Modern cellulose - what is it? Cellulose formula. Chemical physical properties

Cellulose (C 6 H 10 O 5) n – a natural polymer, a polysaccharide consisting of β-glucose residues, the molecules have a linear structure. Each residue of a glucose molecule contains three hydroxyl groups, so it exhibits the properties of a polyhydric alcohol.

Physical properties

Cellulose is a fibrous substance, insoluble either in water or in ordinary organic solvents, and is hygroscopic. Has great mechanical and chemical strength.

1. Cellulose, or fiber, is part of plants, forming cell walls in them.

2. This is where its name comes from (from the Latin “cellulum” - cell).

3. Cellulose gives plants the necessary strength and elasticity and is, as it were, their skeleton.

4. Cotton fibers contain up to 98% cellulose.

5. Flax and hemp fibers are also mainly composed of cellulose; in wood it is about 50%.

6. Paper and cotton fabrics are products made from cellulose.

7. Particularly pure examples of cellulose are cotton wool obtained from purified cotton and filter (un-glued) paper.

8. Cellulose, isolated from natural materials, is a solid fibrous substance that is insoluble in either water or ordinary organic solvents.

Chemical properties

1. Cellulose is a polysaccharide that undergoes hydrolysis to form glucose:

(C 6 H 10 O 5) n + nH 2 O → nC 6 H 12 O 6

2. Cellulose is a polyhydric alcohol that undergoes esterification reactions to form esters

(C 6 H 7 O 2 (OH) 3) n + 3nCH 3 COOH → 3nH 2 O + (C 6 H 7 O 2 (OCOCH 3) 3) n

cellulose triacetate

Cellulose acetates are artificial polymers used in the production of silk acetate, film (film), and varnishes.

Application

The uses of cellulose are very diverse. It is used to produce paper, fabrics, varnishes, films, explosives, artificial silk (acetate, viscose), plastics (celluloid), glucose and much more.

Finding cellulose in nature.

1. In natural fibers, cellulose macromolecules are located in one direction: they are oriented along the fiber axis.

2. The numerous hydrogen bonds that arise between the hydroxyl groups of macromolecules determine the high strength of these fibers.

3. In the process of spinning cotton, flax, etc., these elementary fibers are woven into longer threads.

4. This is explained by the fact that the macromolecules in it, although they have a linear structure, are located more randomly and are not oriented in one direction.

The construction of starch and cellulose macromolecules from different cyclic forms of glucose significantly affects their properties:

1) starch is an important human food product; cellulose cannot be used for this purpose;

2) the reason is that enzymes that promote starch hydrolysis do not act on the bonds between cellulose residues.

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.

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 + 3nHNO3 → n + 3n H2O.

Application of cellulose.

Obtaining acetate fiber

68. Cellulose, its physical properties

Being in nature. Physical properties.

1. Cellulose, or fiber, is part of plants, forming cell walls in them.

2. This is where its name comes from (from the Latin “cellulum” - cell).

3. Cellulose gives plants the necessary strength and elasticity and is, as it were, their skeleton.

4. Cotton fibers contain up to 98% cellulose.

5. Flax and hemp fibers are also mainly composed of cellulose; in wood it is about 50%.

6. Paper and cotton fabrics are products made from cellulose.

7. Particularly pure examples of cellulose are cotton wool obtained from purified cotton and filter (un-glued) paper.

8. Cellulose, isolated from natural materials, is a solid fibrous substance that is insoluble in either water or ordinary organic solvents.

Cellulose structure:

1) cellulose, like starch, is a natural polymer;

2) these substances even have the same structural units in composition - residues of glucose molecules, the same molecular formula (C6H10O5)n;

3) the n value of cellulose is usually higher than that of starch: its average molecular weight reaches several million;

4) the main difference between starch and cellulose is in the structure of their molecules.

Finding cellulose in nature.

1. In natural fibers, cellulose macromolecules are located in one direction: they are oriented along the fiber axis.

2. The numerous hydrogen bonds that arise between the hydroxyl groups of macromolecules determine the high strength of these fibers.

What are the chemical and physical properties of cellulose

In the process of spinning cotton, flax, etc., these elementary fibers are woven into longer threads.

