Speciality Elastomers for
Industrial Applications
presentation by
D. J. Bharucha
Bhimrajka Exim LLP, Mumbai
at
ETDS seminar, New Delhi on 5th March, 2014
Introduction
Rubber is a common material which is used in almost every industrial
application. The requirement of rubber products is constantly towards
better quality standards and higher performance limits, and this is only
possible by continuous improvement in materials, manufacturing process
and management attitude.
Automation and computerization play a great role in product improvement,
so also developments in newer monomers, molecular architecture of
polymers, and more efficient compounding ingredients.
General purpose rubbers like NR and SBR have limited resistance to heat and
environment, special rubbers have been developed where the thermal
performance has been stretched from minus 100 C to over 300 C, and are
serviceable in difficult environments like ozone, chemicals, oils and fuels.
Definitions
Speciality elastomers:
Can be defined as rubbers having higher performance limits in
terms of thermal properties, or chemical resistance or
environmental adaptibility or even in strength properties,
when compared with general purpose rubbers like NR and
SBRs.
It is expected that the products made from these rubbers will
perform better, last longer, and tolerate more difficult
environments, save machine downtime and improve
productivity, at the same time contributing to a safer, cleaner
and healthier working conditions.
Types of rubbers
General purpose;
NR, BR, SBR, IR,
Special rubbers: (mid performance) IIR, EPM/EPDM, CR, NBR, OT
Speciality elastomers: CSM, CM, ECO, ACM, AEM, VMQ,
(high performance)
HNBR, FKM, FFKM, FVMQ
Most of these rubbers have been developed and introduced in
the middle of the last century (1930’s to 1980’s), and to the
best of our knowledge, no new rubbers have been introduced,
except for modifications of existing rubbers.
Performance properties
Rubber
Service
Tg,C
temp. C
Resistance
to OIl #3
Ozone
resistance
Tensile
strength
NR/IR
BR
SBR
70
70
80
- 75
- 85
- 55
poor
poor
poor
poor
poor
poor
v.high
med
high
IIR
EPDM
CR
NBR
OT
HNBR
100
125
100
100
70
150
- 65
- 55
- 50
- 40
-10
- 40
poor
poor
med
good
good
good
med
high
med
poor
high
high
med
med
high
med - high
low
med - high
Performance properties
Rubber
CSM
CM
ECO
ACM
AEM
VMQ
FVMQ
FKM
FFKM
HNBR
Service
temp. C
140
150
130
160
170
225
200
250
300
150
Tg,C
resistance
Ozone
to Oil #3
resistance
- 40
med
high
- 30
med
high
- 45
good
high
- 30
good
high
- 40
med
high
- 110
med
high
- 65
good
high
- 30
good
high
- 10
v.good
high
- 40
good
high
Tensile
strength
med-high
med-high
med
med
med
low
low
med
med
med - high
Application in fluids and chemicals
Hydrocarbon rubbers, e.g. NR, BR, SBR, IIR, EPDM, have little or no
resistance to petroleum based oils and fuels (very high swell in
IRM903 oil).
The introduction of polar groups (containing atoms like Cl, N, O, S, F )
imparts good to very good resistance to oils and fuels, depending
on their polarity. FKM, FVMQ, HNBR/NBR, ECO, ACM have
particularly good resistance to hydrocarbon oils and fuels.
EPDM rubbers, Butyls, CSM and FKM (certain grades) have very good
resistance to acids and aqueous chemicals. EPDM is particularly
preferred for high temperature steam application.
FKM on the other hand are not serviceable in strong bases and
amines, for which special grades like TFE/P are required.
Special rubbers
Apart from good thermal properties and fluid resistance,
polar rubbers have other attributes as well.
- They can conduct electrical charges, and therefore
suitable for anti-static applications. (e.g. NBR types)
- The polar molecules are excited by high frequency
microwave energy, with the result that the compound
gets uniformly heated and cured throughout its mass
even in thick cross-sections.
- Rubbers with halogenated molecules are inherently fire
retardant or self-extinguishing.(e.g. CR, CM,CSM, FKM,)
ASTM D2000/SAE J200 classification
Temp.C
300 Type
FFKM
250
H
FKM
225
G
200
F
175
E
150
D
TFE/P
VMQ
EAM
EOM
CM/
CSM
EPDM
125
C
100
B
75
A
Vol..swell %,# 3 oil
Class
FVMQ
HIIR
IIR
ACM
CR
HNBR
ECO
NBR
SBR
NR
>150
A
140
B
120
C
100
D
80
E
60
F
40
G
20
H
10
K
Processing of special rubbers
Processing involves various steps to convert raw rubber into the final
product. These include compounding, mixing, shaping operations
(e.g. extruding, calendering etc.), curing and finishing.
