Application structure and chemical composition of cellulose. The biological role of cellulose and applications

Cellulose is a natural polymer of glucose (namely, beta-glucose residues) of plant origin with a linear molecular structure. In another way, cellulose is also called fiber. 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 of cellulose, and straw contains thirty percent of cellulose. There is a lot of it in hemp.

The cellulose is white. Sulfuric acid stains it blue, and iodine 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 and seventy-five degrees Celsius (that is, it is a combustible substance), and when heated to three hundred and sixty degrees Celsius, it becomes charred. It cannot be dissolved in water, but it can be dissolved in an ammonia solution with copper hydroxide. Fiber is a very strong and resilient 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. Function of structure and support, since carbohydrates are involved in the construction of support structures, and cellulose is the main component of the structure of plant cell walls.
2. Plant-specific protective function (thorns or thorns). Such formations on plants consist of the walls of dead plant cells.
3. Plastic function (also called 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 are involved in the regulation of osmotic pressure inside a living organism (for example, blood contains from one hundred milligrams to one hundred and ten milligrams of glucose, and the 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 part of 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 the connection with a certain chemical molecule, which transmits an external signal, and transmits this signal to the cell itself.

The biological role of cellulose is as follows:

1. Fiber is the main structural part of the plant cell wall. Formed as a result of photosynthesis. The cellulose of plants is food for herbivores (for example, ruminants), in their body fiber is broken down by the enzyme cellulase. It is quite rare, therefore, in its pure form, cellulose is not used 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 tenths of a gram of liquid per gram of cellulose). In the large intestine, bacteria metabolize it. Fiber is digested without oxygen (there is only one anaerobic process in the body). Digestion results in the formation of intestinal gases and flying fatty acids. Most of these acids are absorbed by the blood and used as energy for the body. And the amount of acids that has not been 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, then the volume of beneficial intestinal bacteria 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 the feces increase from seventy-nine grams to two hundred and twenty-eight grams per day, and their travel time is reduced from fifty-eight hours to forty hours. When fiber is added to food on a regular basis, stool becomes softer, which helps to 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 patient with type 1 diabetes mellitus becomes more resistant to glucose.
5. Fiber, like a brush, removes dirty adhesions from the walls of the intestines, absorbs toxic substances, takes cholesterol and removes it all from the body naturally... Doctors concluded that people who eat Rye bread and bran are less likely to suffer from rectal cancer.

Most of all fiber is found in bran from wheat and rye, in bread made from coarsely ground flour, in bread made from proteins and bran, in dry fruits, carrots, cereals, and beets.

Pulp Applications

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 the industry, chemical treatment wood material began to practice due to the development of the production of paper products.

Currently, cellulose is used in various industrial areas. And it is for industrial needs that they receive it 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 manufacture of organic glass and in other fields of industry.

Let's consider its application in more detail.

Acetate silk is obtained from cellulose and its ethers, unnatural fibers are made, a film of cellulose acetate that does not burn. A smoke-free gunpowder is made from pyroxylin. Cellulose is used to make a dense medical film (collodion) and celluloid (plastic) for toys, film and photographic film. They make threads, ropes, cotton wool, various types of cardboard, construction material for shipbuilding and house building. And they also get glucose (for medical purposes) and ethyl sports. 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 glued and pressed on special equipment to obtain a thin, dense, smooth surface of the paper product (ink should not spread over it). At first, only plant material was used to create paper, from which the necessary fibers were isolated mechanically (rice stalks, cotton, rags).

But book printing developed at a very fast pace, newspapers were also published, so the paper produced in this way became insufficient. People found out that there is a lot of fiber in wood, so they began to add ground wood raw materials to the plant mass from which the paper was made. But this paper was quickly tearing and yellowing for a very a short time, especially when exposed to light for a long time.

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

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.

Sulfurous acid belongs to acidic reagents; it is used for the production of cellulose from wood with a small amount of resin.

Alkaline reagents include:

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

After all the production stages, the paper goes to the manufacture 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 intestine, and is also used in many areas of industry.