4. This is explained by the fact that the macromolecules in it, although they have a linear structure, are located more randomly and are not oriented in one direction.

The construction of starch and cellulose macromolecules from different cyclic forms of glucose significantly affects their properties:

1) starch is an important human food product; cellulose cannot be used for this purpose;

2) the reason is that enzymes that promote starch hydrolysis do not act on the bonds between cellulose residues.

69. Chemical properties of cellulose and its application

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.

69. Chemical properties of cellulose and its application

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: (C6H10O5)n + nH2O = nC6H12O6.

7. Structural units of cellulose (C6H10O5)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 + 3nHNO3 -> n + 3n H2O.

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.

O.A. Noskova, M.S. Fedoseev

Wood chemistry

And synthetic polymers

PART 2

Approved

Editorial and Publishing Council of the University

as lecture notes

Publishing house

Perm State Technical University

Reviewers:

Ph.D. tech. sciences D.R. Nagimov

(CJSC "Karbokam");

Ph.D. tech. sciences, prof. F.H. Khakimova

(Perm State Technical University)

Noskova, O.A.

N84 Chemistry of wood and synthetic polymers: lecture notes: in 2 hours / O.A. Noskova, M.S. Fedoseev. – Perm: Perm Publishing House. state tech. University, 2007. – Part 2. – 53 p.

ISBN 978-5-88151-795-3

Information is provided regarding the chemical structure and properties of the main components of wood (cellulose, hemicelluloses, lignin and extractives). The chemical reactions of these components that occur during the chemical processing of wood or during the chemical modification of cellulose are considered. General information about cooking processes is also provided.

Designed for students of specialty 240406 “Technology of chemical wood processing”.

UDC 630*813. + 541.6 + 547.458.8

ISBN 978-5-88151-795-3 © State Educational Institution of Higher Professional Education

"Perm State

Technical University", 2007

Introduction

Wood chemistry is a branch of technical chemistry that studies the chemical composition of wood; chemistry of formation, structure and chemical properties of the substances that make up dead wood tissue; methods for isolating and analyzing these substances, as well as the chemical essence of natural and technological processes for processing wood and its individual components.

The first part of the lecture notes “Chemistry of Wood and Synthetic Polymers,” published in 2002, addresses issues related to the anatomy of wood, the structure of the cell membrane, the chemical composition of wood, and the physical and physicochemical properties of wood.

The second part of the lecture notes “Chemistry of Wood and Synthetic Polymers” discusses issues related to the chemical structure and properties of the main components of wood (cellulose, hemicelluloses, lignin).

The lecture notes provide general information about cooking processes, i.e. on the production of technical cellulose, which is used in the production of paper and cardboard. As a result of chemical transformations of technical cellulose, its derivatives are obtained - ethers and esters, from which artificial fibers (viscose, acetate), films (film, photo, packaging films), plastics, varnishes, and adhesives are produced. This part of the summary also briefly discusses the production and properties of cellulose ethers, which are widely used in industry.

Chemistry of cellulose

Chemical structure of cellulose

Cellulose is one of the most important natural polymers. This is the main component of plant tissues. Natural cellulose is found in large quantities in cotton, flax and other fibrous plants, from which natural textile cellulose fibers are obtained. Cotton fibers are almost pure cellulose (95–99%). A more important source of industrial production of cellulose (technical cellulose) is woody plants. In the wood of various tree species, the mass fraction of cellulose averages 40–50%.

Cellulose is a polysaccharide, the macromolecules of which are built from residues D-glucose (β units -D-anhydroglucopyranose), connected by β-glycosidic bonds 1–4:

Cellulose is a linear homopolymer (homopolysaccharide) belonging to heterochain polymers (polyacetals). It is a stereoregular polymer in which the cellobiose residue serves as a stereo repeating unit. The total formula of cellulose can be represented as (C6H10O5) P or [C6H7O2 (OH)3] P. Each monomer unit contains three alcohol hydroxyl groups, of which one is primary – CH2OH and two (at C2 and C3) are secondary – CHOH–.

