Dyes

A natural or synthetic substance used to add a colour to or change the colour of something. Such substances with considerable coloring capacity are widely employed in the in the production of consumer products, including paints, textile, printing inks, pharmaceutical, food, cosmetics, plastics, photographic and paper industries.

It is estimated that over 10,000 different dyes and pigments are used industrially and over 7 x 105

tons of synthetic dyes are annually produced worldwide.

Types of dyes

1. Natural dyes 2. Synthetic dyes3. Food dyes4. Other dyes like leather, laser and also based on chemical classification

With respect to the number and production volumes, azo dyes are the largest group of colorants, constituting 60-70% of all organic dyes produced in the world. They have a wide range of applications in the textile, pharmaceutical and cosmetic industries, and are also used in food, paper, leather and paints

Market demand for dye and dye intermediates is expected to grow to 1500,000 tons in 2014. The organized sector dominates, with 65% share of the total market, while the unorganized sector controls the remaining 35% of the market. Exports of dyes are also expected to increase by 6.4% due to the shift of production bases from developed countries to India on account of stringent pollution control measures being adopted in those countries. At present, India contributes about 6% of the share in the global market with a CAGR of more than 15% in the last decade.

The dyeing process in various industries has garnered a lot of attention lately because of the emerging concept of sustainability and eco-friendly variants. Due to the toxicity of the dyes and inappropriate discharge of such waste has led to skin diseases and respiratory problems among many factory workers. This has given an impetus to the rising demand for producing textile, paper, cosmetics products through sustainable dyes and processes.

Let us consider its effects in 2 major industries of application :

1.Textile Industry: Till the midst of nineteenth century all the dyes used for textile products were procured naturally, until the invention of mauvine in 1856 by Perkin. Since then there has been no looking back in the production of synthetic dyes because they were affordable, available in a lot of different colors, good color-fastness, and most of all were easy to produce. The textile industry is accountable for using and producing 1.3 million tons of dyes and pigments, most of which are made synthetically.

o The textile industry is one of the largest sectors globally and produces an astonishing 60 billion kilograms of fabric annually, using up to 9 trillion gallons of water.

o 10-25% of textile dyes are lost during the dyeing process, and 2-20% is discharged as aqueous effluents in different environmental components.

In particular, the discharge of dye-containing effluents into the water environment is undesirable because of their color, released directly and breakdown products are toxic, carcinogenic or mutagenic to life forms mainly because of carcinogens such as benzidine, naphthalene and other aromatic compounds

2.Printing Ink: Heavy metals in the colorants used in printing industry have been reduced significantly in the past 20 years, but many are still in use. For example, titanium oxide, chromate, molybdenum, and iron are used as pigments; titanium oxide is used for pearlescent pigments; and aluminum and brass are used in metallic inks. Heavy metals pose unique and serious environmental problems.

One concern is the ability of heavy metals to leech into ground water, which could lead to serious health issues in both humans and wildlife.

A more potent pathway, however, is the inhalation of finely ground metals, such as those created in ink manufacturing.

Environmental impact of DyesAir pollution - Most processes performed in textile mills produce atmospheric emissions. Gaseous emissions have been identified as the second greatest pollution problem (after effluent quality) for the textile industry. Speculation concerning the amounts and types of air pollutants emitted from textile operations has been widespread but, generally, air emission data for textile manufacturing operations are not readily available. Air pollution is the most difficult type of pollution to sample, test, and quantify in an audit.

Water Pollution – The textile industry consumes a substantial amount of water in its manufacturing processes used mainly in the dyeing and finishing operations of the plants. The wastewater from textile plants is classified as the most polluting of all the industrial sectors, considering the volume generated as well as the effluent composition.

In the textile industry, up to 200,000 tons of these dyes are lost to effluents every year during the dyeing and finishing operations, due to the inefficiency of the dyeing process.

In addition, the increased demand for textile products and the proportional increase in their production, and the use of synthetic dyes have together contributed to dye wastewater becoming one of the substantial sources of severe pollution problems in current times.

Unfortunately, most of the dyes escape conventional wastewater treatment processes and persist in the environment as a result of their high stability to light, temperature, water, detergents, chemicals, soap and other parameters such as bleach and perspiration. Dyes can remain in the

environment for an extended period of time, because of high thermal and photo stability to resist bio degradation.

