The purpose of the lesson: to familiarize students with the structure, properties and use of rubber, to create conditions for the development of the ability to independently acquire knowledge using various sources of information, to develop experience in creative activities, to cultivate interest in the history of chemistry, a sense of patriotism, pride in Russian scientists, to develop students’ ability to conduct experiments of a research nature, analyze the results, form conclusions and generalizations.
During the classes
To work in class, students are divided into groups, each of which receives a specific task on the topic of the lesson.
This story began from the time of the Great Geographical Discoveries. When Columbus returned to Spain, he brought back many wonders from the New World. One of them was an elastic ball made of “wood resin”, which was distinguished by amazing jumping ability. The Indians made such balls from the white sap of the Hevea plant, which grows on the banks of the Amazon. This juice darkened and hardened in the air. Balls were considered sacred and were used in religious ceremonies. The Mayan and Aztec tribes had a religious game - a team game using them, reminiscent of basketball. The winning team was given the highest honors - its members had their heads cut off and sacrificed to the deity. Subsequently, the Spaniards fell in love with playing with balls brought from South America. The Indian game they modified served as the prototype of modern football. The Indians called the juice of the Hevea “caucho” - the tears of the milky tree (“kau” - tree, “uchu” - flow, cry). From this word the modern name of the material was formed - rubber. In addition to elastic balls, the Indians made impenetrable fabrics, shoes, water vessels, and brightly colored balls - children's toys - from rubber.
Home experiment for group No. 1:
“Obtaining rubber from ficus leaves.”
Equipment: test tubes, scalpel, glass slide, alcohol lamp, matches, crucible tongs, glass rod, 5% ammonia solution, dilute potassium permanganate solution, 5% acetic acid, ethanol, calcium sulfate crystals, distilled water, bromine water, gasoline, toluene, ficus leaves.
Progress of the experiment: The houseplant is ficus, its juice contains up to 17.5% polyisoprene.
Experience No. 1. Collect ficus leaves. Make a cut on the ficus leaf and collect the milky sap with a cotton swab moistened with ammonia solution into a test tube. Add the acetic acid solution to the test tube and shake well. Observe the release of flakes, which are natural rubber. Apply milky juice from ficus leaves onto a glass slide and warm it up. A film of natural rubber is formed.
Experience No. 2. Collect the juice from the ficus leaves in a test tube, add a little distilled water and 0.5 g of crystalline calcium sulfate (or ammonium sulfate). After stirring the mixture and adding ethanol to it, rubber flakes form on the surface of the solution. To collect rubber, use a glass rod and transfer the flakes into a test tube with small amounts of different solvents: gasoline, toluene. What are you observing?
Experience No. 3. Divide one of the rubber solutions into two parts and alternately add bromine water or a solution of potassium permanganate to one of them. Discoloration of colored solutions indicates the presence of multiple bonds in the molecules of the isolated sample from ficus juice. Carefully evaporate the other part of the rubber solution on a watch glass. After removing the solvent, a film of rubber will remain on the glass, which can be slightly stretched to demonstrate elasticity. Compare with the film obtained in experiment No. 1.
Summarize your observations about the properties of the substance isolated from ficus juice. What class of compounds does it belong to? Prepare a presentation based on the results of the experiment ( Annex 1).
In Europe, they forgot about the South American curiosity until the 18th century, when members of a French expedition in South America discovered a tree emitting an amazing air-hardening resin, which was given the name “rubber” (in Latin, resin). In 1738, the French researcher C. Condamine presented samples of rubber, products made from it and a description of extraction methods in South America at the Paris Academy of Sciences. Since then, the search began for possible ways to use this substance. And after 1823, when the Scotsman C. Mackintosh came up with the idea of laying a thin layer of rubber between two pieces of fabric, a real “rubber boom” began. Waterproof raincoats made of this fabric, which began to be called “mackintoshes” in honor of their creator, became widespread. Around the same time, it became fashionable in America to wear clumsy Indian rubber shoes - galoshes - over boots in rainy weather.
Experiment for group No. 2:
“The relationship of rubber and rubber to solvents.”
Equipment: test tubes with stoppers, rubber samples, gasoline, kerosene, toluene.
