Nitrile rubber presentation

1. Nitrile Rubber
NBR

2. General information about
Nitrile Rubber - NBR

3. Brief history
 The first literary reference to nitrile rubbers was found in a French
patent published in 1931, covering the polymerization process of
polybutadiene and acrylonitrile. However, it was not manufactured or
commercialized until 1935. Nitrile elastomers were developed in 1936
in the United States and in 1939 the first nitrile rubber was produced in
that country. Nitriflex began production in Brazil in 1971 of the line of
traditional rubbers with Goodyear technology and in 1996 launched a
new Nitriclean line, with less capacity to dirty the mold and free of
Nitrosamines.

4. Main Characteristics - NBR
 The main characteristic of nitrile elastomers is their great resistance to
oils, solvents and fuels; that is, the ability of a vulcanized artifact to
retain its original physical properties after immersion in fluids.
Through this special characteristic, nitrile elastomers present other
equally important properties:
 Low gas permeability
 Anti-static features
 Abrasion resistance
 Heat resistance
 Water resistance
 Solvent resistance

5. Chemical Composition

6. Molecular Structure

7. What is Nitrile Rubber?
 Nitrile rubber is a copolymer of butadiene and an unsaturated nitrile. In
this work we will limit ourselves to explaining the butadiene-
acrylonitrile copolymer, as this is the product that most manufacturers
use.
 Oil resistance is the most important property of nitrile rubbers and this
is the reason for their extensive use, even at a substantially higher cost
than natural rubber or other general purpose rubbers. Oil resistance is
related to the ability of the vulcanized material to retain its original
physical properties, even if it is in contact with it.

8. What is Nitrile Rubber?
 This property is due to the acrylonitrile monomer, as it is a highly polar
substance and, therefore, incompatible with non-polar liquids such as
aliphatic oils, gasoline, etc. This polarity also explains the electrical
conductivity characteristic of the elastomer.
 Variations that can be introduced into the NBR molecule include:
 Degree of branching,
 Molecular weight,
 Radical ratio (CN)-,
and which account for the final characteristics of the elastomer, can
generate a large number of varieties of Nitrile Rubber

9. Nitrile Rubber Production Process
 The nitrile rubber manufacturing process begins with immersion in
emulsions of butadiene and acrylonitrile monomers, in special reactors
under controlled temperature and pressure conditions, in the presence
of an emulsifying agent and reaction-controlling additives.
 From polymerization, we obtain an emulsion that we call latex and to
which we add antioxidants with the aim of protecting the polymers
during the process of obtaining nitrile rubber, as well as its storage.
This latex is coagulated using coagulating agents, which are generally
alkaline or oxidative agents.

10. Nitrile Rubber Production Process
 The coagulated latex undergoes a washing process in order to remove
residues of auxiliary additives from the reaction, in order to adjust the
pH of the elastomer. It is then washed again and then dried in two
stages:
a) the first stage is carried out mechanically, using extruders, where most
of the water is removed;
b) in the second stage, all the water is eliminated using special dryers.

11. Nitrile Rubber Production Process
 The various types of nitrile rubber are produced through changes in
the process, such as:
 Percentage of monomers
 Percentage of cis and trans structures
 Polymerization temperature
 Types of antioxidants
 Degree of polymerization
 Crosslink Agents
These variables are responsible for the final properties of the polymer.

12. Nitrile Rubber Production Process
 In a simple way we can say that:
 Cold polymerized nitrile rubbers have a more linear polymer chain
and are therefore easier to process in transfer and injection molding.
The polymerization temperature is 5ºC. Hot polymerized nitriles have
a more branched structure, as if they had cross-links in the chain and
are more stable during extrusion. When compared to cold nitrile
rubbers, hot nitrile rubbers have a higher crosslinking speed, greater
resistance to swelling and less permanent deformation.

