Cellulose composition physical and chemical properties application. Structure and properties of cellulose and its satellites. Obtaining acetate fiber
Everyday objects that have become familiar to us and are found everywhere in our Everyday life, it would be impossible to imagine without the use of organic chemical products. Long before Anselm Pay, as a result of which he was able to discover and describe a polysaccharide in 1838, which received “cellulose” (a derivative of the French cellulose and the Latin cellula, which means “cell, cell”), the property of this substance was actively used in the production of the most irreplaceable things.
Expanding knowledge about cellulose has led to the emergence of a wide variety of things made from it. Paper of various types, cardboard, parts made of plastic and artificial viscose, copper-ammonia), polymer films, enamels and varnishes, detergents, food additives (E460) and even smokeless powder are products of the production and processing of cellulose.
In its pure form, cellulose is a white solid with quite attractive properties and is highly resistant to various chemical and physical influences.
Nature has chosen cellulose (fiber) as its main building material. IN flora it forms the basis for trees and other higher plants. In nature, cellulose is found in its purest form in the hairs of cotton seeds.
Unique properties of this substance are determined by its original structure. The formula of cellulose has the general notation (C6 H10 O5)n, from which we see a pronounced polymer structure. The β-glucose residue, which is repeated a huge number of times and has a more expanded form as -[C6 H7 O2 (OH)3]-, is combined into a long linear molecule.
The molecular formula of cellulose determines its unique chemical properties to withstand the effects of aggressive environments. Cellulose is also highly resistant to heat; even at 200 degrees Celsius, the substance retains its structure and does not collapse. Self-ignition occurs at a temperature of 420°C.
Cellulose is no less attractive for its physical properties. cellulose in the form of long threads containing from 300 to 10,000 glucose residues without side branches largely determines the high stability of this substance. The glucose formula shows how many give cellulose fibers not only great mechanical strength, but also high elasticity. The result of analytical processing of many chemical experiments and studies was the creation of a model of the cellulose macromolecule. It is a rigid helix with a pitch of 2-3 elementary units, which is stabilized by intramolecular hydrogen bonds.
It is not the formula of cellulose, but the degree of its polymerization that is the main characteristic for many substances. So in unprocessed cotton the number of glucoside residues reaches 2500-3000, in purified cotton - from 900 to 1000, purified wood pulp has an indicator of 800-1000, in regenerative cellulose their number is reduced to 200-400, and in industrial cellulose acetate it ranges from 150 up to 270 “links” in a molecule.
The product used to obtain cellulose is mainly wood. The main technological process of production involves cooking wood chips with various chemical reagents, followed by cleaning, drying and cutting the finished product.
Subsequent processing of cellulose makes it possible to obtain a variety of materials with specified physical and chemical properties, allowing the production of a wide variety of products, without which life modern man it is hard to imagine. The unique formula of cellulose, adjusted by chemical and physical treatment, became the basis for obtaining materials that have no analogues in nature, which made it possible to widely use them in chemical industry, medicine and other branches of human activity.
Being in nature. Physical properties.
- 1. Cellulose, or fiber, is part of plants, forming cell walls in them.
- 2. This is where its name comes from (from the Latin “cellulum” - cell).
- 3. Cellulose gives plants the necessary strength and elasticity and is, as it were, their skeleton.
- 4. Cotton fibers contain up to 98% cellulose.
- 5. Flax and hemp fibers are also mainly composed of cellulose; in wood it is about 50%.
- 6. Paper and cotton fabrics are products made from cellulose.
- 7. Particularly pure examples of cellulose are cotton wool obtained from purified cotton and filter (un-glued) paper.
- 8. Cellulose, isolated from natural materials, is a solid fibrous substance that is insoluble in either water or ordinary organic solvents.
Cellulose structure:
- 1) cellulose, like starch, is a natural polymer;
- 2) these substances even have the same structural units in composition - residues of glucose molecules, the same molecular formula (C 6 H 10 O 5) n;
- 3) the n value of cellulose is usually higher than that of starch: its average molecular weight reaches several million;
- 4) the main difference between starch and cellulose is the structure of their molecules.
