Know What You Wear

Wednesday, December 20, 2017

Denim Washing Process: Objectives, Evolution, Advantages and Limitation

Denim washing:
Denim washing is the aesthetic finish given to the denim garment to enhance its appeal and provide strength. The emphasis is on comfort and softness. Fashion trends favour the broken-in look and worn/faded seams that can only be achieved through garment processing. Much of the appeal of dry denim lies in the fact that with time the fabric will fade in a manner similar to that which artificially distressed denim attempts to replicate.

The indigo dye remains mostly at the surface; hence the dyeing process may be called ring dyeing. Such ring-dyed materials are subjected to treatment with stones or enzymes, which removes dye randomly from portions of the fabric, exposing the white surface. This popular style is used in faded jeans. Microscopy reveals that for indigo dyeing, the cross-section of the resulting dyed cotton yarn depends on the pH of the bath. When the pH of the dye bath is decreased from 13 to 11, the denim yarn progressively becomes more ring-dyed. Associated with increased ring dyeing, more colour yield is obtained, making the wash-down process easier. The highest colour yield was observed within the pH range of 10.8–11.2.

Denim washing process
Fig: Denim washing process
Denim comes in all forms, looks and washes to match every type of dress. In denim, garment washing is done to produce effects such as colour fading with or without patchiness, crinkles, seam puckering, hairiness, depiling, softened hand feel and stabilized dimensions. 

Every small step in denim washing makes a big difference because indigo has poor wet and dry rubbing fastness. All parameters (e.g., pH, material: liquor ratio, rpm of the machine) are critical to maintain repetitive results.

Evolution of denim wash:
Denim garments in the market are originally stiff and uncomfortable when first purchased because of the finishing system used for denim fabrics. Generally speaking, after weaving, the heavily sized fabric is subjected to desizing and compressive shrinkage treatments. After the treatments, the softness of the denim fabric is seriously affected. In the past, many consumers used to take a newly purchased pair of jeans home and soften it by washing once or several times before the first wearing.

In the earliest evolution, the garments were laundered (prewashing) by the manufacturer before selling. These ‘prewashed’ denim garments had a slightly faded appearance and a softer hand that felt comfortable. These prewashed garments generated a trend of fashion and consumers were willing to pay the extra cost involved in this additional processing.

As the popularity of prewashed garments grew, the idea of using abrasive stones to accelerate the colour fading process was developed and ‘stone washing’ became the second step in the evolution. Pumice stones were included in the washing process, or tumbled with the damp garments to wear down the stiffest portions, for example, belt areas, cuffs and pockets. The third development was the use of chlorine (e.g. sodium hypochlorite as a bleaching agent) in the washing process. A new and colour lightened blue denim garments category was the result. With the use of chlorine bleaching, in 1987–1989, ‘ice washing’ was developed, in which the pumice stones were first presoaked in the bleaching agent and then tumbled with dry or slightly damp garments.

In the industry, ‘ice washing’ has alternative names such as ‘acid wash’, ‘snow wash’, ‘white wash’ and frosting, etc. Actually, the term ‘acid wash’ is a misleading term because mineral acids are not used for this process.

Other than bleaching agent, the use of enzyme (cellulase) treatment to obtain the colour fading effect similar to stone washing effect in denim garments has attracted considerable interest over the past several years. The primary attraction is to reduce or eliminate the need for stones or to reduce the time needed to obtain the desired abrasion effect. Moreover, using pumice stones to abrade denim garments is destructive to equipment. In addition, the pumice stones, after washing, get entrapped in pockets of denim garments which must be removed by hand, leading to increased labour and production cost. Also, stone particles and grit play havoc in the effluent. For these reasons, the use of cellulase was promoted with the promise of eliminating stone as the abrasive agent for achieving the ‘stone wash’ look. However, because of the increased time and other considerations, the trend today is to use combinations of stone and cellulase to achieve the worn and faded look in denim garments.

With the increasing awareness about and concern for environmental issues, such as large amounts of effluents produced and high consumption of water and energy, wet processes related to denim washing are considered as not environmentally friendly. To address the environmental concerns, dry finishing techniques such as plasma and laser treatments have been introduced as an alternative to the conventional wet processing.

Washing as final process of denim garments:
Washing can be considered as the final process in denim production and is the core of denim finishing. The washing of denim is directly related to the aesthetic, quality and value of denim garments.

In processing, sizing and coloration form the base of colour in denim garments. However, the washing process is the key to create the style in denim garments which is now becoming an art of creating fashion trends. The three dimensional (3D) effect and worn look can be achieved through different types of finishing and washing processes. Under the influence of different chemicals, washing conditions and washing equipment used, different final effects can be achieved in denim garments. 

As a result, the washing of denim and jeans is aimed at:
  • Preshrinking for good dimensional stability during selling and use.
  • Removing sizing agent and unfixed dyes to remove contaminants added during the manufacturing process so as to generate ‘clean’ denim garments. Also, the washing can increase the surface lustre and lightness of the fabric.
  • Improving the hand feel through various finishing processes such as softening, stiffening or  polishing to enhance the comfort of denim garments.
  • Improving aesthetic properties through fading, bleaching or tinting processes. After these treatments, cloudy, frosted, wrinkle, grinded or peach skin effects are achieved which finally affect aesthetic properties.
  • Improving the functional properties such as wrinkle free, anti soil, water repellence, oil repellence or antistatic, etc.
  • Improving the quality in cases of poor colour yield, dimensional stability, colour fastness or improper surface treatment.
Objects of denim garment washing:
There are several objects of denim garment washing:

  1. To develop softness in garments: Size materials applied during manufacturing that are present in the fabric are removed, which enhances the soft hand feel. Additional softness may be attained by using softeners.
  2. To introduce a fading effect: Dyes or pigments present in the fabric, used during colouration, are washed out locally or partially, resulting in fading or worn-out effects in the garments.
  3. To create new fashion: The washing process of garments creates a different outlook (faded, colour tinted, etc.), thus creating new fashions for new generations especially for teenagers.
  4. To satisfy the consumer: Because contraction or extraction (shrinkage) does not occur during washing, the wearer can use the garments satisfactorily after purchasing them.
Advantages to denim washed garments:
  1. Removal of starch or size materials gives the fabric a soft hand feel.
  2. Softness can be increased by adding a softener at the very last stage of washing.
  3. If dirt, spots, impurities, gum, etc., have accumulated in the garments during manufacturing, they can be removed.
  4. During washing shrinkage may take place; therefore no shrinkage occur during washing of garments.
  5. Washed garments can be worn directly after purchase.
  6. Faded or worn effects can be introduced to the garments, creating a new fashion.
  7. A similar look can be obtained by different washing techniques.
  8. Comparatively lower capital is required to set up a washing plant.
  9. A smaller amount of property and fewer paid workers are required to run a washing plant.
Limitations of denim garments washing:
  1. Garment sizes change: Size change takes place owing to the shrinkage properties of fabric. The amount of shrinkage of the fabric determines the size change of the garments during washing.
  2. Size material is partly removed: Unfixed dyes may remain on the surface of the garments and it is necessary to remove them completely after washing.
  1. Denim : Manufacture, Finishing and Applications. Edited by Roshan Paul
  2. Sustainability in Denim. Editors: Subramanian Muthu