The contribution of mechanised and automated manufacturing to various environmental impacts is enormous. Environmental impacts from manufacturing industries can be seen such areas as toxic chemicals, waste, energy, and carbon emissions. Manufacturing in developed countries is also a heavy user of water, and there have been many cases of air, water and soil contamination which have led to such actions as cleanups, class actions suits and a variety of other corporate liabilities.
Environmental impact can be seen in all phases of textile production and use, from growing or making fibres to discarding a product after its useful life has ended. The physical environment is affected by these processes, including resource depletion, pollution and energy use; the biological environment, by considering what happens as a result of manufacture, and the social environment as it impinges on our psychological, physical and physiological comfort, as well as our financial well-being.
In recent years, textile industry in developed countries has been facing severe problems, the most serious of which are those connected with pollution. In fact, governments have been bringing up environmental laws which strictly prohibit wastewater discharge in rivers and lakes. This situation indeed burdens the textile industries and also leads to increase in production costs. Textile Industry and Process Description The textile industry includes multiple processes and activities.
The four major textile operations are:
- Yarn Formation: preparing and spinning raw materials (natural and synthetic); texturizing man-made filament fibers.
- Fabric Formation: warping and slashing yarn; performing weaving and knitting operations.
- Wet Processing: preparing the fabric for dyeing and finishing; dyeing, printing, and finishing operations.
- Product Fabrication: cutting and sewing the fabric, performing final finishing operations. In the yarn formation process, fibers are bound using spinning operations, grouping, and twisting.
Staple fibers, natural and man-made, are prepared for spinning through a combination of various processing steps such as blending, drawing, carding, opening, combing, and roving. Following drying operations, yarn may then be woven into fabric. From the spun or filament yarn, fabric is formed by knitting or weaving operations.
Yarn e-mail: nreddy. [email protected] com D. Narasimha Reddy 2/11 can be processed directly through knitting operations but typically requires preparation for weaving operations. Preparation for weaving includes warping and slashing (sizing).
Wet processing enhances appearance, durability, and serviceability of the fabric. Chemical Pollution Textile production involves a number of wet processes that may use solvents. Emissions of volatile organic compounds (VOCs) mainly arise from textiles finishing, drying processes, and solvent use. VOC concentrations vary from 10 milligrams of carbon per cubic meter (mg/m3) for the thermosol process to 350 mg carbon/m3 for drying and condensation process. Waste water from processes is a major source of pollutants.
It is typically alkaline and has high BOD5 (700 to 2,000 milligrams per liter (mg/L)) and chemical oxygen demand (COD) (approximately 2 to 5 times the biochemical oxygen demand (BOD) level), solids, oil and possibly toxic organics, including phenols (from dyeing and finishing) and halogenated organics (from processes such as bleaching). Dye effluents are frequently highly colored and may contain heavy metals such as copper and chromium. Pesticides used on natural fibers are transferred to effluents during washing and scouring operations.
Pesticides are also used for moth proofing, brominated flame retardants for synthetic fabrics, and isocyanates for lamination. Effluents might include pesticides (such as DDT and PCP), and metals (such as mercury, arsenic, and copper). Air emissions include dust, oil mists, acid vapors, odors, and boiler exhausts. Cleaning and production changes result in sludges from tanks and spent process chemicals, which may contain toxic organics and metals.
Oils, lubricants, machine maintenance chemicals, and waste yarn and material are also released. Chemical sizing agents are added to the yarn by solution or pad/dry techniques and other chemical additives may be added to increase yarn softness and pliability. Chemicals are also used during fabric formation as fabric processing agents and equipment cleaning and maintenance chemicals. Fabric processing agents include sizing agents and performance enhancing chemicals such as certain glycol ethers, ethylene glycol, and methanol. These chemicals typically volatilize or are washed off during fabric formation. However, some may remain with the fabric throughout the fabric formation process and into the wet processing and finishing operations.
Both fugitive and point source air emissions containing chemicals typically occur during the slashing (sizing) operation or during fabric drying operations. This includes chemicals used as sizing agents or performance enhancing chemicals. Dust air emissions may also be generated during fabric formation. Effluents are generated from fabric cleaning and slashing operations; used oil, lubricants, and other machine maintenance chemicals; and equipment cleaning operations. Solid waste is also released from fabric formation. The primary source of solid waste is excess fabric material and scraps that may contain chemicals not volatilized or removed during fabric formation or chemicals brought on-site with the raw material (e. g. , antimony oxide used as a fire resistant).
Dust containing chemicals is also generated during knitting or weaving operations, which when collected by air pollution control devices or by floor sweepings is a significant solid waste. During slashing operations, residue left in sizing agent or other chemical agent containers may be a source of chemicals. Fugitive emissions are most likely to result from slashing and drying operations when chemicals, such as methanol, evaporate. In wet processing, chemical agents, such as dyes, pigments, strength agents, and flame resistors are applied through a water-intensive process. Synthetic materials may be desized and scoured prior to dyeing or printing. After preparation for wet processing, dyeing or printing can occur, followed by rinsing, drying, or heat setting. Printing operations typically do not use water.
