tag:blogger.com,1999:blog-49399528185052187122024-03-06T01:54:15.770+05:30polymerspmfhttp://www.blogger.com/profile/16410119039801971518noreply@blogger.comBlogger14125tag:blogger.com,1999:blog-4939952818505218712.post-23530960571580821652011-08-20T16:16:00.001+05:302011-08-20T16:22:36.751+05:30THERMOFORMING<div style="text-align: center;"><span class="Apple-style-span" style="color: red; font-size: x-large;"><b>THERMOFORMING</b></span></div>Thermoforming is the process of heating a<br />
plastic material in sheet form to its particular<br />
processing temperature and forming the hot and<br />
flexible material against the contours of a mold<br />
by mechanical means (e.g., tools, plugs, solid<br />
molds, etc.) or pneumatic means (e.g., differentials<br />
in air pressure created by pulling a vacuum<br />
or using the pressures of compressed air).<br />
When held to the shape of the mold and allowed<br />
to cool, the plastic retains the shape and<br />
detail of the mold. Because softening by heat<br />
and curing by the removal of heat are involved,<br />
the technique is applicable only to thermoplastic<br />
materials and not to thermosets.<br />
Advantages of thermoforming over most<br />
other methods of processing plastics include<br />
lower tooling and machinery costs, high output<br />
rates, the ability to use predecorated plastic<br />
sheet, and good-quality physical properties in<br />
finished parts.<br />
Its disadvantages include the need to begin<br />
with sheet or film rather than less costly basic<br />
resins, trimming material used to clamp sheet<br />
for forming, and the problem of trim scrap reclamation.<br />
<a name='more'></a><br />
<span class="Apple-style-span" style="color: blue;"><b><u>METHODS OF THERMOFORMING</u></b></span><br />
There are different technique used in thermoforming some<br />
of them are<br />
<b>1.VACUUM THERMOFORMING</b><br />
<br />
To vacuum form a thermoplastic sheet into a<br />
female mold without prestretching, the ratio of<br />
depth to minor dimension of a given section<br />
should not be greater than 1 : 1, and no sharp<br />
inside radii are required. The sheet stock is<br />
locked in a frame around its periphery only, is<br />
heated to a predetermined temperature, and<br />
then is brought into contact with the edge of<br />
the mold. This contact should create a seal so<br />
that it is possible to remove the air between the<br />
hot plastic and the mold, allowing atmospheric<br />
pressure (about 14 psi) to force the hot plastic against the mold<br />
<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjZdffhikV0hwjfO6Uh4RIphxImYi0qT17fasYaKY4ahrgw2TU1v9cj2X9tsmJ8WNCEJk34djaRMbE4Cz7KfaXe7JScyYVOztZEcepRNosCNg0ZXI1H9cGUW_-RYLBfq9dltcdbdtViQmg/s1600/press.gif" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="268" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjZdffhikV0hwjfO6Uh4RIphxImYi0qT17fasYaKY4ahrgw2TU1v9cj2X9tsmJ8WNCEJk34djaRMbE4Cz7KfaXe7JScyYVOztZEcepRNosCNg0ZXI1H9cGUW_-RYLBfq9dltcdbdtViQmg/s320/press.gif" width="320" /></a></div><br />
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<b><u>2.PRESSURE FORMING</u></b><br />
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In this metod a positive air pressure<br />
is applied against the top of the sheet to force<br />
it into a female mold, and, at the same time,<br />
full vacuum also is applied. As contrasted to<br />
vacuum forming, pressure forming offers a<br />
faster production cycle (the sheet can be formed<br />
at a slightly lower sheet temperature), greater<br />
part definition, and greater dimensional control.<br />
<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhirNy9yDfMf8gOS8AxjkDafBICu4Ycenz2h073iL9oNR__vtBdd9oIPswrBexaq93uIAtFJQkIWYXGGV4KQ0Spvutd5Pt9qKvpEfsMh9x_XP9oc240PiMW0w5r9QPG_dW_xaIjFVpEICM/s1600/350px-Pressure_Thermoforming.gif" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="166" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhirNy9yDfMf8gOS8AxjkDafBICu4Ycenz2h073iL9oNR__vtBdd9oIPswrBexaq93uIAtFJQkIWYXGGV4KQ0Spvutd5Pt9qKvpEfsMh9x_XP9oc240PiMW0w5r9QPG_dW_xaIjFVpEICM/s400/350px-Pressure_Thermoforming.gif" width="400" /></a></div><br />
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<b><u>PLUG ASSIST FORMING</u></b><br />
<br />
Straight cavity forming is not well adapted to<br />
forming a cup or box shape. The sheet, drawn<br />
down by vacuum, touches first along the side<br />
walls and then at the center of the bottom of<br />
the box-shaped mold and starts to cool there,<br />
with its position and its thickness becoming<br />
fixed. As the sheet continues to fill out the<br />
mold, solidification continues in such a way as<br />
to use up most of the stock before it reaches the<br />
periphery of the base; hence this part of the article<br />
will be relatively thin and weak.<br />
<br />
To promote uniformity of distribution in such<br />
shapes, designers use the plug assist-any type<br />
of mechanical helper that carries extra stock toward<br />
an area that otherwise would be too thin.<br />
<br />
Note that it is also possible to reverse<br />
mold and plug assist from the bottom<br />
platen to give better material utilization around<br />
the edges.<br />
<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgC1DvJri52vCLewUdbADDzNWR5Ur66qLUupeFoKD360a6dWfdj-u75izOuEmEowQ-PyEzft8HyNVgnr0dIaM3ZoUBPbEtddMVyRmyKrztFyYdVZRIGjj7XAdv4NCFRZ3VbnJYvGLUJmgI/s1600/plug-assist-forming.gif" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="351" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgC1DvJri52vCLewUdbADDzNWR5Ur66qLUupeFoKD360a6dWfdj-u75izOuEmEowQ-PyEzft8HyNVgnr0dIaM3ZoUBPbEtddMVyRmyKrztFyYdVZRIGjj7XAdv4NCFRZ3VbnJYvGLUJmgI/s400/plug-assist-forming.gif" width="400" /></a></div><br />
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<b><u>4.DRAPE FORMING</u></b><br />
<br />
<br />
This method also is adaptable to either machine<br />
or manual operation. After framing and heating,<br />
the stock is mechanically stretched over a<br />
male mold to allow the framed edge to make a<br />
seal with the periphery of the mold. This<br />
stretching serves to redistribute or preform the<br />
sheet prior to application of the vacuum. It has<br />
the disadvantage of allowing the stock to touch<br />
prominent projections, freeze there, and perhaps<br />
rob other areas of sufficient mass to make<br />
acceptable articles. Careful control of the temperature<br />
of the mold, plus selective heating of<br />
the sheets, can alleviate some difficulties.<br />
<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgXsZiWlRt9XOw60H7p9ISMvIkPcDULFiyNBQNPPk_9neiA6Y83r9iTHdLCbFoqP_o8T8E5zNrsP14bTUsG1QR-Mog_ajZ5hGSMnFTuZiIDYTIURNwIAlWb2U8YIUxzCKO4nC-toOTy6Jk/s1600/images.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgXsZiWlRt9XOw60H7p9ISMvIkPcDULFiyNBQNPPk_9neiA6Y83r9iTHdLCbFoqP_o8T8E5zNrsP14bTUsG1QR-Mog_ajZ5hGSMnFTuZiIDYTIURNwIAlWb2U8YIUxzCKO4nC-toOTy6Jk/s400/images.jpg" width="314" /></a></div><br />
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<b><u>5.MATCHED MOLD FORMING</u></b><br />
<br />
In this operation, the plastic<br />
sheet is locked into the clamping frame and<br />
heated to the proper forming temperature. A<br />
male mold is positioned on either the top or the<br />
bottom platen with a matched female mold<br />
mounted on the other one.<br />
<br />
The mold then is closed, forcing the plastic<br />
to the contours of both molds. The clearance<br />
between the male and female molds determines<br />
the wall thickness. Trapped air is allowed to<br />
escape through both mold faces. Molds are held<br />
in place until the plastic cools and cures.<br />
Matched mold forming offers excellent reproduction<br />
of mold detail and dimensional accuracy.<br />
Internal cooling of the mold is desirable<br />
in this technique.<br />
<div class="separator" style="clear: both; text-align: center;"></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjPFJG4qBI1AkPmBqILGZ67RtDtvoIrWIi6hTjX1uZCJxVzlMrqXeywb24hSOJCdpUFqMoJk4B60smm5ssyaCyQ8eV5FlCMUUbd8N6kqaMtbUBSqYbCUc9iLvM409cOzpJkE-ENvuAv6NQ/s1600/matcheddieform.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjPFJG4qBI1AkPmBqILGZ67RtDtvoIrWIi6hTjX1uZCJxVzlMrqXeywb24hSOJCdpUFqMoJk4B60smm5ssyaCyQ8eV5FlCMUUbd8N6kqaMtbUBSqYbCUc9iLvM409cOzpJkE-ENvuAv6NQ/s1600/matcheddieform.jpg" /></a></div><br />
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pmfhttp://www.blogger.com/profile/16410119039801971518noreply@blogger.com0tag:blogger.com,1999:blog-4939952818505218712.post-12231154359759778822011-06-26T12:54:00.000+05:302011-06-26T12:54:43.679+05:30ROTATIONAL MOLDING<div style="color: red; font-family: Arial,Helvetica,sans-serif; text-align: center;"><span style="font-size: x-large;">Rotational molding </span></div><span style="font-size: small;">Rotational molding (also popularly known as</span><br />
<span style="font-size: small;">rotomolding) is best suited for large, hollow</span><br />
<span style="font-size: small;">products requiring stress-free strength, complicated</span><br />
<span style="font-size: small;">curves, a good finish, a variety of colors,</span><br />
<span style="font-size: small;">a comparatively short (or very long) production</span><br />
<span style="font-size: small;">run, and uniform wall thickness. It has been</span><br />
<span style="font-size: small;">used for products such as fuel tanks, furniture,</span><br />
<span style="font-size: small;">tilt trucks, industrial containers, storage tanks,</span><br />
<span style="font-size: small;">portable outhouses, modular bathrooms, telephone</span><br />
<span style="font-size: small;">booths, boat hulls, garbage cans, light</span><br />
and<b><u>Rotational molding offers a number of advantages</u></b><br />
<div style="color: red;"><b><span style="font-size: small;">1.</span>Virtually unlimited design possibilities(parts as</b></div><div style="color: red;"><b> small as a golf ball to a 22,500-gallon agricultural tank).</b></div><div style="color: red;"><b>2.Relatively low machinery cost.</b></div><div style="color: red;"><b>3. Low tooling costs.<br />
4. Economical prototyping</b></div><div style="color: red;"><b>5 . Strong outside comers in virtually stress-<br />
6. Part finish from matte to high gloss.<br />
7, Simultaneous processing of multiple<br />
8. Simultaneous processing of different<br />
9. Quick mold changes.<br />
10. Possibility of molding in metal inserts.<br />
11. Molded-in multicolor graphics.<br />
12. Multilayer molding for chemical resis-<br />
13. Double-walled parts molding for addi-<br />
14. Possibility of minor undercuts.</b></div><a name='more'></a><br />
<div style="text-align: center;"><span style="color: red; font-size: large;">DIFFERENT TYPES OF MACHINES </span></div><u><span style="color: blue; font-size: large;">Batch-Type Machines</span></u><br />
This type is the least expensive of the rotational<br />
molding machines because it is the least sophisticated<br />
and requires the most manual labor.<br />
In a typical batch operation, the charged mold<br />
is rolled into the oven for rotation and heating.<br />
At the completion of the cycle, the mold is removed<br />
and a newly charged one inserted in its<br />
place. The completed mold then is transferred<br />
manually on rollers to a cooling station for cure<br />
before removal of the parts.<br />
<span style="font-size: large;"><u><span style="color: blue;">Carousel-Type Machines</span></u></span><br />
The most common rotational molding machine<br />
in use is the carousel unit, which is essentially<br />
a three-station rotary indexing type with a central<br />
turret and three cantilevered mold arms .In<br />
operation, individual arms are involved in<br />
different phases simultaneously, so that no arms<br />
are idle at any time. The arms or mold spindles<br />
extend from a rotating hub in the center of the<br />
unit. Thus, while one arm is in the loading/<br />
unloading station, another is rotating within the<br />
oven, and the third is rotating within the cooling<br />
station. All operations are automated, and<br />
at the end of each cycle the turret is rotated<br />
120", thereby moving each mold arm to its next<br />
station.<br />
Newer carousel machines being offered today<br />
use four arms. The additional arm can be used<br />
in a second oven, cooler,or load station,<br />
depending on which is the most<br />
time-consuming part of the overall cycle .<br />
The four-arm carousel machines increase<br />
production by allowing the index from<br />
station to station to occur more frequently that<br />
could be managed on a three-arm machine<br />
<span style="color: blue; font-size: large;"><b><u>Independent-Arm-Type Machines</u></b></span><br />
The independent-arm-type machine offers even<br />
more flexibility. Featuring five stations-one<br />
oven, one intermediate station, one cooler, and<br />
two loadhnload stations<br />
<span style="color: blue; font-size: large;"><b><u>Straight-Line Machines</u></b></span><br />
Used primarily for molding large parts, this<br />
type is a shuttle carriage machine that is generally<br />
a straight-line operation with the oven on<br />
one side, the loadinghnloading station in the<br />
middle, and the cooling station on the opposite<br />
end. The carriage is guided on parallel tracks<br />
that ensure positive placement in the stations.<br />
Variations of this particular design, involving<br />
the placement and relationship of the oven,<br />
cooling stations, and loading/unloading stations,<br />
also are available for handling particular<br />
jobs.<br />
<u><span style="font-size: large;"><b><span style="color: blue;">Jacketed-Mold Machines</span></b></span></u><br />
These units offer precise temperature control up<br />
to a 300°C heat-transfer medium temperature.<br />
This type of machine finds its biggest market<br />
in molding heat-sensitive polymers because of<br />
its accurate temperature control.<br />
Key to the machines are double-walled jacketed<br />
molds that are charged with a hot liquid,<br />
usually oil, to attain temperature control. When<br />
the heating period is over, the oil is drained,<br />
and a coolant is introduced.<br />
The molds rotate biaxially through all production<br />
operations. Significant savings are effected<br />
because the heating medium retains its<br />
heat, and the heat transfer is more rapid, resulting<br />
in faster thermal cycling at lower temperatures<br />