Finding cellulose in nature.
- 1. In natural fibers, cellulose macromolecules are located in one direction: they are oriented along the fiber axis.
- 2. The numerous hydrogen bonds that arise between the hydroxyl groups of macromolecules determine the high strength of these fibers.
- 3. In the process of spinning cotton, flax, etc., these elementary fibers are woven into longer threads.
- 4. This is explained by the fact that the macromolecules in it, although they have a linear structure, are located more randomly and are not oriented in one direction.
The construction of starch and cellulose macromolecules from different cyclic forms of glucose significantly affects their properties:
- 1) starch is important product human nutrition, cellulose cannot be used for this purpose;
- 2) the reason is that enzymes that promote starch hydrolysis do not act on the bonds between cellulose residues.
Chemical properties of cellulose.
- 1. From everyday life it is known that cellulose burns well.
- 2. When wood is heated without air access, thermal decomposition of cellulose occurs. This produces volatile organic compounds, water and charcoal.
- 3. Among the organic products of wood decomposition are methyl alcohol, acetic acid, and acetone.
- 4. Cellulose macromolecules consist of units similar to those that form starch; it undergoes hydrolysis, and the product of its hydrolysis, like starch, will be glucose.
- 5. If you grind pieces of filter paper (cellulose) soaked in concentrated sulfuric acid in a porcelain mortar and dilute the resulting slurry with water, and also neutralize the acid with alkali and, as in the case of starch, test the solution for reaction with copper (II) hydroxide, then the appearance of copper(I) oxide will be visible. That is, hydrolysis of cellulose occurred in the experiment. The hydrolysis process, like that of starch, occurs in steps until glucose is formed.
- 6. In total, the hydrolysis of cellulose can be expressed by the same equation as the hydrolysis of starch: (C 6 H 10 O 5) n + nH 2 O = nC 6 H 12 O 6.
- 7. Structural units of cellulose (C 6 H 10 O 5) n contain hydroxyl groups.
- 8. Due to these groups, cellulose can produce ethers and esters.
- 9. Great importance have cellulose nitrate esters.
Features of cellulose nitrate ethers.
- 1. They are obtained by treating cellulose with nitric acid in the presence of sulfuric acid.
- 2. Depending on the concentration of nitric acid and other conditions, one, two or all three hydroxyl groups of each unit of the cellulose molecule enter into the esterification reaction, for example:
N + 3nHNO 3 > n + 3nH 2 O.
A common property of cellulose nitrates is their extreme flammability.
Cellulose trinitrate, called pyroxylin, is a highly explosive substance. It is used to produce smokeless powder.
Cellulose acetate esters - cellulose diacetate and triacetate - are also very important. Cellulose diacetate and triacetate appearance similar to cellulose.
Application of cellulose.
- 1. Due to its mechanical strength, wood is used in construction.
- 2. Various types of carpentry products are made from it.
- 3. In the form of fibrous materials (cotton, flax) it is used for the manufacture of threads, fabrics, ropes.
- 4. Cellulose isolated from wood (freed from accompanying substances) is used to make paper.
- 27. Lipids. Classification
Fats in nature, their physical properties.
- 1. Along with carbohydrates and proteins, fats are part of all plant and animal organisms and constitute one of the main parts of food.
- 2. Animal fats are usually solids.
- 3. Vegetable fats are often liquid and are also called oils.
- 4. Liquid fats of animal origin (for example, fish oil) and solid fats are also known vegetable oils(eg coconut oil).
- 5. All fats are lighter than water.
- 6. They are insoluble in water, but dissolve well in many organic solvents (dichloroethane, gasoline).
Features of the structure of fats.
