Nitrocellulose denitration

Sir Joseph Swan, as a result of his quest for carbon fiber for lamp filaments (2), learned how to denitrate nitrocellulose using ammonium sulfide. In 1885 he exhibited the first textiles made from this new artificial sHk, but with carbon fiber being his main theme he failed to foUow up on the textile possibihties. Meanwhile Count Hilaire de Chardoimet (3) was researching the nitrocellulose route and had perfected his first fibers and textiles in time for the Paris Exhibition in 1889. There he got the necessary financial backing for the first Chardoimet silk factory in Besancon in 1890. His process involved treating mulberry leaves with nitric and sulfuric acids to form cellulose nitrate which could be dissolved in ether and alcohol. This collodion solution could be extmded through holes in a spinneret into warm air where solvent evaporation led to the formation of soHd cellulose nitrate filaments. 

However, de Bruin and Witte [55c] found that the solubility of partly denitrated nitrocellulose is abnormal. Thus, nitrocelluloses of 13.43 and 12.98% N prepared by direct nitration had solubilities in ethanol-ether (1 2 by volume) of 5 and 100% respectively. 

The authors also denitrated nitrocellulose with nitric acid, obtaining rather non-uniform products. 

Fabel and Fritsche [29] have carried out experiments designed to re-nitrate and denitrate nitrocellulose, as follows. Cellulose was at first nitrated by immersion for 1 hr in one of a series of mixed acids A, B, C, or D (see Table 76). In succession... 

The membrane is critically important in osomometry. Selection of a membrane involves reconciliation of high permeability toward the solvent with virtual impermeability to the smallest polymer molecules present in the sample. Membranes of cellulose are most widely used. Commercially Regenerated cellulose film is a common source. The undried gel cellophane film is often preferred, but the dry film may be swollen in water (or in aqueous solutions of caustic or zinc chloride ) to satisfactory porosity. Useful cellulose membranes may also be prepared by denitration of nitrocellulose films/ and special advantages have been claimed for bacterial cellulose films. The water in the swollen membrane in any case may be replaced by a succession of miscible organic solvents ending with the one in which osmotic measurements are to be made. Membranes of varying porosity may be... 

The substances generally used as osmotic membranes include collodion (nitrocellulose of 11-13.5 per cent nitrogen) regenerated cellulose, obtained by denitration of collodion gel cellophane that has never permitted to dry after manufacture bacterial cellulose, obtained by the action of certain strains of bacteria rubber, poly (vinyl alcohol) polyurethances poly (vinyl butyral) and polychlorotrifluoroethylene. At present gel cellophane is most widely used. 

Soon after the manufacture of nitrocellulose smokeless powder began it was established that the powder obtained by the partial dissolution of nitrocellulose in a mixture of alcohol and ether (partly colloidal powder) has a chemical stability inferior to that of the nitrocellulose from which it derived. Thus Vieille [11] reports that on heating to a temperature of 110°C CPj guncotton undergoes denitration with the evolution of 0.04 cm3 NO/hr/gramme whereas the powder obtained from these substances without a stabilizer undergoes denitration at more than twice the rate, namely 0.10-0.15 cm3 NO/hr/gramme of substance. 

Strong bases have an adverse effect on the stability of smokeless powder as described above. Moreover, Angeli [59] found that pyridine and its homologues cause decomposition of nitrocellulose. (On the action of pyridine on other nitric esters see Yol. II.) At an elevated temperature (e.g. 110°C) pyridine can produce an intense denitration of esters which may even lead to an explosion. 

The spatial configuration, extended in consequence of nitration, is retained despite partial denitration. This is why the cell size of a denitrated cellulose is larger than that of nitrocellulose containing the same nitrogen percentage, but obtained by a direct nitration of cellulose. 

Heterocyclic compounds pyridine, picolines (these substances cause nitrocellulose to denitrate), dimethylpyrone. 

Further, the stabilization boiling of the nitrated cellulose exerts an express influence on the solubility of nitrocellulose. It causes the substance to become more soluble due to partial depolymerization and denitration. (A certain, insignificant decrease of nitrogen value occurs owing to partial hydrolysis). According to Bruley [54] the following relationship exists ... 

Nitrocellulose of the same nitrogen contents prepared by denitration had solubilities of 13 and 45% respectively. 

Treatment of nitrocellulose Nitrogen content o/ /o Viscosity of ether-alcohol solution sec Solubility in 95% alcohol 0/ /o Copper number after denitration... 

