Rubbers are natural or synthetic materials characterized by elasticity, water resistance and electrical insulating properties, of which rubber is obtained by special treatment. Natural rubber is obtained from a milky-white liquid called latex, a milky juice of rubber-bearing plants.
Natural rubber is obtained by coagulating the milky juice (latex) of rubber plants. The main component of rubber is polyisoprene hydrocarbon (91-96%). Natural rubber is found in very many plants that do not constitute one particular botanical family. Depending on the tissues in which rubber accumulates, rubber plants are divided into:
-parenchymal – rubber in the roots and stems;
-chlorenchyme – rubber in the leaves and green tissues of young shoots.
-latex – rubber in the milky juice.
-Herbaceous latex rubber plants from the Asteraceae family (Kok-Sagyz, Crimea-Sagyz and others), growing in the temperate zone, including in the southern republics, containing rubber in small quantities in the roots, have no industrial significance.
What is synthetic rubber? These are synthetic polymers that can be processed into rubber by vulcanization, constitute the bulk of elastomers. Which city produces rubber in Russia? For example, in Tolyatti, Krasnoyarsk.
Synthetic rubber is a high polymer, rubber-like material. It is produced by polymerization or copolymerization of butadiene, styrene, isoprene, neoprene, chloroprene, isobutylene, acrylic acid nitrile. Like natural rubbers, synthetic have long macromolecular chains, sometimes branched, with an average molecular weight equal to hundreds of thousands and even millions. Polymer chains in synthetic rubber in most cases have double bonds, due to which a spatial network is formed during vulcanization, the resulting rubber becomes characteristic physical and mechanical properties.
Usually accepted classification and name of rubber by monomers used to obtain them (isoprene, butadiene, etc.) or by characteristic group (atoms) in the main chain or side groups (urethane, polysulfide, etc.) Synthetic rubbers are also divided by attributes for example, by the content of fillers (filled and unfilled), by molecular weight (consistency) and final form (solid, liquid, powder). Part of the synthetic rubber produced in the form of aqueous dispersions – synthetic latex. A special group of rubbers is thermoplastic elastomers.
Some types of synthetic rubbers (for example, polyisobutylene, silicone rubber) are completely limiting compounds, therefore organic peroxides, amines and other substances are used for their vulcanization. Certain types of synthetic rubbers surpass natural rubber in a number of technical properties.
According to the field of application, synthetic rubbers are divided into general and special purpose rubbers. General purpose rubbers include rubbers with a complex of sufficiently high technical properties (strength, elasticity, etc.) suitable for mass production of a wide range of products. Special-purpose rubbers include rubbers with one or several properties that ensure the fulfillment of special requirements to the product and the yoke of working capacity under often extreme operating conditions.
General purpose rubbers: isoprene, butadiene, styrene butadiene, etc.
Special-purpose rubbers: butyl rubber, ethylene-propylene, chloroprene, fluororubber, urethane, etc. Many do not know that chloroprene rubber was produced in the USSR and they are wondering which of the cities produce rubber now? Unfortunately, chloroprene rubber was produced in Armenia at the Nairit plant, which has been stopped for several years.
In the technique of rubber produce tires for vehicles, airplanes, bicycles; Rubber used for electrical insulation, as well as the production of industrial goods and medical devices.
1. Natural rubber
Rubber exists for as many years as nature itself. The fossilized remains of rubber trees that were found are about three million years old. The first acquaintance of Europeans with natural rubber took place five centuries ago, and in the USA rubber items became popular in the 1830s, rubber bottles and shoes made by South American Indians were sold in large quantities. In 1839, American inventor Charles Goodyear discovered that heating rubber with sulfur eliminates its unfavorable properties. He put on the oven a piece of rubber-covered fabric, on which a layer of sulfur was applied. After some time, he discovered leather-like material – rubber. This process was called vulcanization. The discovery of rubber led to its widespread use: by 1919, more than 40,000 different rubber products had already been launched onto the market.
The word “rubber” comes from two words of the Tupi-Guarani language: “kau” is a tree, “I learn” to flow, to cry. “Couch” is juice of hevea, the first and most important rubber plant. The Europeans added to this word just one letter. Among the herbaceous plants of Russia there is a familiar dandelion, wormwood and spurge, which also contain milky sap.
