Preparation of Fibers.

Preparation of Fibers.

 Most fibers require some preliminary treatment before they are dyed.

Raw cotton  contains impurities like natural waxes and noncellulose. These impurities are removed by a process called kier boiling. Cotton is boiled under pressure with a dilute solution of caustic soda, soap, or other alkali in a special autoclave, or kier. Usually the cotton fabric contains lots of starch. So it is very important to remove  all the starch before dyeing. Enzymes are used for fermenting this starch. For removing of fine fuzzy projecting fibers on cotton fabric processes like bleaching with sodium hypochlorite and dilute acid are practiced.

Before dyeing up of raw natural silk the gummy substance sericin present in it should be removed. Sericin can be removed by a process called degumming.  In this process silk fibers are heated in a dilute soap solution for about two hours.

Wool is derived from animal coat so it contains lot of impurities like dirt and grease. These impurities can be removed by scouring with soap and soap ash. The vegetable impurities  in wool are removed by a process called carbonizing, which includes immersing the fiber in dilute sulfuric acid, drying it, and then heating it to 110°C. (230°F.). Sometimes the wool is bleached or stoved (exposed to sulfur dioxide gas) prior to dyeing

Nylon does not need any treatment before dyeing. Viscose rayon is a type of wrinkle free man made fabric. Viscose rayon yarn, in the form of skeins, cakes, or loose yarn, seldom needs pre dyeing treatment. Woven or knit goods, however, are treated with a hot ammonia soap solution to remove the gelatin size. Acetate rayon is often scoured with soap and ammonia.