Nitrocellulose or smokeless powder is classed as a low-order explosive. Low-order explosives are materials that simply burn very rapidly, a process also known as deflagration. When heated, the constituent fuel and oxidizer in the material combine to produce heat, light, gases and some solid materials. Most low-order explosives must be confined to create an explosion and some of them burn at about the same speed in the open as they do when contained. Some burn much faster and hotter under pressure. Under certain conditions, some low-order explosives can be caused to detonate. Extremely fine black powder packed too tightly has been known to do this.
Nitrocellulose is used primarily as a propellant as are most modern military low-order explosives. Propellants impart motion to something like a rocket or projectile. They are classified as single-base, double-base and composites. Single-base propellants are the simple forms of nitrocellulose powders. Double-based propellants are nitrocellulose powders that have nitroglycerin added to them thus making them more powerful. Composite propellants are mixtures of fuels and oxidizers that are mostly not nitrocellulose and nitroglycerin.
Propellants can be made to perform differently by varying the physical characteristics of the individual grains because burning is mostly a surface phenomenon. Thomas J. Rodman of the U.S. Army originally exploited this characteristic with black powder in the 1850s. These burning characteristics are said to be degressive, neutral and progressive. In a degressive powder, the surface area decreases as the powder is consumed. This makes the combustion process slow down as the material is consumed. If the grains are made so that each grain has a hole in it, it can then be a neutral powder because as it burns, the surface area remains about the same. These are called perforated powders. If the grains have multiple holes, known as multiperforated powders, they can burn progressively meaning that they burn faster as they are consumed. This allows powders to develop more gases after a projectile has begun to move down the barrel of a gun.
Cellulose nitrate is another term for nitrocellulose, the material that modern gunpowder is made of. Before nitrocellulose came into widespread use, black powder was called gunpowder, but after nitrocellulose replaced black powder, it began to be called gunpowder and black powder was called black powder.
Nitrocellulose powders rapidly replaced black powder because when they burn they produce a much higher percentage of gases than black powder and therefore do not foul guns nearly as badly. Nitrocellulose produces far less smoke (solids) during combustion than black powder. That is why nitrocellulose powders are called smokeless powders. They tend to burn progressively, a factor that improves their performance as propellants. Smokeless powder is about three times more powerful than black powder.
Discovery and Development
Nitrocellulose powder was the result of several discoveries and developments of the 19th century. After the material was formulated into a relatively safe and stabile substance it rapidly replaced black powder as a propellant during the late 1800s. Black powder nearly disappeared from use as a military propellant by World War I.
The first step in the development of nitrocellulose was the 1838 discovery by T. J. Pelouze that cotton became explosive after it was dipped in nitric acid and dried. In 1845, Christian Shönbein developed a process of dipping cotton in both nitric and sulfuric acids and then washing out the residual acids. He further discovered that this material could be dissolved in a mixture of ether and ethyl alcohol, thus producing a fibrous solution that could be spun.
This material was extremely flammable and therefore unsuitable for use in textiles, but it was useful as an explosive and it became known as guncotton. It began to be used as a propellant around the time of the US Civil War in the 1860s. Guncotton was the precursor of nitrocellulose, or smokeless powder.
Unfortunately, the washing process frequently failed to remove all of the acids and the material would frequently explode spontaneously. This resulted in many disasters in the early days of the production of this material. This characteristic along with the fact that the material was too powerful for most of the guns of the era kept it from being widely adopted as a propellant right away.
Paul Vieille, a French chemist and physicist, solved the problems associated with guncotton by developing processes to remove all of the residual acids from the material and discovering stabilizers, such as diphenylamine, that could be added to the material to keep it from exploding spontaneously. The resulting compound, after additional processing, could be formed into the material that eventually became known as smokeless powder.
Smokeless powder is nitrocellulose-based powder, the material developed by Paul Vieille in 1884. It was the first stabile and reliable propellant. Nitrocellulose proved to require much more processing than simply dipping cotton in acid. Wood pulp soon became the preferred source of raw cellulose. Cotton linters can also used as a source of raw cellulose. The two sources of raw cellulose have slightly different properties so they are used and blended based upon the intended purpose of the finished product.
To make nitrocellulose gunpowder, the nitrocellulose is dissolved in certain organic solvents such as an ether-ethanol mixture or acetone and it becomes a gelatinous mass. More modern solvents can also be used. When the solvents evaporate, a hard plastic material remains. This gelatinous blob is usually rolled into a sheet before it hardens. Afterwards, it is cut up into flakes of various sizes and shapes. The size and shape of the flakes controls the material’s burning characteristics. The cutting is done on machines because the particles are tiny and it takes a great deal of cutting. Furthermore, it just wouldn’t have been the Industrial Revolution if they had cut it by hand. Nitrocellulose is the principle type of propellant used today. Generally, smokeless powder contains more than 13 percent nitrogen.
Nitrocellulose had many properties that made it an important material apart from its use as a propellant. Since it forms a plastic material when dissolved in organic solvents like ether-alcohol or acetone, it can be made into many different forms that maintain their shape when the solvents evaporate. It can also be hot-formed and will retain its shape when cooled.
The manufacturers of military explosives experienced several instances of extremely high production during the late 19th and early 20th centuries caused by large-scale wars. When peace was reached, there was an enormous excess of production capacity and raw materials with which nitrocellulose could be made. In order to utilize this glut of resources, gunpowder manufacturers began to develop civilian uses for this material.
Since the average consumer has limited need for nitrocellulose gunpowder, other types of uses for this material had to be found. Because it forms a plastic material, it could be developed into other types of products that had broader consumer applications. Gunpowder manufacturers such as E. I. du Pont de Nemours and Company developed the first commercially available plastics for these reasons.
In all reality, the use of excess gunpowder manufacturing capacity for the production of consumer products was the beginning of the commercial plastics industry. One of the primary compounds that was developed into plastics was collodion and it is simply guncotton with a lower nitrate constituent, less than 12%. This material is also known by the trade name Pyroxylin and it was developed into many different consumer products such as artificial leather, plastic and lacquers.
By mixing solid nitrocellulose with camphor, John Wesley Hyatt of Albany, New York developed Celluloid, the first commercially successful plastic. The solid material could be heated until it softened and then molded into various shapes. Hyatt formed the Celluloid Manufacturing Company to manufacture and market these products. The earliest uses of this material were mostly as substitutes for natural materials such as tortoiseshell, horn and ivory. Ivory became very scarce at about this time in part because billiards became very popular. Since billiard balls were heretofore made of ivory, a great amount of ivory was needed to make them. Ivory comes from elephant tusks and therefore the supply is limited.
In keeping with the nitrocellulose origin of these earliest plastics, they tended to be highly flammable. Celluloid and Pyroxylin plastics were only slightly less flammable than gunpowder. In fact, on some occasions items made from Celluloid could explode. This was particularly bothersome with billiard balls where the force of impact would sometimes cause the balls to detonate. While this no doubt occasionally made billiards more interesting, it also had undesirable side effects such as personal injury as well as property destruction. Therefore, the explosive characteristics of Celluloid were generally regarded as negative.
Pyroxylin-type plastics began to be replaced by less flammable plastics in the 1920s and 1930s. Nevertheless they did not disappear. Better chemical manufacturing techniques reduced the incidence of detonation in later years. Celluloid plastics are still used in a few applications such as Ping-Pong balls.
EC Powder, or Explosive Company Powder, is a type of modified nitrocellulose powder used for fragmentation charges in grenades and the like. The grains are coarser than regular smokeless powder and it has additional nitrates added to it.