Cotton and blends
The process of dyeing and finishing for cotton fibres and its blends (see Flow chart No. 4) basically consists of the following operation singeing • Quenching • Scouring • Mercerising and rinsing • Optical and chemical bleaching • Drying • Heat setting • Dyeing and rinsing • Final drying • Finishing
Singeing
The singeing operation is also known as gassing or burning depending on the procedure used. Its aim is to eliminate the fibres and fuzz that protrude from the yarn and also from the fabric.  
Quenching
Quenching or desizing aims to eliminate the pastes which are added to the warp for weaving. 
Desizing procedures are selected according to the type of sizing in the fabric:
• Desizing of starch pastes 
This treatment consists of using amylase-type enzymes to degrade the starch, at an adequate pH and established temperature. Sodium persulphate is also used as a desizing product. 
• Desizing with polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), (CMA), etc. 
Since they are hydrosoluble pastes, they are directly eliminated by washing with a detergent at a suitable pH, depending on the case in question.
• Desizing of special pastes, which always require direct instructions from the manufacturer. Special pastes are used to achieve high efficiency in weaving, for example on looms that insert the weft by means of a jet of water. 
Scouring
The scouring operation on cotton aims to eliminate the natural impurities contained in the 
Scouring
The scouring operation on cotton aims to eliminate the natural impurities contained in the fibre itself, which consist of waxes, pectins and hemicellulose. Treatment is carried out in discontinuous
Description of the dyeing, finishing and printing processes


or continuous systems by means of the action of an alkali, such as caustic soda alone or with detergent products, to solubilise and/or emulsify the impurities of the cotton, sequestrants and small quantities of reductive products, such as sodium hydrosulphite. The process is also known as cotton boiling, and may be done in an autoclave at a temperature of 100ºC to 130-140ºC, for 2 to 8 hours in discontinuous processes. A final rinse with water is needed in order to extract all the impurities separated from the cotton.
Mercerising (caustisizing)
The mercerising operation consists of subjecting the cotton to the action of the concentrated caustic soda (28-30º Be), so as to provide it with some characteristics that it does not possess or that it possesses in insufficient amounts, such as lustre, dye affinity, better dimensional stability, and an 15-20% increase in the mechanical resistance of the yarn.
This is done by subjecting the threads to tension, during or after impregnation in caustic soda of 30ºBe at temperatures lower than 20ºC and, later, successive washes are performed until the concentration of soda has fallen to values that no longer modify the cotton any more. In order to facilitate the impregnation of the cotton, anionic wetting agents are also added which can be phenolic or non-phenolic derivatives, the latter currently being the most commonly used, which are based on sulphur esters of average molecular weight (4 to 12 atoms of carbon).
The final stage is the neutralisation of the alkaline remains, which are still contained in the thread, if the following operation is not to be performed at alkaline pH, generally with chlorhydric acid or sulphuric acid.
A commonly employed variant in the mercerising operation in the so-called caustisizing process, which is done with a lower concentration of soda, 18ºBe, the main objective of which is to increase the cotton’s affinity for the dyes. 

Caustisizing needs not be done in the mercerising machines themselves.