Most important point in processing is to ensure proper dispersion of
the fillers and compounding ingredients.
All these operations are similar to that of general purpose rubbers,
except that extra care has to be taken to control heat history.
Temperature at each step has to carefully maintained to get
maximum output with minimum input of heat energy.
As speciality rubbers are relatively expensive, it makes good sense to
aim for a zero defect production by following good manufacturing
practices.
Polychloroprene (CR)
DuPont’s Neoprene, the world’s first commercial synthetic
elastomer, was introduced in 1931. It is truly the first
multipurpose elastomer, thanks to its combination of useful
properties.
> Outstanding physical toughness
> Good resistance to heat, oxidation, ozone and weathering
> Good resistance to hydrocarbon oils and greases
> Good flame resistance and self-extinguishing characteristics.
CR GRADES
Gradation of Neoprene is based on:
1. Crystallization rate – slow , medium , fast.
Slow - for items requiring long term stability, like bridge bearing pads, etc.
Medium - for general goods, like hoses, molded items etc.
Fast – specially for contact adhesives.
2. Viscosity – low to high, e.g. 20 to 140 ML4/100C.
Low viscosity for ease of processing, good flow properties
High viscosity for improved strength, high loading capability
3. Type of modifier – normal nercaptan grades, or sulfur modified
grades (next slide)
4.Gel content (pre-crosslinked) – reduced ‘nerve’, smoother and
faster extrusion and calendering.
CR grades
Comparison of sulfur- and mercaptan modified grades
sulfurmercaptanmixed (GW type)
(Neoprene type )
( G types)
(W )
(GW )
Storage stability
limited
better
good
Mixing
peptizable
not peptizable
peptizable
Tack
very good
good
medium
Cure rate
fast
medium
fast to medium
Accelerator
not required
required
slight
Tensile, tear properties
very good
good
good
Ageing, heat resistance
good
better
better
Compression set
not so good
good
medium
Dynamic flex
very good
acceptable
good
( Neoprene GW combines the best of both)
Processing of Neoprene
Neoprene or polychloroprene has been around for over 70 years, and compounders
are well versed in handling the same. Nevertheless,
a few points are worth mentioning again.
1. Check the shelf life, as it is limited, and control the heat history to a minimum.
3. Add high active MgO at the start of mixing, and ZnO at the end only.
4. Sulfur-modified grades are peptizable, and more prone to sticking.
Vanax® 552 of R.T. Vanderbilt is an effective chemical peptizer for the
sulfur modified types.
5. Polybutadiene rubber at 5 phr and stearic acid helps prevent mill sticking.
6. Other processing aids include zinc-free lubricants like Struktol® HT204 or WB 16
microbeads for superior dispersion, and improved flow and surface finish.
CR applications
Adhesives: Highly crystalline grades, solid and latex.
Wire and Cable: normal grades, low viscosity for smooth extrusion.
Power transmission belts: S-modified grades, low to medium viscosity.
Hose covers: normal grades, med. to high viscosity, for oil and hydraulic hose,
LPG hoses, etc.
Rollers : for printing machines, paper, textile, steel mills, etc. Sulfur grades,
medium to high viscosity.
Molded goods: bridge bearing pads, expansion joints, etc. (low crystallizing
grades)
Coated fabrics: S-modified grades for frictioning and calandering.
Dipped goods, foams, etc: CR latex
Automobile items: mainly normal grades
and many more
CR rollers
Printing machine roll ( Sh. A 25)
Neoprene GRT 60 phr
Neoprene WHV 40
MgO
4
OCD
2
Stearic acid
1.5
Low mw PE
2
MT black
20
Factice
50
Aromatic pr. oil 50
ZnO
5
High hardness, abrasion resistant (Sh A 85)
Neoprene GRT
100 phr
MgO
4
OCD
2
Stearic acid
1.5
Low mw PE
2
N330 HAF black
30
N990 MT black
20
Precipitated silica
20
CI resin
5
Aromatic pr oil
10
ZnO
5
TETD
1
Nitrile rubber (NBR)
Acrylonitrile-butadiene copolymers, in short Nitrile rubbers are really the
workhorse of the special rubber industry.
They have the best oil resistance with fairly good heat resistance ,and
therefore suitable for a number of applications in the auto and industrial
products sectors.
NBR, like SBR, has good stability, can be easily mixed and processed, and can
be cured with similar sulfur accelerator systems.
Physical properties and compression set is very good , ideally suited for many
sealing applications.
Being unsaturated, ozone and weathering resistance is missing.
