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Plastic


Plastic
Widespread plastics - one of the hallmarks of our time. Virtually all natural fibers, resins and materials are now have their artificial substitutes. It created a lot of other substances with properties that are not found in nature. And that, apparently, only the beginning of a grand revolution, equal in importance the great revolutions of the past material - development of bronze and iron.

Typically, plastic - is a complex organic compound, which includes several components. The most important of them, set up the basic properties of the material, a synthetic resin. Manufacture of any plastics begins with the preparation of the resin. Generally, resins are intermediate between solid and liquid substances. On the one hand, they have many of the qualities of solid bodies, but they are also to a large extent characterized by fluidity, ie the ability to easily change shape. In its internal structure, the resin also occupy an isolated position: they do not have a rigid crystal lattice, like the majority of solids; they have no definite melting point and gradually softens when heated, turns into a viscous liquid. Like rubber, to which they are very similar in their properties, the resins are polymers, that is, their molecules consist of a large number of identical (often very simple in structure) units.

Artificial (synthetic) resin can be obtained as a result of a chemical reaction between two types of reaction and condensation polymerization reaction. During the condensation reaction, the interaction of two or more of the new substance is formed and thus also distinguished by-products (water, ammonia, etc.). Phenolic resins, for example, obtained from phenol and formaldehyde, two molecules of the phenol are linked together as a bridge to a methylene group contained in formaldehyde, and the water is released. Then the already double molecules bind together. In the end, it turns out a large molecule, linear or three-dimensional structure. When the polymerization reaction in the reacting molecules enter the same substance. Interconnected, they form a new material - without isolating the polymer byproducts. As already mentioned in the chapter on the rubber, a polymerization reaction can all organic substances having in its molecule of carbon atoms with a double or triple bond.

The resin binds, or, as is sometimes said, cements, all components of the plastic, giving it flexibility and other valuable properties - hardness, water resistance, mechanical and electrical properties. In addition in many types of resin plastics important (50-70% weight) occupy the so-called fillers, which may be both organic and mineral substances. Among the organic fillers it is considered the most important cellulose (used in the form of paper, fabric or linters - otchesov cotton, impregnated with resin solution, then dried and pressed). For inorganic fillers include mica, slate, talc, asbestos, glass fabric and graphite. Typically, resin fillers considerably cheaper and introducing them with proper selection - hardly deteriorates the properties of plastics. Sometimes the introduction of well-matched filler even improves the quality of plastic. It can be improved also by means of special additives and plasticizers. First taken even in small quantities, impart new properties to plastics (for example, metal additive makes the dielectric a conductive plastic). A plasticizers forming resin solution, it softens and report it extra flexibility.

Start of production of plastics based on artificial materials refers to the first third of the XIX century. kamptulikon - In 1830, one of the first plastic was produced in England. The basis of this laminate was jute fabric, on which the rubber mixture was rolled, shredded tube and some other components. However, due to the high price of rubber, the production of this plastic is not widespread. In 1863, Englishman Walton replaced rubber linoksinom and thus laid the foundation for the production of linoleum. Up until now, its universally used as a floor covering, as it is cleared much more slowly than wood and even marble.

The widespread use of plastics marked the invention of celluloid, created on the basis of cellulose. (Cellulose or cellulose, is the basis of wood and other plant materials, and its molecule consists of a large number of simple in structure units;. In purified form is colorless, infusible and insoluble substance) In 1845, it was found that when processing pulp (cotton wool ) of nitric and sulfuric acids, nitric acid ester is formed, known as pyroxylin. This material is very dangerous and explodes with great force in a dry form. Later, however, we noticed that he was not dangerous when wet. There was a question: if the water deprives guncotton explosive force, then maybe there is another way to affect its properties. It turned out that if the wet nitrocellulose mixed with camphor, it turns plastic, which can be processed at the mill, pressed and molded. In 1869, the brothers received Hayet so celluloid, which began to produce commercially since 1872. Celluloid possessed great strength, was beautiful and could be painted in any color or be used as a transparent film. This plastic soon gained the widest dissemination. From it began to make a photo - and film, combs, boxes, toys, buttons, belts. However, the celluloid was one major drawback - he was very flammable and easily ignited.

