Stabilization of nitrocellulose

Fig. 194. Stability of nitrocellulose powder at 110°C (measured as a reduction of weight)...

Fig. 196. Effect of the addition of amyl alcohol and diphenylamine on the stability of nitrocellulose powder, according to Berger [66],...

More recently Demougin and Landon [67] examined the stability of nitrocellulose powder containing 1.02-7.8% diphenylamine at a temperature of 110°C. After 160 hr of heating they determined the nitrogen content in nitrocellulose isolated from powder (Table 174.). The initial content of diphenylamine in the sample was 7.8% on heating for 180 hr at a temperature of 110°C it was reduced to 1%. 

The systematic studies of T. Urbanski, Kwiatkowski and Miladowski [76] proved that the addition of an aromatic nitro compound distinctly enhances the stability of nitrocellulose and nitrocellulose powder. Thus, nitrocellulose containing 13.4% N which on heating for 5 hr at 120°C had pH=2.28 showed pH=2.89 on addition of 9 1% p-nitrotoluene, pH=3.17 on addition of 9.1 % 2,4-dinitrotoluene and pH=3.34 on addition of the same amount of a-trinitrotoluene. The same samples when heated in a constant volume (Tagliani test) gave at 134.5°C a pressure of decomposition... 

Nitrocellulose (2.7) was discovered by C.F. Schonbeim at Basel and R. Bottger at Frankfurt-am-Main during 1845-47. The stability of nitrocellulose was improved by Abel in 1865 and its detonation properties were developed by Abel s assistant, Brown. 

Loss of weight. One of the oldest and simplest quantitative methods is the determination of the loss of weight of a sample heated at a constant temperature. The original Sy-test [90] used in the U.S.A. for determining the stability of nitrocellulose and nitrocellulose powder ( U.S. Ordnance Department 115° Test ) consisted in heating a sample of the substance on a watch-glass at 115+0.5°C. 

Manometric test. The idea of measuring the pressure of the gaseous products evolved during decomposition of explosives on storage or heating was known as early as in the middle of the last century. It was mentioned by Abel [96] in his classic work on the stabilization of nitrocellulose. Ph. Hess [97] examined the decomposition of nitrocellulose at 70°C and measured the pressure of the decomposition products by means of a mercury manometer. Mittasch [98] applied the same idea... 

It became clear, however, that the methods introduced by Lenk were not sufficient to ensure a high enough chemical stability of the product Also it became clear that a systematic study of stability and stabilization of nitrocellulose are needed. 

The first study of the stability of nitrocellulose seems to be that of de Luca [2], It is described below (p. 307). 

Ropuszynski [26] recently reported that the action of a magnetic field during the boiling of nitrocellulose in water produces a beneficial effect on the stability of nitrocellulose. 

The phenomenon described by Vieille seems to have no direct connection with the chemical stability of nitrocellulose, in the usual sense of this term, meaning the capacity of a substance to endure long storage, but appears to be limited to the... 

Wannow [36] has stated that the nitration of cellulose by means of mixed nitric and phosphoric acid does not reduce the degree of polymerization of the nitrated substance. The stability of nitrocellulose obtained by treatment with H3P04 and HN03 is... 

Fig. 152. General view of digesters for stabilization of nitrocellulose (Hercules Powder Co., [3]).

An important operation in the stabilization of nitrocellulose, particularly for materials containing over 11.5% N involves cutting the fibres into short pieces. Only nitrocellulose of low nitrogen content, below 11.5% N (collodion cotton) can be stabilized adequately without such a treatment. 

The other principal operation in the stabilization of nitrostarch is prolonged boiling, initially in acid water, and finally in alkaline water. As in the stabilization of nitrocellulose premature alkalization of the stabilizing medium is not recommended as this hinders the hydrolysis of sulphuric esters. Nevertheless in some American contributions (as mentioned above) early addition of ammonia for washing nitrostarch is reported to favour the formation of a stable product. 

Figure 65. Fred Olsen. Has done important work on cellulose and has made many improvements in detonating explosives, high explosives, and smokeless powder in particular, has invented processes for the quick stabilization of nitrocellulose and for the production of ball-grain powder. Chief of Chemical Research, Aetna Explosives Company, 1917-1919 Chemical Adviser, Picatinny Arsenal, 1919-1928 Technical Director, Western Cartridge Company, 1929—.

The process for the manufacture of ball-grain powder which Olsen and his co-workers have devised 26 combines nicely with Olsen s process for the quick stabilization of nitrocellulose to form a sequence of operations by which a finished powder may be produced more rapidly and more safely than by the usual process. It supplies a convenient means of making up a powder which contains non-volatile solvents throughout the mass of the grains or deterrent or accelerant coatings upon their surface. 

A method, developed by Bergmann and Junk in 1904, for testing the chemical stability of nitrocellulose it was also subsequently employed for testing single-base powders. The test tube, which contains the specimen being tested, and which is equipped with a cup attachment, is heated at 132 °C= 270.4°F for two hours (nitrocellulose) or five hours (single base powders). At the end of the heating period the sample is extracted with water, and the test tube filled to the 50-ml mark with the water in the cup. The solution is filtered, and the content of nitrous oxides is determined by the Schulze-Tiemann method on an aliquot of the filtrate. 

The formation of starch complexes with other polysaccharides is perhaps best evidenced by the sorption of starch on cellulose and its derivatives. This sorption is selective with respect to amylose and amylopectin.1065 1066 Cotton fibers selectively adsorb amylose and not amylopectin.1667-1071 However, this method cannot be used for starch fractionation because cotton was considered to induce degradation (hydrolysis).1067 On the other hand, a method of purifying amylopectin that involves sorption of amylose on defatted cellulose has been published.1072 Reversible adsorption of amylopectin on cellulose occurs when starch is equilibrated with urea in 32-35% ethanol. There are also published attempts to separate starch components on filter paper.1073-1076 The reverse idea is applied in the stabilization of nitrocellulose by its sorption on starch.1077... 

Nitrocellulose compositions used in explosive applications vary from 10 to 13.5 percent of nitrogen. The thermal stability of nitrocellulose decreases with increasing nitrogen content. It dissolves in organic solvents to form a gel. The gel is used as gun propellant, double-rocket propellant, and gelatine and semi-gelatine commercial blasting explosives. 

Structure of cellulose polymer and determination of molecular weight Pyrolysis of nitrocellulose Thcrmochemical properties of nitrocellulose Mixed esters nitrates and sulphates Stabilization of nitrocellulose Knccht compound Manufacture of nitrocellulose Semi-continuous methodof Bofors-Nobel-Chematur Drying of nitrocellulose Safety in the manufacture of nitrocellulose Starch nitrates (nitrosiarch)... 

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