Electrical resistivity is low therefore suitable for antistatic products, but not
for insulation.
Gradation of NBR
Gradation of NBR is mainly based on the acrylonitrile content which ranges
from a low of 18% to a high of 48%., higher the ACN, better is the oil
resistance, but low temperature properties are affected.
The viscosity of various grades can range from very low to high as with other
rubbers.
Oil extended grades are also available, usually with DOP or now with safer
plasticizers.
Powder grades are also available specially for plastic modification , or for
continuous mixing operations.
Modification of NBR by carboxylation (XNBR) confers improved strength
properties, where as modification by hydrogenation (HNBR) improves
thee ozone and weathering, as well as resistance to wear and tear, and
oils containing aggressive additives.
Processing of NBR and HNBR
The most important point to remember is that sulfur is less soluble in NBR
and difficult to disperse. It has to be added first in the mixing cycle.
Sulphur preparations like Struktol® SU 95 or SU120 dustless powders, or
polymer bound products give good dispersion.
Semi-EV curing system-low sulfur high accelerators is advisable
Whilst mill mixing is quite easy, high viscosity and high ACN grades may take a
longer time to form a band. Processing aids help in dispersion of fillers and
reducing nerve. Struktol WB 222 is particularly effective in NBR as well as
in HNBR.
Tackifiers for NBRs are polar resins like CI resins or PF resins, and other
proprietary resinous tackifiers like Struktol TS 35, are also very effective.
Plasticizers of the ester and ether types are needed for NBRs as they are
easily compatible, and give improvement in low temperature flexibility,
whilst polyethylene glycol ester (Struktol AW-1) improves the anti-static
properties still further.
Applications of NBRs
Main application of NBR is the automobile industry for oil seals,
O-rings, gaskets and hoses in oil environments.
In our country though the biggest use probably is in rice
dehusking rollers due to its wear and tear properties in
combination with phenolic resins and precipitated silicas.
NBR finds use in antistatic products like safety footwear, and
textile products like cots and aprons.
Carboxylated NBR is also ideal for spinning cots where modified
glue is still being used for good performance.
Hydrogenated nitrile (HNBR) has a major application in poly-V
belts and synchronous timing belts.
Typical roller compounds
Printing roll
OE-NBR
150 phr
Sulfur
2
St. acid
1
ZnO
5
A/o TDQ
1
Factice
40
DOP
15
MT (N990)
10
TMTMS
1
Shore A :
40
Textile/Paper mill roll (non-black)
NBR
100 phr
Sulfur
1.5
Stearic acid
1
ZnO
5
A/O TDQ
2
Pptd silica
45
PF resin + hardener 15
TiO2
5
WB222
2
MBTS
1
80
Textile spinning cot
XNBR (X 1.46)
100 phr
Sulfur
10
ZnO
5
TiO2
10
Modified glue
75
Antistatic plasticizer 10
MBTS
1.5
Shore A:
(anti static)
78
Rice dehusking roll
NBR/BR
80/20 phr
Sulfur
2
ZnO
5
Stearic acid
1
Ppted silica
60
PF resin + hardener 20
A/o TDQ
1
DOP
5
CBS
1.2
Shore A:
90
Chlorosulfonated polyethylene
( CSM)
CSM, often termed as Hypalon® of DuPont, is a special
elastomer, akin to CR, but with better heat and fluid
resistance, better weathering and ozone and improved
physical properties.
Various grades contain 28 to 43 % chlorine, but all have around
1% sulfur only, to help crosslinking by different curative
systems.
CSM is a versatile polymer having applications in the cured or
uncured state also. It is the most colour-stable polymer, and
has good storage stability also.
Processing of CSM
Chlorosulfonated polyethylene (CSM) is, or rather was, a speciality of DuPont
Performance Elastomers, now from other sources.
This is also a sticky polymer, in spite of its high viscosity, and the following process
aids are always recommended.
 Low molecular weight polyethylene (2 phr)
 Polyethylene glycol (2 – 4 phr)
 Paraffin and microcrystalline waxes (2 -4 phr)
 Stearic acid and stearates (not zinc), e.g. Struktol® WB222
 High cis-polybutadiene or high ethylene EPDM (3 to 5 phr)
Caution; zinc oxide and zinc compounds to be avoided.
Cold stocks of CSM are dry and tack-free for laminating and building operations; warming the
sheets to 65 – 70°C is a better way of tackifying the compound prior to roll building.
Proprietary tackifiers like Struktol TS35, coumarone resins, etc., and others are also useful,
though they may aggravate mill sticking.
Curing of CSM
The highly reactive sulfonyl chloride crosslinking site offers a
wide choice of practical curing systems.