The structure of fats was established by M. Chevrel and M. Berthelot. By heating fats with water (in the presence of alkali), M. Chevreul at the beginning of the 19th century. found that by adding water, they decompose into glycerin and carboxylic acids - stearic, oleic, etc. M. Berthelot (1854) carried out the reverse reaction. He heated a mixture of glycerin and acids and obtained substances similar to fats; M. Chevreul carried out the hydrolysis reaction of the ester, and M. Berthelot carried out the esterification reaction, i.e., the synthesis of the ester. Based on these data, it is easy to come to a conclusion about the structure of fats.
Characteristics of fats.
- 1. Fats are esters of trihydric alcohol glycerol and carboxylic acids.
- 2. In most cases, fats are formed by higher saturated and unsaturated carboxylic acids, mainly:
- a) palmitic C 15 H 31 -COOH;
- b) stearic C 17 H 35 -COOH;
- c) oleic C 17 H 33 -COOH;
- d) linoleic C 17 H 31 -COOH and some others.
- 3. To a lesser extent, lower acids participate in the formation of fats, for example, butyric acid C 3 H 7 -COOH (in butter), caproic acid C 5 H 11 -COOH, etc.
- 4. Fats, which are formed mainly by saturated acids, are solid (beef fat, lamb fat).
- 5. With an increase in the content of unsaturated acids, the melting point of fats decreases, they become more fusible (lard, butter).
The chemical properties of fats are determined by their belonging to the class of esters. Therefore, the most characteristic reaction for them is hydrolysis.
Fats as nutrients.
1. Fats are important integral part our food.
When they are oxidized, the body releases twice as much heat as when the same amounts of proteins and carbohydrates are oxidized.
- 2. As substances that are insoluble in water, fats cannot be directly absorbed into the body from the digestive organs.
- 28. Acylglycerols. Structure, chemical properties
Acylglycerols
The most important and widespread group of simple neutral lipids are acylglycerols. Acylglycerols (or glycerides) are esters of glycerol and higher carboxylic acids (Table 1). They make up the bulk of lipids (sometimes up to 95%) and, essentially, they are called fats or oils. The composition of fats consists mainly of triacylglycerols (I), as well as diacylglycerols (II) and monoacylglycerols (III) (Fig. 1).
Figure 1 - triacylglycerols (I), diacylglycerols (II) and monoacylglycerols (III); R, R", R"" - hydrocarbon radicals.
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Tianshi cellulose, cellulose
Cellulose(French cellulose from Latin cellula - “cell, cell”) - carbohydrate, polymer with the formula (C6H10O5)n, white solid, insoluble in water, the molecule has a linear (polymer) structure, the structural unit is a β-glucose residue n . Polysaccharide, the main component of the cell walls of all higher plants.
- 1. History
- 2 Physical properties
- 3 Chemical properties
- 4 Receipt
- 5 Application
- 6 Being in nature
- 6.1 Organization and function in cell walls
- 6.2 Biosynthesis
- 7 Interesting facts
- 8 Notes
- 9 See also
- 10 Links
Story
Cellulose was discovered and described by the French chemist Anselme Payen in 1838.
Physical properties
Cellulose is a white, solid, stable substance that does not collapse when heated (up to 200 °C). It is a flammable substance, ignition temperature 275 °C, auto-ignition temperature 420 °C (cotton cellulose). Soluble in a relatively limited number of solvents - aqueous mixtures complex compounds transition metal hydroxides (Cu, Cd, Ni) with NH3 and amines, some mineral (H2SO4, H3PO4) and organic (trifluoroacetic) acids, amine oxides, some systems (for example, sodium iron complex - ammonia - alkali, DMF - N2O4)..
Cellulose is a long thread containing 300-10,000 glucose units, without side branches. These threads are interconnected by many hydrogen bonds, which gives cellulose greater mechanical strength while maintaining elasticity.
Registered as food additives E460.
Chemical properties
Cellulose consists of residues of glucose molecules, which are formed during the hydrolysis of cellulose:
(C6H10O5)n + nH2O nC6H12O6
Sulfuric acid and iodine, due to hydrolysis, color cellulose blue. One iodine - only in brown.