Latex trees, which not only accumulate rubber in large quantities, but also give it away, have industrial significance; of these, the most important is Brazilian Hevea (Hevea brasiliensis), according to various estimates, from 90% to 96% of world production of natural rubber.
Raw rubber from other plant sources is usually clogged with resin impurities that must be removed. Such raw rubbers contain gutta percha, a product of some tropical trees of the Sapotaceae family.
Rubber plants best grow no further than 10 ° from the equator to the north and south. Therefore, this 1300 km wide strip on either side of the equator is known as the “rubber belt”. Here, rubber is mined and supplied for sale to all countries of the world.
Physical and chemical properties of natural rubber
Natural rubber is an amorphous solid that can crystallize.
Natural raw (raw) rubber is a white or colorless hydrocarbon.
It does not swell and does not dissolve in water, alcohol, acetone and some other liquids. Swelling and then dissolving in fatty and aromatic hydrocarbons (gasoline, benzene, ether, and others) and their derivatives, rubber forms colloidal solutions widely used in engineering.
Natural rubber is homogeneous in its molecular structure, characterized by high physical properties, as well as technological, that is, the ability to be processed on the equipment of rubber industry plants.
Especially important and specific property of rubber is its elasticity (elasticity) – the ability of rubber to restore its original shape after the termination of the forces that caused the deformation. Rubber is a highly elastic product, with even small efforts, it has reversible tensile deformation up to 1000%, and for ordinary solids this value does not exceed 1%. The elasticity of rubber is preserved in a wide temperature range, and this is its characteristic property. But with long storage rubber hardens.
At a temperature of liquid air –195 ° C, it is hard and transparent; from 0 ° to 10 ° C – fragile and already opaque, and at 20 ° C – soft, resilient and translucent. When heated above 50 ° C, it becomes plastic and sticky; at a temperature of 80 ° C natural rubber loses its elasticity; at 120 ° C – turns into a resinous liquid, after solidification of which it is no longer possible to obtain the original product. If you raise the temperature to 200-250 ° C, the rubber decomposes with the formation of a number of gaseous and liquid products.
Rubber is a good dielectric, it has low water and gas permeability. Rubber does not dissolve in water, alkali and weak acids; in ethyl alcohol its solubility is small, and in carbon disulfide, chloroform and gasoline, it first swells and only then dissolves. It is easily oxidized by chemical oxidizing agents, slowly – by air oxygen. The thermal conductivity of rubber is 100 times less than the thermal conductivity of steel.
Along with elasticity, rubber is also plastic – it retains the shape acquired by external forces. The plasticity of rubber, which is manifested during heating and machining, is one of the distinguishing properties of rubber. Since elastic and plastic properties are inherent in rubber, it is often called a plastically elastic material.
During cooling or stretching of natural rubber, its transition from the amorphous to the crystalline state (crystallization) is observed. The process does not happen instantly, but in time. In this case, in the case of stretching, the rubber is heated due to the released heat of crystallization. Rubber crystals are very small, they are devoid of clear edges and a certain geometric shape.
At a temperature of about –70 ° C, rubber completely loses its elasticity and turns into a glassy mass.
In general, all rubbers, like many polymeric materials, can be in three physical states: glassy, highly elastic and viscous. The highly elastic state for rubber is most typical.
Rubber easily enters into chemical reactions with a variety of substances: oxygen (O2), hydrogen (H2), halogens (Cl2, Br2), sulfur (S), and others. This high reactivity of rubber is explained by its unsaturated chemical nature. Especially good reactions take place in solutions of rubber, in which rubber is in the form of molecules of relatively large colloidal particles.
Almost all chemical reactions lead to changes in the physical and chemical properties of rubber: solubility, strength, elasticity, and others. Oxygen, and especially ozone, oxidizes rubber even at room temperature. Being introduced into complex and large molecules of rubber, oxygen molecules break them down into smaller ones, and, destructurizing, rubber becomes fragile and loses its valuable technical properties. The oxidation process also underlies one of the transformations of rubber – its transition from a solid to a plastic state.
