Chemical composition of cotton

Native cotton is the purest form of natural cellulose. However usual constituents of a vegetable cell. The contents are proteins, oil and wax, pentose and pectin’s, mineral matters and natural colouring matters

The percentage of impurities of cotton depends upon the origin. i.e. the type of cotton and its maturity. In general, immature cotton has more impurities than mature cotton. The impurities are mostly located on the outer side of the fibre. composition of dry cotton Chemicals Composition ( % ) Cellulose Protein

Cellulose Native cotton contains maximum amount of cellulose in its purest form. Cellulose is composed of glucose molecules, which are arranged in starch manner. In cotton fibre, cellulose is not combined with lignins or pectin’s. cotton cellulose contains about 12,000 to 18,000 glucose residues in its macromolecule. The molecular weight of the cellulose present in cotton is approximately 2 million.

Protein

The proteins in cotton fibre are of vegetable protein. As usual, the proteins are polypeptides and amino acids. The proteins are mainly concentrated in the primary wall and lumen of the fibre .The amount varies between 1-2 % .The colour of the cotton may be due to its protein content.

Oil and wax

Waxes are hydrophobic substances acting as protective coatings on the surface of the fibre. These are basically very complex substances of high molecular weight glycerides and fatty acids present either in free or in esterified form. These are located mainly in the cuticle and in the primary wall of the fibre. The glycerides can easily be saponifiable. the melting point of waxes varies between 68° C to 80° C. Because of the waxes, it is difficult to.wet cotton. Waxes are generally converted into soaps during scouring treatment in alkali solution.

Pectin’s

Cotton fibre contains about 0.4-1.5 % pectin .These are primarily calcium , magnesium and iron pectates with some free pectic acid and methyl pectate. These are carbohydrates similar to cellulose and their esterified form is soluble in water. The free acid and its calcium and magnesium salts soluble in water but they will be converted into soluble product by alkali hydroxides or soda ash. So these can be removed during alkali boiling or scouring of the cotton material.

Minerals

Cotton contains about 0.7-1.6 % mineral matter which is left as ash after cotton is burnt. Due to soil and atmospheric impurities and at the time of bursting of the pod, the mineral matter is added to the impurities on the outside surface of cotton fibre. The mineral matter consists of chlorides, carbonates and sulphates of potassium, calcium and magnesium. The total amount of mineral matter present in the fibre may be reduced by' simply boiling the cotton fibre in water.