Ozone Fading on Denim:
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 associated with this process are that:
- Colour removal is possible without losing strength.
- This method is simple and environmentally friendly because, after laundering, ozonized water can easily be deozonized by UV radiation.
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 for denim:
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
- Short treatment time
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 colour 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 colourant 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 colour fading effect.
Table: Colour 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 fibre 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.