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
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.
