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 the compounds of organic origin 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, straw contains thirty percent of cellulose. A lot of it and 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 break down 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 chars. It cannot be dissolved in water, but it can be dissolved in a solution of ammonia with copper hydroxide. Fiber is a very strong and elastic material.
The value of cellulose for living organisms
Cellulose refers to polysaccharide carbohydrates.
In a living organism, the functions of carbohydrates are as follows:
- 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.
- Protective function characteristic of plants (thorns or thorns). Such formations on plants consist of the walls of dead plant cells.
- Plastic function (another name for anabolic function), since carbohydrates are components of complex molecular structures.
- The function of providing energy, since carbohydrates are an energy source for living organisms.
- Storage function, since living organisms store carbohydrates in their tissues as nutrients.
- 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 blood osmotic pressure depends on the concentration of this carbohydrate in the blood). Osmotic transport delivers nutrients to tall tree trunks, since capillary transport is inefficient in this case.
- The function of receptors, 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 responds in a special way to a connection with a certain chemical molecule that transmits an external signal, and transmits this signal to the cell itself.
Biological role cellulose is:
- Fiber is the main structural part of the cell membrane of plants. Formed as a result of photosynthesis. Plant cellulose is the food of herbivorous animals (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.
- Fiber in food gives a person a feeling of satiety 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). It is metabolized in the large intestine 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. Most of these acids are absorbed by 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 amount of beneficial intestinal bacteria increases and the synthesis of vitamin substances improves.
- If you add thirty to forty-five grams of bran (containing fiber) made from wheat to food, then stool masses increase from seventy-nine grams to two hundred and twenty-eight grams per day, and their movement time is reduced from fifty-eight hours to forty hours. When fiber is added to food regularly, the stool becomes softer, which helps to prevent constipation and hemorrhoids.
- 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 becomes more resistant to glucose.
- Fiber, like a brush, removes dirty deposits from the intestinal walls, absorbs toxic substances, takes cholesterol and removes all this from the body naturally. Doctors have come to the conclusion that people who eat rye bread and bran are less likely to suffer from rectal cancer.
Most fiber is found in bran from wheat and rye, in bread from coarsely ground flour, in bread from proteins and bran, in dry fruits, carrots, cereals, and beets.
Cellulose 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, linen and hemp fibers were used to make various fabrics. For the first time in industry, the chemical treatment 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 manufacture of organic glass and in other industries.
Let's take a closer look at its application.
Acetate silk is obtained from cellulose and its ethers, non-natural fibers are made, a film of cellulose acetate that does not burn. Smokeless 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, building material for shipbuilding and building houses. They also receive 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. The paper is a thin fibrous layer of cellulose that has been sized and pressed on special equipment to obtain a thin, dense, smooth surface of the paper product (the ink should not spread over it). At first, only vegetable material was used to create paper, from which the necessary fibers were isolated mechanically (rice stalks, cotton, rags).
But typography developed at a very rapid pace, newspapers also began to be produced, so the paper produced in this way was not enough. People found out that there is a lot of fiber in wood, so milled wood raw materials began to be added to the plant mass from which paper was made. But this paper was quickly torn and turned yellow in a very short time, especially when exposed to light for a long time.
Therefore, various methods of processing wood material began to be developed. chemicals, which allow you to isolate from it cellulose purified from various impurities.
To obtain cellulose, 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 is an acid reagent, it is used for the production of cellulose from wood with a small amount of resin.
Alkaline reagents include:
- soda reagents ensure the production of cellulose from hardwoods and annuals (such cellulose is quite expensive);
- 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 the manufacture of cellulose from any plants).
After all the production stages, the paper goes to the manufacture of packaging, books 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
cellulose, the main building material flora, which forms the cell walls of trees and other higher plants. The purest natural form of cellulose is cottonseed hairs.