<div style="text-align: center;"><span style="color: red; font-size: large;">MOLD MATERIAL</span></div><b><u>Cast aluminum</u></b> molds are probably the most<br />
widely used, and are the most practical for<br />
small to medium parts requiring a number of<br />
cavities.The initial cavity cost<br />
may be relatively high because a model and/or<br />
a pattern is required. However, subsequent<br />
cavities are moderate in price, and a fair reproduction<br />
of the mold surface on the finished part<br />
may be expected. The process used for casting<br />
aluminum molds is somewhat specialized; an<br />
experienced rotational casting moldmaker is required<br />
<b><u>Electroformed nickel</u></b> molds are best used<br />
where precise detail is required on the finished<br />
part, or where no parting line can be tolerated.<br />
This type of mold is not so durable as cast aluminum<br />
or sheet metal; however, it is widely<br />
used by molders of such objects as automotive<br />
headrests, armrests, and so forth, and by plastisol<br />
molders.<br />
<u><b>Sheet metal</b></u> is appropriate for extremely large<br />
parts or single cavities requiring inexpensive<br />
tools, where a simple sheet metal mold is generally<br />
adequate.pmfhttp://www.blogger.com/profile/16410119039801971518noreply@blogger.com2tag:blogger.com,1999:blog-4939952818505218712.post-655064520542429052011-02-06T09:28:00.004+05:302011-02-06T09:30:41.083+05:30MASTICATION AND MIXING<div style="text-align: center;"><div style="text-align: center;"><link href="file:///C:%5CDOCUME%7E1%5Csyed%5CLOCALS%7E1%5CTemp%5Cmsohtml1%5C01%5Cclip_filelist.xml" rel="File-List"></link><style>
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</style><span style="font-size: large;"><b style="color: red;"><span style="font-family: Arial;">MASTICATION AND MIXING</span></b></span></div><span style="font-family: Arial; font-size: 10pt;"></span></div><span style="font-family: Arial; font-size: 10pt;"> <span style="font-family: Arial,Helvetica,sans-serif;"><span style="font-family: Arial,Helvetica,sans-serif;">Rubbe</span>r </span>Processing is a general term which includes all the operations which are carried out on the rubber and which alter its physical shape or chemical composition.<br />
The raw polymer, natural or synthetic can be softened either by mechanical work, termed action, by heat or by chemicals known as peptisers. The increase of plasticity or decrease of viscosity brought about by mastication and peptisers is permanent; by heat it may be permanent or temporary, depending on the nature of the polymer. When the rubber contains all the ingredients needed it is known as a compound or preferably a mix. If some ingredients have been withheld deliberately, the partially completed compound becomes a master batch. The master batch is converted to the compound by the addition of the withheld ingredients, which are usually the vulcanising or curing ingredients.<a name='more'></a><br />
</span><br />
<div style="text-align: center;"><div style="text-align: center;"><span style="font-family: Arial; font-size: 10pt;"> <b style="color: blue;">MACHINERY</b></span></div><span style="font-family: Arial; font-size: 10pt;"></span></div><span style="font-family: Arial; font-size: 10pt;"> <b style="color: red;">Open Mixing Mill</b></span><br />
<span style="font-family: Arial; font-size: 10pt;">The back roll is driven from the gear box or back shaft and the front roll from the back roll through roll end gears. The gears will come out of mesh on a singly geared mill if the nip ie. The distance between the rolls is set too wide furthermore, there is always a danger of stripping the teeth if the nip is opened so that the gears are working on the tips of the teeth.</span><br />
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<br />
<b style="color: blue;"><span style="color: blue;">Friction Ratio</span> </b><br />
The speeds of the two rolls are often different, the friction ratio depending upon the mills use. For natural rubber mixing a ration of 1:1.25 for the front to back roll is common. High friction ratios are used for refining compounds and even speed rolls on feed mills to calendars ie. When mills are used other than for mixing. For mixing some if the synthetic rubbers, a near even speed is best or even an immense friction ratio, ie. Less than 1.0. Other synthetic rubbers are very difficult to mix on mills, so internal mixers are often used for these.</span><br />
<span style="font-family: Arial; font-size: 10pt;"><br />
<b style="color: blue;">COOLING</b><br />
Two alternative types of cooling are used. The principal, one employees cored rolls ie. Water is sprayed on to the outside of an auxiliary drilled central core, with peripherally drilled rolls the water is circulated through a labyrinth of passages about 50 mm under the roll surface.<br />
<b style="color: blue;"><br />
SAFETY</b><br />
Mills are usually fitted with various safety devices, some to protect the operator, the other to protect the mill.<br />
<br />
<b style="color: blue;">OTHER ATTACHMENTS</b><br />
Nills are fitted with a metal tray under the rolls to collect droppings from the mill and with guides or checks which are plates fitted to the ends of rolls to prevent rubber being contaminated with grease etc. Other attachments which may be added, depending upon the use of the mill are:<br />
<br />
<b>1. A mill apron, which replaces the mill tray and consists a belt running under the nip rolls up to the top of the back roll the belt returns to the mill any powders powders which fall from the nip.<br />
2. A stock blender, which is a device for blending the rubber mechanically instead of depending upon the operator.<br />
3. Cutting knives mounted against the roll to produce strips far feeding other equipment or for removing compound from the mill.</b></span><br />
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</style><span style="font-family: Arial; font-size: 10pt;"><b>4. Scraper blades to remove soft stocks.</b><br />
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<b style="color: red;">INTERNAL MIXERS</b><br />
Since mixing time in open mill is relatively long when a high rate of productions required.so we can use internal mixer whereby the batch mixing time can be reduced.Examples for internal mixer is BANBURY MIXER.In banbury mixer for mixing only take 5-6 minutes</span><br />
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<span style="font-family: Arial; font-size: 10pt;"><b><br />
<span style="color: blue;">MASTICATION</span></b><br />
The mastication stage in processing is, in general only applied to Natural Rubber and the internal mixer is an efficient machine for this. The energy can be put into the rubber quickly the shorter the masticating cycle; the limitations to shortening the mastication cycle are the time to load the machine and the handling of the rubber after discharge from the mixer.<br />
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The shape of the rubber being loaded and the bulk density8 of the rubber affect the loading of the machine. The modern 331/3 kg bale of natural rubber is ideal for loading whole into the type of mixer or alternatively rubber cut from larger bales to the same shape. The low bulk density of certain crepes means that to obtain similar batch weights, larger volumes must be loaded into the machine than for other higher density rubbers. These low density rubbers can take longer to load than to masticate and hence are at a economic disadvantage in processing.<br />
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The handling and storage of masticated rubber in sheet form is not very satisfactory unless the viscosity and dismension stability of the rubbers can be assured. Mastication costs money it reduces the viscosity, but at the same time sults in a reduction in many physical properties of the finished vulcanisate. If the viscosity reduction is obtained by using softeners then a saving in compound volume cost results. The reduction in physical properties of the vulcanisate is probably no greater from using softeners than from extra or separate mastication of the polymer.<br />
With the availability of constant viscosity and low viscosity natural rubber and of synthetic rubbers of suitable viscosity for direct mixing, the need for mastication may well be eliminated in due course. <br />
<b style="color: blue;">Mill Mixing</b><br />
In operation, the ingoing side of the nip is at the top of the rolls and rubber is added to the nip. A band of rubber comes through the nip and is formed around the front roll.<br />
Varying degrees of difficulty arise in forming these bends, depending upon the polymer. Natural rubber if not formasticated is difficult to band initially, but after a time, depending upon mill nip and temperatures, a band form. This starts with many holes and after continued working, the band becomes smooth. Powders process oils etc. are now added into the nip and any which fall into the tray under heath the rolls are returned to the nip until they are absorbed by the rubber.<br />
The compound is blended to homogenise the additives and give adequate distribution of the ingredients. Mills generally give good ingredient dispersion.<br />
Mills have a fairly high power in put. A 1.5-m mill ie. With rolls 105 m long will handle about 50 kg of rubber at sp.gr. 1.0-1.2 and will require 45-75 kw A 2.1 m mill handle 100-150 kg of compound and needs a motor of 115-225 kw. The majority of electric power is converted to heat so, to prevent compounds vulcanising on the mill with the heat produced to rolls are water cooled.<b></b><br />
<b style="color: blue;">MASTER BATCHING</b><br />
It is generally accepted that masterbatching improves the physical properties of those compounds where a high degree of carbon black dispersion must be achieved. Where a master batch can be carried from that used in the compound eg: the masterbatch recipe may (a) be the same as the compound recipe but without curatives; (b) contain only rubber, filler and some softeners, or (c) be richer in filler than the final compound.<br />
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Each of these types of masterbatch is capable of improving black and filler dispersion in a tyre tread or other reinforced compound, but type has been formed less satisfactory than the other twc. The problem is the dispersion in the hard filler masterbatch of the relatively soft polymers added in the next stage of mixing</span>pmfhttp://www.blogger.com/profile/16410119039801971518noreply@blogger.com1tag:blogger.com,1999:blog-4939952818505218712.post-58915628218499373012011-02-06T08:40:00.001+05:302011-02-06T08:41:44.013+05:30POLYMER BLEND<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhHsNOMGKned71qREBz4F6Fr8FzG7OmzsQoyQpsA3YIhwFvGqdQop2kZ_fr80DhkGQKHoqN8TOsSOHQj2qjMPUT6QwUxyzJZSn0cI4k2Zuyjb_utz_PAOOlVRAbOIhelcAGzq5o30th848/s1600/pm.jpeg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><br />
</a></div><div style="text-align: center;"><b><span style="color: red; font-size: large;">POLYMER BLEND</span></b></div>Polymer blend refer to intimate mixture of two monomers of two or more polymers. The individual polymers may be melt mixed, solution blended and co-precipitated, or lattices may be blended and coagulated before final processing.<br />
Blending of polymers is carried out<br />
<b>1. To reduce the cost of expensive engineering thermoplastic.</b><br />
<b>2. To increase the process ability of a high temperature heat sensitive thermoplastic</b><br />
<b>3. To improve the impact strength of a brittle polymer </b><br />
<b>4. To expand temperature range of applications of a polymer<a name='more'></a></b><br />
Commercial blends may be single phase or two phases. If the blend is exhibiting single Tg(glass transition temperature) it is called as miscible blend <br />
Example:- Blend of polystyrene and poly(1,4 phenylene oxide )<br />
<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhZi3cVD8qi9aoEiRJtQlOKu54Qji3-CJwVoGox-mOjLbSRIctB2hrnz9UJSBeWz_G4rYGOVKAHdVXhgl8Lp_2eKf5Nyw76V0KBc8BXVjuFf_qS6w38dv1a3tcIw2F4KK2i2DOOxVeCFTI/s1600/all.jpeg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhZi3cVD8qi9aoEiRJtQlOKu54Qji3-CJwVoGox-mOjLbSRIctB2hrnz9UJSBeWz_G4rYGOVKAHdVXhgl8Lp_2eKf5Nyw76V0KBc8BXVjuFf_qS6w38dv1a3tcIw2F4KK2i2DOOxVeCFTI/s1600/all.jpeg" /></a></div><br />
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Immisible blends shows double Tg<br />
Example:- blends of polystyrene and PMMA(polymethyl methacrylate)<br />
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhHsNOMGKned71qREBz4F6Fr8FzG7OmzsQoyQpsA3YIhwFvGqdQop2kZ_fr80DhkGQKHoqN8TOsSOHQj2qjMPUT6QwUxyzJZSn0cI4k2Zuyjb_utz_PAOOlVRAbOIhelcAGzq5o30th848/s1600/pm.jpeg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhHsNOMGKned71qREBz4F6Fr8FzG7OmzsQoyQpsA3YIhwFvGqdQop2kZ_fr80DhkGQKHoqN8TOsSOHQj2qjMPUT6QwUxyzJZSn0cI4k2Zuyjb_utz_PAOOlVRAbOIhelcAGzq5o30th848/s1600/pm.jpeg" /></a><br />
<div style="text-align: center;"><span style="font-size: large;"><b> <span style="color: blue;">MORPHOLOGY OF POLYMER BLEND </span></b></span></div>Under microscopic inspection a miscible polymer blend consist of a single phase. In order to miscible some attraction between the two polymers must be present to overcome intramolecular cohesive force of the Individual polymers. Totally miscible polymers are rare in practical life.<br />
In the case of immiscible polymers there exist two phase. There is another type of blend in between above two, in which polymers are neither totally miscible nor totally miscible but holds some where in between these two. These types blends are classified as partially miscible polymer blends.pmfhttp://www.blogger.com/profile/16410119039801971518noreply@blogger.com0tag:blogger.com,1999:blog-4939952818505218712.post-31577823116509909962011-01-29T08:38:00.002+05:302011-01-29T08:46:58.744+05:30BLOWING AGENT<div style="text-align: center;"><span style="font-size: large;"><b style="color: red;">BLOWING AGENT </b></span></div>Blowing agent are substances stable at room temperature and decomposes at high temperature by liberating gas.They are classified as follows<br />
1-organic blowing agent<br />
2-inorganic blowing agent<br />
A good blowing agent must be filled following requirement<br />
<b>- Must contain large amount of releasing gas</b><br />
<b>-Must be non toxic </b><br />
<b>-Should not produce bad smell </b><br />
<b>-Should disperse well in rubber </b><br />
<b>-Should not influences vulcanization or Aging properties<a name='more'></a></b><br />
