Waterless Dyeing Techniques

 

WATERLESS DYEING TECHNOLOGIES

Ashutosh Patil
Veermata Jijabai Technological Institute, Mumbai

Introduction:

The demands for colourful and fancy clothes keep on increasing as the fashion changes day after day. Hence, dyeing, which refers to the colouring of fabrics, is one of the most important process in textile field. Dyeing process requires large amount of water for making solutions of different colours and for washing the coloured fabric to remove excess solutions from it. On an average, textile industry uses 1.6 million litres of water for the production of 8000 kg of fabrics daily. Of this total consumption, 16% of it used for dyeing purposes. Dyeing contributes to 15-20% of total water wastage. This waste water also pollutes the water resources near to the mill. In other words, dyeing is the major cause of water usage and pollution in textile mills.

Due to the fresh water scarcity and to overcome these pollution problems, a suitable dyeing method which uses less water had become a requirement. Keeping this in mind, several companies came up with different dyeing methods and technologies which use very less to negligible amount of water as compared to the normal dyeing processes.

Present Technologies

DyeCoo:

DyeCoo is based on the usage of CO₂ for dyeing purpose. The use of CO₂ eliminates the use of water as well as processing chemicals leading to reduction in energy consumption. By using this technology, 15 millions of water and 6500 kg of processing chemicals can be saved per machine annually. Polyester dyeing is done with the help of CO₂.

The liquid CO₂ is poured in the dyeing vessel. Due to the heat and pressure inside the vessel, this liquid CO₂ is transformed into a fluid and this fluid is used for dyeing. The temperature of the vessel with the dyed fabric is reduced and as a result the CO₂ leaves the vessel in the form of a gas. 95% of this released CO₂ is recovered and stored in the form of liquid for further use.

Brands like IKEA and Nike have already accepted this method and started their production. Nike has started a facility in Taiwan with DyeCoo equipments in it to carry out water-free dyeing.

AirDye®:

AirDye technology from Colorep Inc. is similar as the name suggests. For dyeing, the dyes are passed into the fabrics in the gaseous state by opening the structure of the fibre. After passing the dye into the fabric the fibre structure is closed to its original form. The opening of the fibre structure is done by genome sequencing. Genome sequencing is the process to find out the complete DNA sequence of any living thing. The structure can be changed by making changes in the DNA map.

AirDye maintains its colour accuracy by using its special software. The penetration of these dyes is better compared to other dyes. Its dyes not only colour the yarn from outside but also the filaments present inside it.

One of its highlights is both the sides of the fabric can be dyed with different colours at the same time resembling colours or patterns on the same fabric.

Greendye:

Karl Mayer launched a technology named Greendye in ITMA 2019. This technology is used for dyeing jeans without the use of water and 50% less chemicals. The main highlight of this technology is that it increases the amount of dye pickup by 3 times compared to the conventional dye vat.

Greendye technology is the process of indigo dyeing in nitrogen atmosphere. Nitrogen ensures the brilliant setting of dyes in terms of tone and solidity. The nitrogen atmosphere along with the high concentration of dyes in the dye bath increases the migration and diffusion of dyes in the fibre. Due to the absence of oxidation process the possibility of penetration of the colourant increases making a bond with the cotton fibre.

Cadira:

Cadira is a part of resource efficiency program by DyStar. Cadira concept considerably reduces the use of water, waste and energy consumption. Cadira includes Cadira Reactive, Cadira Polyester, Cadira VAT, Cadira Recycled Polyester, Cadira Wool and Cadira Denim.

Cadira Reactive is process for dyeing cellulose fibres. For this purpose, Levafix® and Remazol® dyes are used. It also uses high performance Sera® Fast C-RD for giving  special wash to the fibres.

On the other side, Cadira Polyester uses Dianix® dyes and Sera® process auxiliaries for dyeing polyester.

Upcoming technologies

Dry Indigo:

Gap Inc. announced an initiative for producing waterless dyed denim in June 2019.This denim is scheduled to release in 2020. The process, called Dry Indigo, uses indigo foam-dyeing technique where the foam dye adheres to the yarn giving good dyeing results. According to Gap, this process reduces the water usage by 99%, chemicals by 89% and energy consumption by 65%. The goal of the company is to save 10 billion litres of water by the end of 2020 by using this process.

The foam-dyeing technique is also advantageous in terms of space as it requires less than 65 feet of space compared to long, hundreds of feet of space for the conventional dyeing process.

Washwell

In 2016, Gap Inc. announced a smart denim wash program. It was callled washwell. This program resulted to be very effective allowing the company to save over 229 million of water compared to conventional washing techniques.

Gap has saved over 5.7 billion litres of water by the combined effort of techniques mentioned above.

Promising solutions
As the demand of fresh water is increasing day by day for daily purposes, the above methods/techniques of dyeing can be something which can be relied on to save fresh water rather than wasting large amounts of it on conventional water dyeing. Also the washing process gets eliminated in waterless dyeing methods; hence the water pollution due to disposal of waste water into fresh water resources is also prevented. The more these methods will be used, the more amount of water can be saved.