Procedure of the experiment: Pour 3-4 ml of gasoline, kerosene, and toluene into test tubes. Place pieces of rubber in test tubes. Close the test tubes and observe them for the rest of the lesson. Compare the behavior of rubber and rubber in organic solvents. Why doesn't rubber dissolve under the same conditions as rubber? (Research results: rubber dissolves in organic solvents, forming a viscous liquid (rubber glue), and the pieces of rubber are slightly swollen, but do not change their shape).
Rubber products gained enormous, albeit short-lived, popularity in Europe and North America after the Englishman Chaffee invented rubberized fabric. He dissolved raw rubber in turpentine, added carbon black and, using a specially designed machine, applied a thin layer of the mixture to the fabric. Not only clothes, shoes and hats were made from such material, but also the roofs of houses and vans. However, products made from rubberized fabric had a big drawback. The fact is that the elasticity of rubber manifests itself only in a small temperature range, so in cold weather rubber products hardened and could crack, and in the summer they softened, turning into a sticky, stinking mass. Enthusiasm for the new material quickly faded. And when one day there was a hot summer in North America, a crisis occurred in the rubber industry - all products turned into a vile-smelling jelly. Rubber companies went bankrupt.
Experiment for group No. 3:
“Relation of rubber and rubber to heat.”
Equipment: water bath (T=100 0 C), crucible tongs or tweezers, thin strips of rubber.
Procedure of the experiment: Place a thin strip of natural rubber and a strip of rubber of the same size in boiling water for 5 minutes. Using crucible tongs, remove a strip of rubber and quickly stretch it. Do the same with the rubber strip. Rubber stretches greatly as a result of softening, losing its elasticity, while rubber does not show any change. Rubber is thermoplastic, rubber is not. Rubber is characterized by greater thermal resistance compared to rubber. How can we explain the different attitudes of rubber and rubber to heat?
And everyone would have forgotten about mackintoshes and galoshes if it weren’t for the American Charles Nelson Goodyear, who sincerely believed that good material could be created from rubber. He devoted several years to this idea and spent all his savings. Contemporaries laughed at him: “If you see a man in a rubber coat, rubber boots, a rubber top hat and a rubber wallet, and there is not a single cent in the wallet, then you can be sure that this is Goodyear.” However, Charles Goodyear persistently mixed rubber with everything: salt, pepper, sand, oil and even soup and, in the end, achieved success. In 1839, he discovered that if you add a little sulfur to rubber and heat it, its strength, hardness, elasticity, heat and frost resistance will improve. Currently, it is the new material invented by Charles Goodyear that is commonly called rubber, and the process he discovered is called rubber vulcanization. From this time on, rapid growth in rubber production began.
Experiment for group No. 4:
“Getting rubber.”
Equipment: test tubes, test tube holder, heating devices, rubber, sulfur powder, glass rod, glass of water.
Procedure of the experiment: Place a small piece of rubber in a test tube, add a little powdered sulfur, heat the resulting mixture until the sulfur melts, stir with a glass rod, then cool. The resulting material will be harder and more durable than the original raw material. During the reaction, the rubber vulcanized and rubber was obtained. Check the resulting rubber sample for elasticity, exposure to high and low temperatures. Draw a conclusion about the physical properties of rubber. (Rubber has better mechanical properties than rubber and greater resistance to temperature changes).
It is not surprising that Brazil guarded the source of its wealth like the apple of its eye. The export of Hevea seeds was prohibited under penalty of death. However, in 1876, the British spy Henry Wickham secretly removed 70,000 Hevea seeds from the holds of the English ship Amazonas. The first rubber plantations were established in the British colonies of Southeast Asia. Natural English rubber has appeared on the world market, cheaper than Brazilian rubber.
And the world was conquered by a variety of rubber products. Surprisingly, the invention of rubber tires instead of metal ones was not met with enthusiasm at first, although crews with metal tires were not very comfortable - in England they were called “sparrow fighters” because of the terrible noise and shaking. New quiet carriages with solid solid rubber tires were banned in America. They were considered dangerous because they did not warn passers-by about the approach of the crew. In Russia, quiet horse-drawn carriages running on rubber also caused discontent - they threw mud at pedestrians who did not have time to hurry.