The common acid acceptors used are high activity MgO with
pentaerythritol, 4 + 3 phr, or 8 to 10 phr MgO alone.
The common curatives are :
- TMTD plus sulfur
- Tetrone® A (tetraethyl thiuram tetrasulphide or – hexasulphide.
- HVA-2® (n,n’-m-phenylene dimaleimde)
- Peroxide +coagent
and various combinations of the above.
CSM applications
Automotive: power steering and oil cooler hose, fuel hose cover,
emission and vacuum tubing ,etc.
Industrial : Hydraulic hose covers, oil and fuel hose covers,
rollers for paper and textile industry, tank linings.
Electrical: wire and cable sheathings, appliance wires, etc.
Solution applications: coatings on various substrates, structural
adhesives, primers, collapsible storage tanks, etc.
Uncured applications: magnetisable strips, roofing membranes,
pit liners, rainwater harvesting, etc. ( higher green strength
due to higher ethylene content )
CSM –typical compounds
Power steering hose:
CSM -40
100 phr
MgO
5
Pentaerythritol 3
N762 black
60
DOP
15
Process aids
4
NBC
1
Tetrone A
1
MBTS
0.5
Textile mill roll
CSM-40
100 phr
MgO
5
pentaerythritol
3
Hard clay
60
CaCO3
30
TiO2
15
Chlor paraffin
20
PEG
2
Par. Wax
2
Tetrone A
2
MBTS
0.5
161
CSM applications
Magnetic strips
CSM (24% Cl)
Ba or Strontium ferrite
PE wax
Polyethylene glycol
100 phr
900
2
5
Unvulcanized, good green strength.
Extruded strip passed thru a magnetizer.
EPDM
Ethylene-propylene-diene terpolymer is one of the fastest
growing special rubber in the non-tyre industry. (Global
production may touch a million tonnes by 2018.)
The saturated main chain is responsible for the extremely good
weather and ozone resistance, as well as good resistance to
heat and oxidation.
Being a non-polar rubber, it has resistance to polar oils and
solvents, but not to hydrocarbon mineral oils. It is compatible
with many chemicals including hot water and steam.
At a specific gravity of 0.86 to 0.88, it is the lightest rubber
available giving advantage in volume cost.
EPDM gradation
Gradation is based on:
1. Diene content: from 0 to 10%. Low diene grades are cured with
peroxides, whilst grades with 5 to 10% diene are termed as fast curing
grades with sulfur-accelerator systems.
2. E :P ratio : Grades with ethylene content upto 60% are considered as
amorphous , easier to mix on the mill, and having good set properties.
70 and above ethylene are semi-crystalline grades, having good green
strength and extrusion properties, and can be highly loaded.
3. Mooney viscosity of various grades range from 20 to 85 and even higher
in case of oil extended grades.
4. Other variables: Oil extended grades (20 to 100 phr paraffinic oil )
Molecular weight distribution – narrow, med, broad.
EPDM – properties and characteristics
EPM and EPDM vulcanizates are characterizsed by their following good
properties.
1, Highly resistant to oxidation, weathering and ozone due to its saturated
backbone.
2. Good heat resistance upto 150C with peroxide cures.
3. Very good resistance to hot water and steam (220C, 250 psi).
4. Resistant to polar solvents, e.g. ketones, alcohols, glycols, phosphate
esters,
5. Resistant to vegetable oils, various acids, alkalies, sodium hypochlorite, etc.
6. Good physical properties and compression set, low temp properties.
7. Good electrical properties ( insulation for low and medium voltage cables)
8. Can be loaded highly with fillers and plasticizers (for economy).
81
Applications of EPDM
Main use of EPDM is in the automotive industry for profiles and
weatherstrips, window channels, etc,. When properly compounded
extruded profiles can be continuously cured in microwave tunnels, and
other CV systems.
EPDM is also the main polymer for radiator hoses, brake hoses and cups for
automobiles.
EPDM is also an ideal polymer for wire and cable insulations for low and
medium voltage power cables.
Pipe seals for potable and sewage water.
Automotive FEAD belts for high temperature resistance.
In other industrial applications, EPDM is the only polymer for high pressure
steam and water hoses, and fire fighting hoses.
Rubber rollers with EPDM are also used in certain applications like paper
and textile processing and metal coating industry.
Applications of EPDM
Applications in the rubber roll industry are for steel mills, metal coating rolls,
and plastic processing rolls.
