Rubber

1. CONTENT OF TABLE
Serial No Title Page No
01 Introduction 01
02 Rubber 02
03 Importance of Rubber 03
04 Classification of Rubber 03
05 There are four types of rubber generally 04
06 Natural rubber 06
07 Recovering the Rubber 06
08 Grade of rubber 06
09 Refining of crude Rubber 07
10 Two-roll mil 07
11 Banbury Mixer (Internal Mixer) 08
12 Compounding 08
13 Filler 09
14 Plasticizer 09
15 Age resistors (antidegradants) 09
16 Vulcanizing 10
17 Special-purpose ingredients 10
18 Mixing 10
19 Forming Process 10
20 Calendering process 11
21 Coating or Impregnating Fabrics with Rubber 11
22 Extrusions process 12
23 Molding 14
24 Injection molding 14
25 Advantages of injection molding 15
26 Synthetic rubbers 15
27 Common monomer production 17
28 Production of SBR 20
29 Cold rubbers ,Silicone Rubber ,NBR 21
30 Neoprene, Thiokol, Butyl Rubber 26
31 Conclusion 27

2. 1.0 Introduction:
The rubbers materials can be classified into natural rubber and synthetic rubber.
Natural rubber is exhibit many outstanding properties, such as good oil
resistance, low gas permeability. The natural rubber coming from latex that
bleeds from the wounding in plants. Synthetic rubber is any type of artificially
made by man from petrochemical feedstock obtained by emulsion addition
polymerization and condensation polymerization.In1615, the first practical use of
rubber in the waterproofing footwear, when peoples of South America extracted
this substance from trees Rubber often called "Hevea Brasiliensis" and "Para
Rubber" trees, meaning "weeping wood", these trees represents sources of
natural rubber, that begin grew in the Amazon forests in 1873. At that time the
natural rubber became first demand of a product in world, this is lead to
Amazonas becomes the economic heart of Brazil. During the middle of the 18th
century to about the end of 20th century, the rubber industry experienced those
important steps of development. At that time most rubber tree plantation grew in
British and British Colonies in South and Southeast Asia particularly in Thailand,
Malaysia, India, China and Indonesia, today rubber tree are grew in Africa such as
Nigeria, which became important producers of natural rubber. The history of
natural rubber in Europeans began from the second half of the 19th century,
when increasing demand of the natural rubber. In 1820, British industrialist
produced rubber and attempted to use them in clothing. The first bicycle tire
product in 1830, while in 1832, the first factory was set up rubber product. In this
process, because of added sulfur, the rubber becomes cross linked and also has
better elasticity. In 1845, R.W. Thomson invented the pneumatic tire and the
inner tube, in 1869 made the solid rubber balls and hollow rubber balls for the
golf and tennis, and in 1888, first use of rubber to form of rain jackets.
Fig: Typical Rubber Plantatio

3. 2.0 Rubber:
 Rubber is a polymer with inherent thermoplastic and elastomeric qualities, meaning it
can be stretched to great lengths without permanent deformation and can withstand
both electric and thermal strain. Elastomers are sometimes called rubber or rubbery
materials. Elastomers are usually thermosets but may also be thermoplastic .
 Common characteristics;
– Large elastic elongation (i.e.200%)
– Can be stretched and then immediately return to their original length when the
load was released
An elastomer is a cross-linked or vulcanized polymer. Cross-linking is a chemical way of linking
the long polymer chains. A way to think of this would be to take the bowl of spaghetti and tie
them together with a piece of thread where ever the pieces of spaghetti touch each other
Fig: (1 ) Rubber Vulcanization
There are several ways to crosslink rubber, but the most common is through the use of sulfur.
Sulfur, with the addition of heat and pressure, will crosslink rubber. They connect up the long
individual polymer chains into what is literally a single unit.

