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Industrial manufacturing of Nitrile Rubber
INTRODUCTION
Acrylonitrile Butadiene copolymers are commonly known as
Nitrile rubbers. India has consuming this rubber for over four decades,
however, the consumption remained small and restricted to mainly the
products requiring oil resistance properties. The picture changed rapidly since
1970 as the combined properties of abrasion resistance even at high
temperatures was used for making products like rice dehusking rolls. Today
over 2500 MT of NBR is used in this single application the growth of
automotive industries, oil companies have further spurred the demand of
Nitrile rubbers in India.
The first rubber is to be commercialized is Natural rubber. Since
that time two attempts have been made by scientists world over to study the
structure of natural rubber, elasticity of natural rubber and then try to synthesis
a rubber that can do the job of natural rubber. During the World War II(1941),
these attempts got the boost, when allies realized that natural rubber comes
from East Asia was under the threat of Japanese aggressiveness and that wars
cannot be fought without rubber i.e. rubber tyres etc. Synthetic rubber
manufacturing programs got stabilized and expanded due to improvements
like cold polymerization, oil extensions etc. Synthetic rubbers which can fully
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or partially replace the natural rubbers are generally termed as general purpose
synthetic rubbers. Today we have an array of synthetic rubbers.
The second type of development involved considerations to have
those properties deficient in the natural rubber such as resistance to oil, heat,
ozone etc. to be eliminated. Thus developments of special purpose rubbers like
Nitrile rubber came on scene and has grown substantially.
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SYNTHETIC RUBBER POSITION IN INDIA
At present consumption of all synthetic rubbers together is
approximately 22% of the total rubber consumed in India it is expected that
the synthetic rubber consumption in India can be as much as 40% provided
indigenous availability improves and import duties on rationalized for highly
specialized rubber which are not produced in India. Presently the synthetic
rubber scenario can be as under. Availability of monomers like butadiene,
styrene in the country will play significant role in promoting production of
general purpose rubbers like SBR, PBR in country. Though the SBR
production came in India 1963 by Synthetics and Chemicals Ltd it did not
grow with demand on natural rubber with its sustained growth supported the
growth of rubber industry.
Company Name Type PresentCapacity(MTA) Trade Name
Synthetics & ChemicalsLtd. SBR 40,000 Synaprene
APAR Industries ltd. NBR 10,000 Aparene
APAR Industries ltd. HSR 9000 Powerene
Unimers India ltd EPDM 6000 Herlene
NOCIL EVA 50000 Powerene
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MONOMER SYNTHESIS
Nitrile Rubbers are co-polymers of Butadiene and Acrylonitrile.
A. Butadiene
Butadiene is a major monomer in production of NBR. Butadiene can
be manufactured by various routes. In past routes from acetylene (Berthelot,
REPPE process) ethylalcohol (Ostronislenksy, Lebdev process) has been used
in West. Even today in our country we are using alcohol as starting material
for the production of Butadiene. This can be shown as under :
CH 3 CH 2 OH CH3 CHO + H 2
2CH 3 CHO CH 3 CHOH CH CHO CH 3 CH==CH-CHO
CH 3 CH== CHCHO + CH 3 CH 2 OH CH3 CH==CHCH 2OH+CH 3 CHO
CH 3 CH == CH CH 2OH CH 2==CHCH==CH 2+H 2O
(Approx. 250 parts of Ethylalcohol gives 100 parts of Butadiene)
B. Acrylonitrile
B.1. Acrylonitrile synthesis from acytelyene and hydrogen cyanide Hydrogen
cyanide manufactured by Andrussor reaction as :
Feed ratio NH 3 : Natural gas : air is 11.2:12.0:76.8
2CH 2 + NH 3 +3O 2 HCN + 6H 2O
Addition of hydrogen cyanide to acetylene in presence of an aqueous
catalyst HCN
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Catalyst (HCN)
Ammonium Chloride 21.1%
Cuprous Chloride 54.3%
37% HCL 1.4%
Water 23.2%
pH
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Acrylonitrile monomer can also be synthesized from acetaldehyde and
hydrogen cyanide (KNAPSACK PROCESS). In Distillers process
acrylonitrile is synthesized from acrolein. First acrolein is produced from
propylene, by catalytically oxidized to acrolein. Acrolein in presence of
ammonia and air is converted to acrylonitrile as :
CH 2=CHCHO+NH 3+1/2 O 2 CH 2 = CHCN+2H 2O
This process which operates at elevated temperatures in presence of an
oxidation catalyst (Molybdic Oxide)
There are many other routes for synthesis of Acrylonitrile monomer,
but the above process is used in India by the only producer, i.e. IPCL.