Sulfur cured
Peroxide cured
Nordel™ IP4640
100 phr
Ppted silica
20
Si 69
1
N774 black
50
Zn0
5
St acid
1
Low mw butyl
10
A/o TDQ / ZMTI
1/1
Sulfur
0.5
Accelerator package
5.0
Nordel™ IP 4640
N774 black
ZnO
Struktol WB 16
A/0 TDQ
A/O ZMTI
Paraffinic oil
Peroxide DBPH-50 HP
(TAIC )
100 phr
50
5
2
1
1
5
8
1
Silicone rubbers
Silicone rubbers, or polysiloxanes, are the only
rubbers having an inorganic main chain,
--O—Si—O—Si—O—Si—O– , with organic side
chains.
All other rubbers have a carbon-hydrogen
organic main chain,
-CH—CH—CH—CH—CH—CH--
Silicone rubbers
All silicone rubber have predominantly methyl side groups, i.e. - CH3
However, a few vinyl side groups are always added to help crosslinking.
--CH=CH2.
Most of the commercial grades are VMQ type.
Phenyl groups, - C6 H5 are added to improve the low temperature properties,
and radiation resistance. These are the PVMQ types.
Addition of fluoro groups greatly improves oil and fuel resistance, closer to
Viton, but costlier than FKM. These are the FVMQ types
Heat resistance: VMQ =PVMQ >FVMQ
Oil resistance : FVMQ >> VMQ =PVMQ
Low temp properties: PVMQ >>VMQ>FVMQ
Processing of silicone rubbers(VMQ)
Properties: soft, low viscosity rubbers .Very good low temperature flexibility.
Excellent heat resistance, Good electrical properties. Medium oil resistance.
Curatives: peroxides only. No coagents required.
0R Addition (platinum) curing system also possible for fast cures.
Postcuring 4 hrs at 200C recommended. No post cure grades also available.
Problems faced: Crepe hardening, mill sticking, low green strength, low TS and tear except for some histrength grades.
Processing additives: Proprietary masterbatches, for example Dow Corning’s
Xiameter RBM 9001 to retard crepe hardening,(for overaged stocks).
Xiameter RBM 9004 to improve green strength,
Xiameter RBM 9003 to improve extrusion and calandering.
Xiameter RMB 9010 for better mold release.
Preventive measures; mix on absolutely clean and cold mill.
No contamination from oils and grease from mill guides.
Can be blended with other silicone grades to get intermediate properties.
Addition of color pigments, flame retardants, etc should be in masterbatch form only.
Mill freshening before curing or extruding is helpful.
Properties of Si Rubbers
Thermal properties: Resistant to high and low temperature,
- 110 to 250C. Widest service temperature range among all rubbers.
Maintains physical properties even at high temperature.
Electrical Properties: Very good insulation and dielectric properties, high
dielectric strength, excellent arc and tracking resistance.
Physical Properties: medium to low tensile and tear properties, poor
abrasion resistance, very good compression set resistance.
Environmental Properties: Very good resistance to oxidation, ozone and
weathering, high radiation resistance, medium to good resistance to
chemicals and oils,
Other properties: water repellant, good flame resistance with non-toxic
combustion products, high gas permeability.
Applications of silicone rubbers
Automotive: seals, gaskets, spark plug boots, turbo hoses,
exhaust pipe hangers, air bags, etc.
Wire & Cable: Ignition cable, fire safety cables, furnace leads,
Industrial: extruded and molded parts, rollers, technical textile
coatings, key pads, office automation parts, etc.
Food and medical: cathetors, tubings, feeding botle nipples,
pacifiers, medical instruments, bake ware, household
machines, cake molds, freezer gaskets, oven door profiles, etc.
Sports and life style: swim caps, goggle frames, diving masks, etc
Power T & D : High voltage insulators, surge arrestors, cable
accessories,
Applications of silicone rubbers
Silicone rubber roll
for office automation
(Dow Corning grades RBB -66xx- 30 and 80)
Ethylene/acrylate elastomer
(AEM)
Polyacrylate rubbers ACM and AEM are speciality elastomers
which fill in the gap between the high heat resistant rubbers
of 200C plus, and medium heat of 150C.
Vamac® AEM of DuPont is claimed to have an advantage over
ACM in terms of processing ease, heat resistance, low
temperature and damping characteristics, although the oil
resistance is not as good as in ACM.
Latest developments in Vamac® have increased the Mooney
viscosity as well as thermal limits to 180C for high
temperature applications.
AEM
Whilst compounding of AEM is similar to other rubbers, it is important to add
proper processing additives and aminic crosslinking agents.
Although one grade Vamac DP is peroxide curable, the other popular G types
require a combination of Diak no.1 (hexamethylene diamine carbamate)
with a guanidine, DPG or DOTG
Other safer substitutes are also available, e.g. Vulcofac ACT55, a tertiary
amine complex (DBU)* of Safic Alcan in place of DPG,DOTG.
