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Tin này được trích lại từ:
Butyl rubber.
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| Đệm cao su dùng cao su tổng hợp |
The polymerization of isobutylene is
carried out at -95
C (-139
F), with aluminum chloride as a
catalyst. Isobutylene and the desired proportion of isoprene are fed
continuously into a medium of methyl chloride. After antioxidant is added,
crumbs of butyl rubber form directly, without any latex stage. Zinc stearate (to prevent
agglomeration, or formation of clumps of butyl rubber) also goes into the
mixture. Excess reactants are recovered and re-used.
Because of its excellent air
retention butyl rubber quickly took over from natural rubber for inner tubes in
all but the largest sizes. Butyl rubber also plays an important part in the
inner liners of tubeless tires. Despite excellent road-holding properties under
wet conditions, and quiet, comfortable riding qualities, all-butyl tires have
not proved commercially successful because of their poor tread durability.
Butyl rubber, however, is used for many automobile components, such as window
strips, because of its excellent resistance to oxidation. In its resistance to
heat, butyl rubber also plays an indispensable part in tire manufacture,
forming the container for the hot water or steam required to vulcanize the
inside of tires.
Polybutadiene is produced by a hydrocarbon solution process, in contrast with
the water-emulsion method for styrene-butadiene rubber. Indeed, in making
polybutadiene, water must be rigorously excluded to enable the catalyst to
work. The resulting polybutadiene has better physical properties, particularly
tensile strength and resilience, than styrene-butadiene rubber.
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| Đệm cao su chịu dầu bằng cao su nhân tạo |
Polychloroprene is the
scientific name for the synthetic that bears the proprietary name Neoprene
(which, however, has become generic). One of the first synthetic rubbers to be
discovered, neoprene was first marketed in 1931. It is prepared by treating acetylene (C
H)
with cuprous chloride to form monovinyl acetylene, which, with hydrochloric acid, yields chloroprene. Competitive
methods of production exist. It is manufactured in solid form (chips) and as
latex.
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| Lô cao su được bọc bằng neoprene |
Because of its general properties of high tensile strength, high resilience, good resistance to oxygen, ozone, and tearing, as well as an oil resistance only slightly inferior to nitrile (see below), neoprene is used extensively in the wire and cable industries, hose, extruded automobile parts, and for protective clothing. It also has excellent resistance to flame.
The original
Buna N of German war production, the name nitrile (its symbol NBR) covers
a range of copolymers of butadiene and acrylonitrile, the members
differing from one another in their acrylonitrile content. The
"standard" NBR material contains from 33 to 36 percent acrylonitrile,
and others from 20 to 50 percent. The outstanding property of nitrile is its
oil resistance, which increases in pace with its acrylonitrile content--but at
the expense of low-temperature flexibility. Production is by an emulsion
process quite similar to the styrene-butadiene rubber process; it can be made
as solid sheets or liquid latex. Nitrile requires the addition of carbon black
or other reinforcement to produce satisfactory physical properties, thus
reducing the overall cost of nitrile, which is more expensive than conventional
rubbers.
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| Bánh xe cao su chịu mòn |
The first true equivalent of natural rubber was prepared in 1955 by the
polymerization of isoprene. Its manufacture
follows the hydrocarbon solvent method for making polybutadiene. Synthetic
polyisoprene can replace natural rubber for most purposes, except when the
nonrubber constituents of natural become advantageous. The decision is
therefore usually based on economics, and since the basic monomer isoprene is
expensive, either synthetic polybutadiene or natural rubber is usually
favoured.
A specialty
rubber, silicone is limited in use by
its cost; but its exclusive ability to retain its physical properties at
extreme temperatures, from -74
C (-101
F) to 315
C (599
F), makes up for its high cost. It is the first "inorganic" rubber;
the polymer has a backbone of silicon and oxygen instead of the conventional
carbon chain.
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| Cao su silicone được dùng phổ biến |
Although the raw material silica is cheap and plentiful, the manufacturing process is difficult and expensive. A range of products is available, their properties largely influenced by the molecular structure of the silicone. Its retention of electrical properties, resistance to oxygen and ozone, and inertness at extremely high temperatures recommend uses in aircraft and outer space equipment, and in the automobile field. Its inertness and nontoxicity encourage use for food and surgical applications.
Polysulfide rubber (Thiokol).
Polysulfide rubber is
the technical term for the substance bearing the trade name Thiokol, which has
become generic. Originally synthesized in 1927, it is known for its excellent
resistance to organic solvents and is marketed as a liquid, a putty, and in
solid form. Its tensile strength does not compare with conventional rubbers,
but it offers excellent resistance to weathering and permeability over a wide
range of temperature.
A versatile
new synthetic, ethylene-propylene rubber exhibits excellent
resistance to oxygen, ozone, acids, alkalies, and other chemicals over a wide
range of temperature. It has good electrical properties and is quite
lightweight, with an enormous capacity for acceptance of oil, thereby reducing
the final cost. The addition of carbon black used as a filler, along with the
oil, acts to raise the low tensile strength.
Polyurethane
rubber includes a large range of materials of varied compositions, properties,
and uses. In this group of rapidly growing importance, some of the polymers
help significantly to bridge the gap between rubber and plastics. All are based
on isocyanates, organic compounds
that combine with other organic compounds such as alcohols, esters, ethers, and
amides. The wide variety of materials available, when properly controlled,
offers a series of polymers with a broad range of properties and forms.
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| Đệm cao su từ PU rất hữu hiệu |
Chlorosulfonated polyethylene is normally known by its trade name of
Hypalon. It is made by introducing first sulfur dioxide into a solution of
polyethylene under strictly controlled conditions and then chlorine at higher
temperature. Chlorine content may vary between 20 and 45 percent and sulfur
from 0.5 to 2.75 percent.
The physical properties depend much more upon the sulfur than the chlorine content. Rubbery compounds are produced with low sulfur and metallic oxide curing. Hypalon is outstanding in its resistance to weathering, ozone, heat, flame, and chemicals. Cost alone restricts its wider adoption.
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| Bánh xe cao su được bọc bằng hypalon |
The physical properties depend much more upon the sulfur than the chlorine content. Rubbery compounds are produced with low sulfur and metallic oxide curing. Hypalon is outstanding in its resistance to weathering, ozone, heat, flame, and chemicals. Cost alone restricts its wider adoption.
Fluorocarbon polymers.
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| Teflon cũng là nguyên liệu được ưa dùng |
