Degradation of nitrocellulose

In their more recent paper Claesson, Palm and Wettermark [92b] investigated the magnitude of the degradation of nitrocellulose (12.2% N)... 

See also under Cellulose, Vol 2, p C96 Cellulose Derivatives, Vol 2, p 98-L and Degradation of Nitrocellulose Solutions in this volume... 

Degradation of nitrocellulose involves a complex chemical dissociation into a wide variety of products. Extremely high concentrations of nitrate and nitrite (NOi" /NOi ) are present in leachate from nitrocellulose landfills. Low permeability of the sludge and especially soil/sludge mixture will attenuate effects over long period of time. 

Stability. The stability of nitrocellulose, which was discussed in Chapter 8, is relatively poor. The stability of nitrocellulose based propellants is correspondingly poor. The degradation of nitrocellulose proceeds by two chemical reactions. In the first degradation reaction, nitrocellulose loses nitrogen oxides. The loss of nitrogen oxides... 

The mural paintings in the Monumental Cemetery of Pisa were detached in a restoration after the Second World War, and were later restored on several occasions. They showed an advanced state of degradation. In Figure 11.10 the pyrograms of two samples collected from the paint surfaces (CSG 13bis from Universal Judgement and CSA 5b from Stories of Holy Fathers ) are compared with the pyrograms of nitrocellulose, starch and arabic gum. 

Alcohol from dehydration contains a certain quantity of nitrocellulose, i.e. its soluble fractions, mostly degraded, and a certain amount in suspension. Experiments have shown that about 2.2 g of dissolved nitrocellulose and 1.3 g of nitrocellulose in suspension—a total 3.5 g—occur in 11. of 70% alcohol from centrifuges. Sometimes however, the content of nitrocellulose in the alcohol may reach 10-12 g/1. 

Nitrocellulose with a decreased molecular weight may be obtained as the result of depolymerization (degradation) of the cellulose before nitration, e.g. by keeping it at a temperature of 150-170°C or by treating it with acids. The resultant hydrocellulose, which usually possesses a lower molecular weight than cellulose, is then subjected to nitration to produce a more soluble substance as compared with the nitration product of a non-depolymerized raw material. 

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. 

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... 

Thus Rogovin and Shlakhover [81] performed a stepwise nitration applying mixed acids composed of nitric acid, acetic anhydride and acetic add. Nitrating mixtures of this composition do not bring about degradation, hydrolysis or oxidation of nitrocellulose during the nitration (see p. 344). Each additional nitration causes an increase of viscosity. The results are collected in Table 52. 

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). 

Ultrasonic waves also bring about a reduction in the viscosity of nitrocellulose. The effect is more marked the higher the initial viscosity, and thus the longer the nitrocellulose chains (Sollner [93] Schmidt and Rommel [94]). For instance, nitrocellulose with a molecular weight of 123,000, estimated by means of Staudinger s viscosity equation, subjected in solution form to the action of ultrasonic waves suffered a degradation to a molecular weight of 70,000-80,000. 

In more recent experiments, Edelmann [95] has followed the depolymerization of nitrocellulose in dilute (0.5%) solution. He reported that nitrocellulose of an average polymerization degree n = 1060, and containing considerably amounts of the n > 2500 fraction, was degraded after being subjected for 1 and 4 hr to the action of ultrasonic waves of 800 kc/sec to an average polymerization degree of n = 910 and 630 respectively. By fractionation, the presence of a small quantity of n = 1400 was established in the latter. 

Nitration of chitin was carried out for the first time by Fiirth and Scholl [54J. They tried to produce degradation of the chitin by acting with fuming nitric acid (d 1.525). They obtained two products one insoluble in the common organic solvents, the other soluble in polar solvents. Most likely they were nitrochitin and the oxidation product, respectively. The authors pointed out a similarity between nitrochitin and nitrocellulose. Later on, Schmidt [55] examined the birefringence of chitin and nitrochitin. 

Methods in which stability can be estimated from the physical degradation of a nitrocellulose gel (viscometric measurements). 

The formation of starch complexes with other polysaccharides is perhaps best evidenced by the sorption of starch on cellulose and its derivatives. This sorption is selective with respect to amylose and amylopectin.1065 1066 Cotton fibers selectively adsorb amylose and not amylopectin.1667-1071 However, this method cannot be used for starch fractionation because cotton was considered to induce degradation (hydrolysis).1067 On the other hand, a method of purifying amylopectin that involves sorption of amylose on defatted cellulose has been published.1072 Reversible adsorption of amylopectin on cellulose occurs when starch is equilibrated with urea in 32-35% ethanol. There are also published attempts to separate starch components on filter paper.1073-1076 The reverse idea is applied in the stabilization of nitrocellulose by its sorption on starch.1077... 

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