Nitrocellulose decomposition products

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... 

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. 

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. 

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. 

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) ... 

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. 

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... 

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 ... 

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... 

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). 

Ignition of nitrocellulose and pyrocellulose takes place at a constant temperature of 175 °C for 4 min or 170 C for 10 min. The initial reaction of thermal decomposition is nearly a first-order reaction and denitration and cleavage of the gly-cosidic linkage take place simultaneously. The decomposition products contain NO, NO2, N, CO,... 

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