As an antioxidant, Naugard 445 ( diphenylamine) is most suitable.
Amine cured Vamac needs a post cure for 4 hrs/177 C,
Peroxide cured moldings do not require post curing.
* 1,8-diazabicyclo undec-7-en.
Processing of EAM (contd)
Precautionary measures: Select high viscosity grades wherever possible, and use cold
mill. Don’t mill excessively.
Release package most important to prevent mill sticking –
Stearic acid
1.0 – 2.0 phr
Octadecyl amine 0.5 phr (Armeen® 18D)
Vanfre® VAM
1.0 phr (or Struktol® WB222)
Use low volatility, heat resistant plasticizer ,e.g. mixed polyether/ester like
Struktol KW 759 or TP 759.
Cure under sufficient pressure to prevent blistering.
Do not use any metal oxides like ZnO or MgO.
Applications of EAM
Mostly in the automotive industry for hoses and seals to
withstand increasingly hot and chemically aggressive engine
environments. Due to its excellent damping characteristics,
better than butyl at high temperatures, AEM is used in
torsional dampers, and in cam cover and oil pan gaskets.
In non-tyre applications, AEM in covers for halogen-free, oilresistant, low smoke cables, and also in roll covers due its
damping properties.
Applications of AEM
Industrial roll covers:
Flooring, low fire hazard
Vamac G
100 phr
Naugard 445
2
Stearic acid
1.5
Octadecyl amine
0.5
Vanfre VAM
1
CaCO3
80
Silica fumed
35
Plasticizer
10
Diak # 1
1.5
DPG
4
Shore A:
80
Vamac DP
Elvax 265
Stearic acid
Octadecyl amine
Vanfre VAM
ATH
Mg (OH)2
Pigmentaion
DCP-50
TAC
75 phr
25
2
0.5
1
200
50
3
10
2.5
93
FLUOROELASTOMERS
• General term for elastomers containing fluorine atoms.
• The high heat stability and fluid resistance is due to:
•
High ratio of fluorine to hydrogen atoms
•
Strength of C-F bonds
•
Absence of unsaturation
• Types of fluoroelastomers:
# fluorocarbon rubbers
(FKM/FPM)
•
#perfluoroelastomers
(FFKM )
•
#fluorosilicone rubbers
(FVMQ)
•
#tetrafluoroethylene-propylene (TFE/P)
fluorine,%
66 - 70
72 -73
< 50
~ 55
90
Viton® FKM
The uniqueness of Viton fluoroelastomers is due to:
- high ratio of fluorine to hydrogen.
Bond energy, kcal/m
- very strong carbon-fluorine bond
C–F
105.4
- absence of unsaturation (double bonds)
C–H
80
C – Cl
78.5
(High bond strength increases the thermal and chemical stability of elastomers)
Heat resistance
Hours of service,
>10,000
> 3,000
> 1,000
> 240
> 48
indefinite at 205 C
at 230 C
at 250 C
at 290 C
at 315 C
93
>10000 h
Kalrez® perfluoroelastomer parts
[Depending on the compound]
>1000 h
>3000 h**
10000
Hours of Service*
>1000 h
1000
>240 h
>48 h
100
10
1
205°C
232°C
260°C
287°C
315°C
325°C
Test Temperatures
* Approximate number of hours at which typical vulcanizate of Viton® will retain 50% of its
original elongation at break. Data based on a standard 66% fluorine type (A family).
** car:180’000 km at 60 km/hour. “normal car lifetime”
94
FKM
Apart from its excellent thermal properties, FKM has very good
resistance to a broad range of fluids - oils, fuels, solvents,
hydrocarbons and chemicals.
FKM has good resistance also to oxygenated fuel mixtures like
gasohol, unlike other fuel resistant rubbers like NBR.
However, FKM can be severely affected by the following :
- Ketones ( e.g MEK used as solvents for uncured FKM)
- Esters , e.g. ethyl acetate
- Amines (cause embrittlement)
- Strong bases, e.g NaOH ( special grades required)
95
Processing of fluorocarbon rubbers (FKM)
Properties: Excellent resistance to heat, oils, fuels and chemicals (except bases). High
specific gravity, tough elastomer.
Curatives: Bis-phenols, diamines, peroxides (grade dependent).
Magnesium oxide, calcium hydroxide, zinc oxide
Post cure required in most cases @ 24hrs/230C
Problems faced: sticking to mill rolls and molds, mold fouling, flow marks, rough
extrusion.
