If the connection between macromolecules is carried out using weak van der Waals forces, they are called thermoplastics, if through chemical bonds - thermosets. Linear polymers include, for example, cellulose, branched polymers, for example, amylopectin, and there are polymers with complex spatial three-dimensional structures.
In the structure of a polymer, a monomer unit can be distinguished - a repeating structural fragment that includes several atoms. Polymers consist of a large number of repeating groups (units) of the same structure, for example, polyvinyl chloride (-CH 2 -CHCl-) n, natural rubber, etc. High-molecular compounds, the molecules of which contain several types of repeating groups, are called copolymers or heteropolymers.
A polymer is formed from monomers as a result of polymerization or polycondensation reactions. Polymers include numerous natural compounds: proteins, nucleic acids, polysaccharides, rubber and other organic substances. In most cases, the concept refers to organic compounds, but there are also many inorganic polymers. A large number of polymers are obtained synthetically based on the simplest compounds of elements of natural origin through polymerization reactions, polycondensation and chemical transformations. The names of polymers are formed from the name of the monomer with the prefix poly-: poly ethylene, poly propylene, poly vinyl acetate, etc.
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Special mechanical properties
- elasticity - the ability to undergo high reversible deformations under a relatively small load (rubbers);
- low fragility of glassy and crystalline polymers (plastics, organic glass);
- the ability of macromolecules to orient under the influence of a directed mechanical field (used in the manufacture of fibers and films).
Features of polymer solutions:
- high solution viscosity at low polymer concentration;
- The dissolution of the polymer occurs through the swelling stage.
Special chemical properties:
- the ability to dramatically change its physical and mechanical properties under the influence of small quantities of a reagent (vulcanization of rubber, tanning of leather, etc.).
The special properties of polymers are explained not only by their large molecular weight, but also by the fact that macromolecules have a chain structure and are flexible.
Classification
According to their chemical composition, all polymers are divided into organic, organoelement, inorganic.
- Organic polymers.
- Organoelement polymers. They contain inorganic atoms (Si, Ti, Al) in the main chain of organic radicals, which combine with organic radicals. They don't exist in nature. An artificially obtained representative is organosilicon compounds.
- Inorganic polymers. They do not contain C-C bonds in the repeating unit, but are capable of containing organic radicals as side substituents.
It should be noted that in technology, polymers are often used as components of composite materials, for example, fiberglass. Composite materials are possible, all components of which are polymers (with different compositions and properties).
Based on the shape of macromolecules, polymers are divided into linear, branched (a special case is star-shaped), ribbon, flat, comb-shaped, polymer networks, and so on.
Polymers are classified according to polarity (affecting solubility in various liquids). The polarity of polymer units is determined by the presence in their composition of dipoles - molecules with an isolated distribution of positive and negative charges. In nonpolar units, the dipole moments of atomic bonds are mutually compensated. Polymers whose units have significant polarity are called hydrophilic or polar. Polymers with non-polar units - non-polar, hydrophobic. Polymers containing both polar and non-polar units are called amphiphilic. Homopolymers, each unit of which contains both polar and nonpolar large groups, are proposed to be called amphiphilic homopolymers.
In relation to heating, polymers are divided into thermoplastic And thermosetting. Thermoplastic polymers (polyethylene, polypropylene, polystyrene) soften when heated, even melt, and harden when cooled. This process is reversible. Thermoset When heated, polymers undergo irreversible chemical destruction without melting. Molecules of thermosetting polymers have a nonlinear structure obtained by cross-linking (for example, vulcanization) of chain polymer molecules. The elastic properties of thermosetting polymers are higher than those of thermoplastics; however, thermosetting polymers have practically no fluidity, as a result of which they have a lower fracture stress.
Natural organic polymers are formed in plant and animal organisms. The most important of them are polysaccharides, proteins and nucleic acids, which largely make up the bodies of plants and animals and which ensure the very functioning of life on Earth. It is believed that the decisive stage in the emergence of life on Earth was the formation of more complex, high-molecular molecules from simple organic molecules (see Chemical evolution).
Types
Synthetic polymers. Artificial polymer materials
Man has been using natural polymer materials in his life for a long time. These are leather, fur, wool, silk, cotton, etc., used for the manufacture of clothing, various binders (cement, lime, clay), which, with appropriate processing, form three-dimensional polymer bodies, widely used as building materials. However, the industrial production of chain polymers began at the beginning of the 20th century, although the prerequisites for this appeared earlier.
Almost immediately, the industrial production of polymers developed in two directions - by processing natural organic polymers into artificial polymer materials and by producing synthetic polymers from organic low-molecular compounds.
In the first case, large-scale production is based on cellulose. The first polymer material from physically modified cellulose - celluloid - was obtained in the middle of the 19th century. Large-scale production of cellulose ethers and esters was established before and after World War II and continues to this day. Films, fibers, paints and varnishes, and thickeners are produced on their basis. It should be noted that the development of cinema and photography was possible only thanks to the advent of transparent nitrocellulose film.
The production of synthetic polymers began in 1906, when Leo Baekeland patented the so-called bakelite resin - a condensation product of phenol and formaldehyde, which turns into a three-dimensional polymer when heated. For decades it has been used to make housings for electrical appliances, batteries, televisions, sockets, etc., and is now more often used as a binder and adhesive.
Thanks to the efforts of Henry Ford, before the First World War, the rapid development of the automobile industry began, first on the basis of natural, then also synthetic rubber. The production of the latter was mastered on the eve of World War II in the Soviet Union, England, Germany and the USA. During these same years, the industrial production of polystyrene and polyvinyl chloride, which are excellent electrical insulating materials, as well as polymethyl methacrylate, was mastered - without organic glass called “plexiglass,” mass aircraft production would have been impossible during the war years.
After the war, the production of polyamide fiber and fabrics (nylon, nylon), which had begun before the war, resumed. In the 50s of the 20th century, polyester fiber was developed and the production of fabrics based on it under the name lavsan or polyethylene terephthalate was mastered. Polypropylene and nitron - artificial wool made from polyacrylonitrile - close the list of synthetic fibers that modern people use for clothing and industrial activities. In the first case, these fibers are very often combined with natural fibers from cellulose or protein (cotton, wool, silk). An epochal event in the world of polymers was the discovery in the mid-50s of the 20th century and the rapid industrial development of Ziegler-Natta catalysts, which led to the emergence of polymer materials based on polyolefins and, above all, polypropylene and low-density polyethylene (before this, the production of polyethylene was mastered at a pressure of the order of 1000 atm.), as well as stereoregular polymers capable of crystallization. Then polyurethanes were introduced into mass production - the most common sealants,
The term “polymerism” was introduced into science by J. Berzelius in 1833 to designate a special type of isomerism, in which substances (polymers) having the same composition have different molecular weights, for example, ethylene and butylene, oxygen and ozone. Thus, the content of the term did not correspond to modern ideas about polymers. “True” synthetic polymers were not yet known at that time.
