Pretreatment Process of Textile Materials

Pretreatment:
Pre-treatment means any treatment, which is done before actual (dyeing and printing) process. Pretreatment processes include dsizing, scouring, and bleaching which make subsequent dyeing and softening processes easy. Uneven desizing, scouring, and bleaching in the pretreatment processes might cause drastic deterioration in the qualities of processed products, such as uneven dyeing and decrease in fastness.

Process pretreatment of textile is all mechanic and chemical process to textile materials both for is made from natural and synthetic fiber before dyeing, printing and finishing process ,with purpose the process is fluently better and the result can which as expected.

Object of Pretreatment:

• To Convert fabric from hydrophobic to hydrophilic state.
• To remove dust, dirt etc from the fabric.
• To achieve the degree of desire whiteness.

Pretreatment Process of Textile Materials:
Cellulosic fibers, whether they are natural or regenerated need some form of treatment to make them suitable for dyeing or finishing. This treatment, which removes natural or added impurities, is called preparation pretreatment. It can be carried out on loose fibers, yarns or fabrics.

Unless the fibre is uniform in whiteness, absorbency and chemical composition and has law levels of impurities it is unlikely that it will take up dye or finish in a uniform way or to the maximum extent possible. The prepared fabrics must have ‘fitness for purpose’. For example, a fabric to be given a water-repellent finish must be free from residual surfactant. Fibers used for medicinal end uses must have a law ash content.

All such requirements must be met against economic constraints relating to the costs of water, labour, plant, chemicals and energy. The first, water, is particularly important. Not only can the purity of the water affect many of the requirements but the volume and the environmental impact of effluent can, and is, adding increasingly to the cost per kilogram of textile produced. The effluent with the highest biological/chemical oxygen demand stems from pretreatment.

Successful preparation depends on four factors:

• The level and type of impurities present.
• The chemicals used in the various stages of preparation.
• The water supply.
• The type of machinery used. 

 

Bleaching Process of Silk | Silk Bleaching Process

Natural coloring matters present in silk are associated mainly with sericin and hence are eliminated during degumming. The natural colouring matter of silk can be roughly divided into yellow, green and brown pigments. However the residual pigments are adsorbed by fibroin and hence silk fabrics made from yellow raw silk after degumming are not white but have a cream colour.

Silk Bleaching

The bleaching process may be based on reducing agents or oxidizing agents.

Reductive Bleaching
Predominant reducing agents used are Sulphur dioxide, sodium hydrosulphite and sodium or zinc sulphoxylate formaldehyde. The material bleached with reducing agents tends to reoxidise and the original color may be restored. Hence oxidizing bleaching is most preferred.

Oxidative Bleaching
The oxidative agents used are

• potassium permanganate,
• sodium perborate,
• sodium peroxide  
• hydrogen peroxide.
  

The hydrogen peroxide is the most preferred bleaching agent. A typical process/recipe would be
2 to 4 hours at 70°C
or 1 to 2 hours at 80 to 85°C,
With 10 to 15 ml/l hydrogen peroxide (35% solution),
and 1 g/l EDTA (30% solution)
and 3 g/l sodium pyrophosphate to pH 9,
followed by thorough rinsing.

The Chlorine based bleaching agents such as bleaching powder, sodium hypochlorite and sodium chlorite ,are generally not used since these agents tend to chlorinate the fibroin.