Nitrile rubber 3

NITRILE RUBBER
BY
PRIYABRATA GHOSH
IRI, KOLKATA

PRIYABRATA GHOSH, IRI, KOLKATA
NITRILE RUBBER (NBR)
• NBR IS A COPOLYMER OF BUTADIENE AND ACRYLONITRILE.
CH2 = CH – CH = CH2 + CH = CH
(BUTADIENE) (ACRYLONITRILE)
CN
RANDOM COPOLYMERISATION
~~[~~CH2 – CH = CH – CH2 – CH2 – CH–CH2 – CH = CH – CH2~~]n~~
CN
P-1

PREPERATION OF ACN MONOMER
• ACN HAS B.P. 770C; SP. GR. 0.80; LIQUID AT ROOM TEMPERATURE.
PREPARED FROM ETHYLENE OXIDE AND HYDROGEN CYANIDE.
CH2
O + HCN HO – CH2 – CH2 - CN
CH2 DEHYDRATED
CH2 = CH
CN
ALTERNATIVE METHOD : REACTING ACETYLENE WITH HCN CH2 = CH
CH ≡ CH + HCN MIXED AND EXCESS CH ≡ CH PASSED
THROUGH CON. SOLN. OF Cu2Cl2 CN
P-2

METHOD OF PREPARATION OF POLYMER
• IT IS MADE BY EMULSION OF POLYMERISATION (SIMILAR TO SBR).
RECIPE : P.B.W.
BUTADIENE……………………………………….. 75
ACRYLONITILE…………………………………… 25
EMULSIFIER (SOAP)……………………………… 4.5
STEARIC ACID……………………………………. 0.6 (ACCELERATES
POLYM.)
DODECYL MERCAPTAN………………………… 0.5 (MODIFIER)
Na-PYROPHOSPHATE……………………………. 0.1
KCl…………………………………………………. 0.3 (TO MAINTAIN
pH)
FERRIC SULPHATE………………………………. 0.2
H2O2………………………………………………. 0.35 (INITIATOR)
WATER……………………………………………. 180
P-3 ………..CONTD……….

METHOD OF PREPERATION OF POLYMER………………
• THE REACTOR IS PRESSURISED AS THE INGREDIENTS ARE
STIRRED MECHANICALLY. THE LATEX IS DISCHARGED INTO
BLOW-DOWN TANK AND HYDROQUINONE IS ADDED AS
SHORT-STOP. A DISPERSION OF 2% PBN IS THEN ADDED TO
LATEX.
• THE LATEX IS COAGULATED BY NaCl CREAMING FOLLOWED
BY H2SO4. THE CRUMB IS THEN WASHED AND DRIED AND
COMPRESSED INTO BALES.
• AS WITH SBR, LOW TEMPERATURE POLYMERISATION
RESULTS IN MORE REGULAR STRUCTURE IN POLYMER, BUT
NBR HAS MORE REGULAR STRUCTURE THAN SBR EVEN AT
HIGH TEMPERATURE POLYMERISATION. THIS IS BECAUSE IT
CAN SHOW A PREFERENCE OF 1, 4 ADDITION TO THE
BUTADIENE (END-TO-END).
P-4 ……….CONTD………

METHOD OF PREPERATION OF POLYMER………………………..
ACN CONTENT :-
 ACN CONTENT VARIES IN COMMERCIAL GRADES BETWEEN
27% AND 42% WITH THE AVERAGE OF ABOUT 33%, I.E., 2:1
MOLE OF BUTADIENE AND ACN. (MOL. RATIO IS ABOUT SAME,
C4H6 = 54 & CH2 = CH = 53)
CN
 HIGHER THE ACN CONTENT, BETTER IS THE OIL RESISTANCE,
BUT HIGH NITRILE POLYMER PRODUCES TOUGH PRODUCTS
WHICH ARE DIFFICULT TO PROCESS AND GIVE
VULCANISATES OF LOW RESILIENCE.
P-5

