Recent Development in Washing techniques for denim Jeans

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Naimul Hasan

Background

Different denim washing procedures have been created and applied on various materials to generate a huge diversity of styles for stylish denim clothing and jeans throughout the last few decades. Denim clothing often generates special color effects and washed/vintage characteristics. The cleaned products have a better hand feel than the unwashed goods, making them more ideal for casual use. Other processing methods make it harder to generate these results.

Denim washing outcomes are the consequence of a combination of color breakdown, dye degradation, and mechanical abrasion, which may result in the loss of surface fibers from the materials. Denim clothing with surface dyed (ring dyed effect) colors are therefore more readily wiped away during the washing process. Denim is described as a “traditionally a 3/1 warp faced twill fabric created from yarn colored warp and undyed weft yarn,” according to textile terminology and definitions. The fabric’s typical structure is 32/19; 45/54 tex; 310 g/m2. Other weaves have lately been employed with lighter structures. Jeans are characterized as “a 2/1 or 3/1 warp faced twill fabric with a typical structure of 35/24; 32/21 tex cotton used mostly for overalls or casual clothing.” Despite denim and jeans having separate definitions, they currently have the same meaning in the marketplace. Denim fabric’s warp yarn is traditionally stained with indigo for a ring dyed look.

Evolution of denim garment washing

Because of the finishing procedure used for denim textiles, denim clothing on the market is stiff and unpleasant when initially acquired. The substantially sized cloth is usually treated to desizing and compressive shrinkage treatments after weaving. The suppleness of the denim fabric is severely harmed after the treatments. Many customers used to take a new pair of jeans home and soften them by washing them once or many times before wearing them for the first time. The clothing was cleaned (prewashed) by the manufacturer before being sold in the beginning. These ‘prewashed’ denim pieces had a slightly faded look and a softer, more comfortable touch. These prewashed clothing became a fashion trend, and buyers were ready to pay the higher price for this extra processing.

The notion of employing abrasive stones to expedite the color fading process was developed as the popularity of prewashed clothing rose, and ‘stone washing’ became the second stage in the development. Pumice stones were included into the washing process or tumbled with wet clothes to soften the stiffest parts, such as belt regions, cuffs, and pockets. The third advancement was the use of chlorine in the washing process (for example, sodium hypochlorite as a bleaching agent). As a consequence, a new type of brightened blue denim clothes was created. The use of chlorine bleaching led to the development of ‘ice washing’ in 1987–1989, in which pumice stones were first pre-soaked in the bleaching chemical and then tumbled with dry or slightly wet textiles. Alternative names for ice cleaning in the industry include ‘acid wash, “snow wash,’ ‘white wash,’ and icing, among others. The phrase “acid wash” is really a misnomer since no mineral acids are employed in this operation.

Classification of Recently developed washing techniques    

General finishing sequence of denim

Designers and textile chemists use a wide range of processing procedures to generate unique and attractive fashion styles. This chapter only covers the most fundamental treatment conditions; the number of variants is enormous, and chemical and mechanical approaches are continually evolving. There are often some proprietary and confidential processes. The following are the typical process stages needed to get the desired outcomes, regardless of the selected style and name.

Desizing → Rinsing → Washing (abrasion) → Rinsing → Softening → Drying → Packing

1.0   Desizing

The amylase enzyme is the most common technique for eliminating starch from denim clothes. This product may break down lengthy, water-insoluble starch molecular chains into smaller, water-soluble molecules that can be rinsed away more readily. When starch is removed from a cloth that is being desized, some indigo is normally released into the bath. As a result, a neutral pH nonionic surfactant is employed to suspend free dye in water, preventing redeposition on the clothes and assisting desizing liquid penetration into the interior of the fibers. It’s also crucial to rinse with hot water after the desizing bath. At this stage, putting cold water on the denim clothes might resolve the fats and waxes and cause the gelatinous components to redeposit unevenly on the surface.

2.0 Regular washing

Regular washing is the most basic and widely utilized treatment for denim items. Regular washing causes relatively little color fading, but it does give consistency, depending on whether the denim is deeply colored classic denim or merely lightly dyed with inadequate penetration. In general, detergent is used for routine washing for around 15 minutes at temperatures ranging from 60 to 90 degrees Celsius. After the washing procedure, softening is applied. Denim clothes may be improved in terms of softness and comfort, as well as their aesthetic value, by washing them on a regular basis. Regular washing may be divided into two categories based on the amount of time and chemicals utilized.