<div style="color: blue;"><b>INORGANIC BLOWING AGENT</b></div>Sodium by carbonate in combination with stearic acid and oliec acid is used to make sponge rubber.sodium nitrate combination with ammonium chloride is used to produce hollow product<br />
<div style="color: blue;"><b>ORGANIC BLOWING AGENT</b></div>It can be further classified as follows<br />
-Azo compound<br />
-Hydrazine compound<br />
-Niroso compound<br />
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<div style="color: black;"><u><b>1-AZO COMPOUND</b></u></div><br />
<div style="color: black;"><b><span style="font-size: small;">Diazo Amino Compound</span></b></div><span style="font-size: small;">eg:-<span id="goog_2004428678"></span><a href="http://www.blogger.com/goog_2004428685">1- </a></span><a href="http://www.blogger.com/">Diazo amino benzene<span id="goog_2004428679"></span></a><br />
<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhkS69yWqpcGbRd89S7OXUqGUNrAF_a0zpNB_NB2JcK6o40jNr5LVpwwMNk8C3kLoobO_TjjXkwHA1JBmujjdrXkwjNJTGSNaa-1O1vYyfQxD-dC25Ka78fviFXQGhBKycWdk6oyHU3cV4/s1600/images.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="155" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhkS69yWqpcGbRd89S7OXUqGUNrAF_a0zpNB_NB2JcK6o40jNr5LVpwwMNk8C3kLoobO_TjjXkwHA1JBmujjdrXkwjNJTGSNaa-1O1vYyfQxD-dC25Ka78fviFXQGhBKycWdk6oyHU3cV4/s320/images.jpg" width="320" /></a></div> <br />
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percentage used 2-3phr<br />
decomposition temperature 363-369K<br />
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<b>Azo dicarbon amid</b><br />
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percentage used 2-3phr<br />
decomposition temperature 413-480K<br />
<div style="color: black;"><u><b>2-HYDRAZINE COMPOUND</b></u></div><div style="color: red;"><u><b><span style="color: black;"> </span> </b></u></div>eg:-Benzene sulfohydrazine(BSH)<br />
decomposition temperature 363-373K<br />
BSH has good storage stability<br />
<u><b>3-NITROZO COMPOUND </b></u><br />
eg:-Diniro pentamethylene tetramine(DNPT)<br />
decomposition temperature-205<br />
DNPT are used to make micro cellular sheet(like hawai chappals) <br />
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pmfhttp://www.blogger.com/profile/16410119039801971518noreply@blogger.com0tag:blogger.com,1999:blog-4939952818505218712.post-74104606443958138822011-01-21T20:46:00.007+05:302011-01-27T06:38:28.500+05:30CARBONBLACK<div style="text-align: center; font-weight: bold; color: rgb(255, 0, 0);"><span style="font-size:180%;">CARBON BLACK<br /></span></div><span style=";font-family:Arial;font-size:85%;" > Among the reinforcing fillers used in rubber industry, a lion's share is constituted by different types of carbon blacks. They are essentially elemental carbon prepared by converting liquid or gaseous hydrocarbons into elemental carbon by partial combustion or thermal decomposition. Depending on the process adopted for the preparation, carbon blacks and lampblack. The furnance blacks, channel blacks and lamp blacks. The furnace blacks are produced by incomplete combustion of natural gas or heavy aromatic residue oils from the petroleum industries, in refractory lined steel furnaces and separating the carbon formed by means of cyclones and filter bags. Finally, they are pelleted and packed, In the thermal process, natural gas or oil is thermally decomposed at about 1300°C in the absence of free air, in cylindrical furnaces filled with an open checker work of slice bricks. The channel blacks are produced by feeding the natural gas or oil into thousands of small burner tips where the small flames inpinge either on to a large rotating drum or on to reciprocating channel irons. The black deposited is scraped out and collected. Lamp black is made by burning oil and allowing the black formed to settle out by gravity in a series of chambers.<a name='more'></a><br /><br />The properties imparted by carbon blacks to the rubber Vulcanizates depend on several factors like particle size, structure, physico-chemical nature of the particle surface, chemical nature of the particle surface and particle porosity of the particle surface and particle porosity of the carbon blacks. Carbon blacks, are actually fused clusters of individual carbon particles. The particle size of the blacks range from 10 to 25 nm for the channel blacks, 20 to 80 nm for the furnace blacks and 180 to 470 nm for the thermal ones. The aggregation of carbon particles into long chains is referred to as 'structure' of the blacks. Compared with the other processes, the furnace process gives high structure blacks. The structure of the blacks can be controlled by modifying the furnace design and by the appropriate selection of the raw material. The physico-chemical nature of the particle surface is indicated by the degree of orientation of the particles in layer planes. Those which are less reinforcing were found to have highly oriented layers where as the reinforcing ones are irregular in shape and have less crystallite orientation. The carbon particles contain very small amounts of hydrogen, oxygen and sulphur on the surface, as phenolic, ketonic and carboxylic groups. The presence of these groups affect the rate of cure of the mixed compound.</span>pmfhttp://www.blogger.com/profile/16410119039801971518noreply@blogger.com0tag:blogger.com,1999:blog-4939952818505218712.post-2475168437114947582011-01-19T06:58:00.006+05:302011-01-22T09:38:21.607+05:30EXTENDERS<div style="text-align: center; font-weight: bold; color: rgb(255, 0, 0);"><span style="font-size:130%;">Extenders<br /></span></div><br />These are substances which are added to rubber compounds in lage quantities so that the cost of the compound can be reduced, without seriously affecting the final properties. Important among the commercially used extenders are the following.<a name='more'></a><br /><br /><span style="font-weight: bold; color: rgb(102, 102, 204);">1. Rubber reclaim</span><br /><br />This is a product resulting from the treatment of vulcanized scrap rubber tires, tubes etc. by the application of heat and chemicals, whereby a substantial degree of devulcanisation and regeneration of the rubber compound to its original plastic and state is affected, thus permitting the product to be processed, compounded and vulcvanised. Reclaiming is essentially depolarization, the combined sulphur is not removed. Different types are available, depending upon the original type of waste rubber employed. Whole tyre reclaim (WTR) contains about 50% rubber hydrocarbon and 20-25% carbon black, the rest being plasticisers and miscellaneous ingredients. While using whole tyre reclaim for every 1 part of rubber which is being replaced, 2 parts of reclaim is added. In addition to the economic advantage, use of reclaim has other beneficial affects such as short mixing time, low power consumption, low heat development during processing, reduced swelling and shrinkage, higher cure rate, minimized reversion, good ageing etc.<br /><br /><span style="color: rgb(102, 102, 204);font-size:130%;" ><span style="font-weight: bold;">2.Factice:</span></span><br />This is a class of elastic gums made by reacting certain vegetable oils with sulphur. Most familiars is the one used in erasers. Fictive can be blended with NR and with some synthetic rubbers is a rather high proportion and the blend will remain highly elastic. It will also be soft and suffer much loss of strength and abrasion resistance. Another way in which it is used is to increase the tolerance for liquid softeners in synthetic rubber compounds.<br /><br /><span style="font-size:130%;"><span style="color: rgb(102, 102, 204); font-weight: bold;">3.Mineral rubber</span></span><br />Airs blown petroleum asphalt are called mineral rubber. Products of this sort wold hand only moderate weakening effect on tensile and tear strength. But would relatively be poor in respect of resilience and heat build up and flexing.<br /><br /><span style="color: rgb(102, 102, 204);font-size:130%;" ><span style="font-weight: bold;">White pigments and colours<br /></span></span>White pigments are used in rubber compounds to which them. Its use in coloured compounds mains the colours brighter important among the common white pigments are titanium dioxide and lithophone.<br /><br />Pure titanium is extracted from minerals, precipitated as the hydroxide, calcined to the oxide and ground. It is a semireinforcing filler comparable on a volume basis with zinc oxide, but is mainly used for its whitening power in tyre sidewalks, hospital accessories, floor tiles etc. And as an excellent heat resistant filler for silicone rubber. The agnate form is preferred where extreme wittiness is required. The retile form gives a rather creamier colour, but is more state at high temperatures.<br /><br />Lithophone is a mixture of zinc suphide and barium sulphate, usually co precipitated in equimolecular proportions it is used mainly in cheaper white or coloured compounds as a whitening agent.pmfhttp://www.blogger.com/profile/16410119039801971518noreply@blogger.com0tag:blogger.com,1999:blog-4939952818505218712.post-60254880447420024252011-01-19T06:36:00.006+05:302011-01-22T09:40:30.292+05:30PLASTICIZERS<meta equiv="Content-Type" content="text/html; charset=utf-8"><meta name="ProgId" content="Word.Document"><meta name="Generator" content="Microsoft Word 11"><meta name="Originator" content="Microsoft Word 11"><link rel="File-List" href="file:///C:%5CDOCUME%7E1%5Csyed%5CLOCALS%7E1%5CTemp%5Cmsohtml1%5C01%5Cclip_filelist.xml"><!--[if gte mso 9]><xml> <w:worddocument> <w:view>Normal</w:View> <w:zoom>0</w:Zoom> <w:punctuationkerning/> <w:validateagainstschemas/> <w:saveifxmlinvalid>false</w:SaveIfXMLInvalid> <w:ignoremixedcontent>false</w:IgnoreMixedContent> <w:alwaysshowplaceholdertext>false</w:AlwaysShowPlaceholderText> <w:compatibility> <w:breakwrappedtables/> <w:snaptogridincell/> <w:wraptextwithpunct/> <w:useasianbreakrules/> <w:dontgrowautofit/> </w:Compatibility> <w:browserlevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:latentstyles deflockedstate="false" latentstylecount="156"> </w:LatentStyles> </xml><![endif]--><style> <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} --> </style><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--> <div style="text-align: center;"><span style="color: rgb(255, 102, 102); font-weight: bold;font-size:180%;" ><span style=";font-family:Arial;font-size:10pt;" >PLASTICIZERS</span></span>
<br /><span style=";font-family:Arial;font-size:10pt;" ></span></div><p class="MsoNormal"><span style=";font-family:Arial;font-size:10pt;" >
<br /><span style="font-size:100%;"><span style="font-weight: bold;">Plasticisers are added in rubber compounds with the following objectives</span>.</span>
<br /><span style="font-family:courier new;">1.Increase plasticity and workability of the compound.</span>
<br /><span style="font-family:courier new;"> 2.Aid in wetting and incorporation of fillers </span><o:p style="font-family: courier new;"></o:p></span></p> <p class="MsoNormal"><span style=";font-family:Arial;font-size:10pt;" ><span style="font-family:courier new;">3.Modify the properties of the vulcanised products.</span>
<br /><span style="font-family:courier new;"> 4. Provide lubrication to improve extrusion, moulding or other shaping operations.</span>
<br /><span style="font-family:courier new;"> 5. Reduce batch temperature and power consumption during mixing</span><span style="font-size:85%;">
<br /><span style="font-size:100%;">Plasticisers are divided broadly into two classes:</span></span><o:p></o:p></span></p> <p class="MsoNormal"><span style=";font-family:Arial;font-size:10pt;" ><span style=""></span>1)<span style="color: rgb(102, 102, 204);">chemical Plasticisers</span>:-Chemical Plasticisers act as reducing the molecular weight of the rubber, by chain scission.<o:p></o:p></span></p> <p class="MsoNormal"><span style=";font-family:Arial;font-size:10pt;" >2)<span style="color: rgb(102, 102, 204);">physical Plasticisers:</span>- Physical platiciser not as intermolecular lubricants.</span></p><p style="font-weight: bold; color: rgb(255, 102, 102);" class="MsoNormal"><span style="font-size:100%;"><span style=";font-family:Arial;font-size:10pt;" >
<br /></span></span></p><p class="MsoNormal"><span style=";font-family:Arial;font-size:10pt;" > <span style="font-weight: bold; color: rgb(255, 102, 102);font-size:100%;" >Chemical Plasticisers are used when:</span>
<br /><span style="font-family:courier new;">a) The primary concern is for modifying the properties of the uncured stock rather than those of the vulcanisate.</span>
<br /><span style="font-family:courier new;"> b) The type of rubber being used is one which responds to such agents. </span>
<br /><span style="font-family:courier new;"> c) The other compounding ingredients and mixing conditions are right for maximum activity of the plesticiser </span>
<br /><span style="font-family:courier new;"> d) The cost is favourable in comparison with other methods of getting the same effect.<a name='more'></a></span></span></p><p class="MsoNormal">
<br /><span style=";font-family:Arial;font-size:10pt;" ><o:p></o:p></span></p> <p class="MsoNormal"><span style=";font-family:Arial;font-size:10pt;" >Different chemical Plasticisers and are available which are quite different from one another and are effective under different conditions. Some are listed below:
<br /><span style="font-family:courier new;">1. Certain accelerators (eg. MBT & DPG) have mild Plasticising action on NR.</span>
<br /><span style="font-family:courier new;"> 2. Aromatic mercaptans (eg. Thionaphthol & Xylyl mereaptan) have strong softening effect on NR and reclaim.</span>
<br /><span style="font-family:courier new;"> 3. Phenyl hydrazine salts-strong in NR & SBR.</span>
<br /><span style="font-family:courier new;"> 4. Thiuram disulphides - Strong in neoprenes.</span>
<br /><span style="font-family:courier new;"> 5. Benzami dodipheny1 disulphide - effective only at high temperature.</span>
<br /><span style="font-family:courier new;"> 6. Certain petroleum sulophenol, especially its zinc salt, is powerful in NR and at high temperature in SBR.</span>
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<br />It is important to note that in the absence of a chemical plasticiser NR breaks down most rapidly at low mill temperatures and that the chemical plasticisers work most effectively at high temperatures. For this reason, the compounded should use a fully effective quantity of the chemical plasticiser and masticate at high temperatures or else leave it out altogether and masticate at as low a temperature as possible.
