Technical Report 74
Rhenogran ® P91 and Rhenogran ® AFP –
predispersed, polymer bound aramid
short fiber pulp
Harald Kleinknecht, Rubber Sales Western Europe, Rhein Chemie Rheinau GmbH,
Mannheim
[ Contact: [email protected]]
Key words: automotive, hoses, belts, profiles, seals, molded parts, EPDM, HNBR,
Rhenogran® AFP 40/EPDM, Rhenogran® P91-40 /EPDM, fiber, fibre, reinforcement,
pulp, aramid, Twaron®
Summary
Rhenogran® AFP-40/EPDM (GE 1909)
and Rhenogran® P91-40/EPDM are two
products from a series of predispersed,
polymer-bound aramid short fiber pulp
master batches. They are suitable for use
in many high-quality technical rubber
goods, usually on the basis of EPDM
and HNBR. Rubber products made from
such compounds are usually used in the
automobile and mechanical engineering
industries. Particularly where high standards have to be met in terms of quality,
physical properties as well as the resistance of the parts to temperature and
aggressive media, Rhenogran® P91 and
Rhenogran® AFP are the materials of
choice.
Source: Gates
Page 2
■ Rhenogran® AFP-40/EPDM and Rhenogran® P91-40/EPDM are used as
highly reinforcing additives.
Technical report 74
■
■
■
■
Depending on the orientation of the fiber
bundles, aramid fiber pulp in elastomer
components produces an unusual high
level of reinforcement, in particular at low
Good mixing and dispersing properties,
easy metering as well as integration and elongation. The steel elasticity of aramid
orientation of the fiber pulp in the rubber fibers leads to enormous modulus increase even when only few phr are used.
mixture are decisive for the end quality
While the reinforcement effect of filling
of the rubber products.
materials is only felt at high elongation
EPDM and HNBR mixtures reinforced
levels, and a higher degree of cross-linkwith aramid fiber pulp are used in many
ing only contributes towards a modulus
different applications, for example in
increase at medium elongation levels, the
belts, hoses, seals and molded parts.
use of aramid pulp in the field of low elonGood long-term temperature stability
gation creates a new field of application
(>150°C), dynamic load capacity and
for designing materials with extremely
good resistance to media, in particular
high strength. The uniaxial orientation of
to oil (HNBR products) are made possible.
the fibers and the associated strength
Rhenogran® AFP is manufactured by a
anisotropy are ideal for the use of applicanew process to achieve ultimate distions in which high loads occur with medipersability.
um or low elongation in one direction. In
particular, these are power transmission
belts, pressure hoses or special tires
(motor cycle, off-road vehicle).
Source: Voith
Page 3
Technical report 74
1.
Aramid fibers – characterization
The raw fiber material is polymerized from
two components (P-phenylene diamine and
terephthalyl dichlorine) and is then spun as an
endless fiber from a sulfuric acid solution.
Fig. 1 shows the composition and the various
forms of aramid fibers.
Fig. 1: Aramid fibers - chemical structure and manifestations
Chemical structure of aramid fibers:
para-aramid (poly-p-phenylene terephthal
amide)
Microscopic structure of aramid fibers:
Diameter approx. 10 µm
Length: endless filament
From these high-quality endless fibers, the short fibers are obtained by cutting
them to the required length (chopped or staple fibers).
Aramid staple fibers
Fiber pulp is then produced from these short fibers by means of special
mechanical processing.
Microscopic structure of aramid fiber pulp:
Length approx. 1-2 mm
Diameter: core/fibrils 10 µm/100µm
Specific surface: approx. 14 m2/g
Visual appearance of fiber pulp:
felted fluffs, yellowish mass
Source: Teijin Aramid (4)
Page 4
These fibers have outstanding technological
properties:
Technical report 74
■ extremely high mechanical strength
(approx. 80 MPa)
■ low expansion
■ very good resistance to chemicals
■ very high resistance to high temperatures
(approx. 500°C)
■ no shrinking
■ high dimensional stability
■ no brittleness
2.
The processing of the smooth short fibers to
form highly fibrillated pulp does not change
the above-mentioned properties of the material. In fact, this fibrillation leads to outstanding
mechanical anchoring of the pulp fibers in the
polymer network and gives strength without
the use of adhesion promoters.
A precondition for this is, however, good dispersion of the pulp in the rubber compound.
