17/9/2011 640
Sau đây là một đoạn tài liệu về EPDM đã được Nhóm Nghiên cứu Phát triển Cao su thảo luận trong buổi sinh hoạt câu lạc bộ thứ bảy 17/9/2011.
Nghề nghiệp là một công việc để sống, để làm việc và để sống tốt nên luôn cần bổ sung.
Hy vọng qua các buổi sinh hoạt, nhóm sẽ xác định được nhiều điều. Những điều xác định không phải nằm ở tài liệu mà ở ứng dụng hiệu quả.
Không quá sùng bái vào lý thuyết, không quá khẳng định vào kinh nghiệm, không coi thường những điều đơn giản. Những điều đơn giản luôn làm bất ngờ.
Hoạt động câu lạc bộ là một phần trong hoạt động của vLAB, phòng thử nghiệm cơ lý cao su.
....
Một đoạn trích trong tài liệu:
Rubber Basics, Edited by Richard
B. Simpson, First published in 2002 by Rapra Technology Limited.
General
The copolymerisation of
ethylene and propylene yields useful copolymers, the crystallisation of both polymers being prevented if the
ethylene content is in the range 45-60%; grades with higher ethylene contents, 70-80%, can partially
crystallise.
The lower ethylene types are generally easier to process, whilst green strength and extrudability improve as the ethylene content increases. One disadvantage of the copolymer is that it cannot be crosslinked with sulphur due to the absence of unsaturation in the main chain. |
To overcome this
difficulty a third monomer with unsaturation is introduced, but to maintain
the excellent stability of the main chain the unsaturation is made pendant to
it.
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The three types of third
monomer used commercially are dicyclopentadiene, ethylidene norbornene, and
1,4-hexadiene.
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Generally 4-5% of the
termonomer will give acceptablecure characteristics, whilst 10% gives fast
cures; dicyclopentadiene gives the slowest cure rate and ethylidene
norbornene the highest.
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Since the main chain of
both EPM and EPDM rubbers is saturated, both co- and terpolymers exhibit
excellent stability to oxygen, UV light, and are ozone resistant.
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EPM and EPDM are not oil
resistant, and are swollen by aliphatic and aromatic hydrocarbons, and
halogenated solvents.
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They have excellent
electrical properties and stability to radiation.
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Their densities are the lowest
of the synthetics, and they are capable of accepting large quantities of
filler and oil.
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They exhibit poor tack,
and even if tackifiers are added, it still is not ideal for building
operations.
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Adhesion to metal,
fabrics and other materials, can be difficult to accomplish.
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The copolymers can only
be cured by peroxides or radiation, whilst the terpolymers can be cured with
peroxides, sulphur systems, resin cures and radiation.
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The dicyclopentadiene
terpolymer can give higher states of cure with peroxides than the copolymer,
although in peroxide curing of both the copolymer and terpolymer it is common
practice to add a coagent, to increase the state of cure.
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Triaryl isocyanurate or
sulphur are the most common coagents.
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Bloom can be a problem
in sulphur cures, so selection of the accelerator system is important.
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Resin cures utilise the
same resins that are used for butyl rubber, but more resin (ca. 10-12 phr)
and a halogen donor (10 phr), typically bromobutyl, or polychloroprene, are
required.
Although heat stability
is slightly improved by resin curing when compared to sulphur cures, the
effect is not as marked as in the resin curing of butyl. |
Uses
Wire and cable applications and extrusion profiles,
e.g., window seals and car door seals, probablyform the major applications
for EPM and EPDM rubber, although they are also used in a widevariety of
other extrusion and moulding applications.
Washing machine door seals moulded from EPDM are
starting to replace NR as washer/dryers are becoming more common....  Nguồn tài liệu:
Tuan Van Doan (Ph.D student)
Environmental BioTechnology Lab
Yonsei University, Sinchon 262, Seodaemungu
Seoul, 120-749, South Korea.
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