Experiment for group No. 5:
“The Unsaturated Character of Rubber.”
Equipment: test tubes, natural rubber, gasoline purified from unsaturated hydrocarbons, potassium permanganate solution, bromine or iodine water. (Note: at least 24 hours in advance, dissolve the pieces of rubber in one of the organic solvents - gasoline).
Procedure of the experiment: Add a few drops of a pre-prepared rubber solution to a test tube with a solution of potassium permanganate and bromine (iodine) water and shake. Observe the color change. Why does a rubber solution change the color of solutions of bromine water or potassium permanganate?
With the invention of the conveyor method of assembling cars, the need for rubber became so great that the problem of limited production of natural raw materials urgently arose. It was necessary to look for other sources of rubber. At the end of the 19th – first half of the 20th centuries, extensive research was carried out in many countries on the structure of rubber, its physical and chemical properties, the phenomenon of elasticity, and the vulcanization process. G. Staudinger proved that rubber is a high-molecular compound, that is, it consists of ordinary, albeit giant molecules, the atoms of which are connected by covalent bonds. Based on his studies of rubber and rubber, the scientist put forward a theory of the chain structure of macromolecules and suggested the existence of branched macromolecules and a three-dimensional polymer network.
Natural rubber contains 91–95% polyisoprene hydrocarbon (C 5 H 8) n. A natural rubber molecule can contain 20–40 thousand elementary units, its molecular weight is 1,400,000–2,600,000, it is insoluble in water, but it dissolves well in most organic solvents.
Task for group No. 6.
Find the molecular formula of a substance that, when burned 2 g, produces 2.12 g of water and 6.48 g of carbon dioxide. The relative vapor density of this substance with respect to hydrogen is 34. Write down the structural formula of this substance and all its possible isomers.
Natural rubber polyisoprene is a stereoregular polymer: almost all (98-100%) isoprene units in the macromolecule are attached to each other in the cis-1,4 position. The natural geometric isomer of rubber, gutta-percha, is trans-1,4-polyisoprene. Differences in the spatial arrangement of substituents in rubber and gutta-percha lead to the fact that the shape of the macromolecules of these substances is also different. Rubber molecules are twisted into balls. If a rubber tape is stretched and deformed, then the molecular coils will straighten in the direction in which the deformation is applied, and the tape will lengthen. However, it is energetically more favorable for rubber molecules to be in their original state, therefore, if the tension is stopped, the molecules will roll up into balls again, and the dimensions of the tape will become the same. Gutta-percha molecules are not curled into balls like those of rubber. They are elongated even in the absence of loads. Therefore, gutta-percha has much less elasticity.
What happens to rubber during vulcanization? When rubber is heated with sulfur, the macromolecules of the rubber are “cross-linked” to each other by sulfur bridges. A single three-dimensional spatial network is formed from individual rubber macromolecules. A product made of such a material - rubber - is stronger than rubber, and it retains its elasticity over a wider temperature range.
Experiment for group No. 7:
“Rubber decomposition.”
Equipment: test tubes, test tube with side tube, gas outlet tubes with stoppers, natural rubber, diluted solution of potassium permanganate.
Procedure of the experiment: place pieces of natural rubber in a test tube with a gas outlet tube. When rubber is heated, unsaturated compounds are formed, among which isoprene. Liquid reaction products are condensed in test tube No. 1, and gaseous products are collected in test tube No. 2. Decomposition is accompanied by the formation of substances that have a pungent odor! Discoloration of the potassium permanganate solution in test tube No. 2 indicates the unsaturated nature of the decomposition products of rubber. Investigate the ratio of condensate to potassium permanganate solution. Write an equation for the reaction between isoprene and bromine.
Rice. 1. Device diagram.
Interestingly, in many countries at the beginning of the 20th century, studies were carried out on local plant species for rubber formation. In the Soviet Union, a systematic search for rubber plants was undertaken in the 30s; the total list of such plants amounted to 903 species. The most effective rubber plants, in particular the Tien Shan dandelion kok-sagyz, were grown in the fields of Russia, Ukraine, and Kazakhstan; factories were operating to produce rubber, which was considered to be of equal quality to rubber from Hevea. At the end of the 50s, with the increase in the production of synthetic rubber, the cultivation of rubber dandelion was stopped.