A number of polymers were apparently obtained in the first half of the 19th century. However, chemists then usually tried to suppress polymerization and polycondensation, which led to the “resinization” of the products of the main chemical reaction, i.e., in fact, to the formation of polymers (until now polymers were often called “resins”). The first mentions of synthetic polymers date back to 1838 () and 1839 (polystyrene).
Polymer chemistry arose only in connection with the creation by A. M. Butlerov of the theory of chemical structure (early 1860s). A. M. Butlerov studied the relationship between the structure and relative stability of molecules, manifested in polymerization reactions. A.M. Butlerov proposed considering the ability of unsaturated compounds to polymerize as a criterion for their reactivity. This is where the classical works in the field of polymerization and isomerization processes by A. E. Favorsky, V. N. Ipatiev and S. V. Lebedev originated. From the studies of petroleum hydrocarbons by V.V. Markovnikov and then by N.D. Zelinsky, threads stretch to modern work on the synthesis of all kinds of monomers from petroleum raw materials.
It should be noted here that from the very beginning, the industrial production of polymers developed in two directions: by processing natural polymers into artificial polymer materials and producing synthetic polymers from organic low-molecular compounds. In the first case, large-scale production is based on cellulose; the first material from physically modified cellulose, cellophane, was obtained in 1908.
The science of synthesizing polymers from monomers turned out to be a much larger phenomenon in terms of the tasks facing scientists.
Despite the invention of a method for producing phenol-formaldehyde resins by Baekeland at the beginning of the 20th century, there was no understanding of the polymerization process. Only in 1922, the German chemist Hermann Staudinger put forward the definition of a macromolecule - a long structure of atoms connected by covalent bonds. He was the first to establish the relationship between the molecular weight of a polymer and the viscosity of its solution. Subsequently, the American chemist Herman Mark studied the shape and size of macromolecules in solution.
Then in the 1920-1930s. Thanks to the advanced work of N. N. Semenov in the field of chain reactions, a deep similarity of the polymerization mechanism with the chain reactions that N. N. Semenov studied was discovered.
In the 30s the existence of free radical (G. Staudinger and others) and ionic (F. Whitmore and others) polymerization mechanisms was proven.
In the USSR in the mid-1930s. S.S. Medvedev formulated the concept of “initiation” of polymerization as a result of the decomposition of peroxide compounds with the formation of radicals. He also quantified chain transfer reactions as processes regulating molecular weight. Research into the mechanisms of free radical polymerization was carried out until the 1950s.
A major role in the development of ideas about polycondensation was played by the work of W. Carothers, who introduced the concepts of monomer functionality, linear and three-dimensional polycondensation into the chemistry of high-molecular compounds. In 1931, together with J.A. Newland, he synthesized chloroprene rubber (neoprene) and in 1937 developed a method for producing polyamide for molding nylon-type fibers.
In the 1930s The doctrine of the structure of polymers also developed; A.P. Aleksandrov first developed it in the 30s. ideas about the relaxation nature of deformation of polymer bodies; V.A. Kargin installed it in the late 30s. the fact of thermodynamic reversibility of polymer solutions and formulated a system of ideas about the three physical states of amorphous high-molecular compounds.
Before World War II, the most developed countries mastered the industrial production of SC, polystyrene, polyvinyl chloride and polymethyl methacrylate.
In the 1940s American physical chemist Flory made significant contributions to the theory of polymer solutions and the statistical mechanics of macromolecules; Flory created methods for determining the structure and properties of macromolecules from measurements of viscosity, sedimentation and diffusion.
An epoch-making event in polymer chemistry was the discovery by K. Ziegler in the 1950s. metal complex catalysts, which led to the emergence of polymers based on polyolefins: polyethylene and polypropylene, which began to be produced at atmospheric pressure. Then polyurethanes (in particular foam rubber), as well as polysiloxanes, were introduced into mass production.
In the 1960-1970s. Unique polymers were obtained - aromatic polyamides, polyimides, polyether ketones, containing aromatic rings in their structure and characterized by enormous strength and heat resistance. In particular, in the 1960s. Kargin V.A. and Kabanov V.A. laid the foundation for a new type of polymer formation - complex-radical polymerization. They showed that the activity of unsaturated monomers in radical polymerization reactions can be significantly increased by binding them into complexes with inorganic salts. This is how polymers of inactive monomers were obtained: pyridine, quinoline, etc.
Man's first acquaintance with rubber occurred in the 15th century. On about. Haiti H. Columbus and his companions saw the ritual games of the natives with balls made of elastic tree resin. According to the notes of Charles Marie de la Condamine, published in 1735, Europeans learned that the tree from which rubber is extracted is called “Heve” in the language of the Peruvian Indians. When the bark of a tree is cut, a sap is released, which is called latex in Spanish. Latex was used to impregnate fabrics.
At the beginning of the 19th century, research into rubber began. In 1823, the Englishman Karl Mackintosh organized the production of waterproof rubberized fabrics and raincoats based on them. The Englishman Thomas Hancock discovered the phenomenon of plasticization of rubber in 1826. Then various additives began to be introduced into plasticized rubber and the technology of filled rubber compounds arose. In 1839, American Charles Goodyear discovered a method for producing non-stick, durable rubber by heating rubber with lead oxide and sulfur. The process was called vulcanization. In the second half of the 19th century, the demand for natural rubber grew rapidly. In the 1890s. The first rubber tires appear. A large number of rubber plantations are emerging in various hot countries (currently Indonesia and Malaysia) are leaders in the production of natural rubber.
In 1825, Michael Faraday, while studying the pyrolysis of natural rubber, found that its simplest formula is C 5 H 8. In 1835, the German chemist F.K. Himmli was the first to isolate isoprene C5H8. In 1866, French chemist Pierre Berthelot obtained butadiene by passing a mixture of ethylene and acetylene through a heated iron tube.
In the 1860-1870s. A.M. Butlerov figured out the structure of many olefins and polymerized many of them, in particular isobutylene under the action of sulfuric acid.
In 1878, Russian chemist A.A. Krakau discovered the ability to polymerize unsaturated compounds under the influence of alkali metals.
In 1884, the English chemist W. Tilden proved that he obtained isoprene from the thermal decomposition of turpentine, he also established the composition and structure of isoprene, and suggested that the tendency of isoprene to polymerize can be used to produce synthetic rubber. In the 1870s. French chemist G. Bouchard isolated isoprene from the products of thermal decomposition of rubber; by treating it with high temperature and hydrochloric acid, he obtained a rubber-like product.
