It is obtained from cellulose. Structure and properties of cellulose and its satellites

First of all, it is necessary to explain what exactly cellulose is and what its properties are in general terms.

Cellulose(from Latin cellula - letters, room, here - cell) - cellulose, the substance of plant cell walls, is a polymer of the carbohydrate class - a polysaccharide, the molecules of which are built from the remains of glucose monosaccharide molecules (see diagram 1).

SCHEME 1 Structure of the cellulose molecule

Each residue of a glucose molecule - or, for short, a glucose residue - is rotated by 180° relative to its neighbor and is connected to it by an oxygen bridge -O-, or, as is commonly said in this case, by a glucosidic bond through an oxygen atom. The entire cellulose molecule is thus like a giant chain. The individual links of this chain have the shape of hexagons, or - in chemistry terms - 6-membered cycles. In the glucose molecule (and its residue), this 6-membered cycle is built from five carbon atoms C and one oxygen atom O. Such cycles are called pyran cycles. Of the six atoms of the 6-membered pyran ring in Scheme 1 shown above, only the oxygen atom O is shown at the vertex of one of the corners - a heteroatom (from the Greek heteroatom; - another, different from the rest). At the vertices of the remaining five corners there is a carbon atom C (these “usual” carbon atoms for organics, unlike the heteroatom, are not usually depicted in the formulas of cyclic compounds).

Each 6-membered cycle has the shape not of a flat hexagon, but of a curved one in space, like an armchair (see Scheme 2), hence the name of this shape, or spatial conformation, which is the most stable for a cellulose molecule.

DIAGRAM 2 Chair shape

In diagrams 1 and 2, the sides of the hexagons located closer to us are highlighted with a bold line. Scheme 1 also shows that each glucose residue contains 3 hydroxyl groups -OH (they are called hydroxy groups or simply hydroxyls). For clarity, these -OH groups are enclosed in a dotted frame.

Hydroxyl groups are capable of forming strong intermolecular hydrogen bonds with the hydrogen atom H as a bridge, therefore the bond energy between cellulose molecules is high and cellulose as a material has significant strength and rigidity. In addition, -OH groups promote the absorption of water vapor and give cellulose the properties of polyhydric alcohols (the so-called alcohols containing several -OH groups). When cellulose swells, the hydrogen bonds between its molecules are destroyed, the chains of molecules are pulled apart by water molecules (or molecules of an absorbed reagent), and new bonds are formed between the molecules of cellulose and water (or reagent).

Under normal conditions, cellulose is a solid substance with a density of 1.54-1.56 g/cm3, insoluble in common solvents - water, alcohol, diethyl ether, benzene, chloroform, etc. In natural fibers, cellulose has an amorphous-crystalline structure with a degree of crystallinity of about 70%.

Chemical reactions with cellulose usually involve three -OH groups. The remaining elements from which the cellulose molecule is built react under stronger influences - at elevated temperatures, under the action of concentrated acids, alkalis, and oxidizing agents.

For example, when heated to a temperature of 130°C, the properties of cellulose change only slightly. But at 150-160°C, the process of slow destruction begins - the destruction of cellulose, and at temperatures above 160°C this process occurs quickly and is accompanied by the rupture of glucosidic bonds (at the oxygen atom), deeper decomposition of molecules and charring of cellulose.

Acids have different effects on cellulose. When cotton cellulose is treated with a mixture of concentrated nitric and sulfuric acids, hydroxyl groups -OH react, and as a result, cellulose nitrates are obtained - the so-called nitrocellulose, which, depending on the content of nitro groups in the molecule, has different properties. The most famous of the nitrocelluloses are pyroxylin, used for the production of gunpowder, and celluloid - plastics based on nitrocellulose with some additives.

Another type of chemical interaction occurs when cellulose is treated with hydrochloric or sulfuric acid. Under the influence of these mineral acids, a gradual destruction of cellulose molecules occurs with the rupture of glucosidic bonds, accompanied by hydrolysis, i.e. exchange reaction involving water molecules (see Scheme 3).

SCHEME 3 Hydrolysis of cellulose
This diagram shows the same three links in the cellulose polymer chain, i.e. the same three residues of cellulose molecules as in Scheme 1, only the 6-membered pyran rings are presented not in the form of “armchairs”, but in the form of flat hexagons. This convention for cyclic structures is also generally accepted in chemistry.

