What are the uses of industrial sodium hydroxide?

Sodium hydroxide (also known as caustic soda, caustic soda, or caustic soda) is an inorganic compound with the chemical formula NaOH. Solid sodium hydroxide can be divided into flake and granular forms based on its properties, commonly known as flake alkali and granular alkali. They have strong alkalinity and extremely corrosive properties. It can be used as an acid neutralizing agent, a masking agent, a precipitant, a precipitation masking agent, a coloring agent, a saponification agent, a peeling agent, a detergent, etc. It is widely used in various industries such as chemical, papermaking, printing and dyeing, electricity, agriculture, metallurgy, medicine, and food. So, what are the specific uses of sodium hydroxide in industry?

1、 Refined petroleum

After being washed with sulfuric acid, petroleum products still contain some acidic substances that must be washed with sodium hydroxide solution and then washed with water to obtain refined products.

2、 Printing and dyeing industry

In the printing and dyeing industry, when dyeing cotton fabrics, it is necessary to remove the coverings on the surface of the cotton fibers, such as wax, oil, pectin, etc., by soaking and steaming with dilute alkaline solution at an appropriate temperature to remove impurities. In order to allow the dye to penetrate deep into the inner layer of the fiber during dyeing, it should also be expanded and softened before dyeing. Short term treatment with concentrated caustic soda solution can orient fiber molecules and increase the silky color of the fabric. After this treatment, the fine fibers (cotton wool) on the surface of the fibers can be corroded by caustic soda, making the dyeing more uniform and avoiding uneven patches. The cotton printing and dyeing industry requires a large amount of caustic soda. In the process of reducing dye dyeing, caustic soda solution and sodium hydrosulfite are first used to reduce it to leuco acid. After dyeing, it is then oxidized to its original insoluble state with an oxidant.

3、 Textile fibers

1. Textile cotton and linen fabrics are treated with concentrated sodium hydroxide (caustic soda) solution to improve fiber properties. Artificial fibers such as synthetic cotton, synthetic wool, synthetic silk, etc. are mostly viscose fibers. They are made from cellulose (such as pulp), sodium hydroxide, and carbon disulfide (CS2) as raw materials, and are processed into viscose liquid, which is then spun and solidified.

2. The adhesive fiber first needs to be impregnated with 18-20% caustic soda solution to make it alkaline cellulose. Then, the alkaline cellulose is dried and crushed, and carbon disulfide is added. Finally, the sulfonic acid salt is dissolved in dilute alkaline solution to obtain the adhesive solution. After further filtering and vacuuming (to remove bubbles), it can be used for drawing silk.

4、 Paper industry

The main raw materials for papermaking are wood or grass, which contain not only cellulose but also a considerable amount of non cellulose (lignin, gum, etc.). Mechanical methods can be used to separate fibers by grinding with grinding stones. The fibers of this pulp are short, and the paper produced is easy to break, but the cost is low. Alternatively, chemical methods can be used to process the raw materials by steaming them with ferrous sulfate or alkaline solution. By taking advantage of the characteristic that dilute alkali cannot react with cellulose and can corrode and dissolve non cellulose components, pulp with cellulose as the main component can be produced. This type of pulp has long fibers and strong tensile strength when producing paper, but it comes at a high cost. If two types of pulp are mixed in a certain proportion, high-quality and low-cost paper can be produced.