Nitrocellulose
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Nitrocellulose (Cellulose nitrate, guncotton) is a highly flammable compound formed by nitrating cellulose (e.g. through exposure to nitric acid or powerful nitrating agent).
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Uses
- Nitrocellulose is a major component of smokeless gunpower.
- Photographic film
- Nitrocellulose paper is a sticky membrane used for Western blots and immobilizing DNA.
- When dissolved in ether or other organic solvents, the solution is called collodion, which has been used as a wound dressing and carrier of topical medications since the U.S. Civil War.
- Collodion was also used as the carrier for silver salts in some very early photographic emulsions, particularly spread in thin layers on glass plates. To this day it is used in Compound W Wart Remover as a carrier of salicylic acid, the active ingredient.
- Magician's "flash paper", sheets of paper or cloth made from nitrocellulose, which burn almost instantly, with a bright flash, and leave no ash.
- Nail polish
Guncotton
Henri Braconnot, a French chemist, discovered in 1832 that nitric acid, when combined with starch or wood fibers, would produce a lightweight combustible explosive material which he named Xyloïdine. A few years later in 1838 another French chemist, Theophile Jule Pelouze, treated paper and cardboard in the same way. He obtained a similar material he called Nitramidine. Both of these substances were highly unstable, and were not practical explosives.
However, Christian Friedrich Schönbein, a German-Swiss chemist, discovered a more practical solution around 1846. He was working in the kitchen at his home in Basle when he spilled a bottle of concentrated nitric acid on the kitchen table. Immediately he reached for the nearest cloth, a cotton apron, and wiped it up. He hung the apron on the stove door to dry, and as soon as it dried there was a flash and the apron had exploded. His preparation method was the first to be widely imitated - one part of fine cotton wool to be immersed in fifteen parts of an equal mix of sulphuric and nitric acids. After two minutes the cotton was removed and placed in cold water and washed to set the esterification level and remove all acid residue. It was then slowly dried at a temperature of less than 100 °C.
The process uses the nitric acid (2HNO3) to convert the cellulose (C6H10O5) into cellulose nitrate (C6H8(NO2)2O5) and water. The sulphuric acid is present to prevent the water produced in the reaction from diluting the concentrated nitric acid.
The power of guncotton meant that it was adopted for blasting. As a projectile force, it has around six times the gas generation of an equal volume of gunpowder and produces less smoke and less heating. However the sensitivity of the material during production led to the British, Prussians and French discontinuing manufacture within a year.
Further research indicated that the key was the very careful preparation of the cotton: unless it was very well cleaned and dried it was liable to explode spontaneously. The British, led by Abel, also developed a much lengthier manufacturing process, with the washing and drying times each extended to 48 hours and repeated eight times over. The acid mixture was also changed to two parts sulfuric acid to one part nitric acid.
Guncotton remained useful only for limited applications. For firearms, a more stable and slower burning mixture would be needed. Guncotton-like preparations were eventually prepared for this role, known at the time as smokeless powder.
Nitrate Film
Nitrocellulose itself was used as the first flexible film base beginning with Eastman Kodak products in August, 1889. It was used until 1933 for X-ray films, where the hazard of its flammability was most acute, and continued to be used for motion picture films until 1951. It was replaced by safety film, with an acetate base. The use of nitrocellulose film for motion pictures led to the widespread requirement for fireproof projection rooms with wall coverings made of asbestos. A cinema fire caused by ignition of nitrocellulose film stock (foreshadowed by an earlier small fire) was a central plot element in the Italian film Cinema Paradiso. Nitrocellulose film base manufactured by Kodak can be identified by the presence of the word "Nitrate" in (usually) red letters between perforations; acetate film manufactured during the era when nitrate films were in use was marked "safety" or "safety film" between perforations in (usually) yellow letters.
Color negative film was never manufactured with a nitrate base, nor was 8mm or 16mm motion picture film.
Other Uses
Depending on the manufacturing process, the nitrocellulose is esterified to a varying degree. Table tennis balls and some photographic films, for example, have a fairly low esterification level and burn rather slowly with some charred residue. See celluloid.
The first cine films were made using nitrocellulose; decades later, it was discovered that nitrocellulose gradually decomposed, releasing nitric acid, which further catalysed the decomposition. Salvaging old films which were undergoing this accelerating self-catalysed disintegration became a major problem for film archivists. See film preservation. Low temperatures can delay these reactions indefinitely.
See also
fr:Nitrocellulose it:Nitrocellulosa nl:Schietkatoen ja:ニトロセルロース pl:Nitroceluloza sl:Nitroceluloza sv:Bommulskrut