13. Diagrama de Produção de NBR

14. Main Applications of Nitrile Elastomers
APLICATION NECESSARY
CHARACTERISTICS
Hoses for conveying oils, solvents
and fuels
Resistance to oils and fuels
Abrasion resistance
Hoses for conveying gases Low gas pemeability
Rings, Gaskets and Seals Resistance to oil, heat and abrasion
Coating of cylinders and tanks Resistance to solvents and abrasion
Industrial Soles Resistance to oil and abrasion
Special Adhesives Resistance heat and abrasion
Textile Artifacts Abrasion Resistance
Antistaticity

15. Effect of Acrylonitrile Content
 Nitrile rubbers are classified mainly according to the combined
acrylonitrile content, which varies from 16% to 50%; however, the vast
majority of producers and applications are centered in the 33% ACN
range.
 Low-content nitriles, mainly those with 16 and 28% ACN, are
recommended for applications where resistance to low temperatures is
required - they compete in this application with polychloroprenes,
which have a slight advantage because they have greater tensile
strength and crystallize under tension.

16. Effect of Acrylonitrile Content
 Nitrile rubbers with ultra-high acrylonitrile content (45%) are used in
the manufacture of artifacts that work under extreme conditions of
resistance to oils, temperatures, etc.; those with low content (28%) are
used where moderate resistance to oils and excellent flexibility at low
temperatures are desired. In general, medium content nitrile rubbers
(33%) can meet most specifications.
 As the acrylonitrile content increases, nitrile rubber becomes more
plastic and less compatible with plasticizers.

17. Efeito do Aumento do Conteúdo de
Acrilonitrila
DENSITY INCREASE
PROCESSABILITY INCREASE
CURE RATE INCREASE
OIL RESISTANCE INCREASE
HARDNESS INCREASE
ABRASION RESISTANCE INCREASE
HEAT REISTANCE INCREASE
RUPTURE TENSION INCREASE
COMPATIBILITY WITH POLAR POLYMERS INCREASE
RESILIENCE DECREASE
LOW TEMPERATURE FLEXIBILITY DECREASE
SOLUBILITY IN AROMÁTICS DECREASE
OIL VOLUME CHANGE DECREASE
RESISTANCE TO PERMANENT DEFORMATION BY
COMPRESSION
DECREASE
ELECTRICAL RESISTIVITY DECREASE

18. Effects of Polymerization Temperature
 The first nitrile rubbers were produced using the hot polymerization
system, as the reaction is exothermic. Currently, there are two classes
of nitrile rubbers in relation to polymerization temperature:
Cold polymerization (5oC)
Hot polymerization (50oC)

19. Effects of Polymerization Temperature
 Cold polymerized rubbers are easy to process, presenting linear chains
and having good general physical properties; are the most used in the
artifact industries.
 Hot polymerized rubbers are more difficult to process, having more
nerve as a result of a more branched molecular structure; They are used
where excellent resistance to heavy work or in severe dynamic
situations is required. They also have:
Faster vulcanization
Good adhesiveness
Good resistance to Compression Set

20. General Characteristics of Nitrile Rubbers
RESILIENCE / HYSTERESIS
 The resilience of a vulcanized nitrile rubber product is lower than that
of natural rubbers, styrene-butadiene and chloroprene, but is greater
than that of vulcanized butyl and polyacrylic rubbers; resilience values
of around 40% to 50% are common; in special compositions, these
values can reach 70%.
 Furthermore, to achieve high levels of resilience, requirements such as
soft carbon black, ester-based plasticizers and a high degree of
vulcanization are necessary.
 The hysteresis property of nitrile rubber is poor compared to that of
natural rubber and styrene-butadiene; As a rule, nitrile rubber is not
used where flexural heat development could be a problem; After that,
with decreasing acrylonitrile content, resilience increases.