When reacted with nitric acid, nitrocellulose (cellulose trinitrate) is formed:
In the process of esterification of cellulose with acetic acid, cellulose triacetate is obtained:
Cellulose is extremely difficult to dissolve and undergo further chemical transformations, but in a suitable solvent environment, such as an ionic liquid, this process can be carried out efficiently.
During heterogeneous hydrolysis, the parameter n decreases to a certain constant value (the limiting value of the degree of polymerization after hydrolysis), which is due to the completion of hydrolysis of the amorphous phase. When cotton cellulose is hydrolyzed to its limit, a free-flowing snow-white powder is obtained - microcrystalline cellulose (degree of crystallinity 70-85%; average crystallite length 7-10 nm), when dispersed in water a thixotropic gel is formed. During acetolysis, cellulose is converted into the reducing disaccharide cellobiose (formula I) and its oligomer homologues.
The thermal destruction of cellulose begins at 150 °C and leads to the release of low molecular weight compounds (H2, CH4, CO, alcohols, carbonyl compounds, carbonyl derivatives, etc.) and products of a more complex structure. The direction and degree of decomposition are determined by the type of structural modification, degrees of crystallinity and polymerization. The yield of one of the main degradation products, levoglucosan, varies from 60-63 (cotton cellulose) to 4-5% by weight (viscose fibers).
The process of cellulose pyrolysis general view, according to thermal analysis, proceeds as follows. First, physically bound water evaporates over a wide temperature range from 90 to 150 °C. Active decomposition of cellulose with weight loss begins at 280 °C and ends at approximately 370 °C. The maximum rate of mass loss occurs at 330-335 °C (D7T curve). During the period of active decomposition, about 60-65% of the mass of the sample is lost. Further weight loss occurs at a lower rate; the remainder at 500 °C is 15-20% of the cellulose sample (7T curve). Active decomposition occurs with heat absorption (DHL curve). The endothermic process becomes exothermic with maximum heat release at 365 °C, i.e., after the main mass loss. Exothermics with a maximum at 365 °C are associated with secondary reactions - with the decomposition of primary products. If thermal analysis is carried out in a vacuum, i.e., the evacuation of primary products is ensured, then the exothermic peak on the DTA curve disappears.
Interestingly, with different durations of heating cellulose, different chemical processes occur.
When a sample is irradiated with light with a wavelength< 200 нм протекает фотохимическая деструкция целлюлозы, в результате которой снижается степень полимеризации, увеличиваются полидисперсность, содержание карбонильных и карбоксильных групп.
Receipt
By industrial method, cellulose is produced by boiling wood chips at pulp mills that are part of industrial complexes (mills). Based on the type of reagents used, the following methods of pulp cooking are distinguished:
- Sour:
- Sulfite. The cooking solution contains sulfurous acid and its salt, for example sodium hydrosulfite. This method is used to obtain cellulose from low-resin wood species: spruce, fir.
- nitrate. The method consists of treating cotton cellulose with 5-8% HNO3 for 1-3 hours at a temperature of about 100 °C and atmospheric pressure, followed by washing and extraction dilution with NaOH solution
- Alkaline:
- Natronny. A sodium hydroxide solution is used. The soda method can be used to obtain cellulose from deciduous wood and annual plants. The advantage of this method is the absence of an unpleasant odor of sulfur compounds, the disadvantages are the high cost of the resulting cellulose. The method is practically not used.
- Sulfate. The most common method today. A solution containing sodium hydroxide and sodium sulfide, called white liquor, is used as a reagent. The method gets its name from sodium sulfate, from which sulfide for white liquor is obtained at pulp mills. The method is suitable for producing cellulose from any type of plant material. Its disadvantage is the release of a large amount of foul-smelling sulfur compounds: methyl mercaptan, dimethyl sulfide, etc. as a result of adverse reactions.
The technical cellulose obtained after cooking contains various impurities: lignin, hemicelluloses. If cellulose is intended for chemical processing (for example, to produce artificial fibers), then it is subjected to refining - treatment with a cold or hot alkali solution to remove hemicelluloses.