Complete hydrolysis, carried out by boiling with mineral acids, leads to the production of glucose. The product of partial hydrolysis of cellulose is the so-called hydrocellulose; it has lower mechanical strength compared to conventional cellulose, since mechanical strength indicators decrease with decreasing chain length of the polymer molecule.

A completely different effect is observed if the cellulose is treated for a short time with concentrated sulfuric or hydrochloric acid. Parchmentation occurs: the surface of the paper or cotton fabric swells, and this surface layer, which is partially destroyed and hydrolyzed cellulose, gives the paper or fabric a special shine and increased strength after drying. This phenomenon was first noticed in 1846 by French researchers J. Pumaru and L. Fipoye.

Weak (0.5%) solutions of mineral and organic acids at temperatures up to approximately 70°C, if their application is followed by washing, do not have a destructive effect on cellulose.

Cellulose is resistant to alkalis (diluted solutions). Solutions of caustic soda in a concentration of 2-3.5% are used for alkaline cooking of rags used for paper production. In this case, not only contaminants are removed from cellulose, but also products of destruction of cellulose polymer molecules that have shorter chains. Unlike cellulose, these degradation products are soluble in alkaline solutions.

Concentrated solutions of alkalis have a unique effect on cellulose in the cold - at room and lower temperatures. This process, discovered in 1844 by the English researcher J. Mercer and called mercerization, is widely used for refining cotton fabrics. The fibers are treated under tension at a temperature of 20°C with a 17.5% solution of sodium hydroxide. Cellulose molecules attach to alkali, so-called alkali cellulose is formed, and this process is accompanied by strong swelling of cellulose. After washing, the alkali is removed, and the fibers acquire softness, a silky shine, become more durable and receptive to dyes and moisture.

At high temperatures in the presence of atmospheric oxygen, concentrated solutions of alkalis cause the destruction of cellulose with the rupture of glucosidic bonds.

Oxidizing agents used to bleach cellulose fibers in textile production, as well as to produce papers with a high degree of whiteness, act destructively on cellulose, oxidizing hydroxyl groups and breaking glucosidic bonds. Therefore, under production conditions, all parameters of the bleaching process are strictly controlled.

When we talked about the structure of the cellulose molecule, we had in mind its ideal model, consisting only of numerous residues of the glucose molecule. We did not specify how many of these glucose residues are contained in the chain of the cellulose molecule (or, as giant molecules are commonly called, in the macromolecule). But in reality, i.e. in any natural plant material, there are greater or lesser deviations from the described ideal model. The cellulose macromolecule may contain a certain amount of residues of molecules of other monosaccharides - hexoses (i.e. containing 6 carbon atoms, like glucose, which also belongs to hexoses) and pentoses (monosaccharides with 5 carbon atoms in the molecule). A macromolecule of natural cellulose may also contain uronic acid residues - this is the name given to carboxylic acids of the monosaccharide class; a glucuronic acid residue, for example, differs from a glucose residue in that instead of the -CH 2 OH group it contains a carboxylic group -COOH, characteristic of carboxylic acids.

The number of glucose residues contained in a cellulose macromolecule, or the so-called degree of polymerization, denoted by the index n, is also different for different types of cellulose raw materials and varies widely. Thus, in cotton n averages 5,000 - 12,000, and in flax, hemp and ramie 20,000 - 30,000. Thus, the molecular weight of cellulose can reach 5 million oxygen units. The higher n, the stronger the cellulose. For cellulose obtained from wood, n is much lower - in the range of 2500 - 3000, which also causes lower strength of wood cellulose fibers.

However, if we consider cellulose as a material obtained from any one type of plant raw material - cotton, flax, hemp or wood, etc., then in this case the cellulose molecules will have unequal length, unequal degree of polymerization, i.e. in this cellulose there will be longer and shorter molecules present. The high molecular weight part of any technical cellulose is usually called a-cellulose - this is how the part of cellulose that consists of molecules containing 200 or more glucose residues is conventionally designated. A special feature of this part of cellulose is its insolubility in a 17.5% sodium hydroxide solution at 20°C (these, as already mentioned, are the parameters of the mercerization process - the first stage of viscose fiber production).

