The environmental impact of mechanized and automated manufacturing is considerable. It encompasses toxic chemicals, waste generation, energy consumption, and carbon emissions. Developed countries heavily depend on water for manufacturing processes, further exacerbating the environmental consequences. Furthermore, pollution in the air, water, and soil has led to initiatives for cleanup, legal actions through class action lawsuits, and an increased focus on corporate responsibility.
Throughout the entire process of textile production and use, the environmental impact is evident. This impact is present in various stages, starting from the cultivation or creation of fibers to the disposal of products once their usefulness has expired. These processes have consequences on the physical environment, such as resource depletion, pollution, and energy consumption. Additionally, the manufacturing phase affects the biological environment, while the social environment influences our psychological, physical, and physiological well-being as well as our financial stability.
In developed countries, the textile industry has been experiencing severe issues, particularly related to pollution. Environmental laws have been implemented by governments, strictly forbidding the release of wastewater into rivers and lakes. Consequently, this situation becomes a burden for textile industries and results in higher production costs. The textile industry encompasses various processes and activities.
There are four main textile operations:
- 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, both natural and man-made, undergo a series of processing steps including blending, drawing, carding, opening, combing, and roving in order to be prepared for spinning. Once dried, the yarn can be woven into fabric. Knitting or weaving operations are used to create fabric from either spun or filament yarn.
Yarn e-mail: nreddy. donthi@gmail. com D. Narasimha Reddy 2/11 can undergo knitting operations directly but usually needs to be prepared for weaving operations. This preparation involves warping and slashing (sizing).
Wet processing improves how the fabric looks, lasts, and can be maintained. Chemical Pollution occurs in textile production due to various wet processes that may involve solvents. The release of volatile organic compounds (VOCs) primarily occurs during textiles finishing, drying procedures, and solvent utilization. VOC levels range from 10 milligrams of carbon per cubic meter (mg/m3) for the thermosol process to 350 mg carbon/m3 for drying and condensation processes. The discharge of wastewater from these processes is a significant contributor to pollution.
It is usually alkaline and has a high BOD5 (700 to 2,000 mg/L) and COD (approximately 2 to 5 times the BOD level), solids, oil, and possibly toxic organics, including phenols (from dyeing and finishing) and halogenated organics (from bleaching processes). Dye effluents are often highly colored and may have heavy metals like copper and chromium. Pesticides used on natural fibers are transferred to effluents during washing and scouring operations.
Pesticides are utilized in moth proofing and brominated flame retardants are employed for synthetic fabrics. Additionally, isocyanates are used in lamination processes. The effluents from these processes may contain pesticides like DDT and PCP, as well as metals such as mercury, arsenic, and copper. Air emissions from the industry can include dust, oil mists, acid vapors, odors, and boiler exhausts. Moreover, cleaning and production modifications lead to the creation of sludges stemming from tanks and spent process chemicals. These sludges 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 occur during the slashing (sizing) operation or fabric drying operations, and may contain chemicals such as sizing agents or performance enhancers. Dust air emissions can also be generated during fabric formation. Effluents are produced from fabric cleaning and slashing operations, as well as machine maintenance chemicals and equipment cleaning. Solid waste is released from fabric formation, mainly excess material and scraps that may contain chemicals not volatilized during fabric formation or brought on-site with the raw material (e.g., antimony oxide used as a fire resistant).
Chemical-laden dust is also produced during knitting or weaving activities, which, when gathered through air pollution control devices or sweeping the floor, becomes a significant form of solid waste. When conducting slashing processes, remnants left in containers of sizing agents or other chemical agents can be a potential source of chemicals. Fugitive emissions are most likely to arise from slashing and drying operations as chemicals, such as methanol, evaporate. In wet processing, water-intensive techniques are utilized to apply chemical agents like dyes, pigments, strength agents, and flame resistors. Before dyeing or printing, synthetic materials may undergo desizing and scouring processes. Subsequently, dyeing or printing can take place, followed by rinsing, drying, or heat setting. Water is typically not used in printing operations.
In the wet processing stage, mechanical and chemical finishing techniques are implemented to enhance the fabric’s appearance, texture, and performance. Various methods of dye application are employed, where dyes can be fixed chemically or physically to the textile. This involves bonding them to the fabric or precipitating them by eliminating a solubilizing agent. Color can also be added using pigments, solvents, and resin binders. However, it is crucial to acknowledge that these processes in the textile industry may lead to the release of chemicals like ammonia, specific glycol ethers, and methyl ethyl ketone. Furthermore, alkaline or solvent solutions are utilized during the scouring process.
