Denim bleach effect:


Tradition chemical process:


Denim Bleach is a process that can be used to decolorize indigo from denim In this process a strong oxidative bleaching agent such as sodium hypochlorite or KMnO4 is added during the washing with or without stone addition. Discoloration produced is usually more apparent depending on strength of the bleach liquor quantity, temperature and treatment time. It is preferable to have strong bleach with short treatment time. Care should be taken for the bleached goods so that they should be adequately antichlored or after washed with peroxide to minimize yellowing. Materials should be carefully sorted before processing for color uniformity.


Limitations:


Process is difficult to control i.e. difficult to reach the same level of bleaching in repeated runs. When desired level of bleaching reached the time span available to stop the bleaching is very narrow. Due to harshness of chemical, it may cause damage to cellulose resulting in severe strength losses and/or breaks or pinholes at the seam, pocket, etc.


  • Harmful to human health and causes corrosion to stainless steel.
  • Required antichlor treatment.
  • Problem of yellowing is very frequent due to residual chlorine.
  • Chlorinated organic substances occur as abundant products in bleaching, and
  • Pass into the effluent where they cause severe environmental pollution


Enzymatic bleaching effect on denim:


Laccase is the newest enzyme class to be introduced into denim finishing. Laccases are multi-copper oxidizes that catalyze the oxidation of a wide range of phenols, including indigo, under simultaneous reduction of oxygen to water. Laccases alone are not effective in decolorizing indigo on denim and require a mediator, which mediates electron transfer from indigo to molecular oxygen. Since the laccase and mediator only degrade indigo, without affecting the weft yarns, the resulting finish exhibits unique wash-down of denim.


Conventional hypochlorite bleaching of denim is cheap, fast and efficient, but harsh to the environment and the denim. However, laccase and mediator bleach can be done under mild condition and is much simpler to control. Since the bleaching action is specific to phenol complexes, it is especially useful for stretch denim, without affecting its elasticity, unlike traditional hypochlorite bleach, which has a damaging effect on elastomeric yarn. The laccase and mediator can be alternatively used for abrasion enhancement by further brightening up the denim after cellulose treatment.


On the Horizon

Denim clothing continues to reinvent itself through various fabrications, finishes, and embellishments that enhance its consumer appeal. Its continued and rising popularity has opened new worlds of possibility for its uses, and denim is finding its way into home fashion, being used in upholstery, decorative pillows, comforters, window treatments, slipcovers for furniture or even the tabletop.


The majority of denim fabric finishing with enzymes is currently done in a batchwise process to achieve faded effects and soft feel. However, it might be possible to treat denim fabric in a continuous-process range in the future, if advances in biotechnology enable scientists to create extremely fast-acting and robust cellulases, and if machine manufacturers can build special continuous-range equipment with greater mechanical action. The birth of such an enzyme and process will further enable the textile industry to expand towards a much higher throughput and a more sustainable process by saving time, energy and water consumption.


As environmentally friendly processes consume less energy and raw materials and markedly reduce or even eliminate waste, the challenge to biotechnology is to provide tools that will enable to achieve these goals and thus ensure great industrial sustainability.


New Laccase enzyme based bleaching technique only affects the indigo and natural raw white of weft yarn is retained, giving the woven fabric a darker shade, which is not implicitly achieved with hypochlorite bleaching. The product is so specialised on indigo that it does not attack any other dyes. Laccases open up the door to bleach Lycra containing denim without loosing the strength of the fabric. In case of hypochlorite bleaching Lycra containing product affects adversely by loosing the tear and tensile strength. Finally the process is based on enzyme so no risk of environmental pollution and harmful effluent discharge. This is a new tool in denim processing that will enable the denim finisher to create a number of new fashions and look distinctly different from the finish of traditionally bleached denim.


Benefits:


Den Bleach is an extremely versatile tool for denim finishing as it can be used in a number of applications. As Den Bleach acts directly on the dyestuff, it enables denim finishing with minimum strength loss. This process offers a number of unique feature and advantages over other decolonization technologies, ranging from safety in handing to superior garment quality and process control.

  • Denim finishing with minimum strength loss
  • Grey shade change, creation of new looks, new fashions and new finishes
  • Clean-up of back staining and improved garment contrast
  • Reproducible performance and ease of use
  • Stone-free processing. Enhanced denim abrasion, allowing Avery fast process.
  • Ideal for processing light weight chambray fabrics and stretch garments
  • Creation of super-abraded finishes with minimum strength loss
  • Safe handling and operation



Bio stone wash finish of Denim:


Stonewashing added a new dimension to denim garments in the late 1970s: the process enabled artificial ageing of denim garments which imparted a fashionably aged look. As the name 'stonewashing' implies, the blue jeans were washed with pumice stones to achieve a faded look.