The rubber-like substance was first obtained in 1879 by the French chemist G. Bouchard by treating isoprene with hydrochloric acid. Russian chemist I. Kondakov (Yuryev) synthesized an elastic polymer from dimethylbutadiene in 1901. The first industrial batches of synthetic rubber - dimethyl rubber - were produced based on Kondakov's developments in 1916 in Germany. About 3,000 tons of synthetic rubber were obtained, from which battery boxes for submarines were made. However, dimethyl rubber did not become widespread, and its production was discontinued.
Task for group No. 8.
Prepare a presentation about S.V. Lebedev. (Appendix 2.)
The Russian scientist S.V. Lebedev devoted a significant part of his scientific activity to the problem of polymerization of dienes. He first produced synthetic butadiene rubber in 1910. And Lebedev’s master’s thesis, devoted to the study of the kinetics of polymerization of divinyl (butadiene –1,3) and its derivatives, was awarded a prize from the Russian Academy of Sciences in 1914. S. V. Lebedev returned to the process of butadiene polymerization in 1936, when the USSR government announced a competition for the best development of industrial production of synthetic rubber. Lebedev and his collaborators successfully developed an inexpensive and effective method. It was proposed to use sodium metal as a catalyst, and the polymer obtained by this method is called sodium butadiene rubber. The real discovery was a one-step method for producing butadiene from ethyl alcohol using a mixed zinc-aluminum catalyst. The use of ethanol from plant raw materials as a starting product significantly reduced the cost of production in the conditions of the agricultural Soviet Union at that time. Thanks to the work of S.V. Lebedev, the industrial large-scale production of synthetic rubber began for the first time in the world in the Soviet Union in 1932. The world's first plant for the production of divinyl rubber was launched in Yaroslavl, and soon such plants began operating in Voronezh, Kazan and Efremov. The significance of this event is difficult to overestimate: the ability to equip domestic equipment with tires of our own production played an important role in the victory over Nazi Germany in conditions of complete economic isolation from the outside world. Germany was the second country to launch the production of synthetic rubber, but this happened only in 1936.
Task for group No. 9.
Prepare a presentation about JSC Voronezhsintezkauchuk. (Appendix 3.)
From 1932 until 1990, the USSR ranked first in the world in terms of production volumes of synthetic rubber. And today Russia maintains its position as an exporter of global importance. About half of the production remains on the domestic market. The main consumers of synthetic rubber are tire factories, and about 40% of rubber is used for the production of various rubber products (more than 50,000 items), including technical and surgical products made of soft rubber, shoe soles, conveyor belts, various pipes and hoses of all types, electrical insulation , adhesives, sealants, latex-based paints and much more. With the advent of synthetic rubber technology, the rubber industry has ceased to be entirely dependent on the production of natural rubber. However, synthetic rubber has not replaced natural rubber, the volume of rubber production is still increasing, and the share of natural rubber in the total production volume is 30%. The world's leading producers of natural rubber are currently the countries of Southeast Asia - Thailand, Indonesia, Malaysia, South Vietnam, China. Due to the unique properties of natural rubber, it is indispensable in the production of large tires that can withstand loads of up to 75 tons. The best manufacturing companies make tires for passenger car tires from a mixture of natural and synthetic rubber. Therefore, the main area of application of natural rubber remains the tire industry (70%). In addition, natural rubber is used for the manufacture of high-power conveyor belts, anti-corrosion coatings for boilers and pipes, glue, thin-walled high-strength small products, in medicine, and so on.
At the end of the lesson, we listen to reports on the work of each group and formulate conclusions about the lesson. During the lesson, students found out that the role of natural and synthetic rubber in our lives is great. Rubber is used in the production of automobile and aviation products, as well as in the production of consumer goods (shoes, sporting goods, toys). When studying the chemical properties of natural rubber, it turned out that it has multiple bonds in the polymer chain; it was found that rubber has a cis-form and is
2-methylbutadiene-1,3 (isoprene). Vulcanized rubber is called rubber. Students also became acquainted with rubber plants and methods for obtaining natural rubber from them and continued to develop their theoretical and practical skills.
