Nitrocotton

Process (3) may be slow, hence under industrial conditions it may be broken off before equilibrium is established. This means that chemical reaction (3) is not completed. As a final product, a not very homogeneous nitrocotton is obtained. The higher the nitrating temperature, the more rapid the denitration process, the sooner the reaction balance is established, and hence the more uniform the product ... 

Nitrocotton. A NC prepd by nitration of cotton. See under Cellulose and Derivatives in Vol 2, C95-Rff... 

Dynamit-Collodiumwollen (engl. blasting soluble nitrocotton) Ester- und alkohollosliche Collodiumwollen, Celluloidwollen (Lackwollen)... 

Nobel developed gelatinous dynamite in 1875 by making a jelly from the dissolution of a collodion-type nitrocotton in NG, producing a more powerful explosive than the straight dynamite and one that proved to be safer. Later ammonium nitrate was also used in dynamite, which made it even safer and less expensive to produce. 

Hackel has extended Hibbert s observations concerning the influence of certain substances on the formation of nitroglycerine crystals of different forms. Thus, adding urethane, phenylurethane, collodion, nitrocotton, cyclonite, tetryl, dinitrobenzene, or centralites I and II promotes the formation of the labile form. Admixtures of siliceous earth, trinitrobenzene, TNT, favour the creation of the stable form. 

There exists a range of various kinds of nitrocellulose differing from one another in their physical properties according to the application intended. Nitrocellulose for smokeless powder manufacturing (guncotton) represents one type while other properties are demanded from the raw material to be used for making celluloid or artificial fibres (collodion cotton, collodion nitrocotton). 

Fig. 92. Absorption of acetone by nitrocottons of various nitrogen content, at the acetone activity of 0.64 according to Rubenstein [43].

Nevertheless, such a uniformity in results has not been confirmed by all investigators. Thus G. G. Jones [61] has found a range of less uniform values for high-viscosity collodion nitrocotton HH, with 12.2% N. Some of these data are collected in Table 44. 

Different plasticizers added to nitrocotton solutions can reduce their viscosity. Thus it has been established (Nisizava [63]) that the addition of camphor lowers... 

An addition of diphenylamine causes a marked decrease in viscosity, as reported by Drinberg [62]. The viscosity of high-viscosity nitrocotton solution is decreased under the influence of a 5% admixture of diphenylamine (by weight of nitrocellulose) as much as 24%. 

The problems of the increase in viscosity of nitrocotton and the precipitating gel in the presence of inorganic compounds, owing to the formation of complex compounds, is discussed later (see p. 302). 

The reason why the viscosity falls is the effect of the solvent on the molecules of nitrocotton which tends to degrade the chains. The shortening of the molecular chains is relatively more marked in the case of long chains, i.e. with nitrocellulose... 

As shown experimentally by Piest [75], cotton which was subjected to various operations, e.g. bleaching, treatment with alkalis or acids, strong heating prior to nitration furnishes nitrocellulose solutions of low viscosity. At the same time an increase in the solubility of the nitrocotton was also observed. This is evidence that the cellulose molecules are shortened and their content of terminal group is increased. A certain proportion of hydrocellulose and oxycellulose may result. The total effect is to bring about an increase in the reductive properties of the cellulose, i.e. an increase of the copper number. 

An increase of the nitrogen content is also accompanied by an increase of viscosity, providing that the nitrocotton is prepared under accurately uniform conditions. This relationship is described by Berl and Klaye [77] as tabulated below (Table 51). 

Duclaux et al. [101] came to other conclusions for he established that particular fractions differed only in the viscosity of solutions the nitrogen content being the same. In order to precipitate nitrocotton from its acetone solutions the authors added acetone-water mixtures, richer and richer in water until finally pure water was added. A range of fractions was separated from nitrocellulose acetone solution of viscosity 0.1 P (poises). The viscosity of the first fraction was 0.603 P, and that of the last 0.007 P (2% solutions). 

Similarly Craik and Miles [109] extracted nitrocotton by means of aqueous acetone with a gradually increasing acetone concentration. The fraction which... 

A range of nitrocotton samples containing from 11.3 to 13.1% N, and nitro-ramie of 10% N prepared by denitrating nitroramie of 13% N by acting with nitric acid 80%, have been fractionated by G. G. Jones and Miles [HO] by a method of successive extraction with aqueous acetone every subsequent solvent was richer in acetone than the preceding one. They demonstrated that particular fractions differed in nitrogen content and viscosity. 

