Ozone Fading Process for Denim:
By using this technique, the garment can be bleached. Bleaching of denim garment is done in a washing machine with ozone dissolved in water. Denim garments can also be bleached or faded by using ozone gas in a closed chamber.
The advantages of ozone fading process for denim are that:
- Color removal is possible without losing strength.
- This method is very simple and environmentally friendly because, after laundering, ozonized water can easily be deozonized by ultraviolet
Ozone typically acts as a mild bleaching agent as well as a sterilizing agent. In this technique of denim washing, the garment is bleached with ozone dissolved in water in a washing machine. However, this technique can also be carried out in a closed chamber by using ozone gas.
Advantages of Ozone Finishing / Bleaching for Denim:
A considerable quantity of water and chemicals are being consumed in conventional bleaching of denim garments which contaminate the water with solid particles and chemical components. Environmental concerns have provoked for a suitable solution to reduce the wastewater generated from the bleaching process. The use of ozone (O3) for the preparation of denim is the one way for a decrease in discharged wastewater. The oxidation potential of ozone in bleaching is 2.07 electron-volts (eV), that is more than the commonly used bleaching agent, H2O2 (1.77 eV). The availability of ozone on the earth is in the molecular form of acidic pH.
The equipment used in ozone-bleaching is divided into three components which are ozone generator, ozone applicator, and ozone destroyer. In Supply of significant concentrated amount of ozone-oxygen mixture by the generator to an applicator which is a cylindrical glass tube consists of a diffuser in its bottom. Production of ozone is carried out by feeding 20% oxygen, which is present in the air, for pressurized swing adsorption for raising ozone concentration 90% which further applied by plasma method for generating ozone. Benefits of ozone fading for denim garment finishing as compared to conventional bleaching are summarized as follows.
The advantages of this method are:
- A minimum loss of strength
- It is a simple method that is environmentally friendly.
- Low energy costs for processing because ozone bleaching is done at room temperature.
- 50% reduction in CO2 emissions.
- Short treatment time.
- Short cycle time bleaching resulting in increased the productivity of the process.
- Significant water savings.
Ozone Fading Techniques for Denim Finishing:
The ozonised water after laundering can easily be deozonised by ultraviolet radiation. Nowadays, ozone fading can also be achieved by plasma equipment. Under the influence of plasma treatment, high energy electrons are formed. Some of the high energy electrons react with moisture in air and a mixture of radicals is generated.
After laundering the ozonized water can easily be deozonized by UV radiation. Ozone fading can also be achieved by plasma equipment. Under plasma treatment, high-energy electrons are formed. Some of the high-energy electrons react with moisture in air and a mixture of radicals is generated. During the generation of ozone plasma, a combination of charged particles, free radicals and UV light is generated. The UV light, which is the by-product of the plasma treatment process, also contributes to production of the %OH radical. The hydroxyl radical %OH is the most oxidative radical among radicals generated in the plasma process and is the main radical responsible for degradation of indigo dye in textile materials. The %OH can oxidize indigo dye molecules (RH), producing organic radicals, R%, which are highly reactive and can be further oxidized. As a result, the color fading effect of the indigo-dyed textile is achieved.
The K/S (in which K is the absorption coefficient at a specific wavelength and S is the scattering coefficient) values of different treated denim fabrics are shown in Table. From the results, it is noted that the differently treated denim fabrics have lower K/S values than the untreated denim fabric. The K/S value is linearly related to concentration of the colorant in the medium and it can be concluded that a paler shade is obtained after different treatments. Without the cellulase treatment, the plasma induced ozone treated denim fabric has a paler shade than the enzyme desized denim fabric because during the plasma induced ozone treatment, ozone oxidises indigo dyes on the denim fabric surface leading to a color fading effect.
Table: Color properties of different denim fabrics
|Plasma induced ozone treated
|Plasma induced ozone treated followed by cellulase treatment
|Enzyme desized followed by cellulase treatment
However, in the case of enzyme desizing, the enzyme only reacts with the sizing material at the fiber surface and no breakdown of indigo dyes molecules occurs. Therefore, no significant shade change takes place. In the case of cellulase treatment, cellulase in the aqueous medium can penetrate effectively into the denim fabric. The enzymatic hydrolysis induced by cellulase in the plasma induced ozone treated denim fabric is more severe than the enzyme desized denim fabric. As a result, the cellulase treatment for plasma induced ozone treated denim fabric gives a paler shade than the enzyme desized denim fabric.
- Denim: Manufacture, Finishing and Applications Edited by Roshan Paul
- Sustainability in Denim. Editors: Subramanian Muthu
- Advanced Functional Textiles and Polymers Edited by Shahid-ul-Islam and B.S. Butola
- Handbook of Value Addition Processes for Fabrics by B. Purushothama
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.