Processing additives: Struktol WS280, Struktol HT 290, DuPont’s VPA 2,
Carnauba wax, PAT 777, (dosage 0.5 to 2.00 phr)
Preventive measures: Mix on cool and clean equipment.
No oils, resins, plasticizers, antioxidants to be added.
Avoid sulfur contamination (use new brush).
Refine compound on tight mill before molding.
Use clean molds with semi-permanent mold release agent,
e.g. Permalease 90.
Post cure to start at below 100C, increasing to 230C
gradually.
Curatives for FKM
Commercially available FKM are bisphenol ,with the curative
already incorporated in the rubber. These require only MgO
and Ca hydroxide to be added for curing, and the filler which
is mostly MT black or inert white fillers.
Peroxide cureable grades are getting more popular for better
chemical and steam resistance and for lower temperature
service.
Diamine cures are getting obsolete, although they improve
bonding with metals and textiles.
FKM applications
O-rings
FKM-BP*
100phr
MgO
3
N990 black
30
Ca(OH)2
6
Processing aid 1
Shaft seals
100 phr
6
30
3
1
Low temp seal
FKM-LT
100 phr
ZnO
3
N990 black 30
DBPH-50
3
TAIC
3
FKM-BP = standard grade with bisphenol cure incorporated.
FKM-LT = low temperature grade containing perfluoromethyl vinyl ether and a
cure-site monomer for peroxide cure
DBPH = dimethyl-di-(tertiary butyl peroxy)-hexane (peroxide curing agent)
TAIC = triallyl iso cyanurate (coagent for peroxide cure)
Processing aid = e.g. carnauba wax, or similar proprietary lubricants.
Properties/Applications of FKM
Due to its excellent heat and fluid resistance, its applications are
many and varied in the following:
Automobile industry – Seals, gaskets and hoses in the fuel and
powertrain systems.
Chemical industry – seals, gaskets, valve linings, flange gaskets,
etc.
Industrial use: -high vacuum seals, expansion joints, rolls for
solvent cleaning machine and high speed tin plating lines,
Oil and gas exploration and drilling, refining and many more.
( explosive decompression resistant, seal extrusion resistant)
FKM special grades
Standard grades of FKM are not resistant to high Ph materials
like strong bases and amines.
Based resistant grades, TFE/P (tetrafluoroethylene/propylene
copolymers ) are required for applications in such instances,
like engine oils and gear oils containing aggressive aminic
additives
Perfluoroelastomers (FFKM) on the other end have resistance to
almost all fluids as they have the highest fluorine content of
around 72-73%. ( Very expensive and used for very special
solvents and chemicals and solvent blends as used in the
paint industry, etc.)
Butyl rubbers
Isobutylene based elastomers include
1. Isobutylene-isoprene copolymers (IIR), and
2. Halogenated derivatives ( CIIR ad BIIR )
The unique characteristics of these rubbers is –
 exceptionally low permeability to air and inert gases
good resistance to heat, ozone and weathering and many
chemicals.
 excellent vibration damping property
Butyl rubbers
Polymers of isobutylene alone cannot be vulcanized, hence a
small amount of isoprene is copolymerized to provide
unsaturation to enable vulcanization with sulfur and
accelerators.
Commercial grades of butyl have isoprene content as follows:
Mole % unsaturation ML 1+8/125C
Supplier
0.8 -1.3
29 - 35
Exxon 065
1.5 – 2.0
46 – 56
Lanxess 101-3
1.3 – 1.7
29 – 35
Exxon 165
1.5 – 2.1
46 – 56
Exxon 268, Lanxess 301
1.5 – 1.9
52 – 62
Exxon 269
2.0 - 2.6
29 – 37
Exxon 364, Lanxess 402
(moles % unsaturation is moles of isoprene per 100 moles of isobutylene)
Vulcanization of IIR
Sulfur cure ; Due to the very low level of unsaturation, butyl
requires fast accelerator systems.,e.g. Sulfur 1.5, TMTD 1.0,
and MBT 0.5 is a general purpose system for innertubes.
Variations with faster accelerators are possible.
Resin cure; methylol phenol formaldehyde resins activated with
halogen containing polymer, lIke CR, is recommended for
curing thick articles, without reversion problem associated
with sulfur cures. This is articularly suitable for tyre curing
bladders and airbags.
Brominated resins can be used too without the need for CR.