To remove residual lignin and make the pulp white, it is bleached. Traditional chlorine bleaching in the 20th century included two steps:
- chlorine treatment - to destroy lignin macromolecules;
- alkali treatment - to extract the resulting products of lignin destruction.
Since the 1970s, ozone bleaching has also come into practice. In the early 1980s, information appeared about the formation of extremely dangerous substances - dioxins - during chlorine bleaching. This led to the need to replace chlorine with other reagents. Currently, bleaching technologies are divided into:
- ECF (Elemental chlorine free)- without the use of elemental chlorine, replacing it with chlorine dioxide.
- TCF (Total chlorine free)- completely chlorine-free bleaching. Oxygen, ozone, hydrogen peroxide, etc. are used.
Application
Cellulose and its esters are used to produce artificial fibers (viscose, acetate, copper-ammonia silk, artificial fur). Cotton, consisting mostly of cellulose (up to 99.5%), is used to make fabrics.
Wood pulp is used to produce paper, plastics, film and photographic films, varnishes, smokeless powder, etc.
Being in nature
Cellulose is one of the main components of plant cell walls, although the content of this polymer in different plant cells or even parts of the wall of a single cell varies greatly. For example, the cell walls of the endosperm cells of cereals contain only about 2% cellulose, while the cotton fibers surrounding cotton seeds consist of more than 90% cellulose. The cell walls in the tip region of elongated cells characterized by polar growth (pollen tube, root hair) contain virtually no cellulose and consist mainly of pectins, while the basal parts of these cells contain significant amounts of cellulose. In addition, the cellulose content in the cell wall changes during ontogenesis; usually, secondary cell walls contain more cellulose than primary ones.
Organization and function in cell walls
Individual cellulose macromolecules will include from 2 to 25 thousand D-glucose residues. Cellulose in cell walls is organized into microfibrils, which are paracrystalline assemblies of several individual macromolecules (about 36) interconnected by hydrogen bonds and van der Waals forces. Macromolecules located in the same plane and interconnected by hydrogen bonds form a sheet within a microfibril. The sheets of macromolecules are also connected to each other by a large number of hydrogen bonds. Although hydrogen bonds themselves are quite weak, due to the fact that there are many of them, cellulose microfibrils have high mechanical strength and resistance to the action of various enzymes. Individual macromolecules in a microfibril begin and end in different places, so the length of the microfibril exceeds the length of the individual cellulose macromolecules. It should be noted that the macromolecules in the microfibril are oriented in the same way, that is, the reducing ends (ends with a free, anomeric OH group at the C1 atom) are located on one side. Modern models The organization of cellulose microfibrils suggests that in the central region it has a highly organized structure, and towards the periphery the arrangement of macromolecules becomes more chaotic.
Microfibrils are connected to each other by cross-linking glycans (hemicelluloses) and, to a lesser extent, pectins. Cellulose microfibrils, linked by cross-linking glycans, form a three-dimensional network immersed in a gel-like pectin matrix and providing high cell wall strength.
In secondary cell walls, microfibrils can be associated into bundles called macrofibrils. This organization further increases the strength of the cell wall.
Biosynthesis
The formation of cellulose macromolecules in the cell walls of higher plants is catalyzed by a multisubunit membrane cellulose synthase complex located at the end of elongating microfibrils. The complete cellulose synthase complex consists of catalytic, pore, and crystallization subunits. The catalytic subunit of cellulose synthase is encoded by the CesA (cellulose synthase A) multigene family, which is part of the Csl (cellulose synthase-like) superfamily, which also includes the CslA, CslF, CslH and CslC genes responsible for the synthesis of other polysaccharides.