This is achieved by the use of specially processed Rhenogran® AFP and Rhenogran® P91
short fiber pulp master batches.
Range of Rhenogran® aramid pulp products
Tab. 1: An overview of the Rhenogran® aramid short fiber pulp types
Pulp
%
Binding
system
Appearance
40
EPDM
light yellow chips
Rhenogran P91-40/NR
40
NR
yellowish granules
Rhenogran® P91-40/CR
40
CR
yellowish granules
40
NBR
yellowish granules
Rhenogran® AFP-40/EPDM (GE 1909)
40
EPDM
light yellow chips
Rhenogran® AFP-40/NR (GE 1910)
40
NR
light yellow granules
Product
Rhenogran® P91-40/EPDM
®
®
Rhenogran P91-40/NBR
Development products
Special types e.g. EVA, TPO, HNBR on request.
Product
examples:
Rhenogran® P91-40/EPDM:
light yellow chips, approx. 30x10x5 mm
To make use of the outstanding properties of
the aramid short fibers, in particular the pulp
fibers, for improvement of the technical efficiency of rubber compounds as well, it is nec-
Rhenogran® AFP-40/EPDM:
light yellow chips, approx. 2-6 mm long
essary to process these highly fibrillated fibers
by complete separation to distribute individual
fibers in the compound. This is only possible
when predispersing the fine bundles of fibers.
Page 5
Technical report 74
3.
Typical applications
The products from the Rhenogran® AFP
and the Rhenogran® P91 series are suitable for
use in mixtures of the common polymer types
such as for example NR, IR, BR, SBR, EPDM,
CR, NBR, HNBR. Rubber mixtures can be optimized for specific applications by adding
Rhenogran® AFP or Rhenogran® P91. Similar
improvements can be found in all types of rubber mixtures. An important factor here is the
anisotropic orientation of the fibers, that is, orientation in the direction of flow. In the direction
of flow, the improvement in the properties is
normally significantly more pronounced than at
right angles to the direction of flow. For individual properties such as wear behavior, it may
make sense to align the fibers perpendicular to
the stress level.
Tab. 2: Applications and improvements in properties
Component
Significant property improvement
V-belts, toothed
belts, power transmission belts,
conveyor belts
service life
wear, reduced running noise
increased load, breaking strength
hoses
properties under high thermal load, rigidity,
dimensional stability, pressure stability
seals,
bushings
properties under high thermal load, creep,
shrinking, replacement for fabric reinforcement
membranes
puncture strength, stiffness
cables
modulus, cut resistance, dimensional stability
profiles
green strength, dimensional stability
rubber padding for
tracked vehicles,
dock fenders,
bearings
cut resistance,
wear resistance
shoe soles
wear resistance
tires
green strength, wear resistance, cut resistance,
chip and chunk resistance, tire stability (emergency
running properties), cross-dimensional stability,
apex and beadfiller reinforcement
rollers,
roller coverings
stability under load, apex resilience,
cut resistance, modulus increase
Example recipes with test results
In the test compounds, 10 and 20 phr
Rhenogran AFP-40/EPDM and Rhenogran®
P91-40/EPDM respectively were used. In the
compounds with Rhenogran®, the content of
carbon black was reduced by 10 phr and 20
phr respectively compared with control 01 with
150 phr carbon black N 550, in order to achieve
an approximately comparable hardness level.
Tab. 3: EPDM mixture approx. 70 Sh A with 10 phr and 20 phr Rhenogran® AFP aramid fiber batches
2
1
Control 01 Control 02
4
AFP, 10
1
P91, 20
2
AFP, 20
EPDM
100
100
100
100
100
100
CB N-550
carbon black
150
140
140
140
130
130
Paraffinic oil
plasticizer
70
70
70
70
70
70
activator
3
3
3
3
3
3
dispersing aid
1
1
1
1
1
1
antioxidant
1
1
1
1
1
1
antioxidant
4
4
4
4
4
4
peroxide
5
5
5
5
6
6
Rhenogran P91-40/EPDM
aramid pulp
0
0
10
0
20
0
Rhenogran® AFP-40/EPDM
aramid pulp
0
0
0
10
0
20
®
Rhenofit TAC/S
®
Aflux 42
TMQ
®
Rhenogran ZMMBI-50
®
Poly-Dispersion VC-60P
®
Rhenogran®, the peroxide Poly-Dispersion®
VC-60P was increased from 5 phr to 6 phr in
order to compensate for the higher content of
polymer binder.
