Denim is a characteristic of any indigo denim that only the warp threads are dyed, whereas the weft threads remain plain white. As a result of the warp-faced twill weaving, one side of the fabric shows the blue warp threads, the other side shows the white weft threads. This is why denim fabric is white on the inside. In denim fabric, the warp is dyed with mostly indigo dyes and the weft is white.
After weaving the denim fabric, it must be treated mechanically and chemically to give it correct dimensional stability, and pleasant and soft handling in both warp and weft directions to prevent shrinkage in further washing and finishing. The denim garment washing and finishing mainly focus on the importance of warp yarn. Denim washing can be achieved in many ways, for example by using pumice stones, hypochlorite, or some enzymes. Enzyme washing is mostly preferred as its very simple and also because it is eco-friendly in nature when compared with hypochlorite and pumice stones. Enzyme washing is a process, in which different enzymes are used to clean fabric, especially in the case of denim and other garments having a worn-in look. For the regular cleaning process, enzymes carry numerous economic and environmental benefits. Looking at an industrial aspect, enzyme washing has replaced many laundering techniques such as stone washing, saving companies money and enhancing sustainability too.
The major pollution problems generated by denim wet processing are usually due to water pollution. There are also minor problems related to air pollution, which is due to chemicals, lint, etc. The largest impact, with respect to water and air pollution, occurs mainly during the wet processing of denim. The denim industry consumes a huge amount of water and chemicals, and therefore its generation of wastewater is therefore also very high.
Dyes used for denim-
· Indigo vat
· Indigo sulfur
· Synthetic indigo
· Natural indigo
Since denim is made of 100% cotton, therefore in addition to indigo it can be dyed with dye classes such as direct, vat (other than indigo), reactive, sulfur dyes, and pigment colors. In the last decade, denim was mainly dyed with indigo (67%), sulfur black (26%) and another sulfur color (6%). The changing fashion trends have also led to vat, reactive, and direct dyestuffs, as well as pigments, being used to color denim.
Indigo is commonly used to dye blue jeans. There are different types of indigo dye, both natural and synthetic. Synthetic indigo dye is commonly used in the textile industry. Indigo is challenging to dye because it is not soluble in water.
Generally, the indigo has poor staining to the cotton fiber, which could cause dry- and wet fade and color loss. When dying dark, especially black denim jeans, sulfur dye is used. Like the indigo dye, the sulfur dye is insoluble in water and a reduction has to be made to make it attach to the fiber. Fibre, yarn, fabric, and garments can be dyed. For jeans, it is normal to dye the warp before weaving and keep the weft undyed. Sometimes additional dying is made on the garment, this is called garment dying. Dyes themselves rarely cause damage to the fibers and negatively affect the durability of the jeans. The poor color fastness of cotton can sometimes be a problem.
This article has been written by Darshana Phalke. Darshana Works at Polly Industries as Business Development Executive – Ichalkaranji.