The part of technical cellulose that is soluble under these conditions is called hemicellulose. It, in turn, consists of a fraction of b-cellulose, containing from 200 to 50 glucose residues, and y-cellulose - the lowest molecular weight fraction, with n less than 50. The name “hemicellulose”, as well as “a-cellulose”, is conditional: The composition of hemicelluloses includes not only cellulose of relatively low molecular weight, but also other polysaccharides, the molecules of which are built from the remains of other hexoses and pentoses, i.e. other hexosans and pentosans (see, for example, the content of pentosans in Table 1). Their common property is a low degree of polymerization n, less than 200, and as a result, solubility in a 17.5% sodium hydroxide solution.

The quality of cellulose is determined not only by the content of a-cellulose, but also by the content of hemicelluloses. It is known that with an increased content of a-cellulose, the fibrous material is usually characterized by higher mechanical strength, chemical and thermal resistance, whiteness stability and durability. But to obtain a durable paper web, it is necessary that hemicellulose satellites are also present in technical cellulose, since pure a-cellulose is not prone to fibrillation (splitting of fibers in the longitudinal direction with the formation of the finest fibers - fibrils) and is easily chopped during the grinding process of fibers. Hemicellulose facilitates fibrillation, which in turn improves the cohesion of the fibers in the paper sheet without excessively reducing their length during milling.

When we said that the concept of “a-cellulose” is also conditional, we meant that a-cellulose is not an individual chemical compound. This term refers to the total amount of substances found in technical cellulose and insoluble in alkali during mercerization. The actual content of high molecular weight cellulose in a-cellulose is always lower, since impurities (lignin, ash, fats, waxes, as well as pentosans and pectin substances chemically bound to cellulose) are not completely dissolved during mercerization. Therefore, without parallel determination of the amount of these impurities, the content of a-cellulose cannot characterize the purity of cellulose; it can only be judged if these necessary additional data are available.

Continuing the presentation of the initial information about the structure and properties of cellulose satellites, let us return to Table. 1.

In table Table 1 lists substances found along with cellulose in plant fibers. Pectin substances and pentosans are listed first after cellulose. Pectic substances are polymers of the carbohydrate class, which, like cellulose, have a chain structure, but are built from uronic acid residues, more precisely, galacturonic acid. Polygalacturonic acid is called pectic acid, and its methyl esters are called pectins (see Scheme 4).

DIAGRAM 4 Section of the pectin macromolecule chain

This, of course, is only a diagram, since pectins from different plants differ in molecular weight, the content of -OCH3 groups (the so-called methoxy or methoxyl groups, or simply methoxyls) and their distribution along the macromolecule chain. Pectins contained in plant cell sap are soluble in water and are capable of forming dense gels in the presence of sugar and organic acids. However, pectin substances exist in plants mainly in the form of insoluble protopectin - a polymer of a branched structure in which the linear sections of the pectin macromolecule are connected by cross bridges. Protopectin is contained in the walls of plant cells and intercellular cementing material, acting as supporting elements. In general, pectin substances are a reserve material from which cellulose is formed through a series of transformations and the cell wall is formed. For example, in the initial stage of growth of cotton fiber, the content of pectin substances in it reaches 6%, and by the time the boll is opened it gradually decreases to approximately 0.8%. At the same time, the cellulose content in the fiber increases, its strength increases, and the degree of cellulose polymerization increases.

Pectin substances are quite resistant to acids, but under the influence of alkalis when heated, they are destroyed, and this circumstance is used to clean cellulose from pectin substances (by cooking, for example, cotton fluff with a solution of caustic soda). Pectin substances are easily destroyed by oxidizing agents.

Pentosans are polysaccharides built from pentose residues - usually arabinose and xylose. Accordingly, these pentosans are called arabans and xylans. They have a linear (chain) or slightly branched structure and in plants usually accompany pectin substances (arabans) or are part of hemicelluloses (xylans). Pentosans are colorless and amorphous. Arabans are highly soluble in water; xylans are insoluble in water.

