Cellulose nitric acid reaction. Cellulose nitrates, their production, properties and applications
One of the negative consequences of the development of technology in modern world are car accidents. Every year they claim the lives of more than 1 million people, and more than fifty million are injured of varying severity. The French chemist Edouard Benedictus contributed to the process of reducing the number of victims and injuries on the roads.
At the beginning of the 20th century, Benedictus, during experiments, accidentally caught a flask, which, falling from a shelf, did not shatter, but only cracked, retaining its original shape. This episode made Edward think. An ethereal-alcohol solution of cellulose nitrate was previously stored in this vessel, which, having evaporated, left a very thin layer of cellulose nitrate on the walls of the flask, which did not interfere at all with observing the contents of the vessel.
In those days, car windshields were made of completely ordinary glass, which, in an accident, shattered into a large number of sharp fragments that seriously injured the driver and passengers.
It was one such incident with a car accident, which Benedictus learned about from the newspapers, that made the scientist remember the surviving flask. After some experimentation with cellulose nitrate coating of glass, he found an option that was ideal for automotive glass. Its essence was as follows: a layer of cellulose nitrate was placed between two ordinary glasses. After heating such a “sandwich”, the inner layer melted, and the glasses were reliably glued together.
Such double-glazed windows even withstood a hammer blow, while they cracked, but did not crumble into fragments and retained their original shape. So, in 1909, a glass was invented and patented by Eduard Benedictus under the name "Triplex".
At about the same time, another scientist, the Englishman John Wood, was struggling with the problem of creating safety glasses. He received his patent for the invention of special glass in 1905. However, Wood's glass did not go into mass production due to the high cost of consumables. The essence of his invention was that instead of cellulose nitrate, expensive rubber was used in the inner layer. In addition, the final product lost some of its transparency, which caused discomfort for drivers.
At first, Benedictus's invention was also not to the liking of car manufacturers, as it increased its cost. But it was appreciated by the military. Glasses "triplex" were baptized by fire during the First World War, because they were used in gas masks.
In the automotive industry, Henry Ford was the first to introduce triplexes. This happened in 1919. It took about 15 years for other car manufacturers to start using triplexes. These glasses are still in use today.
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Burning nitrocellulose
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General information
Nitrocellulose - fibrous loose mass white color, By appearance similar to cellulose. One of the most important characteristics is the degree of substitution of hydroxyl groups for nitro groups. In practice, most often not a direct designation of the degree of substitution is used, but nitrogen content, expressed as a percentage by weight. Depending on the nitrogen content, there are [ ]
- colloxylin (10.7 - 12.2% nitrogen)
- pyroxylin No. 2 (12.05 - 12.4% nitrogen)
- pyrocollodium (12.6% nitrogen) - a special type of nitrocellulose, first obtained by D. I. Mendeleev, insoluble in alcohol, soluble in a mixture of alcohol and ether.
- pyroxylin No. 1 (13.0 - 13.5% nitrogen)
- 1832 - French chemist Henri Braconnot discovered that when starch and wood fibers are treated with nitric acid, an unstable combustible and explosive material is formed, which he called Xyloidine (Xyloїdine)
- 1838 - Another French chemist, Theophile-Jules Pelouze, treated paper and cardboard in a similar way and obtained a similar material, which he called Nitramidine. The low stability of the resulting nitrocellulose did not allow it to be used for technical purposes.
- 1846 - Swiss chemist Christian Friedrich Schönbein accidentally discovered a more practical way to produce nitrocellulose. While working in the kitchen, he spilled concentrated nitric acid on the table. To remove the acid, the chemist used a cotton rag and then hung it up to dry on the stove. After drying, the fabric burned with an explosion. Schonbein developed the first acceptable method for producing nitrocellulose - processing one part of cotton fibers in fifteen parts of a mixture of sulfuric and nitric acids in a ratio of 50:50. Nitric acid reacted with cellulose to form water and sulfuric acid was needed to prevent dilution. After several minutes of treatment, the cotton was removed from the acid, washed in cold water before removal of acids and dried.
- 1869 - in England, under the leadership of Frederick Augustus Abel, a technology was developed with the grinding of nitrocellulose in special hollanders and repeated (up to 8 times) long washing and drying, each of which lasted up to 2 days. Hollander puts an oval bath in cross section with transverse knives fixed in it. A shaft passes to the side of the knives, with wavy disc knives. As the shaft rotates, the knives of the shaft pass between the fixed knives and cut the nitrocellulose fiber. The ratio of sulfuric and nitric acids in the mixture was changed to 2:1. Using this technology, it was possible to obtain a product that is quite stable during storage and use.
Ten years after the patenting of this technology, pyroxylin began to be adopted around the world, first as a filling for shells and sea mines. Another application that colloxylin found almost immediately was the production of glue for sealing small wounds. In the absence of a patch (in our current understanding), this glue quickly gained popularity. In fact, it was a kind of thick nitrolac. Several years later, a series of explosions at factories and warehouses occupied by processes involving pyroxylin forced a closer look at the problem of stabilizing this product. Despite all the difficulties, since 1879 to this day, cellulose nitrates are widely used in the technology of energy-saturated compounds and many other areas of industry.
Receipt
The best raw materials for the production of nitrocellulose are long-staple varieties of hand-picked cotton. Machine-assembled cotton and wood pulp contain a significant amount of impurities that complicate preparation and reduce product quality. Nitrocellulose is obtained by treating purified, loosened and dried cellulose with a mixture of sulfuric and nitric acids, called a nitrating mixture.
