The fabric industry is a diverse sector in footings of production of natural stuffs, runing procedures, merchandise development, and equipment. The industry is well-characterized for devouring big sums of H2O, energy, and dispatching high volumes of waste in to public sewerage intervention workss ( STP ) . The chief beginnings of pollution in the fabric sector are derived from runing procedures such as dyeing and completing Millss. These procedures use considerable degrees of H2O ( ex. 70-150L for 1kg of cotton ) , chemicals ( salts, base, wetting agents, etc. ) , and dyestuffs ( e.g. reactive dyes ) to accomplish the coveted belongingss of the textile merchandise of which contribute to the pollution burden in the industry.
Major pollutants of environmental concern in fabric effluent include toxic organic compounds, colour, suspended solids, and biochemical/chemical O demand ( BOD5/COD ) . The disposal of fabric wastewater in the municipal STP is an environmental concern because these industrial pollutants may go through through unchanged and enter the receiving rivers or watercourses potentially harming the public assistance of aquatic life. The inauspicious consequence of these pollutants on the aquatic environment include depletion degrees in dissolved O, decrease in photosynthetic activity, and increase susceptibleness for beings to acids and bases.
Effluent intervention engineerings proposed in literature include activated sludge, curdling, ozone, electrochemical oxidization and membrane filtration engineerings. Conventional intervention methods such as curdling and activated sludge have been used to pull off fabric effluent to governmental criterions for dispatching in sewerage intervention workss nevertheless these procedures are uneffective for taking colour from effluent.
Advanced oxidization processes such as electrochemical oxidization and ozone are alternate applications to efficaciously take colour and toxic organic compounds nevertheless some disadvantages include runing costs and possible production of chlorinated organic byproducts in the receiving Waterss. Membrane filtration processes such as nanofiltration and change by reversal osmosis are assuring engineerings for an ecological friendly attack to handling fabric wastewater for reuse since it consumes less H2O and energy.
The purpose of this reappraisal paper is to depict two fresh methods for cut downing pollution burden in fabric dyeing of cellulose cloths. The first method is the usage of cationic reagents as a pretreatment for cotton fibres to heighten dye arrested development and the 2nd method uses supercritical C dioxide ( CO2 ) to replace H2O as a dye transportation medium.
An overview on textile dyes, dye arrested development, and dyeing procedure will be discussed. Furthermore, outflowing intervention engineerings such as curdling, advanced oxidization procedures ( electrochemical oxidization and ozone ) and membrane filtration engineerings ( nanofiltration and change by reversal osmosis ) in which the mechanism and evaluated as promising applications for handling outflowing H2O to be reuse in fabric moisture treating operations such as dyeing.
Textile Dyes And Dye Fixation
Dyes are described as coloured substances with complex chemical constructions and high molecular weights. By definition the colour arises from the fond regard of the auxochrome to the chromophore ( light absorbing group ) of the dyes that alters both the wavelength and strength of soaking up. Dyes manufactured for apparels shapers are designed to hold good visible radiation stableness and chemical opposition to debasement, nevertheless due to the high solubility of dyes in H2O biological interventions are uneffective in taking colour from the wastewater.
Wash speed is an of import factor to weigh into consideration when finding the lastingness of the merchandise. It is dependent on the covalent bond strength between the fibre and dye against alkaline and acerb hydrolysis, and the efficient usage of H2O to take unreacted dye from the substrate. The grade by which dyes are fixed on to fiber and acquire discharged into the intervention bath after wash-off is referred to as dye arrested development. The influence of dye loss is attributed to several factors such as the type of dye, the deepness of shadiness, application method, and liquid ratio ( water/energy ingestion ) .
Cotton and other celullosic cloths are colored with reactive dyes because these dyes have good visible radiation stableness and good wash speed features but hapless dye-fixation outputs ( 60-70 % ) . Reactive dyes attach on the fibre via a covalent bond formation between the reactive group of the dye and the nucleophilic group in the fibre. The dye-fiber reaction is facilitated by big sums of salt and electrolytes that cut down the charge repulsive force forces between the negatively charge dye molecules and the negatively charge hydroxyl groups in the fibre as a consequence of the ionisation of cellulose hydroxyl groups in H2O.
However, due to the competitory reaction between the hydroxyl anions ( OH- ) in the alkalic bath and negatively charge dye molecules for the ionised hydroxyl groups in the cellulose fibres which are the nucleophiles for the dye-fiber reaction ; about 40 % of hydrolyzed ( un-fixed ) dye remains in the intervention bath at the terminal of dyeing procedure. An extended demand for wash-off is required to accomplish the coveted wash speed features on the merchandise.
