By: Dr. Harshit A. Patel


Scouring


Fiber (especially wool) scouring involves the use of hot water and detergents to remove soil, vegetable impurities, grease and other contaminants from fibers. Wool scouring typically uses water and alkali, although scouring with an organic solvent is also possible. Scouring with alkali breaks down natural oils and surfactants and suspends impurities in the bath. The scouring effluent is strongly alkaline, and a significant portion of BOD and COD loads from textile manufacturing arises from scouring processes. The recommended pollution prevention and control techniques include the following:


  • Design of scouring systems to remove heavy settleable solids continuously; increase recovery of grease; recover heat from the final facility effluent; and control water usage.


  • Use of readily biodegradable detergents / surfactants that do not give rise to toxic metabolites. (e.g. APEO should be replaced with alcohol ethoxylates);


  • Optimization of mechanical removal of water prior to the drying process;


  • Adoption of low volatile organic compound (VOC) emitting solvent wash for removal of water insoluble oils.


Wet processing


Wet processing includes the main processes of fabric preparation, namely desizing, bleaching, mercerizing, dyeing, printing, and other specific treatments. These phases treat fabrics with chemical and liquor baths and often require several washing, rinsing, and drying steps, generating significant wastewater effluents. The recommended pollution prevention and control techniques for the finishing pretreatment steps include the following:


  • Selection of water soluble and biodegradable lubricants for knitted fabrics instead of mineral oil and wash them with water;


  • Use of organic solvent washing for non water soluble lubricants;


  • The thermofixing step may be performed before the washing step. Air emissions generated from the stenter should be treated by dry electrofiltration. The oil separated should be collected to limit effluent contamination;


  • Residual liquor should be minimized through reduced application, reduced tank volumes and padding liquor recycling;


  • Using mechanical dewatering equipment to reduce water content of the incoming fabric and reduce energy consumption in stenter frame.


Desizing


Desizing operations may generate effluents with significant concentrations of organic matters and solids. BOD and COD loads from desizing may be significant (35 to 50 percent of the total load), and COD concentrations up to 20,000 mg/I may be generated. Recommended pollution prevention and control techniques include:


  • Selection of raw material with low add-on techniques (e.g. pre-wetting of the warp yarn);


  • Selection of more bio-eliminable sizing agents (e.g.-modified starches, certain galactomannans, polyvinyl alcohol, and certain polyacrylates);


  • Application of enzymatic or oxidative desizing with starch and modified starch sizing agents, followed by washing systems;


  • Integration of de-sizing / scouring and bleaching in a single step to reduce effluent generation (e.g. reuse of bleach rinse water in desizing);


  • Recovery and reuse of specific water-soluble synthetic sizing agents (e.g. PVA, poly-acrylates, and carboxy-methyl cellulose) by ultra-filtration.

 

Bleaching


Common bleaching reagents include hydrogen peroxide, sodium hypochlorite, sodium chlorite, and sulphur (European Commission, 2003). The degree of bio-elimination should be >80 percent after 7 days. Hydrogen peroxide is the most commonly used bleaching agent for cotton and is typically used with alkali solutions.


The use of chlorine-based bleaches may produce organic halogens (due to secondary reactions) and cause significant concentrations of Adsorbable organic halogens (AOX), particularly trichloromethane, in the wastewater. Sodium hypochlorite bleaching represents the most significant concern, and lower AOX formation should result if sodium chlorite bleaching is used. The wastewater is alkaline.


Recommended pollution prevention and control techniques include the following:


  • Use of hydrogen peroxide bleaching agent, instead of sulfur- and chlorine-based bleaches;


  • Reduce the use of Sodium Hypochlorite;


  • Control of stabilizers employed, using biodegradable products where possible and avoiding products with poorly bioeliminable complexing agents (e.g. ethylene di-amine tetra-acetic acid [EDTA], diethylene triamine penta acetic acid [DTPA])


Mercecrising


During Mercerising, cotton fiber reacts with a solution of caustic soda, and a hot-water wash treatment removes the caustic solution from the fiber. The caustic solution remaining on the fiber is neutralized with acid, followed by a number of rinses to remove the acid. Wastewater from Mercerising is highly alkaline, since it contains caustic soda.