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

Cellulose(from Lat.cellula - letters, room, here - a cell) - cellulose, a substance of the cell walls of plants, is a polymer of the class of carbohydrates - a polysaccharide, the molecules of which are built from the remains of glucose monosaccharide molecules (see Scheme 1).

Each residue of a glucose molecule - or, for short, a glucose residue - is rotated relative to the neighboring one by 180 ° and is connected to it by an oxygen bridge -O-, or, as they say in this case, by a glucosidic bond through an oxygen atom. Thus, the entire cellulose molecule is like a giant chain. The individual links of this chain are in the form of hexagons, or - in terms of chemistry - 6-membered rings. In the glucose molecule (and its remainder), this 6-membered cycle is built of five carbon atoms C and one oxygen atom O. Such cycles are called pyran. Of the six atoms of the 6-membered pyran ring in the above scheme 1, at the vertex of one of the corners only the oxygen atom O is shown - a heteroatom (from the Greek eteros; - another, different from the rest). In the vertices of the other five corners, it is located at the carbon atom C (these "usual" carbon atoms for organics, unlike the heteroatom, are not usually represented in the formulas of cyclic compounds).

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

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

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, the -OH groups promote the absorption of water vapor and give cellulose the properties of polyhydric alcohols (this is the name for alcohols containing several -OH groups). When cellulose swells, the hydrogen bonds between its molecules are destroyed, the chains of molecules are moved apart by water molecules (or molecules of the absorbed reagent), and new bonds are formed - between the molecules of cellulose and water (or reagent).

Under normal conditions, cellulose is a solid 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%.

Usually three OH groups are involved in chemical reactions with cellulose. The rest of the elements from which the cellulose molecule is built react under stronger influences - at elevated temperatures, under the action of concentrated acids, alkalis, and oxidants.

So, 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 already occurs quickly and is accompanied by the rupture of glucosidic bonds (at the oxygen atom), deeper decomposition of molecules and carbonization of cellulose.

Acids act differently on cellulose. When cotton cellulose is treated with a mixture of concentrated nitric and sulfuric acids, hydroxyl groups -OH enter into a reaction, and as a result, nitric acid esters of cellulose - the so-called nitrocellulose, which, depending on the content of nitro groups in the molecule, have different properties. The best known of nitrocelluloses are pyroxylin, which is used for the production of gunpowder, and celluloid, a plastic based on nitrocellulose with some additives.

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

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 a lower mechanical strength compared to conventional cellulose, since the mechanical strength decreases with a decrease in the 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. Parchment 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 after drying a special gloss and increased strength. This phenomenon was first noticed in 1846 by French researchers J. Pumard and L. Fipoye.

Weak (0.5%) solutions of mineral and organic acids at temperatures up to about 70 ° C, if after 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 making paper. In this case, not only impurities are removed from the cellulose, but also the degradation products of polymer cellulose molecules, which have shorter chains. Unlike cellulose, these degradation products are soluble in alkaline solutions.

Concentrated alkali solutions act in a peculiar way 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 to refine cotton fabrics. The fibers are treated in a taut state at a temperature of 20 ° C with a 17.5% sodium hydroxide solution. The cellulose molecules attach alkali, the so-called alkaline cellulose is formed, and this process is accompanied by a strong swelling of the cellulose. After washing, the alkali is removed, and the fibers become soft, silky shine, become more durable and susceptible to dyes and moisture.

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

Oxidizing agents used for bleaching cellulose fibers in textile production, as well as for obtaining papers with high degree whiteness, destructively act on cellulose, oxidizing hydroxyl groups and breaking glucosidic bonds. Therefore, in 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 molecule (or, as giant molecules are called, in the macromolecule) of cellulose. But in reality, i.e. in any natural plant material, there are more or less deviations from the described ideal model. A 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 residues of uronic acids - this is the name of carboxylic acids of the class of monosaccharides, the residue of glucuronic acid, for example, differs from the residue of glucose in that it contains, instead of the -CH 2 OH group, the carboxyl group -COOH, characteristic of carboxylic acids.