In 1872, German chemist Bayer by combining phenol with formaldehyde in the presence of hydrochloric acid synthesized new smoloobrazuyuschee substance. Due to the absence at the time of cheap formaldehyde this discovery has not received industrial applications. Only at the beginning of the XX century it began to build a factory producing phenol resins formaldegidovyh, especially after 1908, the English explorer Bakeland found a way to production of the same raw phenolics, have the ability when heated to move into an infusible and insoluble. They acquired a great technical importance. Plastics based on these resins have been named for the inventor of Bakelite. Raw materials for phenolic resins are formaldegidovyh phenol (carbolic acid) and formalin (formalin - a solution of formaldehyde gas in water, formaldehyde is produced artificially, methanol oxidizing atmospheric oxygen at temperatures of 500-600 degrees). First of all, these resins have been used as a substitute for natural resins - shellac for insulation. But soon it turned out that they have a variety of properties, which had no shellac or other natural resins. Phenoplasts quickly began to conquer large areas of application currently and for a long time occupied a leading place among plastics. Products have different heat resistance, water resistance, very high mechanical strength and good insulating properties. They are widely used for the manufacture of plugs, sockets, cartridges and other items of electrical equipment, and in the chemical industry as a material for tanks, vessels and pipes used in corrosive environments. The filler in these plastics are usually served as wood flour. Later, on the basis of phenolic resins began to receive such widely used in engineering plastics as getinaks, PCB and others. Products are produced by hot pressing of cloth, paper or plywood, impregnated with resin. Thus it is possible to produce a very strong and lightweight parts (for example, gears or bearings), successfully replacing metal. Moreover, unlike the latter, these parts operate silently and not be destructive influence of lubricating oils. Yes, and manufacturing them is much easier and cheaper than metal parts. If the use of glass filaments formed of plastic having high strength as a filler.

Another common type of plastic widely urea became plastic. The main raw material for the production of urea resins is urea. (Urea was the first in the history of organic matter, which managed to synthesize an artificial way, a German chemist Wohler received it in 1828 from potassium cyanide, and ammonium sulfate, but the practical application it has received only a hundred years later.) In 1918, the Czech chemist John took patent for a new method of manufacturing a resin from urea and formaldehyde. This resin had a number of remarkable properties: it was colorless, strong, malogoryuchey, heat-resistant, perfectly missed not only light, but also ultraviolet rays (which does not pass ordinary glass) and is easily painted in any color. At the same time, however, it had one major drawback - it absorbs moisture. Soon began the production of urea plastics. They have spread a beautiful finishing and decorative material. The family of plastics refers mipor as having remarkable heat - and sound insulation properties.

In subsequent years, it was synthesized many new plastics. There was widespread in the technique have gained a strong transparent plastic, successfully replacing the fragile glass. Most suitable for this purpose proved polymethylmethacrylate derived from acetone, hydrocyanic acid and methyl alcohol. From it produce robust and easy organic glass. Indispensable material for the high insulation polystyrene was (it is prepared from ethylene and benzene).

In 1940, German chemist Müller and independently by the Soviet scientist Andrianov received the first silicone plastic. The molecules of these plastics, along with the carbon include silicon. It reports a new kind of plastic are very valuable properties: they are characterized by high heat resistance (can withstand temperatures up to 400-500 degrees), are resistant to water, acids and organic solvents. This provided them with a wide range of applications.

For a long time, chemists have not been able to polymerize ethylene. (. Ethylene - light gas with the formula CH2 = CH2) Only the problem was partly resolved in 1937: under tremendous pressure of 1200 atm ethylene liquefy, thus bursting the double bond in the molecule and begin the polymerization reaction. (The result was a molecule [-CH2-CH2-] n.) Once synthesized 10-30% polyethylene, ethylene dissolved therein, and the reaction was stopped. By lowering the pressure of ethylene was evaporated and then used in a new cycle of reaction. This method was very expensive, so the polyethylene could not then get considerable use. In 1953 godu Tsingler developed a simple method for polyethylene production: at much lower ethylene pressure was dissolved in gasoline, then pressurized to 10 atmospheres and in the presence of a catalyst (titanium trichloride alkylated) polymerization reaction started. With the approval of this production method polyethylene (perfect insulator, impervious to acids) became one of the most widely used plastics.

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