What is Nitrocellulose?

Nitrocellulose (NC), also known as cellulose nitrate, nitrocellulose, or gun cotton, is a crucial high-energy polymer material. It is mainly used in solid propellants and as a key component in energy applications. Nitrocellulose is a semi-rigid chain derived from natural polymers. Highly nitrated nitrocellulose, which contains more than approximately 12.5% nitrogen, transforms into a fluffy white substance upon drying, also referred to as nitrocellulose. Due to its extreme sensitivity to heat, even carefully processed samples of nitrocellulose may ignite spontaneously if exposed to temperatures exceeding 150°C (300°F) for a short period. Nitrocellulose is extensively used in gunpowder, solid rocket propellants, and explosives. Medium nitrated nitrocellulose, with a nitrogen content between 10.5% and 12.5%, although still combustible, has less intense burning characteristics than highly nitrated nitrocellulose and can dissolve in alcohols and ethers. This type of nitrocellulose, known under various names such as nitrocellulose and gun cotton, is used as a film-forming agent in solvent-based coatings, protective coatings, and nail polishes.

Characteristics

Nitrocellulose formula is (C6H7N3O11)n, Nitrocellulose structure:

The basic properties of nitrocellulose are outlined in the table below:

Nitrocellulose is known by many names, such as cellulose nitrate, nitrocellulose, and gun cotton, among others. However, these names are often used incorrectly. Due to its fluffy, almost white appearance, nitrocellulose products are commonly referred to as "cotton" in various terms, including lacquer cotton, celluloid cotton, and gun cotton.

What is Nitrocellulose Lacquer?

Nitrocellulose lacquer is made from the nitrate ester of cellulose, also known as cellulose nitrate ester. Fluffy white material also called nitrocellulose. Early cellulose sources included cotton or its by-products, Nitrocellulose is also known as "nitrocellulose." Besides cotton, wood cellulose and other cellulose sources are also used. Nitrocellulose is produced by reacting cellulose hydroxyl groups with nitric acid in the presence of a dehydrating agent like sulfuric acid. Depending on performance requirements, formulations and processes can produce various nitrate esters with different nitrogen content, such as mono-nitrate, di-nitrate, and tri-nitrate, with nitrogen contents of 6.76%, 11.11%, and 14.14%, respectively. Nitrocellulose used in lacquers has a nitrogen content ranging from 10.5% to 12.2%. These coatings are referred to as nitrocellulose ester coatings, commonly known in the industry as "nitrocellulose lacquers" or "nitrocellulose paints."

Nitrocellulose lacquers are valued for their ease of application, quick drying time, excellent flow properties, good adhesion, smooth and shiny appearance, strength, weather resistance, and good pigment dispersion. They have been widely used in automotive applications (especially automotive primers and repairs), woodwork, engineering machinery, metals, foils, plastic films, leather, toys, and printing inks. With the advent of more durable acrylic coatings, nitrocellulose automotive paints have been gradually replaced. Nitrocellulose lacquers are now primarily used in woodwork, plastics, and leather. Since these coatings are often applied by spraying, they are referred to as "lacquers" in general English literature, unless otherwise specified, indicating nitrocellulose lacquers.

How to make nitrocellulose?

The preparation of nitrocellulose involves a typical esterification reaction using esterifying agents, cellulose, and concentrated sulfuric acid. Common esterifying agents include HNO3 or N2O5. The reaction mechanism is as follows: Nitric acid reacts with the hydroxyl groups (-OH) of cellulose, removing hydrogen atoms (-H) to form water molecules. Nitro groups (-NO2) bind to the cellulose side chains, forming ester groups (-COOR), resulting in nitrocellulose. The reaction formula is:

In the formula, -R represents groups other than hydroxyl groups in cellulose. Due to the oxidative hydrolysis that accompanies nitration, using pure nitric acid is costly and does not yield high-nitrogen nitrocellulose with satisfactory quality and solubility. Therefore, in practical production, a mixture of sulfuric and nitric acids is used. Sulfuric acid serves to: catalyze the formation of nitro groups; swell the cellulose, accelerating the chemical reaction; absorb water, driving the reaction forward; enhance the stability of the product.

References

[1] Liu Guojie, Fan Sen. Current Status and Development Trends of Nitrocellulose in the Coatings Industry [J]. China Coatings, 2014, 29(2): 7-12. DOI:10.3969/j.issn.1006-2556.2014.02.004.
[2] Cao Xiaoxue. Molecular Dynamics Simulation of Plasticizer/Nitrocellulose Performance [D]. Shanxi: North University of China, 2022.
[3] Ren Zhi, Li Xiaojiang. Research Status and Prospects of Nitrocellulose Modification [J]. Chemical Propellants and High Polymer Materials, 2014, 12(5): 48-51.
[4] https://www.britannica.com/science/nitrocellulose

[5] https://en.wikipedia.org/wiki/Nitrocellulose