Purification and isolation. Currently, only two sources of cellulose are of industrial importance - cotton and wood pulp. Cotton is almost pure cellulose and does not require complex processing to become the starting material for the manufacture of man-made fibers and non-fiber plastics. After the long fibers used to make cotton fabrics are separated from the cottonseed, short hairs, or "lint" (cotton fluff), 10-15 mm long, remain. The lint is separated from the seed, heated under pressure for 2-6 hours with a 2.5-3% sodium hydroxide solution, then washed, bleached with chlorine, washed again and dried. The resulting product is 99% pure cellulose. The yield is 80% (wt.) lint, and the rest is lignin, fats, waxes, pectates and seed husks. Wood pulp is usually made from the wood of coniferous trees. It contains 50-60% cellulose, 25-35% lignin and 10-15% hemicelluloses and non-cellulose hydrocarbons. In the sulphite process, wood chips are boiled under pressure (about 0.5 MPa) at 140°C with sulfur dioxide and calcium bisulfite. In this case, lignins and hydrocarbons go into solution and cellulose remains. After washing and bleaching, the cleaned mass is cast into loose paper, similar to blotting paper, and dried. Such a mass consists of 88-97% cellulose and is quite suitable for chemical processing into viscose fiber and cellophane, as well as into cellulose derivatives - esters and ethers. The process of regeneration of cellulose from a solution by adding acid to its concentrated ammonium copper (i.e. containing copper sulfate and ammonium hydroxide) aqueous solution was described by the Englishman J. Mercer around 1844. But the first industrial application This method, which laid the foundation for the industry of copper-ammonia fiber, is attributed to E. Schweitzer (1857), and its further development is the merit of M. Kramer and I. Schlossberger (1858). And only in 1892 Cross, Bevin and Beadle in England invented a process for obtaining viscose fiber: a viscous (whence the name viscose) aqueous solution of cellulose was obtained after treating cellulose first with a strong solution of sodium hydroxide, which gave "soda cellulose", and then with carbon disulfide (CS2), resulting in soluble cellulose xanthate. By squeezing a trickle of this "spinning" solution through a spinneret with a small round hole into an acid bath, the cellulose was regenerated in the form of a viscose fiber. When the solution was squeezed out into the same bath through a die with a narrow slit, a film was obtained, called cellophane. J. Brandenberger, who was engaged in this technology in France from 1908 to 1912, was the first to patent a continuous process for the manufacture of cellophane.
Chemical structure. Despite the widespread industrial use of cellulose and its derivatives, the currently accepted chemical structural formula of cellulose was proposed (by W. Haworth) only in 1934. True, since 1913 its empirical formula C6H10O5 was known, determined from the data of a quantitative analysis of well-washed and dried samples: 44.4% C, 6.2% H and 49.4% O. Thanks to the works of G.Sh Taudinger and K. Freudenberg also knew that this is a long-chain polymer molecule consisting of those shown in Fig. 1 repeating glucosidic residues. Each unit has three hydroxyl groups - one primary (-CH2CHOH) and two secondary (>CHCHOH). By 1920, E.Fischer established the structure of simple sugars, and in the same year, X-ray studies of cellulose showed for the first time a clear diffraction pattern of its fibers. The X-ray diffraction pattern of the cotton fiber shows a well-defined crystalline orientation, but the flax fiber is even more ordered. When the cellulose is regenerated in fiber form, the crystallinity is largely lost. How easy it is to see in the light of achievements modern science, the structural chemistry of cellulose practically stood still from 1860 to 1920 for the reason that all this time the auxiliary scientific disciplines needed to solve the problem.
REGENERATED CELLULOSE
Viscose fiber and cellophane. Both viscose fiber and cellophane are regenerated (from solution) cellulose. Purified natural cellulose is treated with an excess of concentrated sodium hydroxide; after removing the excess, its lumps are ground and the resulting mass is kept under carefully controlled conditions. With this "aging" the length of the polymer chains decreases, which contributes to the subsequent dissolution. Then crushed cellulose is mixed with carbon disulfide and the resulting xanthate is dissolved in a solution of sodium hydroxide to obtain "viscose" - a viscous solution. When viscose enters an aqueous acid solution, cellulose is regenerated from it. Simplified total reactions are as follows:
Viscose fiber, obtained by squeezing viscose through small holes in a spinneret into an acid solution, is widely used for the manufacture of clothing, drapery and upholstery fabrics, as well as in technology. Significant amounts of viscose fiber are used for technical belts, tapes, filters and tire cord.
