The textile industry is the second most polluting industry in the world. Synthetic dyes contribute to a major part of this pollution, with nearly 20 percent of global water pollution being linked to the textile dyeing processes. The main contributors to this problem are the use of non-biodegradable petroleum-based colorants to dye textiles, the use of toxic agents to fix colorants on the textiles, and the release of large proportions of these colorants and fixation agents into the surrounding ecosystem. A year ago, China shut down most of the companies producing synthetic textile dyes after tough new legislation was enacted. In the wake of those closures and strict environmental regulations, industries are now looking into greener ways to color clothes. A viable alternative to synthetic colorants may be the natural colors extracted from biodegradable plant sources. However, toxic fixation agents still need to be used with these colorants. Altogether, textile and fashion industries are now in search of alternative coloring methods. Here are a few of the more benign techniques innovative companies are using to color clothes.
Hybrid pigments:
Ecofoot has developed hybrid pigments composed of a dye chemically linked to a polymer particle that reacts with cellulose fibres at temperatures as low as 25ºC. This technology doesn’t require the use of salt, which otherwise is crucial to drive the dye into the fabric. This technology can be applied for dyeing cotton garments at low temperatures and also to wool in a more ecological process. Ecofoot-Indigo, a hybrid pigment used in dyeing denim, avoids using toxic reducing agents that are traditionally used in converting indigo pigment to a water soluble form. Common reducing agents are considered environmentally unfavorable, as the sulfite and sulfate generated in the dyebath can cause various problems when discharged into the wastewater.
Ecofoot also developed auxiliaries to prevent hydrolysis of the dye in the dyeing process, which typically requires harsh washing-off procedures to remove the hydrolysed dye. Together with hybrid pigments and auxiliaries, more than 50 percent of water in the intermediate and final rinses can be saved in the total process of preparation and dyeing.
Powder dyes from textile fibers:
Officina+39, an Italy based company, developed the sustainable dye range Recycrom using recycled clothing, fiber material, and textile scraps. It developed a sophisticated eight-step system (patent pending) in which all the fabric fibers are crystalized into an extremely fine powder that can be used as a pigment dye for fabrics and garments made of cotton, wool, nylon, or any natural fiber. Recycrom can be applied to the fabrics using various methods such as exhaustion dyeing, dipping, spraying, screen printing, and coating. Recycrom is applied as a suspension while most dyes are used as a chemical solution and hence can be easily filtered from water, thus reducing the environmental impact.
Cotton pretreatment:
Cotton requires more water than other textiles for dyeing. About 200 litres of water are required to produce 1kg of fabric. Dow has developed a pretreatment process called ECOFAST Pure that is applied before the dyeing process to produce cationic cotton. The pretreated cotton acquires a permanent positive charge, enabling it to have a higher affinity for negatively charged molecules such as dyes. This patented technology decreases the use of dye and water by 50 percent for cotton dyeing. ColorZen has innovated a technology for pretreatment of raw cotton fibers using a solution comprising a wetting agent, caustic soda, and an ammonium salt. This pretreated cotton exhibits increased ability to retain the dye without the need of fixation chemicals, thus reducing the usage of toxic chemicals by 95 percent and water wastage by 90 percent.
Natural or engineered microorganisms:
Colorifix employs a synthetic biological approach by using bacteria to color the textiles, which can reduce the use of water by up to 10 times. The innovative steps in this process are to fix the dye-producing bacteria directly onto the fabric using a carbon source solution, followed by deposition and fixation of the dye onto fabrics with a single heating cycle by the lysis of the microorganisms. This technology doesn’t require a dye extraction process, which uses organic solvents, or fixing and reducing agents containing organic compounds. University of California researchers are developing denim dyes using genetically modified E.coli bacteria to produce indican, which can then be turned into indigo by an enzymatic treatment. This new process removes the need for harsh chemical reducing agents for indigo dye solubilization, replacing it with an enzyme. However, the process still needs optimization in the recovery of indican for its sustainability.
Innovative dye and auxiliaries:
Huntsman Textile Effects introduced Avitera, a line of polyreactive dyes for cotton that readily bond to fiber, in contrast to the conventional reactive dyes. Avitera dyes use tri-functional chemical reactivity that provides a high reaction and fixation rate with cellulosic fiber, leaving very little unfixed dye to be removed. This dramatically reduces water and energy usage by up to 50 percent, and uses up to 20 percent less salt. And Huntsman Corporation recently developed the diffusion accelerant Univadine E3-3D, a dyeing auxiliary that enhances the diffusion of a dye into polyester. This diffusion accelerant is said to achieve high-performance dyeing of polyester microfibers and is free of hazardous chemicals, thus complying with current and anticipated industry sustainability standards.
Digital printing:
Intech Digital introduced a new “waterless” textile printing technology using Blackjet reactive pigment textile inks (nanopigment ink) to provide coloration. Blackjet textile inks use a pigment that is insoluble in the ink carrier, rather than a dye, and contains resin binders that help the pigment particles adhere to the fabric. This technology uses a four-step process consisting of a fabric pretreatment, digital printing with reactive pigment inks, and fabric heating for fixing the pigment onto the fabric, followed by a post-treatment process. DuPont Artistri digital textile inks are formulated with similar pigments and dyes to those used in conventional textile printing to provide high-level results in digital printing.
Reference: https://www.prescouter.com/2018/11/sustainable-dyeing-innovations-greener-ways-color-textiles/