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<br /><span style="font-weight: bold; color: rgb(255, 102, 102);font-size:100%;" >Physical plasticisers are used when:</span>
<br /><span style="font-family:courier new;">a) Modification of the vulcanisate properties is also desired </span>
<br /><span style="font-family:courier new;"> b) Processing required the lubricating, tackifying and other special properties that can be obtained with different physical softeners.</span>
<br /><span style="font-family:courier new;"> c) Cost is favourable in comparison with other approaches</span>.<o:p></o:p></span></p> <span style=";font-family:Arial;font-size:10pt;" >
<br />In general, the main factors considered for selection of physical plasticisers are as follows:
<br /><span style="font-family:courier new;">1. Compatibility</span>
<br /><span style="font-family:courier new;"> 2. Cost</span>
<br /><span style="font-family:courier new;"> 3. Efficiency</span>
<br /><span style="font-family:courier new;"> 4. Staining characteristics</span>
<br /><span style="font-family:courier new;"> 5. Low temperature properties</span>
<br /><span style="font-family:courier new;"> 6. Effect on vulcanization and ageing characteristics of the rubber</span>
<br /></span><meta equiv="Content-Type" content="text/html; charset=utf-8"><meta name="ProgId" content="Word.Document"><meta name="Generator" content="Microsoft Word 11"><meta name="Originator" content="Microsoft Word 11"><link rel="File-List" href="file:///C:%5CDOCUME%7E1%5Csyed%5CLOCALS%7E1%5CTemp%5Cmsohtml1%5C03%5Cclip_filelist.xml"><!--[if gte mso 9]><xml> <w:worddocument> <w:view>Normal</w:View> <w:zoom>0</w:Zoom> <w:punctuationkerning/> <w:validateagainstschemas/> <w:saveifxmlinvalid>false</w:SaveIfXMLInvalid> <w:ignoremixedcontent>false</w:IgnoreMixedContent> <w:alwaysshowplaceholdertext>false</w:AlwaysShowPlaceholderText> <w:compatibility> <w:breakwrappedtables/> <w:snaptogridincell/> <w:wraptextwithpunct/> <w:useasianbreakrules/> <w:dontgrowautofit/> </w:Compatibility> <w:browserlevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:latentstyles deflockedstate="false" latentstylecount="156"> </w:LatentStyles> </xml><![endif]--><style> <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} --> </style><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--><span style=";font-family:Arial;font-size:10pt;" >
<br />Most of the important physical plasticisers come from any one of the following sources.
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<br /><!--[if !supportLineBreakNewLine]--></span><meta equiv="Content-Type" content="text/html; charset=utf-8"><meta name="ProgId" content="Word.Document"><meta name="Generator" content="Microsoft Word 11"><meta name="Originator" content="Microsoft Word 11"><link rel="File-List" href="file:///C:%5CDOCUME%7E1%5Csyed%5CLOCALS%7E1%5CTemp%5Cmsohtml1%5C04%5Cclip_filelist.xml"><!--[if gte mso 9]><xml> <w:worddocument> <w:view>Normal</w:View> <w:zoom>0</w:Zoom> <w:punctuationkerning/> <w:validateagainstschemas/> <w:saveifxmlinvalid>false</w:SaveIfXMLInvalid> <w:ignoremixedcontent>false</w:IgnoreMixedContent> <w:alwaysshowplaceholdertext>false</w:AlwaysShowPlaceholderText> <w:compatibility> <w:breakwrappedtables/> <w:snaptogridincell/> <w:wraptextwithpunct/> <w:useasianbreakrules/> <w:dontgrowautofit/> </w:Compatibility> <w:browserlevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:latentstyles deflockedstate="false" latentstylecount="156"> </w:LatentStyles> </xml><![endif]--><style> <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} --> </style><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--><span style=";font-family:Arial;font-size:10pt;" ><span style="font-family:courier new;">1. petroleum (mineral oils, resins, waxes, asphalt) </span>
<br /><span style="font-family:courier new;"> 2. pine tree (Pine tar, pitch, resins)</span>
<br /><span style="font-family:courier new;"> 3. Coal tar (coal tar oil, pitch, resins)</span>
<br /><span style="font-family:courier new;"> 4. Natural fats & Oils (Vegetable oil, blown Oils, fatty acids, fictive)</span>
<br /><span style="font-family:courier new;"> 5. Synthetic organic compounds (Ester Plasticiser, liquid polymers etc.)</span>
<br /><span style="font-family:courier new;">Petroleum oils are the most common among the above</span>.
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<br /><!--[endif]--></span>pmfhttp://www.blogger.com/profile/16410119039801971518noreply@blogger.com0tag:blogger.com,1999:blog-4939952818505218712.post-81602065399451671782010-12-26T07:18:00.005+05:302011-01-23T12:55:26.180+05:30ANTIOXIDANT<div style="text-align: center; font-weight: bold;"><span style="font-size:130%;"><span style="color: rgb(255, 102, 102);">Antioxidants & Antidegradants </span><br /></span></div>Factors Contributing to Polymer Degradation:<br /><br />• All polymers (saturated / highly unsaturated) are vulnerable to reactive degradation factors such as:<br /><br />- Storage aging<br />- Oxygen<br />- Heat<br />- UV Light & Weathering<br />- Catalytic degradation due to the presence of heavy metal Ions (Cu, Mn, Fe etc.)<br />- Dynamic Flex - Fatigue<br />- Ozone (Static / Dynamic / Intermittent exposure)<br /><br />• These factors degrade polymers causing substantial changes in the technical properties of the rubber products and ultimately lead to their failure during service or shorten the expected service life in the absence of Antioxidants.<br /><br /><div style="text-align: center;"><span style="font-size:130%;"><span style="font-weight: bold; color: rgb(255, 102, 102);">Polymer Degradation Chemistry </span><br /></span></div> • The formation of free radicals (R.) during polymerization, processing or service of the rubber product is the first stage of polymer degradation and is called as ‘Initiation’ of degradation process.<a name='more'></a><br /><br />Heat,<br />Mechanical Stress,<br />Light.<br /><br />R – R--> 2 R.<br /><br />• ‘ Propagation ’ is the second stage when atmospheric oxygen reacts with the free radicals (R. ) to form ‘Peroxy’ ( ROO. ) radicals :<br /><br />R.+ O2--> ROO. (where R. represent free radical)<br />• Peroxy radical further reacts with labile Hydrogen atom of the polymer molecules to form unstable hydro peroxides (ROOH).<br /><br />ROO. + RH -->ROOH + R.<br /><br />• Hydro peroxides immediately decompose via hemolytic cleavage to form alkoxy and hydroxyl radicals and further propagate the degradation mechanism.<br /><br />ROOH -->RO. + .OH<br /><br />• Propagation stage of degradation process is very rapid compared to the Initiation stage.<br /><br />• This autocatalytic oxidation reaction progresses until termination takes place by formation of stable products.<br /><br />• Free radicals R. can undergo following reactions depending on their own relative stability :<br /><br /><span style="font-weight: bold;">- Dimerize (cross link), </span><br /><span style="font-weight: bold;">- Disproportionate (exchange H. becoming alkane & olefin), </span><br /><span style="font-weight: bold;">- Abstract H. (chain transfer), </span><br /><span style="font-weight: bold;">- Cleave (rupture polymer chain), </span><br /><span style="font-weight: bold;">- Rearrange, </span><br /><span style="font-weight: bold;">- React with oxygen. </span><br /><br />• Dimerization causes polymer hardening while cleavage reduces polymer chain lengths (change in hardness & elastic properties and causing fatigue – crack initiation points.<br /><br />• Cleavage may also release of gases (resulting in separations).<br /><br />• Since all the vulcanization ingredients are still present; degradation can take place by continued changes in the state of vulcanization during the rubber product service.<br /><br />• This causes Reversion or marching modulus due to changes in the nature of the sulphur cross links.<br /><br />• The Termination Stage reactions progress as follows :<br /><br />A) Chain Scission<br />2 R2HCOO . -->R2C=O + R2CHOH + O2<br />ROO . + . OH -->ROH + O2<br /><br />• Scission predominates in polymers like NR, IR, IIR (unsaturated polymers which have electron donating groups such as ‘-CH3’ attached to the carbon atom adjacent to the double bond and hence vulnerable).<br />•<br />Scission results in the decrease of molecular weight leading to softening of the aged / over cured vulcanizates, reduction in tensile properties etc.<br /><br />B)<br />Cross linking ;<br /><br />2 R . -->R – R<br />2 R3COO . -->R3COOCR3 + O2<br />2 RO . -->ROOR<br />R . + ROO . -->ROOR<br /><br />• Cross linking predominates in case of polymers like BR, SBR, NBR, CR, etc. which have comparatively less active double bonds or somewhat deactivated double bonds due to the presence of electron-withdrawing groups such as halogens (e.g. CR, Chloro/Bromo Butyl Rubbers). Cross linking results in brittleness, gelation and reduction in elongation of the polymer.<br /><br /><div style="text-align: center; color: rgb(255, 102, 102); font-weight: bold;"><span style="font-size:130%;">EFFECT OF OXYGEN:<br /></span></div> • Only 1– 2 % of combined oxygen is enough to render the rubber product useless.<br /><br />• Polymer oxidation is a complex process involving many factors -processing conditions (e.g. temperature, shear rate), presence of catalysts of oxidation, compounding formulation design etc.<br /><br />• Oxidation causes Chain scission and Cross linking resulting in the loss of elastic properties of vulcanizates. Both occur simultaneously - the one which prevails, determines the final product properties.<br /><br />• The ‘cure system’ selection also influences the ageing resistance of the rubber product. The ‘Conventional Cure’ Systems are more prone to oxidative degradation than the ‘Semi EV’ or ‘EV Cure’ systems.<br /><br /><div style="text-align: center; font-weight: bold; color: rgb(255, 102, 102);">EFFECT OF HEAT :<br /></div> • Heat accelerates the process of oxidation and effects of oxidation are observed soonerand are more severe as the temperature increases.<br /><br />• In case of NR, in the absence of oxygen, more cross links are formed initially, followed by ‘Reversion’ as cross links and polymer chains are broken.<br /><br />• The oxidative heat ageing causes loss of Tensile Strength, Elongation at Break and overall Elasticity of the rubber vulcanizates.<br /><div style="text-align: center;"> <span style="font-size:130%;"><span style="font-weight: bold; color: rgb(255, 0, 0);">EFFECT OF UV - LIGHT & WEATHERING:</span></span><br /></div> • UV-light promotes free radical oxidation of the rubber surface which results in the formation of a film of oxidized rubber on the surface of the product (called as Frosting) .<br /><br />• Heat & Humidity accelerate this process.<br /><br />• Light colored rubber products are more prone to UV-light attack than the black colored products (as carbon black itself acts as a UV-light absorber).<br /><br />• UV-light attack is more severe in case of rubber products with a thin cross section.<br /><br /><div style="text-align: center;"><span style="color: rgb(255, 102, 102);font-size:130%;" ><span style="font-weight: bold;">EFFECT OF OZONE: </span></span><br /></div> • Longer wave length UV light photolyzes Nitrogen Dioxide to yield Oxygen atoms [O.] and Nitrogen Oxide.<br /><br />• The Oxygen atoms then combine with Oxygen molecules present in the atmosphere to form Ozone.<br /><br />• In unpolluted areas the ozone concentration is 2 to 5 pphm. In more polluted areas it can reach to 40 to 50 pphm.<br /><br />• Ozone is also formed in the stratosphere by the action of short wave length UV-light on oxygen. Although the flux of short wave length UV light is absorbed in the upper<br />atmosphere, the concentration of ozone in the troposphere is still appreciable due to the<br />presence of Nitrogen Oxide.<br /><br />• Oxygen atoms liberated by this photolysis of oxygen molecules also combine with oxygen molecules to form ozone.<br /><br />• Since ozone is formed by photolytic reaction, its concentration in the atmosphere peaks at mid-day and is negligible at night.<br /><br />• Ozone concentration in the atmosphere is not temperature dependent but it does peak off during the summer months when the sun light is more directly incident.<br /><br />• The atmospheric ozone concentration varies on daily basis and is dependant on the severity of the sun light, weather conditions, geographic location, air pollution and the season.<br /><br />• The ozone absorption occurs at a linear rate for a typical elastomer.<br /><br />• The ozone absorption is proportional to the concentration of ozone.<br /><br />• The rubber surface which is not stressed also undergoes reaction with ozone to form oxidized film but does not show typical ozone cracks.<br /><br />• No crack growth occurs unless the specific stress value is exceeded. This value is known as ‘Critical Stress Value’.<br /><br />• When the rubber is stressed just above the critical stress value, the ozone cracks are few in numbers but are large in length and depth.<br /><br />• As the stress is increased to a high stress value, the ozone cracks increase in number and are finer in size.<br /><br />• In addition to large number of double bonds present in the highly unsaturated rubbers, ozone also reacts with saturated polymers and the polysulphide chains at a comparatively slower rate.<br /><br />• Unsaturated polymers which contain electron donating groups (e.g. methyl groups in NR) are more vulnerable to ozone attack.<br /><br />• The unsaturated polymers containing electron-withdrawing groups (e.g. Chlorine in CR, Bromine in BIIR) are less vulnerable to ozone attack due to the deactivating effect imposed on the double bonds by the halogen atoms.<br /><br />• Ozone reacts with the double bonds in the rubber molecule causing chain scission. The chain scission results in the formation of surface cracks in the direction perpendicular to the applied strain.<br /><div style="text-align: center;"><span style="font-size:180%;"><span style="font-weight: bold; color: rgb(255, 102, 102);">Role of Antidegradants: </span><br /></span></div> • Antioxidants & Antiozonants are used to protect the polymers from degradation.