The amount of glucose residues contained in the cellulose macromolecule, or the so-called degree of polymerization, denoted by the index n, is also different for different types of cellulosic raw materials and varies widely. So, in cotton n is on average 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 determines the lower strength of wood cellulose fibers.

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

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", like "a-cellulose", is conditional: the composition of hemicelluloses includes not only cellulose of a 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 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 hemicellulose. It is known that with an increased content of α-cellulose, the fibrous material is usually characterized by a higher mechanical strength, chemical and thermal resistance, brightness stability and durability. But to obtain a strong web of paper, 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 in the process of grinding the fibers. Hemicellulose facilitates fibrillation, which in turn improves the adhesion of the fibers in the paper sheet without excessively reducing their length during refining.

When we said that the concept of "a-cellulose" is also conditional, we meant that a-cellulose is not an individual chemical compound either. This term denotes 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 associated with cellulose) do not completely dissolve 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 be judged only 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. one.

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

This, of course, is only a diagram, since pectins different plants differ in molecular weight, the content of -OCH3 groups (the so-called methoxy or methoxy groups, or simply methoxyls) and their distribution along the macromolecule chain. The pectins contained in the cell sap of plants are soluble in water and 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 branched polymer in which the linear sections of the pectin macromolecule are linked by transverse bridges. Protopectin is contained in plant cell walls and intercellular cementitious material, acting as support elements... In general, pectin substances are a reserve material from which cellulose is formed through a series of transformations and a cell wall is formed. So, for example, at the initial stage of cotton fiber growth, the content of pectin substances in it reaches 6%, and by the time the capsule is opened, it gradually decreases to about 0.8%. In parallel, the content of cellulose in the fiber increases, its strength increases, and the degree of cellulose polymerization increases.

Pectin substances are quite resistant to acids, but under the action of alkalis they are destroyed when heated, and this circumstance is used to purify cellulose from pectin substances (by cooking, for example, cotton fluff with sodium hydroxide solution). Pectin substances are easily destroyed by the action of oxidants.

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 weakly branched structure and in plants usually accompany pectin substances (arabans) or are part of hemicelluloses (xylans). Pentosans are colorless and amorphous. Arabans are readily soluble in water, xylans do not dissolve in water.

The next most important companion of cellulose is lignin, a branched polymer that causes lignification of plants. As you can see from the table. 1, lignin is absent in cotton fiber, but in the rest of the fibers - linseed, hemp, ramie and especially jute - it is contained in smaller or large quantities... It fills mainly 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. Especially a lot of lignin is contained in wood - 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 polyatomic phenols, i.e. refers to the so-called fatty aromatic compounds. Its essential difference from cellulose lies in the fact that the lignin macromolecule has an irregular structure, i.e. a polymer molecule is not made up of identical residues of monomeric molecules, but a variety of structural elements. However, the latter have in common that they consist of an aromatic nucleus (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 a phenylpropane link (see diagram 5).

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 various origins differ markedly from each other, and even lignins obtained from the same type of plant material, but different ways, sometimes very much differ in elemental composition, the content of certain substituents (this is the name of the groups connected to the benzene ring or the side propane chain), solubility and other properties.

The high reactivity of lignin and the heterogeneity of its structure complicate the study of its structure and properties, but nevertheless it was found that phenylpropane units, which are derivatives of guaiacol (i.e., pyrocatechol monomethyl ether, see Scheme 6), are found in the composition of all lignins.

Some differences in the structure and properties of lignins were also revealed. 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, on which we dwell in more detail) dissolve relatively well in alkalis, while lignins of wood are difficult. This leads to more stringent parameters of the process of removing lignin (delignification) from wood by the method of soda cooking of wood (such as: more high temperatures and pressure) compared to the process of removing lignin from young shoots and grasses by boiling in lye, a method that was known in China at the beginning of the first millennium AD and which was widely used in Europe under the name of maceration or boiling in the processing of rags and all kinds waste (linseed, hemp) into paper.