In 1901-1905 V.N. Ipatiev synthesized butadiene from ethyl alcohol at high pressures of 400-500 atm. He was the first to polymerize ethylene in 1913, which no other researcher had been able to do before.
In 1908 M.K. Kucherov obtained sodium isoprene rubber (the result was published in 1913).
In 1909 S.V. Lebedev was the first to demonstrate rubber obtained from divinyl.
Back in 1899, I. L. Kondakov developed a method for producing dimethylbutadiene and proved that the latter is capable of turning into a rubber-like substance under the influence of light, as well as certain reagents, such as sodium. Based on Kondakov’s work in Germany in 1916, Fritz Hoffmann organized the production of the so-called. methyl rubber: hard (“H”) and soft (“W”) synthetic rubber.
In 1910, Carl Dietrich Harries patented a method for polymerizing isoprene under the influence of sodium metal. In 1902, he developed a method for ozonating rubber and, using this method, established the structure of various types of rubbers.
In 1911, I. I. Ostromyslensky obtained butadiene from acetaldehyde. In 1915, B.V. Byzov received a patent for the production of butadiene by pyrolysis of oil.
Starting from the second half of the 19th century, the efforts of many chemists from different countries were aimed at studying methods for producing monomers and methods for their polymerization into rubbery compounds. In 1911, I. I. Ostromyslensky proposed the production of butadiene from alcohol in three stages with a yield of 12%. In Russia this work was rated very highly. The fact is that Russian chemists, as opposed to Western chemists, sought to obtain synthetic rubber from butadiene, and not isoprene. It is possible that it was precisely thanks to this and the presence of a large alcohol base in Russia that it became possible to create a technical base for the production of synthetic rubber in Russia.
In 1926, the Supreme Economic Council of the USSR announced a competition for the development of a technology for producing synthetic rubber, in accordance with the terms of which, on January 1, 1928, it was necessary to submit a description of the process and at least 2 kg of rubber obtained by this method. The projects of Lebedev S.V. and Byzov B.V. turned out to be the most developed. Both projects involved the production of synthetic rubber from butadiene. Lebedev proposed the production of butadiene from alcohol in one stage using a catalyst he developed that had dehydrogenating and dehydrating properties. Byzov proposed producing butadiene from petroleum hydrocarbons. Despite the great achievements of Russian and Soviet chemists in the field of oil refining, there was no raw material base for the production of butadiene using the Byzov method. Therefore, in January 1931, the Council of Labor and Defense decided to build three large similar SK plants using the Lebedev method. The Leningrad experimental plant “Liter B” (now VNIISK) was created, where in 1931 the first batch of divinyl rubber was produced. In 1932-1933 SK factories began operating in Yaroslavl, Voronezh, Efremov, and Kazan.
In 1941, a chloroprene rubber plant was launched in Yerevan.
In 1935, a new era began in the production of synthetic rubbers - they began to be made from copolymers obtained by radical polymerization of 1,3-butadiene in the presence of styrene, acrylonitrile and other compounds. In 1938, industrial production of styrene-butadiene rubber was organized in Germany, and in 1942, large-scale production of synthetic rubber was organized in the USA.
It should be noted here that after 1945 there was a gradual shift away from the production of butadiene from food alcohol with a gradual transition to the production of monomers from oil.
In 1948, Korotkov established that the physical and mechanical properties of the polymer improve with an increase in the content of addition units at the cis-1,4 positions; the largest number of cis units are formed in the presence of organolithium compounds.
In 1955, K. Ziegler discovered new catalytic systems that lead the polymerization process using an ionic mechanism to produce polymer materials similar to those obtained in the presence of lithium. Subsequently, these studies were deepened in Italy in the laboratory of Giulio Natta.
The domestic industrial polyisoprene produced on lithium catalysts was called SKI, and the one obtained in the presence of Ziegler-Natta catalytic systems was known by the abbreviation SKI-3.
In 1956, a method was proposed for the production of stereoregular polybutadiene rubbers (SKD), which were superior in frost resistance and abrasion resistance to rubbers obtained from natural rubber and SKI-3.
Polymers were obtained based on double copolymers of ethylene and propylene - SKEPs (1955-1957). These rubbers do not have double bonds in the polymer structure; for this reason, rubbers based on them are very resistant in aggressive environments, in addition, they are resistant to abrasion.
In the 1960s The industrial production of SKD and SKI-3 rubbers was mastered in Sterlitamak, Togliatti, and Volzhsk. In general, all these enterprises used monomers obtained from oil rather than from alcohol as feedstock.
Copolymers of butadiene and isoprene began to quickly replace natural rubber in the production of car tires. So, if in 1950 the share of K. s. in the total production of natural and synthetic rubbers was about 22%, in 1960 about 48%, then by 1971 it increased to ~60% (5 million tons of synthetic and 3 million tons of natural rubber), in 1985 there were 12 million tons of synthetic rubber were produced and only 4 million tons of natural rubber. By the beginning of the 1970s. There was an opinion that synthetic rubbers would replace natural ones. However, as a result of the oil embargo in 1973, oil prices increased sharply and at the same time great strides were made in the production of natural rubber in Malaysia, which made it possible to sharply reduce its price. To this day, it is not possible to get rid of natural rubber in the tire industry. Thus, Japan, which does not have its own natural oil reserves, is more profitable to purchase natural rubber from Malaysia and Indonesia. Russia, which has large oil reserves, should in no case neglect the existing technologies and capacities for the production of synthetic rubber.
Intense developments in the field of rubber technology in the USSR and Germany before World War II were explained by the fact that these countries understood that in the event of war they would be cut off from supplies of natural rubber. The United States approached the issue differently; the United States sought to create a strategic reserve of natural rubber. As life has shown, reserves were not enough when Japan invaded Southeast Asia in 1941. From what has already been written it is clear that rubber played an important role in world politics.
Phenol-formaldehyde resins.
The world's first process for the industrial production of a completely synthetic polymer was patented by L. Baekeland in 1907. L. Baekeland patented the so-called. Bakelite resin is a condensation product of phenol and formaldehyde, which turns into a three-dimensional polymer when heated. Bakelite has been used for decades as a material for electrical enclosures and is now used as a binder and adhesive. The discoverer of the reaction between phenol and formaldehyde was A. Bayer, who observed the formation of resin in this reaction back in 1872, but he was not interested in the result. From the 1940s to the mid-1970s. Due to the emergence of new types of plastics, the share of phenolic resins was rapidly declining. But starting in 1975, the rapid growth in the production of these polymers began again for the needs of aviation, rocketry, astronautics, etc., as well as due to the fall in oil reserves. The fact is that phenol is obtained from coal, the reserves of which incomparably exceed those of oil. In addition, based on phenol-formaldehyde resins, there was a wide range of materials for thermal insulation needs (chipboard, fiberboard), which became relevant in the fight against the energy crisis.
