何謂硫化Vulcanization？？？www.tool-tool.com
在
高分子化學中，
硫化（Vulcanization）指的是
橡膠膠料通過生膠
分子間交聯，生成具有三維網路結構的硫化膠的過程。含有
雙鍵的
彈性體在工業上多採用
硫或
有機硫化合物來進行硫化交聯，因此在橡膠工業中，硫化與交聯是同義詞。交聯的目的是為了使膠料具備高強度、高彈性、高耐磨、抗腐蝕等優良性能，消除永久形變，使橡膠在變形之後，能迅速並完全地恢復原狀。因為最早發現的交聯劑是硫磺，故得名硫化。
一般需經過硫化的橡膠品種有
丁二烯、
氯丁二烯、
異戊二烯的1,4-聚合物——
順丁、
異戊、
氯丁橡膠，以及共聚物
丁苯、
丁基和
丁腈橡膠等。
具體過程
二烯烴類化合物在經過
聚合後，
主要生成的是線形的高分子長鏈。這樣的橡膠通常性能較差，不易成型，受熱變軟，遇冷變硬變脆，容易磨損和老化。硫化是對橡膠性能進行改良的一種過程。在這
個過程中，線性結構的大分子發生交聯生成具有三維立體網狀結構的分子，穩定了分子的立體結構，從而使橡膠的彈性、強度等諸多性能都得到增強。
單以
硫作為二烯烴聚合物的交聯劑時，實驗表明
自由基引發劑、
阻聚劑都對反應沒有影響，
電子順磁共振也未檢測出
自由基，而相反，有機酸鹼和
介電常數大的
溶劑卻能加速硫化的過程，從而說明該硫化過程是一個
離子型連鎖反應。一般認為，硫化過程的第一步是聚合物的雙鍵與
極化後的硫或硫
離子對反應，形成一個環狀的
鋶離子。鋶離子從聚合物鏈奪取氫原子，使後者生成
烯丙基碳正離子。該碳正離子先與硫反應，然後再與大分子的雙鍵
加成，從而產生交聯。之後再發生一個氫轉移，繼續與大分子反應，從而再生出碳正離子，推動反應一直進行下去。硫化後的分子結構大致如下：
加速硫化
用硫單獨對聚二烯烴進行硫化時，硫化速度相當慢，通常需要幾小時才能完成，效率也較低，只有40～50％的硫能有效地達到交聯的目的。而其他的硫，主要浪費在大分子的分子間相鄰雙交聯（實際上只起到單交聯的作用），以及分子內的硫化成環上。所以實際生產時，常常需要加入
促進劑，來加快硫化的速率以及提高硫化的效率。促進劑主要是
有機硫化合物，特別是
二硫化物和
多硫化物，例如
四甲基秋蘭姆二硫化物、
二甲基二硫代氨基甲酸鋅、
2-巰基苯並噻唑和
苯並噻唑二硫化物。少數不含硫的化合物，如
二苯胍類，也可作為促進劑。
促進劑一般還需要與金屬
氧化物、
脂肪酸等活化劑連用，使效率達到最大。最常用的活化劑是
氧化鋅和
硬脂酸。
雖
然加速硫化的具體機理目前還不清楚，但加速硫化的效果是顯著的。原來用硫需要用數小時才能完成的硫化，在促進劑和活化劑的作用下幾分鐘內就可以完
成。反應的效率也有所提高，硫的浪費程度大大降低，有些時候促進劑和活化劑體系的交聯效率可達到每交聯略少於2個硫原子，大多數交聯是單硫鍵和
雙硫鍵，甚少相鄰雙交聯和硫環。
Vulcanization or
vulcanisation is a
chemical process for converting
rubber or related
polymers into more durable materials via the addition of
sulfur or other equivalent "curatives". These additives modify the polymer by forming
crosslinks (bridges) between individual polymer chains.
[1]The vulcanized material is less sticky and has superior mechanical
properties. A vast array of products are made with vulcanized rubber
including tires, shoe soles, hoses, and hockey pucks. The process is
named after
Vulcan, Roman god of
fire. Hard vulcanized rubber is known as
ebonite or vulcanite and is used to make hard articles such as
bowling balls and
clarinet mouth pieces.
Uncured
natural rubberis sticky, easily deforms when warm, and is brittle when cold. In this
state it cannot be used to make articles with a good level of
elasticity.
The reason for inelastic deformation of unvulcanized rubber can be
found in its chemical structure: rubber is composed of long
polymerchains. These chains can move independently relative to each other,
which enables the material to change shape. Crosslinking introduced by
vulcanization prevents the polymer chains from moving independently. As
a result, when stress is applied the vulcanized rubber will deform, but
upon release of the stress, the article will revert to its original
shape.