<br /><br />• Antioxidants are highly effective ingredients and have a dramatic impact on the service life of the rubber product although being present at extremely low concentrations (0.5 – 3.5 phr).<br /><br />• Antioxidants do not completely eliminate oxidative degradation, but they substantially inhibit the rate of auto oxidation by interfering with the radical propagation reaction.<br /><br />• Depending on the types and combinations of antioxidants used, the polymer can be protected during the entire phase of the product’s life cycle.<br /><br />• The Antioxidants are categorized as :<br /><br />A) Primary Antioxidants (Chain Terminating)<br />e.g. Amines & Phenolic.<br />B) Secondary Antioxidants (Peroxide Decomposers)<br />e.g. Phosphites & Thioesters.<br /><br />• Addition of an Antioxidant ( AH ) in small dosage ( 1.0 - 2.0 phr ) interrupts the degradative reactions as follows :<br /><br />R˙ + AH -->RH + A˙ ……………. (Scavenges free radicals.)<br />ROO˙ + AH -->ROOH + A˙ …………. (Prevents chain breaking.)<br />RO˙ + AH -->ROH + A˙ ……........... (Scavenges alkoxy free radicals.)<br />ROOH + AH -->Inert products ……… (Prevents degradation.)<br />ROH + AH -->Inert products………. (Prevents degradation.)<br />• In order to inhibit the degradation cycle (cascading effect) the antioxidants function as follows :<br /><br />a) Scavenge the free radicals before they have opportunity to grow in numbers rapidly,<br />b) Reduce the peroxides & hydro peroxides to alcohols before they produce additional radicals.<br />•Secondary Aryl Amines, Diamines as well as Sterically Hindered Phenolic Antioxidants act by donating their reactive hydrogen atom (N-H, O-H ) to the free radicals as shown below:<br /><br />R . + AH -->RH + A .<br />ROO . + AH --> ROOH + A . ………….(A . is harmless radical)<br />•Thus the Peroxy Radical is offered a more easily abstractable hydrogen by an externally added hydrogen donor (antioxidant) and the polymer backbone remains unaffected until the H-donor (antioxidant) is consumed.<br /><br />•In the above process, the Antioxidants themselves get converted to relatively stable radicals which do not propagate further.<br /><br />•According to the mode of action the antioxidants may be grouped as :<br /><br />H-donors, Hydroperoxide decomposers, Metal deactivators, UV- Light stabilizers etc.<br /><br />•Amine class of primary antioxidants is highly effective due to their ability to act as chain terminators and peroxide decomposers. Antioxidants of this class are most widely used in rubber compounds requiring high degree of protection.<br /><div style="text-align: center; color: rgb(255, 102, 102);"><span style="font-size:180%;"><span style="font-weight: bold;">Role of Antiozonants:</span></span><br /></div>•The exact mechanism of ozone protection of rubber vulcanizates is still not established!<br /><br />•Following four theoretical models have been proposed :<br />1. Inert barrier theory.<br />2. Competitive reaction theory.<br />3. Reduced critical stress theory.<br />4. Chain repair theory.<br /><br />•The Inert Barrier Theory proposes that the antiozonant migrates from the bulk of the rubber to the surface to form a film. This film functions as a physical barrier which protects the reactive polymer double bonds by keeping ozone out of contact.<br /><br />•The Inert Barrier Theory Mechanism is similar to ozone protection offered by waxes and non reactive polymers such as EPDM, Halogenated butyl rubber, halogenation of the surface of rubber vulcanizate etc.<br /><br />•The ‘Reduced Critical Stress Theory’ proposes that the rubber vulcanizate surface is modified by the migration of the antiozonant on the surface or just below the surface of the rubber.<br /><br />•This modification relieves the internal and surface stresses and the vulcanizate behaves as if it was unstressed or at lower than critical stress required for ozone crack formation.<br /><br />•The ‘Chain Repair Theory’ proposes that antiozonant reacts directly with the ozonide or the carbonyl oxide forming a low molecular weight, inert & self healing film which attaches the antiozonant to the rubber.<br /><br />•The Competitive Reaction Theory is sub divided into ‘Scavenger Theory’ & ‘Protective Film Theory’.<br /><br />•The ‘Scavenger Theory’ proposes that as the antiozonant migrates to the surface; it selectively reacts with ozone and protects the polymer double bonds until the antiozonant is exhausted.<br /><br />•‘Protective Film Theory’ proposes that once the antiozonant has been fully exhausted, the reaction products of the antiozonant form an Inert Protective Film over the surface of the rubber vulcanizate.<br /><br />•The Competitive Reaction theory is substantiated by experiments and is well accepted.pmfhttp://www.blogger.com/profile/16410119039801971518noreply@blogger.com0tag:blogger.com,1999:blog-4939952818505218712.post-37968815495641043222010-12-22T19:57:00.010+05:302011-01-22T09:44:50.521+05:30ACCELERATORS<div style="text-align: center; font-weight: bold;"><span style="color: rgb(255, 0, 0);">ACCELERATORS: DEFINITION & CLASSIFICATION</span>
<br /></div> •An accelerator is defined as the chemical added into a rubber compound to increase the speed of vulcanization and to permit vulcanization to proceed at lower temperature and with greater efficiency.
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<br />•Accelerator also Decreases the Quantity of Sulphur necessary for vulcanization thus improving 'aged' properties of the rubber vulcanizates.
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<br />•Over 150 different chemicals belonging to different classes of composition are known to function as accelerators for rubber vulcanizates of which around 50 accelerators are most commonly used by the Rubber Industry.
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<br />•The accelerators are generally classified as follows :
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<br />Chemical Composition Accelerators Vulcanisation Speed
<br />Aldehyde Amines BA, HMT Slow
<br />Guanidines DPG, DOTG Slow
<br />Thiazoles ZMBT, MBT, MBTS Moderate
<br />Thiophosphates ZDBP Semi-Fast
<br />Sulphenamides CBS, TBBS, MBS Fast (delayed action)
<br />Thioureas ETU, DPTU, DBTU Fast
<br />Thiurams TMTM, TMTD, TETD, DPTT Very Fast
<br />Dithiocarbamates ZDEC, ZDMC, ZDBC Very Fast<a name='more'></a><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgKLiFijdTAsIH82fEd1OKNjc89eyDL7eY9ejOLh46GMbdH53tePtSrhRrLnSlD8_fwTwbm9h_mOQwlbfrE8eHO2zU22xmQbO_DHMJPBH7QqwotL8zUH2dXGaj0fkz8_zKuI_NahSL0LgQ/s1600/Untitled-2.jpg"><img style="cursor: pointer; width: 400px; height: 300px;" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgKLiFijdTAsIH82fEd1OKNjc89eyDL7eY9ejOLh46GMbdH53tePtSrhRrLnSlD8_fwTwbm9h_mOQwlbfrE8eHO2zU22xmQbO_DHMJPBH7QqwotL8zUH2dXGaj0fkz8_zKuI_NahSL0LgQ/s400/Untitled-2.jpg" alt="" id="BLOGGER_PHOTO_ID_5553537748405991202" border="0" /></a>
<br />Xanthates ZIX, SIX Extremely Fast
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mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--></a><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"><div class="Section1"><div style="text-align: center;"></div><p class="Default" style="margin: 6pt 0in 6pt 0.25in; text-indent: -0.25in; text-align: center;"><b style="color: rgb(255, 102, 102);"><span style="font-size:11pt;">SELECTION OF ACCELERATOR SYSTEM </span></b><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default" style="margin-left: 0in; text-indent: 0in;"><!--[if !supportLists]--><span style=";font-family:";font-size:11pt;" ><span style=""><span style="font: 7pt "Times New Roman";">
<br /></span></span></span><span style=";font-family:";font-size:11pt;" ><o:p></o:p></span></p> <p class="Default"><span style="font-size:11pt;">-Before selecting an Accelerator system for the manufacture of a particular rubber product, following points have to be taken into account.
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >- <o:p></o:p></span><span style="font-size:11pt;">Expected shelf life of the compound,
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >- <o:p></o:p></span><span style="font-size:11pt;">Accelerators solubility in rubber (high solubility to avoid bloom and improve dispersibility),</span></p><p class="Default">
<br /><span style="font-size:11pt;"> <o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >- <o:p></o:p></span><span style="font-size:11pt;">Various processing stages the rubber compound be required to undergo,
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >- <o:p></o:p></span><span style="font-size:11pt;">Adequate processing safety for 'scorch free' processing operations,
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >- <o:p></o:p></span><span style="font-size:11pt;">Faster curing rate for economical production of rubber product,
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >- <o:p></o:p></span><span style="font-size:11pt;">No reversion on over cure,
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >- <o:p></o:p></span><span style="font-size:11pt;">Vulcanisation method to be used (mode of heat transfer),
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >- <o:p></o:p></span><span style="font-size:11pt;">Maximum vulcanisation temperature available,
<br /></span></p><p class="Default">
<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >- <o:p></o:p></span><span style="font-size:11pt;">Cure cycle desired at the available vulcanisation method and temperature and requirements of vulcanizates properties,
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >- <o:p></o:p></span><span style="font-size:11pt;">Effectiveness of the accelerator system over a wide range of cure temperatures and suitability for use with different polymers,
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >- <o:p></o:p></span><span style="font-size:11pt;">No adverse effects on other properties (e.g. bonding, ageing, adhesion, etc.) and no adverse effects on other non-rubber components in the rubber product,
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >- <o:p></o:p></span><span style="font-size:11pt;">No known health hazards upon usage as chemical / its decomposition products on cure,
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >- <o:p></o:p></span><span style="font-size:11pt;">No adverse effects during end-use of the rubber product (e.g. accelerators used in the manufacture of rubber articles intended for food contact / surgical use),
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >- <o:p></o:p></span><span style="font-size:11pt;">Stability of the accelerator as a chemical (e.g. problems with the use of decomposed sulphenamide accelerators),
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >- <o:p></o:p></span><span style="font-size:11pt;">Easy to handle and dust suppressed physical form. <o:p></o:p></span></p> <p class="Default"><span style="font-size:11pt;"><o:p>
<br /></o:p></span></p> <p class="Default" style="margin: 6pt 0in; text-align: center;"><b><i><span style="font-size:11pt;"><span style="color: rgb(255, 102, 102);">THIAZOLE CLASS ACCELERATORS</span> </span></i></b><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><!--[if !supportLists]--><span style=";font-family:";font-size:11pt;" ><span style=""><span style="font: 7pt "Times New Roman";"> </span></span></span><!--[endif]--><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">This class of accelerators include commercially available and widely used accelerators such as Pilcure MBT, Pilcure MBTS and Pilcure ZMBT (also sodium salt of MBT finds use in few rubber and non rubber applications).
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">Thiazoles are medium-fast primary accelerators with only moderate processing safety. Thiazoles are most widely used accelerators in the rubber industry for the production of wide variety of goods such as cycle tyres and tubes, footwear, beltings, hoses and other moulded and extruded goods.
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">Thiazoles are activated by zinc oxide/Stearic acid combination and produce flat cure with vulcanizates having very good reversion resistance.
<br /></span></p> </div> <span style=";font-family:Arial;font-size:11pt;color:black;" >
<br /></span> <div class="Section2"><p class="Default"><!--[if !supportLists]--><span style=";font-family:";font-size:11pt;" ><span style=""><span style="font: 7pt "Times New Roman";"> </span></span></span><!--[endif]--><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">Activity of Thiazole accelerators with respect to cure characteristics can be summarised as follows: <o:p></o:p></span></p> <p class="Default" style="margin: 6pt 0in 6pt 0.25in; text-indent: -0.25in;"><span style="font-size:11pt;"><o:p> </o:p>1. Scorch Safety </span><span style=";font-family:Wingdings;font-size:11pt;" >:---</span><span style="font-size:11pt;">Longer…. (MBT <></span></p> <p class="Default" style="margin: 6pt 0in 6pt 0.25in; text-indent: -0.25in;"><span style="font-size:11pt;">2. Cure Rate </span><span style=";font-family:Wingdings;font-size:11pt;" >:---</span><span style="font-size:11pt;">Faster….. (ZMBT <></span></p> <p class="Default" style="margin: 6pt 0in 6pt 0.25in; text-indent: -0.25in;"><span style="font-size:11pt;">3. Crosslink Density:---</span><span style=";font-family:Wingdings;font-size:11pt;" ></span><span style="font-size:11pt;">Higher at equal dosage….. (ZMBT <></p><p class="Default" style="margin: 6pt 0in 6pt 0.25in; text-indent: -0.25in;"><span style="font-size:11pt;">
<br /></span></p> <p class="Default"><!--[if !supportLists]--><span style=";font-family:";font-size:11pt;" ><span style=""><span style="font: 7pt "Times New Roman";"></span></span></span><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">Thiazoles act as retarders of cure in rubber compounds accelerated using Thiurams (TMTD/TMTM)/Dithiocarbamates (ZDC, ZDBC) or ETU class accelerators as main accelerator and also reduce bloom of Thiurams and dithiocarbamates in EV cure systems.
