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Файл:Chemistry, technology and properties of synthetic rubber. Tutorial
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pigmentconcentrates, 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
tireinner tubes. This remains an important segment of its market even
today.
Fuel and lubricant additive
Polyisobutylene (in the form of polyisobutylene succinimide,
PIBSI) has interesting properties when used as an additive in
lubricating oils and motor fuels. Polyisobutylene added in small
amounts to the lubricating oils used in machining results in a
significant reduction in the generation of oil mist and thus reduces
the operator's inhalation of oil mist. It is also used to clean up
waterborne oil spills. When added to crude oil it increases the oil's
viscoelasticity when pulled, causing the oil to resist breakup when it
is vacuumed from the surface of the water.
As a fuel additive, polyisobutylene has detergent properties.
When added to diesel fuel, it resists fouling of fuel injectors, leading
to reduced hydrocarbon and particulate emissions. It is blended with
other detergents and additives to make a "detergent package" that is
added to gasoline and diesel fuel to resist buildup of deposits and
engine knock.
Polyisobutylene is used in some formulations as a thickening
agent.
Explosives
Polyisobutylene is often used by the explosives industry as a
binding agent in plastic explosives such as C-4. Polyisobutylene
binder is used because it makes the explosive more insensitive to
premature detonation as well as making it easier to handle and mold.
Sporting equipment
Butyl rubber is used for the bladders in sporting balls to
provide a tough, airtight inner compartment.
Roof Repair
111
Butyl rubber sealant is used for rubber roof repair and for
maintenance of roof membranes. It is important to have the roof
membrane fixed, as a lot of fixtures (i.e., air conditioner vents,
plumbing and other pipes, etc.) can considerably loosen it.
Rubber roofing typically refers to a specific type of roofing
materials that are made of ethylene propylene diene monomers
(EPDM). It is crucial to the integrity of such roofs to avoid using
harsh abrasive materials and petroleum-based solvents for their
maintenance.
Polyester fabric laminated to butyl rubber binder provides a
single-sided waterproof tape that can be used on metal, PVC, and
cement joints. It is ideal for repairing and waterproofing metal roofs.
Gas masks and chemical agent protection
Butyl rubber is one of the most robust elastomers when
subjected to chemical warfare agents and decontamination materials.
It is a harder and less porous material than other elastomers, such as
natural rubber or silicone, but still has enough elasticity to form an
airtight seal. While butyl rubber will break down when exposed to
agents such as NH3 (ammonia) or certain solvents, it breaks down
more slowly than comparable elastomers. It is therefore used to
create seals in gas masks and other protective clothing.
Medical Stoppers
Butyl and Bromobutyl rubber are commonly used for
manufacturing rubber stoppers used for sealing medicine vials and
bottles.
Chewing gum
Most modern chewing gum uses food-grade butyl rubber as
the central gum base, which contributes not only the gum's elasticity
but an obstinate, sticky quality which has led some municipalities to
propose taxation to cover costs of its removal.
Tires
Butyl rubber and halogenated rubber are used for the inner liner that
holds the air in the tire.
112
3.6 Ethylene-Propylene Rubber
m
CH2CH2CH2CH
n
CH
3
Ethylene-propylene rubber (EPM)
Terpolymers: Ethylene-propylene-diene-methylene rubbers
(EPDM):
CH2CH2CH2CH
n
CH
3
m
CH CH
CH
2
k
Ethylene-propylene-dicyclopentadiene rubber
CH2CH2CH2CH
n
CH
3
m
CH CH
CH
2
k
CH CH
3
Ethylene-propylene-ethylidenenorbornene rubber
CH2CH2CH2CH
n
CH
3
CH2CH
m
CH
CH
CH
CH
k
2
3
Ethylene-propylene-1,4-hexadiene rubber
Sometimes it is called EPM, the E refers to ethylene, P to propylene
and M refers to its classification in ASTM standard D-1418 since the
M class includes rubbers having a saturated chain of the
polymethylene type. It is a type of synthetic elastomer that is closely
113
related to EPDM rubber (EPM is a copolymer of ethylene and
propylene whereas EPDM rubber is a terpolymer of ethylene,
propylene and a diene-component). Since it began to be produced in
the 1960s, production has increased to 870 metric tons per annum,
mostly due to advances in polymerization and catalyst technologies
which allow polymers to be designed for specific purposes.
Properties
EPM is considered a valuable elastomer due to its useful
chemical and physical properties: it is resistant to heat, oxidation,
ozone and the weather (owing to its stable, saturated backbone) and
it is also not susceptible to color loss. As a non-polar compound,
EPM is an electrical resistor and it is insoluble in many polar
solvents, both protic and aprotic. Amorphous forms of EPM are
flexible at low temperatures (with glass transition points around -60
°C). Via selection of certain sulfur compounds EPM can remain heat
resistant up to 130°C and up to 160°C with peroxide curing. These
two tables contain some of the main properties of EPM.