The most popular route today use predominantly hydrogen-rich
straight-chain C4 units which results from petroleum (naphtha) cracking
which is shown below.
1. Butadiene Oil Naphtha Butadiene
2. Acrylonitrile Oil Naphtha Propylene + Ammonia & air Acrylonitrile
MONOMER SUPPLIERS
Gujrat Apar Polymer Limited.
National Organic Chemical Industries Limited.
Indian Petrochemical Corporation Limited.
Reliance Petrochemicals; Surat.
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CHEMICAL STRUCTURE OF NBR
Chemical structure of NBR is generalized as copolymer of butadiene
and acrylonitrile as shown below
-----(CH 2-CH=CH-CH 2)x---(CH-CH 2)y-------|
CNToday the commercial grades are available with 16 50% of the
acrylonitrile (ACN) content. The chemical structure of NBR is very similar to
SBR. The replacement of benzene group by cinogen group introduces the
polarity in the molecule. The influence of this group enhances the properties
like oil, heat, air permeability resistance, electrical conductivity properties of
vulcanizates. However low temperature (Tg value) properties are affected with
increase in ACN content.
Like SBR, NBR can be vulcanized by conventional cure system based
on sulphur and accelerator or with organic peroxides. Polarity in the molecules
decreases electrical resistance of the polymer and bring it in antistatic range,
so that NBR can be compounded for products where dissipation of electrical
charges are essential e.g. textile cots and aprons.
NBR is amorphous in nature and needs reinforcing fillers like carbon
black, precipitated silica to develop physical properties such as tensile
strength, modulus, resistance to abrasion etc.
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METHODS OF MANUFACTURING OF NBR
Nitrile rubbers are manufactured by Emulsion co-polymerization of
butadiene and acrylonitrile together. The stainless steel reactors are mirror
finished to exercise excellent temperature controls and entire latex production
is through the digital control system. Thus the addition of all ingredients and
reactions are automatically controlled. This ensures the excellent quality with
high consistency in properties of polymer manufactured. At present the
emulsion polymerization is carried out at 5 oC compaired to 50 o C in the earlier
days.
Nitrile rubbers are produced by
I ) Emulsion process :
a) hot polymerization -------------------- 50 o C
b) cold polymerization-------------------- 05 o C
II) Solution process--- this process has found limited applications so far
REACTION MECHANISM OF FREE RADIAL EMULSION
POLYMERISATION
Following are the three steps involved in this process :
1) Initiation 2) Propagation and 3) Termination
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1. Initiation
ROOH + Fe 2+ ----------------------------------> RO* + Fe 3+ + OH -
Fe 3 + Sodium Sulfoxilate ---------------------> Fe 2+
RO* + CH 2 = CH - CH = CH 2 --------------> RO- CH 2-CH=CH-CH 2*
2. Propagation
RO - CH 2 - CH = CH - CH 2 * + CH 2= CH - CH = CH 2
----> RO - CH 2 - CH = CH - CH 2 - CH 2- CH = CH - CH 2* + CH 2 =CH|
CN
RO - CH 2 - CH = CH - CH 2 - CH 2- CH = CH - CH 2 - CH 2 -CH*|
CN
There is a random arrangement of monomer in the polymer, can be
represented as
------B-B-B-A-A-B-B-A-A-A------ A for AcrylonitrileB for Butadiene
3. Termination
S R R - || | |
RO* + S -C - N + H 2O ----------------> ROOH + CS 2 + NH| |
(From Hydroperoxides ) R R
Polymerization Reaction
CH 2 = CH - CH= CH 2+ CH 2=CH -----(-CH 2 - CH = CH- CH 2) x -----CH 2-CH-----------| |
CN CN y n
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Emulsifier Initiator Activator Modifier
Refrigerant
Flow
DiagramofNitrileRubberManufacturing
Butadienerecycle
ACNrecycle
Coagulation
Water
SerumRecycle
WashWaterRecycle
Steam
Vent
FinishedProduct
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Figure Index
1. Butadine Storage .
2. ACN storage .
3. Reactor .
4. Flash Tank .
5. Stripper .
6. Latex storage tank.
7. Coagulation tank .
8. Conversion tank .
9. & 9A Dewatering screens .
