Desizing Test

Desizing Test/Starch indicator

Starch is often used in fabric weaving to avoid breaking of the thread. It increases the strength of thread and also decreases the friction during weaving. This starch is must to remove before any kind of dyeing or chemical washing of garment. A number of desizing process (removal of starch /size)  are in practice in industry.

Starch forms a very dark blue-black compound with iodine. The indicator is not disturbed by the presence of iodide (I^-). Starch forms an un-stable complex (blue colored) in low concentrations of Iodine. However, this complex is highly stable in high concentrations of Iodine solution (It can’t be decolorized and it spoils the reaction medium). Starch indicator solutions may be synthesized in the laboratory. Alternatively, commercially available preparations are also available.

When a garment is desized, then to check the extent to which starch is removed, a few drops of starch indicator are dropped on the garment. If it changes its color to blue-black, that indicates that desizing process is incomplete and starch is still present there.

Starch

Starch or Amylum (C₆H₁₀O₅)_n) is a polysaccharide carbohydrate consisting of a huge number of glucose units joined with one another by glycosidic bonds. Starch is formed by all green plants as an energy store and is a main food source for humans.

Pure starch is a white, tasteless and odorless residue that is insoluble in cold water or alcohol. It is made up by two types of molecules: the linear and helical amylose and the branched amylopectin. Depending on the source plant, starch generally contains 20 to 25 percent amylose and 75 to 80 percent amylopectin.Glycogen, the glucose stockpile of animals, is a more branched form of amylopectin.

The word “starch” is derivative from Middle English sterchen, meaning to harden, which is appropriate since starch can be used as a thickening or glueing negotiator when dissolved in water and heated, giving wheatpaste.

In Textile it is used to decrease breaking of yarns during weaving, the warp yarns are sized. Starch is one of the main agents utilize for cotton sizing. Starch also is used as printing thickener.

Iodine solution is used to test for starch; a blue color points to the existence of starch. The details of this reaction are not yet completely known, but it is thought that the iodine (I₃^− and I₅^− ions) fits inside the twirl of amylose, the charge transfers between the iodine and the starch, and the energy plane spacing’s in the resulting complex match to the absorption spectrum in the visible light region. The strength of the resultant blue color depends on the amount of amylose present.

Starch indicator solution containing of water, starch and iodine is regularly used in redox titrations: in the existence of an oxidizing agent the solution turns blue, in the presence of reducing agent the blue color vanish because triiodide (I₃^−) ions break up into three iodide ions, dis-assembling the starch-iodine complex. A 0.3% w/w solution is the typical concentration for a starch indicator. It is made by accumulation 4 grams of soluble starch to 1 litre of heated water; the solution is cooled prior to use keep in mind that starch-iodine compound becomes unstable at temperatures above 35 °C).

Cotton

Cotton is the most common textile fiber. Almost three quarter of our textile fabrics are made from cotton. Cotton is also blended with other natural as well as man made fibers to develop a variety of Textiles. At present, almost sixty countries of the world are producing cotton. Cotton fabrics were made by the ancient Egyptians and by the earliest of Chinese civilizations using different techniques. Samples of cotton fabrics have been found in Indian tombs dating back to year 3000 B.C. There is no doubt about the fact that spinning and weaving of cotton was started by Indians. Later, this technique was adopted by European countries. It is natural cellulosic fiber. It has hairy growth on the seeds of plant named Genus Gossipium which is cultivated in tropical areas.

a)  Cotton Crop:

The cotton is an annual crop. It is sown in March to April and the crop is ready to be picked in September to October.

b)  Formation of Fiber:

Cotton seed is sown in spring. After two to three months, many creamy white flowers appear, which turn pink towards the end of the first day. On the third day, the flower dies to leave a small green seed pot or ball. After a few days, fibers start growing around the cotton seed. The growth of cotton fibers carries on throughout the ball ripening period. Each cotton seed may produce as many as twenty thousand fibers on its surface and a single ball contains about 150,000 fibers or more. The ball itself is called fruit.

c)  Fiber Growth:

For the first six days, the growth of young cotton fiber is comparatively slow. For the next 15 days, it is much more rapid. Then, for the next three days, it grows more slowly until the length wise growth come to sudden stop. During the period of rapid growth, the cotton fiber is in state of a thick walled tube of cellulose with one end attached to the seed. After the stoppage of length wise growth , the cell opens and the finer is ready to be picked in a few days.

d) Picking of Cotton:

Cotton picking is carried out by hands during the autumn. As the balls on the plant do not mature all at the same time, field has to be picked, over several times. Mechanical picking has also been developed but it is not in universal use.

Many varieties of cotton plant are grown commercially in different areas of the world, under a wide range of growing conditions. As a result, there are many different grades and qualities of cotton which vary widely in their properties and characteristics.

The assessment of cotton is a difficult job, requiring great experience and skill. In general, quality is linked directly to the fiber length. Cotton is specified into following categories with respect to its fiber length.   Â

Varieties of Cotton

Sr. #.	Fiber Length in inch	Quality	Country
1	1 to 2.5	Fine Quality	Egypt, USA
2	0.5 to 1.30	Medium Quality	USA, Peru
3	0.4 to 1	Coarse Quality	Pakistan, China, India

Properties:

i. Texture:

                  It is a comfortable fiber with soft hand.

ii. Burning Properties:

                  It burns with papery smell without forming beads. Scorching begins above 210⁰C.

iii. Effect of acids and alkalis:

                  It is severely attacked by acids. Dilute alkalis have no effect on it. Conc. Alkalis reduce its strength.

iv. Solubility:

                  It dissolves in 80% Sulphuric acid cold.

v. Moisture Regain:

                  8.5 %

vi. Absorbency:

                   It has good absorbency.

vii. Dyeability:

                   It can be dyed and printed with a variety of dyes and has good fastness properties.