Solvents are no longer being used and are instead being replaced with aqueous chemicals. Bleaching agents and other chemical additives are used in bleaching operations, but they are not typically considered solvents. Acids are used to neutralize the remaining caustic soda in mercerizing operations. Chemicals like solubilizing agents, dye carriers, salts, and fixing agents may be used during dyeing or printing operations to expedite or enhance the process. Finishing operations involve the use of chemicals such as optical brighteners, softeners, and flame resistant chemicals. Effluents are produced from spent process baths, solutions, and rinses.
Process effluents consist of various types of waste liquids generated during the textile production process. These include spent sizing solutions, scouring and dyeing baths, cleaning rinses, dyeing rinses, textile cleaning water, and water from mercerizing operations. The chemicals found in these effluents are primarily dyes, pigments, and salts. The salts can originate from either the raw materials used in the process, such as metal compound salts, or as byproducts resulting from neutralization or other chemical reactions, such as nitrate compounds. Additionally, common compounds like copper compounds and chromium compounds are often present. Other contributors to the wastewater include water used for equipment and container cleaning, as well as used lubricants and machine operating aids. Some cleaning solvents may also end up in the wastewater after scouring operations and equipment cleaning.
The US EPA states that there are about 135 major source facilities in the US engaged in printing, coating, and dyeing textiles. These facilities emit hazardous air pollutants including toluene, methyl ethyl ketone (MEK), methanol, xylenes, methyl isobutyl ketone (MIBK), methylene chloride, trichloroethylene, n-hexane, glycol ethers (ethylene glycol), and formaldehyde. Scientific evidence has proven that these substances cause adverse health effects like irritation of the eye, lung, and mucous membranes. They also affect the central nervous system and can lead to liver damage. Methylene chloride and trichloroethylene have been classified by the EPA as potential carcinogens for humans.
In history, dyeing has been a widespread practice using natural dyes from plants and sea snails to color fabric. However, synthetic dyes have become more common in modern times. These dyes only partially stick to the cloth, resulting in excess dye that is treated and released into rivers and streams. Globally, approximately 400,000 tons of dye are discharged each year. To determine how long a garment’s color lasts, the textile industry uses colorfastness as a standard. This measure evaluates how well a garment retains its color after washing. For garments needing excellent color retention, resin pretreatment is done. Outerwear garments can benefit from cationic fixatives which provide moderate resistance to fading when washed but high durability when dry cleaned.
Poor shade repeat occurrences result in significant economic loss and pollution during dyeing processes. On average, a dye worker performs 300 weighings per day, with numerous sources of error including sorption of moisture from the atmosphere, which can lead to up to a maximum of 20% error in dye weight. Other factors such as water quality and fiber variations also contribute to reworks and off-quality. Achieving a balance between enhanced productivity in dyeing and minimizing water, energy, and effluent discharge is crucial in the textile industry. It is necessary to regulate the usage of dyes to improve shade consistency in textiles while optimizing water, dye, and energy utilization.
Combining dyes is commonly done to achieve the desired color, offering a broad spectrum of colors using minimal dyes. However, it can be challenging to obtain the precise shade required and may necessitate additional shading through re-dyeing. In more severe cases, stripping the fabric of its current color and re-dyeing it may be necessary, although this option is considered a last resort due to environmental and commercial concerns. The difficulty in achieving the desired shade primarily arises from variations in dyeing profiles among the dyes used in the mixture, leading to potential changes in color and depth over time. Therefore, precise timing during the dyeing process is crucial.
In the production of textiles, the challenge of achieving consistent shade and depth can result in decreased productivity and an increase in the environmental impact of reactive dyeing. This is due to the additional resources such as water, chemicals, energy, and time required to achieve the desired shading. The dyes and auxiliary chemicals used in textile mills are designed to resist environmental factors, making them difficult to remove from wastewater produced during the dyeing process. In India, the negative effects of the synthetic dye industry have been acknowledged.
The Central Pollution Control Board of India classifies synthetic dye production and use as “hyper-red,” one of the seventeen most polluting industries in the country. Currently, there is no assessment available regarding the specific costs linked to this procedure. The Tamil Nadu Pollution Control Board states that around 80.70 million liters of wastewater originating from dyeing and bleaching establishments in Tirupur are discharged into the Noyyal River daily.
Water usage in textile processing is vital and varies across different operations, even within similar ones. Water baths are used to treat textile substrates with dyes, specialty chemicals, and finishing chemicals. Aqueous systems are also commonly employed for fabric preparation steps like desizing, scouring, bleaching, and mercerizing.