The next most important companion of cellulose is lignin, a branched polymer that causes lignification of plants. As can be seen from table. 1, lignin is absent in cotton fiber, but in other fibers - flax, hemp, ramie and especially jute - it is contained in smaller or larger quantities. It mainly fills the spaces between plant cells, but also penetrates into the surface layers of the fibers, playing the role of an encrusting substance that holds cellulose fibers together. Wood contains especially a lot of lignin - up to 30%. By its nature, lignin no longer belongs to the class of polysaccharides (like cellulose, pectin substances and pentosans), but is a polymer based on derivatives of polyhydric phenols, i.e. refers to the so-called fatty-aromatic compounds. Its significant difference from cellulose is that the lignin macromolecule has an irregular structure, i.e. A polymer molecule is composed not of identical residues of monomer molecules, but of various structural elements. However, the latter have in common that they consist of an aromatic core (which in turn is formed by 6 carbon atoms C) and a side propane chain (of 3 carbon atoms C); this structural element common to all lignins is called the phenylpropane unit (see diagram 5).

SCHEME 5 Phenylpropane unit

Thus, lignin belongs to the group of natural compounds having the general formula (C 6 C 3)x. Lignin is not an individual chemical compound with a strictly defined composition and properties. Lignins of different origins differ markedly from each other, and even lignins obtained from the same type of plant material, but in different ways, sometimes differ greatly in elemental composition, the content of certain substituents (this is the name of groups connected to a benzene ring or a side propane chain ), solubility and other properties.

The high reactivity of lignin and the heterogeneity of its structure make it difficult to study its structure and properties, but nevertheless it has been established that all lignins contain phenylpropane units, which are derivatives of guaiacol (i.e., pyrocatechol monomethyl ether, see Scheme 6).

SCHEME 6 Guaiacol derivative

Some differences were also revealed in the structure and properties of lignins of annual plants and cereals, on the one hand, and wood, on the other. For example, lignins of grasses and cereals (these include flax and hemp, which we will discuss in more detail) dissolve relatively well in alkalis, while wood lignins do not. This leads to more stringent parameters for the process of removing lignin (delignification) from wood using soda pulping (such as higher temperatures and pressures) compared to the process of removing lignin from young shoots and grasses using lye cooking - a method that was known in China at the beginning of the first millennium AD and which was widely used under the name of maceration or hemping in Europe when processing rags and various types of waste (linen, hemp) into paper.

We have already talked about the high reactivity of lignin, i.e. about its ability to enter into numerous chemical reactions, which is explained by the presence in the lignin macromolecule of a large number of reactive functional groups, i.e. capable of undergoing certain chemical transformations inherent in a certain class of chemical compounds. This especially applies to alcohol hydroxyls -OH, located at the carbon atoms in the side propane chain; these -OH groups, for example, cause sulfonation of lignin during sulfite cooking of wood - another method of its delignification.

Due to the high reactivity of lignin, its oxidation easily occurs, especially in an alkaline environment, with the formation of carboxyl groups -COOH. And under the action of chlorinating and bleaching agents, lignin is easily chlorinated, and the chlorine atom Cl enters both the aromatic ring and the side propane chain; in the presence of moisture, simultaneously with chlorination, oxidation of the lignin macromolecule occurs, and the resulting chlorinated lignin also contains carboxyl groups. Chlorinated and oxidized lignin is more easily washed out of cellulose. All these reactions are widely used in the pulp and paper industry to purify cellulose materials from lignin impurities, which is a very unfavorable component of technical cellulose.

Why is the presence of lignin undesirable? First of all, because lignin has a branched, often three-dimensional, spatial structure and therefore does not have fiber-forming properties, i.e., threads cannot be obtained from it. It imparts rigidity and fragility to cellulose fibers, reduces the ability of cellulose to swell, color, and interact with reagents used in various fiber processing processes. When preparing paper pulp, lignin complicates the grinding and fibrillation of fibers and impairs their mutual adhesion. In addition, it itself is colored yellow-brown, and when the paper ages, it also increases its yellowing.

Our discussions about the structure and properties of cellulose satellites may seem, at first glance, unnecessary. Indeed, are even brief descriptions of the structure and properties of lignin appropriate here if the graphic restorer deals not with natural fibers, but with paper, i.e. material made from lignin-free fibers? This, of course, is true, but only if we are talking about rag paper made from cotton raw materials. There is no lignin in cotton. There is practically no it in rag paper made of flax or hemp - it was almost completely removed during the process of weaving the rags.

However, in paper made from wood, and especially in types of newsprint in which wood pulp serves as a filler, lignin is contained in fairly large quantities, and this circumstance should be kept in mind by a restorer working with a wide variety of papers, including low-grade ones. .

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 an ammonia solution of 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).

