Industrial Manufacturing Of Nitrile Rubber

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

C.O.E.& T.,Akola

1

Industrial manufacturing of Nitrile Rubber

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.

C.O.E.& T.,Akola

2

Industrial manufacturing of Nitrile Rubber

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

Present Capacity(MTA)

Trade Name

Synthetics & Chemicals Ltd.

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

C.O.E.& T.,Akola

3

Industrial manufacturing of Nitrile Rubber

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 : CH3 – CH2–OH 2CH3 –CHO

CH3 – CHO + H2

CH3 – CHOH –CH –CHO

CH3 – CH== CH–CHO + CH3–CH2–OH CH3 –CH == CH – CH2OH

CH3 –CH==CH-CHO

CH3–CH==CH–CH2OH+CH3–CHO CH2==CH–CH==CH2+H2O

(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 NH3 : Natural gas : air is 11.2:12.0:76.8 2CH2 + NH3 +3O2

HCN + 6H2O

Addition of hydrogen cyanide to acetylene in presence of an aqueous catalyst HCN

C.O.E.& T.,Akola

4

Industrial manufacturing of Nitrile Rubber

Catalyst (HCN) Ammonium Chloride

21.1%

Cuprous Chloride

54.3%

37% HCL

1.4%

Water

23.2%

pH

<6

This process was developed by 'BAYER' while 'Dupont Process' hydrogen cyanide is added to acetylene in presence of an anhydrous catalyst as under : Copper Chloride

30 - 50%

Adiponitrile

30 - 60%

X-Pyrolidene

2 - 30%

B.2. Synthesis of Acrylonitrile from Hydrogen Cyanide and Ethylene Oxide CH2 –CH2+HCN

HOCH2–CH2–CN

H2O+CH2=CH–CN

Catalysts used in above reaction are sodium cyanide, MgO etc. Ethylene oxide is produced by catalytic oxidation of ethylene. Dupont developed a dry process.

In the Duponts process gaseous

ethylene oxide and HCN in presence of a suitable catalyst and at elevated temperature (2000- 4000 C) from acrylonitrile in one step.

C.O.E.& T.,Akola

5

Industrial manufacturing of Nitrile Rubber

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 : CH2=CH–CHO+NH3+1/2 O2

CH2 = CH–CN+2H2O

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. C.O.E.& T.,Akola

6

Industrial manufacturing of Nitrile Rubber

CHEMICAL STRUCTURE OF NBR Chemical structure of NBR is generalized as copolymer of butadiene and acrylonitrile as shown below -----(CH2-CH=CH-CH2)x---(CH-CH2)y------| CN

Today 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.

C.O.E.& T.,Akola

7

Industrial manufacturing of Nitrile Rubber

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 5oC compaired to 50o C in the earlier days. Nitrile rubbers are produced by I ) Emulsion process : a) hot polymerization -------------------- 50o C b) cold polymerization-------------------- 05o 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

C.O.E.& T.,Akola

and

3) Termination

8

Industrial manufacturing of Nitrile Rubber

1. Initiation ROOH + Fe2+ ----------------------------------> RO* + Fe3+ + OHFe3 + Sodium Sulfoxilate ---------------------> Fe2+ RO* + CH2 = CH - CH = CH2 --------------> RO- CH2-CH=CH-CH2* 2. Propagation RO - CH2 - CH = CH - CH2 * + CH2= CH - CH = CH2 ----> RO - CH2 - CH = CH - CH2 - CH2- CH = CH - CH2* + CH2 =CH | CN RO - CH2 - CH = CH - CH2 - CH2- CH = CH - CH2 - CH2 -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 Acrylonitrile B for Butadiene

3. Termination

-

S R

R

||

|

|

RO* + S -C - N + H2O (From Hydroperoxides)

----------------> ROOH + CS2 + NH

|

|

R

R

Polymerization Reaction CH2 = CH - CH= CH2+ CH2=CH -----(-CH2 - CH = CH- CH2) x -----CH2-CH----------| | CN CN y n

C.O.E.& T.,Akola

9

Industrial manufacturing of Nitrile Rubber

Butadiene recycle ACN recycle

Wash Water Recycle

Vent

Refrigerant

Serum Recycle

Flow Diagram of Nitrile Rubber Manufacturing Steam

Emulsifier Initiator Activator Modifier

Coagulation

Water

Finished Product

C.O.E.& T.,Akola

10

Industrial manufacturing of Nitrile Rubber

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.