COMPOUNDING• CURING : CONVENTIONALLY SULPHUR VULCANISATION IS APPLIED. RATE OF
CURE IS SLOWER THAN NR AND SBR. HIGHER DOSES OF ACCELERATOR ARE
PREFERRED FOR CONSIDERABLE GOOD RATE OF CURE
NR SBR NBR
SULPHUR…………….. 2.5 2.0 1.75
ZnO……………………. 5 5 5
ST. ACID……………... 1 1 1
MBTS………………… 1 1.25 1.5
0.2 – 0.5 TMTD
• TMTD IS SECONDARYACCELERATOR WHICH GIVES ‘TIGHT’ CURE
RESULTING IN BETTER OIL RESISTANCE.
• MC SULPHUR IS PREFERRED FOR PROPER DISPERSION; SULPHUR IS ADDED
AT FIRST AND ACCELERATOR AT LAST.
PEROXIDE CURE : DICUMYL PEROXIDE IS OFTEN USED TO HAVE MINIMUM
STRESS RELAXATION AND VERY LOW COMPRESSION SET; HENCE MORE
RESILIENT AND IMPORVED HIGH TEMPERATURE AGEING PROPERTIES. E.G., 4
– 5 P.H.R. DICUP 40C (40% DCP DISPERSED IN CHINA CLAY).

COMPOUNDING……………………………………….
EV SYSTEM CURE : IT INVOLVES TMTD CURE OR TMTD/LOW
SULPHUR. EXAMPLE FOR EXCELLENT HEAT AGEING
PROPERTIES :-
CdO……….. 5
MgO………. 5
SULPHUR.. 0.5
CDC……… 2.5 (CADMIUM DIETHYL DITHIO-
CARBONATE)
MBTS…….1.0
DIOCTYL
DIPHENYLAMINE. 1.0 ( ANTIOXIDANT )
• THIS MIX IS RATHER SCORCHY AND TENDS TO BLOOM.
P-7 ……………CONTD………….

COMPOUNDING…………………..
• FILLER : NBR DOES NOT CRYSTALLISE ON STRETCHING, SO GUM
STRENGTH IS POOR. SO REINFORCING FILLERS ARE REQUIRED
FOR IMPORVED TENSILE PREPERTIES. HAF/FEF/GPF ARE
COMMON BLACKS. FEF GIVES TENSILE STRENGTH TO 3000 P.S.I.
• PLASTICIZERS : PETROLEUM OILS ARE NOT COMPATIBLE WITH
NBR. THEY CAN BE FORCIBLY MIXED, BUT BLOOM AFTER
VULCANISATION.
• SEMIPOLAR NBR NEEDS ESTER TYPE PLASTICIZERS. DIOP IS THE
BEST USE FOR HEAT RESISTANCE. FOR LOW TEMPERATURE
FLEXIBILITY, DOA (DIOCTYLADEPATE) OR DOS (DIOCTYL
SEBACATE) MAY BE ADDED. SEBACATE TYPES ARE COSTLIER.
P-8 ………………CONTD……….

COMPOUNDING……………………………………
• FOR VERY HIGH TEMPERATURE RESISTANCE, POLYPROPYLE
ADEPATE IS ADDED. DIOP IS VOLATILE AT HIGH
TEMPERATURE.
• IT IS IMPORTANT THAT SOFTENER WHICH IS COMPATIBLE
WITH THE OIL THAT THE NBR PRODUCT IS BROUGHT INTO
CONTACT WITH THAT OIL, IT WILL RESULT IN SHRINKAGE
AND HARDENING OF THE VULCANISATE DUE TO LEACHING
OUT OF THE SOFTENER USED IN THE COMPOUND.
• NBR IS TOUGH AND DRY AND DIFFICULT TO PROCESS AND
GENERALLY REQUIRES MORE SOFTENER THAN OTHER
RUBBERS (USUAL DOSES ARE 10-30 P.H.R.).
TACKIFIERS : NBR IS VERY ‘DRY’ POLYMER. FOR IMPROVED
GREEN TACK VERY LITTLE AMOUNT OF NR (UPTO 5 P.H.R.) IS
ADDED. MORE ADDITION OF NR WILL INCREASE THE
SWELLING IN CONTACT LIQUIDS.
• CI RESINS ARE ALSO USED AS TACKIFIER.
P-9 ……….CONTD………..

