeing compared to

traditional methods. This is an effective method of dyeing small amounts of fiber or fabric

in the microwave using reactive dyes.

Figure 9. Comparing the conventional and microwave heating method

The dry yarn or fiber to be dyed is weighed and thoroughly soaked the fiber/yarn

into the dyebath (overnight soaking or one hour in hot water). The dye powder is weighed

and mixed ¾ of a cup of hot water and stirred thoroughly. A wide shallow microwave-safe

container such as pyrex is taken and the fiber is distributed to cover the base in one-inch

thickness, a spoon can be used for even distribution of fibers. The content is covered

loosely and cooked for 6 minutes, after which it is allowed to cool. All the dye should be

absorbed into the fiber leaving just cloudy water. Rinsing in cold water and drying in shade

is done. Uniform dyeing is obtained however in some cases of yarn dyeing white streaks

are seen, which will be a defect in dyeing. Uneven depth of color, more amount of dye in

the water are other drawbacks.

Both mordant and dye extraction can be done using microwaves, which is a clean

source of energy ad easily made available. In a particular study, the stock solution of

0.5%, 1%, and 2% will be prepared by boiling 0.5g, 1g, and 2 g of mordant in 100 ml of

water at 90 degrees Celcius and above, checking the best temperature to extract mordant.

It is then subject to microwave at 900 W power supply. The extract is filtered and used as

a mordant. The maximum adsorption wavelength and optical density of both dye solution

and mordant were checked using a single and double beam spectrophotometer. The

dyeing was done with the liquor and material ratio to be 30:1. The fabric in the mordant

solution was heated to 90 degrees for one hour. After pre-mordanting, excess mordant

was squeezed and dyed in the same Rota Dyer machine for one hour at 90 degrees. The

dyed fabric is washed in cold water followed by testing of wash and light fastness property

to characterize the material. The technique demonstrated the quick extraction of dye

however increase in shade was not obtained.

Microwaves will be able to start chemical reactions through selective heating, which

results in new materials to be formed, which is not evident in conventional processing

techniques. These waves are used in making composites, ceramics, polymers, minerals,

and powders. Microwaves use the selective heating technique by which the energy wasted

can be minimized. Homogenized heating, power consumption, and reduced operational

time are the merits of using microwaves in textile processing. The high cost of the

equipment, limited applications, variation in dielectric properties with temperature, and

ingrained inefficiency of electric power are some of the demerits of the technique. This is

however less popular at industrial scale and usually done in the lab, or for sample dyeing.

4. Ink Jet or Digital Printing

Figure 10. Inkjet printing machine

The domestic printer helps in printing any image from the computer to a paper. This

is of different types like a laser, inkjet, etc. The same technology is also in printing designs

on textiles and termed as digital printing/ inkjet printing. It is with the advent of digital color

printing various design possibilities have opened up and the technique seems to perform

better than conventional screen printing. Inkjet is a technology wherein there is no printing

master and hence only the ink drops make contact with the substrate. It is therefore

classified as a non-impact printing method. Digital printing includes pre-treatment of the

fabric before the printing process. Pre-treatment of textiles in preparation for ink-jet printing

is carried out because the inclusion of auxiliary chemicals and thickeners into the low

viscosity ink has proved troublesome. Thus, the methodology is akin to `two-phase'

conventional printing as opposed to the `all-in' approach. In the latter case all the dyes,

chemicals, and thickeners required are included in the print paste, whereas in the former

some of the ingredients, particularly chemicals, are applied before or after printing.

Figure 11. Digital printed textile as upholstery (Sofa cover and cushions)

When printing cotton the choice has generally been between reactive dyes and

pigments. The pigment printing process is simpler, as it involves three main stages (print,

dry, bake/cure), whereas reactive printing has two extra processes (print, dry, steam,

wash-off, dry). Pigment printing is therefore a more economical procedure but we avoid

the use in inkjet printing because pigments produced much duller shades than could be

achieved with dyes, and there was a tendency for nozzles to block, in other words, the

`run-ability' was poor. Reactive printing by the `all-in' method is the normal approach for

screen printing, but for jet printing it has certain dangers. As a result, the jet printing of

cotton, wool, and silk has generally been carried out by the `two-phase' method, the ink

containing only purified dyes, the thickener, and chemicals being applied to the substrate

in a pre-treatment. Although the quality of the resulting prints is excellent, the extra

expense of pre-treating the fabric by a pad/dry process makes the process uneconomical

for anything but short runs.

Figure 12. Screen Printing

The main reasons for separating the dye ink from thickeners and other chemicals and

applying them separately to the fabric. 'All-in' inks are less stable and have lower storage

stability, e.g. reactive dyes are more likely to hydrolyze when alkali is present in the ink.