<br /></span></p><p class="Default">
<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">All thiazole accelerators can be further boosted to increase speed of vulcanisation by using small quantities of basic accelerators such as DPG, DOTG, TMTM, TMTD, ZDC, etc
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">Thiazole based accelerators can be retarded using small proportion of Pilgard PVI or other retarders like NDPA, pthalic anhydride, salicylic acid, etc.
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">Addition of extra Stearic acid or partial replacement by sulphenamide accelerator also control scorch to some extent.
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">Thiazoles are particularly preferred for rubber to metal bonding applications. <o:p></o:p></span></p> <p class="Default"><span style="font-size:11pt;"><o:p> </o:p></span></p> <p class="Default" style="margin: 6pt 0in; text-align: center;"><b style="color: rgb(255, 102, 102);"><i><span style="font-size:11pt;">SULPHENAMIDE CLASS ACCELERATORS </span></i></b><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><!--[if !supportLists]--><span style=";font-family:";font-size:11pt;" ><span style=""><span style="font: 7pt "Times New Roman";"> </span></span></span><!--[endif]--><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">The sulphenamide class accelerators are most popular in the rubber industry due to the <b>delayed action as well as faster cure rate </b>offered by them during vulcanisation of rubber specially containing furnace blacks.
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">The sulphenamide accelerators are the reaction products of 2- mercaptobenzothiazole with basic amines such as cyclohexylamine / tert-butylamine / morpholine / dicyclohexyl amine.
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">Sulphenamide accelerators are usually incorporated in the rubber compound at the end of mixing cycle when temperature is above melting point of the accelerator to ensure proper dispersion.
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">Generation of excess heat is avoided to prevent decomposition of sulphenamide accelerator.</span></p><p class="Default">
<br /><span style="font-size:11pt;"> <o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">In case sulphenamide accelerator is to be added at a later stage; addition in the form of sulphenamide rubber master batch is recommended.
<br /></span></p><p class="Default">
<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">These accelerators provide wide range of crosslink densities depending on type and dosage of accelerator used and exhibit flat reversion resistant cure.
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<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">Progressive increase in dosage of sulphenamide accelerator shows improvement in scorch delay, cure rate and state of cure.</span></p><p class="Default">
<br /><span style="font-size:11pt;"> <o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">Sulphenamide accelerators can be boosted by using DPG, DOTG, TMTM, TMTD type basic accelerators for further increasing the cure rate (but at the expense of scorch safety)
<br /></span></p><p class="Default">
<br /><span style="font-size:11pt;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:";font-size:11pt;" >• <o:p></o:p></span><span style="font-size:11pt;">Vulcanizates of sulphenamide accelerators have a typical 'aminic' odour and exhibit higher stress-strain properties along with better resilience and flex-fatigue resistance as compared to Thiazoles. <o:p></o:p></span></p> </div> <span style=";font-family:Arial;font-size:11pt;color:black;" >
<br /></span> </a><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"></a><div class="Section3"><div style="text-align: left;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a></div><p class="Default" style="margin: 6pt 0in 6pt 0.25in; text-align: left;"><!--[if !supportLists]--><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">PVI (CTP) is a very effective prevulcanisation (scorch) inhibitor for Sulphenamide / activated Sulphenamide cure systems without compromise on the rate of cure . The improvement in scorch safety is directly proportional to the dosages of and minimum dosages are required for <o:p></o:p>obtaining desired scorch safety. Excess dosage of PVI is avoided as same may cause undesired delay for onset of cure besides affecting the state of cure to some extent. <o:p></o:p></a></span></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><!--[if !supportLists]--><span style=";font-family:";font-size:11pt;" ><span style=""><span style="font: 7pt "Times New Roman";"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a></span></span></span><!--[endif]--><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Sulphenamide accelerators decompose rapidly in the presence of steam and hence are preferred for manufacture of open steam cured rubber products requiring faster onset of cure for better shape retention. However, this advantage is lost in the case of hot air cured products.
<br /></a></span></p><p class="Default"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Activity of Sulphenamide accelerators can be summarised as follows: <o:p></o:p></a></span></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style="font-size:11pt;"><o:p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a></o:p></span></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default" style="margin: 6pt 0in;"><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">1. Scorch safety </a></span><span style=";font-family:Wingdings;font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">:---</a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Longer (CBS <></a></span></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default" style="margin: 6pt 0in;"><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">2. Cure Rate </a></span><span style=";font-family:Wingdings;font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">:---</a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Faster (DCBS <></a></span></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default" style="margin: 6pt 0in;"><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">3. Crosslink density </a></span><span style=";font-family:Wingdings;font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">:---</a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Higher at equal dosage (DCBS <></a></span></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default" style="margin: 6pt 0in 6pt 0.25in; text-indent: -0.25in;"><!--[if !supportLists]--><span style=";font-family:Wingdings;font-size:11pt;" ><span style=""><span style="font: 7pt "Times New Roman";"></span></span></span><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default" style="margin: 6pt 0in; text-align: center;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"><b style="color: rgb(255, 102, 102);"><i><span style="font-size:11pt;">THIURAM CLASS ACCELERATORS </span></i></b><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><!--[if !supportLists]--><span style=";font-family:";font-size:11pt;" ><span style=""><span style="font: 7pt "Times New Roman";"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a></span></span></span><!--[endif]--><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Thiuram class includes accelerators such as TMTM, TMTD, TETD and DPTT.
<br /></a></span></p><p class="Default"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Thiurams are ultra-fast accelerators for NR, SBR, BR, NBR and other highly unsaturated rubbers and the most preferred primary accelerator for sulphur cured low-unsaturation content rubbers like butyl (IIR) and EPDM.
<br /></a></span></p><p class="Default"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Thiurams exhibit higher processing safety and late onset of cure compared to dithiocarbamate accelerators.
<br /></a></span></p><p class="Default"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Thiurams are widely used as secondary accelerator generally at 0.05 - 0.4 phr with thiazole / sulphenamide class accelerators to achieve faster curing rate, higher crosslink density with a compromise on scorch safety and Vulcanizate exhibits lower heat build up compared to DPG/DOTG activated sulphenamide cures.
<br /></a></span></p><p class="Default"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Thiurams, when used as vulcanising agents (2.5 - 3.0 phr) in the absence of sulphur, vulcanizates attain high degree of state of cure exhibiting high tensile strength, high modulus, lower elongation at break, higher rebound resilience at elevated temperatures and lower tear resistance.
<br /></a></span></p><p class="Default"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Thiurams are also used along with Guanidines in Polychloroprene compounds to achieve good processing safety.
<br /></a></span></p><p class="Default"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">In combination with Dithiocarbamates and Xanthates, Thiurams have retarding effect without changing the rate of vulcanisation. <o:p></o:p></a></span></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a></div><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> <span style=";font-family:Arial;font-size:11pt;color:black;" > </span>
<br /> </a><p class="Default"><!--[if !supportLists]--><span style=";font-family:";font-size:11pt;" ><span style=""><span style="font: 7pt "Times New Roman";"></span></span></span><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Thiuram accelerators do not discolour the vulcanizates & the products are tasteless. <o:p></o:p></a></span></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style="font-size:11pt;"><o:p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /></a></o:p></span></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><!--[if !supportLists]--><span style=";font-family:";font-size:11pt;" ><span style=""><span style="font: 7pt "Times New Roman";"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a></span></span></span><!--[endif]--><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Activity of various thiuram accelerators with respect to cure characteristics can be summarised as follows : <o:p></o:p></a></span></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default" style="margin: 6pt 0in;"><span style="font-size:11pt;"><o:p></o:p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">1. Scorch Safety </a></span><span style=";font-family:Wingdings;font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">:-</a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">--Longer (TMTD <><span style=";font-family:Wingdings;font-size:11pt;" >:--- </span><span style="font-size:11pt;">Faster (TMTM = TETD = TMTD) 3. Crosslink density at equal dosage </span><span style=";font-family:Wingdings;font-size:11pt;" >:--- </span><span style="font-size:11pt;">Higher (TMTM = TETD = TMTD) <o:p></o:p></span></a></span></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><div style="text-align: center;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"><p class="Default" style="margin: 6pt 0in 6pt 0.25in; text-indent: -0.25in;"><b style="color: rgb(255, 102, 102);"><span style="font-size:11pt;">DITHIOCARBAMATE CLASS ACCELERATORS </span></b><span style="font-size:11pt;"><o:p></o:p></span></p></a></div><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><!--[if !supportLists]--><span style=";font-family:";font-size:11pt;" ><span style=""><span style="font: 7pt "Times New Roman";"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a></span></span></span><!--[endif]--><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Dithiocarbamate class includes accelerators such as ZDBC, ZDEC, ZDMC, etc.
<br /></a></span></p><p class="Default"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Dithiocarbamate accelerators are widely used as ultra fast accelerator for NR latex based compounds and also finds applications as primary or secondary accelerators in most dry rubber based sulphur cured compounds.
<br /></a></span></p><p class="Default"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">The dithiocarbamate class accelerators require Zinc oxide and Stearic acid for activation and produce rapid vulcanisation.
<br /></a></span></p><p class="Default"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Dithiocarbamate s exhibit very low scorch safety, faster cure rate and higher crosslink density and rubber products can be vulcanised in a short time at low temperature (115 - 120°C).
<br /></a></span></p><p class="Default"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Compounds accelerated with dithiocarbamates have a very narrow plateau hence reversion due to over cure can take place very rapidly. <o:p></o:p></a></span></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Low unsaturation content rubbers such as EPDM and IIR can be cured using dithiocarbamate as a secondary accelerator (at relatively higher dosage) along with Thiazoles and thiuram class accelerators.</a></span></p><p class="Default"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"> <o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Compounds accelerated with dithiocarbamates have a very narrow plateau hence reversion due to over cure can take place very rapidly.
<br /></a></span></p><p class="Default"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Dithiocarbamate accelerators have limited solubility in rubber compounds and hence excess quantity tends to bloom on the surface of the vulcanizates.
<br /></a></span></p><p class="Default"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Dithiocarbamates are non staining and non discolouring even on exposure to light and are suitable for the manufacture of transparent goods.
<br /></a></span></p><p class="Default"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">
<br /><span style="font-size:11pt;"><o:p></o:p></span></a></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default"><span style=";font-family:";font-size:11pt;" ><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">• <o:p></o:p></a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Activities of various dithiocarbamate accelerators with respect to cure characteristics in dry rubber compounds can be summarised as follows: <o:p></o:p></a></span></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="Default" style="margin: 6pt 0in;"><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">1. Scorch Safety </a></span><span style="" face="Wingdings" size="11pt"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">:--- </a></span><span style="font-size:11pt;"><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg">Longer (ZDMC <><span style="font-size:11pt;">Faster (ZDBC = ZDEC = ZMDC) 3. Crosslink density at equal dosage :---</span><span style="font-size:11pt;">Higher ( ZDBC = ZDEC = ZDMC) <o:p></o:p></span></a></span></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><p class="MsoNormal"><o:p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a></o:p></p><a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4c0EAzeS_3XOGwhRvQ85eCB-8BEwYhG7dfKucn3_08VADuClGh38YyQBT9KQhBDS-rSAUUqwbJvs8KerootvtOAVx4qR-ZIZIeSRJA99tZgWk2KB5JWy_fYsdV3ugig-TiFpaEP5wqRY/s1600/Untitled-1.jpg"> </a><a style="color: rgb(51, 0, 0);" onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgnFeLQHtdbLLHrgCR_rnNLI9SZm7T-QQXD67pdJUoC76nYfM4fRKRrZ7wwH360fmeJQzGXkBjyZ4AcVB6vV4D9hySOnqg4nz13JfRualb6HOy87VxympxzHJXlTH9zGJcCY25a072bic8/s1600/Untitled-1.jpg"></a>pmfhttp://www.blogger.com/profile/16410119039801971518noreply@blogger.com0tag:blogger.com,1999:blog-4939952818505218712.post-52666812832262300032010-12-20T20:27:00.005+05:302011-01-23T09:36:20.310+05:30VULCANIZATIONVulcanization is a cross linking process in which individual molecules of a polymer (such as rubber)
<br />is converted into three dimensional network of interconnected polymer chains through a chemical cross link.
