How is cuprammonium rayon made?
The process of manufacturing cuprammonium rayon from cellulose is mentioned below:
• Preparation of Schweitzer’s Solution: To make Schweitzer’s solution basic Cupric Carbonate is mixed with liquid ammonia. In this solution, the carbonate reacts with liquid ammonia to form a solution of tetra-ammine cupric hydroxide which is deep blue in color. After this, through the filtration process, the remaining copper carbonate was removed from the solution.
• Preparation of cellulose: Cotton linters pulp or wood pulp are the raw materials that are used for making cuprammonium rayon. But before proceeding to the next stage of manufacturing, the purification of cotton linters is carried out. It is done in two stages:
Mechanical Treatment: The transportation of cotton linters are done by compressing them into bales and packing them in a highly compressed state. The main objective of mechanical treatment is to loosen up the cotton bales and impurities such as dust, sand particles, seed residues, etc.
Chemical Treatment: The loosen up cotton linters are mixed with diluted soda ash solution with a small amount of caustic soda. This solution is boiled for several hours under high pressure. This process is done to convert the natural fatty matter present in the cotton into soluble substance with the reaction of soda ash. And then these soluble substances are removed from cotton linters.
• Copper cellulose: In the first step, these cotton linter pulp or wood pulp which is insoluble cellulose are made soluble by dissolving it in Schweitzer’s Solution which contains copper, ammonia and sodium hydroxide. This results in the formation of copper cellulose.
Then to remove the leftover chemical liquid from this copper cellulose, it is filtered, grounded completely, and then dissolved in a solution of ammonia in water.
• Spinning preparation: Then, to make this cuprammonium cellulose solution more suitable for spinning, it is mixed with certain chemical compounds like glycerine, glucose, tartaric acid, citric acid, oxalic acid, can sugar, etc.
• Spinning process: In the spinning process, the cuprammonium cellulose solution is passed through a spinneret. The spinneret is like a showerhead with very small holes. From these nozzles, threadlike fibers are extruded which are subsequently pulled and stretched to make them into very fine filaments.
• Hardening process: This is the last step of fiber formation in which the filaments of cuprammonium cellulose are passed into a solution of sulphuric acid and other types of the bath which act as the hardening agent.
This not only neutralizes the sodium hydroxide but also removes the remaining copper and ammonia from the fibers and reconstructs the cellulose.