10.Wash Tank .
11. Dewatering Press.12.Shredder .
13.Dryer .
14.Baler .
15. Magnetic detector .
16.Film wrapping .
17. Bagging and stitching.
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EMULSION POLYMERIZATION
The basic polymer recipe in addition to the monomers contains water,
stabilizers, emulsifiers, catalysts, activators, electrolytes and terminating
agents. The basic steps involved in the manufacture are polymerization,
coagulation, washing and drying.
In polymerization, the monomers are emulsified in water, a free radical
generating catalyst is added and the mixture is agitated while a constant
temperature is maintained. Following the polymerization cycle, the material is
transferred to a blow down tank in which the terminating agent is added to
control the molecular weight of the polymer according to the grade, the
residual monomers are removed. Then the latex is stabilized and coagulated
into fine crumbs by the addition of various coagulating agents like alum,acids, and salts. This is then washed, dewatered, and finally dried crumbs are
compacted to form the bales. Nitrile rubbers are available in several forms
such as sheets, crumbs, powers and liquids as per requirement.
POLYMERIZATION
NBR is produced from the emulsion polymerization of butadiene and
acrylonitrile at 5 0c for cold and 50 0c for hot process. Redox system of initiator
is used for cold while for hot process K 2 SO 8 is used. The monomer or is used
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for cold while for hot process K 2 SO 8 is used. The monomer ratio and the
temperature at which polymerization are carried out are important features of
NBR manufacturing. The properties of product may also be influenced by
other things like amount and nature of modifiers and emulsifiers. The
conversion of monomer to copolymer is not carried out to completion for
quality reasons. The reaction is stopped at predetermined stage when desired
properties are obtained in the product. The unreacted monomers are stripped
from latex and recovered for the reuse in the stripper column. Following
parameters affects the polymer properties during polymerization.
1. polymerization temperature
2. emulsifier
3. modifier
1. Polymerization temperature
Polymerization temperature influences the branching, cross-linking, the
stereoregular configuration of the enchained butadiene units and the molecular
weight distribution of the polymer. In general the lower polymerization
temperature, the less branched and crosslinked is the rubber and lower will be
the gel content. In microstructure the proportion of vinyl groups in the
polymer varies little over the rang of polymerization temperature from -200c
to 1000c. By contrast, the balance between cis-1,4, and trans- 1,4 structure is
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markedly affected by polymerization temperature, the ratio of cis and trans
falls as the polymerization temperature is decreased. The presence of
acrylonirtile unit has little effect upon the microstructure of the enchained
butadiene butadiene units. The improved mechanical properties of NBR
vulcanizate from cold process have been attributed to the greater structural
regularity caused by increased trans- 1,4 content as well as to the formation of
less branched and crosslinked structure in polymer.
2. Effect of emulsifier
Emulsion polymerization is a heterogeneous system. The
polymerization is carried out using water as a liquid or solvent but in
emulsion. The emulsifying agents are used for this purpose. It has two
portions, first is hydrophobic due to long hydrocarbon chain of emulsifier and
second is the hydrophilic due to the polar end (e.g. sodium or potassium
sulphonate) attached to the emulsifier carbon chain. Emulsifiers are hardly
soluble in water. There lies a critical concentration of the emulsifier called as
CMC. above which they are insoluble and forms insoluble spherical structures
called as micelle. Increase in emulsifier causes the formation of smaller
particles. The synthetic emulsifier having a low temperature water solubility
shows no tendency to gel even down to 5 0C due to their branched structure
their calcium and magnesium salts are more soluble. Therefore they shows
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less tendency to be precipitated from hard water. For synthetic soap, rate of
polymerization increases linearly with the square root of the soap level.