<br />comparing with unvulcanized polymer the vulcanized polymer has
<br />
<br /><span style="font-weight: bold;"><span style="font-size:130%;">-<span style="font-size:100%;">High viscosity
<br />-High modulus
<br />-high tensile strength
<br />-low elongation
<br />-high hardness
<br />-high resilience
<br />-high abrasion resistance
<br />-high elasticity
<br />-high flex-fatigue<a name='more'></a>
<br /></span></span></span>
<br /><meta equiv="Content-Type" content="text/html; charset=utf-8"><meta name="ProgId" content="Word.Document"><meta name="Generator" content="Microsoft Word 11"><meta name="Originator" content="Microsoft Word 11"><!--[if !mso]> <style> v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} </style> <![endif]--><!--[if gte mso 9]><xml> <w:worddocument> <w:view>Normal</w:View> <w:zoom>0</w:Zoom> <w:punctuationkerning/> <w:validateagainstschemas/> <w:saveifxmlinvalid>false</w:SaveIfXMLInvalid> <w:ignoremixedcontent>false</w:IgnoreMixedContent> <w:alwaysshowplaceholdertext>false</w:AlwaysShowPlaceholderText> <w:compatibility> <w:breakwrappedtables/> <w:snaptogridincell/> <w:wraptextwithpunct/> <w:useasianbreakrules/> <w:dontgrowautofit/> </w:Compatibility> <w:browserlevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:latentstyles deflockedstate="false" latentstylecount="156"> </w:LatentStyles> </xml><![endif]--><style> <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; 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charset=utf-8"><meta name="ProgId" content="Word.Document"><meta name="Generator" content="Microsoft Word 11"><meta name="Originator" content="Microsoft Word 11"><!--[if gte mso 9]><xml> <w:worddocument> <w:view>Normal</w:View> <w:zoom>0</w:Zoom> <w:punctuationkerning/> <w:validateagainstschemas/> <w:saveifxmlinvalid>false</w:SaveIfXMLInvalid> <w:ignoremixedcontent>false</w:IgnoreMixedContent> <w:alwaysshowplaceholdertext>false</w:AlwaysShowPlaceholderText> <w:compatibility> <w:breakwrappedtables/> <w:snaptogridincell/> <w:wraptextwithpunct/> <w:useasianbreakrules/> <w:dontgrowautofit/> </w:Compatibility> <w:browserlevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:latentstyles deflockedstate="false" latentstylecount="156"> </w:LatentStyles> </xml><![endif]--><!--[if !mso]><object classid="clsid:38481807-CA0E-42D2-BF39-B33AF135CC4D" id="ieooui"></object> <style> st1\:*{behavior:url(#ieooui) } </style> <![endif]--><style> <!-- /* Font Definitions */ @font-face {font-family:Wingdings; 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mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--><span style="font-size:100%;">• </span><span style=";font-family:Arial;font-size:100%;" >The vulcanization process was discovered in 1839 and the individuals responsible for this discoverywere - Charles Goodyear in <st1:country-region st="on">USA</st1:country-region> and Thomas Hancock in <st1:country-region st="on"><st1:place st="on">England
<br />
<br /></st1:place></st1:country-region><!-- more>Both discovered the use of <st1:city st="on"><st1:place st="on">Sulphur</st1:place></st1:city> and White Lead as a vulcanization system for Natural Rubber. This discovery was a major technological breakthrough.<o:p></o:p></span><div> </div><p class="MsoNormal" style="margin: 3pt 0in 3pt 0.25in; text-align: center; text-indent: -0.25in;" align="center"></p><p style="text-align: left;" class="Default"><span style=";font-family:Arial;font-size:100%;"><span style=""> </span><o:p></o:p></span></p><p></p><div style="text-align: left;"> </div><p class="MsoNormal" style="margin: 3pt 0in 3pt 0.25in; text-align: center; text-indent: -0.25in;" align="center"></p><p style="text-align: left;" class="Default"><span style="font-size:100%;">• </span><span style=";font-family:Arial;font-size:100%;">The structure of speciality elastomer such as - EPDM and Butyl had to be chemically modified to make sulphur vulcanization possible for their commercial success.<br /></span></p><p style="text-align: left;" class="Default"><br /><span style=";font-family:Arial;font-size:100%;"><o:p></o:p></span></p> <p class="Default"><span style="font-size:100%;"><o:p> </o:p></span></p> <p style="text-align: left;" class="Default"><span style="font-size:100%;">•</span><span style=";font-family:Arial;font-size:100%;">Vulcanization of elastomer by sulphur alone is an extremely slow and inefficient process.<br /></span></p><p style="text-align: left;" class="Default"><br /><span style="font-size:100%;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:Arial;font-size:100%;"><o:p> </o:p></span></p> <p style="text-align: left;" class="Default"><span style="font-size:100%;">• </span><span style=";font-family:Arial;font-size:100%;">The chemical reaction between <st1:city st="on"><st1:place st="on">Sulphur</st1:place></st1:city> and the Rubber Hydrocarbon occurs mainly at the C = C double bonds and each crosslink requires 40 to 55 sulphur atoms (in the absence of accelerator). The process takes around 6 hours at 140°C for completion, which is uneconomical by any production standards.<br /></span></p><p style="text-align: left;" class="Default"><br /><span style="font-size:100%;"><o:p></o:p></span></p> <p class="MsoNormal"><span style="font-size:100%;"><o:p> </o:p></span></p> <p style="text-align: left;" class="Default"><span style="font-size:100%;">• </span><span style=";font-family:Arial;font-size:100%;">The vulcanizates thus produced are extremely prone to oxidative ageing and do not possess adequate mechanical properties for practical applications. These limitations are overcome by use of <o:p></o:p></span></p> <p class="Default" style="margin: 3pt 0in 3pt 0.25in; text-indent: -0.25in; text-align: left;"><span style=";font-family:Arial;font-size:100%;">- <b>Accelerators </b><o:p></o:p></span></p> <p class="Default" style="margin: 3pt 0in 3pt 0.25in; text-indent: -0.25in; text-align: left;"><span style="font-size:100%;"><b><span style="font-family:Arial;">- Antioxidants / Antidegradants<o:p></o:p></span></b></span></p> <p class="Default" style="margin: 3pt 0in 3pt 0.25in; text-indent: -0.25in;"><span style="font-size:100%;"><b><span style="font-family:Arial;"><span style=""> </span></span></b></span><span style=";font-family:Arial;font-size:100%;"><o:p></o:p></span></p> <p style="text-align: left;" class="Default"><span style="font-size:100%;">• <st1:place st="on"><st1:city st="on"><span style="font-family:Arial;">Sulphur</span></st1:city></st1:place></span><span style=";font-family:Arial;font-size:100%;"> as vulcanizing agent has a limitation that, the elastomer must contain chemical unsaturation (double bonds) for cross linking.</span></p><p style="text-align: left;" class="Default"><br /><span style=";font-family:Arial;font-size:100%;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:Arial;font-size:100%;"><span style=""> </span><o:p></o:p></span></p> <p style="text-align: left;" class="Default"><span style="font-size:100%;">• </span><span style=";font-family:Arial;font-size:100%;">In case of fully saturated elastomer organic peroxides are often used for cross linking.<br /></span></p><p style="text-align: left;" class="Default"><br /><span style=";font-family:Arial;font-size:100%;"><o:p></o:p></span></p> <p class="Default"><span style="font-size:100%;"><o:p> </o:p></span></p> <p style="text-align: left;" class="Default"><span style="font-size:100%;">• </span><span style=";font-family:Arial;font-size:100%;">Other chemicals used for cross linking of polymers are Sulphur monochloride, Tellurium, Selenium, Thiuram accelerators, Polysulphide polymers, p- Quinonedioximes, Metallic Oxides, Organic Peroxides, Di-isocyanates, etc. (mostly for specialized applications).<br /></span></p><p style="text-align: left;" class="Default"><span style="font-size:100%;"><br /></span><span style="font-size:100%;"><o:p></o:p></span></p> <p style="text-align: left;" class="Default"><span style="font-size:100%;">• <st1:city st="on"><st1:place st="on">Sulphur</st1:place></st1:city> alone was not economically suitable as a vulcanising agent . Efforts continued to increase the Speed and Efficiency of sulphur vulcanisation. </span><span style="font-size:100%;"><o:p></o:p></span></p> <p class="MsoNormal" style=""><span style=";font-family:Arial;font-size:100%;"><o:p> </o:p></span><span style="font-size:100%;"><o:p><br /></o:p></span></p> <p style="text-align: left;" class="Default"><span style="font-size:100%;">• </span><span style=";font-family:Arial;font-size:100%;">Only the cross links which form bridges between the chains are stress bearing members contributing to elasticity and strength,</span></p><p style="text-align: left;" class="Default"><br /><span style=";font-family:Arial;font-size:100%;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:Arial;font-size:100%;"><span style=""> </span><o:p></o:p></span></p> <p style="text-align: left;" class="Default"><span style="font-size:100%;">• </span><span style=";font-family:Arial;font-size:100%;">Cyclic sulphides, accelerator fragments, vicinal cross links do not contribute to elasticity</span></p><p style="text-align: left;" class="Default"><br /><span style=";font-family:Arial;font-size:100%;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:Arial;font-size:100%;"><span style=""> </span></span><span style="font-size:100%;"><o:p></o:p></span></p> <p style="text-align: left;" class="Default"><span style="font-size:100%;">• </span><span style=";font-family:Arial;font-size:100%;">‘Sx’ refers to cross links consisting of more than two sulphur atoms (Polysulphidic cross links)</span></p><p style="text-align: left;" class="Default"><br /><span style=";font-family:Arial;font-size:100%;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:Arial;font-size:100%;"><span style=""> </span></span><span style="font-size:100%;"><o:p></o:p></span></p> <p style="text-align: left;" class="Default"><span style="font-size:100%;">• </span><span style=";font-family:Arial;font-size:100%;">‘Sx’ gets desulphurated to form cross links with two sulphur atoms or one sulphur atom (di or mono sulphidic cross links) with the action of heat (as low as at 90 - 100°C).<br /></span></p><p style="text-align: left;" class="Default"><br /><span style=";font-family:Arial;font-size:100%;"><o:p></o:p></span></p> <p class="Default"><span style="font-size:100%;"><o:p> </o:p></span></p> <p style="text-align: left;" class="Default"><span style="font-size:100%;">• </span><span style=";font-family:Arial;font-size:100%;">The crosslink structure depends on the nature of rubber, ratio of sulphur to accelerator and temperature of vulcanisation. </span><span style="font-size:100%;"><o:p></o:p></span></p> <p class="Default"><span style=";font-family:Arial;font-size:100%;"><o:p> </o:p></span></p> <p class="MsoNormal" style="margin: 3pt 0in 3pt 0.25in; text-indent: -0.25in; font-weight: bold; text-align: center;"><span style=";font-family:Arial;font-size:100%;color:black;"><span style="color: rgb(255, 102, 102);">GENERAL MECHANISM OF ACCELERATED </span><st1:city style="color: rgb(255, 102, 102);" st="on"><st1:place st="on">SULPHUR</st1:place></st1:city><span style="color: rgb(255, 102, 102);"> VULCANIZATION </span><o:p></o:p></span></p> <p class="MsoNormal" style="margin: 3pt 0in 3pt 0.25in; text-indent: -0.25in; text-align: left;"><span style=";font-size:100%;color:black;">• </span><span style=";font-family:Arial;font-size:100%;color:black;">Three competing reactions occur. <b>Cross linking, Desulphuration & Degradation. <o:p></o:p></b></span></p> <p class="MsoNormal" style="margin: 3pt 0in 3pt 0.25in; text-indent: -0.25in;"><span style=";font-family:Arial;font-size:100%;color:black;"><o:p> </o:p></span></p> <p class="MsoNormal" style="text-align: left;"><span style=";font-size:100%;color:black;">• </span><span style=";font-family:Arial;font-size:100%;color:black;">Accelerator, Activators and <st1:city st="on"><st1:place st="on">Sulphur</st1:place></st1:city> interact in the presence of Heat to form Active Sulphurating Agent . </span><span style=";font-size:100%;color:black;"><o:p></o:p></span></p> <p class="MsoNormal" style=""><span style=";font-family:Arial;font-size:100%;color:black;"><o:p> </o:p></span></p> <p class="MsoNormal" style="margin: 3pt 0in 3pt 0.25in; text-align: center; text-indent: -0.25in;" align="center"><span style="font-size:100%;"><b><span style=";font-family:Arial;color:black;">Ac + S</span></b><b><span style=";font-family:Arial;color:black;">8 </span></b></span><span style=";font-family:Wingdings;font-size:100%;color:black;">�� </span><span style="font-size:100%;"><b><span style=";font-family:Arial;color:black;">Ac-S</span></b><b><span style=";font-family:Arial;color:black;">x</span></b><b><span style=";font-family:Arial;color:black;">-Ac ( Active Sulphurating Agent ) </span></b></span><span style=";font-family:Arial;font-size:100%;color:black;"><o:p></o:p></span></p> <p class="MsoNormal" style="text-align: left;"><span style=";font-size:100%;color:black;">• </span><span style=";font-family:Arial;font-size:100%;color:black;">Polymer Chains ( RH ) interact with the ‘Active Sulphurating Agent ‘ to form ‘Polysulphidic Pendant Groups‘ terminated by accelerator groups. <o:p></o:p></span></p> <p class="MsoNormal" style=""><span style=";font-family:Arial;font-size:100%;color:black;"><o:p> </o:p></span></p> <p class="MsoNormal" style="margin: 3pt 0in 3pt 0.25in; text-align: center; text-indent: -0.25in;" align="center"><span style="font-size:100%;"><b><span style=";font-family:Arial;color:black;">Ac-S</span></b><b><span style=";font-family:Arial;color:black;">x </span></b><b><span style=";font-family:Arial;color:black;">-Ac + RH </span></b></span><span