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

Due to the high reactivity of lignin, its oxidation also easily occurs, especially in alkaline environment, with the formation of carboxyl groups -COOH. And under the action of chlorinating and whitening agents, lignin is easily chlorinated, and the chlorine atom Cl enters both the aromatic nucleus and the side propane chain, in the presence of moisture, the lignin macromolecule is oxidized simultaneously with chlorination, and the resulting chlorolignin 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 for the purification of cellulosic materials from the impurity of lignin, 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, that is, filaments cannot be obtained from it. It imparts stiffness, fragility to cellulose fibers, reduces the ability of cellulose to swell, color and interact with reagents used in different processes fiber processing. When preparing paper pulp, lignin complicates the grinding and fibrillation of fibers, impairs their mutual adhesion. In addition, by itself, it is colored yellow-brown, and as the paper ages, it also intensifies its yellowing.

Our reasoning about the structure and properties of cellulose satellites may seem, at first glance, superfluous. 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 is, of course, so, but only if it comes about rag paper made from cotton raw materials. There is no lignin in cotton. It is practically absent in rag paper made of linen or hemp - it was almost completely removed in the process of drilling rags.

However, in paper made from wood, and especially in newsprint grades in which wood pulp serves as a filler, lignin is contained in rather large quantities, and this circumstance should be borne in mind by a restorer who works with a variety of papers, including low-grade papers. ...

Cellulose is a derivative of two natural substances: wood and cotton. In plants, it performs an important function, giving them flexibility and strength.

Where is the substance found?

Cellulose is a natural substance. Plants are capable of producing it on their own. The composition contains: hydrogen, oxygen, carbon.

Plants produce sugar when exposed to sunlight, it is processed by cells and enables the fibers to withstand high wind loads. Cellulose is a substance that participates in the process of photosynthesis. If sugar water is sprinkled on a cut of fresh wood, the liquid is quickly absorbed.

Pulp production starts. This natural way of obtaining it is taken as the basis for the production of cotton fabric on an industrial scale. There are several methods by which pulp of various qualities is obtained.

Manufacturing method # 1

Cellulose is obtained by a natural method - from cotton seeds. The hairs are collected by automated mechanisms, but a long growing period of the plant is required. The fabric produced in this way is considered the cleanest.

More quickly cellulose can be obtained from wood fibers. However, with this method, the quality is much worse. This material is only suitable for making non-fibrous plastic, cellophane. Also, artificial fibers can be produced from such material.

Natural receiving

The production of cellulose from cotton seeds begins with the separation of long fibers. This material is used to make cotton fabric. Small parts, less than 1.5 cm, are called

They are suitable for the production of cellulose. The assembled parts are heated under high pressure... The process can take up to 6 hours. Before starting to heat the material, sodium hydroxide is added to it.

The resulting substance needs to be washed. For this, chlorine is used, which also bleaches. The cellulose composition with this method is the purest (99%).

Manufacturing method # 2 from wood

To obtain 80-97% of cellulose, chips are used conifers, chemical substances... The whole mass is mixed and subjected to temperature treatment. As a result of cooking, the required substance is released.

Calcium bisulfite, sulfur dioxide and wood pulp are mixed. Cellulose in the resulting mixture is not more than 50%. As a result of the reaction, hydrocarbons and lignins are dissolved in the liquid. The solid material goes through a cleaning stage.

A mass is obtained that resembles poor-quality paper. This material serves as the basis for the manufacture of substances:

• Efirov.
• Cellophane.
• Viscose fiber.

What is produced from a valuable material?

Fibrous, which makes it possible to make clothes from it. Cotton fabric is 99.8% natural, obtained by the natural method above. It can also be used to make explosives as a result of a chemical reaction. Cellulose is active when acids are applied to it.

The properties of cellulose are useful for the production of textiles. So, artificial fibers are made from it, resembling natural fabrics in appearance and to the touch:

• viscose and;
• artificial fur;
• copper-ammonia silk.

Mainly, wood pulp is used to make:

• varnishes;
• photographic film;
• paper products;
• plastics;
• dishwashing sponges;
• smokeless powder.

As a result of a chemical reaction, cellulose is obtained:

• trinitrocellulose;
• dinitrocellulose;
• glucose;
• liquid fuel.

