Добавил:
ivanov666
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Chemistry, technology and properties of synthetic rubber. Tutorial
.pdf
Continuation of Table 2
Butadiene-nitrile SKN-18 55%
Butadiene-nitrile SKN-26 42
Butadiene-nitrile SKN-40 25
Butadiene-nitrile SKN-50 -10 ÷ -7
Chloroprene -45 ÷ -40
Ethylene-propylene (SKEP, SKEPT) -55 ÷ -50
Butyl rubber -69 ÷ -67
Fluorine rubber SKF-26 -22 ÷ -20
Fluorine rubber SKF-32 -20 ÷ -18
Acrylate (BAC, Bakhit-7) -32 ÷ -35
Urethane SKU-7 30
Polysulfide -53 ÷ -43
Polipropilenoxide (SKPO) 75%
Despite the fact that the role of supramolecular structures in
the properties of elastomers is relatively small, the processes of
crystallization and microphase separation can affect the technological
and operational properties of materials. With increasing of
crystallinity the rigidity of the polymer increases. Therefore, the
rubbers which are able to crystallization become more rigid during
the storage, and it is necessary to melt the crystalline phase before
the processing (additional technological operation). Crystallization in
cross-linked polymers proceeds much slower than in linear ones, so it
is often possible to obtain noncrystallized rubbers on the base of
crystallizing rubbers. At the same time, tensile ability of the polymer
to crystallize leads to the effect of self-empowerment, which enables
the strength of materials. Thus, the distinction of the structure of
elastomeric chains is that the polymer crystallization should occur
only in tension.
21
1.3 Status of Synthetic Rubber Industry
Rubbers are natural or synthetic materials that are characterized by
elasticity, water resistance and electrical insulating properties, of
which the rubbers are received by special treatment. Natural rubber is
a product produced by many plants (rubber-bearing plants or rubber
gens). Rubber is produced in the form of colloidal dispersions in
water, called milky sap or natural latex.
Among the large number of rubber gens the industrial
importance has only Brazilian Hevea (Hevea brasiliensis) - a tree
native to the tropical zone of South America. Therefore, the
birthplace of natural latex and natural rubber (NR) is considered to
be Brazil. However, it was found that in Mexico, Honduras and
Guatemala, where Mayan culture once flourished, there were
widespread ball games made of flexible material, called "kaa-uchu,"
which translated from the Indian language as "tears of a tree." Their
tribes made waterproof cloth, shoes, water tanks, and various
religious figures from the same material. The Spaniards who arrived
in South America with the famous Columbus expedition (1493-1496)
have seen these items, but they were described much later. It took a
long time, almost 2.5 centuries, until scientists learned to process
rubbers into rubber and to apply these materials in technology.
With the technical and economic point of view the discovery
of NR occurred in Brazil. In Brazil wild Hevea occupies large areas
in the Amazon basin. It is a powerful tree reaching 45 m in height
and 2.5 m in diameter. There is a system of vessels in the bark of
these trees filled with milky sap (latex), and the pressure in the
vessels is up to 1 MPa. Therefore, when cutting of the bark (tapping)
the latex begins to ooze out.
There are various clones of Hevea, which productivity varies
from 20 to 200 g of rubber per day. The content of the polymer in the
latex ranges from 2 to 45% as well. Climatic conditions, land
treatment, tree age, the way of machining a cut - all these factors play
an important role.
22
At first the transportation of the gathered latex over
considerable distances was impossible because of its instability, so
up to 1853 it was coagulated on the collecting ground and
transported in the form of rubber. But after the discovery of the
stabilization methods of the latex, it became possible to transport,
that was not profitable due to the low concentration of polymer in the
latex.
At the beginning of the XIX century the first processing of
NR appeared primarily for waterproof cloths and shoes. The
discovery of the effect of mechanical mastication (T. Genkok, 1826)
and curing (Ch. Goodyear, 1839), of natural rubber laid the
foundations of the traditional technology of processing rubbers into
rubber products, which have continued generally to this day.
At the same time it was studied the structure of the NR. The
studies by M. Faraday, J. Dumas, F. Himli, J. von Liebig, J. Dalton,
G. Williams et al. (1826-1860) led to the conclusion that the
structural element of natural rubber is a hydrocarbon C5H9 called
isoprene. This conclusion was confirmed by G. Busharda who
received the rubber-like material in the processing of isoprene with
concentrated hydrochloric acid.