COMPOUNDING…………………….
• ANTIOXIDANT : DIOCTYL DIPHENYL AMINE IS USED FOR
GOOD AGEING PROPERTIES. HIGH NBR SHOWS BETTER
OZONE RESISTANCE.
• P- PHENYLENE DIAMINE IS GOOD FOR BETTER OZONE
RESISTANCE.
P-10

PROCESSING
• NBR DOES NOT RESPONSE MARKEDLY DURING
MASTICATION. IT IS BROKEN DOWN IN TIGHT NIP OF COLD
MILL.
• MV OF 40-50 HAS GOOD FLOW PROPERTIES. FOR TUBES
FROM EXTRUDER HIGH MV (80-90) IS CHOSEN AS THE SOFT
COMPOUND MAY COLLAPSE.
• SULPHUR IS DIFFICULT TO MIX IN NBR. THAT IS WHY
SULPHUR IS MIXED AT FIRST (MC SULPHUR IS PREFERRED
FOR BETTER DISPERSION).
EXTRUSION : LARGE AMOUNT OF FILLERS AND OILS ARE
GENERALLY USED IN NBR TO CONTROL DIE-SWELL DURING
EXTRUSION. FOR BEST EXTRUSION , TERPOLYMER WITH
DIVINYL BENZENE IS USED WHICH IS PARTLY X-LINKED.
P-11 ………….CONTD…………

PROCESSING………………………..
CALENDERING : HIGHER ROLL TEMPERATURE (750-800C) THAN NR
AND SBR IS REQUIRED.
MOULDING : DUE TO LACKNESS OF TACK, NBR COMPOUND HAS
‘MARRY’ PROBLEM RESULTING IN WEAK ADHESION OF
LAYERS.
o IT HAS POOR HOT TEAR STRENGTH LIKE SBR AND UNLIKE NR.
P-12

VULCANISATE PROPERTIES
1) BEING RANDOM COPOLYMER, NBR COMPOUND DOES NOT
CRYSTALLISE ON STRETCHING; HENCE LOW GUM STRENGTH.
SO SMALL SIZE P.S. REINFORCING BLACKS ARE REQUIRED FOR
HIGH TENSILE PROPERTIES.
2) MODERATE COLD TEAR STRENGTH, HOT TEAR STRENGTH IS
POOR.
3) VERY GOOD ABRASION RESISTANCE.
4) AGEING PROPERTIES ARE BETTER THAN NR AND SBR. BUT NOT
USED WHERE GOOD AGEING PROPERTIES ARE REQUIRED. AT
HIGH TEMPERATURES IT HARDENS AND THEN RESINIFIES.
5) LOW TEMPERATURE FLEXIBILITY DEPENDS ON ACN CONTENT.
NORMALLY USED UPTO -100C, BUT CAN BE IMPROVED (UPTO -
300 – 400C) BY COMPOUNDING WITH SUITABLE PLASTICIZERS
(DOA, DOS).
P-13 …………CONTD…………….

VULCANISATEPROPERTIES…………………
6) OIL RESISTANCE IS EXCELLENT, HIGHER WITH HIGHER ACN
CONTENT. BY INCREASED ACN CONTENT, OIL RESISTANCE,
TENSILE PROPERTIES, HARDNESS AND ABRASION
RESISTANCE ARE IMPROVED. BUT LOW TEMPERATURE
FLEXIBILITY AND RESILIENCE PROPERTIES ARE
DECREASED.
7) BEING SEMI-POLAR POLYMER, NBR IS SEMI-CONDUCTOR.
SO NOT USED AS INSULATORS.
P-14

USEFUL BLENDS OF NBR
1. NBR/PVC BLEND :
NBR AND PVC ARE COMPATIBLE TO EACH OTHER AND THEY ARE
EACH COMPATIBLE WITH SIMILAR TYPES OF SOFTENER.
TYPICAL FORMULATION : P.H.R.
MED. NBR ………………………………………………….. 100 HOT
PVC …………………………………………………………. 60 MIX AT
STABI- Pb-CARBONATE ………………………………….. 3 1600C
LISERS Cd OR Ca-STEARATE ………………………………… 1
STEARIC ACID ……………………………………………. 1
ZINC OXIDE ……………………………………………….. 4
FEF BLACK ………………………………………………… 50
DOP …………………………………………………………. 20
MC SULPHUR ……………………………………………… 1.75
MBTS ……………………………………………………….. 1.5
P-15 ………..CONTD……….