Vulcanization is generally irreversible, similar to other
thermosets and in contrast to
thermoplastic processes (the melt-freeze process) that characterize the behavior of most modern
polymers. The
cross-linking is usually done with
sulfur, but other technologies are known, including
peroxide-based systems.
The main polymers subjected to vulcanization are
polyisoprene (natural rubber) and
styrene-butadienerubber (SBR), which are used for most passenger tires. The "cure
package" is adjusted specifically for the substrate and the
application. The reactive sites - "cure sites" - are allylic hydrogen
atoms. These C-H bonds are adjacent to carbon-carbon double bonds.
During vulcanization, some of these C-H bonds are replaced by chains of
sulfur atoms that link with a cure site of another polymer chain. These
bridges contain between one and eight atoms. The number of sulfur atoms
in the crosslink strongly influences the physical properties of the
final rubber article. Short crosslinks give the rubber better heat
resistance. Crosslinks with higher number of sulfur atoms give the
rubber good dynamic properties but with lesser heat resistance. Dynamic
properties are important for flexing movements of the rubber article,
e.g., the movement of a side-wall of a running tire. Without good
flexing properties these movements will rapidly lead to formation of
cracks and, ultimately, to failure of the rubber article.
"Vulcanization
curve" showing the increase in viscostiy of the polymeric material
during crosslinking. The steepness of the curve is strongly affected by
the nature of the accelerators and other additives.
Vulcanization methods
A
variety of methods exist for vulcanization. The economically most
important method (the vulcanization of tires) uses high pressure and
temperature. A typical vulcanization temperature for a passenger tire
is 10 minutes at 170 °C. This type of vulcanization is called
compression molding. The rubber article is intended to adopt the shape
of the mold. Other methods, for instance to make door profiles for
cars, use hot air vulcanization or microwave heated vulcanization (both
continuous processes).
Four types of curing systems are in common use. They are:
Sulfur systems Peroxides Urethane crosslinkers Metallic oxidesVulcanization with sulfur
By
far the most common vulcanizing methods depend on sulfur. Sulfur, by
itself, is a slow vulcanizing agent and will not vulcanize synthetic
polyolefins. Even with natural rubber, large amounts of sulfur, as well
as high temperatures and long heating periods are necessary and one
obtains an unsatisfactory crosslinking efficiency with unsatisfactory
strength and aging properties. Only with vulcanization accelerators can
the quality corresponding to today's level of technology be achieved.
The multiplicity of vulcanization effects demanded cannot be achieved
with one universal substance; a large number of diverse additives,
comprising the "cure package," are necessary.
The combined cure package in a typical
rubbercompound consist of sulfur together with an assortment of compounds
that modify the kinetics of crosslinking and stabilize the final
product. These additives include
accelerators, activators like
zinc oxide and
stearic acid and antidegradants. The accelerators and activators are
catalysts.
An additional level of control is achieved by retarding agents that
inhibit vulcanization until some optimal time or temperature.
Antidegradants are used to prevent degradation of the vulcanized
product by heat, oxygen, and ozone.
[2] Vulcanization of silicones
"Room-temperature
vulcanizing" (RTV) silicone is constructed of reactive oil base
polymers combined with strengthening mineral fillers. There are two
types of room-temperature vulcanizing silicone:
RTV-1 (One-component systems)
RTV-1
hardens directly under the action of atmospheric humidity. The curing
process begins on the outer surface and progresses through to its core.
The product is packed in airtight cartridges and is either in a fluid
or paste form. RTV-1 silicone has good adhesion, elasticity and
durability characteristics. The Shore A hardness can be varied between
18 and 60. Elongation at break can range from 150% up to 700%. They
have excellent aging resistance due to superior resistance to UV
radiation and weathering. Industrial RTV-1 products are referred to as
CAFs.
RTV-2 (Two-component systems)
RTV-2 elastomer are
two-component products that, when mixed, cure at room-temperature to a
solid elastomer, a gel, or a flexible foam. RTV-2 remains flexible from
-80 °C to +250 °C. Break down occurs at temperatures above 350 °C
leaving an inert silica deposit that is non-flammable and
non-combustible. They can be used for electrical insulation due to
their dielectric properties. Mechanical properties are satisfactory.
RTV-2 is used to make flexible moulds, as well as many technical parts
for industry and paramedical applications.
