Nitrocellulose solution viscosity

An important factor influencing the dimensions of the predried powder is the viscosity of the nitrocellulose solution. The lower the viscosity of the nitrocellulose, the greater is the shrinkage of the nitrocellulose gel on drying. This produces flakes or tubes of considerably smaller size than those from nitrocellulose of higher viscosity. 

With regard to their viscosity, nitrocellulose solutions demonstrate the typical properties of lyophilic colloids. The action of pressure, temperature and concentration causes anomalies to appear indicating that these solutions deviate from the... 

The viscosity of nitrocellulose solutions is to some extent dependent on the composition of the solvent, and on its solvent capacity or strength . Masson and McCall [58] have examined the viscosity of nitrocellulose solutions in acetone to which different amounts of water had been added. They obtained a curve, reproduced in Fig. 101, that illustrates the effect of the water content of the acetone on the viscosity of nitrocellulose solutions. 

The viscosity of nitrocellulose solutions in ether-alcohol undergoes similar changes as the composition of the solvent is modified. 

Fig. 102. Influence of the composition of the solvent (alcohol and ether) on the viscosity of nitrocellulose solutions (Gibson and McCall [57]).

The addition of aromatic hydrocarbons to a nitrocellulose solution in amyl acetate produces an increase in the viscosity of the solutions, as shown in a diagram published by Drinberg [62] (Fig. 103). 

It is very interesting to observe the influence of aldehydes on nitrocellulose solutions. This has been done by Kozlov and Bedushevskaya [66]. This effect is most complicated, since in accordance with the said authors two processes were occurring simultaneously the formation of cross links which produced an increase of viscosity, and a degradation of the long-chain molecules which reduced the viscosity. 

The effect of temperature on the viscosity of nitrocellulose solutions has been studied by many authors, e.g. Nishida [68], Drinberg [62], E. Karrer et al. [69], Kozlov [70] and Goldman [71]. These experiments showed that the viscosity of concentrated nitrocellulose solutions is lowered more quickly, the higher the concentration of the solution. Attempts were made by E. Karrer, Berl and Umstatter [69] to find a formula expressing the relationship between the viscosity and the temperature (from 20 to 48°C). Shor [72] has examined the viscosity of nitrocellulose solutions within the concentrations range 14.9-17.9% and at temperatures from 0 to 40°C. On the basis of a mathematical analysis of the numerical results, the author has deduced the following formula ... 

Ageing of nitrocellulose solutions. The tendency of nitrocellulose solutions to undergo changes in the course of time (to age ) has been known for many years. It consists mainly in a decrease of viscosity during the first ten to twenty hours after dissolution. At room temperature the decrease of viscosity stops after 1-2 days. At an elevated temperature it continues, and the viscosity approaches a certain asymptotic limiting value, that may be estimated by means of extrapolation. 

Fig. 104. Change of viscosity of nitrocellulose solution with temperature (o —experimental and h— calculated values), according to Shor...

Effect of the degree of polymerization on the viscosity. It has been made clear by the experiments of many authors that operations leading to the degradation of cellulose prior to nitration contributes to the production of a less viscous nitrocellulose. Moreover, the degree of polymerization of cellulose before nitrating depends upon the origin of the cellulose the type of plant, its age and so on. The properties of the cellulose, such as polymerization degree, are passed on to the nitrocellulose, as already stressed (p. 246), to exert an influence on the viscosity of the product. Hence cotton yields nitrocellulose solutions more viscous than these from wood... 

The relationship between the viscosity of nitrocellulose solutions and the age of poplar wood cellulose according to Pascal [74], is shown in Table 45. 

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. 

The effect of heat treatment of cellulose on the viscosity of nitrocellulose solutions... 

Effect of the conditions of nitration. The conditions under which the nitration was carried out exert an appreciable influence on the viscosity of nitrocellulose solutions. Thus a high nitrating temperature produces low viscosity nitrocellulose... 

In order to avoid the degradation of cellulose Wannow [82] used a mixture of nitric add with phosphoric add and water at temperatures of 0 and 20°C. The constant degree of polymerization was demonstrated by measuring the osmotic pressure. It has been confirmed that the viscosity of nitrocellulose solutions depends upon the nitrogen content of the substance (Fig. 105). 

The extent to which the composition of the mixed add influenced the viscosity of the nitrocellulose was followed by Berl and Berkenfeld [83]. They demonstrated that enriching the nitrating mixtures with sulphuric acid caused a considerable decrease in the viscosity of the nitrocellulose solutions. 

Fig. 105. Change of viscosity of nitrocellulose solutions with nitrogen content (Wannow [82]). h— Nitration at 0PC, o — at 20°C.

Viscosity determinations at the highest convenient concentration are of practical value, because in most of the applications of nitrocellulose, solutions of these concentrations are used, and there is usually little difference between the concentration in use and that used for the determination. All nitrocellulose solutions that are not very dilute show more or less abnormal viscosity, i.e. the rate of flow is not proportional to the applied stress or pressure. The ease of flow of a solution at one degree of stress cannot then be inferred from a viscosity determined at another. Nevertheless the measured viscosity of a comparatively concentrated solution is in general useful information. This advantage is sacrificed in what is the most rational of all viscosity systems, the German I.G. Method. Measurements are made in dilute solutions and the results are expressed in terms of the Eigenviscositat (k) of Fikentscher and Mark [99] a function which to a large extent is independent of concentration ... 

Apard [27] found that the addition of finely powdered plumbous oxide, calcium oxide or calcium hydroxide to a 1% nitrocellulose solution in acetone, ether-alcohol or amyl acetate initially brought about an increase of the viscosity. Further addition of these substances caused the nitrocellulose to coagulate, together with the added... 

There exist instances where an increase in the viscosity of nitrocellulose solutions is recommended as in the product intended for manufacture of blasting gelatine, i.e. for the solution of nitrocellulose nitroglycerine. The solution must have the consistency of firm gelatine. 

Radiation of 253.6 mft wave-length especially is capable of reducing the viscosity of nitrocellulose solutions. Radiation of 366 mfi wave-length has practically no influence on the viscosity. Nitrogen content was decreased in both cases. With 366 mp, radiation applied under specific experimental conditions, the nitrogen content was reduced after 48 hr from 11.85 to 11.68%. 

Dynamite nitrocotton is pulped within as short a period of time as possible, e.g. 2 hr, because excessive beating of the product reduces the viscosity of the nitrocellulose solutions. The pulping is followed by washing or by a short poaching in boilers, after which the purity is checked by means of the heat test. After stabilization, the nitrocotton is freed from sand and. other impurities. 

The viscosity of nitrostarch solutions is appreciably lower than the viscosity of the corresponding nitrocellulose solutions. Taking the viscosity of water as 100, the viscosity of 1% nitrostarch solutions varies within the relative values of 45 and 70. Due to such low viscosity and non-oriented crystal structure, nitrostarch solutions leave very fragile film after evaporation. Hence nitrostarch is valueless for varnish production, and for smokeless powder making. 

T. Urbanski (I27j suggested recrystallization to add a protective colloid such as an acetone solution of nitrocellulose (low viscosity grade collodium cotton). 

Both these characteristics are responsible for the veiy high viscosity of nitrocellulose solutions. 

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