Polyethylene and polypropylene.
Ethylene is extremely difficult to polymerize. Polymerization of ethylene was first observed in 1933 as a side reaction. Already in 1937, English chemists developed the first industrial method for the production of polyethylene, and in 1946 the production of polyethylene bottles began.
In 1954, Karl Ziegler and Giulio Natta discovered a new organometallic catalyst, thanks to which they were able to carry out ionic polymerization of polyethylene at atmospheric pressure and a temperature of 60 ° C.
They also obtained stereoregular polypropylene using a metal complex catalyst.
Polytetrafluoroethylene (Teflon).
It was accidentally discovered in 1938 by R. Plunkett, who observed the spontaneous formation of a white powdery mass in cylinders with tetrafluoroethylene. In 1941, he patented his technology (USA, DuPont). In 1954, French engineer Marc Gregor proposed the use of Teflon as a coating for cookware. Teflon is extremely chemically inert, and its softening temperature reaches almost 300 0 C.
Polystyrene.
In 1866, M. Berthelot identified the formation of a solid mass from styrene upon heating as a polymerization process. In 1946, G. Staudinger established the mechanism of this reaction. Polystyrene was first produced in Germany in 1931.
Polymethyl methacrylate.
Polymethyl methacrylate (PMMA) or plexiglass or plexiglass was created in 1928. In 1933, the production of PMMA began in Germany, in 1936 PMMA was obtained in the USSR at the Plastics Research Institute. The polymer is widely used in the aviation industry, the automotive industry, and construction.
Polyvinyl chloride.
The polymerization of vinyl chloride was first carried out in 1872 by the German chemist Eugen Baumann. The merit of this researcher was the development of a method for the radical polymerization of vinyl chloride in the presence of organic peroxides. Active practical use of polyvinyl chloride (PVC) began only in the middle of the 20th century. The problem was that pure PVC has many disadvantages. At room temperature it is very brittle and inelastic. In addition, it is difficult to dissolve or melt, making the polymer very difficult to recycle. In the 30s Scientists have managed to find stabilizers that increase PVC’s resistance to heat and light. A new material - plasticized polyvinyl chloride - has become widespread.
The first chemical fiber was obtained in 1884 by the French chemist N. Chardonnay. His main research is related to the development of nitrocellulose fiber technology (nitrosilk). In 1892, the viscose fiber production method was mastered. The first acetate fibers began to be produced at the same time in England and the USA.
Polyvinyl chloride fibers began to be produced in 1934, and fibers based on a copolymer of vinyl chloride with vinyl acetate (vignon) since 1937. In 1939. polyamide fibers appeared, and in 1943 polyacrylonitrile (Orlon).
The creation of fiber technology is associated with the names of such scientists as Cloete, who predicted the possibility of producing fibers from polyvinyl chloride back in 1913, and G. Staudinger, who in 1927 obtained fibers from a melt of polyoxymethylene and polyethylene oxide.
In the USSR, independently of the USA and Germany, in 1947 the results of research by Knunyants, Rogovin and Romashevsky on the production of polyamide fibers were published.
In 1936, the technology of synthetic polyhexamethylene adipamide was created, on the basis of which the production of nylon fiber began in 1939.
In the USA, in 1939, the production of nylon-6,6 fiber based on caprolactam began.
The technology of polyacrylonitrile fibers was developed simultaneously and independently in the USA and Germany; in 1934, the USA began producing polyamide fiber at the DuPont plant. In Germany, its production began several years later.
In the USSR, the first batch of nylon fiber was produced in 1948; in 1957, the first installation for producing lavsan fiber began operating; in the 1960s. production of “nitron” fiber based on polyacrylonitrile began.
At the very beginning, enterprises producing chemical fibers were highly specialized, but as the assortment of fibers increased, the profile of chemical fiber factories expanded, and they were already producing 3-4 types of fibers.
Until the mid-1930s. All production of paints and varnishes in our country was based on imported raw materials. Only in 1936 did the production of glyphthalic resins for the production of corresponding varnishes begin to develop. The synthesis of alkyd resins by reacting glycerin, rosin and tung oil freed the country from the import of copals (copal is a hard, amber-like natural resin).
In 1947-1948 Workshops for the production of urea, melamine, and phenol-formaldehyde resins were launched in Moscow and Yaroslavl. The development of pentaphthalic resins began, in which glycerin was replaced by pentaerythritol.
Since 1951, the production of varnishes based on perchlorovinyl resins for the aviation industry and railway transport began. In the 1950s Alcohol-soluble varnishes were created based on copolymers of butyl methacrylate with methyl methacrylate, methacrylamide, acrylonitrile, and methacrylic acid. Several dozen brands of varnishes, primers and enamels were created, incl. varnish DS-583, which is still produced to this day. At the same time, the production of A-15, a copolymer of vinyl chloride with vinyl acetate, was mastered. The combination of A-15 with epoxy resins made it possible to create anti-corrosion paints and reduce the number of paint layers during application.
Since 1956, automotive nitro enamels have been completely replaced by alkyd-melamine ones.
In 1963, the production of epoxy resins for the needs of the paint and varnish industry, as well as anti-fouling coatings based on chlorinated polyvinyl chloride, was mastered.
In 1976-1980 Research and production associations and an independent research and design institute for inorganic pigments and ship coatings were created.
Currently, almost all types of polymer materials are used to produce paint and varnish compositions for various purposes: epoxy resins, urethane elastomers, chloroprene rubbers, fluorine rubbers, polyacrylates, polyorganosiloxanes, etc.
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3. K. Manalov Great chemists in 2 vols., M.: Mir, 1986.
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Polymers
However, there are many directions that make it possible to use giant molecules for peaceful purposes. So, if fully nitrated cellulose is an explosive and can only be used as such, then partially nitrated cellulose ( pyroxylin) is safer to handle and can be used not only for military purposes.
The American inventor John Wesley Hyatt (1837-1920), trying to win a prize established for the creation of an ivory substitute for billiard balls, first of all paid attention to partially nitrated cellulose. He dissolved it in a mixture of alcohol and ether and added camphor to make the new substance easier to process. By 1869 Hyatt had what he called celluloid, and won a prize. Celluloid was the first synthetic plastic- a material that can be cast into molds.
However, as it turned out, partially nitrated cellulose can not only be molded into balls, but also drawn into fibers and films. The French chemist Louis Marie Guillard Bernigo, Count of Chardonnay (1839-1924), obtained such fibers by pressing a nitrocellulose solution through very thin holes. The solvent evaporated almost immediately.
From the resulting fibers it was possible to weave a material that resembled silk in its luster. In 1884, Chardonnay patented his rayon. Chardonnay named this fabric region- emitting light, as the fabric shone and seemed to be emitting light.