4. 2.1 Importance of Rubber:
 Rubber is a polymer with inherent thermoplastic and elastomeric qualities, meaning it
can be stretched to great lengths without permanent deformation and can withstand
both electric and thermal strain.
 Flexibility is another important property of rubber.
 strength as well as toughness are notable properties of rubber due to which its elastic
property may be put to be used even under abnormal condition.
 Rubber is highly impermeable to water and air.
 highly resistant to cutting, tearing and abrasion over a wide range of temperatures.
 Not attacked by atmospheric gases and chemicals have no corrosive effects on it.
3.0 Classification of Rubber:
A. According to source
 Natural rubber: latex, Gutta Purcha etc
 Synthetic rubber: SBR, IR, NBR etc
B. According to initial raw materials
 Rubbers made from single monomer: Butadiene rubber (BR)
 Rubbers made from two/more monomers: styrene-Isoprene rubber (SIR)
C. Depending on application, they are classified as
 General purpose rubber:
 Special purpose rubber:
D. General classification of rubber:
3.1 There are four types of rubber generally-
 Elastomer
 Hard plastic
 Reinforcing
 Paint vehicle

5. Another classification Depending on the dry and latex form of rubber shall be classified and
coded from chemical composition of polymer chain –
 M—Rubbers having a saturated chain of the polymethylene type.
 N—Rubbers having nitrogen, but not oxygen or phosphorus, in the polymer chain.
 O—Rubbers having oxygen in the polymer chain.
 R—Rubbers having an unsaturated carbon chain, for example, natural rubber and
synthetic rubbers derived at least partly from diolefins.
 Q—Rubbers having silicon and oxygen in the polymer chain.
 T—Rubbers having sulfur in the polymer chain.
 U—Rubbers having carbon, oxygen, and nitrogen in the polymer chain.
 Z—Rubbers having phosphorus and nitrogen in the polymer chain.
The “M” class includes rubbers having a saturated chain of the polymethylene type.
 ACM—Copolymers of ethyl or other acrylate and a small amount of monomer which
facilitates vulcanization.
 AEM—Copolymers of ethyl or other acrylates and ethylene.
 ANM—Copolymers of ethyl or other acrylate and acrylonitrile.
 BIMSM—Brominated polymers derived from a copolymer of isobutylene and p-
methylstyrene.
 CM—Chloro-polyethylene.
 CFM—Polychloro-trifluoro-ethylene.
 CSM—Chloro-sulfonyl-polyethylene.
 EOM—Copolymers of ethylene and an octene
The “R” class shall be defined by inserting the name of the monomer or monomers before the word
“rubber” from which it was prepared
The following classification shall be used for rubbers of the “R” class:
 ABR—Acrylate-butadiene.
 BIIR—Bromo-isobutene-isoprene.
 BR—Butadiene.
 CIIR—Chloro-isobutene-isoprene.
 CR—Chloroprene.
 ENR—Epoxidized natural rubber.
 HNBR—Hydrogenated acrylonitrile-butadiene.

6. 4.0 Natural rubber:
Natural rubber is tapped from rubber trees (Hevea brasiliensis) as latex.The trees are grown on
plantations in Southeast Asia and other parts of the world.Latex is a colloidal dispersion of solid
particles of the polymer polyisoprene in water. Polyisoprene is the chemical substance that
comprises rubber, and its content in the emulsion is about 30%.The latex is collected in large
tanks, thus blending the yield of many trees togetherThe more the latex is removed, the more
the plant regenerates it.
Latex composition:
water- 60%, rubber polymer- 35%
protien,enzyme and nucleic acid- 3%; fatty acid and ester- 1%;
inorganic salt- 0.5%
4.1 Recovering the Rubber:
The preferred method of recovering rubber from latex involves coagulation - adding an acid
such as acetic/formic acid (HCOOH); coagulation takes about 12 hours
The coagulum, now soft solid slabs, is then squeezed through a series of rolls which drive out
most of the water and reduce thickness to about 3 mm (1/8 in)
The sheets are then draped over wooden frames and dried in smokehouses
– Several days are normally required to complete the drying process
– It is then treated for preparing different grade natural rubbers.
4.2 Grade of rubber:
The resulting rubber, now in a form called ribbed smoked sheet, is folded into large bales for
shipment to the processor - It has a characteristic dark brown color.
In some cases, the sheets are dried in hot air rather than smokehouses, and the term air
‑dried sheet is used; this is considered to be a better grade of rubber
A still better grade, called pale crepe rubber, involves two coagulation steps, followed by warm
air drying