3. Modifier
These are mercaptans, which are used to control molecular weight and
acts as a reaction transferring agent in the free radical reaction. It does not
effects the rate of polymerization. On increasing the modifier amount in
polymerization recipe, both polymer plasticity and gel content falls sharply.
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VULCANIZATION
The vulcanizing agents are usually sulfur compounds, which react with
the polymer to produce a cross-linked material in which the linkages are -C-S x
-C-. The cross links may be mono-, di-, or polysulfidic. The type of linkage
is determined by the concentrations of sulfur, accelerators, and retardants, and
temperature. Most of the conditions to produce a given products are
empirical, but some advances in knowledge are beginning to allow a scientific
basis for vulcanizing conditions.
The accelerators reduce the time required for the vulcanization of
rubber from several hours to a few minutes. In addition, less sulfur is needed
and a more uniform product is obtained. The mechanism of accelerator action
is not well understood, in spite of much research, but presumably involves the
formation of an activated form of sulfur, which forms a "sulfur bridge" at
reactive sites within the rubber molecule, linking the large molecules into a
tight network structure. Most accelerators contain nitrogen and sulfur. Two-
thirds of all the accelerators made, consist of mercaptobenzothiozole (MBT)
and its derivatives.
Nitrile rubbers are some what similar to SBR's in comparison, however,
Sulphur is less soluble in NBR. Thus early addition of sulphur or sulphur
donor systems are more appropriate. Semi-EV and EV cure systems play a
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special role in NBR vulcanization and provide high heat resistance & low
compression set. Like other diene rubber, Nitrile rubber is vulcanized by
sulphur cure system (S+Accelerator+ZnO). This can be depicted as below.
1. CH 2-CH=CH- CH 2 - CH 2 -CH -------->| -H -
CN
2. CH 2-CH=CH- CH 2 - CH 2 -C* + S n + Accelerator * -------->|
CNCN|
CH 2-CH=CH- CH 2 - C|
Sx|
CH 2-CH=CH- CH 2 - C|
CNThus cross-linking continues.
Conventional accelerator system such as MBTS, Sulfenamides, Dithio-
Carbamates, Guanidins have given best results. A good heat resistance is
easily obtained by using TMTD with low or no sulphur or a sulphur donor
(0.5phr). Cadmium oxide (0.25phr.) provides very high heat resistant
however very toxic in nature. Carboxylated NBR needs multifunctional
reagents such as ZnO or Zinc Peroxides. Curing of NBR is also common for
achieving better heat resistant properties with additional use of co-activators
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such as EDMA(Ethylene Diamine Methacrylate) high hardness grades can be
produced.
However peroxide cures give lower tensile, tear, swell resistance &
poorer dynamic properties. They restrict flexibility in compound development.
Vulcanization can be achieved with Sulphur, Dioxide or peroxide system. As
with NR, SBR, ZnO at 3-5 phr. level & stearic acid at a 1-2 phr. level are
added for proper activation.
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COMPOUNDING
Pure rubber (natural or synthetic) is usually not suitable for use. The
desirable properties of plasticity, elasticity, toughness, hardness or softness,
abrasion resistance, impermeability and the myriad combinations possible are
achieved by the art of the rubber compounder.
A broad range of properties can be obtained from properly
compounded Nitrile rubber. In general, NBR is compounded along lines
similar to those practiced with NR and SBR.
As mentioned earlier, selection of grade of rubber is very important
criteria depending on the oil and fuel resistance is required. Higher
acrylonitrile NBR rubber is chosen when high resistance is required. Lower
acrylonitrile rubbers are used when low temperature and dynamic properties
are important. Activation system generally used contains 3-5 phr of zinc oxide
with 1-2 phr of stearic acid. This system is used along with sulphur donor
vulcanization system. With peroxide curing system cynurate (Tac) can be used
as activator.