When studying the surface of the plasma membrane of plant cells using the freezing-cleavage method, so-called rosettes or terminal complexes with a size of about 30 nm and consisting of 6 subunits can be observed at the base of cellulose microfibrils. Each such subunit of the rosette is, in turn, a supercomplex formed from 6 cellulose synthases. Thus, as a result of the operation of such a rosette, a microfibril is formed, containing about 36 cellulose macromolecules in a cross section. In some algae, cellulose synthesis supercomplexes are organized linearly.
Interestingly, glycosylated sitosterol plays the role of a primer for the initiation of cellulose synthesis. The direct substrate for cellulose synthesis is UDP-glucose. Sucrose synthase, associated with cellulose synthase and carrying out the reaction, is responsible for the formation of UDP-glucose:
Sucrose + UDP UDP-glucose + D-fructose
In addition, UDP-glucose can be formed from a pool of hexose phosphates as a result of the work of UDP-glucose pyrophosphorylase:
Glucose-1-phosphate + UTP UDP-glucose + PPi
The direction of the synthesis of cellulose microfibrils is ensured by the movement of cellulose synthase complexes along microtubules adjacent to the plasmalemma on the inside. In a model plant, Tal's rhizomet, the CSI1 protein was discovered, which is responsible for the fixation and movement of cellulose synthase complexes along cortical microtubules.
Mammals (like most other animals) do not have enzymes that can break down cellulose. However, many herbivores (for example, ruminants) have symbiont bacteria in the digestive tract that break down and help the hosts absorb this polysaccharide.
Notes
- 1 2 Glinka N.L. General chemistry. - 22nd edition, rev. - Leningrad: Chemistry, 1977. - 719 p.
- Ignatyev, Igor; Charlie Van Doorslaer, Pascal G.N. Mertens, Koen Binnemans, Dirk. E. de Vos (2011). "Synthesis of glucose esters from cellulose in ionic liquids". Holzforschung 66 (4): 417-425. DOI:10.1515/hf.2011.161.
- 1 2 CELLULOSE.
- 1 2 Pyrolysis of cellulose.
see also
Wiktionary has an article "cellulose"- List of countries producing pulp
- Sulfate process
- Cellulose acetate
- Anselm Paya
- Airlaid (non-woven fabric from Cellulose)
Links
- article “Cellulose” (Chemical Encyclopedia)
- (English) LSBU cellulose page
- (English) Clear description of a cellulose assay method at the Cotton Fiber Biosciences unit of the USDA.
- (English) Cellulose Ethanol Production - First commercial plant
Microcrystalline cellulose in technology medicines
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| Geometry | Anomeres Mutarotation Haworth projection | ||||||||||||||
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| Organelles | Plastids (Leucoplasts Chromoplasts Chloroplasts Elaioplasts Etioplasts Amyloplasts Proteinoplasts Gerontoplasts Statoliths Tannosomes); Vacuole | |
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Pulp Information About
Chemical structure of cellulose
O.A. Noskova, M.S. Fedoseev
Wood chemistry
And synthetic polymers
PART 2
Approved
Editorial and Publishing Council of the University
as lecture notes
Publishing house
Perm State Technical University
Reviewers:
Ph.D. tech. sciences D.R. Nagimov
(CJSC "Karbokam");
Ph.D. tech. sciences, prof. F.H. Khakimova
(Perm State Technical University)
Noskova, O.A.
N84 Chemistry of wood and synthetic polymers: lecture notes: in 2 hours / O.A. Noskova, M.S. Fedoseev. – Perm: Perm Publishing House. state tech. University, 2007. – Part 2. – 53 p.
ISBN 978-5-88151-795-3
Information is provided regarding the chemical structure and properties of the main components of wood (cellulose, hemicelluloses, lignin and extractives). The chemical reactions of these components that occur during the chemical processing of wood or during the chemical modification of cellulose are considered. Also given general information about cooking processes.
Designed for students of specialty 240406 “Technology of chemical wood processing”.