Presentations are attached to the article (Appendix, ,).
Bibliography:
- Magazine “Potential. Chemistry. Biology. Medicine” Moscow publishing house. LLC “Azbuka-2000” 2011, article by E. A. Mendeleev “History about rubber” pp. 9–14.
- O. S. Gabrielyan, L. P. Vatlina “Chemical experiment at school”, Moscow “Drofa” 2005.
- A. I. Artemenko “The Amazing World of Organic Chemistry”, Moscow “Drofa” 2008.
Action of halogens
In the process of contact of natural rubber with halogens, along with the addition of a halogen via a double bond, the process of replacing hydrogen begins with the formation of hydrogen chloride.
Chlorination of natural rubber is carried out by passing chlorine through a solution of rubber in tetrachloride carbon or when rubber comes into contact with chlorine under pressure. Chlorination occurs after the formation of a number of intermediate products. The final product of chlorination in tetrachloride carbon is high molecular weight a compound with a cyclic structure called chlorinated rubber. This saturated product is the result of chlorine addition, chlorine substitution of hydrogen, and cyclization.
Chlorinated rubber is easily soluble in all natural rubber solvents, with the exception of gasoline. Its solutions have almost the same viscosity as solutions original rubber, therefore, chlorination does not lead to noticeable rupture of macromolecules and a decrease in molecular weight. Typically, chlorinated rubber is obtained both in the form of white powder and transparent films. At a temperature close to 70 °C it softens, turning into a soft and elastic state, at 180-200 °C it decomposes with the formation of chlorine.
Being a saturated compound, chlorinated rubber has relatively high chemical resistance: It is resistant to acids, salts and alkalis. It is used in the process of making various paints, anti-corrosion coatings and refractories, and is also the basis of a composition for fastening rubber elements to metal surfaces.
Chlorination of synthetic butadiene and butadiene styrene rubbers in a solution of carbon tetrachloride occurs mainly through double bonds and is accompanied by cross-linking of macromolecules; In this case, almost no cyclization is observed. The products of partial chlorination of these rubbers, containing up to 35% chlorine, can be vulcanized with sulfur and metal oxides to form unfilled vulcanizates with a tensile strength of up to 13 MPa (130 kgf/cm2). The maximum chlorine content in the products of chlorination of styrene-butadiene rubber is 53%, and in the products of chlorination of butadiene rubber 65-71%. These products are characterized by high chemical resistance.
By chlorinating nairite in dichloroethane or chloroform one obtains chlornairitis containing 68% chlorine, which corresponds to the formula (C4H5CI3) P. Chlornairite is used for the manufacture of adhesives used for attaching rubber to metals during the vulcanization process of rubber-metal products.
When natural rubber interacts with bromine in the cold, bromine joins at the site of the double bond to form rubber dibromide, a high-molecular compound with the composition (C5H 8 Br 2)n. This reaction is used in practice for the quantitative determination of rubber in mixtures with other substances. Dibromide is relatively unstable; at temperatures above 60 °C, its decomposition occurs.
When natural rubber interacts with iodine and fluorine, rubber oxidation occurs simultaneously. Only under special conditions is it possible to obtain high-molecular-weight products of interaction with iodine and fluorine, similar to dibromide.
Effect of sulfuric acid and sulfates
When natural rubber is exposed to sulfuric acid and sulfonic acids, so-called thermoprenes. Depending on the production conditions and the amount of acid taken, thermoprenes of different hardness can be obtained. All thermoprenes are thermoplastic, that is, they can soften when heated.
Some thermoprenes in the form of glue are used for attaching rubber to the surface of metal and wood, when lining the surface of metal equipment (gumming).
The chemical process for producing thermoprene uses non-volatile sulfonic acids that are more evenly distributed in the rubber. This process is carried out by mixing n-Toluenesulfonic acid in an amount of 8-9% with isoprene rubber on calenders, and further heating the resulting mixture to a temperature close to 140 ° C for 3 hours. After the end of the heat treatment, the resulting mixture is washed on rollers, thereby removing acids with further drying of the resulting substance.