7. ribbed smoked air‑dried sheet pale crepe
Fig:(2) Grade of rubber
4.3 Refining of crude Rubber:
1. Breakdown: The polymeric chains of the rubber are broken by masticating/kneading the
raw rubber between the warm rollers. During breakdown, the rubber loses its
reversibility gradually and turns plastic.
2 Mastication :Mastication is a preliminary stage of processing the raw rubber. At low
temperatures the process cut the rubber molecules into smaller units. It improves the
plasticity and reduces the viscosity. Mastication is a mechanical shearing process using
two roll mill for reduced the molecular weight, reduced the viscosity and to soften the
raw rubber.
After mastication the processing will be much easier and increased the effectiveness of
dispersions of compounding ingredients.
4.4 Two-roll mil:
 There are one pair of rollers with a vertical ‘nips’ between them
 The polymer and additives are subjected to high shear in the nip as the rolls rotate in
opposite directions
 Two-roll mill mixing started with rubber processing, now exist for various function
 Mixing on two-roll mill is time consuming, 2 h for a 200 kg mix on a 84” wide mill.
Fig: (3) Schematic illustration of two-roll mill

8. 4.5 Banbury Mixer (Internal Mixer):
 2 rotors-counter-rotating within a chamber
 Each has two or four ‘blades’ which mix by smearing the materials against the chamber
wall
 A weighted ram keeps the mix in place inside the chamber
 The rate of output (200 kg batch of rubber compound would take 2 h- two-roll mill. A
number 11 Banbury mixer produce 350 kg in 15 min or less)
Fig:(4) Banbury Mixer (Internal Mixer):
4.6 Compounding:
The compounding process uses the two roll mill and internal mixer.Rubber compounding is the
way of making useful products from raw rubber. The process involves the addition of additives
to change the masticated raw rubber to rubber compound before a forming process (Shaping
process).
Rubber is always compounded with additives
Compounding adds chemicals for vulcanization, such as sulfur .

9. The various ingredients may be classified according to their specific functions in the following
groups:
4.6.1 Filler:
The single most important reinforcing filler in rubber is carbon black, a colloidal form of carbon,
obtained by thermal decomposition of hydrocarbons.
 Carbon black also provides protection from ultraviolet radiation.
 Most rubber parts are black in color because of their carbon black content.
 Carbon black forms strong bonds with rubber. It is assumed that carbon particles
possess unsaturated atoms on their surface which act as bonding sites on the rubber
molecules, thus reinforcing the rubber.
 China clays - hydrous aluminum silicates (Al2Si2O5(OH)4) provide less reinforcing than
carbon black but are used when black is not acceptable.
4.6.2 Plasticizer :A substance which incorporated into rubber to increase its flexibility,
workability is called plasticizer. Plasticizers include a large variety of organic liquids e.g.,
petroleum fractions, coal tar distillates, animal fats, plant extracts, etc.
 Protect rubber goods from attack by oxygen and ozone in the atmosphere.
 They are classified as antioxidants, antiozonants, or anti-cracking agents.
4.6.3 Age resistors (antidegradants) : Age resistors Protect rubber goods from attack by
oxygen and ozone in the atmosphere. The age-resistors used must be capable of reacting with
the agents to prevent the polymer breakdown.
 The loss in physical properties caused by crosslinking, or some form of chemical
alteration of the polymer chains.
 Commercial age resistors are the amine type or the phenolic type.
 Amines are strong protective agents.
Examples: N-Phenyl-2-naphthylamine, alkylated diphenylamine
4.6.4 Vulcanizing : Vulcanization process is the process that produce a crosslinking i.e sulfur,
sulfur monochloride, selenium, tellurium, thiuram disulfides, p-quinone, dioximes, polysulfide
polymers.
Vulcanization agents increase vulcanization process and reduce the time of vulcanization.

10. Example: 2-Mercaptobenzothiazole, zinc diethyldithiocarbamate, tetramethylthiuram disulfide,
tetramethylthiuram monosulfide, 1,3-diphenylguanidine
4.6.5 Special-purpose ingredients :
 Coloring pigments: Carbon black, zinc oxide, certain clays, calcium carbonate,
titanium dioxide
 Blowing agents: Sodium or ammonium bicarbonate, diazoaminobenzene,
fluorocarbons, etc.,
 Flame retardants
 Antistatics agents retarders
 Peptizers: Aromatic mercaptan (thiophenols)
5.0 Mixing :The mixing process is performed in heavy internal mixers, capable of processing
200 kg batch weight in two minutes.
 This process has two functions:
 Firstly, to soften the rubber (this is often known as mastication) and,
 Secondly, the rubber with the compounding ingredients, which may include fillers,
vulcanizing agents, protective agents. This technique is known as compounding.
After mixing, the compounded rubber is plastic and is ready to be shaped. This is done in a
variety of ways and is frequently combined with vulcanization in which the rubber undergoes a
chemical reaction at a high temperature and converted from the plastic state into a strong,
highly elastic material.
6.0 Forming Process (Shaping):
 After all compounding ingredients have been properly mixed the compounded green
stock is tacky and thermoplastics
 In this plastic condition, the stock can be shaped by the applications of force.
 This can be accomplished by
i. Calendering