Cellophane. Cellophane, obtained by extruding viscose into an acidic bath through a spinneret with a narrow slot, then passes through the washing, bleaching and plasticizing baths, passes through the dryer drums and is wound into a roll. The surface of cellophane film is almost always coated with nitrocellulose, resin, some kind of wax or varnish to reduce the transmission of water vapor and provide thermal sealing, since uncoated cellophane does not have the property of thermoplasticity. In modern industries, polymer coatings of the polyvinylidene chloride type are used for this, since they are less moisture permeable and give a stronger connection during thermal sealing. Cellophane is widely used mainly in packaging production as a wrapping material for haberdashery goods, food products, tobacco products, as well as the basis for self-adhesive packaging tape.
Viscose sponge. Along with obtaining a fiber or film, viscose can be mixed with suitable fibrous and finely crystalline materials; after acid treatment and water leaching, this mixture is converted into a viscose sponge material (Fig. 2), which is used for packaging and thermal insulation.
Copper fiber. Regenerated cellulose fiber is also produced commercially by dissolving cellulose in a concentrated ammonium copper solution (CuSO4 in NH4OH) and spinning the resulting solution into a fiber in an acid spinning bath. Such a fiber is called copper-ammonia.
PROPERTIES OF CELLULOSE
Chemical properties. As shown in fig. 1, cellulose is a high polymeric carbohydrate consisting of C6H10O5 glucosidic residues connected by ester bridges at position 1,4. The three hydroxyl groups on each glucopyranose unit can be esterified with organic agents such as a mixture of acids and acid anhydrides with an appropriate catalyst such as sulfuric acid. Ethers can be formed by the action of concentrated sodium hydroxide, leading to the formation of soda cellulose, and subsequent reaction with an alkyl halide:
Reaction with ethylene or propylene oxide gives hydroxylated ethers:
The presence of these hydroxyl groups and the geometry of the macromolecule are responsible for the strong polar mutual attraction of neighboring units. The forces of attraction are so strong that conventional solvents are unable to break the chain and dissolve the cellulose. These free hydroxyl groups are also responsible for the high hygroscopicity of cellulose (Fig. 3). Etherification and etherization reduce hygroscopicity and increase solubility in common solvents.
Under the action of an aqueous solution of acid, oxygen bridges in the 1,4-position are broken. A complete break in the chain gives glucose, a monosaccharide. The initial chain length depends on the origin of the cellulose. It is maximum in the natural state and decreases in the process of isolation, purification and conversion into derivative compounds (see table).
CELLULOSE POLYMERIZATION DEGREE
Material Number of glucoside residues
Raw cotton 2500-3000
Cleaned cotton linter 900-1000
Purified wood pulp 800-1000
Regenerated cellulose 200-400
Industrial cellulose acetate 150-270
Even mechanical shear, for example during abrasive grinding, leads to a decrease in the length of the chains. When the length of the polymer chain decreases below a certain minimum value, the macroscopic physical properties cellulose. Oxidizing agents affect cellulose without causing cleavage of the glucopyranose ring (Fig. 4). The subsequent action (in the presence of moisture, for example, in environmental tests), as a rule, leads to chain scission and an increase in the number of aldehyde-like end groups. Since aldehyde groups are easily oxidized to carboxyl groups, the content of carboxyl, which is practically absent in natural cellulose, increases sharply under atmospheric conditions and oxidation.
