-An article by Chitranshu Katiyar
A series of processing operations applied to gray fabric to enhance their appearance and hand, properties and possible applications.
In textile manufacturing, finishing refers to the processes that convert the woven or knitted cloth into a usable material and more specifically to any process performed after dyeing the yarn or fabric to improve the look, performance, or “hand” (feel) of the finish textile or clothing.
A finish is a treatment given to a fabric, to change its appearance, handling /touch or Its purpose is to make the fabric more suitable for its end use.
Finish includes any general treatment given to clean and iron fabrics and create exclusive variations of them by using chemical treatments, dyeing & printing to make fabric attractive and appealing.
Why we need finishing?
- Improve the appearance of fabric
- Produce variety in fabrics through dyeing and printing
- Improve the feel or touch of the fabric
- Improve the draping ability of light weight fabrics
- Make fabric suitable for an end (specific)
- Enhance sale appeal
Eco-Friendly Garment Finishes
Eco-friendly finishes refer to suitable textile processing methods that deliver not only eco friendly finished products but also does not hamper the surrounding atmosphere and environment by polluting the air and water respectively, due to emissions of harmful gases and effluent water discharges.
Now world around us is fully aware of the implications of the damages already done to it for its water and environmental resources by way of gas and effluent discharges from polluting industries such as textile and leather processing. In order to reduce and save earth from the pollutions of industries, automotives etc., there comes in to existence stipulated norms and standards for the finished goods and the way of operation.
Throughout the world almost all countries have forms certain rules and regulations for importing and exporting processed textile goods. This paper depicts the various textiles finishes employed in the finishing of garments with a major concern on the environment and new innovative concepts that can be employed in finishing.
Eco-friendly technologies for finishing
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.
Some of the new technologies for the textile industry:
- Plasma Technology
- Super critical carbon dioxide
- Laser treatment
- Micro encapsulation method
There are no harmful chemicals, wet processes, waste water and mechanical hazards to textiles, etc. It has specific action on the all types of fibers and textiles.
Plasma technology has been shown to improve fiber surface properties without affecting desirable bulk properties. It also offers environmental advantages. Therefore, there are increasing uses of plasma treatment of synthetic fibers such as polyethylene terephthalate, nylon, and polypropylene. A general effect is in improvement in their hydrophilic properties.
Plasma Technology in Textiles
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:
- 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.
- Increase of micro-roughness: this effect an anti-pilling finishing of wool.
- Generation of radicals: The presence of free radicals induces secondary reactions such as cross linking. Furthermore, graft polymerization can be carried out as well as reaction with oxygen to generate hydrophilic surfaces in hydrophobic fibers such as polyester or polypropylene.
- 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.
- 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 80ᵒc 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.
Another physical surface treatment method to create the hydrophilic groups on hydrophobic fibers and enhance the dyeing process is laser treatment. Extensive research has been carried out into the possibility of surface finishing of synthetic fiber 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 fiber. Surface properties affected include particle adhesion, wettability and optical properties.
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.
Nanotechnology is the science of the small with big potential. It is one of the most rapidly emerging key technologies of the 21st century. In recent years, noble metal nanoparticles have been the subject focused research due to their unique electronic, optical, mechanical, magnetic and chemical properties that are significantly different from those of bulk materials. Therefore, metallic nano particles have found use in many applications in various fields. Materials in the range of 1 nm- 100 nm hold much interest because it is in this range that a number of newer properties become effective. The most widely used example of textile finishes by nanotechnology is of anti-microbial finishing. Though the use of textile finishing agents have been known from decades, it is only in the recent years that attempts have been made on finishing of textiles with nano-particles as antibacterial compounds. Due to increase in awareness about health and hygiene, people increasingly want their clothing to be hygienically fresh.
Many of the anti-microbial agents available in the market are synthetic based and may not be environmentally friendly. Due to this, many of the consumers are opting for herbal anti-microbial finishes for textiles. It must be ensured that these substances are not only permanently effective but also that they are compatible with skin and environment.
Complex metallic compounds based on metals like copper, silver, zinc etc. cause inhibition of metabolism. Among these metals, silver compounds are very popular and have already been used in the preparation of anti-microbial drinking water.
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 colored 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:
- 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.
- 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.
- When dyeing would carried out in wound packages by the process of the invention, no unevenness would occurs with respect to penetration of the packages, which unevenness 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. 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.