In the control compounds 01 and 02, the additional polymer content of the mixtures with
added Rhenogran® AFP-40/EPDM was not
compensated. In the compounds with 20 phr
4.1
3
P91,10
BunaTM EP G 8450
Mooney, scorch and rheometer measurements
Fig. 2: Viscosity, Mooney ML 1+4/100°C
ME
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Technical report 74
4.
140
Control 01
120
Control 02
100
P91-40/EPDM,
10 phr
80
AFP-40/EPDM,
10 phr
60
P91-40/EPDM,
20 phr
40
AFP-40/EPDM,
20 phr
20
0
0
1
2
3
4
5
6
min.
With higher carbon black content, the mixtures
show correspondingly higher viscosity levels.
A higher fiber content, by contrast, does not
lead to an increase in viscosity.
ME
120
Control 01
Control 02
100
P91-40/EPDM,
10 phr
80
AFP-40/EPDM,
10 phr
60
P91-40/EPDM,
20 phr
40
AFP-40/EPDM,
20 phr
20
0
0
5
10
15
20
25
30
35
40
45
min.
No systems show any scorching at 121°C curing temperature.
Fig. 4: Rheometer test
Nm
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Technical report No. 74
Fig. 3: Scorch behavior (121°C)
1,6
Control 01
1,4
Control 02
1,2
P91-40/EPDM,
10 phr
1
AFP-40/EPDM,
10 phr
0,8
P91-40/EPDM,
20 phr
0,6
AFP-40/EPDM,
20 phr
0,4
0,2
0
0
2
4
6
8
10
12
14
16
18
min.
The rheometer curves are similar in terms of
cross-linking speed as well as in terms of
torque maximum. With an increased carbon
black content as well as a higher content of
Rhenogran® AFP-40, however, the torque maximum achieves a higher level than control
compound 02 (10 phr carbon black).
Physical properties
Hardness
An increase of carbon black content of 10 phr
(control 02 versus control 01) results in an increase in hardness of 3 ShA units. The addition
of 10 and 20 phr Rhenogran® AFP-40/EPDM
and Rhenogran® P91-40/EPDM respectively
leads to an increase in hardness of
approximately 7 to 9 ShA units, independent
from fiber load.
Basically the same picture arises after aging
(14 days/125°C). Aramid short fiber pulp thus
has a considerable reinforcing effect even at
rather low dosage.
ShA
Fig. 5: Hardness ShA, vulcanization (13 min, 180°C)
76
74
72
70
68
66
64
62
60
01
02
P91, 10
AFP, 10
P91, 20
AFP, 20
P91, 20
AFP, 20
Fig. 6: Hardness ShA, after aging (14 d/125°C)
ShA
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Technical report 74
4.2
96
94
92
90
88
86
84
82
80
01
02
P91, 10
AFP, 10
remains widely unchanged (Fig. 8).
This is of major significance for components
with an uniaxial direction of stress (e.g. power
transmission belts). Ideal fiber orientation is
achieved by calendering or extruding the compounds. Laboratory mixes are prepared on an
open mill.
MPa
Fig. 7: Modulus at low elongation levels, longitudinal
5
Modulus 20%
4.5
4
Modulus 50%
3.5
3
Modulus 100%
2.5
2
1.5
1
0.5
0
01
02
P91, 10
AFP, 10
P91, 20
AFP, 20
Fig. 8: Modulus at low elongation levels, transverse
MPa
Page 9
Technical report 74
Modulus
Carbon black leads to a slight modulus increase. Compared with carbon black, short
fiber pulp leads to a significant modulus increase in the direction of the fiber orientation,
and depending on the amounts added (20 phr
Rhenogran® AFP-40/EPDM) can cause the
modulus to increase fourfold (20% elongation)
(Fig. 7). In cross direction (at right angles to
fiber orientation) the level of modulus 100
2.5
Modulus 20%
2
Modulus 50%
1.5
Modulus 100%
1
0.5
0
01
02
P91, 10
AFP, 10
P91, 20
AFP, 20
This effect becomes particularly clear after
aging.
Fig. 9: Tear resistance after vulcanization and after hot air aging
N/mm
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Technical report 74
Tear strength
Tear strength increases when Rhenogran®
aramid short fiber pulp types are used.