Unlike natural and polychloroprene rubbers, NItrile rubbers does not
crystallize on stretching (self reinforcement) and therefore is a balanced
reinforcing system. When used alone, low reinforcing carbon blacks are
preferred as the highly reinforcing blacks which tend to stiffen the uncured
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stock as vulcanizate and pose problems during processing. Consequently high
reinforcing carbon blacks are used mainly at low loadings or in conjunction
with the less reinforcing fillers. Non-black application will require the use of
reinforcing silicas of various types of calcium carbonates hard clays, talc and
other pigments. Silicas are capable of imparting properties as good as carbon
black barring compression set and resilience. Nitrile rubbers needs proper
choice of antioxidants to perform under heat, air and ozone. Ozone resistance
can be improved by blending it with PVC, EPDM and Epichlorohydrine.
In summarizing Nitrile rubbers can be compounded with :
a) filler types: carbon blacks, silica, silicates, alumina
b) plasticizers: esters, polymeric esters, aromatic oils and resins
c) cure systems: ebonite conventional sulphur and peroxidesADDITIONAL DATA ON COMPOUNDING
Pure rubber (natural or synthetic) is usually not suitable for use. The
desirable properties of plasticity, elasticity, toughness, hardness or softness,
abrasion resistance, impermeability, and the myriad combinations possible are
achieved by the art of the rubber compounder. A typical rubber compound is
shown in Table .
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Table - Typical Rubber Compound
Ingredient PartsRubber
Sulfur
Zinc oxide
Stearic acid
Accelerator
Loading or filling pigment
Reclaim, softeners, extenders, colors, blowingagents, antioxidants, antiozonants, odorants,
etc.
100.0
2.0
5.0
3.0
1.5
50
As required
1. Selection of NBR Grade : In formulating compound, one of the important
step is to select correct grade of rubber, to meet and product
specifications/requirements.
The major variables which permit various grades are :
a) Type of Soap Fatty Acids, FattyAcids/Rosin Acids, Synthetic
b) Mooney value 20 ML - 80 ML
c) ACN Percentage 18% - 50%
d) Types of stabilizer Staining, Non-staining
e) X-linked polymers
2. Selection of Reinforcing Filters :
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NBRs are like SBR in amorphous character, and being unable to
crystallize on stretching requires presence of reinforcing fillers to attain good
physicals. Carbon blacks and silica fillers are major fillers used for improving
physicals. In carbon black one can use right from SAF. ISAF mix , down
upto MT blacks. Fine particle blacks are difficult to disperse and gives tough
compounds to process. Thus softer and medium blacks like FEF, GPF, SRF,
MTS are used. FEF is selected as the name indicates for Fast Extrusions.
The effect of SRF-HM is given below to give guidance of physicals it imparts
LoadingCB
Plasticizer T.S.(psi)
Elongation.@Break
Hard-ness
300% Mod(psi)
Angle Tear lbs/In.
25 phr 10
20
2200
2000
550
600
55
50
650
500
250
210
3. Curatives :
Normal accelerator, sulphur combination is NBR 100, MBTS or CBS
1.5, Sulphur 1.5. For improved compression set, heat resistance EV systems
are used. EV cures affect tear and flex properties of the vulcanizate.
Vulcanizates, which have been made with TMTD with little or no
sulphur, tend to 'bloom' because of the high dosage, but this can be reduced or
even eliminated by simultaneous use of MBT, MBTS or CBS. Then too, the
blooming can be suppressed by the partial replacement of the TMTD with
another thiuram disulphide. NBR can be cured with peroxides giving better
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heat and compression set properties. The following characteristics are attained
with nitrile rubber compounds optimally prepared with dicymyl peroxide.
a) Good tensile strength at room temperature but relatively lower values at
elevated temperatures,
b) Low elongation at break,
c) High modulus
d) Low permanent set at break,
e) Moderate tear resistance at room temperature and very low values at higher
temperatures,
f) Excellent performance under dynamic loading with the Goodrich flexometer
and in ball fatigue testing,
g) Low compression set especially in hot air at high temperatures and in hotoils.
h) Very good aging in hot air,
i) Good aging in steam and hot oils, and
j) Relatively strong swelling when kept in boiling water.
