Rubber, properties and characteristics, preparation and use.
Rubber is a natural or synthetic product of some polymerization of diene hydrocarbons with conjugated bonds.
Rubber is a natural or synthetic product of some polymerization of diene hydrocarbons with conjugated bonds. Their most important physical characteristics are the flexibility (rubber is able to recover shape), electrical, water and gas impermeability. Of rubbers by vulcanization are getting rubber and ebonite.
Natural rubber has been known since ancient times. Scientists found fossils of rubber-bearing plants, their age – millions of years. Five hundred years ago, with the discovery of America, the representatives of the civilization I learned about this material. At that time, the Indians smartly sold to white people bottles and shoes made of rubber. However, real demand rubber was relatively recently, in the 30-ies of the XIX century: Charles Goodyear (Charles Goodyear) in 1839, invented the vulcanization process, the rubber got. To do this, he heated the rubber with sulfur, the properties of the material improved. Thus was invented the rubber, and began its widespread use. In 1919, a market already existed more than forty thousand kinds of products using this material.
The rubber on 91-96 % of polymer of isoprene and has the following characteristics and properties: density of 910-920 kg/m3, frost resistance or the glass transition temperature of 70 °C (i.e., it ceases to be plastic and takes on some qualities of glass), heat resistance up to 200 °C.
In most liquids (water, alcohol, acetone, fatty acids) does not dissolve and does not swell. Swelling, gradually dissolves itself in such substances: gasoline, benzene, ether, toluene and other aromatic hydrocarbons.
Compression of natural rubber is accompanied by the absorption of the stretching – heat.
Upon cooling, the rubber becomes brittle when heat – softened. And in either process the rubber to lose its elasticity. The interaction of the natural rubber from ozone, oxygen and other oxidants leads to embrittlement and cracking. I.e., increased brittleness, it is “old”.
Like most polymers, depending on temperature, the rubber may be in one of three States: highly elastic, viscous and glassy. Under normal temperature conditions, the rubber is highly elastic.
More other rubber appreciated due to its elasticity. Glassware is able to quickly regain its original shape. This happens every time no longer apply the deformation force. Elasticity of rubber is one of the best in its class. For example, if the product will stretch up to 1000%, it will still return to its original shape. By the way, for regular solids, the figure is 1%. These unique properties of rubber saves and when heated and when cooled.
In addition, the advantage of rubber is manifested in the fact that it has a high plasticity. This means that under the influence of external forces the material will acquire and retain the shape imparted. During machining or heating this property is particularly noticeable. Therefore, rubber is considered a plasto-elastic substance.
However, natural rubber has a drawback: with time it hardens and thus loses its properties.
For the natural rubber raw material source is the milky juice of some plantsthat produce latex (a white liquid with special properties). The latex is a fairly common component of plants and is found in representatives of rubber-bearing plants of different Botanical groups.
It is located in different parts of the plants. So they (i.e. plants) klassificeret as follows:
1. latex, when the substance accumulates in the milky juice,
2. chlorenchyma – a substance accumulating in the young green shoots and leaves,
3. parenhimy – a substance accumulates in the roots and stems,
4. latex herbaceous plants of the family Compositae is a Kok-Sagyz, Krym-Sagyz, and others, where the rubber in a small amount is accumulated in the underground organs. These plants are not used in industrial production of rubber.
Rubber trees grow mainly in the area of the equator, not away from him more than 10° to the North and the South, i.e. a zone with a width of 1300 km and it is called: “rubber belt”. Here rubber trees are grown for industrial use in the world. Mainly natural rubber is obtained from latex of the tropical tree hevea Brazilian. On the bark of a tree, under 5 years old, make V-shaped incisions. One tree hevea receive an average of 2-3 kg of rubber.
To get the rubber extracted from hevea Brazilian, milky juice (latex) is subjected to a coagulation or zhelatinirovatsja, adding acetic or formic acid, after washed with water, rolled into sheets and smoked.
Natural rubber is a polymer of unsaturated hydrocarbon, having a large number of double bonds. It generic chemical formula looks like this: (C5H8)n, where the degree of polymerization (n) is 1000-3000 units. The monomer of natural rubber is called isoprene.