(1) light washing (about 5 minutes); (2) regular washing (approximately 15 minutes); and (3) heavy washing (approximately 30 minutes) (washing time about 30 min). However, since it depends on the exact washing circumstances, there is no substantial difference between light, normal, and heavy regular washing. The general washing procedure is as follows:

Wetting → Desizing → Regular washing → Softening.

3.0   Bleach washing

Bleach washing is usually done using sodium hypochlorite (NaOCl) or potassium permanganate, which are both powerful oxidative bleaching agents (KMnO4). With or without the use of stone, bleach washing may be done. The strength of the bleach liquor, the amount of liquor, the temperature, and the treatment duration all influence the bleach washing result and discolouration. To prevent later yellowing or tendering of the bleached denim fabric, it should be adequately antichlored or washed with peroxide thereafter. The following are the fundamental processes in denim bleach washing:

Garment loading with or without stone → Desizing (10–15 min, at 55–60 °C) → Rinsing → Bleaching (15–30 min) → Rinsing →Bleaching with cold water → Optical brightening → Softening

4.0 Stone washing

Abradants such as volcanic rocks or pumice stones are used during the washing process. The color fading is more noticeable, but less consistent. The amount of color fading is determined by the washing duration (60–120 minutes), stone ratio (weight of stones vs. garment weight) (0.5: 1–3:1), stone size (diameter: 1–7 cm), liquor ratio (10:1), and garment load. The world’s biggest pumice stone suppliers are the United States, Turkey, Italy, Germany, Iceland, New Zealand, Japan, Indonesia, and the Philippines. The following are the fundamental processes in denim stone washing:

Desizing (10–15 min) → Rinsing → Stone washing → Rinsing (with perborate and optical brightener if necessary) → Softening

5.0 Enzyme washing

Cellulase enzymes are employed in enzyme washing. The surface fibers are weakened by the hydrolysis of cellulose, which is catalyzed by cellulase, and they are subsequently eliminated when there is either fabric-to-fabric or fabric-to-stone abrasion.

During the process of washing the temperature and pH must be adjusted according to the kind of cellulase utilized. Acid cellulases are usually treated at pH 4.5–5.5, whereas neutral cellulases are usually applied at pH 6–7. However, since the latter is more penetrative, it causes more back discoloration. A dosage of 2–4 g/L of enzyme is usually adequate, as long as the enzyme activity is not hampered. The color of enzyme washed items is more consistent in general, especially when stone is not added. Because cellulases only react with cellulose, any large materials or other contaminants must be eliminated prior to the cellulase treatment. The following are the fundamental procedures in denim enzyme washing:

Desizing (10–15 min) → Rinsing → Enzyme washing

6.0 Acid washing

Pumice stones are presoaked in a strong oxidizing agent solution (either sodium hypochlorite (5–10 percent) or potassium permanganate (3–6 percent) before being dry tumbled over the clothing. As a consequence, a localized washing effect with a vivid blue/white contrast is created. This method is also known as “acid washing,” “snow cleaning,” or “ice washing.”

Acid cleaning does not need the use of water. A later optical brightening operation may improve the color contrast after tumbling. This procedure works well with soft stones that readily dust off. The following are the fundamental processes in denim acid washing:

Desizing (10–15 min) → Soaking stones with strong oxidizing agent → Draining excess liquor → Dry tumbling (10–30 min) → Rinsing to remove stone dust → Rinsing with oxalic acid (in case of potassium permanganate)/antichlor with reducing agent (in case of sodium hypochlorite) → Optical brightening → Softening.

7.0 Sandblasting

Sandblasting is a mechanical procedure that results in localized abrasion or color change on denim garments. The procedure entails blasting a granular, powdered abrasive substance at a high speed and pressure via a nozzle on certain parts of the garment, such as the knees and elbows. The treated surface has a worn/distressed appearance. Sand and metal grains are the most frequent blasting ingredients. Denim garments are stone washed to the necessary degree of washing before being sand blasted during the sand blasting process. A solution of sodium hypochlorite or potassium permanganate is often sprayed over the desired part of the garment to achieve the same effect. The clothing is then neutralized, washed, softened, and dried. Because sandblasting is a waterless technique, no drying is necessary.