4. Selection of Plasticizers :
Nitrile Rubbers are polar (due to ACN) and hence only aromatic/highly
a aromatic oils/plasticizers are compatible. The most common plasticizers are
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DBP/DOP types. Adipates/sebacate ester plasticizers are used when low
temperatures flexibility is desirable. Paraffinic and Naphthanic oils should be
avoided as it would tend to 'exdue' from the vulcanizate. The recent trend is
supply DBP/silicate blend (e.g. E-2 Mix DBP from C.P. Hall) to facilitate easy
addition. When flame retardance is required Triaryl/Trieresyl phosphate is
added.
NBR is a polar rubber and hence for better compatibility only aromatic
plasticizers and its compounds (with high polarity) are used. The plasticizers
have far reaching effect on NBR vulcanizate. The mol. wt. also has an
important effect on its plasticizing action. Thus, the viscosity of the
compound the physical properties of the vulcanizates are largely dependent on
the type and the amount of the plasticizer.Plasticizers are added to improve processing, impart tackiness, improve
low-temperature performance and to lower hardness of the vulcanizate.
Plasticizers also assist in filler dispersions during mixing. Esters of carboxylic
acid or phosphoric acid are most suitable in compounding NBR. These can be
either monomeric or polymeric in nature. Monomeric plasticizers get easily
extracted, when in contact with oils.
All plasticizers decrease the viscosity and the elastic recovery forces of
unvulcanized NBR and these increase with increasing easing amounts. The
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degree of reduction is especially variable in magnitude. Plasticizers can be
classified in two different groups, depending on whether they have a strong or
weak effect on the elastic, restoring forces.
Fats, waxes, resins, and polymeric plasticizers belong to one group. In
general, they strongly reduce the resilience of the vulcanized compounds and
thus exert a most favorable effect on processibility; that is to say, they
improve the calendar ability, extrudability and building tack.
Stearic acid, wool fat and some others of this group are relatively
poorly compatible and, therefore, may readily sweat out if sued in too high
concentrations and cause trouble in building operations. This same thing
holds, as has been said, for petroleum plasticizers which are high in aliphatics.
The molecular weight of the plasticizer is significant for compatibility.Easter and ether plasticizers are typical representatives of the other
group. They work by solvation, in the previously given sense, swelling the
NBR compounds strongly and causing pronounced softening. Actually they
lower the elasto-recovery forces relatively little. Because of their ability to
increase the elasticity of the vulcanisates, they are usually referred to an
"elastomers".
Certain viscous xylene-formaldehyde resins, alkyd resins, aldol resins
as well as rosin, Koresin, coumarone resins and swell-resistant and liquid
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factices, have found value as processing aids for improving calendarability
and extrudability as well as the building tack. Viscous butadiene/acrylonitrile
copolymers (10,000-300,000 cp) also serve very well. Being the same type of
material, they do not tend to sweat out when used in large amounts and thus
are oil resistant and non-volatile at higher temperatures.
PROCESSING
Nitrile rubber compounds are fabricated into a wide variety of articles
requiring many different types of processing involving milling, internal
mixing, extrusion, calendaring and vulcanizing in many different ways. All of
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commercially available Nitrile rubber can be mixed either on a two rollmill is
of no exception. The only care taken during mixing is the addition of sulphur
immediately after rubber has formed smooth band on the roll.
Compounds can be designed to be easily extruded, calendared or
molded with injection, compression, or transfer techniques. Optimum
breakdown and dispersion are required for both calendaring and extrusion,
sometimes requiring remilling operation, at least 16 hrs after original mixing.
In extrusion the screw and barrel should be at about 60-70 0c with head at
about 90 0c and die in the region of 120 oc. While for calendaring conditions,
for unsupported sheet, coating or plying are generally as follows:
Top roll ------ 75-85 o c Middle roll------ 60-70 o c Bottom roll----- 75-85 o c
For excellent extrusion, high Mooney viscosity rubber is chosen particularly when high green strength is required. Low or medium Mooney
viscosity polymers will lend excellent calendaring characteristics molding of
Nitrile rubber can be carried out conventional way and at conventional
operating conditions.
VERSATILITY IN NBR GRADESWide range of ACN content (16-50%).
16%, 20%, 23% ACN, for Very Low Temperature Service.