The final wet processing step is mechanical and chemical finishing; these operations are used to improve appearance, texture, and performance of the fabric. Dye application includes various dye types and methods. Dyes can be fixed to the textile chemically and/or physically. Dyes may be bonded to the fabric or precipitated by removal of a dye solubilizing agent. Color can be affixed through the use of pigments, solvents, and resin binders. For the textile industry, wet processing operations are significant sources of chemical release. Typical chemicals include ammonia, certain glycol ethers, and methyl ethyl ketone. Alkaline or solvent solutions are used during scouring.
Solvents, although used in the past, are being replaced with aqueous chemicals. Bleaching agents and other chemical e-mail: nreddy. [email protected] com D. Narasimha Reddy 4/11 additives are used during bleaching operations, however, these are usually not chemicals. Acids are used for neutralizing remaining caustic soda during mercerizing operations. During dyeing or printing operations, chemicals such as solubilizing agents, dye carriers, salts, and fixing agents may be employed to speed the process or enhance the process effects. Chemicals used during finishing operations include optical brighteners, softeners, and flame resistant chemicals. Effluents are generated from spent process baths, solutions, and rinses.
Process effluents include spent sizing solutions, scouring and dyeing baths, cleaning rinses, dyeing rinses, textile cleaning water, and mercerizing operations. Chemicals in textile effluents include dyes, pigments, and salts. Salts present in process effluents may be either raw materials (e. g. , metal compound salts) or byproducts from neutralization or other chemical reactions (e. g. , nitrate compounds). Metal compounds such as copper compounds and chromium compounds are also commonly present. Other sources include equipment cleaning wastewater, container cleaning wastewater, and used lubricants and other machine operating aids. Cleaning solvents may become part of the wastewater after scouring operations and equipment cleaning.
The US EPA has estimated that there are approximately 135 major source facilities, in US, in the printing, coating, and dyeing of fabrics and other textiles source category. The principal hazardous air pollutants emitted by these sources include toluene, methyl ethyl ketone (MEK), methanol, xylenes, methyl isobutyl ketone (MIBK), methylene chloride, trichloroethylene, n- hexane, glycol ethers (ethylene glycol), and formaldehyde. Exposure to these substances has been demonstrated to cause adverse health effects such as irritation of the eye, lung, and mucous membranes, effects on the central nervous system, and damage to the liver. The EPA has classified two of the hazardous air pollutants, methylene chloride and trichloroethylene, as probable or possible human carcinogens.
Dyeing The art of textile dyeing dates back thousands of years, when dyes extracted from plants or sea snails were used to color cloth. Today, most dyes are synthetically manufactured, yet only 40-90% actually resides on the cloth. The residual dye is treated and discharged into our rivers and streams. World wide, it is estimated that this accounts for over 400,000 tons of dye per year. Colorfastness is a textile industry standard that determines how stable the color is in a garment. Good colorfastness means the garment won’t fade after one washing. Resin pretreatment is done for garments that require excellent colorfastness. Cationic fixatives could be used for outerwear garments where colorfastness to washing is moderate but colorfastness to dry cleaning is high.
Poor shade repeats are a major cause of economic loss and pollution in dyeing operations. An average dye worker makes 300 weighings per day. Sources of error are many, e-mail: nreddy. [email protected] com D. Narasimha Reddy 5/11 including sorption of moisture from the atmosphere which way amout to up to a maximum of 20% error in dye weight. Other factors such as water quality, fiber variations, and the like also contribute to reworks and off quality. There needs to be a balance between improved productivity in dyeing, and the need to minimize water, energy, and effluent discharge in the textile industry. There is a need to regulate usage of dyes in improving shades on textiles while optimizing water, dye and energy utilization.
Under most circumstances, a mixture of dyes is utilised to achieve the desired shade. This means that a small number of dyes can be used to achieve an infinite number of colours, but also means that achieving the exact shade desired requires some skill and can often entail redyeing with a shading addition to correct the shade. In extreme cases, the cloth can be stripped of colour and completely redyed, but this is an environmental and commercial last resort. One of the root causes of problems in achieving the required shade is that if dyes in a mixture have different dyeing profiles the shade and depth of dyeing may change with time and the timing of the dyeing process is therefore crucial.
Thus, the difficulty associated with reliable attainment of shade and depth provides a hidden cost in production through reduced capacity and proportionately increases the environmental impact of reactive dyeing through the extra water, chemicals, energy and time needed to make a shading addition. Dyes and auxiliary chemicals used in textile mills are developed to be resistant to environmental influences. As a result, they are hard to remove from wastewater generated during the dyeing processes. In India, the detrimental nature of the synthetic dye industry has been recognised.
The Central Pollution Control Board of India has included it in its “hyper-red” category reserved for the seventeen most polluting industries in the country. The true costs of synthetic dye production and application have never, to our knowledge, been assessed. According to the Tamil Nadu Pollution Control Board, an estimated 80. 70 million litres of effluent water is discharged daily into the Noyyal River from dyeing and bleaching units in Tirupur.
Water is used extensively throughout textile processing operations. Textile operations vary greatly in water consumption. Water use can vary widely between similar operations as well. Almost all dyes, specialty chemicals, and finishing chemicals are applied to textile substrates from water baths. In addition, most fabric preparation steps, including desizing, scouring, bleaching, and mercerizing, use aqueous systems.