Nitrocellulose


Nitrocellulose is a highly flammable compound formed by nitrating cellulose through exposure to a mixture of nitric acid and sulfuric acid.
One of its first major uses was as guncotton, a replacement for gunpowder as propellant in firearms. It was also used to replace gunpowder as a low-order explosive in mining and other applications. In the form of collodion, it was also a critical component in an early photographic emulsion, the use of which revolutionized photography in the 1860s. In the 20th century, it was adapted to automobile lacquer and adhesives.

Production

The process uses a mixture of nitric acid and sulfuric acid to convert cellulose into nitrocellulose. The quality of the cellulose is important. Hemicellulose, lignin, pentosans, and mineral salts give inferior nitrocelluloses. In organic chemistry, nitrocellulose is a nitrate ester, not a nitro compound. The glucose repeat unit within the cellulose chain has three OH groups, each of which can form a nitrate ester. Thus, nitrocellulose can denote mononitrocellulose, dinitrocellulose, and trinitrocellulose, or a mixture thereof. With fewer OH groups than the parent cellulose, nitrocelluloses do not aggregate by hydrogen bonding. The overarching consequence is that the nitrocellulose is soluble in organic solvents such as acetone and esters; e.g., ethyl acetate, methyl acetate, ethyl carbonate. Most lacquers are prepared from the dinitrate, whereas explosives are mainly the trinitrate.
The chemical equation for the formation of the trinitrate is
.
The yields are about 85%, with losses attributed to complete oxidation of the cellulose to oxalic acid.

Use

The principal use of cellulose nitrate is for the production of lacquers and coatings, explosives, and celluloid.
In terms of lacquers and coatings, nitrocellulose dissolves readily in organic solvents, which upon evaporation leave a colorless, transparent, flexible film. Nitrocellulose lacquers have been used as a finish on furniture and musical instruments.
Guncotton, dissolved at about 25% in acetone, forms a lacquer used in preliminary stages of wood finishing to develop a hard finish with a deep lustre. It is normally the first coat applied, then it is sanded and followed by other coatings that bond to it.
Nail polish contains nitrocellulose, as it is inexpensive, dries quickly to a hard film, and does not damage skin.
The explosive applications are diverse and nitrate content is typically higher for propellant applications than for coatings. For space flight, nitrocellulose was used by Copenhagen Suborbitals on several missions as a means of jettisoning components of the rocket/space capsule and deploying recovery systems. However, after several missions and flights, it proved not to have the desired explosive properties in a near vacuum environment. In 2014, the Philae comet lander failed to deploy its harpoons because its 0.3 grams of nitrocellulose propulsion charges failed to fire during the landing.

Other uses

Collodion, a solution of nitrocellulose, is used today in topical skin applications, such as liquid skin and in the application of salicylic acid, the active ingredient in Compound W wart remover.

Laboratory uses

  • Membrane filters made of a mesh of nitrocellulose threads with various porosities are used in laboratory procedures for particle retention and cell capture in liquid or gaseous solutions and, reversely, obtaining particle-free filtrates.
  • 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 and atomic force microscopy for its nonspecific affinity for amino acids. Nitrocellulose is widely used as support in diagnostic tests where antigen-antibody binding occurs; e.g., pregnancy tests, U-albumin tests, and CRP tests. Glycine and chloride ions make protein transfer more efficient.
  • Radon tests for alpha track etches use nitrocellulose.
  • Adolph Noé developed a method of peeling coal balls using nitrocellulose.
  • It is used to coat playing cards and to bind staples together in office staplers.

    Hobbies

  • In 1846, nitrated cellulose was found to be soluble in ether and alcohol. The solution was named collodion and was soon used as a dressing for wounds.
  • 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.
  • Magicians' flash paper are sheets of paper consisting of pure nitrocellulose, which burn almost instantly with a bright flash, leaving no ash or smoke.
  • As a medium for cryptographic one-time pads, they make the disposal of the pad complete, secure, and efficient.
  • Nitrocellulose lacquer is spin-coated onto aluminium or glass discs, then a groove is cut with a lathe, to make one-off phonograph records, used as masters for pressing or for play in dance clubs. They are referred to as acetate discs.
  • Depending on the manufacturing process, nitrocellulose is esterified to varying degrees. Table tennis balls, guitar picks, and some photographic films have fairly low esterification levels and burn comparatively slowly with some charred residue.