Before the cloth enters the dyeing procedure it must be decently treated to take all natural drosss and chemical residues applied during operating procedures such as fiber production, and fabric weaving and knitwork. The pretreatment procedure includes desizing, bleaching, and mercerization of which contribute about 50 per centum of waste pollution generated by the industry. Conventional dyeing procedures use big sums of H2O about 100L of H2O per 1kg of fabric. Water is a “poor” medium for reassigning dyes on to the cloth from an environmental point of position because of the increasing deficit of H2O available.
Salts and bases are added when dyeing cotton with reactive dyes in order facilitate the affinity for the dye molecules on the fibre. The intervention bath at the terminal of dyeing procedure is to a great extent polluted with toxic organic compounds, electrolytes, and remainder of dyes of which can be expensive to retrieve and sublimate. Effluent disposal is the primary option since treated H2O to be reuse in the industry needs to hold no colour, no suspended solids, low COD, and low conduction degrees. Therefore, the development of environmentally safe production methods is disputing since both the effluent quality and measure depend to a considerable grade on the technique used for a certain substrate ( fibre ) .
Influence Of Cationization For Dying Cellulose Fibers With Reactive Dyes
The influence of cationization for dyeing cotton with reactive dyes enables an environmentally friendly attack to increase dye use, lower H2O and energy ingestion, and cut down outflowing disposal/treatment. Cationization of cotton is by and large performed by presenting amino groups in the cellulose fibre through the reaction of the hydroxyl groups in the cellulose fibre and the reactive group ( e.g. epoxy and 4-vinylpyridine ) of the quarternary cationic agents.
The pretreatment of cellulose fibres with reactive cationic agents will increase dye surface assimilation as a consequence of the columbic attractive force between anionic dye molecules and nucleophiles on the substrate. The dye-fiber reaction can happen under impersonal or mild acidic conditions without the usage of electrolytes and hence terrible wash-off processs can be eliminated since hydrolysis of dyes by and large occurs in alkalic conditions.
EPTMAC, 2,3-epoxypropyltrimethylammonium chloride, is an illustration of a quarternary cationic agent used in research surveies to look into the usage of cationization for bettering dye surface assimilation of cellulose with reactive dyes. Under alkalic conditions EPTMAC will respond with intoxicants to organize quintessences and therefore bring forth a cationized fibre when it reacts with the methyl hydroxyl groups at the C6 place of the cellulose polymer.
A combination of electrostatic interactions such as ion-ion or ion-dipole forces, intramolecular and intermolecular H bonds, and van der waal forces may act upon the surface assimilation of the cationic group of the pretreatment agent to the anionic carboxylic groups in the cellulose fibre. The reaction between the reactive group of dye molecules and the amino-functional nucleophiles of the cationized fibre has been proposed by Blackburn and Burkinshaw ( 2003 ) to happen via a nucleophilic permutation mechanism or a Michael add-on to a dual bond.
Factors that appear to act upon the cationic procedure of dyeing cloths include cationic reagent concentration, dye concentration, and temperature. Kanik and Hauser ( 2004 ) demonstrated that increasing the cationic reagent concentration in the pretreatment solution caused a lessening in dye incursion of the substrate suggesting that an addition in surface colour occurred as consequence of the strong ionic attractive force of dye molecules for the cationic charges on the fibre. Montazer et Al. ( 2007 ) reported that the colour strength ( K/S ) values for dyeing with treated cotton with cationic procedure were frequently 2-4 times better than that of dyeing via conventional methods ( K/S values range from 1-4 ) . The consequence of temperature influenced the per centum of entire dye use by increasing the soaking up of cationic reagent for the substrate.
Subramanian et Al. ( 2006 ) demonstrated that better colour strength values ( K/S value 12.987 ) and maximal entire dye use ( T value 95.1 % ) were obtained when 20 % concentration of cationic reagent ( CIBAFIX WFF ) , 10g/L of sodium carbonate ash, and an optimum temperature of 70?C was used as the cationization parametric quantities. A significant decrease in industrial pollutants such as BOD5, COD, and entire dissolved solids were determined utilizing cationic reagent CIBAFIX WFF compared to dyeing untreated cloth by conventional methods. Blackburn and Burkinshaw ( 2003 ) reported the pretreatment of fabric via cationization reduced the degree of H2O ingestion to about half of that applied during the normal dyeing procedure ( & lt ; 100L per 1kg of cotton cloth ) of which by and large is applied to take un-reacted dyes from the fibre.
Fabric Dying In SuperCritical Carbon Dioxide
Supercritical fluid engineering is a promising application for the development of a water-free dyeing procedure in that it can be environmental friendly, energy economy, addition productiveness, and extinguish outflowing intervention and disposal. The good belongingss of dyeing fabrics in supercritical C dioxide ( SC-CO2 ) are that it is expensive, non-toxic, non-flammable, CO2 can be recycled, and control in dye application rate. SC-CO2 exhibits densenesss and solvating powers similar to liquid dissolvers adding to its advantages in fabric processing, since its low viscousness and rapid diffusion belongingss allow the dye to spread faster into the fabric fibres.