Due to the disadvantages of using pumice stones, such as


  • Machine damage
  • blocking of the drainage system
  • difficulty in removing pumice-stone residues
  • excessive damage to garment hems and seams
  • large amount of stone required for small batch



So the alternative methods for stonewashing were developed. Cellulose enzymes were introduced in the 1980s as a denim-washing, aid to achieve a faded and abraded look similar to that provided by pumice stones. Cellulose works by loosening the indigo dye on the denim in a process know as 'biostonewashing'. A small dose of enzyme can replace several kilograms of pumice stones.


Biostonewashing has opened up new possibilities in denim finishing by increasing the variety of finishes available. For example, it is now possible to fade denim to a greater degree without running the risk of damaging the garment. Productivity can also be increased because laundry machines contain fewer stones or no stones and more garments. The use of less pumice stone results in less damage to garment and machine, and less pumice dust in the laundry environment.

A range of celluloses for denim finishing, each with its own unique properties, is available in the market. These can be used either alone or in combination with pumice stones in order to obtain a specific look. An ideal biostone wash enzyme would possess high abrasive activity (the ability to remove indigo from denim) as well as low back staining with lower fabric strength loss.


Celluloses have been used for the past twenty years and it is estimated that approximately 80% of denim garments are processed in this way. Celluloses are enzymes that are specific for the hydrolysis of the beta-1, 4 glucose linkage of cellulose. The reaction mechanism of the naturally occurring cellulose enzymes on cellulose is very complicated and several different enzymes endoglucanases, cellobiohydrolases and beta-glucosidases are synergistically involved in the chain of reactions needed to break down cellulose into glucose. The first type of celluloses introduced to market was derived from the Trichoderma family, a fungus with the longest history of cellulose research. The second phase in the, development of cellulose was the introduction of products based on another fungus called Humicola insolens. These celluloses soon became known as the neutral celluloses, as they could work in a more neutral pH environment. A special feature of the neutral celluloses is their ability to provide the stonewashed look with minimal indigo redeposition during the treatment. Thus the jeans and other denim garments would have a higher contrast between white and blue yarns, and the inside pockets as well as the leather labels would not be stained with indigo. However, the reaction time of this enzyme is slow and its use requires a longer processing time.


Since then, much progress has been made in the development of cellulose compositions, which are customized to achieve specific applications. Research and development activities have been focused on a new generation of cellulose enzymes whose composition has been altered through genetic engineering to provide higher abrasion contrast, reduced back staining, improved fabric-strength retention and broadened operating pH and temperature ranges. The development of modern biotechnology brought new tools for scientists to create new, better cellulose products for textile applications.


Benefits:

Valumax A 376 is a high-per formation. Ready-to-use cellulose for the abrasion of denim (stone washing) .this produce allows new shades and finishing to be created and cost-effectively in an environmentally friendly way.

 

  • High color contrast finish
  • Low degree of indigo back staining
  • Optimum strength retention
  • High degree of reproducibility and reliability
  • Maximized fabric strength retention
  • Improved wash look or creation of new looks
  • Easy handling
  • Cost effectiveness


References:


  1. Enzymatic Treatment of Wool with Modified Proteases(Prof. Doutor Artur Cavaco-Paulo Textile Engineering Department, University of Minho)
  2. A Cavaco-Paulo, G Gubitz, Graz Textile processing with enzymes. Woodhead Publishing Limited. August 2003. ISBN-13: 978 1 85573 610 8.
  3. Elisabeth Hein & Hatwing Hocker, Enzyme treatments for wool and cotton
  4. Biotecnology and coloration bjmc charthy.
  5. Chemicals & enzyme profiles of novezyme
  6. Enzyme application in the textile industry nylson and Marcela
  7. Kh. M. Gaffar Hossain, Maria Diaz Gonzalez, Guillem Rocasalbas Lozano and Tzanko, Multifunctional modification of wool using an enzymatic process in aqueous- organic media. Journal of biotechnology Volume 141, Issue 1-2, April 2009.


Image Courtesy:


  1. feltraiger.com


This article was originally published in Textile learner blog run by Mazharul Islam Kiron.