The recommended pollution prevention and control technique involves the recovery and reuse of alkali from Mercerising effluent, particularly rinsing water, subject to colour limitations that may apply to mercerized cloth woven from dyed yarn.


Dyeing


Wastewater from dyeing may contain color pigments, Halogens (especially in vat, disperse, and reactive dyes), metals. This agent should be considered only for flax and bast fibers that cannot be bleached, with hydrogen peroxide. Consider use of a two-step process with a Hydrogen peroxide stage to remove impurities, which would act as a precursor for AOX formation, followed by elemental chlorine-free bleaching.


Printing


Print paste components consist of color concentrates, solvents, and binder resins. Color concentrates contain pigments (insoluble particles) or dyes. Organic solvents are used exclusively with pigments. De-foamers and resins are aimed at increasing color fastness. Printing blankets or back grays (fabric backing material that absorbs excess print paste)


New Developments


The most important factor to influence the Indian textile industry is it innovation capacity to create new effects, styles, fabric/garment characteristics and simplify manufacturing processes.


The potential for innovation resides in the following fields:


Nano Technology related fabric coatings to invisibly enhance fabrics to have better water repellency, protection from stain, extremely high fabric strength and the list goes on and on.


These properties can be incorporated into fabrics at the processing stage without compromising on natural softness and comfort of the garments manufactured from these fabrics.


 

Another method under development to coat fabrics with water/oil repellent layers that are so thin (but uniform) that the fabric appearance and feel does not change. This is done using plasma polymerization on the surface of the fabric.


There are several unknowns regarding nano-technology and textiles. Textile industry involves extremely complicated processes. Incorporation of nanotreated fabrics in the further value addition processes like printing or effect of prevalent dyes on a dyed fabric that could affect the nano-coating process itself raise many compatibility related questions that remain to be answered.


Garments that employ new technologies: technological developments have made it possible to integrate electronic components into conventional garments. In demanding conditions, such as working in heavy industries, very specific demands are placed on work apparel and materials, as they must protect the wearer from any hazards found in the working environment.


Automated tracking using RFID based technology that keeps track of your garments on the manufacturing floor, wardrobe, laundry, etc.


New fashion driven technology like illuminated garments call for integration of electric circuitry, illuminated surfaces and power supply in a washable garment with no loss of ergonomics.


Re-inventing old technology: In addition to developing new technology focus is needed on re-inventing old technology as well as developing new technology; keeping in mind the current structure of the Indian Textile Industry.


At Electron, we strive to provide the small scale industries all over India with the much needed technical and chemical support for the textile industry driven by the principles of eco-friendliness and economic sustainability of the processes.


Some of the new developments include the eco-friendly "Laser Magic Holi T-shirt, Garments with integrated fiber-optics, high colour yield and eco-friendly "Laser Reactive" dyes, 100% Natural dyes, Foil binder for monotone(foil gradient) effect, Multicolour flock printing system for standard flocking equipment and several other projects in the pipeline.


The eco-friendly "Laser Magic Holi T-shirt" is a perfect example of how innovative engineering can touch lives and do wonders for the environment. The "Laser Magic Holi T-shirt" is made out of light coloured fabric with all-over monochromatic print that transforms into a multi-colour t-shirt when in contact with water. This reduces the need of using harmful metallic colours usually used during Holi all over India. It also reduces the wastage of water needed to clean up after holi. After proper washing the t-shirt can be reused for normal wearing purposes.


India has a very experienced textile sector, cIever entrepreuners, and extremely large skilled work force. With the infrastructure improving rapidly and the growing economy like ours we need to reach for the stars. After all The world is changing very fast. Big will not be in a position to bully small anymore. Only the the fast and the innovative will succeed.


About the Author:


Dr. Harshit A. Patel is associated with Electron Group as a Research Director.



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