Microencapsulation is one of the novel methods of getting functional finishes on textiles. Microencapsulation is a micro-packaging technique involving deposition of thin polymeric coating on small particles of solid or liquid. This process is more advantageous to conventional process in terms of economy, energy saving, eco-friendliness and controlled release of substances. The anti-bacterial agents reside in colloidal suspension with the amorphous zone of the polymeric binder so that a reservoir of agent is present in solid/ solution within the polymer matrix
ECO-FRIENDLY WASHING AND FINISHING EFFECTS OF GARMENTS
- STONEWASH EFFECT
- ENZYME WASH
- HYDROPHILIC FINISH
- WRINKLE FREE TREATMENT
- WATER/OIL REPELLENT FINISH
- UV PROTECTION
- ANTI-MICROBIAL FINISH
- SOIL RELEASE FINISH
To produce this effect cellulose enzymes were introduced. Earlier Acid cellulose was used. To achieve this, Genetically Modified enzymes were produced, called GMO’s (Genetically Modified Organisms).
The bio-polishing process targets the removal of the small fiber ends protruding from the yarn surface and thereby reduces the hairiness or fuzz of the fabrics. The hydrolysis action of the enzyme weakens the protruding fibers to the extent that a small physical abrasion force is sufficient to break and remove them. Bio polishing can be accomplished at any time during wet processing but is most convenient performed after bleaching.
It can be done in both continuous or batch processes. However, continuous processes require some incubation time for enzymatic degradation to take place. Removing the fuzz makes the color brighter, the fabric texture more obvious, and reduces pilling. Unfortunately, the treatment also reduces the fabric strength. Smoother yarns also increase the fabric softness, appearance and feel. Since it is an additional process, the bio-polished garments may cost slightly more. Next time you buy apparel, look for the label “Bio-Polished.”
In traditional washing process, volcanic rocks or pumice stones are added to the garments during washing as abradant. Due to ring dyeing and heavy abrasion fading is more apparent but less uniform. The degree of color fading depends on the garment to stone ratio, washing time, size of stones, material to liquor ratio and load of garments. Normally after desizing, stone wash process starts with pumice stone addition in rotary drum type garment washer. Process time varies from 60-120 mins. Stone wash effect is one of the oldest but highly demanded washing effects. Stone wash process gives “used” look or “vintage” on the garments, because of varying degree of abrasion in the area such as waistband, pocket, seam and body.
Sand blasting technique is based on blasting an abrasive material in granular, powdered or other form through a nozzle at very high speed and pressure onto specific areas of the garment surface to be treated to give the desired distressed/ abraded/used look.
Cellulose enzymes are natural proteins which are used in denim garment processing to get stone wash look on to the denim garments without using stones or by reducing the use of pumice stone. Cellulose attacks primarily on the surface of the cellulose fiber, leaving the interior of the fiber as it is, by removing the indigo present in the surface layer of fiber.
Cellulose enzymes are classified into two classes:
- Acid Cellulose: It works best in the pH range of 4.5-5.5 and exhibit optimum activity at 50 ᵒC.
- Neutral cellulose: It works best at pH 6 however its activity is not adversely affected in the range of ph 6-8 and show maximum activity at 55 ᵒC.
Ever since synthetic fibers became popular for clothing purposes, there has been the desire for a finish to change the hydrophobic character of these fibers. The main reason was to improve the wearing comfort. Hence the necessity to improve synthetic fibers with regard to their absorbency. Area of textile finishing where improving the absorbency is still one of the main considerations are sportswear, some of which is also made with functional jersey with hydrophobic synthetic fibers on the inside and hydrophilic cellulosic fibers on the outside. The mode of action consists of the finest fibrilled microfibers (PES, PA or PP) transporting the moisture rapidly from the skin through the capillary interstices to the absorbent outer layer. In this way the textile layer of synthetic fibers next to the skin remains dry. After dyeing the hydrophobic synthetic fibers usually exhibits no absorbency. Only after application of a suitable hydrophilic agent can the material fulfill its function. This significantly increases the speed at which the moisture is spread to the hydrophilic outer layer and thus considerably accelerates drying.
WRINKLE FREE TREATMENT
By applying resins it is possible to improve specific properties of cellulosic fibers. Examples of this kind are the improvement in crease recovery, dimensional stability, non-iron, reduced pilling and particularly with knit goods an improved appearance after several washes. For successful resin finishing, it is absolutely essential that the goods are well prepared and the recipes and processes are adhered to and monitored exactly.
