Caustic soda is mainly used in textile in the form of caustic soda flakes or pearls. It is also known as sodium hydroxide, has a white solid appearance and a formula of NaOH. It is an inorganic alkali salt, hygroscopic in nature and is soluble in water and polar solvents. It has a slippery feel and also absorbs carbon dioxide in the atmosphere to from sodium carbonate.
Being a base, it will undergo neutralization reaction with acid and form relevant salt and water. It will also corrode metals such as aluminum, generating hydrogen gas that has potential to behave as an explosive gas. Caustic soda also has decomposing effects on proteins and may penetrate deep tissues.
By reacting sodium carbonate with calcium hydroxide, the reaction yields sodium hydroxide and calcium carbonate. Since sodium hydroxide is soluble while calcium carbonate is not, by doing filtration, calcium carbonate can be easily removed to obtain a crude solution of sodium hydroxide. This solution is then purified, processed and standardized for industrial consumption.
With the electrolysis of sodium chloride solution, solid sodium hydroxide is manufactured and obtained with the evaporation of water. Chlorine gas is also produced as a main by-product. Electrolysis occurs through three main types of cells, mainly mercury cell, diaphragm cell and membrane cell.
Caustic soda is used in the manufacturing of textile. Caustic soda is used in the scouring process, mercerization process, as well as dyeing process. During the process of scouring, it aids in the removal of natural oil, wax and fat. During the process of mercerization, it aids in improving the tensile strength, smoothness and dye substantively of the cellulosic. Caustic soda also serves as a pH regulator and controls the pH of dyeing bath, which is required to be precise and constantly maintained throughout the process.
Caustic soda is also used in pulp and paper industry during the cooking process and oxygen delignification process. Both sulfate and sulfite pulps are purified by removing lignin compounds in the caustic extraction stages of multistage bleach plants. In some kraft mills, caustic soda is also used as a makeup chemical. It is also used as the initial treatment in deinking secondary fibers.
It is also used to manufacture soap and detergents, applied during the saponification process in soap industry and neutralization process in detergent industry. Caustic soda saponifies fats into water soluble sodium-based soaps.
In addition, caustic soda helps to extract alumina from bauxite ore via Bayer process and is employed to produce an array of organic and inorganic chemicals.