Decomposition products, of nitrocellulose

In view of those experiments some results reported by later authors who did not find NOz among the thermal decomposition products of nitrocellulose should be subjected to revision. There is in fact, a serious controversy concerning this question as shown in the following paragraphs. 

Vandoni has also examined the decomposition produced by treatment with water at 130°C of high-nitrated guncotton, 14% N, and the decomposition products of nitrocellulose of 12% N evolved when treated at 50°C with dilute (25% HN03) nitric acid. 

The lower stability of smokeless powder in comparison with that of nitrocellulose is accounted for by its content of residual solvent and of the oxidation products of this solvent. Since in a finer powder the ratio of the surface to weight is high, the oxidation processes are more intense. A larger amount of decomposition products of residual solvent is formed by oxidation, and their destructive effect... 

Nitrocellulose, treated with different hydrolysing agents such as aqueous solutions of alkalis, does not yield cellulose and the corresponding metal nitrate, but a range of highly variable decomposition products of cellulose as well as of inorganic substances. 

Koehler and Marqueyrol [69] investigated the products of nitrocellulose decomposed under pressure. The decomposition products were removed in order to avoid the possibility of starting side reactions and to preclude any catalytic action by the decomposition products on the nitrocellulose. It has been stated that the composition of the gases evolved during decomposition is almost independent of the temperature and this is compatible with the data reported by Robertson. However, the composition of the products differs from that found by Robertson. These are as follows (omitting the water formed) ... 

On introducing nitroglycerine in the nitrocellulose, the effect of copper oxide sharply decreases, and at more than 40% NG it disappears completely. In the thermal decomposition of NG much more CO than C02 is formed, and in the decomposition of NC more C02 than CO is formed. Hence, on introducing NG into NC, the proportion of CO in the decomposition products is increased. The C0/C02 ratio in the decomposition products of NC, NG, and their mixtures (V = 20cm3/g at STP) is as follows ... 

Ettre and Varady used these techniques in the investigations of decomposition products of poly(vinyl alcohol), poly(n-butyl methacrylate), and nitrocellulose from 500 to 950 °C (cf. Section 4.2.1.1 and Table 4.15). 

The products of decomposition of smokeless powder resemble those formed by the decomposition of its ingredients, i.e. nitrocellulose or nitrocellulose with either nitroglycerine or dinitrodiglycol. 

Indeed, it was found that amyl alcohol is converted into amyl nitrite and nitrate by the action of nitric oxides resulting from the decomposition of nitrocellulose. These substances are then oxidized to form valeric acid and amyl valerate products distinguishable by their characteristic smell. 

As early as 1867 Abel [73] realized that nitrocellulose tends to decompose in an acid medium, and suggested that sodium carbonate should be added to it to neutralize the acid products of the decomposition of the impurities in the powder or of nitrocellulose and nitroglycerine per se. However more than 2% sodium carbonate in the powder proved detrimental—due to its strongly alkaline reaction it impairs the stability of the powder. 

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... 

R. Robertson [62] examined the decomposition of nitroglycerine at temperatures from 90 to 135°C, using a carbon dioxide stream to remove volatile decomposition products. The concentration of nitrogen oxides in the jet of carbon dioxide was established spectrographically. He found in this way that nitroglycerine decomposed in a manner similar to that of fairly well stabilized nitrocellulose, but more rapidly. In the temperature range of 95—125°C, every 5° elevation of temperature doubled the decomposition rate in these conditions. 

Bleaching. Crude wood cellulose is bleached by means of calcium or sodium hypochlorite in large tanks, bleachers , equipped with stirrers. Bleaching cellulose is of great importance for nitrocellulose manufacture, particularly in the case of nitrocellulose intended for the production of smokeless powder. It is essential that the powder should be pale in colour, as a change in the colour of the powder often indicates decomposition. Similarly, cellulose destined for manufacturing collodion cotton, for varnishes, celluloid and film, should be carefully stripped of colour so that the final products are colourless. 

The spontaneous decomposition of nitrocellulose in the air produces nitrous and nitric acids which promote a further decomposition. If these products however are removed continuously, the uncatalyzed decomposition is extremely slow, and smokeless pow-... 

In addition to the ability of certain substances to combine with the products of the decomposition of nitrocellulose, it is possible that the same or other substances may have a positive or a negative catalytic effect and may hasten or retard the decomposition by their presence. But it has not yet been made clear what types of chemical substance hasten the decomposition or why they do so. Nitrogen dioxide hastens it. Pyridine hastens it, and a powder containing 2 or 3% of pyridine will inflame spontaneously if heated for half an hour at 110°. Powders containing tetryl are very unstable, while those containing 10% of trinitronaphthalene (which does- not react with the products of decomposition) are as... 

The transformations of diphenylamine16 in consequence of its reaction with the products of the decomposition of nitrocellulose are indicated by the following formulas. None of these substances imparts any very deep color to the powder. 

Nitrocellulose, pulped and given a preliminary or sour boiling, may be used directly without poaching. Deteriorated smokeless powder, containing nitro derivatives of diphenylamine and acidic decomposition products, may be reduced to a coarse powder under water in a hammer mill, and may then be used. Whichever is used, the first necessity is to stabilize it by complete removal of the acid. For this purpose, the material in the presence of water (which may contain a little chalk in suspension or urea in solution) is introduced into a still where it is dissolved with agitation in ethyl acetate to form a heavy syrup or lacquer, and is treated with some substance which is adsorbed by nitrocellulose more readily than acid is adsorbed. It is a curious fact that nitrocellulose is dissolved or dispersed by ethyl acetate much more readily... 

Stabilizers are necessary because nitrocellulose decomposes with age. The decomposition reaction yields dinitrogen tetraoxide which acts as an autocatalyst and accelerates the decomposition.58 Stabilizers act as dinitrogen tetraoxide scavengers consequently shelf life is increased. Stabilizers are normally added in the region of 0.5 to 2.0%. To neutralize the decomposition products, which could cause corrosion of the firearm, calcium carbonate is added to some propellants. A common stabilizer is diphenylamine or its nitro derivatives (Figure 10.2). 

An improved version of the manometric test developed by Obermuller in 1904. The method was considerably modified, first by Goujan and, very recently, by Brissaud. In all modifications of the method, the test tube containing the sample preheated to the desired temperature is evacuated, and the increase in pressure produced by the gaseous decomposition products is measured with a mercury manometer. The test is usually terminated when the pressure has attained 100 mm Hg. The test temperature are for nitrocellulose 135°C = 275°F... 

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