Cellulose can also be used in food. Some plants (celery, lettuce, bran) contain its fibers. It also serves as a material for the production of starch. We have already learned how to make thin threads out of it - the artificial web is very strong and does not stretch.

The chemical formula of cellulose is C6H10O5. It is a polysaccharide. It is used to make:

• medical cotton wool;
• bandages;
• tampons;
• cardboard, chipboard;
• food additive E460.

Advantages of the substance

Cellulose is able to withstand high temperatures up to 200 degrees. The molecules are not destroyed, which makes it possible to make reusable plastic tableware out of it. At the same time, an important quality is preserved - elasticity.

Cellulose can withstand prolonged exposure to acids. Absolutely insoluble in water. It is not digested by the human body, it is used as a sorbent.

Microcrystalline cellulose is used in alternative medicine as a cleaning agent digestive system... The powdery substance acts as a food additive to reduce the calorie content of the meals consumed. This helps to eliminate toxins, lower blood sugar and cholesterol.

Manufacturing method # 3 - industrial

At production sites, pulp is prepared by cooking in various environments. The material used depends on the type of reagent - the type of wood:

• Resinous rocks.
• Deciduous trees.
• Plants.

There are several types of cooking reagents:

• Otherwise, the method is referred to as sulfite. Sulfurous acid salt or its liquid mixture is used as a solution. With this production option, cellulose is isolated from coniferous species. Fir and spruce are well processed.
• The alkaline medium or the sodium method is based on the use of sodium hydroxide. The solution separates cellulose well from plant fibers (corn stalks) and trees (mainly deciduous).
• The simultaneous use of sodium hydroxide and sulfide is used in the sulfate method. It is widely used in white liquor sulphide production. The technology is quite negative for the surrounding nature due to the resulting third-party chemical reactions.

The latter method is the most common because of its versatility: cellulose can be obtained from almost any tree. However, the purity of the material is not entirely high after one brew. Impurities are disposed of by additional reactions:

• hemicelluloses are removed with alkaline solutions;
• lignin macromolecules and products of their destruction are removed with chlorine, followed by treatment with alkali.

The nutritional value

Starch and cellulose have a similar structure. As a result of experiments, it was possible to obtain a product from inedible fibers. Man needs it all the time. The food consumed consists of more than 20% starch.

Scientists have succeeded in obtaining amylose from cellulose, which has a positive effect on the state of the human body. At the same time, glucose is released during the reaction. It turns out a waste-free production - the last substance is sent to the manufacture of ethanol. Amylose also serves as a means of preventing obesity.

As a result of the reaction, the cellulose remains in a solid state, settling to the bottom of the vessel. The rest of the components are removed with the help of magnetic nanoparticles, or they dissolve and are removed with the liquid.

Types of substances on sale

Suppliers offer pulp of various qualities at reasonable prices. Let's list the main types of material:

• Sulphate cellulose white made from two types of wood: softwood and hardwood. There is unbleached material used in packaging material, poor quality paper for insulating materials and other purposes.
• There is also a white sulphite, made from conifers, for sale.
• The white powder material is suitable for the production of medical substances.
• Premium cellulose is produced using chlorine-free bleaching. Conifers are taken as raw materials. The wood pulp consists of a combination of spruce and pine chips in a ratio of 20/80%. The purity of the material obtained is the highest. It is suitable for the manufacture of sterile medical materials.

To select a suitable cellulose, standard criteria are used: material purity, tensile strength, fiber length, tear resistance index. The chemical state or aggressiveness of the water extract medium and humidity are also quantitatively indicated. For pulp supplied as a bleached pulp, other parameters are applicable: specific volume, brightness, grind size, tensile strength, degree of purity.

An important indicator for the mass of cellulose is the tear resistance index. The purpose of the materials produced depends on it. Consider the raw material used and the moisture content. The level of tar and fat is also important. Powder uniformity is important for certain technological processes... For similar purposes, the toughness and bursting strength of the sheet material are evaluated.