Like all polymers, cellulose breaks down under the influence of atmospheric factors as a result of the combined action of oxygen, moisture, acidic components of the air and sunlight. Importance has an ultraviolet component of sunlight, and many good UV protection agents increase the life of products made from cellulose derivatives. Acidic components of the air, such as nitrogen and sulfur oxides (and they are always present in atmospheric air industrial areas) accelerate decomposition, often with a stronger effect than sunlight. For example, in England, it was noted that samples of cotton, tested for exposure to atmospheric conditions, in winter, when there was practically no bright sunlight, degraded faster than in summer. The fact is that the burning of large amounts of coal and gas in winter led to an increase in the concentration of nitrogen and sulfur oxides in the air. Acid scavengers, antioxidants, and UV-absorbing agents reduce the sensitivity of cellulose to weathering. Substitution of free hydroxyl groups leads to a change in this sensitivity: cellulose nitrate degrades faster, while acetate and propionate degrade more slowly.
physical properties. Cellulose polymer chains are packed into long bundles, or fibers, in which, along with ordered, crystalline, there are also less ordered, amorphous sections (Fig. 5). The measured percentage of crystallinity depends on the type of pulp, as well as on the method of measurement. According to x-ray data, it ranges from 70% (cotton) to 38-40% (viscose fiber). radiographic structural analysis provides information not only on the quantitative ratio between crystalline and amorphous material in the polymer, but also on the degree of fiber orientation caused by stretching or normal growth processes. The sharpness of the diffraction rings characterizes the degree of crystallinity, while the diffraction spots and their sharpness characterize the presence and degree of preferred orientation of crystallites. In a sample of recycled cellulose acetate obtained by the "dry" spinning process, both the degree of crystallinity and orientation are very small. In the triacetate sample, the degree of crystallinity is greater, but there is no preferred orientation. Heat treatment of triacetate at a temperature of 180-240 ° C significantly increases the degree of its crystallinity, and orientation (drawing) in combination with heat treatment gives the most ordered material. Linen exhibits a high degree of both crystallinity and orientation.
see also
CHEMISTRY ORGANIC;
PAPER AND OTHER WRITING MATERIALS ;
PLASTICS.
Rice. 5. MOLECULAR STRUCTURE of cellulose. Molecular chains pass through several micelles (crystalline regions) of length L. Here A, A" and B" are the ends of the chains lying in the crystallized region; B - chain end outside the crystallized region.
LITERATURE
Bushmelev V.A., Volman N.S. Processes and devices of pulp and paper production. M., 1974 Cellulose and its derivatives. M., 1974 Akim E.L. etc. Technology of processing and processing of cellulose, paper and cardboard. L., 1977
Collier Encyclopedia. - Open Society. 2000 .
What is the role of cellulose in the human body, you will learn from this article.
What is cellulose?
Cellulose is a natural polymer of glucose, which is of plant origin and has a linear molecular structure. In other words, it is also called checkered. On our planet, among all organic compounds, it ranks first.
Cellulose biomedical value:
- Cellulose is the main component that makes up the structure of plant cell walls.
- In plants, it performs a protective function.
- The component is the basis of complex molecular structures.
- They provide living organisms with the necessary energy for existence.
- They feed the cells of organisms with nutrients, as they are concentrated in the tissues and feed the cell at the right time.
- Cellulose takes an active part in the regulation of osmotic pressure.
- It is part of the perceiving parts of the receptors of all cells.
The biological significance of cellulose:
- Fiber is the main structural part of the cell wall in plants. Plant cellulose is the main food of herbivores, as their body has a special enzyme - cellulase, which is responsible for the breakdown of this component. But a person in its pure form does not use cellulose.
- It binds fluid in intestinal peristalsis. It also metabolizes bacteria in the large intestine. Cellulose energy supports its microflora and dietary fiber in it.
- Fiber is the prevention of hemorrhoids and constipation.
- When a person suffering from type 1 diabetes consumes enough cellulose, his body becomes much more resistant to glucose.
- This element acts as a “brush”, removing dirty buildup from the intestinal walls - it removes toxic substances and cholesterol.
We hope that from this article you have learned what is the biological function of cellulose in the cell of organisms.