21. General Characteristics of Nitrile Rubbers
FLEXIBILITY AT LOW TEMPERATUR
 The flexibility of nitrile rubber compounds at low temperatures varies
depending on the acrylonitrile content of the polymer and the type of
plasticizer. There are two basic methods for measuring this property:
- impact test (ASTM D 2137)
- the torsion modulus (ASTM D 1053).
 A compound can be very consistent, resistant to fracture and have
excellent low temperature resistance; on the other hand, the compound
can be quite viscous and difficult to flex.
 In general, nitrile rubber compounds can withstand -57ºC (ASTM D
2137) and -40ºC (ASTM D 1053).

22. General Characteristics of Nitrile Rubbers
VOLUME VARIATION IN OIL
 The oil resistance of nitrile rubber compounds is determined by the
acrylonitrile content of the polymer, the nature of the oil, and the
polarity of the polymer molecule. Nitrile rubbers are highly resistant to
oils and non-polar solvents.
 There are three standard tests to measure the swelling effect of a
compound of commercial oil types with different aniline points: the
lower the aniline point of an oil, the greater the swelling effect.

23. General Characteristics of Nitrile Rubbers
VOLUME VARIATION IN OIL
Test ASTM D 471-75
Condition: 70 hs @ 100oC
ASTM OIL
No 1 No 2 No 3
Aniline Point (ºC) 124 94 70
Volume Chnage (%) +1 +8 +17
 Aniline is a highly polar liquid and strongly swells nitrile rubber. This
is the explanation for the correlation between swelling and aniline
point. Aniline point is the temperature at which oil and aniline are
completely miscible; the lower the temperature, the more the oil
resembles aniline in terms of polarity.

24. General Characteristics of Nitrile Rubbers
PERMANENT DEFORMATION BY COMPRESSION
 Resistance to permanent deformation by compression is a function of
the vulcanization state. A complete vulcanization study can be
achieved by long curing times, high temperatures, or alternative
accelerator systems; results between 8 and 12% were obtained in tests
lasting 70 hours at 100oC.

25. General Characteristics of Nitrile Rubbers
ELECTRICAL RESISTIVITY
 Nitrile rubber does not offer electrical properties, necessary for
primary insulation. On the contrary, compounds with excellent
electrical conductivity can be obtained.
 With a nitrile rubber with a high acrylonitrile content and suitable
additives, a volumetric resistivity of less than 100 Ohm/cm can be
obtained. If insulating properties are required, it is recommended to use
mineral fillers and polymers with greater water resistance.

26. General Characteristics of Nitrile Rubbers
HEAT RESISTANCE
 Nitrile rubber vulcanizates are suitable for use up to 121ºC under
continuous use; Under certain conditions (immersion in oil, absence of
air, etc.) it is possible to retain flexibility after 70 hours at 149ºC, even
if it cannot be considered an indication of service use.
 Nitrile rubbers are practical in terms of resistance to high temperatures
for short periods of time, retaining flexibility after an hour at 204oC or
half an hour at 232oC.
 Maximum retention of properties after aging can be obtained by using
certain mineral fillers such as magnesia or alumina, replacing carbon
black.

27. General Characteristics of Nitrile Rubbers
ABRASION RESISTANCE
 Nitrile rubbers have excellent resistance to abrasion. In the NBS
sandpaper test, values between 100 to 150 can be obtained compared
to the standard index of 100 for natural rubber. In "Peak" abrasion
(knife blade rubbing and cutting the test piece), it produces values
between 50 and 80, compared to 100 for natural rubber.
 Carboxylated nitrile rubbers are extremely resistant to abrasion: we
have reported values up to 2000; Even though a value of this order of
magnitude can be questioned, the fact is that carboxylated nitrile
rubber has excellent resistance to abrasion.

28. General Characteristics of Nitrile Rubbers
GAS IMPERMEABILITY
 Nitrile rubbers offer excellent gas diffusion resistance properties.
Nitrile rubber with 40% ACN has the same impermeability to air,
oxygen and several other gases as butyl rubber-based compounds.
Nitrile rubbers with ultra-high acrylonitrile content also have greater
resistance to gas diffusion; we can obtain values smaller than 1 x 10-4
thousand feet/psi/day.