We owe the appearance of plastic films to the American inventor George Eastman (1854-1932). Eastman was interested in photography. In an attempt to simplify the development process, he began mixing an emulsion of silver compounds with gelatin to make the emulsion dry. The mixture obtained in this way could be stored and, therefore, prepared for future use. In 1884, Eastman replaced glass plates with celluloid ones.
Celluloid is non-explosive, but it is highly flammable, which can cause fires, so Eastman began searching for less flammable materials. When acetyl groups were introduced into cellulose instead of nitro groups, the resulting product remained as plastic as nitrocellulose, but it was no longer flammable. Since 1924, cellulose acetate films began to be used in the production of motion pictures, since the developing film industry was in especially dire need of a celluloid substitute.
By studying high-molecular-weight natural compounds, chemists hoped not only to obtain their synthetic analogues, but also to discover new types of compounds. One of the methods for the synthesis of giant molecules is polymerization of monomers(monomer is a substance whose molecules are capable of reacting with each other or with molecules of other substances to form a polymer).
The method of combining monomers into a giant molecule can be explained at least using the example of ethylene C 2 H 4. Let's write the structural formulas of two ethylene molecules:
Let's imagine that a hydrogen atom has moved from one molecule to another, as a result, instead of a double bond, a free single bond appears in this molecule. A free bond also appeared in the first molecule from which hydrogen left. Therefore, these two molecules can connect with each other.
Such a molecule already contains four carbon atoms and one double bond, just like the original ethylene molecule. Therefore, when this molecule interacts with another ethylene molecule, the displacement of a hydrogen atom and the breaking of the double bond can also occur. The resulting molecule will contain six carbon atoms and one double bond. In this way, a molecule with eight, ten or more carbon atoms can be obtained successively. In fact, it is possible to obtain molecules of almost any given length in this way.
American chemist Leo Hendrik Baekeland (1863-1944) was looking for a substitute for shellac, a waxy substance secreted by certain species of tropical insects. For this purpose, he needed a solution of a sticky tar-like substance. Baekeland began by polymerizing phenol and formaldehyde and obtaining a polymer for which he could not find a solvent. This fact led him to the idea that such a solid, practically insoluble and, as it turned out, non-conductive polymer could turn out to be a valuable material. For example, parts can be cast from it that can be easily processed on machines. In 1909, Baekeland reported on the material he had obtained, which he called bakelite. This phenol-formaldehyde resin was the first synthetic plastic, which remains unsurpassed in a number of properties.
Synthetic fibers have also found application. This direction was led by the American chemist Wallace Hume Carothers (1896-1937). Together with the American chemist Julius Arthur Newland (1878-1936), he investigated rubber-related elastomers. The result of his work was the receipt in 1932. neoprene- one of the synthetic rubbers.
Continuing his study of polymers, Carothers attempted to polymerize a mixture of diamines and dicarboxylic acids and obtained a fibrous polymer. The long molecules of this polymer contain combinations of atoms similar to the peptide bonds (see section “Proteins”) in silk protein. By pulling out these fibers, we get what we call today nylon. Carothers completed this work just before his premature death. The outbreak of the Second World War forced chemists to temporarily forget about Carothers' discovery. However, after the end of the war, nylon began to displace silk and soon replaced it (in particular, in the production of hosiery).
The first synthetic polymers were obtained, as a rule, by chance, by trial and error, since little was known at that time about the structure of giant molecules and the mechanism of polymerization. The German chemist Hermann Staudinger (1881-1965) was the first to study the structure of polymers and did a lot in this area. Staudinger managed to reveal the general principle of the construction of many high-molecular natural and artificial substances and outline ways for their research and synthesis. Thanks to Staudinger's work, it became clear that the addition of monomers to each other can occur randomly and lead to the formation of branched chains, the strength of which is much lower.
Intensive searches began for ways to obtain linear, unbranched polymers. And in 1953, the German chemist Karl Ziegler (1898-1973) discovered his famous titanium-aluminum catalyst, which produced polyethylene with a regular structure.
Italian chemist Giulio Natta (1903-1979) modified Ziegler's catalyst and developed a method for producing a new class of synthetic high-molecular compounds - stereo-regular polymers. A method for producing polymers with desired properties was developed.
One of the main sources of essential organic compounds needed for the production of new synthetic products is oil. This liquid has been known since ancient times, but in order to use it in large quantities, it was necessary to discover a way to pump oil out of vast underground deposits. American inventor Edwin Laurentian Drake (1819-1880) was the first to begin drilling oil wells in 1859. A century later, oil became the main source of organic compounds, heat and energy.
An even more important source of organic products is coal, although in the age of internal combustion engines we tend to forget about it. Russian chemist Vladimir Nikolaevich Ipatiev (1867-1952) at the turn of the century began to study complex hydrocarbons contained in oil and coal tar, and, in particular, to study their reactions occurring at high temperatures. The German chemist Friedrich Karl Rudolf Bergius (1884-1949), using data from Ipatiev, developed in 1912 practical methods for treating coal and oil with hydrogen to produce gasoline.
However, world reserves fossil fuel(coal plus oil) are limited and irreplaceable. All forecasts indicate that there will come a day when fossil fuel reserves will be depleted, and that this day is not far off, especially since the world's population is rapidly increasing and, consequently, the need for energy is increasing.
Ministry of Education and Science of the Russian Federation
federal state autonomous educational institution
higher professional education
"NATIONAL RESEARCH
TOMSK POLYTECHNIC UNIVERSITY"
Institute of Natural Resources
Direction of training (specialty) Chemical technology
Department of Chemical Technology of Fuel and Chemical Cybernetics
Essay
Abstract title:
“ Natural polymers, polymers around us “
in the discipline "Introduction to Engineering"
Completed by students gr. 2D42 Nikonova Nyurguyaana
Prokopchuk Kristina
Dayanova Regina
Abstract accepted:
Moises O. E.
(Signature)
2014
(date of report verification)
Tomsk 2014
1.Introduction…………………………………………………………………………………………..2
2. Concept of polymer and classification ………………………………………………….3
3.Pulp……………………………………………………………………………………………………………3
4. Starch……………………………………………………………………………………………………………5
5. Glutin……………………………………………………………………………………………………………..6
6.Casein……………………………………………………………………………………………………………6
7. Rubber………………………………………………………………………………………………………………….7
8. Rubber……………………………………………………………………………………………………………7
9. Synthetic polymers………………………………………………………………...9
10.Properties and most important characteristics……………………………………………10
11. Chemical reactions………………………………………………………………………………….11
12.Receipt……………………………………………………………………………………………………………12
13.Polymers in agriculture…………………………………………………………..12
14.Polymers in industry…………………………………………………………….14
Introduction
The term “polymerism” was introduced into science by I. Berzelius in 1833 to designate a special type of isomerism, in which substances (polymers) having the same composition have different molecular weights, for example, ethylene and butylene, oxygen and ozone. This content of the term did not correspond to modern ideas about polymers. “True” synthetic polymers were not yet known at that time.