The composition and structure of natural rubber
Natural (natural) rubber (NK) is a high-molecular unsaturated hydrocarbon, the molecules of which contain a large number of double bonds; its composition can be expressed by the formula (C5H8) n (where the value of n is from 1000 to 3000); It is a polymer of isoprene.
Natural rubber is found in the milky juice of rubber-bearing plants, mainly tropical (for example, the Brazilian hevea tree). Another natural product – gutta percha – is also a polymer of isoprene, but with a different configuration of molecules.
A long rubber molecule could be observed directly with the help of modern microscopes, but this is not possible, because the chain is too thin: its diameter corresponds to the diameter of one molecule. If the rubber macromolecule is stretched to the limit, it will look like a zigzag, which is explained by the nature of the chemical bonds between the carbon atoms that make up the skeleton of the molecule.
The links of the rubber molecule can not rotate freely in any direction, but only limitedly around single bonds. The thermal vibrations of the links cause the molecule to bend, while its ends in a quiescent state are brought together.
When the rubber is stretched, the ends of the molecules are moved apart and the molecules are oriented in the direction of the tensile force. If the force that caused the stretching of the rubber is eliminated, the ends of its molecules come together again and the sample assumes its original shape and size.
A molecule of rubber can be imagined as a round, open spring, which can be strongly stretched by spreading its ends. The released spring takes up its position again. Some researchers represent a rubber molecule in the form of a spring spiral. Qualitative analysis shows that rubber consists of two elements – carbon and hydrogen, that is, it belongs to the class of hydrocarbons.
The originally adopted rubber formula was C5H8, but it is too simple for such a complex substance as rubber. The determination of molecular weight indicates that it reaches several hundred thousand (150,000 – 500,000). Rubber is therefore a natural polymer.
It has been experimentally proven that mainly macromolecules of natural rubber consist of residues of isoprene molecules, and natural rubber itself is a natural polymer cis-1,4-polyisoprene.
A natural rubber molecule consists of several thousands of initial chemical groups (links) connected to each other and in continuous vibrational-rotational motion. Such a molecule is similar to a tangled coil, in which the components of its threads in places form correctly oriented sections.
The main product of the decomposition of rubber is a hydrocarbon, the molecular formula of which is unambiguous with the simplest formula of rubber. We can assume that the macromolecules of rubber are formed by isoprene molecules. There are similar polymers that do not exhibit such elasticity as rubber has. What explains this is his special property?
The molecules of rubber, although they have a linear structure, are not elongated in a line, but are repeatedly curved, as if rolled into balls. When the rubber is stretched, such molecules become straightened, and the rubber sample becomes longer from this. When removing the load, due to internal thermal motion, the links of the molecule return to their former collapsed state, the size of the rubber is reduced. If the rubber is stretched with a sufficiently large force, then not only will the molecules be straightened, but they will also be displaced relative to each other – the rubber sample may break.
2. Synthetic rubber
In Russia, natural sources for the production of natural rubber were not known, and rubber from other countries was not imported to us, and at that time they did not know what synthetic rubber was. And so, on December 30, 1927, 2 kg of divinyl rubber was obtained by polymerizing 1,3-butadiene under the action of sodium. Since 1932, the industrial production of 1,3-butadiene was started, and from 1,3-butadiene – the production of rubber.
Ethanol is the raw material for the synthesis of butadiene. Butadiene production is based on dehydrogenation and alcohol dehydration reactions. These reactions proceed simultaneously when passing alcohol vapor over a mixture of the corresponding
In order to make the monomer molecule connect with each other, they must first be excited, that is, they should be brought into such a state when they become capable, as a result of the opening of double bonds, to interconnection. This requires the cost of a certain amount of energy or catalyst participation.
In catalytic polymerization, the catalyst is not part of the resulting polymer and is not consumed, but is released at the end of the reaction in its original form. S. Lebedev chose metallic sodium, first used for the polymerization of unsaturated hydrocarbons by the Russian chemist A. A. Krakau, as a catalyst for the synthesis of butadiene rubber.
A distinctive feature of the polymerization process is that while the molecules of the original substance or substances are interconnected with the formation of the polymer, while not emitting any other substances.