C.O.E.& T.,Akola

11

Industrial manufacturing of Nitrile Rubber

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 50c for cold and 500c for hot process. Redox system of initiator is used for cold while for hot process K2 SO8 is used. The monomer or is used

C.O.E.& T.,Akola

12

Industrial manufacturing of Nitrile Rubber

for cold while for hot process K2 SO8 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 C.O.E.& T.,Akola

13

Industrial manufacturing of Nitrile Rubber

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 50C due to their branched structure their calcium and magnesium salts are more soluble. Therefore they shows C.O.E.& T.,Akola

14

Industrial manufacturing of Nitrile Rubber

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.

C.O.E.& T.,Akola

15

Industrial manufacturing of Nitrile Rubber

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-Sx -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. Twothirds 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 C.O.E.& T.,Akola

16

Industrial manufacturing of Nitrile Rubber

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.

CH2-CH=CH- CH2 - CH2 -CH | CN

--------> -H-

2.

CH2-CH=CH- CH2 - CH2 -C* | CN

+ Sn + Accelerator * -------->

CN | CH2-CH=CH- CH2 - C | Sx | CH2-CH=CH- CH2 - C | CN

Thus cross-linking continues. Conventional accelerator system such as MBTS, Sulfenamides, DithioCarbamates, 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 such as C.O.E.& T.,Akola

17

Industrial manufacturing of Nitrile Rubber

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.

C.O.E.& T.,Akola

18

Industrial manufacturing of Nitrile Rubber

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 C.O.E.& T.,Akola

19

Industrial manufacturing of Nitrile Rubber

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 peroxides ADDITIONAL 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 .

C.O.E.& T.,Akola

20

Industrial manufacturing of Nitrile Rubber

Table - Typical Rubber Compound Ingredient Rubber

Parts 100.0

Sulfur

2.0

Zinc oxide

5.0

Stearic acid

3.0

Accelerator

1.5

Loading or filling pigment

50

Reclaim, softeners, extenders, colors, blowing As required agents, antioxidants, antiozonants, odorants, etc. 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 : C.O.E.& T.,Akola

21

Industrial manufacturing of Nitrile Rubber

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 Loading CB 25 phr

Plasticizer 10

T.S. (psi) 2200

Elongation.@ HardBreak ness 550 55

20

2000

600

50

300% Mod (psi) 650

Angle Tear lbs/In. 250

500

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

C.O.E.& T.,Akola

22

Industrial manufacturing of Nitrile Rubber

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 hot oils. 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

C.O.E.& T.,Akola

23

Industrial manufacturing of Nitrile Rubber

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

C.O.E.& T.,Akola

24

Industrial manufacturing of Nitrile Rubber

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

C.O.E.& T.,Akola

25

Industrial manufacturing of Nitrile Rubber

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

C.O.E.& T.,Akola

26

Industrial manufacturing of Nitrile Rubber

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 60-700c with head at about 900c and die in the region of 120oc. While for calendaring conditions, for unsupported sheet, coating or plying are generally as follows: Top roll ------ 75-85o c Middle roll------ 60-70o c

Bottom roll----- 75-85o 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 GRADES  Wide range of ACN content (16-50%).  16%, 20%, 23% ACN, for Very Low Temperature Service.  26%, ACN, with Carboxylation, for improved abrasion. C.O.E.& T.,Akola

27

Industrial manufacturing of Nitrile Rubber

 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. C.O.E.& T.,Akola

28

Industrial manufacturing of Nitrile Rubber

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.

APPLICATIONS OF NBR NBR is one of the most widely consumed rubber worldwide. It's applications in different fields are discussed below.

C.O.E.& T.,Akola

29

Industrial manufacturing of Nitrile Rubber

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.

CONCLUSION

C.O.E.& T.,Akola

30

Industrial manufacturing of Nitrile Rubber

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.

C.O.E.& T.,Akola

31

Industrial manufacturing of Nitrile Rubber

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

C.O.E.& T.,Akola

32