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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Plastics. History of invention and production
Directory / The history of technology, technology, objects around us Plastics (plastic masses) or plastics are organic materials based on synthetic or natural macromolecular compounds (polymers). Plastics based on synthetic polymers have received exceptionally wide use. The name "plastics" means that these materials, under the influence of heat and pressure, are able to form and maintain a given shape after cooling or curing. The molding process is accompanied by the transition of a plastically deformable (ductile) state into a glassy (solid) state.
The widespread use of plastics is one of the hallmarks of our time. Virtually all natural fibres, resins and materials now have their artificial substitutes. Many other substances have been created with properties that are not found in nature. And this, apparently, is only the beginning of a grandiose upheaval, equal in significance to the great material revolutions of the past - the development of bronze and iron. As a rule, plastic is a complex organic compound that includes several components. The most important of them, which determines the basic properties of the material, is artificial resin. The production of any plastic begins with the preparation of this resin. In general, resins occupy an intermediate position between solid and liquid substances. On the one hand, they have many of the qualities of solids, but they also have a great deal of fluidity, that is, the ability to easily change their shape. In terms of their internal structure, resins also occupy a separate position: they do not have a rigid crystal lattice, like most solids; they do not have a definite melting point and, when heated, gradually soften, turning into a viscous liquid. Like rubber, to which they are very close in their properties, resins are polymers, that is, their molecules consist of a huge number of identical (often very simple in structure) units. Artificial (synthetic) resins can be obtained as a result of two types of chemical reactions: condensation reactions and polymerization reactions. During the condensation reaction, when two or more substances interact, a new substance is formed and by-products (water, ammonia, and others) are still released. Phenolic resins, for example, are obtained from phenol and formaldehyde: two molecules of phenol are linked together, as it were, by a bridge with a methylene group contained in formaldehyde, and water is released. Then these, already double, molecules bind to each other. In the end, a large molecule of linear or three-dimensional structure is obtained. In a polymerization reaction, molecules of the same substance enter into interaction. Combining with each other, they form a new substance - a polymer without isolating by-products. As already noted in the chapter on rubber, all organic substances that have carbon atoms with a double or triple bond in their molecule are capable of polymerization reactions. The resin binds, or, as it is sometimes said, cements, all the constituent parts of the plastic, gives it plasticity and other valuable qualities - hardness, water resistance, mechanical and electrical insulating properties. In addition to resin in many types of plastics, an important place (50-70% of the mass) is occupied by the so-called fillers, which can be both organic and mineral substances. Among organic fillers, cellulose is considered the most important (used in the form of paper, fabric or linter - cotton fleeces; they are impregnated with a resin solution, then dried and pressed). Inorganic fillers include mica, slate, talc, asbestos, glass cloth and graphite. As a rule, fillers are much cheaper than resins, and their introduction, with the right selection, almost does not impair the properties of plastics. Sometimes the introduction of a well-chosen filler even improves the quality of the plastic. It can also be improved with the help of special additives and plasticizers. The former, taken even in small quantities, impart new properties to plastics (for example, the addition of a metal makes a conductive plastic from a dielectric). And plasticizers, forming a solution with the resin, soften it and give it additional plasticity. The beginning of the production of plastics based on artificial materials dates back to the first third of the 1830th century. In 1863, one of the first plastics, camptulikon, was produced in England. The basis of this layered material was jute fabric, on which a mixture of rubber, crushed cork and some other components was rolled. However, due to the high price of rubber, the production of this plastic is not widespread. In XNUMX, the Englishman Walton replaced rubber with linoxin and thus began the production of linoleum. Until now, it has been widely used as a floor covering, since it is erased much more slowly than wood and even marble. The invention of celluloid, based on cellulose, began the widespread use of plastics. Cellulose, or fiber, forms the basis of wood and other plant materials; its molecule consists of a huge number of structurally simple units; in its purified form, it is a colorless, infusible and insoluble substance. In 1845, it was found that when cellulose (cotton wool) is treated with nitric and sulfuric acids, nitric acid ester is formed, known as pyroxylin. This material is very dangerous and explodes with great force when dry. However, it was later noticed that when wet, it is not dangerous at all. The question arose: if water deprives pyroxylin of explosive power, then maybe there is another way to influence its properties. It turned out that if wet nitrocellulose is mixed with camphor, you get a plastic that can be processed on rollers, pressed and molded. In 1869, the Hayeth brothers obtained celluloid in this way, which began