Век химии (Английский язык для студентов химического профиля). Учебное пособие

automotive industry, and was transmitted by the processor back to the producers of the raw materials.

The major raw materials of the rubber industry are, in addition to the rubber itself, carbon black, other fillers, oils and various chemicals. For each of the categories the processors have to establish the minimum requirements for suppliers.

Many rubber processors today have in place a supplier accreditation system, or audit, whereby raw material suppliers’ plants, processes, laboratories and quality systems can be assessed against objective standards. This type of close communication between suppler and processor generates confidence that the guaranteed quality is being provided and, eventually, leads to reduction, even elimination, of incoming raw material testing and minimization of inventories. It also enables development of specifications and standards that are both right for the customer, and feasible for the producer.

3.Make up the plan to the text.

4.Give a brief summery of the text.

Text D

1. Read the text and choose the most suitable title out of the given ones:

a)Chemical Constitution of Rubber.

b)Chemical Reactions of Rubber.

c)The Molecular Weight of Rubber.

From the moment of its introduction into Europe the unusual nature and properties of rubber attracted the attention of chemists. A knowledge of the structure assumed an added importance as a first step towards ultimate synthesis; indeed an account of natural rubber and its chemistry is indispensable as a logical approach to the problems of the so-called modern synthetic rubbers.

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Faraday made combustions of rubber and found the composition to correspond to C5 H8 – a formula which has since been confirmed.

An important contribution to the elucidation of the rubber hydrocarbon was later made and a ring formula for rubber was put forward. The existence of the long chains of molecules has been verified by X-ray examination.

Raw rubber disso1ves incompletely in ethyl ether and this fact serves to distinguish between the sol fraction and the gel fraction is insoluble. The hydrocarbon in Hevea rubber latex just taken from the tree has a very broad molecular - weight distribution; it ranges from several million down to below 100,000.

The molecular weight of raw rubber is lower than that of fresh latex, but may be as high as 460,000. The decrease in molecular weight from the latex state to the raw rubber state is due to the breakdown of the polymer, which occurs in the creping and sheeting operations. When the rubber is compounded, the milling which is necessary for proper distribution of sheeting the chemicals throughout the mass, results in an additional decrease in molecular weight.

2. Write out:

a)the key word and terms;

b)the sentences expressing the main idea of each paragraph.

Unit 10

GRAMMAR: Participles, Gerund.

1. a) Using a dictionary translate the following words, word combinations and chemical terms into Russian:

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Rubber-like elasticity, extensibility, stretched, weight, flexible, fibrous, gelatin, substance, sulphur, polyvinyl alcohol, molecular chains, linkage, condition, force.

b) Find (in the list given below) synonyms to the following words. Translate these words into Russian:

can, certain, complete, contracted, to detect, different, evident, lightly, motion, obtain, property, shape, substance, sufficient, total, violent.

(be able to, behaviour, compressed, definite, enough, to find out, form, full, get, matter, movement, obvious, slightly, strong, various, whole).

c) Translate the following sentences paying attention to the -ing- forms:

1.On reheating, “melting” occurs and rubber increases in

volume.

2.Reinforcing agents harden the rubber and make it more wear

resistant.

3.Katz showed that ordinary, unstretched rubber has a disordered structure, resembling that of a liquid.

4.In an ideal rubber-like substance no energy is used in separating chains and in increasing their separation during stretching.

5.The highly coiled and folded condition of the rubber chains permits their being extended up to seven times their original length.

6.New ways of modifying the properties of existing products are being discovered widening the field of application of the rubberlike state.

7.When parts of the long molecules of natural rubber arrange themselves in an ordered state crystallizing they are assumed to exhibit a first order transition.

8.The problems regarding the use of pigments in latex are similar to those in other types of coatings and finishes.

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2. Choose the correct forms.

1.Latex may be used for (impregnating, impregnated) paper, leather, or cloth, the rubberized product being water proof.

2.Synthetic rubbers are high polymeric elastic substances (manufactured, manufacturing) from a wide range of chemical compounds.

3.In an ideal rubber-like substance no energy is used in (separating, being separating) chains and (being increasing, increasing) their separation during stretching.

4.This result was clearly demonstrated by Katz (being used, using) X-ray diffraction to detect the crystallinity.

5.On (being reheated, reheating), “melting” occurs and rubber increases in volume.