Cellulose nitrates
Cellulose nitrates- esters of cellulose and nitric acid. Cellulose nitrates are obtained by the reaction of cellulose esterification with nitric acid, called the nitration reaction:
[C 6 H 7 O 2 (OH) 3] n + xn HNO 3 [C 6 H 7 O 2 (OH) 3- X(ONO 2) X]n + xn H 2 O.
cellulose nitrate
This reaction is reversible, so it is carried out in the presence of water-removing agents. In industry, a mixture of HNO 3 - H 2 SO 4 - H 2 O is used for nitration. Sulfuric acid not only binds water, but also causes swelling of cellulose and thereby accelerates the diffusion of nitric acid into its crystalline part. During nitration, side reactions of cellulose proceed: hydrolytic degradation under the action of water (catalyst H 2 SO 4) and oxidative destruction under the action of HNO 3.
Cellulose nitrates are thermoplastics. Depending on the degree of substitution, estimated by the nitrogen content, they are divided into colloxylins(nitrogen content 10.5–12.2%) and pyroxylins(nitrogen content 12.3–13.7%). The theoretical mass fraction of nitrogen in cellulose trinitrate (i.e., the degree of substitution is 3) is 14.14%. Cellulose nitrates are flammable, highly flammable and explosive if high in nitrogen.
Pyroxylins and colloxylins with a high nitrogen content are used in the production smokeless powder, dynamite, solid propellant and other explosives. Colloxilin is used in the production of etrols, celluloid, varnishes, adhesives.
Etrol is a thermoplastic material obtained on the basis of plasticized cellulose nitrate with mineral and organic fillers, and is used for various parts of technical products and consumer goods. Previously, photographic and film films were obtained from cellulose nitrates, but due to the easy flammability, the production of such a film was discontinued. The nitrocellulose film has been replaced by a non-combustible cellulose acetate film.
Celluloid- plastic based on cellulose nitrate plasticized with camphor. Essentially, it is a solid solution of cellulose nitrate in camphor. It is widely used for the manufacture of haberdashery, toys, table tennis balls. However, due to its high flammability, its use is being phased out, as is that of nitrocellulose etrol.
Nitro-varnishes- solutions of cellulose nitrate in solvents, usually in mixtures of solvents, containing plasticizers. The basis of the varnish is colloxylin. On the basis of nitro-varnishes, nitro-paints, nitro-enamels, nitro-mastics are made.
Cellulose nitrate properties
Cellulose nitrates (NC) are high-molecular explosives of the general formula n. They are nitrate polyesters of cellulose polysaccharide. These are compounds containing ONO2 nitrate groups bound to the carbon atom. Technical cellulose nitrates are complex polymers, chemically heterogeneous, containing from 5 to 15% of unsubstituted hydroxyl groups, with different nitrogen content.
The specific properties of cellulose nitrates determine the scope of their application. Ease of ignition, the possibility of transformation by plasticization into a material that burns according to a certain law in parallel layers, release a large number gases during their combustion, a large raw material base explain the almost monopoly of their use for smokeless powders.
Due to the high mechanical strength of cellulose nitrates, good compatibility with plasticizers and the transition to a plastic state with a slight increase in temperature, it is advisable to use them for the manufacture, in particular, of celluloid.
Solubility of cellulose nitrates in common solvents such as alcohol, ether, acetone and high mechanical properties The obtained films make it possible to use them for the production of nitro-varnishes and lacquer coatings. Their solubility is affected by their nitrogen content, viscosity, temperature, uniformity in degree of esterification, and the composition of the solvent.
The industry produces the following main types of cellulose nitrates:
Colloxilin with a content of 10.7-12.2% nitrogen;
Pyroxylin No. 2 with a content of 12.2-12.4% nitrogen;
Pyroxylin No. 1 with a content of 13-3.5% nitrogen.
In the production of varnishes and paints, cellulose nitrates are required to ensure the manufacturability of the solution. low viscosity, which corresponds to the degree of polymerization in the range of 100-300. Great importance has the viscosity of pyroxylins in the production of pyroxylin powders. The most rational conditional viscosity for pyroxylin No. 1 is 6-10? Uh, for pyroxylin No. 2-4-8? E. In the paint and varnish industry, where colloxylins are mainly used, during analytical control their quality is estimated by the viscosity of their solutions in the combined solvent of the composition,%: technical normal butyl acetate-12.5; technical acetone-5; ethyl alcohol-17.5; butyl synthetic alcohol-15; petroleum toluene-50.
Depending on the tested brand of colloxylin, solutions are prepared in this solvent with a mass fraction of 8.20 and 25%.
To expand the field of application, it is necessary to obtain colloxylins that are readily soluble in lower alcohols, such as ethyl, methyl. The dissolving effect of methyl alcohol, like ethyl alcohol, depends on the degree of esterification of cellulose nitrates.
To obtain the alcohol-soluble colloxylin we need, it is necessary to modify its properties by saponification with various reagents, namely, solutions of acid salts of hydrosulfide acid, solutions of caustic soda, solutions of sulfuric and nitric acids. But, first of all, it is necessary to study the properties of colloxylin, its scope, methods of obtaining and determine the optimal conditions for obtaining alcohol-soluble colloxylin, the main characteristics of which correspond to the following values:
Conditional viscosity 1.5-1.7;
Degree of polymerization 300-600.
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