· Preparation 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.

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. Cellulose nitrates are of great importance.

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 + 3n H 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 are similar in appearance 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.

70. Obtaining acetate fiber

Characteristic features of acetate fiber.

1. Since ancient times, people have widely used natural fibrous materials to make clothing and various household products.

2. Some of these materials are of plant origin and consist of cellulose, for example flax, cotton, others are of animal origin and consist of proteins - wool, silk.

3. As the needs of the population and developing technology for fabrics increased, a shortage of fibrous materials began to arise. There was a need to obtain fibers artificially.

Since they are characterized by an ordered arrangement of chain macromolecules oriented along the fiber axis, the idea arose to transform a natural polymer of a disordered structure through one or another treatment into a material with an ordered arrangement of molecules.

4. The starting natural polymer for producing artificial fibers is cellulose extracted from wood, or cotton fluff remaining on cotton seeds after the fibers are removed from it.

5. In order to place linear polymer molecules along the axis of the fiber being formed, it is necessary to separate them from each other and make them mobile and capable of movement.

This can be achieved by melting the polymer or dissolving it.

It is impossible to melt cellulose: when heated, it is destroyed.

6. Cellulose must be treated with acetic anhydride in the presence of sulfuric acid (acetic anhydride is a stronger esterifying agent than acetic acid).

7. The esterification product - cellulose triacetate - is dissolved in a mixture of dichloromethane CH 2 Cl 2 and ethyl alcohol.

8. A viscous solution is formed in which the polymer molecules can already move and take on one or another desired order.

9. In order to obtain fibers, the polymer solution is forced through dies - metal caps with numerous holes.

Thin jets of solution are lowered into a vertical shaft approximately 3 m high, through which heated air passes.

10. Under the influence of heat, the solvent evaporates, and cellulose triacetate forms thin long fibers, which are then twisted into threads and go for further processing.

11. When passing through the holes of the spinneret, macromolecules, like logs when rafting down a narrow river, begin to line up along the stream of solution.

12. In the process of further processing, the arrangement of macromolecules in them becomes even more ordered.

This leads to greater strength of the fibers and the threads they form.

Cellulose is a natural polymer of glucose (namely, beta-glucose residues) of plant origin with a linear molecular structure. Cellulose is also called fiber in another way. This polymer contains more than fifty percent of the carbon found in plants. Cellulose ranks first among organic compounds on our planet.

Pure cellulose is cotton fibers (up to ninety-eight percent) or flax fibers (up to eighty-five percent). Wood contains up to fifty percent cellulose, and straw contains thirty percent cellulose. There is a lot of it in hemp.

Cellulose is white. Sulfuric acid turns it blue, and iodine turns it brown. Cellulose is hard and fibrous, tasteless and odorless, does not collapse at a temperature of two hundred degrees Celsius, but ignites at a temperature of two hundred seventy-five degrees Celsius (that is, it is a flammable substance), and when heated to three hundred sixty degrees Celsius, it chars. It cannot be dissolved in water, but can be dissolved in a solution of ammonia and copper hydroxide. Fiber is a very strong and elastic material.

The importance of cellulose for living organisms

Cellulose is a polysaccharide carbohydrate.

In a living organism, the functions of carbohydrates are as follows:

1. The function of structure and support, since carbohydrates are involved in the construction of supporting structures, and cellulose is the main component of the structure of plant cell walls.
2. Protective function characteristic of plants (thorns or thorns). Such formations on plants consist of the walls of dead plant cells.
3. Plastic function (another name is anabolic function), since carbohydrates are components of complex molecular structures.
4. The function of providing energy, since carbohydrates are an energy source for living organisms.
5. Storage function, since living organisms store carbohydrates in their tissues as nutrients.
6. Osmotic function, since carbohydrates take part in regulating osmotic pressure inside a living organism (for example, blood contains from one hundred milligrams to one hundred and ten milligrams of glucose, and blood osmotic pressure depends on the concentration of this carbohydrate in the blood). Osmosis transport delivers nutrients in tall tree trunks, since capillary transport is ineffective in this case.
7. Receptor function, since some carbohydrates are found in the receptive part of cell receptors (molecules on the cell surface or molecules that are dissolved in the cell cytoplasm). The receptor reacts in a special way to a connection with a specific chemical molecule that transmits an external signal, and transmits this signal into the cell itself.