Chemicals in the ink cause corrosion of jet nozzles; the deleterious effect of sodium

chloride on steel surfaces is well known, for instance; inks for use in `charged drop'

continuous printers should have low electrical conductivity. Thickeners in the ink often do

not have the desired rheological properties. Some chemicals can be utilized in pre-treated

fabric but would cause stability problems in the ink; e.g. sodium carbonate as alkali for

reactive dye fixation is acceptable on the fabric but not in the ink. The presence of large

amounts of salts in aqueous inks reduces the solubility of the dyes; concentrated inks are

required in jet printing due to the small droplet size. The advantage of applying thickeners

and chemicals separately from the dyes is that it allows the wettability and penetration

properties of the fabric to be adjusted. The conventional printing adopted in the industry

was screen printing (Figure 12), which was not sustainable due to water consumption and

toxic chemicals involved in processing. The Table 1 compares the conventional method to

the latest inkjet/ digital printing

Table 1. Comparison between Conventional Screen Printing and Digital Printing

Factors Screen printing Digital printing

Tools and technique

The process involves making a stencil using a drawn/digitized image or a photograph, attaching to a screen, placing it over the desired canvas, and spreading the ink over the image.

A computer and a printer with ink cartridges are the requisites

Efforts Takes a lot of time-consuming effort, because the screens need to be made and the process is slow

Easy to operate and gives results at the touch of a key. It is relatively quicker

Quality It offers better quality imaging as the ink gets deeply absorbed and lasts longer. Screen printing also gives clearer edges to the image printing, because of the precision that is carefully done in preparing the stencil blocks

The ink does not spread because the image is directly printed on the fabric, but tends to fade quicker. To print a colorful image, all the colors are present in the single image, and the laborer does not need a separate screen for the same.

Cost Costs escalate with the numbers of screens. If a person wants a more complex image with many colors, then individual slides for every color are created. Since this technique requires skill, the training of labor will be essential. The method is most apt if a person wanted a large quantity of fabric

The computer and printers are one time investments and digital printing is cheaper compared to screen printing as the charge is an offer for per imprinted image.

To sum up, Inkjet or Digital printing has revolutionized the way businesses create

their printed materials. It is fast, effective, and provides an alternative to the more

traditional method of textile printing. The various merits of inkjet printing are discussed

below;

▪ Quality: When it comes to quality, nothing surpasses digital printing. Images are

essentially flawless, alignment and registration issues are non-existent, and the

color is vibrant. Digital printers can also use the entire length of a printable item. 

▪ Speed: Digital printing’s ability to switch over to a new label almost instantly is

another perk of using digital printing. Because there’s no lost time setting up plates

and printing machinery, your order is likely to reach its intended destination days, if

not weeks earlier. 

▪ Short-run printing advantage: Digital textile printing efficiently produces

designs at run lengths as low as one yard of fabric without the need for screen

changes.

▪ Lower water and power consumption: Digital textile printing eliminate the

substantial amount of water and electrical energy one requires for rotary screen

preparation, printing, and cleanup. Even greater water and power savings can be

achieved with disperse/sublimation and pigment digital textile inks, which only

require a heat-fixation step for post-treatment. 

▪ Less chemical waste: Digital textile printing results in significantly less ink usage

and waste relative to screen-printing. Taking into account the additional chemistry

and chemical waste from screen production, printing digitally offers a greener

advantage for printing.

▪ Large repeat sizes: Digital textile printers can print large designs (e.g. cartoon

characters on sheets and blankets) on roll fabric without the usual rotary screen-

printing limitation in pattern repeat size.

▪ Reduced production space requirements: By not having to prepare and store

customer screens for future use, the production footprint for digital printing is a

fraction of the size one requires for a rotary screen print facility.

▪ Less printed inventory needed: Digital textile printing permits the option to print a

design at will. This means that manufacturers with an integrated digital printing

system in their production chain can keep a stock of unprinted textiles on hand to

print as required. This reduces the need for a pre-printed inventory of fabric that

may or may not is used.

▪ Sampling and production were done on the same printer: By being able to print

samples (strike-offs) on the same printer one uses for production, digital textile print

shops can present their customers with proof samples of designs that will exactly

match the final printed material.

▪ Print flexibility: Printing houses utilizing both digital and screen technologies can

choose to print a small number of designs with different color combinations

(colorways) first with their digital textile printing solutions to test the market. They

can later opt to print higher volumes of the most desired color designs using rotary

screen technology.

▪ Variety of creative design choices for printing: Digital textile printing provides

the option to print photographic/continuous tone images, spot color pattern designs,

or a combination of both. This expands the creative printing alternatives for fashion

and interior designers.

▪ Low capital investment: The relatively low capital investment to set up a digital

textile print shop, especially compared to rotary screen-printing production, makes it

possible to start small and expand as business grows.

The demerits of Inkjet Printing are as follows;

▪ Limitation of particle size: Metallic colors cannot be printed by these machines

due to large particle size.

▪ Large Volumes are expensive: Without getting too technical, digital printing

presses run at a maximum of about 50 feet per minute. While this speed is sufficient

for low volume (10,000 – 15,000 item) projects, larger volume work will benefit from

using traditional presses that can run at speeds between 300 and 500 feet per

minute. Although traditional presses are more expensive to configure and operate,

they will be economical.