8.0 Monkey wash

Monkey wash refers to a unique color fading phenomenon seen on denim jeans’ thighs and buttocks. Denim jeans are sprayed with a powerful oxidizing chemical, such as potassium permanganate, in this procedure. As a result, monkey wash is referred to as ‘PP spray’ in technical terms (with PP being potassium permanganate). Before applying the PP spray, the denim clothing should be put flat or carefully secured in the manikin. The color is faded when a 2–5% dose of potassium permanganate is sprayed over the designated surface. After PP spraying, the brown tint of manganese oxide may be eliminated using oxalic acid or hydrogen peroxide. The following are the fundamental procedures for using PP spray on denim garments:

PP spraying → Washing → Treating with oxalic acid or hydrogen

9.0 Brushing/grinding

For the worn-out effect, abraded appearance, or used look, brushing/grinding (manual or mechanical) is performed manually or mechanically. In order to remove the indigo, certain mechanical techniques based on mechanical abrasion have been devised. Sueding, rising, submerging, peaching, and brushing are some of these techniques. These processes have the following advantages:

  • The abrasion is under control.
  • On the garment, many appearances may be produced.
  • All of the procedures are dry.
  • Economical, ecological, and good to the environment.

10.0 Whisker

Whisker is one of the most popular denim designs, and it is inspired by the worn-out lines and imprint patterns created by natural wear on the hips and front thigh region. Several patterns may be discovered in vintage jeans that are related to the fabric, the user’s body form, or their sitting position. Two varieties of whiskers exist: two-dimensional (2D) and three-dimensional (3D).

11.0 Ozone fading

Ozone is often used as a light bleaching and sterilization agent. The garment is bleached with ozone dissolved in water in a washing machine in this method of denim washing. However, utilizing ozone gas, this method may also be done in a closed room. This approach has the following advantages: (1) little strength loss; and (2) it is a simple, ecologically friendly procedure.

12.0 Laser treatment

For several years, the CO2 laser treatment has been used in various areas of the textile industry because it allows for quick surface pattern design with good precision, desirable effects, and a variety of sizes and intensities without causing significant damage to the bulk properties of the textile materials. For faded looks and worn-out effects, the CO2 laser treatment, considered a dry treatment, may be used to tex-tile materials as an alternative to traditional wet treatments like stone washing, sand washing, and bleaching. CO2 laser treatment has been shown to be an effective way to fade the color from denim fabric surfaces in a short time, depending on the laser process parameters. It depicts the color fading impact on denim fabric under different resolution and pixel time combinations. It can be seen that when the resolution and pixel time grow, the color fading effect in the denim fabric rises as well.

13.0 Pigment washing

Pigment washing is a method of adding pigments to textiles that have been pigment dyed or printed. The following causes need pigment washing:

  • To achieve a fading/aged appearance on clothing as well as the seam region.
  • After purchase, use the clothing for a nice feel.
  • To meet the buyer’s washing requirements.
  • To improve color and rubbing resistance.

The following are the fundamental processes in pigment washing:

Immersing garment in pigment → Drying → Baking (130–150 °C) → Washing (with or without pumice stones/with or without enzyme, 30–90 min) → Washing twice with water at 70 °C → Removing stones → Softening → Drying.

14.0 Tie dyeing

A rubber band or similar material is used to tie/bunch the denim garment to produce varied designs. The dye will not be able to penetrate the knotted section when dying with a direct dye. Patterns may be produced after dying; however, fixation is required. Tie-dyeing may also benefit from the usage of pigments. If a bleaching agent is employed, a bleaching effect is known as ‘tie bleach’ may be achieved.

Conclusion

The earliest appearance of denim fabric dates from the late seventeenth century. The weft runs beneath two or more warp strands in this cotton twill fabric. Denim was historically coloured blue, with a ring dyed look, utilizing indigo dye. Denim has changed through time and is now one of the most popular goods in the fashion and textile industries. It may give garments and fashion goods durability and a variety of aesthetic impacts. Several washing effects have been devised to make denim clothes like jeans more appealing to customers. Denim washing machines also play a significant role, and depending on market demands, these machines may provide consistent color fading or appearance impacts in a short amount of time. New forms of sustainable denim washing procedures may be created in the future; nevertheless, several issues, such as color uniformity, piece-to-batch repeatability, yellowing, and staining, must to be solved.

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