Eco – Friendly in Textile Wet Processing

Asst Professor, Dept of Textile Chemistry, D.K.T.E S. Textile Engineering College, Ichalkaranji, M.S India

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.      Aravin Prince Periyasamy- Super Critical Carbondioxide Dyeing – Man made Textile In India, May 2011.

5.      Dr Bhaarathi dhurai Application of enzyme in textile processing – National Conference held in PSG Tech Coimbatore

6.       www.resil.com

7.      www.mapsenzyme.com

8.      www.bharattextile.com