The researches of Russian scientists in the field of obtaining
and polymerization of unsaturated hydrocarbons had great
importance for solving the problem of synthesis of rubber. The first
was the work of A.M. Butlerov who established the possibility of
zinc and sulfuric acid polymerization of butylenes, which initiated
the study of the polymerization of unsaturated compounds. In 1878
A.A. Krakau in Russia obtained a polymer of styrene on metallic
sodium. Later L.M. Kucherov reported receiving sodium-isoprene
rubber (1908), but this information was published only in 1913.
Serious series of studies of thermal polymerization of dienes was
carried out by S.V. Lebedev, which in 1910 published his findings
and pointed out that the butadiene and dimethylbutadiene form
rubber-like substances along with oligomers upon heating.
23
At the same time it became known about the work of K.D.
Garries, received a rubber by thermal polymerization of isoprene,
and in 1913 he got such rubber in the presence of metallic sodium.
However, the quality of the rubber was poor, and therefore there was
given more attention to dimetilbutadiene rubber.
During the First World War, Germany was cut off from
markets of NR that was the reason for organizing the production of
synthetic dimethylbutadiene-based rubber. During the war, this
rubber was released at the rate of 2350 tons. However, after the war
that production was shut down, because the received rubber was too
expensive, and the rubber on its basis was significantly worse than
the rubber from the NR.
In the first half of the twentieth century, the focus of scientists
was aimed at developing methods of producing monomers that are
suitable for rubber obtaining, as well as methods of their
polymerization.
In 1910 O.G. Filippov described the butadiene production
process through the reduction of vapors of diethyl ether, and three
years later I.I. Ostromyslensky and S.S. Kelbasinsky showed the
possibility of synthesizing this monomer from ethanol and
acetaldehyde. The method was of industrial interest to the United
States and it has been used when organizing the production of
butadiene from ethyl alcohol (1942-1944). The second method of
obtaining butadiene proposed by I.I. Ostromyslensky was multistage. Initially, ethanol was converted to acetaldehyde, and the latter
through the acetaldol and 1,3-butanediol - to butadiene. This method
has been implemented in industry in Germany in 1936-1938, but
acetaldehyde was obtained by the hydration of acetylene in the
presence of sulfate salts of mercury using the method described by
L.M. Kucherov in 1881, not from alcohol.
Since 1913 B.V. Byzov conducted systematic research to find
the opportunities to use oil as a raw material for monomers. In 1916
he proposed a synthesis method of diene hydrocarbons through the
oil pyrolysis at normal and low pressure, or through the dilution of
24
the initial hydrocarbons with an inert gas. Later in the USSR there
was a pilot plant for the synthesis of butadiene according to this
method (SR Plant, letter A). In that time it was impossible to
overcome the serious difficulties connected with the organization of
industrial production of butadiene by this method. After the Second
World War, the work in this direction had been renewed. Owing to
the works of N.D. Zelinsky, A.A. Balandin and other domestic
scientists there were found the conditions and catalysts for the
dehydrogenation of hydrocarbons allowing to nearly theoretical yield
of butadiene from butylenes.
In our country, the first industrial method of the butadiene
obtaining was the catalytic decomposition of ethanol proposed by
S.V. Lebedev. This method was developed in the laboratory of
general chemistry of the Military Medical Academy (Leningrad) and
in the laboratory of oil in Leningrad State University with the
participation of his students and employees I.A. Volzhinsky, S.G.
Kibarkshtis, V.P. Krauze, Ya.M. Slobodin, A.I. Yakubchik, A.V.
Voronova and F.F. Voronov. Butadiene, obtained by this method,
was converted into butadiene rubber through the polymerization on
the metal sodium. This method was implemented in early 1931 on a
pilot plant (SR pilot plant, letter B).
The first synthetic rubber plant was started in Yaroslavl, June
15, 1932, the second plant of SR went into operation in October in
Voronezh, the third the Efremov Plant of SR began to manufacture
industrial products in July1933, the fourth the Kazan plant of SR was
implemented in 1936. Thus a new industry of chemical
manufacturing was born, which allowed the rubber industry of our
country to develop independently from the supply of the natural
rubber that played an important role in World War II.
The polymerization technology of butadiene on the sodium
catalyst has been developed under the leadership of G.G.
Koblyansky. At Yaroslavl and Voronezh plants polymerization was
carried out periodically in the liquid phase while at the Efremov and
Kazan factories it was proceed in the gas phase.
