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Файл:Polimers. Учебное пособие по подготовке к интернет-экзамену по английскому языку
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Due to their insolubility in water and relative chemical
inertness, pure plastics generally have low toxicity in their
finished state, and will pass through the digestive system with no
ill effect (other than mechanical damage or obstruction).
However, plastics often contain a variety of toxic additives.
For example, plasticizers like adipates and phthalates are often
added to brittle plastics like polyvinyl chloride (PVC) to make
them pliable enough for use in food packaging, children's toys
and teethers, tubing, shower curtains and other items. Traces of
these chemicals can leach out of the plastic when it comes into
contact with food. Out of these concerns, the European Union has
banned the use of DEHP (di-2-ethylhexyl phthalate), the most
widely used plasticizer in PVC. Some compounds leaching from
polystyrene food containers have been found to interfere with
hormone functions and are suspected human carcinogens.
Moreover, while the finished plastic may be non-toxic, the
onomers used in its manufacture may be toxic; and small
m
amounts of those chemical may remain trapped in the product.
The World Health Organization's International Agency for
Research on Cancer (IARC) has recognized the chemical used to
make PVC, vinyl chloride, as a known human carcinogen.
[10]
Some polymers may also decompose into the monomers or other
toxic substances when heated.
The primary building block of polycarbonates, bisphenol A
(BPA), is an estrogen-like hormone disrupter that may leach into
food Research in Environmental Health Perspectives finds that
BPA leached from the lining of tin cans, dental sealants and
polycarbonate bottles can increase body weight of lab animals'
offspring.
[11]
A more recent animal study suggests that even lowlevel exposure to BPA results in insulin resistance, which can
lead to inflammation and heart disease
Bis(2-ethylhexyl) adipate, present in plastic wrap based on
PVC, is also of concern, as are the volatile organic compounds
present in new car smell.
While certain chemicals in water bottles have been found to
be strongly correlated with health problems, the belief of many
that toxic chemicals such as dioxins have been the subject of
urban legend.
Bakelite Бакелит
[по имени изобретателя - бельгийско-американского химика
Л. Бакеланда (L. Baekeland, 1863-1944)], устаревшее
техническое название резольных феноло-формальдегидных
смол, получае-мых взаимодействием фенола с
формальдегидом в присутствии щелочных катализаторов.
ASSIGNMENTS
1. Say whether the following statements true or false:
1.Plastics seldom contain a variety of toxic additives. 2.We never
use plastics in food packaging.3. Finished plastic may be nontoxic
2. Make up a short summary of the text
Theme: Elastomer
1. State to what parts of speech these words belong:
polymer, possible, elasticity althoughglass transition temperature
covalent useful directly first heated existing above
consequentially synthetic
2. Translate into Russian:
1.An elastomer is a polymer with the property of elasticity.2.
Each of the monomers is usually made of carbon, hydrogen,
oxygen and/or silicon.3. .Elastomers will have less mobile
chains.4. It is also possible for a polymer to exhibit elasticity
3. Find the nouns in the following word-groups:
glass transition temperature ,their primary uses are, the long
chains of natural rubber reconfigured chains, temperature effects
are.
Elastomer
An elastomer is a polymer with the property of elasticity.
The term, which is derived from elastic polymer, is often used
interchangeably with the term rubber, although the latter is
preferred when referring to vulcanisates. Each of the monomers
which link to form the polymer is usually made of carbon,
hydrogen, oxygen and/or silicon. Elastomers are amorphous
polymers existing above their glass transition temperature, so that
considerable segmental motion is possible. At ambient
temperatures rubbers are thus relatively soft (E~3MPa) and
deformable. Their primary uses are for seals, adhesives and
molded flexible parts..
Elastomers are usually thermosets (requiring vulcanization)
but may also be thermoplastic (see thermoplastic elastomer). The
long polymer chains cross-link during curing, i.e., vulcanizing.
The molecular structure of elastomers can be imagined as a
'spaghetti and meatball' structure, with the meatballs signifying
cross-links. The elasticity is derived from the ability of the long
chains to reconfigure themselves to distribute an applied stress.
The covalent cross-linkages ensure that the elastomer will return
to its original configuration when the stress is removed. As a
result of this extreme flexibility, elastomers can reversibly extend
from 5-700%, depending on the specific material. Without the
cross-linkages or with short, uneasily reconfigured chains, the
applied stress would result in a permanent deformation.
Temperature effects are also present in the demonstrated
elasticity of a polymer. Elastomers that have cooled to a glassy or
crystalline phase will have less mobile chains, and
consequentially less elasticity, than those manipulated at
temperatures higher than the glass transition temperature of the
polymer.