Applications of IIR
Mainly automotive tubes
Butyl 268
85 phr
EPDM *
15
N660 black
70
Paraffinic oil
25
ZnO
5
Stearic acid
1
TMTD
MBT
Sulfur
1
0.5
1.5
and
tyre curing bladders
Butyl 268
Neoprene W
N 300 black
Process oil
ZnO
Reactive PF resin
* Low diene ENB grade, e.g.Nordel IP 3640
100phr
5
50
5
5
10
Halogenated butyl
Normal butyl rubbers have a drawback that they cannot covulcanize or stick to other rubbers due to its limited cure
activity. This creates problems in the mixing room in case
butyl gets contaminated with other rubbers or vice versa.
The introduction of a halogen, chlorine or bromine, in the
molecule improves the crosslinking activity and provides the
ability to co-vulcanize with other unsaturated rubbers like NR,
SBR, etc.
Both, CIIR and BIIR can be vulcanized with ZnO.
BIIR can also be vulcanized by peroxides, whereas IIR and CIIR
cannot be cured by peroxides.
Halogenated butyl
Butyl rubbers have the same positive attributes as normal butyl
rubber, and additionally have the advantage of more versatile
curing systems, better heat resistance and ability to
covulcanize with diene rubbers.
The main applications of Halo-IIRs are :
1. Tire innerliners for tubeless tires.
2. Tire inner tubes.
3. Pharmaceutical stoppers
4. Heat resistant conveyor belting
5. Tank lining, hoses, sealants, etc.
Grades of HIIR
Grade
Exxon 1066
Exxon 1068
Lanxess 1240
Exxon 2211
Exxon 2222
Exxon 2235
Exxon2244
Exxon 2255
Lanxess X2
Lanxess
Lanxess 2040
Chlorobutyl, % Cl
1.2 - 1.3
1.2 – 1.3
1.2 – 1.3
Bromobutyl, %Br
1.9 – 2.3
1.8 – 2.2
1.8. - 2.2
1.9.-.2.3
1.8 – 2.2
1.6 – 2.0
1.6 – 2.0
1.6 – 2.0
ML1+8/125C
33 – 43
45 – 55
34 – 42
27 – 37
27 – 37
34 - 44
41 – 51
41 – 51
42 – 50
28 – 36
35 - 43
Applications of halobutyls
Innerliner compounds
BIIR 2255
100 phr
N660 black
50
Paraffinic oil
8
Stearic acid
2
MgO
0.5
Struktol 40MS
5
ZnO
3
Sulfur
0.5
MBTS
1.5
CIIR
NR
N660 black
P F resin
MgO
Struktol 40MS
Naphthenic oil
Stearic acid
ZnO
Sulfur
MBTS
100
60
4
0.15
7
8
2
3
0.5
1,5
80
20
55
8
0.1
10
2
3
0.5
1,5
Applications of HIIR
Zinz, sulfur free
BIIR 2211
Calcined clay
Talc
Process aid
DPTH
MgO
PHARMA STOPPER,
Normal
100
CIIR
100
60
Calcined clay
90
40
PE wax
5
0.5
Stearic acid
1
2
ZnO
3
1
PF resin (SP1045)
2
MgO
0.25
The ultimate search
The ideal rubber vulcanizate should have the following :
-
High mechanical strength (like PU)
High service temperature, resistant to oxidative degradation.
(like FKM or VMQ))
Good low temp properties (like PVMQ)
Good ozone and weathering resistance (like EPM or VMQ)
Good oil and fluid resistance (like FKM or HNBR, or EPDM in case of polar
fluids)
Good impermeability to gases and fuel vapours (like FKM, ECO)
And all these at a reasonable cost !
Unfortunately, the ideal rubber does not exist, but efforts continue to modify
existing polymers and compounds towards higher performance limits..
General guidelines for processing
• Everybody in the company should be involved in following good
manufacturing practices. Good house keeping most important for a clean
and healthy work environment !
• Make sure to use the right type and grade of rubber and other
compounding ingredients.
• Follow proper storage system (see next slide)
• Operators should be instructed to start work with clean machines and
surroundings.
• Always start with a clean and cool mill/mixer; keep heat history to a
minimum.
• Reworking of process scrap to be controlled at a reasonable and uniform
rate.
• Follow manufacturers’ instructions and guidelines. Avoid short cuts.
Storage of rubbers
A few points regarding proper storage of special raw rubbers:
- Store under cool conditions & closed containers.
- Protect from direct sunlight and UV rays.
- Keep wrapped in plastic sheets.
- Follow ‘first-in-first-out’ system for use.
- Use well before shelf life expiry (specially CR, Silicone
rubbers). Revalidate if shelf life has expired.
- Store away from chemicals.
Special rubbers
Ref : The information contained in this presentation is given in good faith but
without warranty. It is mainly based on printed information from various
companies and texts and believed to be true. It is strongly recommended
that trials be made at customers’ laboratories and plants before adapting
the same.
THANK YOU