The soft part of plants and animals mainly contains cellulose. It is cellulose that gives plants their flexibility. Cellulose (fiber) - plant polysaccharide, which is the most abundant organic matter on the ground

Almost all green plants produce cellulose for their needs. It contains the same elements as sugar, namely carbon, hydrogen and oxygen. These elements are found in air and water. Sugar is formed in the leaves and dissolves in the sap and spreads throughout the plant. Most of the sugar is used to promote plant growth and recovery work, the rest of the sugar is converted to cellulose. The plant uses it to create a shell for new cells.

Dissolving cellulose in Schweitzer's reagent

What is cellulose?

Cellulose is one of those natural products that is almost impossible to obtain artificially. But we use it in various fields. A person gets cellulose from plants even after they die off and there is no moisture in them. For example, wild cotton is one of the purest forms of natural cellulose that humans use to make clothing.

Cellulose is a part of plants used by humans as food - lettuce, celery, and bran. The human body is unable to digest cellulose, but it is useful as "roughage" in his diet. In the stomach of some animals, such as sheep, camels, there are bacteria that allow these animals to digest cellulose.

Acid precipitation of cellulose

Cellulose is a valuable raw material

Cellulose is a valuable raw material from which a person obtains various products. Cotton, 99.8% cellulose, is great example what a person can produce from cellulose fiber. If cotton is treated with a mixture of nitric and sulfuric acid, we get pyroxylin, which is an explosive.

After various chemical treatment of cellulose, other products can be obtained from it. Among them: a base for photographic film, additives for varnishes, viscose fibers for the production of fabrics, cellophane and other plastic materials. Cellulose is also used in papermaking.

All our life we ​​are surrounded by a huge number of objects - carton boxes, offset paper, cellophane bags, viscose clothing, bamboo towels and more. But few people know that cellulose is actively used in their manufacture. What is this truly magical substance, without which practically no modern industrial enterprise can do? In this article we will talk about the properties of cellulose, its use in various fields, as well as what it is extracted from, and what it is. chemical formula... Let's start with the origins.

Substance detection

The cellulose formula was discovered by the French chemist Anselm Payen during experiments on the separation of wood into its constituents. After treating it with nitric acid, the scientist found that during a chemical reaction, a fibrous substance similar to cotton is formed. After careful analysis of the material obtained, Payen obtained the chemical formula of cellulose - C 6 H 10 O 5. The description of the process was published in 1838, and the substance received its scientific name in 1839.

Gifts of nature

It is now known for certain that almost all soft parts of plants and animals contain some amount of cellulose. For example, plants need this substance for normal growth and development, or rather, for the creation of membranes of newly formed cells. In terms of composition, it belongs to polysaccharides.

In industry, as a rule, natural cellulose is mined from conifers and deciduous trees- dry wood contains up to 60% of this substance, as well as by processing cotton waste, which contains about 90% of cellulose.

It is known that if wood is heated in a vacuum, that is, without access to air, cellulose will thermally decompose, resulting in the formation of acetone, methyl alcohol, water, acetic acid and charcoal.

Despite the rich flora of the planet, forests are no longer sufficient to produce the amount of chemical fibers required for industry - the use of cellulose is too extensive. Therefore, it is increasingly harvested from straw, reeds, corn stalks, bamboo and reeds.

Synthetic cellulose is obtained using various technological processes from coal, oil, natural gas and shale.

From the forest to the workshops

Let's look at the extraction of technical cellulose from wood - it is a complex, interesting and time-consuming process. First of all, timber is brought to production, it is sawn into large fragments and the bark is removed.

Then the peeled bars are processed into chips and sorted, after which they are boiled in lye. The pulp thus obtained is separated from the alkali, then dried, cut and packaged for shipment.

Chemistry and physics

What chemical and physical secrets conceal the properties of cellulose besides the fact that it is a polysaccharide? First of all, this substance is white. Highly flammable and burns well. It dissolves in complex compounds of water with hydroxides of some metals (copper, nickel), with amines, as well as in sulfuric and orthophosphoric acids, a concentrated solution of zinc chloride.