Text A

3. Read the text and translate it using a dictionary.

THE NATURE OF RUBBER-LIKE ELASTICITY

The characteristic properties of rubber, its extensibility and complete recovery after even very large deformations, is shown also by many other substances. Of these we may mention supercooled molten sulphur and selenium, gelatin, muscle fibrils, substances built from long chain molecules such as polyvinyl alcohol, etc. These substances are very different chemically, but their common feature is a long flexible molecule. There is a rubber-like state which many substances made from long molecules may assume under suitable conditions.

The two factors which are necessary if perfect rubber-like elasticity is to be obtained are, firstly, that whole molecules must not be able to slip past each other under the action of deforming forces, and, secondly, that these forces shall meet with little resistance in straightening out the coiled molecular chains. In lightly vulcanized rubber, the long chains are connected across at certain points by the

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strong sulphur linkages. The presence of only a few such points of linkage is sufficient to prevent slipping of the whole molecules, which would result in plastic flow. The atoms of the molecule share in the general thermal motion at any temperature, so that a free molecule would be continually coiling, twisting and changing its shape. There are many more ways in which such molecules can be arranged to give a crumbled chain.

The lengths of chain between sulphur crosslinks behave in essentially the same way as the free rubber molecule, so that the vast majority of them are in a contracted form, which changes momentarily with the thermal motion. This freedom comes from the weakness of the van der Waals forces between the chains, which are not strong enough to hold them permanently in position side by side.

When we apply a force to the rubber, the flexible chains are slightly straightened, but are always attempting to return to their folded condition. It is evident that, the more violent the thermal motion, the greater the tendency of the chains to return to their normal positions. If a rubber band is stretched by means of a weight, it contracts on heating owing to the effect of the increased thermal motion. This is contrary to the behaviour of normal substances, which deform more easily at high temperatures.

The highly coiled and folded condition of the rubber chains permits their being extended up to seven times their original length. Long before this, however, some of the chains will have been pulled approximately parallel. When this occurs, the attractive forces between them become sufficiently strong to bind them together in a regular arrangement. Thus the rubber is crystallized by tension. This result was clearly demonstrated by Katz using X-ray diffraction to detect the crystallinity. He showed that ordinary, unstretched rubber has a disordered structure, resembling that of a liquid. Sufficient stretching gives an X-ray diffraction picture similar to that shown by fibrous materials. If the rubber is cooled, while under tension, to a low temperature, it does not contract when the tension is removed, and still gives a crystalline X-ray diffraction pattern. On reheating, “melting” occurs and the rubber contracts. If the frozen stretched rubber is pulverized when cold, it splits up into fibrous pieces, owing to the parallel orientation of the chains.

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If unstretched rubber is cooled, a slow crystallization takes place, giving a harder and less extensible material. On warming “melting” again occurs, but unlike that of ordinary crystalline substances, it takes place over a range of some 10 °С, in temperature. These effects may be observed in crepe soles kept for some exposed to very cold weather.

In an ideal rubber-like substance no energy is used in separating chains and increasing their separation during stretching. As a result there is no change in the total volume of the substance when extended. This condition is not fulfilled by most rubber-like substances, so that their properties only partially correspond to those of the ideal substance.

Commercial rubbers are very complex systems, in which variation of the proportions of the constituents can give an immense range of products.

4. Answer the questions:

1.What substances are known to display the characteristic properties of rubber?

2.What factors is perfect rubber-like elasticity due to?

3.What happens if one applies a force to rubber?

4.In what way did Katz succeed in detecting crystallinity?

5.In what case does the process of slow crystallization take place?

5. Complete the following sentences using some active words and word combinations (see below).

1.The characteristic properties of rubber, its extensibility and complete recovery after even very large deformations, is shown also by many other ... .

2.The common feature of these substances is a long flexible ….

3.In lightly vulcanized rubber, the long chains are connected across at certain points by the strong … linkages.

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4.The lengths of chain between sulphur crosslinks behave in essentially the same way as the free … molecule.

5.If a rubber band is stretched by means of a weight, it con tracts on heating owing to the effect of the increased … .

6.The rubber is crystallized by … .

7.In an ideal rubber-like substance no energy is used in separating chains and increasing their separation during … .

8.Commercial rubbers are very complex … .

Tension, stretching, thermal motion, substances, rubber, molecule, sulphur, systems

6. Retell the text using the scheme (see Un.1).

Text B

1. Match the English words and word combinations in A with their Russian equivalents in B.

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2. Read the text trying to understand its main idea.

RUBBER LATEX

Latex, before the advent of synthetic rubber, was a term applied solely to the milk of tropical plants and rubber trees which are known to yield a rubber latex, a natural emulsion of rubber particles.