The wrinkle free treatment package comprises of a low formaldehyde resin, silicones and polyethylene emulsion. This treatment involves chemical application of the elements comprising of this package through a cross linking effect that prevents the formation of creases and wrinkles which result in easy to iron fabric. Resins do however also have several effects on the fibers. Resins reduce the (tear) strength of cotton. The extent of the loss depends on a wide variety of factors such as
- Amount and type of resin applied
- Amount and type of catalyst
- Curing conditions
- Quality of cotton
- Processes preceding finishing
Tensile strength losses up to 30-45% could be expected. For the so called non-iron finishes, it is therefore often necessary to use qualities with a higher initial strength than for normal softening finishes. In this connection, it should be mentioned that the tensile strengths is not normally improved by the additives and softeners used.
WATER / OIL REPELLANT FINISH
This finish gives hydrophobic features to the substrate. There are three main product groups for this finish
- Metal salt paraffin dispersion
When finishing with these products, the surface of the goods must be covered with molecules in such a way that their hydrophobic radicals are ideally positioned as parallel as possible facing outwards. Aluminium salt paraffin dispersions are positively charged products due to the trivalent aluminium salt. This produces a counter polar charge on the fiber surface which is significant for the adsorption of the product.
After drying, the fat radicals form a so-called “brush” perpendicular to the fiber surface which prevents water drops from penetrating into the fiber. Polysiloxanes form a fiber-encircling silicone film with methyl group’s perpendicular to the surface. The oxygen atoms are facing towards the fiber. The film formation and direction of the methyl groups are responsible for the hydrophobic properties of the finish.
Fabric treated with UV absorbers ensures that the clothes deflect the harmful ultraviolet rays of the sun, reducing a person’s UVR exposure and protecting the skinfrom potential damage. The extent of skin protection required by different types of human skin depends on UV radiation intensity and geographical location, time of day, and season. This protection is expressed as SPF (Sun Protection Factor), higher the SPF value better is the protection against UV radiation.
The SPF value of textile depends on fiber type, the fabric construction (porosity and thickness), and the finish. It means that transmission, absorption and reflectance nature of textile influences SPF value. It provides vital information about the fabric’s sun protection ability. By using UV absorbers, exposure of the textile to UV lights is reduced on the one hand as well as the intensity of the transmitted UV light on the other. Good skin protection is achieved by the textile itself with a sufficient weight of fabric. An UV absorber can be applied either during fiber manufacture or in the final finish which also offers the same degree of protection.
The inherent properties of textile fibers provide room for the growth of microorganisms. The structure and chemical process may induce the growth, but it is the humid and warm environment that aggravates the problem further. Antimicrobial finish is applied to textile materials with a view to protect the wearer and textile substrate itself. Antimicrobial finish provides the various benefits of controlling the infestation by microbes protect textiles from staining, discoloration, and quality deterioration and prevents the odor formation. Anti-microbial agents can be applied to the textile substrates by exhaust, pad-dry-cure, coating, spray and foam techniques. The application of the finish is now extended to textiles used for outdoor, healthcare sector, sports and leisure.
SOIL RELEASE FINISH
Soil release finish facilitate removal of waterborne and oil stains from fabrics such as polyester and cotton blends and fabrics treated for durable press, which usually show some resistance to stain removal by normal cleaning processes. This finish is especially suitable for sportswear, underwear, uniforms and work wear etc. These finishes are provided by nano-particles which have a high surface energy, the finish being durable upto 50 washes.
Textile industries are now able to provide one-stop sustainable solution along the whole textile value chain from pretreatment, through dyeing to finishing. The whole apparel supply chain can add value by adopting the eco-friendly finishes. Manufacturers benefit from using less water and lowering energy consumption, while consumers will not need to use higher temperature to wash their garment or spend time ironing.
In order to add value in the garments, different types of finishes are adopted. The application of Nano finishes has also been growing to obtain better level of performance properties. Ecology and Fashion are also the driving factors for the adoption of these innovative technologies. This will result in more greener and eco friendly textile industries and products.
Plasma technique, Enzymatic finishing, Nanotechnology and Microencapsulation are also very good processes for giving eco-friendly finishes. The plasma technique has been proved very effective as it consumes low energy and chemicals and there is no problem with the disposal of waste. Enzymes being natural products are completely bio-degradable and leave no pollutant behind. With the introduction of these processes in textile processing, the scenario has changed in recent times ensuring eco-friendly production.
With the increase in the pollution, the environment related problems are increasing day by day. And the textile industry holds a major position in this environmental pollution. So, it is a moral duty of every individual to adapt such technologies that imparts in the well-being of environment which in turn will be the well-being of living organisms too.
- Journal of the Iranian Chemical Society, Vol. 3, No. 4, December 2006, pp. 351-359.
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