nitrocellulose

Nitrocellulose[1]
Other names	Cellulose nitrate; Flash paper; Gun cotton; Collodion; Pyroxylin
Identifiers
CAS number	9004-70-0 Y
Properties
Molar mass	Variable
Appearance	Yellowish white cotton-like filaments
Melting point	160–170 °C (ignites)
Hazards
Flash point	4.4 °C
LD50	10 mg/kg (mouse, IV)
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Nitrocellulose (also: cellulose nitrate, flash paper) is a highly flammable compound formed by nitrating cellulose through exposure to nitric acid or another powerful nitrating agent. When used as a propellant or low-order explosive, it is also known as guncotton.

Guncotton

Various types of smokeless powder, consisting primarily of nitrocellulose

Henri Braconnot 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 Théophile-Jules Pelouze (teacher of Ascanio Sobrero and Alfred Nobel) 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. As he was working in the kitchen of his home in Basle, he spilled a bottle of concentrated nitric acid on the kitchen table. 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 was dry, there was a flash as the apron 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 blend of sulfuric and nitric acids. After two minutes, the cotton was removed and washed in cold water to set the esterification level and remove all acid residue. It was then slowly dried at a temperature below 100 °C. Schönbein collaborated with the Frankfurt professor Rudolf Christian Böttger, who had discovered the process independently in the same year. By a strange coincidence, there was even a third chemist, the Braunschweig professor F. J. Otto, who had also produced guncotton in 1846 and was the first to publish the process, much to the disappointment of Schönbein and Böttger.^[2]

The process uses the nitric acid to convert the cellulose into cellulose nitrate and water:

3HNO₃+ C₆H₁₀O₅ → C₆H₇(NO₂)₃O₅ + 3H₂O

The sulfuric acid is present as a catalyst to produce nitronium ion, NO₂⁺. The reaction is first order and proceeds by electrophilic substitution at the C-OH centers of the cellulose.^[3]

The power of guncotton made it suitable for blasting. As a projectile driver, it has around six times the gas generation of an equal volume of black powder and produces less smoke and less heating. However the sensitivity of the material during production led the British, Prussians and French to discontinue manufacture within a year.

Jules Verne viewed the development of guncotton with optimism. He referred to the substance several times in his novels. His adventurers carried firearms employing this substance. The most noteworthy reference is in his From the Earth to the Moon, in which guncotton was used to launch a projectile into space.

Further research indicated that the key was the very careful preparation of the cotton: Unless it was very well cleaned and dried, it was likely to explode spontaneously. The British, led by Frederick Augustus Abel, also developed a much lengthier manufacturing process at the Waltham Abbey Royal Gunpowder Mills, patented in 1865, 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.

Guncotton remained useful only for limited applications. For firearms, a more stable and slower burning mixture would be needed. Guncottonlike preparations were eventually prepared for this role, known at the time as smokeless powder.

Guncotton, dissolved at approximately 25% in acetone, forms a lacquer used in preliminary stages of wood finishing to develop a hard finish with a deep luster. It is normally the first coat applied, sanded, and followed by other coatings that bond to it.

Production

In general, cotton is used as the cellulose basis, and is saturated with sulfuric acid and either nitric acid or potassium nitrate. While guncotton is dangerous to store, its risks can be reduced by storing it wet – or soaking it in nitroglycerin, which causes it to take a stable gelatinous form.^[4]

Nitrocellulose film

Nitrocellulose was used as the first flexible film base, beginning with Eastman Kodak products in August, 1889. Camphor is used as plasticizer for nitrocellulose film. It was used until 1933 for X-ray films (where its flammability hazard was most acute) and for motion picture film until 1951. It was replaced by safety film with an acetate base.

The use of nitrocellulose film for motion pictures led to a widespread requirement for fireproof projection rooms with wall coverings made of asbestos. The US Navy shot a training film for projectionists that included footage of a controlled ignition of a reel of nitrate film, which continued to burn even when fully submerged in water. Unlike many other flammable materials, nitrocellulose does not need the oxygen in the air to keep burning and once it is burning, it is extremely difficult to put out. Immersing burning film in water may not extinguish the fire and it could actually increase the amount of smoke produced.^[5] Owing to public safety precautions, the London Underground forbade transport of nitrate films on its system until well past the introduction of safety film.

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 (1988), and more recently, Inglourious Basterds (2009) and was also the cause of the 1926 Dromcolliher Cinema Tragedy in County Limerick, Ireland in which 48 people died. Today nitrate film projection is normally highly regulated and requires extensive precautionary measures including extra projectionist health and safety training. In addition, projectors certified to run nitrate films have many containment strategies in effect, among them including the chambering of both the feed and takeup reels in thick metal covers with small slits to allow the film to run through. Furthermore, the projector is modified to accommodate several fire extinguishers with nozzles all aimed directly at the film gate; the extinguishers automatically trigger if a piece of flammable fabric placed near the gate starts to burn. While this triggering would likely damage or destroy a significant portion of the projection components, it would prevent a devastating fire, which could cause far greater damage. In addition, projection rooms may be required to have automatically operating metal covers for the projection windows, preventing the spreading of a fire to the auditorium.