A number of polymers were apparently prepared as early as the first half of the 19th century. However, chemists then usually tried to suppress polymerization and polycondensation, which led to the “resinization” of the products of the main chemical reaction, i.e., in fact, to the formation of polymers (polymers are still often called “resins”). The first mentions of synthetic polymers date back to 1838 (polyvinylidene chloride) and 1839 (polystyrene),
Polymer chemistry arose only in connection with the creation of the theory of chemical structure by A.M. Butlerov. A.M. Butlerov studied the relationship between the structure and relative stability of molecules, manifested in polymerization reactions. The science of polymers received its further development mainly thanks to the intensive search for methods of synthesizing rubber, in which the leading scientists of many countries participated (G. Buscharda, W. Tilden, the German scientist K. Harries, I. L. Kondakov, S. V. Lebedev and others ). In the 30s, the existence of free radical and ionic polymerization mechanisms was proven. The works of W. Carothers played a major role in the development of ideas about polycondensation.
Since the beginning of the 20s of the 20th century, theoretical ideas about the structure of polymers have also been developing. Initially, it was assumed that biopolymers such as cellulose, starch, rubber, proteins, as well as some synthetic polymers similar to them in properties (for example, polyisoprene), consist of small molecules that have the unusual ability to associate in solution into complexes of colloidal nature due to non-covalent bonds (the theory of “small blocks”). The author of a fundamentally new concept of polymers as substances consisting of macromolecules, particles of unusually large molecular weight, was G. Staudinger. The victory of this scientist’s ideas forced us to consider polymers as a qualitatively new object of study in chemistry and physics.
Polymer concept and classification
Polymers- chemical compounds with high molecular weight (from several thousand to many millions), the molecules of which (macromolecules) consist of a large number of repeating groups (monomer units). The atoms that make up macromolecules are connected to each other by forces of principal and (or) coordination valences.
Classification.
Based on their origin, polymers are divided into:
natural (biopolymers), for example proteins, nucleic acids, natural resins
synthetic, for example polyethylene, polypropylene, phenol-formaldehyde resins.
Natural polymers used in printing include: polysaccharides (cellulose starch, gums), firs, glutin, casein, albumin), polydienes (rubber).
Cellulose
Cellulose, or fiber (from the Latin word "cellulula" - cell), is widespread in nature. Cellulose is a strong fibrous substance of organic origin that makes up the supporting tissue of all plants (plant cells).
Physical properties of cellulose
Cellulose fibers are distinguished by their whiteness, flexibility, strength, elasticity, i.e. the ability to reversibly deform without destruction even under high mechanical stress, insolubility in water and organic solvents, and infusibility.
Cellulose can withstand heating up to 150° without destruction; at higher temperatures, depolymerization of cellulose and the associated loss of strength are observed, and at 270° and above, thermal decomposition begins with the release of decomposition products: acetic acid, methyl alcohol, ketones, with the remainder being tar and coal.
The structure of cellulose fiber.
Each plant fiber, for example cotton, flax, wood, etc., is one cell, the shell of which consists mainly of cellulose. Inside the fiber there is a channel - a capillary, accessible for the penetration of air and moisture. Technical cellulose fibers have an average length of 2.5-3 mm (spruce, pine, birch, poplar) and 20-25 mm (flax, cotton, hemp) with a diameter of 25 microns.
Cellulose plant fiber has a fibrillar structure. Fibrils are thread-like, elementary roll windows - packs of cellulose molecules firmly connected to each other by hydrogen bonds, 50 µm long and 0.1-0.4 µm in diameter. Most likely, cellulose forms an ordered system of threads - fibrils, located more tightly around the internal channel (capillary) of the fiber and more loosely in its outer layers. In the spaces between the fibrils there are micelluloses and lignin, and their content increases from the inner layers of the cell structure to the outer ones. The intercellular spaces of cellulose are filled predominantly with lignin.
The main source of cellulose is wood... Wood is the internal part of trees, lying under the bark and constituting the main plant tissue from which the tree trunk is formed.
A living cell of a growing tree has a cellulose shell (walls), an internal cavity filled with protoplasm, and a nucleus. A living cell is capable of growing and forming new wood formations in the cambium layer, under the bark, from year to year in a growing tree.
Living cells undergo lignification over time, ultimately leading to their complete death, or lignification. Cell lignification occurs mainly as a result of the appearance of lignin in it. Wood consists of 90-95% of such dead cells - fibers, devoid of protoplasm and nucleus, but capable of division, with an internal cavity filled with air and water.
Chemical structure and properties of cellulose. Cellulose is a natural polysaccharide polymer belonging to the carbohydrate class. The giant molecule (macromolecule) of cellulose is built from repeatedly repeating structural units - β-glucose residues (O6H10O5)p. The number n, or polymerization coefficient, shows how many times the structural unit - the β-glucose residue - is repeated in the cellulose macromolecule, and therefore characterizes the length of the molecular chain (molecule length) and predetermines its molecular weight.
The polymerization coefficient of cellulose of different origins is different. So, for wood cellulose it is 3000, for cotton - 12,000, for flax - 36,000 (approximately). This explains the great strength of cotton and flax fibers compared to wood cellulose fibers.
Alkaline cellulose is obtained by treating cellulose with a solution of sodium hydroxide. In this case, the hydrogen atoms of alcohol hydroxyls are partially or completely replaced by sodium atoms. Alkaline cellulose, without losing its fibrous structure, is characterized by increased chemical activity, which is used in the production of cellulose ethers, for example carboxymethylcellulose.
Carboxymethylcellulose (CMC) is an ether of cellulose and glycolic acid. The industrial method for the production of carboxymethylcellulose is based on the interaction of alkali cellulose with monochloroacetic acid.
Hemicelluloses are a cross between cellulose and starch. They are also polysaccharides. Hemicellulose molecules are built from monosaccharide residues: mannose (hexose) and xylose (pentose). Hemicelluloses do not have a fibrous structure. They serve as a reserve nutrient for plants and protect them from infections. Hemicelluloses swell in water and are relatively easily hydrolyzed even by very dilute acids; they dissolve in 18.5% alkali. Hemicelluloses are not harmful impurities of cellulose used for making paper. On the contrary, wood cellulose with a high content of hemicelluloses is easy to grind, and paper made from it has increased strength (especially surfaces), since hemicelluloses are a very good natural sizing agent.