11. ii. Coating
iii. Extruding
iv. Molding and casting
6.1 Calendering process:
 In the calendering process, rubber is passed through a three- to five-roll calender either
to produce a sheet of controlled thickness or to force the rubber into close contact with
a textile or metal cord.
 Stock is passed through a series of gaps of decreasing size made by a stand of rotating
rolls.
 Rubber sheet thickness determined by final roll gap.
Figure:(5) Calendering Figure:(6) Roller die process - rubber extrusion
followed by rolling
6.2 Coating or Impregnating Fabrics with Rubber:
 Rubber compounds are applied to fabric by calendering, i.e., rolling the rubber
compound into the fabric on multiroll calender machines.
 Tire cord is a special case in which cotton, rayon, nylon, or polyester cords are arranged
in parallel and bound together by rubber on a calendar.

12. Figure: (7) Coating of fabric with rubber using a calendering process
6.3 Extrusions process:
 During the rubber extrusions process, rubber material is processed through a screw
extruding machine very similar to those used in extruding plastic.
 Rubber extruders consist of a heated shearing screw conveyor or twin screw conveyor
and a die through which the plasticized and pressurized rubber is squeezed.
 Pre-heating of the material is optional, depending on the precision of the die and the
desired qualities of strength.
 Stock rubber material enters the screw conveyor channel, often by way of an attached
hopper.
 It is softened through heating and shearing, and the stock material is then pressurized
through the rotation of a screw.
 Heaters around the extruder’s barrels heats the stock and liquefies them
 The pressure pushes the rubber through the die, which is located at the end of the
extruder.
 The rubber then emerges from the extruder in a profile resembling the die shape
 After being extruded, the material is cured and sometimes vulcanized using various
methods.

13. Fig: (8) Extrusions process
Basically an extruder screw has three different zones
• Feed zone:
The function of feed zone is to preheat the plastic and convey it to the subsequent zones.
• Compression zone:
In compression zone the screw depth gradually decreases so as to compact the plastic. This
compaction has the dual role of removing any trapped air pockets and improving the heat
transfer through the reduced thickness of material.
• Metering Zone:
In metering zone the screw depth is again constant but much less than the feed zone. In the
metering zone, the melt is homogenized so as to supply at a constant rate, material of a
uniform temperature and pressure to the die.

14. 7.0 Molding:
Principal molding processes for rubber are:
 Compression molding
 Transfer molding, and
 Injection molding
7.1 Injection moulding:
Injection moulding is a process in which the compound is forced under high pressure into a
mould cavity through an opening (sprue).
 The rubber material in form of strips is fed into an injection moulding machine. The
material is then conveyed forward by a feeding screw and forced into a split mould,
filling its cavity through a feeding system with sprue gate and runners.
 An injection moulding machine is similar to an extruder.
 The main difference between the two machines is in screw operation.
 In the extruder type the screw rotates continuously providing output of continuous
long product (pipe, rod, sheet).
Fig: (9) Injection moulding is a proces

15. 7.2 Advantages of injection molding:
 The complete elimination of pre-forms. The production and need for pre-forms is a
labor intensive step that can potentially affect the finished product through variability in
pre-form weight and shape.
 Elimination of operator placement of pre-forms. Since pre-forms are eliminated, the
need for operators to place the pre-forms in a cavity or pot is removed.
 Injection screw pre-heats material before forcing it into cavities. This process decreases
the viscosity of the material.
 Reduced cycle time
 Economical process for high volumes of medium to high precision components
 Minimal material waste
8.0 Synthetic rubbers:
 Synthetic rubbers are complex chemical compounds formed through the polymerization
of monomers.
 Synthetic rubber production starts with the refining process of oil, coal or other
hydrocarbons with naphtha as one of the desired products.
 The naphtha is then combined with natural gas to produce monomers.
 Typical monomers used for production feed material include butadiene, styrene,
isoprene, chloroprene, acrylonitrile, ethylene or propylene.
 These monomers are then polymerized using catalyst and process steam to form chains
of polymers which results in rubber intermediaries.
 These substances are then processed to their final rubber products by vulcanization