Fig. 107. Viscosity-concentration ratio (togio VCR) (plain lines) and distribution of logio VCR of fractions of nitrocotton (broken lines), according to G. G. Jones and Miles [16a]. Designation...

Kruger [113] tried fractionating nitrocellulose by diffusion. The principle of the method was that a nitrocellulose solution in acetone, methyl alcohol or amyl acetate diffused into a pure solvent layer on the surface of the solution. Clearly molecules of smaller size penetrate more rapidly. A nitrocellulose solution of 12.8% N was separated into two layers in this way after 42 days diffusion. The lower fraction comprised nitrocotton with a nitrogen content of 13.1% N, the upper layer one of 12.1% N. 

The absorption spectrum of nitrocellulose solutions has been examined (Rassow and Aehnelt [135]). It has been established that the capacity to absorb light differs with the origin of the nitrated cellulose. Thus nitrocellulose made from wood pulp gives a slightly different absorption spectrum from that of nitrocotton. 

In point of fact it has been established by many workers that a nitrocotton freshly produced and washed from acid could contain up to 8% of sulphuric add cellulose esters. Berl and Boltenstem [7] stated in later investigations that sulphuric add always occurred in the stabilized nitrocotton in two forms (a) as an inorganic salt, for the most part CaS04 (b) as sulpho groups chemically combined with cellulose. Their data are given in Table 62. 

Later experiments were carried out with a nitrocellulose stabilization process that consisted in treating a partially purified nitrocotton in an ammonia bath (e.g. Reeves and Giddens [12]). This was based on the supposition that ammonia was capable of neutralizing accurately adds contained in the interior of nitrocellulose fibres. However, this method has not been adopted in practice, since it was feared that the sulpho groups attached to cellulose in the form of mixed esters would undergo only partial hydrolysis in the presence of ammonia and later spontaneous hydrolysis of these substituents in the finished (stabilized) product might reduce its stability. 

Smith carried out his experiments by means of the following technique nitrocotton removed from the nitrating add was washed in running water until the water was no longer acid. The total acid content (by titrating its acetone solution), and the concentration of sulphuric acid esters were determined in the products. The results are shown in Table 63. 

An interesting observation has been made while attempting to purify nitrocotton by dissolving it in acetone followed by predpitation with water. Guncotton (sample 1) was fairly well purified and stabilized by this method, but collodion cotton (sample 4) retained almost the whole amount of add present in it before purification and it was just as unstable as before, because the sulphuric esters were dissolved and reprecipitated with the nitrocellulose. Inddentally this is convincing chemical evidence confirming the existence of sulphuric acid cellulose esters in lower nitrated cellulose. 

Smith also stated that the sulphuric add content in nitrocotton was dependent of the proportion of H2S04 in the mixed acid. Thus if the sulphuric add content... 

Similar observations were also published earlier by Tribot and Marsaudon [16]. Recently, however, Lhoste [17] has questioned the validity of the hypothesis of the formation of sulphuric acid esters during the nitration of cellulose. On the basis of analytical data the author has arrived at the idea that sulphuric acid is bound with nitrocellulose solely by occlusion. He found no evidence to confirm the existence of cellulose sulphates in nitrocotton. 

Lhoste has also drawn attention to the fact that the rate of removal of sulphuric acid from nitrocellulose depends on its nitrogen content. The more highly nitrated the nitrocotton, the more slowly sulphuric add is eliminated from it. Thu s in the instance of nitrocellulose of 13.40% N, a 100 hours boiling is necessary to attain the same sulphuric add content as that of nitrocellulose with 12.19% N-content boiled for lOhr. 

Certain differences in numerical data reported in various publications can be justified to some extent by differences in the analytical methods used. On the other hand, the values given by Lhoste seem to show that the sulphuric acid in nitrocotton could be combined with nitrocellulose molecules less firmly than in an ester group. For instance, it is not out of the question that sulphuric add may be bound with nitrocellulose as an inclusion (clathrate) compound. (Attention was also drawn to this point by Miles [15] in his monograph on cellulose nitrate.)... 

Research into the course of partial nitrocellulose denitration occurring during stabilization boiling has provided material for a further inquiry into the question of removing both sulphuric acid, and sulpho groups contained in nitrocotton during the stabilization process. 

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