In available household solvents and plain water cellulose does not dissolve. This is because the long filamentous molecules of this substance are linked in peculiar bundles and are located parallel to each other. In addition, this whole "structure" is reinforced with hydrogen bonds, which is why the molecules of a weak solvent or water simply cannot penetrate inside and destroy this strong plexus.

The finest threads, the length of which ranges from 3 to 35 millimeters, connected in bundles - this is how you can schematically represent the structure of cellulose. Long fibers are used in the textile industry, while short ones are used in the manufacture of, for example, paper and cardboard.

Cellulose does not melt and does not turn into steam, however, it begins to break down when heated above 150 degrees Celsius, while releasing low molecular weight compounds - hydrogen, methane and carbon monoxide (carbon monoxide). At temperatures of 350 ° C and above, cellulose is charred.

Change for the better

This is how cellulose is described in chemical symbols, the structural formula of which clearly shows a long-chain polymer molecule consisting of repeating glucosidic residues. Note the "n" indicating a large number of them.

By the way, Anselm Payen's cellulose formula has undergone some changes. In 1934, an English organic chemist, laureate Nobel Prize Walter Norman Howors studied the properties of starch, lactose, and other sugars, including cellulose. Having discovered the ability of this substance to hydrolysis, he made his own adjustments to Payen's research, and the cellulose formula was supplemented with the value "n", indicating the presence of glycosidic residues. On the this moment it looks like this: (C 5 H 10 O 5) n.

Cellulose ethers

It is important that the cellulose molecule contains hydroxyl groups that can be alkylated and acylated to form various esters. This is another of the most important properties that cellulose has. The structural formula of various compounds may look like this:

Cellulose ethers are simple and complex. Simple ones are methyl, hydroxypropyl, carboxymethyl, ethyl, methyl hydroxypropyl and cyanoethyl cellulose. Complex ones are nitrates, sulfates and cellulose acetates, as well as acetopropionates, acetylphthalyl cellulose and acetobutyrates. All these ethers are produced in almost all countries of the world in hundreds of thousands of tons per year.

From film to toothpaste

What are they for? As a rule, cellulose ethers are widely used for the production of artificial fibers, various plastics, all kinds of films (including photographic ones), varnishes, paints, and are also used in the military industry for the manufacture of solid rocket fuel, smokeless powder and explosives.

In addition, cellulose ethers are included in plaster and gypsum-cement mixtures, fabric dyes, toothpastes, various adhesives, synthetic detergents, perfumery and cosmetics. In a word, if the cellulose formula had not been discovered back in 1838, modern people would not have many of the benefits of civilization.

Almost twins

Few ordinary people know that cellulose has a kind of double. The formulas of cellulose and starch are identical, however, they are two completely different substances. What's the difference? Despite the fact that both of these substances are natural polymers, the degree of polymerization of starch is much lower than that of cellulose. And if you go deeper and compare the structures of these substances, you can find that cellulose macromolecules are arranged linearly and in only one direction, thus forming fibers, while starch microparticles look slightly different.

Applications

One of the best visual examples of practically pure cellulose is ordinary medical cotton wool. As you know, it is obtained from thoroughly refined cotton.

The second, no less used cellulose product is paper. In fact, it is the thinnest layer of cellulose fibers, carefully pressed and glued together.

In addition, viscose fabric is produced from cellulose, which under skillful hands craftsmen magically turns into beautiful clothes, upholstery for upholstered furniture and various decorative draperies. Also, viscose is used for the manufacture of technical belts, filters and tire cords.

Let's not forget about cellophane, which is obtained from viscose. It is difficult to imagine supermarkets, shops, packaging departments of post offices without it. Cellophane is everywhere: candy is wrapped in it, cereals and bakery products are packed in it, as well as pills, tights and any equipment, from a mobile phone to a TV remote control.

In addition, pure microcrystalline cellulose is included in weight loss tablets. Once in the stomach, they swell and create a feeling of fullness. The amount of food consumed per day is significantly reduced, respectively, the weight falls.

As you can see, the discovery of cellulose made a real revolution not only in the chemical industry, but also in medicine.