The end links are different from the rest of the chain links. One terminal link (conditionally right - non-reducing) has an additional free secondary alcohol hydroxyl (at C4). The other terminal link (conditionally left - reducing) contains free glycosidic (hemiacetal) hydroxyl (in C1 ) and, therefore, can exist in two tautomeric forms - cyclic (coluacetal) and open (aldehyde):

The terminal aldehyde group gives cellulose its reducing (reducing) ability. For example, cellulose can reduce copper from Cu2+ to Cu+:

Amount of copper recovered ( copper number) serves as a qualitative characteristic of the length of cellulose chains and shows its degree of oxidative and hydrolytic destruction.

Natural cellulose has a high degree of polymerization (DP): wood - 5000-10000 and above, cotton - 14000-20000. When isolated from plant tissues, cellulose is somewhat destroyed. Technical wood pulp has a DP of about 1000–2000. The DP of cellulose is determined mainly by the viscometric method, using some complex bases as solvents: copper-ammonia reagent (OH)2, cupriethylenediamine (OH)2, cadmiumethylenediamine (cadoxene) (OH)2, etc.

Cellulose isolated from plants is always polydisperse, i.e. contains macromolecules of various lengths. The degree of cellulose polydispersity (molecular heterogeneity) is determined by fractionation methods, i.e. separating a cellulose sample into fractions with a certain molecular weight. The properties of a cellulose sample (mechanical strength, solubility) depend on the average DP and the degree of polydispersity.

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Structure, properties, functions of polysaccharides (homo- and heteropolysaccharides).

POLYSACCHARIDES- these are high molecular weight substances ( polymers), consisting of a large number of monosaccharides. Based on their composition, they are divided into homopolysaccharides and heteropolysaccharides.

Homopolysaccharides– polymers consisting from monosaccharides of one type . For example, glycogen and starch are built only from molecules of α-glucose (α-D-glucopyranose); the monomer of fiber (cellulose) is also β-glucose.

Starch. This reserve polysaccharide plants. The monomer of starch is α-glucose. Leftovers glucose V starch molecule in linear sections are interconnected α-1,4-glycosidic , and at branch points – α-1,6-glycosidic bonds .

Starch is a mixture of two homopolysaccharides: linear - amylose (10-30%) and branched – amylopectin (70-90%).

Glycogen. This is the main one reserve polysaccharide human and animal tissues. The glycogen molecule has approximately 2 times more branched structure than starch amylopectin. Glycogen monomer is α-glucose . In the glycogen molecule, glucose residues in linear regions are interconnected α-1,4-glycosidic , and at branch points – α-1,6-glycosidic bonds .

Cellulose. This is the most common structural plant homopolysaccharide. IN linear fiber molecule monomers β-glucose interconnected β-1,4-glycosidic bonds . Fiber is not digestible in the human body, but, due to its rigidity, irritates the mucous membrane of the gastrointestinal tract, thereby enhances peristalsis and stimulates the secretion of digestive juices, promotes the formation of feces.

Pectic substances- polysaccharides, the monomer of which is D- galacturonic acid , the residues of which are connected by α-1,4-glycosidic bonds. Contained in fruits and vegetables, they are characterized by gelation in the presence of organic acids, which is used in the food industry (jelly, marmalade).

Heteropolysaccharides(mucopolysaccharides, glycosaminoglycans) – polymers consisting from various types of monosaccharides . By structure they represent

straight chains built from repeating disaccharide residues , which necessarily include amino sugar (glucosamine or galactosamine) and hexuronic acids (glucuronic or iduronic).

Physical and chemical properties of cellulose

They are jelly-like substances that perform a number of functions, including: protective (mucus), structural, are the basis of the intercellular substance.

In the body, heteropolysaccharides are not found in a free state, but are always associated with proteins (glycoproteins and proteoglycans) or lipids (glycolipids).

Based on their structure and properties, they are divided into acidic and neutral.

ACID HETEROPOLYSACHARIDES:

They contain hexuronic or sulfuric acids. Representatives:

Hyaluronic acidis the main structural component of the intercellular substance capable of binding water (“biological cement”) . Solutions of hyaluronic acid have a high viscosity, therefore they serve as a barrier to the penetration of microorganisms, participate in the regulation of water metabolism, and are the main part of the intercellular substance).

Chondroitin sulfates are structural components cartilage, ligaments, tendons, bones, heart valves.

Heparin – anticoagulant (prevents blood clotting), has an anti-inflammatory effect, activator of a number of enzymes.