16. Fig: (10) Block diagram of synthetic Rubber

17. 9.1 Common monomer production:
 Styrene:
The production of styrene is via ethylbenzene, which is made by alkylating benzene with
ethylene and dehydrogenating to styrene over an aluminium chloride, solid phosphoric acid, or
silica-alumina catalyst.
 1,3 Butadiene:
(A) From ethyl alcohol
(B) From petroleum
Butene is passed over calcium nickel phosphate catalyst stabilized with 2% chromium oxide at
625-700°C and a low butene pressure. The overall conversion is about 40-50%.
 Acrylonitrile:
Acrylonitrile is produced by the sohio process that reacts with propylene with air and ammonia
in a catalytic reactor.

18.  Chloroprene:
Chlorloprene is manufactured from acetylene and hudrogen chloride. Acetylene is dimerized to
monovinylacetylene, which in turn reacted with hydrogen chloride to form chloroprene

19. 10.0Crumb:
The emulsion and solution type of polymerization reaction are used to produce styrene-
butadiene copolymers. The emulsion products can be sold as a granular solid form,
known as crumb.
Another definition,The acid and brine mixture causes the emulsion to break, releasing
the styrene-butadiene copolymer as crumb product. The coagulation vessels are open to
the atmosphere. At this point, the product is called “crumb”
 Production of crumb rubber by emulsion polymerization has been the traditional
process for the production of synthetic rubber.
 Emulsion crumb production involves producing an emulsion of raw materials, resulting
in bulk polymerization of droplets of monomers suspended in water.
 Copolymers containing less than 45 weight percent styrene are known as styrene-
butadiene rubber (SBR).
 Production of crumb rubber by emulsion polymerization has been the traditional
process for the production of synthetic rubber.
 It is the most commonly used method, accounting for 90% of the world’s production of
SBR.
 Solution crumb production involves mixing the raw materials in a homogeneous
solution, wherein polymerization takes place.
11.0 Latex:
The emulsion and solution type of polymerization reaction are used to produce styrene-
butadiene copolymers. The emulsion products can be in a liquid form, known as latex.

20. 12.0 Production of SBR:
12.1 The flow diagram for SBR production
Fig.: (11)simplified flow diagram for SBR production

21. 12.2 Cold rubbers:
 Cold rubbers have improved properties, compared with hot rubbers but require more
extensive process management.
 The emulsified mixture resulting from the initial mixing of monomers and additives must
be kept cool by means of an ammonia refrigerant prior to entering the reactors.
12.3 Silicone Rubber:
Silicone rubber is a“Organosiloxanes Polymer”.It has been originated from its
unique molecular structure that carry both inorganic and organic properties . In other words,
due to the Si-O bond of Silicone Rubber and its inorganic properties, Silicone Rubber is superior
to ordinary organic rubbers in terms of heat resistance, chemical stability, electrical insulating,
abrasion resistance, weather ability and ozone resistance etc...
Fig:(12) Silicone Rubber
12.3.1 Why silicone rubber is the better choice
 Longer service life in adverse environments, Virtually unaffected by weather --
rain, snow, humidity, ozone, or the sun's damaging ultraviolet rays.
 Wider operating temperature range -- from -100 to 316ºC Organoelastomers
soften and deform irreversibly at temperatures >100ºC ,they become brittle at
temperatures <-25ºC .
 Inherently good electrical insulating qualities that do not change significantly
under exposure to severe environmental stress (heat, cold, moisture, oil, ozone,
UV rays)
 Retains its natural flexibility and resilience across a wider temperature range

22.  Enhances the comfort and feel of consumer goods
 Excellent sealing performance
 Inert (no taste or smell); many food-contact options
 More fabricating options , increased productivity
12.4.0 Nitrile Butadiene Rubber – NBR:
Nitrile Rubber (NBR) is a co-polymer of 75% butadiene and 25% acrylonitrile monomer.This is
prepared by emulsion polymerization same as SBR. Nitrile rubber, also known as Buna-
N, Perbunan, acrylonitrile butadiene rubber.
NBR, is a synthetic rubber copolymer of acrylonitrile (ACN) and butadiene. Trade names
include Nipol, Krynac and Europrene.
12.4.1 Physical properties of NBR:
 It is generally resistant to oil, fuel and other chemicals. Increase in acrylonitrile content
increase the resistance.
 The freezing point also increase with the increase in nitrile content.
 NBR’s has the ability to withstand a range of temperatures from -40 °C to +125 °C.
 . It has inferior strength and flexibility, compared to natural rubber.
 This rubber is also resistant to aliphatic hydrocarbons. It is less resistant to ozone,
aromatic hydrocarbons, ketones, esters and aldehydes.
 This is low in tensile strength as the chain structure of polymer is irregular.

