Sodium hydroxide, chemical formula NaOH, commonly known as caustic soda or lye, is a strong inorganic base with strong corrosiveness. As a fundamental chemical raw material, it finds wide application in industrial production, daily life, environmental protection, and many other fields. Owing to its unique physicochemical properties, it has become an indispensable core material in modern industrial systems.
I. Physicochemical properties of sodium hydroxide
The application value of sodium hydroxide is closely related to its unique physicochemical properties. Its physical and chemical characteristics jointly determine its suitability for various scenarios; they complement each other and form the basis of its widespread use. These properties can be divided into the following two categories:
1. Physical properties
Pure sodium hydroxide is a colorless transparent crystalline solid. Industrial‑grade products, due to the presence of small amounts of sodium chloride, sodium carbonate, and other impurities, usually appear as white opaque solids, available in various forms such as lumps, flakes, granules, and rods, which can be flexibly selected according to the usage requirements of different industries, facilitating storage and feeding operations. The core physical characteristics are as follows and serve as the fundamental prerequisites for application in various industries:
① Solubility: Extremely soluble in water, releasing a large amount of heat during dissolution. Solubility increases significantly with temperature: about 111 g per 100 g water (approximately 1110 g/L) at 25 °C, and about 347 g per 100 g water (approximately 3470 g/L) at 100 °C. It is also soluble in ethanol and glycerol, but insoluble in acetone, ether, and other organic solvents. This property makes it convenient to prepare alkaline solutions of different concentrations, flexibly meeting various needs such as chemical reactions, cleaning, and pH adjustment, and is the key physical basis for its wide application.
② Hygroscopicity: It has strong hygroscopicity. When exposed to air, it rapidly absorbs moisture and deliquesces; it also absorbs carbon dioxide from the air and deteriorates, forming sodium carbonate, which reduces purity. Therefore, sodium hydroxide must be stored in sealed corrosion‑resistant containers, protected from air contact, to ensure its effectiveness and safety. This is also a critical point to note during storage and transportation.
③ Other properties: Density 2.13 g/cm³, melting point 323 °C, boiling point 1388 °C. It has high thermal stability; upon heating to melting, it volatilizes without decomposition. Its aqueous solution is strongly alkaline, with a 1 mol/L solution having a pH of 14. It turns litmus blue and phenolphthalein red, visually indicating its alkalinity, which also provides an intuitive basis for applications such as acid‑base regulation and neutralization reactions.
II. Multi‑industry applications of sodium hydroxide
As a basic chemical raw material, sodium hydroxide is used in many fields including industry, daily chemicals, food, environmental protection, and medicine. Different industries have developed diverse applications based on its physicochemical properties, serving both industrial production and people’s livelihoods. Meanwhile, with the industry’s green transformation, its applications are becoming more efficient and environmentally friendly, as detailed below:
1. Industrial production fields
The industrial sector is the main application area for sodium hydroxide. Its strong alkalinity and reactivity make it a core raw material for many sub‑industries, supporting the normal operation of industrial production while also playing an important role in the industry’s green transition:
① Paper industry: Used as a key chemical in the pulping process, for cooking raw materials, decomposing lignin and impurities in wood, reeds, and other materials, and separating pure cellulose, laying the foundation for producing white, tough paper. The use of sodium hydroxide greatly improves cellulose separation efficiency and is one of the indispensable key raw materials in the paper industry; without it, efficient separation and purification of cellulose would be difficult to achieve.
② Textile industry: Used for desizing, scouring, and mercerizing cotton fabrics, removing impurities, oils, and natural pigments from the fabric surface, making the fabric whiter and softer to the touch, while also enhancing gloss and dyeing uniformity, reducing dyeing defects. This application is widely used in the processing of cotton, linen, viscose, and other textile fibers, and is a key step in improving product quality in the textile industry.
③ Petroleum refining: Used to neutralize acidic impurities in petroleum, adjust the pH of drilling mud, remove sulfides and other harmful components, improve the purity and stability of petroleum products, ensure fuel quality, reduce pollutant emissions, and support the green development of the petroleum industry. Its strong alkalinity can also be used for refining petroleum products to increase added value.
④ Metal processing: Plays a core role in alumina production (Bayer process), where it dissolves alumina in bauxite, separates impurities, and improves alumina purity. It is also used for rust removal, cleaning, and electroplating pretreatment of metal surfaces, removing oxide layers and oils, improving corrosion resistance and appearance quality, and extending service life. With the green transition, the use of high‑purity sodium hydroxide can further reduce energy consumption and impurity emissions in metal processing.
⑤ Chemical synthesis: Used as a catalyst or reactant in the synthesis of many chemicals such as borax, sodium cyanide, formic acid, oxalic acid, phenol, etc. It is a basic raw material for the fine chemical industry, supporting the production of pharmaceutical intermediates, dyes, coatings, and other products. Its strong alkalinity can accelerate reaction rates and improve synthesis efficiency, providing support for the development of the fine chemical industry.
2. Daily chemical and food sectors
Applications of sodium hydroxide in daily chemicals and food are closely related to people’s daily lives and are subject to strict usage specifications and industry standards. Industrial‑grade sodium hydroxide is strictly prohibited in food processing to ensure product safety and health:
① Daily chemical industry: Mainly used in manufacturing soaps, laundry powders, detergents, and other cleaning products, utilizing its saponification reaction to decompose oils and achieve soil and grease removal, suitable for household and industrial cleaning scenarios. It is also used for pH adjustment in cosmetics to ensure product stability and safety, meeting skin care needs, and must comply with relevant industry standards with strict control over concentration and residue. In addition, some strong cleaners (such as drain cleaners) contain low concentrations of sodium hydroxide to dissolve grease, hair, and other blockages.
Post time: Jul-30-2026