Similar results due to irradiation were also established by Rogovin and Glas-man [90]. Clement, Riviere and Beck [91] found that under the influence of the light only the viscosity of high-viscosity nitrocellulose was decreased, low-viscosity nitrocellulose did not undergo any change. In view of the experiments of Mine [92], quoted below, this observation appears to be inaccurate. Clement, Riviere and Beck observed, moreover, that the solubility was increased by irradiation. The increase of solubility may be brought about to some extent by a certain denitration... 

More recently Staudinger and Dreher [96] have confirmed these observations, by determining the effect of the time of pulping nitrocellulose in a colloid mill on its molecular weight as determined by viscosity measurement. They further established that owing to intensive milling a partial denitration of nitrocellulose took also place, as seen in Table 56. 

Both Mangenot and Raison, Fenson and Fordham have established from their microscopic studies on swelling and solution of nitrocellulose fibres that the surface of the fibres consists of a thin coating of a distinctively less soluble substance than the interior of fibres. Fenson and Fordham assumed that this was a superficial layer that had been partially denitrated in consequence of drastic stabilization processes. Therefore in the instance of a nitrocellulose of 11% N a solvent penetrates into the fibres through the damaged points of this layer. 

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. 

This method of denitrating cellulose nitrate was widely used industrially to regenerate cellulose from the first (nitrocellulose) artificial fibre (Chardonnet [49]). 

According to a statement of Oldham [53] nitrocellulose can be denitrated by reduction with iron or an iron-zinc mixture in an acetic acid solution. 

Clement and Riviere [59] also reported that cellulose acetate or a mixed ester — a nitrate-acetate — can be obtained by reacting cellulose nitrate with acetic anhydride, acetic acid, and sulphuric acid. According to more recent contributions, e.g. Wolfrom, Bower and Maker [60], the reaction should be performed as follows Cellulose nitrate is dissolved in the cold in a little sulphuric add and acetic anhydride, the surplus of acetic anhydride is then hydrolysed also in the cold, and cellulose acetate is extracted with a suitable solvent, such as chloroform. Other methods of acetylating nitrocellulose consist in reduction, for instance with zinc and hydrogen chloride, which entails denitration of the ester, followed by acetylation with acetic anhydride. All these reactions are carried out in the same vessel. Further, it is possible to synthesize mixed esters, cellulose nitrate-acetates, by subjecting cellulose to the action of a mixture that includes nitric acid, acetic add and acetic anhydride in the presence of sulphuric acid (Kruger [61]). The use of a large amount of nitric acid favours the formation of nitrocellulose only. Mixed esters are formed... 

Tn one of the experiments, a denitration of the nitrocotton without any perceptible loss of weight was observed. This showed that nitrocellulose of low nitrogen content (12.13%), was denitrated with ease, and is in good agreement with Vieille s observation (mentioned above), that lower nitrated nitrocellulose was more easily decomposed when boiled with an acid. Gelernter et al. [96] examined the decomposition of nitrocellulose (10.8-11.8% N) labelled with 15N at 157°C and found the secondary 0N02 groups less stable than those of C6. 

The results obtained by de Bruin and Witte [28a] make it clear that denitration of nitrocellulose with mixed acid may not reach completion even after one year (e.g. denitration of nitrocellulose of 13.95% N with mixed acid containing 21.9% HNOj and 16.9% HzO which yields nitrocellulose of 12.4% N on nitration). 

They pointed out that the rate of denitration is much lower than that of nitration. A theory recently advanced by Trommel [80] explained this in terms of the relative accessibility of the reacting groups in cellulose and nitrocellulose (see p. 239). 

Craik [30] has determined the influence of temperature, and in consequence the effect of the denitration rate, on the solubility of nitrocellulose (Table 78). 

While regarding the formation of the O-nitro derivative of cellulose as an effective resultant from the nitration and denitration processes, the following picture of the course of reaction leading to the formation of nitrocellulose should be kept in mind. 

A new concept of the mechanism of O-nitration of cellulose and denitration of nitrocellulose was recently advanced by Trommel [80]. On the basis of his experiments on the nitration equilibrium of cellulose he came to the conclusion that various reacting groups in cellulose and nitrocellulose molecules differ in their accessibility to nitration and denitration respectively. 

The concentration of the dilute acid in the tanks I, II and III, was maintained more or less constant, so that the acid could be used again for washing nitrocellulose. Excess add went to the denitration plant. 

The essential problem in the operation of kiering whether it takes place in autoclaves or in tubes, lies in the removal of add vapours evolved from the nitrocellulose as a result of the denitration of unstable cellulose esters. Vapours collected in the kiers are removed from time to time by opening a gas-release valve which allows the compressed gases to pass into a special duct. In the continuous boiling process in pipes, the gases are entrained with the suspended nitrocellulose. 

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