▪ Ink limitations: While digital printing certainly handles color and ink well, digital

inks tend to fade more quickly than offset inks when exposed to direct sunlight.

Also, the opacity of digital ink is not quite up to par with offset ink, because digital

ink is naturally thinner (though the difference between the two is only noticeable

when dealing with clear or metallic media). There are types of laminations available

to help prevent this problem from occurring.

6. Other sustainable technologiesCotton Pretreatment

Cotton requires more water than other textiles for dyeing. About 200 liters of water

are required to produce 1kg of fabric. Dow has developed a pretreatment process called

ECO FAST Pure that is applied before the dyeing process to produce cationic cotton. The

pretreated cotton acquires a permanent positive charge, enabling it to have a higher

affinity for negatively charged molecules such as dyes. This patented technology

decreases the use of dye and water by 50 percent for cotton dyeing. ColorZen has

innovated technology for pretreatment of raw cotton fibers using a solution comprising a

wetting agent, caustic soda, and an ammonium salt. This pretreated cotton exhibits

increased ability to retain the dye without the need for fixation chemicals, thus reducing the

usage of toxic chemicals by 95 percent and water wastage by 90 percent.

b. Natural or Engineered MicroorganismsColorifix employs a synthetic biological approach by using bacteria to color the

textiles, which can reduce the use of water by up to 10 times. The innovative steps in this

process are to fix the dye-producing bacteria directly onto the fabric using a carbon source

solution, followed by deposition and fixation of the dye onto fabrics with a single heating

cycle by the lysis of the microorganisms. This technology does not require a dye extraction

process, which uses organic solvents, or fixing and reducing agents containing organic

compounds. University of California researchers are developing denim dyes using

genetically modified E.coli bacteria to produce indican, which can then be turned into

indigo by enzymatic treatment. This new process removes the need for harsh chemical

reducing agents for indigo dye solubilization, replacing it with an enzyme. However, the

process still needs optimization in the recovery of indican for its sustainability.

c. Innovative Dyes and AuxiliariesHuntsman Textile Effects introduced Avitera, a line of polyreactive dyes for cotton

that readily bonds to fiber, in contrast to the conventional reactive dyes. Avitera dyes use

tri-functional chemical reactivity that provides a high reaction and fixation rate with

cellulosic fiber, leaving very little unfixed dye to be removed. This dramatically reduces

water and energy usage by up to 50 percent and uses up to 20 percent less salt. And

Huntsman Corporation recently developed the diffusion accelerant Univadine E3-3D, a

dyeing auxiliary that enhances the diffusion of a dye into the polyester. This diffusion

accelerant is said to achieve high-performance dyeing of polyester microfibers and is free

of hazardous chemicals, thus complying with current and anticipated industry sustainability

standards

d. Powder Dyes from Textile FibersOfficina+39, an Italy based company, developed the sustainable dye range

Recycrom using recycled clothing, fiber material, and textile scraps. It developed a

sophisticated eight-step system (patent pending) in which all the fabric fibers are

crystallized into an extremely fine powder that can be used as a pigment dye for fabrics

and garments made of cotton, wool, nylon, or any natural fiber. Recycrom can be applied

to the fabrics using various methods such as exhaustion dyeing, dipping, spraying, screen

printing, and coating. Recycrom is applied as a suspension while most dyes are used as a

chemical solution and hence can be easily filtered from the water, thus reducing the

environmental impact.

e. Hybrid PigmentsEco foot has developed hybrid pigments composed of a dye chemically linked to a

polymer particle that reacts with cellulose fibers at temperatures as low as 25ºC. This

technology does not require the use of salt, which otherwise is crucial to driving the dye

into the fabric. This technology can be applied for dyeing cotton garments at low

temperatures and also to wool in a more ecological process. Eco foot-Indigo, a hybrid

pigment used in dyeing denim, avoids using toxic reducing agents that are traditionally

used in converting indigo pigment to a water-soluble form. Common reducing agents are

considered environmentally unfavorable, as the sulfite and sulfate generated in the

dyebath can cause various problems when discharged into the wastewater. Eco foot also

developed auxiliaries to prevent hydrolysis of the dye in the dyeing process, which typically

requires harsh washing-off procedures to remove the hydrolyzed dye. Together with hybrid

pigments and auxiliaries, more than 50 percent of water in the intermediate and final rinses

can be saved in the total process of preparation and dyeing.

Conclusion The next biggest global challenge is forecasted to be the Greywater Footprint,

which is the hazard caused by textile dyed wastewater that is polluting the river bodies.

Huntsman Dyes launched the water and energy-efficient technology for reactive dyeing of

natural fiber. In 2010, Levi Strauss & Co., launched its denim made without water,

polyester, and synthetics using air dyeing technique. This has a lot of options to create

diversified designs in different prints and colors on opposite sides of the fabric. Many such

technologies are being developed to create sustainable alternatives to cease pollution.

Water conservation, energy alternatives should be the themes to be discussed for living in

cohesion with nature.

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_vis-a-vis_dyeings

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