Dyes lead to number of environmental & health hazards which are as follows:

1. The greatest environmental concern with dyes is their absorption and reflection of sunlight entering the water. Light absorption diminishes photosynthetic activity of algae and seriously influences the food chain.

2. Many dyes and their breakdown products are carcinogenic, mutagenic and/or toxic to life. Dyes are mostly introduced into the environment through industrial effluents.

3. Triple primary cancers involving kidney, urinary bladder and liver of dye workers have been reported.

4. Textile dyes can cause allergies such as contact dermatitis and respiratory diseases, allergic reaction in eyes, skin irritation, and irritation to mucous membrane and the upper respiratory tract.

5. Reactive dyes form covalent bonds with cellulose, woollen and PA fibres. Certain reactive dyes have caused respiratory sensitisation of workers occupationally exposed to them.

6. The presence of very small amounts of dyes in the water, which are nevertheless highly visible, seriously affects the quality and transparency of water bodies such as lakes, rivers and others, leading to damage to the aquatic environment.

7. The highly toxic and mutagenic dyes decrease light penetration and photosynthetic activity, causing oxygen deficiency and limiting downstream beneficial uses such as recreation, drinking water and irrigation.

8. Azo dyes have toxic effects, especially carcinogenic and mutagenic. They entering the body by ingestion and are metabolized by intestinal microorganisms causing DNA damage.

The parameters of water to be checked for pollution:

o pH o Temperatureo Alkalinity o Dissolved oxygen (DO) o Electrical conductivity

Examples of the effects of environment pollution in India as a result of Dye Industries: In India there are estimated to be about 1,000 small-scale entities and 50 large industrial plants.  While the organized dye industry does dominate the market, there are many unorganized small-

o Total dissolved solids (TDS) o Total suspended solids (TSS)o Total hardness o Chemical oxygen demand (COD)o Total solids (TS)

scale plants that disproportionately add to the problem of pollution. The top pollutants are chromium, lead and cadmium.

Maharashtra and Gujarat account for 90% of dyestuff production in India due to the availability of raw materials and dominance of textile industry in these regions.

Jodhpur, India, contains the biggest bloc of textile dyeing and printing industries. About 215 textile industries exist in Jodhpur, with a population of nearly 900,000. 

Pollution Monitoring control program launched for river Kshipra, MP

The results indicate that the effluents affects the water quality which lead to significant environmental and health risk to the rural communities who rely on the receiving water as their source of domestic water purpose without treatment. The study revealed that there was an adverse impact on physicochemical characteristics of the river Kshipra as a result of discharge of untreated effluents of Bhairavgarh Ujjain.

Dyeing Industrial Effluents has adversely impacted the groundwater Quality in Kancheepuram, India

In Tirupur, India, home to scores of factories and workshops where workers dye materials for t-shirts and other garments marketed around the world. Local dye houses have long dumped wastewater into the local river, rendering groundwater undrinkable and local farmland ruined. Despite tougher regulations, a watchful local press, and the closure of companies in non-compliance, water pollution has festered. The city's 350,000 residents, not multinational textile companies, pay the price.

River Bandi affected by textile dyeing and printing effluents, Pali, Western Rajasthan

Legal laws governing dye industry

With respect to the legislation, there is no consensus amongst the different countries concerning effluent discharge, and there is no official document listing the different effluent limit values applied in different countries. Many federal countries, such as the United States of America, Canada and Australia have national environmental legislation, which, as in Europe, establishes the limits that must be complied with. Some countries, such as Thailand, have copied the American system, whereas others, such as Turkey or Morocco, have copied the European model. In some countries, for example India, Pakistan and Malaysia, the emission limits are recommended, but are not mandatory.

With respect to the color, in some countries such as France, Austria and Italy, there are limits for the color of the effluent, but since they use different units, a comparison is impossible.

Listed below are the Acts formed by Central Pollution Control Board.

The Water (Prevention and Control of Pollution) Act, 1974 - To provide for the prevention and control of water pollution and the maintaining or restoring of wholesomeness of water.