Table 9.
Polymer Properties
Property Type EPM Property
Mooney viscosity at 125°C 5-200
Ethylene content percentage by weight 45-80
Diene content percentage by weight 0-15
Specific gravity 0.855-0.880
Table 10.
Vulcanizate Properties
Property Type EPM Property
Hardness (Shore A durometer) 30-95
Tensile strength, MPa 7-21
114
Continuation of Table 10
Elongation percentage 100-600
Compression set B percentage 20-60
Useful temperature range °C -50 to +160
Tear resistance Fair to good
Abrasion resistance Fair to good
Resilience Fair to good
Electrical properties Insulator
Application
EPM has a large number of uses due to the many ways in
which the polymer can be designed, for example; it is used in
automotive weather-stripping and seals, glass run channels, radiators,
garden and appliance hoses, tubing, belts, roofing membranes, rubber
mechanical goods, plastic impact modification, thermoplastic
vulcanisates and motor oil additive applications. EPM is even more
prevalent as an insulator for high voltage cables since it has
improved insulative characteristics over more traditional cables, such
as cross-linked polyethylene, enabling a smaller cross sectional area
for the same load carrying capacity. The cable is flexible and suited
to applications where regular cable movement is required such as in
the mining industry.
Manufacturing process
EPM manufacture uses the same monomers as polyethene
and polypropene, the ethylene and propylene monomers are
randomly combined to yield a rubbery, stable polymer. By varying
the monomer ratios and method by which the monomers are
combined different forms of EPM can be formed (with a wide range
of Mooney viscosities); ranging from amorphous to semi-crystalline.
A third, non-conjugated diene monomer can be terpolymerized in a
controlled manner to maintain a saturated backbone ready for
vulcanization or polymer modification.
115
Trade names
Major producers and suppliers of EPM include Bayer Polymers,
Crompton Corporation, Exxon-Mobil, DSM, Dupont, Herdillia, JSR,
Kumho Polychem, Mitsui Chemicals, Polimeri Europa and
Sumitomo Chemical, Nizhnekamskneftekhim, JSR.
3.7 Nitrile Rubber
CH2CH CH CH
CH2CH
2
n m
C N
Nitrile rubbers (NBR/HNBR) is a family of unsaturated copolymers
of 2-propenenitrile (acrylonitrile (ACN)) and various butadiene
monomers (1,2-butadiene and 1,3-butadiene).
Properties
Although its physical and chemical properties vary depending
on the polymer’s composition of nitrile, this form of synthetic rubber
is generally resistant to oil, fuel, and other chemicals (the more nitrile
within the polymer, the higher the resistance to oils but the lower the
flexibility of the material).
It is used in the automotive and aeronautical industry to make
fuel and oil handling hoses, seals, and grummets. It is used in the
nuclear industry to make protective gloves. NBR’s ability to
withstand a range of temperatures from -40°C to +108°C makes it an
ideal material for aeronautical applications. Nitrile butadiene is also
used to create moulded goods, footwear, adhesives, sealants,
sponges, expanded foams, and floor mats.
Its resilience makes NBR a useful material for disposable lab,
cleaning, and examination gloves. Nitrile rubber is more resistant
than natural rubber to oils and acids, but has inferior strength and
flexibility. Nitrile gloves are nonetheless three times more punctureresistant than natural rubber gloves.
Nitrile rubber is generally resistant to aliphatic hydrocarbons.
Nitrile, like natural rubber, can be attacked by ozone, ketones, esters
and aldehydes.
116
Production
Emulsifier (soap), 2-propenenitrile, various butadiene
monomers (including 1,3-butadiene, 1,2-butadiene), radical
generating activators, and a catalyst are added to polymerization
vessels in the production of hot NBR. Water serves as the reaction
medium within the vessel. The tanks are heated to 30–40°C to
facilitate the polymerization reaction and to promote branch
formation in the polymer. Because several monomers capable of
propagating the reaction are involved in the production of nitrile
rubber the composition of each polymer can vary (depending on the
concentrations of each monomer added to the polymerization tank
and the conditions within the tank). One repeating unit found
throughout the entire polymer may not exist. For this reason there is
also no IUPAC name for the general polymer. The reaction for one
possible portion of the polymer is shown below:
1,3-butadiene + 1,3-butadiene + 2-propenenitrile + 1,3butadiene + 1,2-butadiene → nitrile butadiene rubber
Monomers are usually permitted to react for 5 to 12 hours.
Polymerization is allowed to proceed to ~70% conversion before a
“shortstop” agent (such as dimethyldithioсarbamate and diethyl
hydroxylamine) is added to react with the remaining free radicals.