SC-CO2 has been successfully employed as a dissolver system in the dyeing and coating procedures for man-made fibres such as polyesters. In polyester dyeing, SC-CO2 penetrates inside the fibres doing them to swell thereby doing the fibres accessible to the dye molecules. As the force per unit area is lowered the dye molecules are trapped inside the shriveling polyester fibres and no waste is generated since the dye molecules can non be hydrolyzed and no extra energy is required to dry the cloth after dyeing [ 18 ] .
Since non-polar dyes are chiefly used in supercritical CO2 dyeing farther development is required to heighten the dyeing of natural fibres with ionic dyes such as acerb dyes or reactive dyes because the affinity of natural fabrics with dyes occurs by chemical ( covalent bonds ) interactions or fixed by physical ( van der waals ) forces.20-21 Kraan et Al. ( 2003 ) reported four factors that influence the function of supercritical CO2 dyeing for natural fibres “ ( 1 ) dye solubility at operating force per unit area and temperature, ( 2 ) fibre handiness to let diffusion of dye molecules on substrate pores, ( 3 ) dye-fiber substantivity, and ( 4 ) the responsiveness of dye with the textile.”
Sawada et Al. ( 2004 ) investigated the action of co-surfactant on the stage boundaries of the pentaethylene glycol n-octyl quintessence C8H5 contrary micelle utilizing assorted sorts of intoxicants and discussed he solubility of ionic dyes in the C8H5 contrary micellar system when co-surfactant denseness of CO2 and temperature are varied. The research scheme was to fade out the ionic dye in a SC-CO2/reverse micellar system that involves scattering a little measure of H2O in SC-CO2 and co-surfactant suited dye bath that contained conventional ionic dyes in SC-CO2.
Alcohol, peculiarly 1-pentanol seems is a suited co-surfactant to speed up the solubilization of H2O in SC-CO2 ; it assists the formation of stable contrary micelles. Pentaethylene glycol n-octyl ether C8H5 as a wetting agent is soluble in liquid and SC-CO2 ; the complex C8H5/CO2 system has a possible to heighten the solubility of H2O by an add-on of co-surfactant in comparing with a typical contrary micellar system in organic media.
Beltrame et Al ( 1998 ) investigated the consequence of polythene ethanediol as a pre-treatment of cotton cloths in SC-CO2 and the consequences showed that the dye consumption was strongly increased if cotton was pretreated with PEG. PEG is able to organize H bonds with cellulose ironss this prevents the complete deswelling of the fibres during the SC-CO2 intervention therefore keeping to cotton the more accessible to dyeing. At the terminal of the intervention nevertheless when the CO2 is evacuated the dyes migrate out of the polymer in the undissolved province through the polymer pores and rinsing speed is accordingly really low.
In order to avoid these unsought effects benzamide which is soluble in SC-CO2 is a good dissolver for disperse dyes as a interactive agent ; it is able to organize H bonds with cotton and PEG therefore prefering dye entrapment through the partial occlusion of cellulose pores. The consequences yield good dye uptake, light and wet-washing speed are good increasing the lastingness of the merchandise. Fernandez Cid et Al ( 2005 ) prior to dyeing the cotton it was presoaked in a solution of methyl alcohol to swell the fibres. The methyl alcohol replaces the H2O in the cotton and will attach the cotton H bonds. The hydrophobic portion of the methyl alcohol will do diffusion of hydrophobic non-polar reactive dyes into the cotton possible.
Application In Wastewater Treatments
The intervention of fabric effluent for reuse in fabric operations represents an ecological and economical challenge since fabric wastewaters vary in composing due to the different chemicals or physical procedures used on cloths and machinery. Textile pollutants of environmental concern include residuary dyes, colour, BOD, COD, heavy metals, pH, high suspended solids, and toxic organic compounds.2 Typical wastewaters characterized in the fabric industry and their measurings are presented in Table 1 [ 23 ] .
Table 1. Effluent Characteristics of Textile Wastewater [ derived from Kdasi et al. , 2004 ]
Biochemical Oxygen Demand ( mg/L )
Chemical Oxygen Demand ( mg/L )
Sum suspended solids ( mg/L )
Entire dissolved solids ( mg/L )
Chloride ( mg/L )
Entire Kjeldahl Nitrogen ( mg/L )
Color ( Pt-Co )
The remotion of COD and BOD are of import from an environmental point position since high degrees can consume the degree of dissolved O in having rivers doing an increased sum of non-biodegradable organic matter.23 Some advantages and disadvantages for the assorted chemical-physical intervention processes applied for cleansing effluent is listed in table 3 ( edited from baboo et Al ) .
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20. kraan et Al
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