The most important types of synthetic rubber
The above butadiene rubber (SKB) is of two types: stereoregular and non-stereoregular. Stereo-regular butadiene rubber is mainly used in the production of tires (which are superior to natural rubber tires in durability), non-stereo-regular butadiene rubber – for the production of, for example, acid and alkali-resistant rubber, ebonite.
Currently, the chemical industry produces many different types of synthetic rubbers, surpassing natural rubber in some properties. In addition to polybutadiene rubber (SCB), copolymer rubbers are widely used – products of the joint polymerization (copolymerization) of butadiene with other unsaturated compounds, for example, styrene (SCS) or acrylonitrile (SKN). In the molecules of these rubbers, the butadiene units alternate with the units of styrene and acrylonitrile, respectively.
Styrene butadiene rubber is notable for its increased wear resistance and is used in the manufacture of car tires, conveyor belts, rubber shoes.
Nitrile butadiene rubbers are benzo- and oil-resistant, and therefore are used, for example, in the production of stuffing boxes.
Vinylpyridine rubbers are products of copolymerization of diene hydrocarbons with vinylpyridine, mainly butadiene with 2-methyl-5-vinylpyridine.
Rubber from them are oil-, benzo-and frost-resistant, well stick together with various materials. They are mainly used in the form of latex for impregnation of tire cord.
In Russia, the production of synthetic polyisoprene rubber (SKI), similar in properties to natural rubber, has been developed and introduced into production. SKI rubbers are characterized by high mechanical strength and elasticity. SKI serves as a substitute for natural rubber in the production of tires, conveyor belts, rubber, footwear, medical and sports products.
Silicone rubbers, or siloxane rubbers, are used in the manufacture of sheaths of wires and cables, tubes for blood transfusion, prostheses (for example, artificial heart valves), etc. Liquid silicone rubbers – sealants.
Polyurethane rubber is used as the basis for the wear resistance of rubber.
Fluorine-containing rubbers have, as a feature, increased heat resistance and therefore are mainly used in the production of various seals, which are operated at temperatures above 200 ° C.
Chloroprene rubbers – polymers of chloroprene (2-chloro-1,3-butadiene) – are similar in nature to natural rubber; in rubber they are used to increase the atmospheric, benzo and oil resistance.
Foamed rubber finds its application. Various types of rubbers are exposed to foaming. There is also an inorganic synthetic rubber – polyphosphonitrile chloride.
Natural and synthetic rubbers are used mainly in the form of rubber, as it has a significantly higher strength, elasticity and a number of other valuable properties. Rubber is vulcanized to produce rubber. Many scientists worked on the vulcanization of rubber. Only after receiving high-quality rubber, they fully understood what synthetic rubber is.
Modern technology of rubber production is carried out in the following stages:
1. Manufacturing of semi-finished products:
-weighing rubber and ingredients;
-tissue gumming, calendering, extrusion;
-cutting rubberized fabrics and rubber sheets; assembling products from semi-finished products.
2. Vulcanization, after which finished rubber products are obtained from raw rubber compounds.
From the mixture of rubber with sulfur, fillers (carbon black is a particularly important filler) and other substances form the necessary products and heat them. Under these conditions, the sulfur atoms are attached to the double bonds of rubber macromolecules and "sew" them, forming disulfide "bridges". As a result, a giant molecule is formed, which has three dimensions in space – like length, width and thickness. Such rubber (rubber) will, of course, be stronger than unvulcanized.
The solubility of the polymer also changes: rubber, although slowly, dissolves in gasoline, rubber only swells in it. If you add more sulfur to rubber than you need to form rubber, then vulcanization will cause the linear molecules to be "crosslinked" in very many places, and the material will lose elasticity, become solid – ebonite will turn out. Before the advent of modern plastics, ebonite was considered one of the best insulators.
Vulcanized rubber has greater strength and elasticity, as well as greater resistance to temperature change than unvulcanized rubber; rubber is impermeable to gases, resistant to scratching, chemical attack, heat and electricity, and also shows a high coefficient of sliding friction with dry surfaces and low – with moist.