25
In 1938 in Germany polymerization of isobutylene was
commercially ran at low temperature in the presence of boron
trifluoride. This polymerization catalyst had been previously
suggested by A.M. Butlerov. Later, since 1940, in the U.S.A. R.E.
Tomas and V.J. Sparks had been published their works on the
copolymerization of isobutylene and isoprene underlying the
production of butyl rubber. This rubber was first released in1940 by
"Standard Oil Jersey" company.
Due to the work of G. Bayer, G.L. Fisher, M. Moskovits and
J.K. Patrik, each of which stroke a blow for the theory and practice
of polycondensation of dichlorderivatives and alkali metal
polysulfides, the production of polysulfide rubbers (Thiokol) started
in 1930. Soon, however, it was halted as the rubber had a strong odor
and poor quality. Later, numerous studies had been conducted to
improve the properties of these polymers, but the most interesting
were liquid Thiokol (polysulfide oligomers), not rubber-like ones. In
our country, the works on establishing of such oligomers industry
were conducted under the direction of N.P. Apuhtina. In 1957 it was
started the production of polysulfide rubbers and oligomers with
different molecular weight.
The studies of American scientists (J. Newland, etc.) on the
synthesis of chloroprene from acetylene through vinyl acetylene and
the discovery of its polymerization method allowed the U.S. to start
production of chloroprene rubber called Dupre in 1932, and it was
produced in amount of 250 tons that year.
In the Soviet Union there were successful studies of the
chloroprene synthesis and its rubber by A.L. Klebansky, I.M.
Dolgopolsky, L.G Tsurih et al. As a result of these studies the pilot
batches of polychloroprene were produced in 1934, and the industrial
production of this rubber began in Yerevan in 1940.
In 1922 in Germany (the company "IG Farbenindustrie")
there was extensive research on the synthesis of rubber based on
butadiene. G. Ebert developed two types of rubber (Buna 85 and
Buna 115) for the industry, obtained by polymerization of butadiene
26
on the metallic sodium. For a number of significant problems of this
method of polymerization, even in 20-30 years "IG Farbenindustrie"
company received numerous patents for carrying out the
polymerization of dienes in emulsion. (the "Bayer" company was the
first one which patented an emulsion polymerization in 1912).
Simultaneously, the copolymerization of butadiene with other
monomers was studied. As a result there had been developed
emulsion styrene-butadiene and butadiene-nitrile rubbers (Buna S
and Buna N, respectively), received at a pilot plant since1934.
In the Soviet Union the work on emulsion polymerization was
carried out under the direction of B.A. Dolgoplosk, who proposed the
redox systems for initiating the polymerization of butadiene. Famous
Soviet scientists as S.S. Medvedev, H.S. Bagdasaryan, A.D Abkin,
A.I. Yurzhenko, P.M. Homikovsky, etc. made an invaluable
contribution to developing ways to initiate radical polymerization
and studying the mechanism of emulsion.
During the Great Patriotic War the leading scientists of our
country were keeping up developing the processes of petroleum
monomers production for synthetic rubber. In 1941-1945 it was first
established the possibility of copolymerization of α-methylstyrene
with butadiene (butadiene-α-methylstyrene rubbers). Commercially
synthesis of such rubbers had been implemented in the SR plant after
the war.
Center for the basic researches on the synthesis of elastomers
was all-USSR S.V. Lebedev Scientific Research Institute of
Synthetic Rubber (VNIISK) organized in 1945 in Leningrad.
After the release of our country temporarily occupied by Germans,
the Voronezh and Efremov Synthetic Rubber Plants were restored,
and in 1948 the pre-war level of rubber production was reached.
Simultaneously, retooling and modernization of the existing SR
plants were conducted. Particularly, the Voronezh plant was
renovated and enlarged, where for the first time in the country the
emulsion styrene-butadiene rubbers were received. Due to the rapid
development of economy and increasing demand for the synthetic
27
rubber such new SR plants as Sterlitamak, Nizhnekamsk, Togliatti,
Krasnoyarsk, Volzhsk and Omsk were put into operation in the late
50s and early 60s. During construction there were used the most
advanced methods for monomers production (mostly petroleumbased monomers) and new processes of radical and ion-coordination
polymerization.