When thermoprenes are formed, rubber cyclization occurs as a result of the interaction of adjacent double bonds. The composition of thermoprene approaches the formula (C 5 H 8)n, which indicates that the acid does not attach to the rubber, but only causes a change in its molecular structure, while the number of double bonds in the molecules decreases by almost 2-2.5 times.
Thermoprenes are soluble in the same solvents as rubber.
The viscosity of thermoprene solutions is significantly lower than the viscosity of solutions of the original rubber, which indicates a decrease in molecular weight under the influence of sulfonic acids. Thermoprenes are capable of being vulcanized by sulfur, like the original rubber, by adding halogens and hydrogen halides.
Synthetic cis- 1,4-polyisoprene reacts with sulfonic acids, and cyclization occurs with the formation of products that have a structure similar to the structure of the products of the interaction of natural rubber with sulfonic acids.
Oxidation of rubbers
Oxidation is the main reason for the aging of rubber, as a result of which their physical, mechanical and technological properties deteriorate. The interaction of rubber with oxygen is very significant when carrying out a number of technological processes, such as plasticization, vulcanization and regeneration, leading to changes in the properties of rubber.
The products of rubber oxidation are both volatile and non-volatile compounds. In the mixture of highly volatile products of the oxidation reaction of natural rubber, the following were found: carbon dioxide, water and hydrogen, hydrogen peroxide, formaldehyde. The volatile oxidation products of butadiene rubber include water, formaldehyde, and formic acid.
In non-volatile oxidation products, oxygen is contained in functional groups.
When oxidized, rubbers can absorb significant amounts of oxygen. It has become known that natural rubber absorbs up to 30% oxygen during the oxidation process.
Crude rubber, intended for subsequent industrial use, is a dense amorphous elastic material with a specific gravity of 0.91-0.92 g/cm? and a refractive index of 1.5191. Its composition varies among different latexes and plantation preparation methods. The results of a typical analysis are presented in the table.
Rubber hydrocarbon is polyisoprene, a hydrocarbon polymer chemical compound having the general formula (C5H8)n. Exactly how rubber hydrocarbons are synthesized in wood is unknown. Unvulcanized rubber becomes soft and sticky in warm weather and brittle in cold weather. When heated above 180°C in the absence of air, rubber decomposes and releases isoprene. Rubber belongs to the class of unsaturated organic compounds that exhibit significant chemical activity when interacting with other reactive substances. Thus, it reacts with hydrochloric acid to form rubber hydrochloride, and also with chlorine by addition and substitution mechanisms to form chlorinated rubber. Atmospheric oxygen acts on rubber slowly, making it hard and brittle; ozone does the same thing faster. Strong oxidizing agents, such as nitric acid, potassium permanganate and hydrogen peroxide, oxidize rubber. It is resistant to alkalis and moderately strong acids. Rubber also reacts with hydrogen, sulfur, sulfuric acid, sulfonic acids, nitrogen oxides and many other reactive compounds, forming derivatives, some of which have industrial applications. Rubber is insoluble in water, alcohol or acetone, but swells and dissolves in benzene, toluene, gasoline, carbon disulfide, turpentine, chloroform, carbon tetrachloride and other halogenated solvents, forming a viscous mass used as an adhesive. Rubber hydrocarbon is present in latex in the form of a suspension of tiny particles, the size of which ranges from 0.1 to 0.5 microns. The largest particles are visible through an ultramicroscope; they are in a state of continuous motion, which can illustrate a phenomenon called Brownian motion. Each rubber particle carries a negative charge. If a current is passed through the latex, then such particles will move to the positive electrode (anode) and be deposited on it. This phenomenon is used in industry to coat metal objects. On the surface of rubber particles there are adsorbed proteins that prevent the latex particles from approaching each other and their coagulation. By replacing the substance adsorbed on the surface of the particle, you can change the sign of its charge, and then rubber particles will be deposited on the cathode. Rubber has two important properties that determine its industrial use. In the vulcanized state, it is elastic and, after stretching, returns to its original shape; in the unvulcanized state it is plastic, i.e. flows under the influence of heat or pressure. One property of rubbers is unique: when stretched, they heat up, and when compressed, they cool. Instead, rubber contracts when heated and expands when cooled, demonstrating a phenomenon called the Joule effect. When stretched by several hundred percent, the rubber molecules are oriented to such an extent that its fibers give an X-ray pattern characteristic of a crystal. The molecules of rubber extracted from Hevea have a cis configuration, while the molecules of balata and gutta percha have a trans configuration. Being a poor conductor of electricity, rubber is also used as an electrical insulator.