Today, latex is a term also used to refer to any rubber-like polymer in emulsified form.

The rubber molecule is in the form of a very long hydrocarbon

chain.

It may have a molecular weight as high as 250,000. In natural rubber the molecules are interwined and held together by van der Waals forces to give “drops” of rubber about 3 μ in diameter. These drops are suspended in water, when first obtained from the plant, the system resembling an emulsion. Proteins, fats, soaps and other substances are present in the milky fluid, which is called “latex”.

The usual process applied to rubber latex is to add acid, usually formic, which renders the emulsion unstable and coagulates the rubber. A spongy mass is produced which is passed through rolls to squeeze out excess latex and to form a sheet of rubber. The sheet is usually “smoked” with the fumes from burning green wood, which helps to preserve the rubber. This compound is called “crepe rubber” and is the raw material for most rubber manufacture,

It is necessary, for certain purposes, to make use of the latex itself as a raw material. This necessitates two modifications to the natural latex. Firstly a preservative must be added to suppress bacterial action, which would eventually lead to coagulation. This is achieved by the addition of ammonia. This prevents the development of acidity, which is the means of causing coagulation. The second necessity is to concentrate the latex. The natural product contains only 35 per cent rubber suspended in about 60 per cent of water. Concentration may be effected by using a centrifuge, in a manner similar to the centrifuging of to give cream. It has recently been shown that the addition of konnyaku meal, which is a complex carbohydrate soluble in water, to latex is very effective in producing a rich cream of high rubber

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content. Rubber is lighter than water and hence forms a cream and not a sediment.

The creaming is done in a tank. The initial effect of the creaming agent is to cause a clustering of the rubber particles. The resulting large effective size of the units reduces their Brownian motion and increases the speed with which they rise through the liquid. Clustering differs from coagulation in that it is reversible, suitable changes being able to redisperse the particles. This is of importance since coagulation would prevent the use of latex for special methods of manufacture. Soon after the addition of the creaming agent to the tank, a very deep cream layer is formed, which is built of clusters linked together, with water filling the spaces. Water then passes out of the cream layer, the lower boundary line gradually ascending. After about four days the liquid may be run off from valve A and the latex cream from valve B. Proteins and swollen meal particles may then be centrifuged off, and the cream is stabilized with ammonia for shipment in drums.

The colloidal behaviour of latex rubber is largely the result of the protective layer of protein with which the particles are surrounded. Clustering is influenced by the action of the creaming agent on this surface layer. Coagulation occurs when the acidity is such as to render the adsorbed protein molecules electrically neutral. These facts are closely related to the protective action of proteins on gold sols.

3.Divide the text into some logical parts and entitle them.

4.Translate the following sentences into English using lexical material of the text.

1.В настоящее время синтетические каучуки широко используются как для замены натурального каучука, так и для изготовления изделий со специальными свойствами.

2.Известно, что латекс, полученный из гевеи, представляет собой дисперсию частиц каучука в воде.

3.Действие агента сливкоотделения на первой стадии

заключается в том, что он вызывает агрегацию каучуковых частиц.

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4. Агрегация, как известно, представляет собой коагуляцию, которая может быть обратима, а именно: при соответствующих условиях агрегаты глобул могут распадаться.

5. Установлено, что коагуляция по своему существу является не химическим, а физическим процессом.

6. Нагрев, замораживание, интенсивное перемешивание и т.д. относятся к внешним воздействиям, обуславливающим коагуляцию.

Text C

1.Pay attention to the following words and word combinations:

crude rubber – необработанный каучук; sulphur – сера;

melting point – температура плавления; raw rubber – сырой каучук;

extremes of temperature – резкие изменения температуры; resistance to flow under stress – сопротивляемость текучести при нагрузке;

abrasion resistance – сопротивление истиранию; resilience – эластичность;

impermeability to fluids – непроницаемость для жидкости; linear molecules – линейные молекулы;

slippage under stress – скольжение под нагрузкой; compounding – зд. наполнение (приготовление смеси); internal mixer – закрытый резиносмеситель; accelerator – ускоритель;

zinc oxide – окись цинка; fatty acid – жирная кислота; carbon black – сажа;

filler – наполнитель;

antioxidant – противоокислитель; to extrude – шприцевать;

to calender – каландровать, каландрировать;

heat and solvent resistant rubbers – каучуки, устойчивые к

перемене температуры и растворителям;

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