In 1953-54 a revolutionary event took place in the field of
polymerization (including the synthesis of rubber) - there were
catalytic systems, allowing to obtain stereoregular polymers. Such
catalysts were discovered by German scientist K. Ziegler and studied
in details by the Italian chemist G. Natta, so they are called by the
names of two researchers. With the use of Ziegler-Natta catalysts it
was possible to obtain the synthetic 1,4-cis-polyisoprene, identical in
structure and approaching the properties of natural rubber. The
development of research in the field of stereospecific polymerization
and industrial development of isoprene, butadiene, ethylenepropylene and other rubbers became rapid. In our country, the
research in this area was carried out under the direction of A.A.
Korotkov (1948-1953), as well as B.A. Dolgoplosk and his numerous
students and staff.
In 1960 the "Shell" company in California started the first
stereospecific polyisoprene production plant. Commercialization of
the rubber was growing rapidly, and in the seventies of last century
the United States had produced 140 tons already, Western Europe 150 tons, Japan - about 90 tons of stereoregular isoprene rubber.
However, the largest volume of production of 1,4-cis-polyisoprene
reached in the Soviet Union - about 800 tons per year. Such large
production volumes of isoprene rubber in our country are related to
the tendency to avoid the import of the NR, to preserve the economic
independence of the country and fully provide the mechanical
engineering with rubber products of necessary quality.
Currently in the United States and Western Europe the tire
rubber is composed of NR from 40 to 55%, while in the tire industry
28
of Russia its part does not exceed 1% of the total volume of the used
elastomers.
In the postwar years, Malaysia had been long led in the
production of NR, where the peak production was reached in 1988
(1.66 million tons), but it has been producing only about 20% of the
world's NR as yet. In the 90's of Twentieth century, Thailand became
the largest producer of NR (1.79 million tons in 1995, 2.24 million
tons in 2000). Still a lot of natural rubber is produced in Indonesia;
its production is rapidly growing in India, China, Vietnam and other
countries.
Amid the energy crisis and the oil reserve depletion the
production of NR acquires special significance. It should be noted
that the energy intensity of NR production is only 10% of styrene
butadiene synthetic rubber energy use. The environmental aspects of
the problem are also important: a small impact on the environment
when receiving the NR and sustainability of vegetable raw materials.
Table 3 shows the synthetic rubber production capacity in various
regions of the world in 2004.
Table 3.
The SR production capacity in 2004
Regions and countries Th. tonnes Total
production share, %
Russia 1598 12.9.
North America 2494 21
Western Europe 1854 15
Asia and Oceania 3835 32
Central Europe and the CIS 1787 15
China 1087 9
Latin America 658 6
Middle East and Africa 145 1
Modern, developing and increasingly complex technology
requires various properties and high-quality rubbers, which would
29
not dissolve in oils and gasoline, withstand high and low
temperatures, show resistance to oxidants and various corrosive
mediums. In this regard, the research works on the modification of
rubbers and rubber based on them gain in contemporary importance.
Rubber-based rubber tires are made for vehicles, aircraft,
farm equipment, bicycles, various industrial, household and medical
rubber products; rubbers are used for electrical insulation, as well as
construction equipment. The main rubber consumers are the tire
industry and the manufacturing of various industrial rubber products.
Rubbers accounts for more than 50% of all the materials used for
tires manufacturing. The range of industrial rubber products
produced in our country exceeds 100 thousand items. To complete a
modern car it is necessary to have 300-500 rubber products on the
average (KamAZ has about 800 components). One plane contains 10
000-12 000, and the ship - up to 30 000 rubber products.
The output characteristics of rubber and tires in the most
depend on the nature and quality of rubbers used for their
manufacturing. In the world rubber tire manufacture 30% of the total
amount of used rubber accounts for natural rubber (NR). For the
necessity of a significant import relief of NR Russia turned out the
world's leading producer of synthetic 1,4-cis-isoprene rubber, the
natural rubber counterpart.
In terms of production volume synthetic polyisoprene
occupies the first position in Russia, and its share now accounts for
about 37% of the total production volume of SR. In the world the
main type of producible synthetic rubber is general purpose
butadiene-styrene rubber (BSR) which accounts for 58% of industrial
capacities of SR. In our country, BSR production volumes occupy
the second position and account for 25%, while butadiene rubber
accounts for about 13% of the total production of SR, and butyl
rubber - 11%.
In 2005 total production volume of synthetic rubber in Russia
total a little over 1.1 million tons. Table 4 presents some types of
30
Соседние файлы в предмете [НЕСОРТИРОВАННОЕ]