All About Nitrocellulose: Manufacturing Process, Applications

12th January 2024

What is nitrocellulose?

Nitrocellulose (NC), is a product of the nitration reaction of cellulose with nitric acid. Its chemical formula is (C6H7N3O11)n, representing an organic polymer. Nitrocellulose appears as white or slightly yellow cotton-like fibers, with no distinct odor. It is soluble in organic solvents such as acetone and benzene but insoluble in water. Nitrocellulose is characterized by its resistance to dilute acids, water, and weak alkalis, making it widely used in adhesive, ink, explosives, coatings, and medical applications.

Back then, nitrocellulose was primarily used for explosives found by Braconnet in France (1832), Schoenbein in Switzerland (1845), and Parkes in the United Kingdom (1855). After the First World War, nitrocellulose with nitrogen content ranging from 10.5% to 12.2% saw rapid application in the coatings industry, particularly in automotive finishes. Nitrocellulose became a traditional and effective film-forming material for automotive paints due to its durability, strength, solubility, and rapid release of solvents under external drying conditions.

How to make nitrocellulose

In industrial production, nitrocellulose is manufactured through two main processes: batch and continuous.

Batch Production Process:

In the batch production of nitrocellulose, defatted cotton serves as the raw material, undergoing acetification with a mixed acid solution of nitric and sulfuric acids. The reaction between nitric acid, sulfuric acid, and cellulose is carefully and precisely controlled until the desired degree of nitration is achieved. Sulfuric acid is used to remove the water formed during the reaction. The resulting product, known as nitrocellulose, undergoes processes such as acid removal, stabilization, pressurized de-viscosification, dehydration, and is then mixed with a wetting agent (ethanol, isopropanol, or butanol). The final product typically available in the market contains 70% nitrocellulose and 30% alcohol wetting agent.

Continuous Production Process:

In the continuous production process, cellulose (primarily refined wood pulp) and a mixed nitration acid are continuously and simultaneously conveyed to a container where cellulose nitration takes place. After nitration, both the nitrated cellulose and the used acid are continuously transported to a centrifuge designed for sectional separation. Nitrocellulose is intermittently transferred from one section to the next. In the initial section, most of the nitrated original acid is removed. In subsequent sections, the acid in nitrocellulose is replaced by weaker acids, and in the final section, it is replaced by water. The amount of acid replaced and the water used for washing are precisely adjusted to ensure that the concentration of the recovered acid leaving the system closely matches the concentration of the used acid.

Continuous Process for Manufacture of Nitrocellulose

Continuous Process for Manufacture of Nitrocellulose

What is nitrocellulose used for?

Nitrocellulose is primarily utilized in various industries, including adhesives, inks, explosives, coatings, and medicine. In the adhesive sector, nitrocellulose serves as a solvent-based adhesive and finds extensive application in the preparation of engineering plastics. In the realm of inks, nitrocellulose enhances the rapid drying characteristics of printing inks. In the explosives field, nitrocellulose's flammability makes it a key component in terminal products such as torpedoes, smokeless explosives, and naval mines.

In the coatings industry, nitrocellulose is employed in the production of cement coatings, decorative coatings, and metal coatings. In the medical field, nitrocellulose membranes are used to manufacture testing reagents for virus antigen detection.

Nitrocellulose vs Cellulose

Nitrocellulose and cellulose are related compounds, but they differ significantly in their chemical structures and properties due to a specific chemical modification process.

  • Cellulose:

Natural Polymer: Cellulose is a naturally occurring polymer found in the cell walls of plants. It is a complex carbohydrate made up of glucose units linked together by β-1,4-glycosidic bonds.

Chemical Structure: The chemical formula of cellulose is (C6H10O5)n, and it forms long, linear chains.

Properties: Cellulose is insoluble in water and many organic solvents. It is a major component of plant cell walls and provides structural support to plants. It is not flammable and does not undergo rapid combustion.

  • Nitrocellulose:

Chemical Modification: Nitrocellulose is derived from cellulose through a chemical modification process called nitration, where cellulose reacts with a mixture of nitric acid and sulfuric acid.

Chemical Structure: The chemical formula of nitrocellulose is (C6H7N3O11)n, reflecting the addition of nitro groups to the cellulose structure.

Properties: Nitrocellulose is highly flammable and can burn rapidly. It is soluble in organic solvents such as acetone and ethanol but insoluble in water. Nitrocellulose is commonly used in explosives, coatings, inks, and medical applications due to its unique properties.

In summary, cellulose is the natural, unmodified polymer found in plants, while nitrocellulose is a modified form of cellulose obtained through the nitration process. Nitrocellulose is notable for its increased solubility in certain solvents, flammability, and applications in various industrial fields.