The biological role of cellulose is:

1. Fiber is the main structural part of the plant cell wall. Formed as a result of photosynthesis. Plant cellulose is food for herbivores (for example, ruminants); in their bodies, fiber is broken down using the enzyme cellulase. It is quite rare, so cellulose in its pure form is not consumed in human food.
2. Fiber in food gives a person a feeling of fullness and improves the mobility (peristalsis) of his intestines. Cellulose is capable of binding liquid (up to zero point four grams of liquid per gram of cellulose). In the large intestine it is metabolized by bacteria. Fiber is welded without the participation of oxygen (there is only one anaerobic process in the body). The result of digestion is the formation of intestinal gases and flying fatty acids. More of these acids are absorbed into the blood and used as energy for the body. And the amount of acids that are not absorbed and intestinal gases increase the volume of feces and accelerate its entry into the rectum. Also, the energy of these acids is used to increase the amount of beneficial microflora in the large intestine and support its life there. When the amount of dietary fiber in food increases, the volume of beneficial intestinal bacteria also increases and the synthesis of vitamin substances improves.
3. If you add thirty to forty-five grams of bran (contains fiber) made from wheat to food, then feces increase from seventy-nine grams to two hundred and twenty-eight grams per day, and the period of their movement is reduced from fifty-eight hours to forty hours. When fiber is added to food regularly, stool becomes softer, which helps prevent constipation and hemorrhoids.
4. When there is a lot of fiber in food (for example, bran), the body of both a healthy person and the body of a person with type 1 diabetes becomes more resistant to glucose.
5. Fiber, like a brush, removes dirty deposits from the intestinal walls, absorbs toxic substances, takes away cholesterol and removes all this from the body naturally. Doctors have concluded that people who eat rye bread and bran are less likely to suffer from colon cancer.

The most fiber is found in bran from wheat and rye, in bread made from coarsely ground flour, in bread made from proteins and bran, in dried fruits, carrots, cereals, and beets.

Applications of cellulose

People have been using cellulose for a long time. First of all, wood material was used as fuel and boards for construction. Then cotton, flax and hemp fibers were used to make various fabrics. For the first time in industry, chemical processing of wood material began to be practiced due to the development of the production of paper products.

Currently, cellulose is used in various industrial fields. And it is for industrial needs that it is obtained mainly from wood raw materials. Cellulose is used in the production of pulp and paper products, in the production of various fabrics, in medicine, in the production of varnishes, in the production of organic glass and in other areas of industry.

Let's consider its application in more detail

Silk acetate is obtained from cellulose and its esters, unnatural fibers and a film of cellulose acetate, which does not burn, are made. Smokeless gunpowder is made from pyroxylin. Cellulose is used to make thick medical film (collodion) and celluloid (plastic) for toys, film and photographic film. They make threads, ropes, cotton wool, various types of cardboard, building material for shipbuilding and building houses. They also get glucose (for medical purposes) and ethyl alcohol. Cellulose is used both as a raw material and as a substance for chemical processing.

A lot of glucose is needed to make paper. Paper is a thin fibrous layer of cellulose that has been sized and pressed using special equipment to produce a thin, dense, smooth surface of the paper product (the ink should not bleed over it). At first, only material of plant origin was used to create paper; the necessary fibers were extracted from it mechanically (rice stalks, cotton, rags).

But book printing developed at a very fast pace, newspapers also began to be published, so the paper produced in this way was no longer enough. People found out that wood contains a lot of fiber, so they began to add ground wood raw materials to the plant mass from which paper was made. But this paper was easily torn and turned yellow in a very short time, especially when exposed to light for a long time.

Therefore, various methods of treating wood material with chemicals began to be developed, which make it possible to isolate cellulose from it, purified from various impurities.

To obtain cellulose, wood chips are boiled in a solution of reagents (acid or alkali) for a long time, then the resulting liquid is purified. This is how pure cellulose is produced.

Acid reagents include sulfurous acid; it is used to produce cellulose from wood with a small amount of resin.

Alkaline reagents include:

1. soda reagents ensure the production of cellulose from hardwoods and annuals (such cellulose is quite expensive);
2. sulfate reagents, of which the most common is sodium sulfate (the basis for the production of white liquor, and it is already used as a reagent for the production of cellulose from any plants).