50
vulc. 9 min/180°C
longitudinal
45
40
vulc. 9 min/180°C
transversal
35
30
aging
14d/125°C
longitudinal
25
20
15
aging
14d/125°C
transversal
10
5
0
01
02
P91, 10
AFP, 10
P91, 20
AFP, 20
Dynamic performance and flex crack stability
The dynamic lifetime of fiber reinforced elastomers is highly dependent on fiber dispersion.
While evenly dispersed fibers exhibit equivalent
lifetime of comparable carbon black filled compounds. When rating Rhenogran® AFP in com-
parison to Rhenogran® P91 elastomers containing AFP-dispersion showed the best flex
crack stability as a result of further dispersion
improvement.
Visual characterization of the fiber dispersion
The dispersion of the fibers plays a significant
role in the property profile of the material, in
particular with respect to uniaxial reinforcement, as well as in the dynamic service life of
the component. As can be seen from Fig. 10,
when pure aramid pulp is mixed into EPDM
mixtures, large, undispersed agglomerates of
pulp remain, and these can reach a length of
several millimeters in diameter.
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Technical report 74
Fig. 10: Dispersion of the fibers in the compound
AFP-40/EPDM (20 phr) in EPDM compound
(magnification: 10-fold)
Rhenogran® AFP-40/EPDM, homogeneously distributed and fully dispersed
(line of cut parallel to fiber orientation)
AFP-40/EPDM (20 phr) in EPDM mixture
(magnification: 10-fold)
Rhenogran® AFP-40/EPDM, homogeneously distributed and fully dispersed
(line of cut perpendicular to fiber orientation)
Pure short fiber pulp,
(8 phr) in EPDM mixture
(magnification: 10-fold)
undispersed fiber pulp (line of cut parallel to fiber orientation)
Undistributed pulp leads to imperfections,
which in general can lower the level of physical
properties and can lead to premature failure of
the component. From the photos in Fig. 10
it can clearly be seen that correct dispersing is
achieved with conventional mixing methods
when using predispersed aramid short fiber
pulp, parallel as well as perpendicular to the
direction of fiber orientation. Pure pulp fiber result in large undispersed structures that resist
prolonged mixing even at high shear.
Page 12
Technical report 74
5.
Summary
■ Aramid short fiber pulp is characterized by
unusually high strength, under static and
dynamic load. In particular at low elongation, extremely high moduli can be achieved
in the direction of fiber orientation.
■ Aramid short fibre pulp is extremely resistant to thermal load and chemical influences.
■ Aramid short fiber pulp only achieves practical dispersibility when predispersed qualities are used, such as for example
Rhenogran® AFP-40/EPDM or Rhenogran®
P91-40/EPDM.
■ In terms of the level of strength, dynamic resistance and the morphological evaluation of the
quality of distribution, Rhenogran® AFP-40/EPDM
proves to be the best dispersing product quality.
■ For this reason, the types from the Rhenogran®
AFP and Rhenogran® P91 series are used for
modern high-performance materials for belts,
pressurized hoses, special tires and molded
goods for heavy duty applications.
Our technical advice - whether verbal, in writing or by way of trials - is given in good faith but without warranty, and this also applies where proprietary rights of third parties are involved. It does not
release you from the obligation to test the products supplied by us as to their suitability for the intended processes and uses. The application, use and processing of the products are beyond our
control and, therefore, entirely your own responsibility. Should, in spite of this, liability be established for any damage, it will be limited to the value of the goods delivered by us and used by you.
We will, of course, provide products of consistent quality within the scope of our General Conditions of Sale and Delivery.
Aflux®, Rhenofit® and Rhenogran® are registered trademarks of Rhein Chemie Rheinau GmbH,
Germany.
BunaTM is a registered trademark of Lanxess Deutschland AG, Germany.
Poly-Dispersion® is a registered trademark of Rhein Chemie Corporation, USA.
Twaron® is a registered trademark of Teijin Aramid BV, Netherlands.
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Phone: +49 (0)621-8907-0
Fax: +49 (0)621-8907-269
[email protected]
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G 239/pdf/KR/0408
Images by courtesy of Gates Power Transmission Europe BVBA, Belgium, Teijin Aramid BV, The
Netherlands and Voith Paper Holding GmbH & Co. KG, Germany.