Chemical Properties of Cotton Fiber:
Cotton fiber, as it is picked from the plant is about 94 per cent cellulose. The remaining 6 percent is made up of protein, pectic materials, mineral substances, wax and small amounts of organic acids, sugars and pigments. Much of this non cellulosic material is removed from cotton by scouring and bleaching processes, leaving a fiber that consists of about 99 per cent cellulose.
The purification of cotton cellulose provides a stronger and white fiber which absorbs moisture more readily. The natural wax has a useful lubricating effect during spinning, however and most cotton is spun with its wax still present in the fiber.
Analyses of fibers from different sources have shown that the amount of wax, pectin and protein increases with increasing immaturity of the fiber. Cotton is highly resistant to the chemicals encountered in normal use. Dyestuffs, mild bleaching agents and similar materials have no significant deleterious effects on cotton fabrics if used with reasonable care. Cotton is attacked by strong oxidizing agents, including hydrogen peroxide and chlorine bleaching compounds.
The purity of scoured and cleaned cotton and the chemical stability of cellulose together make cotton into a remarkably durable material.
Effect of Acids:
Cotton is attacked by hot dilute acids or cold concentrated acids, in which it disintegrates. It is not affected by cold weak acids.
Effect of Alkalis:
Cotton has an excellent resistance to alkalis. It swells in caustic alkali but is not damaged. It can be washed repeatedly in soap solutions without taking harm.
Effect of Organic Solvents:
There are very few solvents that will dissolve cotton completely. It has a high resistance to normal solvents but is dispersed by the copper complexes cuprammonium hydroxide and cupriethylene diamine and by concentrated sulphuric acid.
Cotton is not attacked by moth grubs or beetles.
Cotton is attacked by fungi and bacteria. Mildews, for example will feed on cotton fabric, rotting and weakening the material. They have a characteristic musty smell and stain the fabric with naturally produced pigments.
Mildews are particularly troublesome on cotton that has been treated with starchy finishes and much of the damage can be avoided by thorough scouring. The pure cellulose is a less attractive food for mildew than the starch.
Mildews and bacteria will flourish on cotton under hot, moist conditions. When cotton fabrics are to be used under conditions favorable to attack by micro-organisms, they can be protected by impregnation with certain types of chemical. Copper compounds such as copper naphthenate will destroy organisms that would otherwise attack the cotton cellulose.