Vulcanization accelerators improve the properties of vulcanizers, reduce the time of vulcanization and the consumption of the main raw material, prevent perevulkanization. Inorganic compounds (magnesium oxide MgO, lead oxide PbO and others) and organic are used as accelerators: dithiocarbamates (derivatives of dithiocarbamic acid), thiurams (derivatives of dimethylamine), xanthates (salts of xanthic acid) and others.
Activators of vulcanization accelerators facilitate the reaction of interaction of all components of the rubber mixture. Basically, zinc oxide ZnO is used as activators.
Antioxidants (stabilizers, antioxidants) are introduced into the rubber mixture to prevent the "aging" of rubber.
Fillers – increase the physicomechanical properties of rubbers: strength, wear resistance, abrasion resistance. They also contribute to an increase in the volume of raw materials, and, consequently, reduce the consumption of rubber and reduce the cost of rubber. Fillers include various types of carbon black (technical carbon), mineral substances (chalk CaCO3, BaSO4, gypsum, talc, silica sand SiO2).
Plasticizers (softeners) – substances that improve the technological properties of rubber, facilitate its processing (lower the viscosity of the system), provide the possibility of increasing the content of fillers. The introduction of plasticizers increases the dynamic endurance of rubber, resistance to "abrasion". As plasticizers, oil refining products (fuel oil, tar, paraffins), vegetable substances (rosin), fatty acids (stearic, oleic) and others are used.
The strength and insolubility of rubber in organic solvents are related to its structure. The properties of rubber are determined by the type of feedstock. For example, rubber from natural rubber is characterized by good elasticity, oil resistance, wear resistance, but at the same time it is little resistant to aggressive media; SKD rubber is even more wear resistant than NK rubber. Butadiene-styrene rubber SKS contributes to increased wear resistance. Isoprene rubber SKI determines the elasticity and tensile strength of rubber, and chloroprene rubber determines its resistance to the action of oxygen.
In which of the cities produce rubber and when it began production? In Russia, the first major manufacturing enterprise in the rubber industry was founded in St. Petersburg in 1860, later called the Triangle (since 1922, the Red Triangle). Behind him were founded and other Russian rubber products factories (RTI): “Kauchuk” and “Bogatyr” in Moscow, “Provodnik” in Riga and others.
The use of rubber in industrial products
Rubber is of great economic importance. Most often it is used not in pure form, but in the form of rubber. Rubber products are used in the technique for insulating wires, making various tires, in the military industry, in the manufacture of industrial goods: footwear, artificial leather, rubberized clothing, and medical products.
Rubber is a highly elastic, strong compound, but less plastic than rubber. It is a complex multicomponent system consisting of a polymer base (rubber) and various additives.
The largest consumers of rubber technical products are the automotive industry and agricultural engineering. The degree of saturation with rubber products is one of the main signs of perfection, reliability and comfort of mass types of engineering products. As part of the mechanisms and assemblies, modern car and tractor there are hundreds of names and up to a thousand pieces of rubber parts, and simultaneously with the increase in the production of machines, their rubber capacity increases.
Types of rubber and their application
Depending on the structure of rubber is divided into non-porous (monolithic) and porous.
Non-porous rubber is made on the basis of butadiene rubber. It has high resistance to abrasion. The period of wear of the sole rubber is 2–3 times longer than the period of wear of the plantar skin. The tensile strength of rubber under tension is less than that of genuine leather, but the relative elongation at break is many times greater than the elongation of natural plantar leather. Rubber does not pass water and practically does not swell in it.
Rubber is inferior to the skin in frost resistance and thermal conductivity, which reduces the heat-shielding properties of shoes. And finally, rubber is absolutely air and vapor tight. Non-porous rubber can be plantar, leather-like, and transparent. Conventional non-porous rubber is used for the manufacture of molded soles, linings, heels, semi-heels, heels and other parts of the bottom of the shoe.
Porous rubbers are used as soles and platforms for spring, autumn and winter shoes.
Leather-like rubber is a rubber for the bottom of shoes, made on the basis of rubber with a high styrene content (up to 85%). The increased styrene content gives the rubber its hardness, as a result of which it is possible to reduce their thickness to