Cellulose Nitrate

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Cellulose Nitrate

OVERVIEW

Cellulose nitrate (SELL-you-lohs NYE-trate) is a derivative of cellulose made by adding nitric acid (HNO₃) to cellulose. Its physical properties tend to differ somewhat depending on the relative amount of nitrogen present in the compound. For example, the so-called "high nitrogen" form is soluble in both acetone but insoluble in an alcohol/ether mixture. The "low-nitrogen" form is soluble in both solvents. Cellulose nitrate is available in a variety of forms, ranging from colorless to white flakes or powder to a liquid or semi-solid gel-like material.

KEY FACTS

OTHER NAMES:

Nitrocellulose; nitrocotton; guncotton; pyroxylin

FORMULA:

C₁₂H₁₆N₄O₁₈

ELEMENTS:

Carbon, hydrogen, nitrogen, oxygen

COMPOUND TYPE:

Carbohydrate polymer (organic)

STATE:

Solid

MOLECULAR WEIGHT:

Varies, but very large

MELTING POINT:

Not applicable; ignites at about 170°C (340°F)

BOILING POINT:

Not applicable

SOLUBILITY:

Insoluble in water, alcohol, ether, and most organic solvents; also see Overview

Cellulose nitrate was first discovered in 1845 by the Swiss-German chemist Christian Friedrich Schönbein (1799–1868). The story is told that Schönbein used his wife's cotton apron to clean up some nitric acid that he had spilled on his laboratory floor. He was amazed to discover that the cotton and nitric acid reacted to form a new compound that exploded when heated, releasing a puff of black smoke. He immediately recognized the potential application for the new material as an explosive and suggested the name guncotton for it. He developed a more efficient method for making the product and, within a short period of time, guncotton had become very popular as an explosive for both construction and military purposes.

Researchers soon found that modifying the way in which cellulose nitrate is prepared could significantly change its chemical and physical properties, and, therefore, its uses. For example, the British inventor Alexander Parkes (1813–1890) experimented with using a variety of solutions to dissolve cellulose nitrate, after which the material could be precipitated in one or another form. At first he called the reformulated cellulose nitrate "synthetic ivory," because of its similarity to natural ivory, but later referred to the product as parkesine, named after himself. He was unable to obtain financing needed for the commercial manufacture of his invention, however, and it fell to an American inventor, John Wesley Hyatt (1837–1920) to reinvent a similar product less than a decade later. Hyatt and his brother Isaiah developed a mixture of cellulose nitrate and camphor that was an even more satisfactory substitute for ivory than was Parke's parkesine. The Hyatts obtained a patent for their new product, to which they gave the name celluloid. Originally developed to meet a growing demand for an ivory-like material that could be use to make billiard balls, celluloid eventually had a number of other applications, including false teeth and photographic film.

Interesting Facts

Cellulose nitrate was first used for the manufacture of photographic film in 1889 by the Eastman Kodak company. Films made in that era are highly unstable, with a tendency to catch fire spontaneously. Efforts are now under way to protect and preserve some classic motion pictures originally captured on cellulose nitrate film that are unlikely to survive for many more years without such treatment.
Although the Hyatt billiard balls made out of celluloid were very popular at first, they had one serious disadvantage: They had a tendency to explode upon contact with each other.
Items of clothing made from cellulose nitrate in the late nineteenth century were sometimes known as "mother-in-law" clothing. They were so flammable that some people thought that the item of clothing along with a cigarette lighter was the perfect gift for an unappreciated mother-in-law.

HOW IT IS MADE

Cellulose nitrate is produced in essentially the same way as it was (albeit accidentally) by Christian Schoönbein in 1845. A mixture of nitric acid and sulfuric acid are added to cellulose in one of various forms (as wood pulp, powder, flakes, or a colloidal mixture with water, for example). The properties of the product formed depend on the relative quantities of each reagent used and the conditions under which the reaction is carried out. One of the most important variables is the amount of nitrogen present in the cellulose nitrate formed. The more nitrogen present, the less stable the compound is and the more appropriate it is for use as an explosive. The less nitrogen present, the more stable the compound, and the more suitable it is for household and commercial applications.

COMMON USES AND POTENTIAL HAZARDS

Cellulose nitrate continues to be used as an explosive, most commonly in a product known as smokeless gunpowder. The name comes from the fact that, when ignited, the compound produces less smoke than is the case with most other explosives. Smokeless gunpowder is used primarily for smaller weapons, such as artillery rockets and projectiles. A solution of cellulose nitrate dissolved in ether, known as collodion, has been used for a number of applications since its discovery independently in 1846 by the French chemist Louis-Philippe Ménard (dates not available) and the American physician Dr. J. P. Maynard (dates not available). These uses include the coating of wounds; preparation of bandages, surgical dressings, and other medical paraphernalia; the production of photographic film; and the manufacture of laboratory equipment and devices. Cellulose nitrate is also used as a coating material in fast-drying automobile lacquers, on the cloth used to cover hardbound books, and as a leather covering.

Cellulose nitrate poses two major health risks. First, old film made of cellulose nitrate has a tendency to deteriorate and decompose. That process results in the release of oxides of nitrogen, which may be toxic to a greater or lesser degree. This problem is of special concern to people who have occasion to work with old films, but not usually to the general public. Second, cellulose nitrate is a very flammable material that ignites when exposed to even minimal flames or sparks. Most products that contain cellulose nitrate today have been treated to minimize that risk. However, products that were made many years ago do not have the same protection and may pose safety risks to people who come into contact with them.

FOR FURTHER INFORMATION

"Caring for Cellulose Nitrate Film." Conserve O Gram. http://www.cr.nps.gov/museum/publications/conserveogram/14-08.pdf (accessed on September 30, 2005).

"Cellulose Nitrate." Conservation and Art Material Encyclopedia Online. http://www.mfa.org/cameo/frontend/material_description.asp?name=cellulose+nitrate&language=1 (accessed on September 30, 2005).

"DiscoverLight™ Membrane." Pierce Biotechnology. http://www.piercenet.com/files/5186.pdf (accessed on September 30, 2005).

Fox, Berry. "Not Fade Away." New Scientist (March 1, 2003); 40.

"Nitrocellulose-Applications, Characterisation, Production and Storage." Bayer Material Science. http://www.azom.com/details.asp?ArticleID=2785 (accessed on September 30, 2005).

Chemical Compounds