style=";font-family:Wingdings;font-size:100%;color:black;">�� </span><span style="font-size:100%;"><b><span style=";font-family:Arial;color:black;">R -S</span></b><b><span style=";font-family:Arial;color:black;">x</span></b><b><span style=";font-family:Arial;color:black;">- Ac + AcH ( Pendant Sulphurating Group ) <o:p></o:p></span></b></span></p> <p class="MsoNormal" style="margin: 3pt 0in 3pt 0.25in; text-align: center; text-indent: -0.25in;" align="center"><span style=";font-family:Arial;font-size:100%;color:black;"><o:p> </o:p></span></p> <p class="MsoNormal" style="text-align: left;"><span style=";font-size:100%;color:black;">• </span><span style=";font-family:Arial;font-size:100%;color:black;">Pendant Sulphurating Agent interacts with another Polymer Chain ( RH ) to form Cross links. </span><span style=";font-size:100%;color:black;"><o:p></o:p></span></p> <p class="MsoNormal" style=""><span style=";font-family:Arial;font-size:100%;color:black;"><o:p> </o:p></span></p> <p class="MsoNormal" style="margin: 3pt 0in 3pt 0.25in; text-align: center; text-indent: -0.25in;" align="center"><span style="font-size:100%;"><b><span style=";font-family:Arial;color:black;">R-S</span></b><b><span style=";font-family:Arial;color:black;">x</span></b><b><span style=";font-family:Arial;color:black;">-Ac + RH </span></b></span><span style=";font-family:Wingdings;font-size:100%;color:black;">�� </span><span style="font-size:100%;"><b><span style=";font-family:Arial;color:black;">R-S</span></b><b><span style=";font-family:Arial;color:black;">x</span></b><b><span style=";font-family:Arial;color:black;">-R + AcH ( Cross links ) <o:p></o:p></span></b></span></p> <p class="MsoNormal" style="margin: 3pt 0in 3pt 0.25in; text-align: center; text-indent: -0.25in;" align="center"><span style=";font-family:Arial;font-size:100%;color:black;"><o:p> </o:p></span></p> <p class="MsoNormal" style=""><span style=";font-size:100%;color:black;">• </span><span style=";font-family:Arial;font-size:100%;color:black;">Network maturing and competing side reactions also occur which does not lead to effective cross links.<o:p></o:p></span></p> <p class="MsoNormal" style=""><span style=";font-family:Arial;font-size:100%;color:black;"><span style=""> </span></span><span style=";font-size:100%;color:black;"><o:p></o:p></span></p> <p class="MsoNormal" style="text-align: left;"><span style=";font-size:100%;color:black;">• </span><span style=";font-family:Arial;font-size:100%;color:black;">Thermal decomposition leads to following reactions : </span><span style=";font-size:100%;color:black;"><o:p></o:p></span></p> <p class="MsoNormal" style=""><span style=";font-family:Arial;font-size:100%;color:black;"><o:p> </o:p></span></p> <p class="MsoNormal" style="margin: 6pt 0in 6pt 0.25in; text-indent: -0.25in;"><span style="font-size:100%;"><b><span style=";font-family:Arial;color:black;">R-S</span></b><b><span style=";font-family:Arial;color:black;">x</span></b><b><span style=";font-family:Arial;color:black;">-Ac </span></b></span><span style=";font-family:Wingdings;font-size:100%;color:black;">�� </span><span style="font-size:100%;"><b><span style=";font-family:Arial;color:black;">Cyclic Sulphides + Dienes + ZnS (Degradation) </span></b></span><span style=";font-family:Arial;font-size:100%;color:black;"><o:p></o:p></span></p> <p class="MsoNormal" style="margin: 6pt 0in 6pt 0.25in; text-indent: -0.25in;"><span style="font-size:100%;"><b><span style=";font-family:Arial;color:black;">R-S</span></b><b><span style=";font-family:Arial;color:black;">x</span></b><b><span style=";font-family:Arial;color:black;">-Ac </span></b></span><span style=";font-family:Wingdings;font-size:100%;color:black;">�� </span><span style="font-size:100%;"><b><span style=";font-family:Arial;color:black;">R-S</span></b><b><span style=";font-family:Arial;color:black;">x-y</span></b><b><span style=";font-family:Arial;color:black;">-Ac + S</span></b><b><span style=";font-family:Arial;color:black;">x-1 </span></b><b><span style=";font-family:Arial;color:black;">( Desulphuration ) </span></b></span><span style=";font-family:Arial;font-size:100%;color:black;"><o:p></o:p></span></p> <p class="MsoNormal" style="margin: 6pt 0in;"><span style="font-size:100%;"><b><span style=";font-family:Arial;color:black;">R-S</span></b><b><span style=";font-family:Arial;color:black;">y</span></b><b><span style=";font-family:Arial;color:black;">-R </span></b></span><span style=";font-family:Wingdings;font-size:100%;color:black;">�� </span><span style="font-size:100%;"><b><span style=";font-family:Arial;color:black;">R-S-R + S</span></b><b><span style=";font-family:Arial;color:black;">y-1 </span></b><b><span style=";font-family:Arial;color:black;">( Monosulphidic Cross links ) </span></b></span><span style=";font-family:Arial;font-size:100%;color:black;"><o:p></o:p></span></p> <p class="MsoNormal" style="margin: 6pt 0in 6pt 0.25in; text-align: center; text-indent: -0.25in; font-weight: bold;" align="center"><span style=";font-family:Arial;font-size:100%;color:black;">R-S</span><span style=";font-family:Arial;font-size:100%;color:black;">x+y</span><span style=";font-family:Arial;font-size:100%;color:black;">-R + Ac-S</span><span style=";font-family:Arial;font-size:100%;color:black;">x</span><span style=";font-family:Arial;font-size:100%;color:black;">-Ac </span><span style=";font-family:Wingdings;font-size:100%;color:black;">�� </span><span style=";font-family:Arial;font-size:100%;color:black;">R-S</span><span style=";font-family:Arial;font-size:100%;color:black;">x</span><span style=";font-family:Arial;font-size:100%;color:black;">-R + Ac -S</span><span style=";font-family:Arial;font-size:100%;color:black;">y+z </span><span style=";font-family:Arial;font-size:100%;color:black;">-Ac ( <st1:city st="on"><st1:place st="on">Sulphur</st1:place></st1:city> Exchange )</span><span style=";font-family:Arial;font-size:11px;color:black;"><o:p></o:p></span></p> <!--[endif]--><p></p> </span>pmfhttp://www.blogger.com/profile/16410119039801971518noreply@blogger.com0tag:blogger.com,1999:blog-4939952818505218712.post-61320705755224728402010-06-26T20:30:00.007+05:302011-01-23T09:27:50.682+05:30biodegradable polymers<div style="text-align: center;"><div style="text-align: left;"><div style="text-align: center;"><span style="font-weight: bold;">BIODEGRADABLE POLYMERS</span><br /></div><br /><a href="http://polymerbooks.blogspot.com/2010/06/polymers.html">polymers</a> are widely used in the form of packing material and throw away that bag.The plastic thrown away after use are not biodegradable.this produce a serious waste disposal problem.Scientist these days are carrying on researches to develope plastic which are capable of biodegradability over the period of time<a name='more'></a><br /><br />Biodegradable polymers can broken in to small segment by enzyme-catalyzed reaction.the required enzymes are produced by microorganisms.Ii is observed that carbon-carbon bonds of chain growth polymers are inert to enzyme -catalyzed reactions,hence they are non biodegradable.In order to make these polymers degradable,we have to insert certain bonds in the chain so that these can be easily broken by enzymes.one of the best methods of making a polymer biodegradable is by inserting hydrolysable ester group into the polymer. <br /></div><br /><br /></div>pmfhttp://www.blogger.com/profile/16410119039801971518noreply@blogger.com0tag:blogger.com,1999:blog-4939952818505218712.post-89708631585681191682010-06-26T10:37:00.004+05:302011-01-23T09:28:33.549+05:30Classifications of polymersPolymers can be classified in number of ways<br /><br /><div style="text-align: center;"><span style="font-size:130%;">1)</span><span style="font-weight: bold;font-size:130%;" >classification based upon source</span><br /></div>polymers can be classified based upon source are<br /><br /><span style="color: rgb(255, 102, 102);">a</span><span style="color: rgb(255, 102, 102);">)<span style="font-weight: bold;">Natural polymers</span></span>:- these are the naturally occurring polymers such as starch cellulose nucleic acid<img src="file:///D:/Users/pmf/AppData/Local/Temp/moz-screenshot-2.png" alt="" />s and natural rubber.natural rubber is a polymer of isoprene(2-methyl buta 1,3-diene) <a><img style="width: 215px; height: 245px;" class="bps-asset-img bps-inline-asset" onlinewidth="237" onlineheight="318" bigwidth="237" bigheight="318" fullsrc="/bps/image/1426103//" src="http://media-2.web.britannica.com/eb-media/66/15466-004-6C816B76.gif" settings=" { id : '', title : '', caption : '', thumbnail : '/eb-media/66/15466-004-6C816B76.gif', source : '/EBchecked/topic-art/1426103//', credit: '' } " /><br />b)<span style="color: rgb(255, 102, 102);"><span style="font-weight: bold;">Synthetic polymers</span>:- <span style="color: rgb(0, 0, 0);">these are man made polymers such as poly vinyl chloride (PVC),Bakelite,nylon,polystyrene etc<br /><br /></span></span></a><div style="text-align: center;"><a style="font-weight: bold;"><span style="color: rgb(255, 102, 102);"><span style="color: rgb(0, 0, 0);">2)CLASSIFICATION BASED ON SYNTHESIS</span></span></a><br /></div><a><span style="color: rgb(255, 102, 102);"><span style="color: rgb(0, 0, 0);"><br />based on the method of synthesis polymers can be classified as follows<br /><span style="color: rgb(255, 102, 102); font-weight: bold;">a)</span><span style="color: rgb(255, 102, 102);"><span style="font-weight: bold;">Addition polymers:</span>-<span style="color: rgb(0, 0, 0);"><span style="color: rgb(0, 0, 0);">these type polymers are formed by the repeated additions of monomeric unit .the monomers involved are unsaturated compounds and are usually the derivatives of ethene<br /><br />eg:-polypropylene, PVC,polythene,etc belongs in this type<br /><br /><span style="font-weight: bold; color: rgb(255, 102, 102);">b)</span><span style="color: rgb(255, 102, 102);"><span style="font-weight: bold; color: rgb(255, 102, 102);">Condensation polymers</span>:-<span style="color: rgb(0, 0, 0);">these are formed by a s</span></span>eries of condensation reaction between two monomers each monomers having two functional group.during condensation simple molecule like H2O,HCl,NH3 etc are eliminated.The reaction is called condensation polymerisation<br /><br />eg nylone66<br /></span></span></span></span></span></a><div style="text-align: center;"><a style="font-weight: bold;"><span style="color: rgb(255, 102, 102);"><span style="color: rgb(0, 0, 0);"><span style="color: rgb(255, 102, 102);"><span style="color: rgb(0, 0, 0);"><span style="color: rgb(0, 0, 0);">CLASSIFICATION BASED ON INTERMOLECULAR FORCES</span></span></span></span></span></a><br /></div><a><span style="color: rgb(255, 102, 102);"><span style="color: rgb(0, 0, 0);"><span style="color: rgb(255, 102, 102);"><span style="color: rgb(0, 0, 0);"><span style="color: rgb(0, 0, 0);"><br />based on the inter molecular forces polymers can mainly classified in to 4<br />a)<span style="color: rgb(255, 102, 102); font-weight: bold;">Elastomers</span> :-the polymers that have elasticity, like rubber are referred to as elastomers.the polymer chain in elastomers are held together by the weakest intermolecular forces.they have ability to be elongated under stress and regain their former shapes when the stress is removed<br /><br />b)<span style="font-weight: bold; color: rgb(255, 102, 102);">Fibers</span>:-these are thread like polymers which can be woven into fabric.they have high tensile strength and high modulus.this is due to strong inter molecular forces like hydrogen bond.<br />eg:- cotton,wool,silk,nylon and Dacron etc<br /><br />c)<span style="font-weight: bold; color: rgb(255, 102, 102);">Thermoplastic</span>:-The inter molecular forces of attraction in the thermoplastics polymers are intermediate between those of elastomers and fibres .As a result thermoplastic polymers when heated became melt and can be molded again in different forms.<br />eg:- polyethylene polypropylene and polystyrene<br /><br />d)<span style="color: rgb(255, 102, 102); font-weight: bold;">Thermosetting plastic</span>:- These polymers are prepared from low molecular mass semifluid polymers .thy cannot be reshaped on heating because the polymer chain under go extensive cross linking resulting in the formation of three dimensional network of inter connected polymer chain<br /><br />eg:- Bakelite,melamine etc </span></span></span><br /> </span><span style="font-weight: bold;"><span style="color: rgb(0, 0, 0);"></span></span></span><br /></a>pmfhttp://www.blogger.com/profile/16410119039801971518noreply@blogger.com1tag:blogger.com,1999:blog-4939952818505218712.post-31421595163239522722010-06-12T15:12:00.000+05:302010-06-12T15:38:36.171+05:30polymers<span style="color: rgb(255, 102, 102);">polymers</span> are macromolecules formed from same or different type of small molecule.the term polymer is a Greek word(poly=many,mer=part ).The smallest molecules that form the repeating unit in polymer are known as<span style="font-weight: bold; color: rgb(255, 102, 102);"> monomer unit</span>.The process by which a polymer is produced from monomers known as<span style="color: rgb(255, 102, 102); font-weight: bold;">polymerization</span>.<br />for example consider the polymerization of ethylene monomers to form poly ethylene.<br /> n(CH2=CH2)-> <img src="file:///D:/Users/pmf/AppData/Local/Temp/moz-screenshot.jpg" alt="" /><img src="file:///D:/Users/pmf/AppData/Local/Temp/moz-screenshot-1.jpg" alt="" /><img src="file:///D:/Users/pmf/AppData/Local/Temp/moz-screenshot-2.jpg" alt="" />-(CH2-CH2-CH2-CH2)-n<br /><img src="file:///D:/Users/pmf/AppData/Local/Temp/moz-screenshot-3.jpg" alt="" />pmfhttp://www.blogger.com/profile/16410119039801971518noreply@blogger.com0