Lignin is a chemically unstable substance: under the influence of light, moisture, oxygen, air and heat, lignin is destroyed, as a result of which plant fibers lose strength and darken. Lignin, unlike cellulose, dissolves in dilute acids and alkalis. Methods for producing cellulose from wood, straw, reed and other plant tissues are based on this property of lignin. The structure of lignin is very complex and has not yet been sufficiently studied; It is known that lignin is a natural polymer, the structural unit of which is the residue of a very reactive aromatic alcohol - β-hydroxyconiferyl.
Polymers are chemical compounds with a high mol. mass (from several thousand to many millions), the molecules of which (macromolecules) consist of a large number of repeating groups (monomer units). The atoms that make up macromolecules are connected to each other by forces of principal and (or) coordination valences.
Based on their origin, polymers are divided into natural (biopolymers), for example, proteins, nucleic acids, natural resins, and synthetic, for example, polyethylene, polypropylene, phenol-formaldehyde resins. Atoms or atomic groups can be located in a macromolecule in the form of: an open chain or an elongated sequence of cycles (linear polymers, for example, natural rubber); branched chains (branched polymers, e.g. amylopectin), three-dimensional networks (cross-linked polymers, e.g. cured epoxy resins). Polymers whose molecules consist of identical monomer units are called homopolymers (for example, polyvinyl chloride, polycaproamide, cellulose). chemical polymer synthetic supramolecular
Macromolecules of the same chemical composition can be built from units of different spatial configurations. If macromolecules consist of the same stereoisomers or of different stereoisomers alternating in the chain at a certain periodicity, the polymers are called stereoregular.
Polymers whose macromolecules contain several types of monomer units are called copolymers. Copolymers in which units of each type form sufficiently long continuous sequences that replace each other within the macromolecule are called block copolymers. One or more chains of another structure can be attached to the internal (non-terminal) links of a macromolecule of one chemical structure. Such copolymers are called graft copolymers.
Polymers in which each or some stereoisomers of a unit form sufficiently long continuous sequences that replace each other within one macromolecule are called stereoblock copolymers.
Depending on the composition of the main (main) chain, polymers are divided into: heterochain, the main chain of which contains atoms of various elements, most often carbon, nitrogen, silicon, phosphorus, and homochain, the main chain of which is built from identical atoms. Of the homochain polymers, the most common are carbon chain polymers, the main chains of which consist only of carbon atoms, for example, polyethylene, polymethyl methacrylate, polytetrafluoroethylene. Examples of heterochain polymers are polyesters (polyethylene terephthalate, polycarbonates), polyamides, urea-formaldehyde resins, proteins, and some organosilicon polymers. Polymers whose macromolecules, along with hydrocarbon groups, contain atoms of inorganogenic elements are called organoelement. A separate group of polymers is formed by inorganic polymers, for example, plastic sulfur, polyphosphonitrile chloride.
Properties and most important characteristics. Linear polymers have a specific set of physicochemical and mechanical properties. The most important of these properties: the ability to form high-strength anisotropic highly oriented fibers and films, the ability to undergo large, long-term reversible deformations; the ability to swell in a highly elastic state before dissolving; high viscosity of solutions. This set of properties is due to the high molecular weight, chain structure, and flexibility of macromolecules. When moving from linear chains to branched, sparse three-dimensional networks and, finally, to dense mesh structures, this set of properties becomes less and less pronounced. Highly cross-linked polymers are insoluble, infusible and incapable of highly elastic deformations.
Polymers can exist in crystalline and amorphous states. A necessary condition for crystallization is the regularity of sufficiently long sections of the macromolecule. In crystalline polymers, various supramolecular structures (fibrils, spherulites, single crystals) can appear, the type of which largely determines the properties of the polymer material. Supramolecular structures in non-crystallized (amorphous) polymers are less pronounced than in crystalline ones.
Non-crystallized polymers can exist in three physical states: glassy, highly elastic and viscous. Polymers with a low (below room) temperature of transition from a glassy to a highly elastic state are called elastomers, while those with a high temperature are called plastics. Depending on the chemical composition, structure and relative arrangement of macromolecules, the properties of polymers can vary within very wide limits. Thus, 1,4.-cispolybutadiene, built from flexible hydrocarbon chains, at a temperature of about 20 ° C is an elastic material, which at a temperature of -60 ° C transforms into a glassy state; polymethyl methacrylate, built from more rigid chains, at a temperature of about 20 ° C is a solid glassy product that turns into a highly elastic state only at 100 ° C. Cellulose, a polymer with very rigid chains connected by intermolecular hydrogen bonds, generally cannot exist in a highly elastic state before its decomposition temperature.
Large differences in the properties of polymers can be observed even if the differences in the structure of macromolecules are, at first glance, small. Thus, stereoregular polystyrene is a crystalline substance with a melting point of about 235 °C, while non-stereoregular polystyrene is not able to crystallize at all and softens at a temperature of about 80 °C.
Polymers can enter into the following main types of reactions: the formation of chemical bonds between macromolecules (so-called cross-linking), for example, during the vulcanization of rubbers and tanning of leather; decomposition of macromolecules into separate, shorter fragments, reactions of side functional groups of polymers with low molecular weight substances that do not affect the main chain (so-called polymer-analogous transformations); intramolecular reactions occurring between functional groups of one macromolecule, for example intramolecular cyclization. Cross-linking often occurs simultaneously with destruction. An example of polymer-analogous transformations is the saponification of polytyl acetate, leading to the formation of polyvinyl alcohol. The rate of reactions of polymers with low molecular weight substances is often limited by the rate of diffusion of the latter into the polymer phase. This is most obvious in the case of cross-linked polymers. The rate of interaction of macromolecules with low-molecular substances often significantly depends on the nature and location of neighboring units relative to the reacting unit. The same applies to intramolecular reactions between functional groups belonging to the same chain.
Some properties of polymers, for example, solubility, ability to viscous flow, stability, are very sensitive to the action of small amounts of impurities or additives that react with macromolecules. Thus, to transform a linear polymer from soluble to completely insoluble, it is enough to form 1-2 cross-links per macromolecule.
The most important characteristics of polymers are their chemical composition, molecular weight and molecular weight distribution, the degree of branching and flexibility of macromolecules, stereoregularity, and others. The properties of polymers depend significantly on these characteristics.
Natural polymers are formed during the process of biosynthesis in the cells of living organisms. Using extraction, fractional precipitation and other methods, they can be isolated from plant and animal materials. Synthetic polymers are produced by polymerization and polycondensation. Carbochain polymers are usually synthesized by the polymerization of monomers with one or more multiple carbon bonds or monomers containing unstable carbocyclic groups (for example, from cyclopropane and its derivatives). Heterochain polymers are obtained by polycondensation, as well as the polymerization of monomers containing multiple bonds of a carbon element (for example, C=O , C=N, N=C=O) or weak heterocyclic groups.
