Nitrocellulose is produced by nitric acid reacting with cellulose. Nitrocellulose is nontoxic but highly flammable. It is classified as an explosive when nitrogen content exceeds 12.6 percent. Used since the 19th century, nitrocellulose is a multiuse chemical employed across many industries. Different nitrogen content in various formulations allows nitrocellulose to be used in pharmaceuticals, paint, lacquers, plastics, explosives and propellants
Nitrocellulose is an explosive compound produced by the reaction of cellulose and nitric acid, or other strong nitrating agent. Nitrocellulose can appear as a pulpy, cotton-like solid when dry. It is a clear liquid to semisolid when dissolved in alcohol, acetone or an ether-alcohol mixture. The low-nitrogen form of nitrocellulose is soluble in acetone and an ether-alcohol mixture. The explosive, high-nitrogen form is soluble in acetone, but not in ether-alcohol mixtures. Nitrocellulose has a flash point of 12.7 degrees C (55 degrees F) and an autoignition temperature of 170 degrees C (338 degrees F).
Types of Nitrocellulose
Nitrocellulose characteristics vary according to the source of cellulose, the strength of reacted acid, the temperature of reaction, the time of reaction and the acid to cellulose ratio. Nitrogen content, varying from 10 to 14 percent, can be produced by controlling the components and conditions of reaction. Variations in nitrogen content give different characteristics to each formulation. Nitrocellulose with nitrogen below 12.3 percent is used for lacquers, coatings and inks. Nitrogen content above 12.6 percent is considered an explosive.
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Nitrocellulose is a flammable solid and presents a moderate explosion hazard. In the dry state, exposure to heat or strong oxidizers poses an extreme fire hazard. Wet nitrocellulose exhibits the flammability characteristics of the solvent it is in, similar to gasoline. Nitrocellulose exhibits low toxicity.
Benefits of Nitrocellulose
Nitrocellulose is used in explosives, rocket propellant, lacquer, flash paper, smokeless gunpowder, leather finishing, as a printing ink base, in coating bookbinding cloth, in laboratory testing films, in ping-pong balls, in pharmaceuticals and in celluloid used for early x-ray, photographic and movie film. Mixed with nitroglycerin, nitrocellulose is used as a blasting agent and a rocket propellant. High-gloss automotive finishes often are made with nitrocellulose lacquer. Compound W® contains nitrocellulose to carry the salicylic acid used to treat warts.
History of Nitrocellulose
Nitrocellulose was discovered by French chemist Henri Braconnot in 1832. He formulated the compound by combining nitric acid with wood fibers or starch. The nitrocellulose was an unstable, lightweight, combustible explosive. In 1846, a German-Swiss chemist, Christian Shönbein, discovered an easier method of synthesizing nitrocellulose. He accidentally spilled concentrated nitric acid on a table. He used a cotton apron to clean up the spill. He hung the apron on a stove to dry. When dry, the apron flashed and exploded. Shönbein refined the process to soaking cotton in a mixture of nitric and sulfuric acids. Nitric acid (2HNO3) converts cellulose (C6H10O5) into cellulose nitrate (C6H8(NO2)2O5) and water. Sulfuric acid was added to prevent the water formed from diluting the nitric acid. The cotton was rinsed in water to stop the reaction and dried slowly at 100oC (212oF) to prevent ignition. This was the predominant method of nitrocellulose synthesis. The nitrocellulose produced in this way could be used as a blasting agent. It was more powerful than gunpowder as a propellant. Yet, it was highly sensitive and hard to handle. British chemists refined nitrocellulose synthesis to reduce its sensitivity during handling. In 1889, Eastman Kodak used nitrocellulose to formulate a flexible film base. This film was used mostly for x-rays. The ever-present hazard of combustion led to the replacement of this film in 1933. Nitrocellulose was used as a coating for billiard balls when ivory became scarce in the 1920s. The use of these billiard balls was stopped after they were discovered to be highly flammable and, in some circumstances, explosive.