USEFUL BLENDS OF NBR………………………….
METHOD : FIRST NBR IS ADDED EITHER TO MILL OR BANBURY. DOP
AND PVC ARE ADDED ALONGWITH LUBRICANT AND
STABILIZERS. THEN TEMPERATURE IS RAISED TO 1600C FOR
SEVERAL MINUTES, AND TAKEN OUT AND COOLED..
• THEN IT IS PUT IN A COOL MIXER TO ADD REST OF THE
INGREDIENTS.
SPECIAL MIXING TECHNIQUE :
THE USUAL METHOD IS TO MAKE A WET PREMIX OF PVC AND
PLASTICIZER IN A CONVENTIONAL VESSEL FOR 24 HOURS IN
ORDER TO ALLOW SOME LIMITED SURFACE ABSORPTION OF
THE PLASTICIZER. THEN THE MIXTURE IS PUT IN A MIXER AT A
TEMPERATURE OF 1600C. THIS HIGH TEMPERATURE FUSING IS
CALLED ‘FLUXING’.
P-16 ………..CONTD…….

USEFUL BLENDS OF NBR……………………
PROPERTIES OF NBR/PVC BLEND :
i. BETTER RESISTANCE TO OZONE AND WEATHERING.
ii. BETTER GLOSSY SURFACE AND DIMENSIONAL STABILITY OF
EXTRUDATES AND MOULDINGS. FLOW PROPERTIES ARE IMPROVED
SUBSTANTIALLY.
iii. VULCANISATES HAVE BRIGHT COLOUR.
iv. HIGHER ABRASION AND OIL RESISTANCE.
v. GOOD FLAME RESISTANCE IF SUITABLE PLASTICIZERS ARE USED.
P-17 …………..CONTD……….

USEFUL BLENDSOF NBR……………………………
2. NBR/PF RESIN BLEND :
 PF RESINS ARE COMPATIBLE WITH NBR AND CAN BE CO-
VULCANISED.
 PF RESINS ARE THERMOPLASTIC MATERIALS AND ARE
THERMOVISCOUS IN POWDER FORM. THEY CAN BE X-
LINKED BY HEATING WITH 8% HEXAMINE
(HEXAMETHYLENE TETRAMINE).
 NBR IS TOUGH POLYMER AND NEEDS HIGH AMOUNT OF
PLASTICIZER. PF RESIN ITSELF BEHAVES AS PLASTICIZER
AND TACKIFIER.
 BUT DURING VULCANISATION IT X-LINKS AND FORM A
HARD RESINOUS REINFORCING MATERIAL. THE
SOFTENING POINT OF THIS RESIN IS ABOUT 800-900C, BUT IT
X-LINKS WITH HEXAMINE AT 1300C.
P-18

USUAL BLENDS OF NBR…………………..
TYPICAL FORMULATIONS :
P.H.R.
NBR………………………….. 100
PF RESIN……………………. 50
HAF BLACK………………… 75
ZnO…………………………… 4
ST. ACID…………………….. 1
MC SULPHUR……………… 1.75
MBTS………………………… 1.5
P-19

USUALBLENDSOF NBR……………………
• PROPERTIES :
i. SHOWS HIGH TENSILE STRENGTH, HARDNESS AND RESILIENCE.
THEY MAY BE ENHANCED BY INTERACTION WITH FILLERS,
SUCH AS C-BLACKS, SILICA.
ii. GIVES EXCELLENT FLOW PROPERTIES DURING MOULDING,
CALENDERING AND EXTRUSION.
iii. SHOWS HIGH OIL RESISTANCE AND ABRASION RESISTANCE.
iv. COMPRESSION SET PROPERTIES ARE LOWERED WITH
INCREASING PF CONTENT.
P-20