    Historical uses

Early work on nitration of cellulose

In 1832 Henri Braconnot discovered 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, treated paper and cardboard in the same way. Jean-Baptiste Dumas obtained a similar material, which he called nitramidine.

Guncotton

Around 1846 Christian Friedrich Schönbein, a German-Swiss chemist, discovered a more practical formulation. As he was working in the kitchen of his home in Basel, he spilled a mixture of nitric acid and sulfuric 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, a flash occurred as the apron ignited. His preparation method was the first to be widely used.
The method was to immerse one part of fine cotton in 15 parts of an equal blend of sulfuric acid and nitric acid. After two minutes, the cotton was removed and washed in cold water to set the esterification level and to remove all acid residue. The cotton was then slowly dried at a temperature below 40 °C. Schönbein collaborated with the Frankfurt professor Rudolf Christian Böttger, who had discovered the process independently in the same year.
By coincidence, a third chemist, the Brunswick professor F. J. Otto had also produced guncotton in 1846 and was the first to publish the process, much to the disappointment of Schönbein and Böttger.
The patent rights for the manufacture of guncotton were obtained by John Hall & Son in 1846, and industrial manufacture of the explosive began at a purpose-built factory at Marsh Works in Faversham, Kent, a year later. The manufacturing process was not properly understood and few safety measures were put in place. A serious explosion in July that killed almost two dozen workers resulted in the immediate closure of the plant. Guncotton manufacture ceased for over 15 years until a safer procedure could be developed.
The British chemist Frederick Augustus Abel developed the first safe process for guncotton manufacture, which he patented in 1865. The washing and drying times of the nitrocellulose were both extended to 48 hours and repeated eight times over. The acid mixture was changed to two parts sulfuric acid to one part nitric. Nitration can be controlled by adjusting acid concentrations and reaction temperature. Nitrocellulose is soluble in a mixture of ethanol and ether until nitrogen concentration exceeds 12%. Soluble nitrocellulose, or a solution thereof, is sometimes called collodion.
Guncotton containing more than 13% nitrogen was prepared by prolonged exposure to hot, concentrated acids for limited use as a blasting explosive or for warheads of underwater weapons such as naval mines and torpedoes. Safe and sustained production of guncotton began at the Waltham Abbey Royal Gunpowder Mills in the 1860s, and the material rapidly became the dominant explosive, becoming the standard for military warheads, although it remained too potent to be used as a propellant. More-stable and slower-burning collodion mixtures were eventually prepared using less concentrated acids at lower temperatures for smokeless powder in firearms. The first practical smokeless powder made from nitrocellulose, for firearms and artillery ammunition, was invented by French chemist Paul Vieille in 1884.
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. In his From the Earth to the Moon, guncotton was used to launch a projectile into space.
Because of their fluffy and nearly white appearance, nitrocellulose products are often referred to as cottons, e.g. lacquer cotton, celluloid cotton, and gun cotton.
Guncotton was originally made from cotton but contemporary methods use highly processed cellulose from wood pulp. While guncotton is dangerous to store, the hazards it presents can be minimized by storing it dampened with various liquids, such as alcohol. For this reason, accounts of guncotton usage dating from the early 20th century refer to "wet guncotton."
File:Gws-jamtinbomb.jpg|thumb|Jam tin grenades were made in World War I using gun cotton
The power of guncotton made it suitable for blasting. As a projectile driver, it had around six times the gas generation of an equal volume of black powder and produced less smoke and less heating.
Artillery shells filled with gun cotton were widely used during the American Civil War, and its use was one of the reasons the conflict was seen as the "first modern war." Fired from breech-loading artillery, such high explosive shells could cause greater damage than previous solid round shot.
During the first World War, British authorities were slow to introduce new grenades, with soldiers at the front improvising by filling ration tin cans with gun cotton, scrap and a basic fuse.
Further research indicated the importance of washing the acidified cotton. Unwashed nitrocellulose may spontaneously ignite and explode at room temperature, as the evaporation of water results in the concentration of unreacted acid.