Advantages and disadvantages of different physical and chemical methods used for discoloration of denim

Denim garments are elegant fashionable textile products with very high level of market all over the World. It has been well-known that unfinished denim textiles are uncomfortable to wear due to their heavy and rigid structures, therefore, it is necessary to achieve a soft handle, an enhanced comfort as well as a desirable worn-out look by finishing. Great efforts have been hailed to explore different chemical and physical finishing procedures for discoloration and improving the handle of denim. They include oxidizing-bleaching treatment, stonewashing, electrochemical reduction, bio-washing, plasma treatment, laser irradiation and combination of nanoparticles with enzymes. Oxidizing agents and stone washing with pumice were first introduced in garment industry for aged-look denim finishing. However, several negative impacts were observed on finished products and washing machines by these two methods. To overcome their drawbacks, electrochemical reduction technique has been later adopted to bleach denim fabrics by in-situ producing reactive radical scavengers, but it has not yet been a simple scale-up procedure. Enzymatic treatment of textiles has also been demonstrated as an environmentally friendly method for textile finishing. In this regard, great efforts have been devoted for denim finishing by pure laccase, mixture of laccase/cellulase, pure acid cellulase, pure neutral cellulase, mixture of amylase/cellulase/laccase, mixture of cellulase/methacrylate copolymer and mixture of liquid ammonia/cellulase. It is worth mentioning that plasma and laser etching methods are recently introduced as environmentally friendly physical approaches to reduce the chemical agents and water consumption usage in textile industry.

Several research groups have found that stone-washing technique can be replaced by low temperature plasmas of O², air, argon and helium gases for removing the oxidized indigo from denim surface. Laser has also been known as another environmentally friendly approach for discoloration of denim in garment industry. However, considerations should be undertaken to control laser procedure parameters in order to avoid damaging in denim structure and preventing reduction in the tensile strength. The advantages and disadvantages of different methods are described in table below:

Methods	Advantages	Disadvantages
Oxidizing-Bleaching Treatment	Strong Discoloration power Simple Application	Relatively high cost Possibility to reduce mechanical properties Yellowing effect Not environmentally friendly Toxic chemical usage Corrosion of equipment Unpleasant odor in working environment
Stone Washing	Desired vintage effect Desired Softness Desired worn-out look	Corrosion of equipment Time consumed stone dust removing Possible to damage denim Not environment friendly
Electrochemical Reduction	Versatility and high-energy efficiency Environmentally friendly	Not available in scale-up Relatively high cost
Bio-washing	Mild processing conditions Environment friendly Low risk in denim damage Recyclability of enzymes	Necessity of enzyme neutralization Chances of back staining in enzyme treatment Inability to create different designs
Plasma Treatment	Environment friendly Fast discoloration No solid waste and air pollution Dry operation No negative effect on bulk properties	Necessity to have operational skills Necessity to optimize process parameters for effective discoloration Technical challenges in scale-up Yellowing effect
Laser Irradiation	Environment friendly Fast discoloration Dar operation Repeatability of designs	Necessity to control laser parameters Necessity to have operational skills Yellowing effect Possibility to reduce the mechanical properties
Combination of Nana-particles with enzymes	Additional functionality on denim depending on nanoparticle type No negative impact on mechanical properties	Yellowing effect