Friday, 29 November 2019

Sand Blasting


Sand blasting is a mechanical process in which localised abrasion or colour change on the denim garment is created. The process involves blasting an abrasive material in granular, powdered form at a very high speed and pressure through a nozzle, on certain areas of the garment such as knees and elbows. The treated surface shows distressed/abraded/used look.

Monday, 25 November 2019

Acid Washing


Pumice stones are first pre-soaked in a solution of a strong oxidising agent (either sodium hypochlorite (5–10%) or potassium permanganate (3–6%)) and are then applied to the garments by means of dry tumbling. This results in a localised washing effect with clear blue/white contrast. This technique is also termed ‘acid washing’, ‘snow washing’ or ‘ice washing’.

Saturday, 23 November 2019

Enzyme Washing

In enzyme washing, cellulase enzymes are used. Hydrolysis of the cellulose, which is catalysed by cellulase, causes the surface fibres to become weakened and later they get removed when there is either fabric-to-fabric abrasion or fabric-to-stone abrasion during washing. The temperature and the pH used are specific to the type of cellulase employed. Usually neutral cellulases are applied at pH 6–7, while acid cellulases are applied at pH 4.5–5.5. However, the latter result in a greater extent of back staining, being more penetrative. An enzyme dose of 2–4 g/L is normally enough, provided that the enzyme activity is not impaired. In general, the colour of the enzyme washed goods is more uniform, particularly when stone is not added. Because cellulases are reactive only on cellulose, any size materials or other impurities must be removed before the cellulase treatment.

Friday, 8 November 2019

Stone Washing


In this Process of denim washing volcanic rocks or pumice stones are added during washing as abradants. The color fading is more apparent but less uniform. The degree of color fading depends on the washing time (30–120 min), stone ratio (weight of stones relative to weight of the garment) (0.5: 1–3:1), size of stones (diameter: 1–7 cm), liquor ratio (10:1) and garment load. The world’s major pumice stone supplying countries include the USA, Turkey, Italy, Germany, Iceland, New Zealand, Japan, Indonesia and Philippines.

Thursday, 7 November 2019

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

 

Wednesday, 6 November 2019

Bleach Washing


Bleach washing is normally carried out with a strong oxidative bleaching agent such as sodium hypochlorite (NaOCl) or potassium permanganate (KMnO4). Bleach washing may be carried out with or without the addition of stone. The bleach washing effect and discoloration usually depend on strength of the bleach liquor, liquor quantity, temperature and treatment time. The bleached fabric materials should be properly antichlored or after washed with peroxide to reduce the subsequent yellowing or tendering of the bleached denim fabric.

Tuesday, 5 November 2019

Regular Washing/Rinse Washing


Rinse washing is the simplest and most commonly used washing method for denim garments. The degree of color fading using regular washing is comparatively slight, but it provides uniformity, depending on whether it is deeply dyed classic denim or only moderately dyed with poor penetration.

Sunday, 3 November 2019

Classification of Denim Washing Techniques


General finishing sequence of denim

There are almost countless variations of processing techniques used by designers and textile chemists to achieve fashionable looks that are distinctive and desirable. The number of variations is very large and the evolution of chemical and mechanical techniques is continuing. There often are some secret and proprietary methods. Regardless of the specific look and name chosen, the following are the process steps normally used to attain the desired results.