Dyeing Printing Finishing

Textile finishing sector faces worldwide environmental problems

by Dr. Noor Ahmed Memon

Textiles and clothing trade is a vital part of the world economy with many nations heavily dependent on the sector for foreign exchange earnings and employment generation. Increasing environment consciousness, newer legislations to preserve environment and human rights etc have further created challenges. Many chemicals used in the textile industry cause environmental and health problems. These problems may occur during the production process, with respect to emissions or occupational health problems. Finishing process: Finishing operation entails production of finished textile fabric from greige goods. Finishing operations are predominantly wet operations requiring large amounts of thermal energy for water heating and drying as well as dyes and chemicals. Woven greige goods require some additional steps prior to dyeing, as compared to knit goods. As the first step in finishing woven goods, singeing burns protruding fibers by passing the fabric over an open flame or heated plates to produce a cleaner fabric and reduce hairiness. Sizes and other ingredients added during slashing in the weaving mill are removed in the desizing operation by washing them in a detergent solution at temperatures up to 200°F and then rinsing them with fresh water. The process produces a waste water stream of 100°F to 120°F. Scouring is another washing process using steam and detergents to remove oils and mineral materials. The scouring can be done by batch in pressurized vessels known as kiers or on a continuous basis. In either case, high temperatures, to 250°F, and long retention times, up to 12 hours, are used to ensure thorough saturation and cleaning. Finally, the fabric is rinsed. A waste stream of warm, contaminated water is produced. Next, the fabric is bleached, washed, and rinsed several times to achieve uniformity and improve its ability to absorb dyestuffs later in the finishing operation. Mercerizing is an optional step and consists of a caustic spray, tensioning, water rinse, water wash, acid dip, and final water wash, and produces a warm wastewater stream. Knitted goods do not require de-sizing and bleaching. The finishing process requires only scouring to thoroughly clean the goods prior to dyeing. As with woven fabric, the step involves hot water washes and rinsing, and produces warm, contaminated waste water. The process of dyeing fabrics and garments is an age old process, in which only natural dyes were used until the industrial revolution made them obsolete with the discovery of chemical and petroleum based dyes. Most textiles today are dyed chemically and can contain harmful substances such as lead, other heavy metals, and even arsenic. Naturally dyed fabrics, on the other hand, are completely biodegradable and non-toxic, if an organic substrate is being used. The natural dye process is environmentally sound. The water and energy used in the process is minimized, and the water run-off is clean and can be returned directly to the water table. However using natural dyes is expensive while the mass produced dyes are more economical. However with the increasingly strict regulations and their implementation harmful dyes such as AZO dyes have now been eliminated. Textile printing has become a concept rather than just an embellishment on an outfit contributing to the style and shape of the garment. Digital printing, the newest as well as the most potential textile printing means, is increasingly becoming more accessible for the textile printers around the world to enable the designers to produce innovative prints as per their imagination in the right colour on the right fabric. Technological advancements in textile printing made the two aspects associated with textile printing - the designing and the printing, more interdependent. Today’s textile printing technology facilitates precise and exact placing of prints on a garment, enables the manufacturers to decrease or increase the size of the print, modify the background tones, produce optical illusions, print advanced graphics, and offer the best translation of every single design. According to a market research report on “Textile Printing”, Asia Pacific represents the world’s largest as well as fastest growing region in textile printing production. Asia Pacific accounts for more than half of the world textile printing production with China and India, the two most populous countries in the world. By fabric type apparel represents the largest fabric segment, while interior/ furnishings represent the fastest growing and second largest fabric segment for textile printing. In textile processing the concept of eco-friendly products and processes have received significant appreciation all over the world; and the legislation and public enforcement and awareness in developed countries are responsible for that. Indirectly, such enforcement had partly resulted in the growth and development of conventional textile processing in developing countries, where low-waged work force and reduced environment control are prevalent.