26%, ACN, with Carboxylation, for improved abrasion.
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27%, 29% ACN ,for Low Temperature Service.
33% ACN ,For General purpose use.
39% ACN ,For Fuel ,Oil, High Temp and Oil Drilling application .
40% ACN, For Fuel ,Oil, High Temp and Freon resistance application.
45% ACN, For Fuel, Freon and High Temp. Service products.
INCREASE IN ACN CONTENT LEAD TO THE FOLLOWING
1. Improves resistance to fuels and oils.
2. Increases abrasion resistance and hardness.
3. Improves tensile strength and modulus.
4. Improves processing behaviour.
5. Increases permeability resistance to gas diffusion.
6. Decreases Low temperature flexibility.
7. Reduces Resilience and Elasticity.
8. Improves heat resistance.
9. Decreases electrical insulation resistance.
10. Increases compatibility with polar plastics.
PROPERTIES OF NBR
1. Excellent resistance to Oils & Fuels.
2. Excellent resistance to Abrasion & wear.
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3. Good heat and chemical resistance.
4. Low permeability to air & gases.
5. Excellent overall physical properties when compounded with
reinforcing filler.
6. Low electrical insulation resistance, hence excellent Anti-static
properties.
7. Excellent compatibility with PVC; NBR/PVC fluxed properly displays
excellent resistance to ozone and weather.
8. Blends with PVC permits developments of TPEs. suitable for many
applications including footwear soling, gas tubing, garden hoses etc.
9. Excellent compatibility with Phenol-formaldehyde resins. Such blends
are useful for adhesives, high hardness products, leather like products etc.
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APPLICATIONS OF NBR
NBR is one of the most widely consumed rubber worldwide. It's
applications in different fields are discussed below.
1) In Military applications : Increase in ACN content of NBR improves
resistance to fuels and oils with increased abrasion resistance. Hence it is used
for manufacturing fuel, hydraulic, pneumatic hoses, diaphragms, oil seals,
valves, abrasion resistance soles, combat boots and engine mounts.
2) Automotive applications : NBR is prone to have excellent resistance to
fuels and oils, so it is used advantageously used for manufacturing of fuel
hose, oil seals, ('O' rings), 'V' packings, crash pads, hydraulic hoses, power
stearing hose and pressure bellows.
3) Industrial applications : Variety of grades of NBR can be obtained with
varying heat resistance depending on ACN contents, so NBR is used for
manufacturing water pipe insulations, cots & aprons, gaskets & friction material.
NBR is having low electrical insulation resistance hence excellent
antistatic properties and liable to be used for conveyor beltings.
4) Commercial applications : Commercial applications include food and
solvent handling hoses and Belts, Rice Rolls, Printing Rolls, Adhesive, Shoe
Soles, Milking Inflations, Floorings, Astro-turf underlays, Hawai Chappals,
Printing blankets and Blocks.
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CONCLUSION
So our country has been using the NBR and it should gather higher uses
as there is increase in availability in NBR indigenously. Some latest
advancements in the field and NBR technology are also taking place like
1) Emergence of carboxylated NBR
2) Halogenated NBR
3) Nitrile rubbers containing based antioxidants
4) NBR-Polyolefin blends (NBR+PVC)
5) NBR in powder form.
Importantly NBR can be efficiently used for the manufacture of various
molded products due to its excellent processibility & easy of availability. It
should replace the applications of some inferior rubbers, also new applications
should be bourn for nitrile rubber.
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BIBLIOGRAPHY
C.M. Blow & C. Hepburn : " Rubber Technology and Manufacture "
(2nd Edition) Butterworths P.N. 130-137
Maurice Morton : " Rubber Technology "
(3rd Edition ) Van Nostrand Reinhold Newyork P.N. 322-338
Harry Barron : " Modern Rubber Chemistry"
D Van Nostrand Company.inc Newyork P.N. 303-318
J.Y. Brydson : " Plastic Materials "
(6th Edition) Butterworth Heinemann Publication P.N. 267-268
Industrial Manual of APAR INDUSTRIES LIMITED, Mumbai.
WEBSITES
www.aparindustries.com
www.azon.com