History of vulcanization of rubber
Although vulcanization is a 19th century invention, the history of rubber cured by other means goes back to
prehistoric times. The name "
Olmec" means "rubber people" in the
Aztec language. Ancient
Mesoamericans, spanning from ancient
Olmecs to
Aztecs, extracted
latex from
Castilla elastica, a type of
rubber tree in the area. The juice of a local vine,
Ipomoea alba, was then mixed with this latex to create an ancient processed
rubber as early as 1600 BC
[3] In the western world, rubber remained a curiosity although it was used in the production of waterproofed products such as
Mackintosh rainwear.
Goodyear's contribution
Charles Goodyear (1800–1860) invented vulcanization of
rubber when he heated a mixture of rubber and
sulfur.
The Goodyear story is one of either pure luck or careful research.
Goodyear insisted that it was the latter, though many contemporaneous
accounts indicate the former. Goodyear claimed that he discovered
vulcanization in 1839 but did not patent the invention until June 15,
1844, and did not write the story of the discovery until 1853 in his
autobiographical book
Gum-Elastica. Meanwhile,
Thomas Hancock (1786-1865), a
scientist and
engineer, patented the process in the UK on November 21, 1843, eight weeks before Goodyear applied for his own UK
patent.
Here is Goodyear's account of the
invention, taken from
Gum-Elastica. Although the book is an
autobiography, Goodyear chose to write it in the
third person, so that 'the inventor' and 'he' referred to in the text are in fact the author. He describes the scene in a
rubber factory where his brother worked:
...
The inventor made some experiments to ascertain the effect of heat on
the same compound that had decomposed in the mail-bags and other
articles. He was surprised to find that the specimen, being carelessly
brought into contact with a hot stove, charred like leather.
Goodyear goes on to describe how his discovery was not readily accepted.
He
directly inferred that if the process of charring could be stopped at
the right point, it might divest the gum of its native adhesiveness
throughout, which would make it better than the native gum. Upon
further trial with heat, he was further convinced of the correctness of
this inference, by finding that the India rubber could not be melted in
boiling sulfur at any heat ever so great, but always charred. He made
another trial of heating a similar fabric before an open fire. The same
effect, that of charring the gum, followed; but there were further
indications of success in producing the desired result, as upon the
edge of the charred portion appeared a line or border, that was not
charred, but perfectly cured.
Goodyear then goes on to describe how he moved to
Woburn, Massachusetts and carried out a series of systematic experiments to optimize the curing of rubber.
...
On ascertaining to a certainty that he had found the object of his
search and much more, and that the new substance was proof against cold
and the solvent of the native gum, he felt himself amply repaid for the
past, and quite indifferent to the trials of the future.
Goodyear did not profit from his invention.
Later developments
Whatever
the true history, the discovery of the rubber-sulfur reaction
revolutionized the use and applications of rubber, and changed the face
of the
industrial world.
Up
to that time, the only way to seal a small gap between moving machine
parts, such as between a piston and its cylinder in a steam engine, was
to use
leathersoaked in oil. This was acceptable up to moderate pressures, but above
a certain point, machine designers had to compromise between the extra
friction generated by packing the leather more tightly and greater leakage of precious steam.
Vulcanized
rubber offered the ideal solution. With vulcanized rubber, engineers
had a material which could be shaped and formed to precise shapes and
dimensions, and which would accept moderate to large deformations under
load and recover quickly to its original dimensions once the load was
removed. These, combined with good durability and lack of stickiness,
are the critical requirements for an effective sealing material.
Further
experiments in the processing and compounding of rubber by Hancock and
his colleagues led to a more repeatable and stable process.
In 1905
George Oenslager discovered that a derivative of
aniline called
thiocarbanilide accelerated the action of sulfur to rubber, leading to shorter cure times and
reducing energy consumption. This breakthrough, although less famous, is almost as fundamental to the development of the
rubber industry as that of Goodyear in discovering the
sulfur cure.
Acceleratorsmade the cure process improved the reliability of the vulcanization
process and, although not obvious at the time, enabled vulcanization to
be applied to synthetic polymers. One year after his discovery,
Oenslager had found hundreds of applications for his additive.
Thus, the science of accelerators and retarders was born. An
acceleratorspeeds up the cure reaction, while a retarder delays it. In the
subsequent century, various chemists have developed other accelerators
and ultra-accelerators, that make the reaction extremely fast, and are
used to make most modern rubber goods.