NEUTRAL HETEROPOLYSACHARIDES: are part of glycoproteins in blood serum, mucins in saliva, urine, etc., built from amino sugars and sialic acids. Neutral GPs are part of the plural. enzymes and hormones.

SIALIC ACIDS - a combination of neuraminic acid with acetic or amino acid - glycine, are part of cell membranes and biological fluids. Sialic acids are determined for the diagnosis of systemic diseases (rheumatism, systemic lupus erythematosus).

A complex carbohydrate from the group of polysaccharides that is part of the cell wall of plants is called cellulose or fiber. The substance was discovered in 1838 by the French chemist Anselme Payen. The formula of cellulose is (C 6 H 10 O 5) n.

Structure

Despite the common characteristics, cellulose differs from another plant polysaccharide - starch. The cellulose molecule is a long, exclusively unbranched chain of saccharides. Unlike starch, which consists of α-glucose residues, it includes many β-glucose residues linked to each other.

Due to the dense linear structure of the molecules, they form fibers.

Rice. 1. The structure of the cellulose molecule.

Cellulose has a higher degree of polymerization than starch.

Receipt

In industrial conditions, cellulose is boiled down from wood (chips). For this purpose, acidic or alkaline reagents are used. For example, sodium hydrosulfite, sodium hydroxide, lye.

As a result of cooking, cellulose with an admixture of organic compounds is formed. To clean it, use an alkali solution.

Physical properties

Fiber is a tasteless, white, solid fibrous substance. Cellulose is poorly soluble in water and organic solvents. Dissolves in Schweitzer's reagent - an ammonia solution of copper (II) hydroxide.

Basic physical properties:

• destroyed at 200°C;
• burns at 275°C;
• self-ignites at 420°C;
• melts at 467°C.

In nature, cellulose is found in plants. It is formed during photosynthesis and performs a structural function in plants. Is a food additive E460.

Rice. 2. Plant cell wall.

Chemical properties

Due to the presence of three hydroxyl groups in one saccharide, fiber exhibits the properties of polyhydric alcohols and is able to enter into esterification reactions to form esters. When decomposed without oxygen, it decomposes into charcoal, water and volatile organic compounds.

The main chemical properties of fiber are presented in the table.

Rice. 3. Pyroxylin.

Cellulose is mainly used for making paper, as well as for the production of esters, alcohols, and glucose.

What have we learned?

Cellulose or fiber is a polymer from the carbohydrate class, consisting of β-glucose residues. Part of plant cell walls. It is a white, tasteless substance that forms fibers that are poorly soluble in water and organic solvents. Cellulose is isolated from wood by cooking. The compound undergoes esterification and hydrolysis reactions and can decompose in the absence of air. When completely decomposed, it forms water and carbon dioxide.

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 manufacture of paper and cardboard. We found out what structure cellulose has and what the process of its production is.

The soft part of plants and animals mainly contains cellulose Cellulose is what gives plants their flexibility. Cellulose (fiber) is a plant polysaccharide, which is the most common organic substance on Earth.

Almost all green plants produce cellulose for their needs. It contains the same elements as sugar, namely carbon, hydrogen and oxygen. These elements are present in air and water. Sugar is formed in the leaves and, dissolving in the juice, spreads throughout the plant. The main part of the sugar is used to promote plant growth and restoration work, the rest of the sugar is converted into cellulose. The plant uses it to create the shell of 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 receives cellulose from plants even after they die and there is a complete lack of moisture in them. For example, wild cotton is one of the purest forms of natural cellulose that humans use to make clothing.

Cellulose is part of plants used by humans as food products - lettuce, celery, and bran. The human body is unable to digest cellulose, but it is useful as “roughage” in the human diet. The stomachs of some animals, such as sheep and camels, contain 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 people obtain various products. Cotton, which is 99.8% cellulose, is a remarkable example of what man can produce from cellulose fiber. If cotton is treated with a mixture of nitric and sulfuric acid, we obtain pyroxylin, which is an explosive.

After various chemical treatments of cellulose, other products can be obtained from it. Among them: base for photographic film, additives for varnishes, viscose fibers for fabric production, cellophane and other plastic materials. Cellulose is also used in paper making.