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Rubber solutions are characterized by high viscosity and other characteristic properties of polymer solutions. The colloidal properties of rubber solutions are explained by the significant size of the rubber molecules and micelles present in the solution. The viscosity of rubber solutions increases noticeably with increasing concentration and decreasing temperature. The destruction of rubber leads to a decrease in the viscosity of adhesives.
A solution of rubber in decalin was placed in an ozonizer-type device, consisting of two tubes nested one inside the other, and was subjected to a discharge from an alternating current of 4500 volts.
Rubber solutions, or, as technologists call them, rubber adhesives, are widely used in various fields of industry. Therefore, the study of their properties is of direct technological interest. At the same time, these solutions have a number of very characteristic properties, the study of which is of particular importance for the study of rubber, structure, technical qualities, natural and technological changes in it. Nowhere are the structural features of rubber reflected so subtly and sensitively as in the properties of its solutions. To know the properties of rubber solutions means to a large extent to know the properties and structural features of the rubber itself.
The rubber solution is fed into the apparatus and spread over its walls by a rotor. The gap between the housing and the rotor blades is 1 - 3 mm. It is necessary to strive for a minimum gap, but the difficulty of centering the rotor and the inability to maintain the correct cylindrical shape of the housing during its welding and assembly make it necessary to work with a relatively large gap. The rubber is heated by silent steam through the wall of the apparatus. To speed up the degassing process, the device operates under vacuum.
A rubber solution obtained by infusing natural rubber in gasoline or benzene.
| Kinetics of rubber swelling. |
Rubber solutions are characterized by high viscosity and other characteristic properties of polymer solutions. The colloidal properties of rubber solutions are explained by the significant size of the rubber molecules and micelles present in the solution. The viscosity of rubber solutions increases noticeably with increasing concentration and decreasing temperature. The destruction of rubber leads to a decrease in the viscosity of adhesives.
Solutions of sodium butadiene, butadiene-styrene and buta-diene-nitrile rubbers in xylene or solvent naphtha are varnishes that, after drying at 150 - 170, form a very hard, elastic film of golden color on metals, satisfactorily protecting metal products from atmospheric corrosion. When 3-5% cobalt linoleate or another drying agent is added to a solution of sodium butadium rubber, colorless varnish films are cured at room temperature in 1-2 days.
If a rubber solution is subjected to ultraviolet irradiation in the presence of oxygen, then a sharp decrease in the minimum surface tension and its shift to the region of higher concentrations is observed. On the other hand, when § is irradiated in an inert gas atmosphere, the surface tension isotherm § remains almost unchanged, while the viscosity drops sharply.
Next, the rubber solution, which already has a high viscosity, passes through a series of tubular sections, in the intertubular space of which the refrigerant circulates. In the tubes of each section, the solution moves in laminar mode, as a result of which a temperature gradient is established along the radius of the tubes. When moving to the next section, the layers of the solution are mixed and the temperature is averaged.
Chlorine gas is passed through a rubber solution located in an enameled reactor equipped with refrigerators. Carbon tetrachloride is returned from the reflux condenser to the reactor, and excess chlorine and the resulting hydrochloric acid volatilize. Hydrochloric acid is absorbed in absorbers made of tantalum. After chlorination is completed, the solution is transferred to a storage tank lined with acid-resistant bricks. The solution is then pumped into a tank of hot water, where the chlorinated rubber falls out of solution. The precipitate is thoroughly washed and then dried. Below it will be shown that there are four grades of this product, differing in viscosity. When rubber is chlorinated, both addition and substitution reactions occur. The rubber chlorination product acquires maximum stability, acid and alkali resistance, as well as non-flammability only with a high chlorine content.