It is also possible for a polymer to exhibit elasticity that is not
due to covalent cross-links, but instead for thermodynamic
reasons.
Rubber
Natural rubber is an elastomer (an elastic hydrocarbon
polymer) that was originally derived from latex, a milky colloidal
suspension found in the sap of some plants. It is useful directly in
this form (indeed, the first appearance of rubber in Europe is cloth
waterproofed with unvulcanized latex from Brazil) but, later, in
1839, Charles Goodyear invented vulcanized rubber; this a form
of natural rubber heated with, mostly, sulfur forming cross-links
between polymer chains (vulcanization), improving elasticity and
durability.
Synthetic rubber
The first fully synthetic rubber was synthesized by Lebedev
in 1910. In World War II, supply blockades of natural rubber
from South East Asia caused a boom in development of synthetic
rubber, notably Styrene-butadiene rubber (a.k.a. Government
Rubber-Styrene). In 1941, annual production of synthetic rubber
in the U.S. was only 231 tons which increased to 840 000 tons in
1945. In the space race and nuclear arms race, Caltech researchers
experimented with using synthetic rubbers for solid fuel for
rockets. Ultimately, all large military rockets and missiles would
use synthetic rubber based solid fuels, and they would also play a
significant part in the civilian space effort.
Butyl rubber - also known as polyisobutylene and PIB
(C4H8)n is a synthetic rubber, a homopolymer of 2-methyl-1-
opene. Polyisobutylene is produced by polymerization of about
pr
98% of isobutylene with about 2% of isoprene. Structurally,
polyisobutylene resembles polypropylene, having two methyl
groups substituted on every other carbon atom. It has excellent
impermeability, and the long polyisobutylene segments of its
polymer chains give it good flex properties. Polyisobutylene is a
colorless to light yellow viscoelastic material. It is generally
odorless and tasteless, though it may exhibit a slight characteristic
odor.
The formula is: -(-CH2-C(CH3)2-)n-
It can be made from the monomer isobutylene or
CH2=C(CH3)2 only via cationic addition polymerization.
A synthetic rubber, or elastomer, polyisobutylene is
impermeable to air and used in many applications requiring an
airtight rubber. Polyisobutylene is used in making adhesives,
agricultural chemicals, fiber optic compounds, caulks and
sealants, cling film, electrical fluids, lubricants (2 cycle engine
oil), paper and pulp, personal care products, pigment
concentrates, for rubber and polymer modification, for protecting
and sealing certain equipment for use in areas where chemical
weapons are present, as a gasoline/diesel fuel additive, and even
in chewing gum. The first major application of butyl rubber was
tire inner tubes. This remains an important segment of its market
even today.
Butyl rubber was first developed by BASF in 1931 and sold
under the trade name Oppanol B. It was later developed in 1937,
by researchers William J. Sparks and Robert M. Thomas, at
Standard Oil's (which became Exxon in 1972) Linden, N.J.
laboratory. Texas Petrochemicals and Lubrizol Corporation are
one of the largest manufacturers of PIB in North America.
In 1950s and 1960s, halogenated butyl rubber (halobutyl)
was developed, in its chlorinated (chlorobutyl) and brominated
(bromobutyl) variant, providing significantly higher curing rates
and allowing covulcanization with other rubbers like natural
rubber and styrene-butadiene rubber. Halobutyl is today the most
important material for inner tubes. The butyl rubber is vulcanized
by elemental sulfur.
ASSIGNMENTS
1. Explain the meaning of the terms:
Elastomer, rubber, polymer
2. Give the English equivalents of the following:
длинные полимерные цепи, этот термин часто используется
для…., при температуре…, впервые каучук был
синтезирован…, главным образом, они использовали
синтетический каучук, играть важную роль
3. Find out key words in the text “ elestomers” and try to
retell it using these words.
4. Prepare to make a report on the theme “elestomers”.
Справочно – грамматический
материал
для подготовки
к интернет - экзамену
Предлоги
Употребление предлогов в словосочетаниях
• in the morning – утром
• in the evening – вечером
• in spring – весной
• in autumn – осенью
• in January – в январе
• in 1940 – в 1940
• in the picture – на картине
• in the street – на улице
• in the country – за городом
• in the hospital – в больнице
• in five minutes – через 5 минут
• in a week – через неделю
• in a day – через день
• in a month – через
• at home – дома
• at schoo – (н
• at 5 o'clock – в пять часов
• at the window – у окна
месяц
а работе) в школе
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