After all production stages, the paper is used for the production of packaging, book and stationery products.

From all of the above, we can conclude that cellulose (fiber) has an important cleansing and healing value for the human intestines, and is also used in many areas of industry.

Cellulose - what is it? This question worries everyone involved in organic chemistry. Let's try to find out the main characteristics of this compound, identify its distinctive features, and areas of practical application.

Structural features

Chemical cellulose has the formula (C 6 H 10 O 5) p. It is a polysaccharide that includes β-glucose residues. Cellulose is characterized by a linear structure. Each residue of its molecule includes three OH groups, therefore this compound is characterized by the properties of polyhydric alcohols. The presence of a ring aldehyde group in the molecule gives cellulose restorative (reducing) properties. It is this organic compound that is the most important natural polymer, the main component of plant tissue.

It is found in large quantities in flax, cotton, and other fibrous plants, which are the main source of cellulose fiber.

Technical cellulose is isolated from woody plants.

Wood chemistry

The production of cellulose is covered in this separate section of chemistry. It is here that it is expected to consider the characteristics of the composition of wood, its chemical and physical properties, methods of analysis and isolation of substances, the chemical essence of the processes of processing wood and its individual components.

Wood cellulose is polydisperse, containing macromolecules of varying lengths. To determine the degree of polydispersity, the fractionation method is used. The sample is divided into separate fractions, then their characteristics are studied.

Chemical properties

When discussing what cellulose is, it is necessary to conduct a detailed analysis of the chemical properties of this organic compound.

Technical cellulose can be used in the production of cardboard and paper, as it can be chemically processed without any problems.

Any technological chain related to the processing of natural cellulose is aimed at preserving its valuable properties. Modern processing of cellulose makes it possible to carry out the process of dissolving this substance and to produce completely new chemical substances from cellulose.

What properties does cellulose have? What is the destruction process? These questions are included in the school course of organic chemistry.

Among the characteristic chemical properties of cellulose are:

• destruction;
• stitching;
• reactions involving functional groups.

During destruction, a break in the chain of the macromolecule of glycosidic bonds is observed, accompanied by a decrease in the degree of polymerization. In some cases, complete rupture of the molecule is possible.

Options for cellulose destruction

Let's find out what main types of destruction cellulose has, what is the rupture of macromolecules.

Currently, several types of destruction are distinguished in chemical production.

In the mechanical version, the breaking of C-C bonds in the cycles, as well as the destruction of glycosidic bonds, is observed. A similar process occurs during mechanical grinding of a substance, for example, during grinding for paper making.

Thermal destruction occurs under the influence of thermal energy. It is on this process that the technological pyrolysis of wood is based.

Photochemical destruction involves the destruction of macromolecules under the influence of ultraviolet radiation.

For the radiation type of destruction of a natural polymer, the presence of X-ray radiation is assumed. This type of destruction is used in special devices.

When exposed to atmospheric oxygen, oxidative destruction of cellulose is possible. The process is characterized by the simultaneous oxidation of alcohol and aldehyde groups present in a given compound.

When cellulose is exposed to water, as well as aqueous solutions of acids and alkalis, the process of cellulose hydrolysis occurs. The reaction is purposefully carried out in cases where it is necessary to conduct a qualitative analysis of the structure of a substance, but when cooking this substance it is not desirable.

Microorganisms, such as fungi, can biologically degrade cellulose. To obtain a quality product, it is important to prevent its biological destruction when producing paper and cotton fabrics.

Due to the presence of two functional groups in the molecules, cellulose exhibits properties characteristic of polyhydric alcohols and aldehydes.

Cross-linking reactions

Such processes imply the possibility of obtaining macromolecules with specified physical and chemical properties.

They are widely used in the industrial production of cellulose and give it new performance characteristics.

Preparation of alkali cellulose

What is this cellulose? Reviews indicate that this technology is considered the oldest and most widespread in the world. Nowadays, the polymer obtained in the manufacture of viscose fiber and films and the creation of cellulose ethers are refined in a similar way.

Laboratory studies have found that after such treatment, the shine of the fabric increases and its mechanical strength increases. Alkaline cellulose is an excellent raw material for making fibers.

There are three types of such products: physical-chemical, structural, chemical. All of them are in demand in modern chemical production and are used in the production of paper and cardboard. We found out what structure cellulose has and what the process of its production is.