History

HISTORY OF NITROCELLULOSE

The history of modern high explosives generally is considered to date from the middle of the nineteenth century, although picric acid and some of the fulminates were discovered much earlier. The early history and dis­coveries of these products are well known from contemporary literature, and in this respect they differ from the oldest explosive, black powder, the early history of which is shrouded  in mystery.

The year 1846 saw the discovery of both nitroglycerin and nitrocellulose (“guncotton”), which have played such an important role in human history. It is true that Braconnot and Pelouze, in 1838, nitrated starch, paper, and cotton fibers with nitric acid vapors, but Schonbein first prepared nitrocellulose from absorbent cotton by means of a mixture of nitric and sulfuric acids, and realized its true significance and value. However, a few weeks after this discovery, Hootger obtained the same result, independently, and the two inventors combined to exploit the product. Schonbein had great hopes for his nitrocellulose. In a letter to Fara­day he said that he expected that it would soon displace black powder as a propellant for firearms. However, it was many years before this hope was realized, although a number of plants were built in short order.

The first “guncotton” plant was erected in the same year at Faversham, in England, but in July of the next year the whole plant was destroyed by an explosion, with the loss of twenty-one lives. In 1848, similar accidents occurred in the French factories at Bouchet and Vincennes. The result was that the manufacture of “guncotton” was prohibited and a German confederation refused to purchase the process. The inventors succeeded, however, in selling their secret to Austria and two plants were operated under the direction of an artillery officer, Baron von Lenk, until 1862 and 1865, respectively, when they also blew up and put a stop to further work there. Although Lenk had been extremely careful to purify his “guncotton” by treating it with waterglass, his accidents as well as the previous ones in England and France were due to insufficient stabilization rather than from incomplete neutralization of the acids.

In the meantime an English chemist, Sir Frederick Abel, had come to the conclusion that the instability was due to traces of acid retained so tenaciously in the fine capillaries of the cotton fiber that simply washing or neutralization with alkaline solutions did not completely eliminate them. In order to reach these traces of acid he broke up the fibers by pulping them in the beating engine of the paper industry (1). He also devised a test, still known as the Abel heat test, for revealing the smallest traces of acid. Beating or pulping of the nitrocellulose is still practiced, although it is now realized that this does not re­move all causes of instability. In 1965, when Austria stopped manufacturing “guncotton, England had two plains,, one at Stowmarket and one at Waltham Abbey. The latter was under Abel’s management and had in 1872 a production of about 250 tons/year.

During the ensuing years, it was established that even complete removal of acid does not stabilize “guncotton”. It was not until publication of the experimental results of Will (2) in 1900-1902, and Robertson (3) in 1906 on the puri­fication of nitrocellulose that a reliable method was developed for producing stabilized “guncotton”; namely, boiling in acidulated water followed by pulping, and poaching (boiling in slightly alkaline water followed by several cold water washes). Since that time these basic purification pro­cesses have remained essentially unchanged.

Aside from the troubles due to instability, there was another reason why “guncotton” did not immediately dis­place black powder as a propellant. It was too brisant, its rate of detonation was too great, and could not be suf­ficiently controlled, even by pressing it into solid blocks under heavy hydraulic pressure, to make it safe for use in rifle or cannon. Its chief military use was, therefore, as a charge for mines and torpedoes.

Early Uses for Nitrocellulose

In the meantime, nitrocellulose found uses in the peaceful arts and the developments here resulted later in serviceable nitrocellulose powders. Schonbein himself had observed that by varying the conditions of nitration he was able to obtain nitrocellulose insoluble, partly soluble, and entirely soluble in a mixture of ether and alcohol. As early as 1848, Maynard made use of this solution in medicine under the name of collodion, which is still used as a dressing for wounds.  In 1851, Frederick Scott Archer introduced the use of the same solution in photography. From that time on the use of nitrocellulose, or pyroxylin, as it was generally called in the industry, increased rapidly as new solvents were discovered.  In 1869, John Wesley Hyatt obtained his patent covering the use of camphor as a latent solvent or plasticizing agent for pyroxylin and thereby laid the foundation for the celluloid industry. It is true that Parkes and Daniel Spill had previously used camphor and camphor oil in nitrocellulose solutions to obtain a plastic film but Hyatt depended on heat and pressure to develop the latent solvent powers of the camphor.  Another extremely important patent is that of Stevens covering the use of amyl acetate, which inaugurated the lacquer and artificial leather industries.

In working with these industrial plastics, it was found that they burned with comparative slowness.  This observation led the French chemist, Paul Vieille, to the development of a completely gelatinized nitrocellulose powder in 1866.  Two years later, Alfred Nobel invented dynamite and patented smokeless powders consisting of nitrocellulose gelatinized with nitroglycerine.  From that time on, these two types of nitrocellulose powders slowly but surely pushed black powder out of the place it had held in military affairs for  centuries. In the United States, however, it was not until after the Spanish American War that smokeless power was finally adopted as the service propellant.

 

(1)    Frederick Abel, English Patent No. 1102 (1865)

(2)  Will, Central Station for Scientific-Technical Investigation, NeuBabelsbeg near Berlin, Reports I & II (1900-1902) (p119)

(3)  Robertson, J. Soc. Chem. Ind. 25, 624.(1906)

(4)  See also Ott, Spurlin, & Grafflin, Cellulose and Cellulose Derivatives, Research Department, Hercules Powder Company, Wilmington, Delaware. Copyright, 1954, by Interscience Publishers, Inc.