Recycling and devulcanization
The market for new raw rubber or equivalent remains enormous, with
North America alone using over 10 billion
pounds (circa 4.5 million
tons)
every year. The auto industry consumes approximately 79% of new rubber
and 57% of synthetic rubber. To date, recycled rubber has not been used
as a replacement for new or synthetic rubber in significant quantities,
largely because the desired properties have not been achieved. Used
tiresare the most visible of the waste products made from rubber; it is
estimated that North America alone generates approximately 300 million
waste tires annually, with over half being added to existing
stockpiles. It is estimated that less than 10% of waste rubber is
reused in any kind of new product. The United States, the
European Union,
Eastern Europe,
Latin America,
Japan and the
Middle Eastcollectively produce about one billion tires annually, with estimated
accumulations of three billion in Europe and six billion in North
America.
The rubber recycling process begins with the shredding. After the
steel and reinforcing
fibersare removed and a secondary grinding, the resulting rubber powder is
ready for product remanufacture. The manufacturing applications that
can utilize this inert material are restricted to those which do not
require its vulcanization. In the rubber recycling process,
devulcanization begins with the delinking of the sulfur molecules from
the rubber molecules, thereby facilitating the formation of new
cross-linkages. Two main rubber recycling processes have been
developed: the
modified oil process and the
water-oil process. With each of these processes,
oiland a reclaiming agent are added to the reclaimed rubber powder, which
is subjected to high temperature and pressure for a long period (5-12
hours) in special equipment and also requires extensive mechanical
post-processing. The reclaimed rubber from these processes has altered
properties and is unsuitable for use in many products, including tires.
Typically, these various devulcanization processes have failed to
result in significant devulcanization, have failed to achieve
consistent quality, or have been prohibitively expensive.
加硫（かりゅう）とは、
架橋反応の一種で、
ゴム系の原材料（生ゴムなど）を加工する際に、
弾性や
強度を確保するために、
硫黄などを加える行程のことである。
1839年、アメリカの発明家
チャールズ・グッドイヤー(C.Goodyear)により発見され、
1843年にイギリスの発明家
トーマス・ハンコック(T.Hancock)により、反応の仕組みが解明された。
材料の
分子内にある多重
結合部に反応し、加えられた硫黄を媒介とした分子間結合が、新たに作り出される。この反応により、材料の
分子量は増大し、それに伴い、ゴムの弾性や強度が飛躍的に向上する。
ただし、過剰な加硫を行うと、多重結合や分子間の流動性が失われ、弾性が失われる。この性質を利用した
材料に
エボナイトがある。
加硫剤としては、硫黄のほか
過酸化物なども使用され、加える化学物質により、様々な特性を持つゴムを製造することができる。加硫剤の働きを促進させる加硫助剤には、無機系の
酸化亜鉛や
酸化マグネシウムなど、有機系の
ステアリン酸や
アミン類などが使われる。加硫時間の短縮などの目的で、
チアゾール系を中心とした加硫促進剤が添加されることもある。
タ
イヤやゴム製品に使用される。スチールラジアルタイヤに入れられている鋼線は鋼とゴムは接着性が良くないので銅めっきが施されている。加硫によってゴム
に数％含まれる硫黄と銅が強力なイオン結合を形成する。1970年代のスティールラジアルタイヤのワイヤは銅メッキで、現在はより強度があるブラス(真
鍮)メッキになった。ブラスメッキは銅と亜鉛を陽極に並べてメッキする。最近は鋼線とゴムとの接着をナフテン酸コバルトというものを介在させる界面活性剤
で解決する方法が見付かったが環境に悪影響を与える可能性がある。
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Çok geniş ürün yelpazesine sahip olan firmanın başlıca ürünlerini
Karbür Parmak Frezeler, Kalıpçı Frezeleri, Kaba Talaş Frezeleri, Konik
Alın Frezeler, Köşe Radyüs Frezeler, İki Ağızlı Kısa ve Uzun Küresel
Frezeler, İç Bükey Frezeler vb. şeklinde sıralayabiliriz. BW специализируется
в научных исследованиях и разработках, и снабжаем самым
высокотехнологичным карбидовым материалом для поставки режущих /
фрезеровочных инструментов для почвы, воздушного пространства и
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инструменты. Пожалуйста, посетите сайт www.tool-tool.com для получения большей информации. BW
is specialized in R&D and sourcing the most advanced carbide
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include solid carbide / HSS end mills, micro electronic drill, IC card
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這是鑽石4C的第四個C，大多數含有顏色的鑽石都屬於黃色系列。其他顏色的鑽石較為稀少，且其顏色如明顯時均屬於彩色鑽石範圍，故鑽石成色等級的劃分，僅限於含有黃色的鑽石。 
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