Denim garments are very popular in people with different ages and genders. Before the production of jeans, based on the requirements, denim needs to be treated with different chemicals. To achieve desired effects, a variety of dry and wet processing techniques can be used by manufacturers. Wet processing in denim washing is not environment-friendly. Problems that can be brought about include the huge consumption of water and energy, the producing of waste water and solid waste like pumice stone.
Sodium hypochlorite is heavily used in denim washing, in which AOX (absorbable halogenated organic compounds) may cause serious environmental problems. As a result, some manufacturers are turning to chlorine-free bleaching techniques to deal with the problem. However, comparatively, ozonation is a better solution. Ozone denim washing is an easy and sustainable process that does not require the use of steam and water. With the use of ozone, it will reduce the processing time while reducing the consumption of water, chemicals, energy and the amount of waste water produced. For its high oxidation potential, ozone can break down indigo and other dyes.
In addition to denim and jeans washing, ozone denim washing can also be applied to treat T-shirts, shirts, chinos, as well as casual wear. Ozone can commercially provide a desired bleaching effect in the ozonation process. In other words, ozone can decolorize cloth like a washing machine. When ozone is used, it will be applied to the whole garment. There will be bleached spots left on the spots by ozone. It will spread out over the denim fabric in a controlled velocity.
Researches on Ozone Denim Washing
Parameters of denim fabric ozonation have been studied by expert Özdemir. By treating pre-washed denim, he found that the efficiency of ozonation can be affected by the water content of the denim. Ozonation of wet denim is particularly suitable for bleaching, where 50-60% WPV (water pick up value) is optimal for bleaching. With a too high WPV value, the bleaching efficiency of ozonation will be negatively affected. Acidic and neutral pH values are better than basic pH values. In an ozone denim washing process, temperature also needs to be considered since a high temperature condition can shorten the half-life of ozone.
The influence of parameters in dry and wet ozone bleaching on denim fabrics are also studied. The study results of Hmida on the bleaching effect of WPV on denim were consistent with the result from Ozdemir. Research has shown that covering the surface of fabric with water can help the swelling of the fiber. In this way, ozone can penetrate into the fibers more easily, thus improving the bleaching efficiency. Besides, ozone denim washing can also solve the backstaining problem.
Another study focused on the treatment of denim with a combination of ozonated water, ultrasound and hydrogen peroxide. The results shows that ultrasonic cavitations can promote ozone’s penetration into fabric and decompose indigo. So, with the help of ultrasound, the ozonation process can be more effective.
By comparing with other commonly used bleach used for denim washing, ozone is one of the strongest agents. Although it is listed behind potassium permanganate and benzoyl peroxide, ozone has the advantage of being environment-friendly, thus making it the best alternative. What’s more, ozone’s instability is also its advantage in ozone denim washing. Since ozone mainly decomposes indigo, the strength of denim will not suffer a great loss after the ozonation process.
There are relatively few researches on the ozonation of yarn. A few researches are the use of ozone to fade indigo-dyed yarn before it is weaved and for making clothing. In addition, the origin of raw materials will also have an impact on the fading degree of yarn. The count of yarn is an important reference for consideration for yarn strength reduction after ozonation. The conclusion is that ozonation conditions can be determined according to the desired effect of the yarn, and different fading effects can be achieved by an ozonation treatment.
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