It was found that nitrocellulose gradually decomposes, releasing nitric acid, further catalyzing the decomposition (eventually into a still-flammable powder or goo). Decades later storage at low temperatures was discovered as a means of delaying these reactions indefinitely. It is thought that the great majority of films produced during the early twentieth century were lost forever either through this accelerating, self-catalyzed disintegration or through studio warehouse fires. Salvaging old films is a major problem for film archivists (see film preservation).

Nitrocellulose film base manufactured by Kodak can be identified by the presence of the word Nitrate in dark letters between the perforations. Acetate film manufactured during the era when nitrate films were still in use was marked Safety or Safety Film between the perforations in dark letters. Letters in white or light colors are print-through from the negative. Film stocks in the non-standard gauges, 8 mm or 16 mm, were not manufactured with a nitrate base.

The material was replaced by polyester or PET film, which is much more resistant to polymer degradation.

Uses

An M13 rocket for the Katyusha launcher on display in the Musée de l'Armée. Its solid-fuel rocket motor was prepared from nitrocellulose

• A nitrocellulose slide, nitrocellulose membrane or nitrocellulose paper is a sticky membrane used for immobilizing nucleic acids in southern blots and northern blots. It is also used for immobilization of proteins in western blots for its non-specific affinity for amino acids. Nitrocellulose is widely used as support in diagnostic tests where antigen-antibody binding occur, e.g., pregnancy tests, U-Albumin tests and CRP. Glycine and chloride ions make protein transfer more efficient.
• When the solution is dissolved in ether, alcohol or other organic solvents it produces collodion, discovered in 1846 and introduced as a wound dressing during the Crimean War. It is still in use today in topical skin applications, such as liquid skin and in the application of salicylic acid, the active ingredient in Compound W wart remover.
• In 1851, Frederick Scott Archer invented the Wet Collodion Process as a replacement for albumen in early photographic emulsions, binding light-sensitive silver halides to a glass plate.^[6]
• Magician's flash paper, sheets of paper or cloth made from nitrocellulose, which burn almost instantly with a bright flash leaving no ash.
• Radon tests for alpha track etches.
• Nitrocellulose lacquer was used as a finish on guitars and saxophones for most of the 20th century and is still used on some current applications. Manufactured by (among others) DuPont, the paint was also used on automobiles sharing the same color codes as many guitars including Fender and Gibson brands.^[7]
• Nitrocellulose lacquer is also used as an aircraft dope, painted onto fabric-covered aircraft to tauten and provide protection to the material.
• As a medium for cryptographic one-time pads, thus making the disposal of the pad complete, secure, and efficient.
• Depending on the manufacturing process, nitrocellulose is esterified to varying degrees. Table tennis balls, guitar picks and some photographic films have a fairly low esterification level and burn comparatively slowly with some charred residue. See celluloid.

Because of its explosive nature, not all applications of nitrocellulose were successful. In 1869, with elephants having been poached to near extinction, the billiards industry offered a $10,000 prize to whoever came up with the best replacement for ivory billiard balls. John Wesley Hyatt created the winning replacement which he coated with a new material he discovered called camphored nitrocellulose—the first thermoplastic, better known as celluloid. The invention enjoyed a brief popularity, but the Hyatt balls were extremely flammable, and sometimes portions of the outer shell would explode upon impact. An owner of a billiard saloon in Colorado wrote to Hyatt about the explosive tendencies, saying that he did not mind very much personally but for the fact that every man in his saloon immediately pulled a gun at the sound.^[8][9] The process used by Hyatt to manufacture the billiard balls, (US Patent 239,792, 1881) involved placing the mass of nitrocellulose in a rubber bag, which was then placed in a cylinder of liquid and heated. Pressure was applied to the liquid in the cylinder, which resulted in a uniform compression on the nitrocellulose mass, compressing it into a uniform sphere as the heat vaporizes the solvents. The ball was then cooled and turned to make a uniform sphere. Ironically, in light of the explosive results, this process was called the "Hyatt Gun Method".^[10]

References

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See also

Wikisource has original text related to this article: Harper's New Monthly Magazine/Vol. XLIV/No. 261/February 1872/Editor's Scientific Record/Explosion of Gun-Cotton at Stowmarket

• Smokeless powder
• Cordite
• Nitroglycerine
• Nitrostarch
• Potassium nitrate

External links

• Pictures of a projector after a nitrate film fire
• Nitrocellulose Paper Video (aka:Flash paper)