The Water (Prevention and Control of Pollution) CESS Act, 1977 - To provide for the levy and collection of cess on water consumed by persons carrying on certain industries.

The Air (Prevention and Control of Pollution) Act, 1981 – To provide for prevention and control of air pollution

The Environment protection Act, 1986 – to provide for protection and improvement of environment

The Public Liability Insurance Act, 1991 – To provide for public liability insurance for the purpose of providing immediate relief to the persons affected by accident occurring while handling any hazardous substance and for matters connected therewith or incidental thereto

The National Environment Tribunal Act, 1995 – To provide for strict liability for damages arising out of any accident occurring while handling any hazardous substance and for the establishment of National Environment Tribunal for effective and expeditious disposal of cases arising from such accident.

In addition to the above the Gujrat pollution Control Board has initiated Plans to create 10,000 skilled personnel with in-depth knowledge of water, air and earth pollution

Suggested measures

The release of improperly treated textile effluents into the environment can become an important source of problems for human and environmental health.

Based on all the problems cited above regarding the discharge of effluents into the environment, it is obvious there is a need to find alternative treatments that are effective in removing dyes from effluents.

Enhance the existing effluent treatment plants through Reverse Osmosis (RO) and the resultant water can be used as fresh water for the region

Industries should switch over to Cleaner Production Technologies (CPT) by using combination of soft flow machines, low salt dyes and membranes filtration. This effectively reduces the water consumption by 50%.

Air Dyeing Technology is a dyeing process that uses air instead of water to dye gar-ments, allowing companies to create garments with vivid designs and colors, without polluting the water and environment.

o It uses 95 percent less water. o Emits 84 percent less Green House Gases (GHG)o Requires 87 percent less energy

Ultrasound-assisted textile dyeing: Ultrasound-assisted textile dyeing was first reported by Sokolov and Tumansky in 1941. Due to the revolution in environmental protection,

the use of ultrasonic energy as a renewable source of energy in textile dyeing has been increased, due to the variety of advantages associated with it.

Ultrasonic energy can clean or homogenize materials, accelerating both physical and chemical reactions, and these qualities can be used to improve textile processing methods. Environmental concern has been focused on textile processing methods for quite some time, and the use of ultrasonic energy has been widely studied in terms of improving washing fastness. The textile dyeing industry has long been struggling to cope with high energy costs, rapid technological changes and the need for a faster delivery time, and the effective management of ultrasonic energy could reduce energy costs and improve productivity.

Use of activated carbon in the absorption of chemicals in waste from the dye process, which has shown to greatly reduce some of the pollutants in the waste.

Dye fed silk worms' take silk farming to the next level: Researchers have come up with a process wherein by adding a chemical dye to the diet of the silkworms, cocoons are produced in bright; luminous hues. The process is expected to eliminate the requirements of conservative dyeing such as huge volumes of water. It would to result in restricting water and environmental pollution.

The Dyestuffs Manufacturers Association of India, popularly known as DMAI was set up in 1950, to promote and protect trade, commerce & Industries connected with dyestuffs & to encourage friendly feelings & unanimity amongst those engaged in the manufacture of dyestuffs in India. The organization needs to promote environment concerns of this industry and the ways to manage it.

Eco – Friendly in Textile Wet ProcessingEnvironmental 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:

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.

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.

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 fibers but also the natural fibers 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 fiber damage. Color fastness of a wool fabric that was low-temperature air-plasma treated and dyed with an acid dye has been evaluated. Color 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.

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.

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.

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.

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 PHENOMENONUltrasound 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 PRINCIPLEIn 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.

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 aneconomically 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.

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.

Conclusion

An alternative to minimize the problems related to the treatment of textile effluents would be the development of more effective dye that can be fixed fiber with higher efficiency decreasing losses on tailings waters and reducing the amount of dye required in the dyeing process, reducing certainly improve the cost and quality of the effluent.

The global demand for cheap end products like paints, textiles, printing inks, paper, plastics and food will push dye houses to simply react to local regulations by moving operations to another city. Moral outrage will not convince many leading manufacturers to change their ways; as long as companies do not pay a price for the land and water their suppliers poison, the excessive use and abuse of environmental parameters like air and water to dye products will continue.