Once the resultant latex has “shortstopped”, the unreacted monomers
are removed through a steam in a slurry stripper. Recovery of
unreacted monomers is close to 100%. After monomer recovery,
latex is sent through a series of filters to remove unwanted solids and
then sent to the blending tanks where it is stabilized with an
antioxidant. The yielded polymer latex is coagulated using calcium
nitrate, aluminium sulfate, and other coagulating agents in an
aluminium tank. The coagulated substance is then washed and dried
into crumb rubber.
The process for the production of cold NBR is very similar to
that of hot NBR. Polymerization tanks are heated to 5–15°C instead
of 30–40°C. Under lower temperature conditions, less branching will
117
form on polymers (the amount of branching distinguishes cold NBR
from hot NBR).
Applications
The uses of nitrile rubber include non-latex gloves for the
healthcare industry, automotive transmission belts, hoses, O rings,
gaskets, oil seals, V belts, synthetic leather, printer's roller, and as
cable jacketing; NBR latex can also be used in the preparation of
adhesives and as a pigment binder.
Unlike polymers meant for ingestion, where small
inconsistencies in chemical composition/structure can have a
pronounced effect on the body, the general properties of NBR are not
altered by minor structural/compositional differences. The
production process itself is not overly complex; the polymerization,
monomer recovery, and coagulation processes require some additives
and equipment, but they are typical of the production of most
rubbers. The necessary apparatus is simple and easy to obtain. For
these reasons, the substance is widely produced in poorer countries
where labor is relatively cheap. Among the highest producers of
NBR are mainland China and Taiwan.
A hydrogenated version of nitrile rubber, HNBR, also known
as HSN (highly saturated nitrile) is commonly used to manufacture
o-rings for automotive air-conditioning systems.
Criminals have also been known to wear these gloves during
the commission of their crimes. These gloves are often chosen
because of their tight, thin fit that allows the hands to remain
dexterous. Ironically, because of the thinness of these gloves,
fingerprints may actually pass through the material as glove prints,
thus transferring the wearer's prints onto whatever surface is touched
or handled.
Dangers
Do not use these gloves when working with red fuming nitric
acid, as sudden combustion of these two chemicals could cause
serious chemical burns. Caution must be taken when working with
the acid and the gloves at the same time.
118
Trade names
Nitrile rubber, also known as Buna-N, Perbunan, or NBR, is a
synthetic rubber copolymer of acrylonitrile (ACN) and butadiene.
Trade names include Nipol, Krynac and Europrene.
XNBR
An improved version of Nitrile Butadiene Rubber NBR is
Carboxylated Nitrile Butadiene Rubber (XNBR). In this execution
there are beside the sulfur bridges also carboxyl groups R-COO- on
the double bond of the butadiene part. These groups will make ionic
cross links with zinc Zn2+ to give improved physical properties as
compared to a non-carboxylated Nitrile rubber. These ionic
crosslinks are formed along with sulfur links. The carboxyl groups
which are needed for these extra links are distributed randomly and
are present at levels of 10% or less.
CH2CH CH CH2CH
C
O
O
Zn
COO
CH2CH CH CH2CH2CH CH
CH2CH CH CH2CH
C
O
O
Zn
O
C
O
CH2CH CH CH2CH
2
C N
CH CH
C N
2
CH CH CH
2
CH
CH CH
2
C N
C N
CH CH
2
CH CH
2
CH2CH CH CH
2
119
CH
CH CH
2
CH
CH CH
2
S
CH2CH CH CH
S
S
S
S
S
2
S
2
2
CH2CH CH CH
2
CH2CH CH CH
2
2
3.8 Epichlorohydrin Polymer
Epichlorohydrin content, %
-
18
Epichlorohydrin polymers (CO/ECO/ETER) are homo and
copolymers of epichlorohydrin.
Chemistry
Epichlorohydrin homopolymer of general formula
CH2CH (CH2Cl) O
n
,
epichlorohydrin and ethyleneoxide copolymer of general formula
CH2CH (CH2Cl) O CH2CH2O
n
and epichlorohydrin, ethyleneoxide and allyl glycidyl ether
terpolymer of general formula
CH2CH (CH2Cl) O CH2CH2O CH
CH ( nCH2O CH2CH CH2) O
2
are currently produced.
Properties
Table 11.
Composition and properties of Epichlorohydrin Polymers and
Rubbers thereof
Characteristics Homopolymer Copolymer Terpolymer
Rubbers SKEHG* SKEHG-
С**
SKEHG-
СТ***
100 68 63
mass
Ethylenoxide content, %
_ 32 30-34
mass
Chlorine content, % mass 38 20-25 20-25
ρ, kg/m3 1390 1280 1240
Tg,оС -29 -45 -55
Mooney viscosity at 100°С
Permeability for nitrogen,
35-100 50-80 40-80
(2-4) х 10
— —
m2/(с·Pa)
120
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