The chemical analysis of natural rubber shows that it is composed only of carbon and hydrogen. This allows it to be hydrocarbons. Proof of this is the basic formula of the rubber. The molecular weight of individual units may exceed the half-million grams per mole. Thus, natural rubber is a natural polymer of isoprene, and more specifically CIS-1,4-polyisoprene.
If you imagine a molecule of rubber is not atomically thin, it could be seen in the microscope, due to the fact that it is very long. And if it does and the maximum stretch, you get a big zigzagoon line. This is due to the type of carbon bonds.
Due to the fact that isoprene alternate single and double bond, of the molecule can only rotate around single bonds. And as a result of such fluctuations, the molecule is bent constantly, and even in rest she has drawn together the ends.
The molecule of natural rubber is similar to the almost circular springthat allows them to easily and strongly be stretched and increase in size when breeding ends.
Natural rubber is divided into 8 types, forming 35 varieties.
The most common and valuable type of natural rubber is considered to be “smoked yesterday“, which means smoked sheet. It is made in the form of fairly transparent amber with a corrugated surface.
Less common type-called “pale crepe“. To get to the latex before zhelatinirovatsja added for bleaching sodium bisulfite. The leaves of this type rubber have a cream color, they are opaque.
The least valued type, which is called “para rubber“. It is extracted from wild rubber trees in the handicraft way.
In the twentieth century with the advent of the automotive industry began to grow, the demand for rubber, then the rubber. Therefore, the rubber produced from the SAP of the hevea, there was a deficit. There was a question of obtaining synthetic rubber. In 1927, Soviet scientist S. V. Lebedev received the first divinely synthetic rubber through polymerization reaction of 1,3-butadiene with sodium catalyst. Now it has become so popular that it almost replaced a natural rubber. Synthetic rubber is divided into more than 30 types, which form more than 220 brands.
Currently in Russia produced synthetic rubber, special purpose and General purpose. Moreover, synthetic rubber is divided into stereoregularity and nectarivory. Stereoregularity, more durable and wear resistant than natural rubber. It is applied to, for example, as source material for tires. Nectarivory – used in the manufacture of ebonite and rubber, more resistant to aggressive environments.
Synthetic rubbers of General purpose are:
1. butadiene rubber,
2. isoprene rubber,
3. styrene-butadiene rubber,
4. butyl rubber,
5. the ethylene-propylene rubber,
6. chloroprene (Nairit) rubber , etc.
Synthetic rubbers special purpose are:
1. the nitrile butadiene rubber,
3. urethane SKU,
4. polysulfide rubber,
5. fluorine-containing rubber,
6. methylvinylpyridine rubber,
7. siloxane rubber , etc.
Scientists are constantly engaged in synthesis of artificial rubberwhich qualities constitute a better material than natural. For example, their properties are remarkable substances are the copolymers of styrene, butadiene and Acrylonitrile. During the polymerization process, the chain is built of alternating butadiene with the respective other monomer. This allows you to achieve excellent properties, which have no classical rubbers.
Russia is now the classic is made of synthetic rubber with properties similar to the properties of natural substances. Vulcanization of such rubber turns rubber, strength, elasticity and plasticity which is not practically different from those inherent in the natural material.
The main application of natural and synthetic rubber is the production of rubber.
Rubber is the product of vulcanizing rubber with a filler which is carbon black. The vulcanization of rubber necessary for the reason that the rubber in its pure form is rather brittle and less elastic materialthan vulcanized. Vulcanization of the rubber occurs treatment of a mixture of rubber and sulfur under the influence of temperature. The essence of curing is the process by which the sulfur atoms are joined to threadlike linear rubber molecules in locations of double bonds and, as if sewn together by disulfide bridges these molecules among themselves, forming a three-dimensional reticulated polymer.
If vulcanization of rubber is taken to be 2-3 % sulphur by weight, the vulcanization product are rubber. It is less susceptible to temperature fluctuations, mechanical damage, exposure to gases and electric current, the action of different chemical reagents and summer heat than rubber. In addition, a vulcanized rubber is obtained a high degree of frictional sliding on dry surfaces and low on wet.
If the rubber to add more than 30% of the sulfur, the vulcanization process will ebonite: hard material, non-plasticity.
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