TIPYCAL MIX FOR HEAVY DUTY CABLE
SHEATHING
P.H.R.
MED. NBR…………………………………. 100
PVC…………………………………………. 60
ZnO………………………………………….. 5
ST. ACID…………………………………… 1
MBTS………………………………………. 1
TMTD……………………………………… 0.5
MC SULPHUR…………………………….. 1.75
HAF BLACK………………………………. 40
CHINA CLAY……………………………… 30
TRIOLYL PHOSPHATE…………………. 50
PBN…………………………………………. 1
(STABILISER FOR PVC) Ca-STEARATE. 2.5
P-21

OIL SEAL COMPOUND RECIPE
P.H.R.
MED/HIGH NBR………………………………… 100
ZnO………………………………………………… 5
ST.ACID…………………………………………… 1
FEF BLACK………………………………………. 70
CHINA CLAY…………………………………….. 75
DIOP……………………………………………….. 25
TDQ………………………………………………… 1
MC SULPHUR…………………………………….. 1.75
MBTS………………………………………………. 1.50
TMTD………………………………………………. 0.25
P-22 ………..CONTD……………

OIL SEAL COMPOUND RECIPE…………………………
• IF HIGHER OIL RESISTANCE IS REQUIRED, THEN –
1) HIGH NBR RUBBER.
2) INCREASE OF TMTD A BIT TO HAVE MORE TIGHT CURE.
3) INCREASE OF FEF BLACK AND PLASTICIZER.
• FOR INCREASED BUILDING TACK, VERY LITTLE (MAXIMUM 5
P.H.R.) NR IS ADDED, BUT HIGHER AMOUNT WILL RESULT IN
LOWER RESISTANCE TO OILS.
P-23

NBR PROPERTIES – RELATIONASHIP TO ACN
CONTENTS
NBR WITH LOWER ACN CONTENT NBR WITH HIGHER ACN
CONTENT
• PROCESSABILITY ……………………………… BETTER
• CURE RATE WITH S-CURE SYSTEM…………. BETTER
• OIL/FUEL RESISTANCE………………………… BETTER
• COMPATIBILITY WITH POLAR POLYMER…. BETTER
• AIR/GAS IMPERMEABILITY…………………… BETTER
• TENSILE STRENGTH ……………………………. BETTER
• ABRASION RESISTANCE ……………………….. BETTER
• HEAT AGEING ……………………………………. BETTER
P-24 …….CONTD……

NBR PROPERTIES – RELATIONASHIP TO ACN CONTENTS
NBR WITH LOWER ACN
CONTENT
NBR WITH HIGHER ACN CONTENT
BETTER CURE RATE WITH PEROXIDE CURE
BETTER COMPRESSION SET
BETTER RESILIENCE
BETTER HYSTERESIS
BETTER LOW TEMPERATURE FLEXIBILITY
P-25

HYDROGENATEDNITRILE RUBBER (HNBR)
 PROPERTIES OF HNBR DEPEND ON ACN CONTENT AND ON THE
DEGREE OF HYDROGENATION.
 THEY CAN BE ‘TAILORED-MADE’TO PARTICULAR APPLICATIONS.
 GENERAL ADVANTAGES OF HNBR OVER STANDARD NBR OF
HAVING HIGHER TEMPERATURE RESISTANCE AND HIGHER
STRENGTH.
 THEY HAVE GOOD HIGH TEMPERATURE OIL AND CHEMICAL
RESISTANCE.
P-26

• ADDITION OF CARBOXYLIC ACID GROUPS TO NBR POLYMER
BACKBONE SIGNIFICANTLY ALTERS PROCESSING AND CURED
PROPERTIES.
• SUCH POLYMER MATRIX SHOW IMPROVED TENSILE, TEAR,
MODULUS AND ABRASION RESISTANCE PROPERTIES.
• DEMERITS ARE REDUCTION IN COMPRESSION SET, WATER
RESISTANCE, RESILIENCE AND SOME LOW-TEMPERATURE
PROPERTIES.
END

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