UDC 630 * 813. + 541.6 + 547.458.8
ISBN 978-5-88151-795-3 © State Educational Institution of Higher Professional Education
"Perm State
Technical University", 2007
Introduction
Wood chemistry is a branch of technical chemistry that studies the chemical composition of wood; chemistry of formation, structure and chemical properties of the substances that make up dead wood tissue; methods for isolating and analyzing these substances, as well as the chemical essence of natural and technological processes processing of wood and its individual components.
The first part of the lecture notes “Chemistry of Wood and Synthetic Polymers,” published in 2002, addresses issues related to the anatomy of wood, the structure of the cell membrane, chemical composition wood, physical and physical and chemical properties wood
The second part of the lecture notes “Chemistry of Wood and Synthetic Polymers” discusses issues related to the chemical structure and properties of the main components of wood (cellulose, hemicelluloses, lignin).
The lecture notes provide general information about cooking processes, i.e. on the production of technical cellulose, which is used in the production of paper and cardboard. As a result of chemical transformations of technical cellulose, its derivatives are obtained - ethers and esters, from which artificial fibers (viscose, acetate), films (film, photo, packaging films), plastics, varnishes, and adhesives are produced. This part of the summary also briefly discusses the preparation and properties of cellulose ethers, which were found wide application in industry.
Chemistry of cellulose
Chemical structure of cellulose
Cellulose is one of the most important natural polymers. It is the main component of plant tissues. Natural cellulose is found in large quantities in cotton, flax and other fibrous plants, from which natural textile cellulose fibers are obtained. Cotton fibers are almost pure cellulose (95–99%). A more important source of industrial production of cellulose (technical cellulose) is woody plants. In the wood of various tree species, the mass fraction of cellulose averages 40–50%.
Cellulose is a polysaccharide, the macromolecules of which are built from residues D-glucose (β units -D-anhydroglucopyranose), connected by β-glycosidic bonds 1–4:
Cellulose is a linear homopolymer (homopolysaccharide) belonging to heterochain polymers (polyacetals). It is a stereoregular polymer in which the cellobiose residue serves as a stereo repeating unit. The total formula of cellulose can be represented as (C 6 H 10 O 5) P or [C 6 H 7 O 2 (OH) 3 ] P. Each monomer unit contains three alcohol hydroxyl groups, of which one is primary –CH 2 OH and two (at C 2 and C 3) are secondary –CHOH–.
The end links are different from the rest of the chain links. One terminal link (conditionally right - non-reducing) has an additional free secondary alcohol hydroxyl (at C 4). The other terminal link (conditionally left - reducing) contains free glycosidic (hemiacetal) hydroxyl (at C 1 ) and, therefore, can exist in two tautomeric forms - cyclic (coluacetal) and open (aldehyde):
The terminal aldehyde group gives cellulose its reducing (reducing) ability. For example, cellulose can reduce copper from Cu 2+ to Cu +:
Amount of copper recovered ( copper number) serves as a qualitative characteristic of the length of cellulose chains and shows its degree of oxidative and hydrolytic destruction.
Natural cellulose has a high degree of polymerization (DP): wood - 5000-10000 and above, cotton - 14000-20000. When isolated from plant tissues, cellulose is somewhat destroyed. Technical wood pulp has a DP of about 1000–2000. The DP of cellulose is determined mainly by the viscometric method, using some complex bases as solvents: copper-ammonia reagent (OH) 2, cupriethylenediamine (OH) 2, cadmium ethylenediamine (cadoxene) (OH) 2, etc.
Cellulose isolated from plants is always polydisperse, i.e. contains macromolecules of varying lengths. The degree of cellulose polydispersity (molecular heterogeneity) is determined by fractionation methods, i.e. separating a cellulose sample into fractions with a certain molecular weight. The properties of a cellulose sample (mechanical strength, solubility) depend on the average DP and the degree of polydispersity.
Cellulose (fiber) is a plant polysaccharide, which is the most common organic substance on Earth.
1. Physical properties
This substance is white, tasteless and odorless, insoluble in water, and has a fibrous structure. Dissolves in ammonia solution copper(II) hydroxide - Schweitzer's reagent.