Today we can talk about at least four main areas of using polymer materials in agriculture. Both in domestic and in world practice, the first place belongs to films. Thanks to the use of perforated mulching film in the fields, the yield of some crops increases up to 30%, and ripening time is accelerated by 10-14 days.
The use of polyethylene film for waterproofing created reservoirs ensures a significant reduction in losses of stored moisture. Covering haylage, silage, and roughage with film ensures their better preservation even in adverse weather conditions. But the main area of use of film polymer materials in agriculture is the construction and operation of film greenhouses. Currently, it has become technically possible to produce sheets of film up to 16 m wide, and this makes it possible to build film greenhouses with a base width of up to 7.5 and a length of up to 200 m. In such greenhouses, all agricultural work can be carried out mechanized; Moreover, these greenhouses allow you to grow produce all year round. In cold weather, greenhouses are heated again using polymer pipes buried in the soil to a depth of 60-70 cm.
From the point of view of the chemical structure of polymers used in greenhouses of this kind, one can note the predominant use of polyethylene, unplasticized polyvinyl chloride and, to a lesser extent, polyamides. Polyethylene films are characterized by better light transmission, better strength properties, but poorer weather resistance and relatively high heat loss. They can only serve properly for 1-2 seasons. Polyamide and other films are still used relatively rarely.
The other two main areas of use of polymer materials in agriculture are construction, especially livestock buildings, and mechanical engineering.
A special culture of microbes is grown on spent sulfite liquors in special fermenters at 38 ° C, while ammonia is added there. The yield of feed protein is 50-55%; it is eaten with appetite by pigs and poultry.
Traditionally, many sporting events are held on grass courts. Football, tennis, croquet... Unfortunately, the dynamic development of sports, peak loads at the goal or at the net lead to the fact that the grass does not have time to grow from one competition to another. And no amount of gardeners’ tricks can cope with this. It is possible, of course, to hold similar competitions on, say, asphalt surfaces, but what about traditional sports? Synthetic materials came to the rescue. Polyamide film with a thickness of 1/40 mm (25 microns) is cut into strips 1.27 mm wide, stretched, crimped, and then intertwined to obtain a light, voluminous mass that imitates grass. To prevent fire, fire retardants are added to the polymer ahead of time, and to prevent electrical sparks from falling under the athletes’ feet, an antistatic agent is used. Synthetic grass mats are glued onto the prepared base - and then a grass court or football field, or other sports ground is ready. And as individual sections of the playing field wear out, they can be replaced with new mats made using the same technology and the same green color.
It is not surprising that this industry is the main consumer of almost all materials produced in our country, including polymers. The use of polymer materials in mechanical engineering is growing at a rate that has no precedent in all of human history. For example, in 1976 1. the mechanical engineering of our country consumed 800,000 tons of plastics, and in 1960 - only 116,000 tons. It is interesting to note that ten years ago 37-38% of all products produced in our country were sent to mechanical engineering plastics, and in 1980 the share of mechanical engineering in the use of plastics decreased to 28%. And the point here is not that the need might decrease, but that other sectors of the national economy began to use polymer materials in agriculture, construction, and the light and food industries even more intensively.
It is appropriate to note that in recent years the function of polymer materials in any industry has changed somewhat. More and more responsible tasks began to be trusted to polymers. More and more relatively small, but structurally complex and critical parts of machines and mechanisms began to be made from polymers, and at the same time, polymers increasingly began to be used in the manufacture of large-sized body parts of machines and mechanisms that carry significant loads. Another area specific to polymers, where their advantages over any other materials are most clearly manifested, is the area of interior and exterior finishing.
Another area of application of polymer materials in mechanical engineering, worthy of special mention, is the production of metal-cutting tools. As the use of strong steels and alloys expands, increasingly stringent requirements are placed on processing tools. And here, too, plastics come to the rescue of the toolmaker and machine operator. But not quite ordinary plastics of ultra-high hardness, those that dare to compete even with diamond. The king of hardness, the diamond, has not yet been dethroned from his throne, but things are getting closer. Some oxides (for example, from the genus of cubic zirconia), nitrides, carbides, already today demonstrate no less hardness, and also greater heat resistance. The trouble is that they are still more expensive than natural and synthetic diamonds, and besides, they have a “royal flaw” - they are mostly fragile. So, in order to keep them from cracking, each grain of such abrasive has to be surrounded with polymer packaging, most often made of phenol-formaldehyde resins. Therefore, today three quarters of abrasive tools are produced using synthetic resins.
These are just some examples of the main trends in the introduction of polymer materials in the mechanical engineering sub-sectors. The automotive industry now occupies the first place in terms of growth in the use of plastics among other sub-sectors. Ten years ago, from 7 to 12 types of different plastics were used in cars; by the end of the 70s, this number exceeded 30. From the point of view of chemical structure, as one would expect, the first places in terms of volume are occupied by styrene plastics, polyvinyl chloride and polyolefins. They are still slightly inferior to them, but polyurethanes, polyesters, acrylates and other polymers are actively catching up.
The list of car parts that are made from polymers in certain models these days would take more than one page. Bodies and cabins, tools and electrical insulation, interior trim and bumpers, radiators and armrests, hoses, seats, doors, hood. Moreover, several different companies abroad have already announced the start of production of all-plastic cars. The most characteristic trends in the use of plastics for the automotive industry are, in general, the same as in other sub-sectors. Firstly, it saves materials: waste-free or low-waste molding of large blocks and assemblies. Secondly, thanks to the use of light and lightweight polymer materials, the overall weight of the car is reduced, which means that fuel will be saved during its operation. Thirdly, made as a single unit, blocks of plastic parts significantly simplify assembly and save labor.
By the way, the same advantages stimulate the widespread use of polymer materials in the aviation industry. For example, replacing an aluminum alloy with graphite plastic in the manufacture of an aircraft wing slat allows you to reduce the number of parts from 47 to 14, fasteners from 1464 to 8 bolts, reduce weight by 22%, and cost by 25%. At the same time, the safety margin of the product is 178%. It is recommended to make helicopter blades and jet engine fan blades from polycondensation resins filled with aluminosilicate fibers, which reduces the weight of the aircraft while maintaining strength and reliability. According to English patent No. 2047188, coating the load-bearing surfaces of aircraft or helicopter rotor blades with a layer of polyurethane with a thickness of only 0.65 mm increases their resistance to rain erosion by 1.5-2 times. Strict requirements were set before the designers of the first Anglo-French supersonic passenger aircraft, Concorde. It was calculated that friction with the atmosphere would heat the outer surface of the aircraft to 120-150° C, and at the same time it was required that it should not succumb to erosion for at least 20,000 hours. A solution to the problem was found by surface coating the aircraft protection with a thin film of fluoroplastic.