to be produced commercially from 1872. Celluloid had great strength, was beautiful and could be dyed any color or used as a transparent film. This plastic soon became widespread. They began to make photos from it - and film, combs, boxes, children's toys, buttons, belts. However, celluloid had one important drawback - it turned out to be combustible and ignited very easily. In 1872, the German chemist Bayer synthesized a new resinous substance by combining phenol with formaldehyde in the presence of hydrochloric acid. Due to the lack of cheap formaldehyde at that time, this discovery did not receive industrial application. It was only at the beginning of the 1908th century that the factory production of phenol-formaldehyde resins began to be established, especially after the English researcher Baekeland in 500 found a method for the production of phenolic plastics from the same raw materials, which have the ability to become infusible and insoluble when heated. They have acquired great technical importance. Plastics based on these resins were named after their inventor Bakelites. The raw materials for phenol-formaldehyde resins are phenol (carbolic acid) and formalin (formalin is a solution of formaldehyde gas in water; formaldehyde is obtained artificially by oxidizing methyl alcohol with atmospheric oxygen at a temperature of 600-XNUMX degrees). First of all, these resins began to be used as a substitute for natural resin - shellac for electrical insulation. But it soon turned out that they had many properties that neither shellac nor other natural resins had. Phenoplasts began to quickly conquer vast areas of application for themselves and for a long time occupied a leading position among plastics. Products made from them were distinguished by heat resistance, water resistance, very high mechanical strength and good insulating properties. They were widely used for the manufacture of plugs, sockets, cartridges and other items of electrical equipment, as well as in the chemical industry as a material for vats, tanks and pipes used in aggressive environments. The filler in these plastics was usually wood flour. Later, on the basis of phenolic resins, such widely used plastics in mechanical engineering as getinaks, textolite and others began to be obtained. Products from them are obtained by hot pressing fabric, paper or plywood impregnated with resin. In this way, very strong and light parts (for example, gears or bearings) can be made that successfully replace metal ones. Moreover, unlike the latter, these parts operate silently and are not susceptible to the destructive effects of lubricating oils. Yes, and making them is much easier and cheaper than metal parts. If glass threads are used as a filler, plastics are formed that have increased strength. Another widespread variety of plastics has become carbamide plastics. The main starting material for the production of carbamide resins is urea. Urea was the first organic substance in history to be artificially synthesized; the German chemist Wöhler obtained it in 1828 from potassium cyanide, sulfate and ammonium, but it received practical application only a hundred years later. In 1918, the Czech chemist John took out a patent for a method for making a new resin from urea and formaldehyde. This resin had many remarkable properties: it was colorless, durable, low-flammable, heat-resistant, perfectly transmitted not only light, but also ultraviolet rays (which ordinary glass does not transmit) and was easily dyed in any color. At the same time, however, it had one significant drawback - it absorbed moisture. Soon the production of carbamide plastics began. They have become widespread as an excellent finishing and decorative material. Mipor, which has excellent heat and sound insulation properties, also belongs to the family of these plastics. In subsequent years, many new plastics were synthesized. Strong transparent plastics have become widespread in technology, successfully replacing fragile glass. The most suitable for these purposes was polymethyl methacrylate obtained from acetone, hydrocyanic acid and methyl alcohol. It is used to produce durable and lightweight organic glass. Polystyrene (it is obtained from ethylene and benzene) has become an indispensable material for high-frequency insulation. In 1940, the German chemist Müller and, independently of him, the Soviet scientist Andrianov obtained the first silicone plastics. The molecules of these plastics, along with carbon, include silicon. This gives a new type of plastics very valuable properties: they are highly heat resistant (withstand temperatures up to 400-500 degrees), resistant to water, acids and organic solvents. All this provided them with a wide range of applications. For a long time, chemists failed to polymerize ethylene. (Ethylene is a light gas with the formula CH2=CH2.) It was only in 1937 that this problem was partly resolved: under a huge pressure of 1200 atm, ethylene liquefied, while the double bond in its molecule was broken and the polymerization reaction began. (The result was the molecule [-CH2-CH2-]n.) After 10-30% of polyethylene was synthesized, ethylene was dissolved in it, and the reaction was stopped. When the pressure was lowered, ethylene evaporated and was then used in a new reaction cycle. This method was very expensive, so polyethylene could not then receive significant use. In 1953, Zingler developed a simpler method for the production of polyethylene: at a much lower pressure, ethylene was dissolved in gasoline, then under a pressure of 10 atmospheres and in the presence of a catalyst (alkylated titanium trichloride), the polymerization reaction began. With the approval of this method of production, polyethylene (an excellent insulator, resistant to acids) has become one of the most widely used plastics. Author: Ryzhov K.V.
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