Video experiment “Dissolving cellulose in an ammonia solution of copper (II) hydroxide”
2. Being in nature
This biopolymer has great mechanical strength and acts as a supporting material for plants, forming the wall of plant cells. Cellulose is found in large quantities in wood tissue (40-55%), flax fibers (60-85%) and cotton (95-98%). The main component of the membrane of plant cells. It is formed in plants during the process of photosynthesis.
Wood consists of 50% cellulose, and cotton, flax, and hemp are almost pure cellulose.
Chitin (an analogue of cellulose) is the main component of the exoskeleton of arthropods and other invertebrates, as well as in the cell walls of fungi and bacteria.
3. Structure
Consists of β-glucose residues
4. Receipt
Obtained from wood
5. Application
Cellulose is used in the production of paper, artificial fibers, films, plastics, paints and varnishes, smokeless powder, explosives, solid rocket fuel, for the production of hydrolytic alcohol, etc.
· Production of acetate silk - artificial fiber, plexiglass, non-flammable film from cellulose acetate.
· Preparation of smokeless gunpowder from triacetylcellulose (pyroxylin).
· Production of collodion (thick film for medicine) and celluloid (production of films, toys) from cellulose diacetyl.
· Production of threads, ropes, paper.
· Production of glucose, ethyl alcohol (for rubber production)
The most important cellulose derivatives include:
- methylcellulose(cellulose methyl ethers) of the general formula
N ( X= 1, 2 or 3);
- cellulose acetate(cellulose triacetate) – ester of cellulose and acetic acid
- nitrocellulose(cellulose nitrates) – cellulose nitrates:
N ( X= 1, 2 or 3).
6. Chemical properties
Hydrolysis
(C 6 H 10 O 5) n + nH 2 O t,H2SO4→ nC 6 H 12 O 6
glucose
Hydrolysis proceeds in stages:
(C 6 H 10 O 5) n → (C 6 H 10 O 5) m → xC 12 H 22 O 11 → n C 6 H 12 O 6 (
Note, m
starch dextrinmaltoseglucose
Video experiment “Acid hydrolysis of cellulose”
Esterification reactions
Cellulose is a polyhydric alcohol; there are three hydroxyl groups per unit cell of the polymer. In this regard, cellulose is characterized by esterification reactions (formation of esters). Reactions with nitric acid and acetic anhydride are of greatest practical importance. Cellulose does not produce a “silver mirror” reaction.
1. Nitration:
(C 6 H 7 O 2 (OH ) 3) n + 3 nHNO 3 H 2 SO4(conc.)→(C 6 H 7 O 2 (ONO 2 ) 3) n + 3 nH 2 O
pyroxylin
Video experiment “Preparation and properties of nitrocellulose”
Fully esterified fiber is known as gunpowder, which, after proper processing, turns into smokeless gunpowder. Depending on the nitration conditions, cellulose dinitrate can be obtained, which in technology is called colloxylin. It is also used in the manufacture of gunpowder and solid rocket propellants. In addition, celluloid is made from colloxylin.
2. Interaction with acetic acid:
(C 6 H 7 O 2 (OH) 3) n + 3nCH 3 COOH H2SO4( conc. .)→ (C 6 H 7 O 2 (OCOCH 3) 3) n + 3nH 2 O
When cellulose reacts with acetic anhydride in the presence of acetic and sulfuric acids, triacetylcellulose is formed.
Triacetyl cellulose (or cellulose acetate) is a valuable product for the manufacture of flame retardant film andacetate silk. To do this, cellulose acetate is dissolved in a mixture of dichloromethane and ethanol, and this solution is forced through dies into a stream of warm air.
And the die itself schematically looks like this:
1 - spinning solution,
2 - die,
3 - fibers.
The solvent evaporates and the streams of solution turn into the finest threads of acetate silk.
Speaking about the use of cellulose, one cannot help but say that a large amount of cellulose is consumed for the production of various papers. Paper- This is a thin layer of fiber fibers, glued and pressed on a special paper-making machine.