23. 12.4.2 Production processes of Nitrile Rubber:
Fig:(12) Simplified flow diagram for NBR production
12.4.2.1 Types of NBR :
(A) Cold NBR:
Cold NBR has a wide variety of compositions. Acrylonitrile content ranges from 15% to 51%.
Mooney values range from a very tough 110, to pourable liquids, with 20-25 as the lowest
practical limit for solid material.

24. (B) Hot NBR :
Hot NBR polymers are polymerized at the temperature range of 30 to 40°C. This process
produce highly branched polymers. Branching supports good tack and a strong bond in
adhesive applications.
(C) Crosslinked Hot NBR :
Crosslinked hot NBR are branched polymers that are further cross-linked by the addition of a di-
functional monomer. These products are used in molding forces, or back pressure to eliminate
trapped air. Another use is to provide increased dimensional stability .
Figure : (13) HNBR Production Process

25. (D) Neoprene:
 Chloroprene Rubber is known as Neoprene.
 It is the first oil resistant synthetic rubber.
 It has better chemical, oil, ozone and heat resistance than natural rubber .
 Chloroprene tends to slowly absorb water and its electrical properties are poor.
 Its gas permeability is fairly low and flame resistance is excellent.
(E) Thiokol:
Thiokol is a polymer of ethylene polysulphide. It can be prepared by the condensation of 1,2-
dichloroethane with sodium polysulphide

26. Properties:
 Thiokol is resistant to the action of oxygen and ozone.
 It is also resistant to the action of petrol lubricants and organic solvents
 Thiokol films are impermeable to gases to a large extent.
 Thiokols are vulcanized with metal oxides such as zinc oxide.
Uses:
 Thiokol mixed with oxidizing agents is used as a fuel in rocket engine.
 It is used to engine gaskets and other such products that come into contact with oil.
 Thiokols are used for hoses and tank lining for the handling and storage of oils and
solvents
(F) Butyl Rubber:
Butyl Rubber is a copolymer of 98% isobutene and 2% butadinene or isoprene. The butadinene
is added to introduce the necessary ethylenic linkages for vulcanization.
Properties
 Very high tensile strength
 Very impermeable to gases including air.
 Excellent resistance to heat, abrasion, ageing and chemical.
 Soluble in hydrocarbon solvents (benzene) but highly insoluble in polar solvents
(alcohol, acetone etc.)
 High resistance to ozone.
 It can be vulcanized but cannot be hardened much because of very low unsaturation.

27. 13.0 Conclusion:
It is cheaper, stable in price and contributes to consistency in qualities of the products Speeds up mixing
operation, breaks down quickly, wets pigments and blend the mixture
together with ease. Imparts firmness to compounds making the processing easier. It permits faster and
safer extrusion and calendering. Reclaim rubber decreases shrinkages of uncured compound before and
during curing is made faster thus reducing mould or press time. Introduction of reclaimed rubber
imparts excellent ageing properties It is cheaper, stable in price and contributes to consistency in
qualities of the products.Speeds up mixing operation, breaks down quickly, wets pigments and blend
themixture together with ease Imparts firmness to compounds making the processing easier. It permits
faster and safer extrusion and calendering.Reclaim rubber decreases shrinkages of uncured compound
before and during curing.curing is made faster thus reducing mould or press time.Introduction of
reclaimed rubber imparts excellent ageing propertiesThe basic structure of an HNBR elastomer is
provided in Figure 1. As outlined below, the process begins with the production of an emulsion-
polymerized NBR. This polymer is then dissolved in an appropriate solvent. After the dissolution
process is complete, the addition of hydrogen gas, in conjunction with a precious metal catalyst
at a designated temperature and pressure, brings about a selective hydrogenation to produce a
“highly saturated nitrile” (HSN) polymer. The solvent and catalyst are then recovered and the
remaining crumb is dried.