Rhenogran® P91 and Rhenogran® AFP – predispersed, polymer bound aramid short fiber pulpHarald Kleinknecht, Rubber Sales Western Europe, Rhein Chemie Rheinau GmbH,Mannheim[Contact: harald.kleinknecht@rheinchemie.com]

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 twoproducts from a series of predispersed,polymer-bound aramid short fiber pulpmaster batches. They are suitable for usein many high-quality technical rubbergoods, usually on the basis of EPDMand HNBR. Rubber products made fromsuch compounds are usually used in theautomobile and mechanical engineeringindustries. Particularly where high stan-dards have to be met in terms of quality,physical properties as well as the resist-ance of the parts to temperature and aggressive media, Rhenogran® P91 andRhenogran® AFP are the materials ofchoice.

Technical Report 74

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■ Good long-term temperature stability (>150°C), dynamic load capacity and good resistance to media, in particular to oil (HNBR products) are made possible.

■ Rhenogran® AFP is manufactured by a new process to achieve ultimate dis-persability.

■ Rhenogran® AFP-40/EPDM and Rhe-nogran® P91-40/EPDM are used as highly reinforcing additives.

■ Good mixing and dispersing properties, easy metering as well as integration andorientation of the fiber pulp in the rubbermixture are decisive for the end quality of the rubber products.

■ EPDM and HNBR mixtures reinforced with aramid fiber pulp are used in many different applications, for example in belts, hoses, seals and molded parts.

Depending on the orientation of the fiberbundles, aramid fiber pulp in elastomercomponents produces an unusual highlevel of reinforcement, in particular at lowelongation. The steel elasticity of aramidfibers leads to enormous modulus in-crease even when only few phr are used.While the reinforcement effect of fillingmaterials is only felt at high elongationlevels, and a higher degree of cross-link-ing only contributes towards a modulusincrease at medium elongation levels, theuse of aramid pulp in the field of low elon-gation creates a new field of applicationfor designing materials with extremelyhigh strength. The uniaxial orientation ofthe fibers and the associated strengthanisotropy are ideal for the use of applica-tions in which high loads occur with medi-um or low elongation in one direction. Inparticular, these are power transmissionbelts, pressure hoses or special tires(motor cycle, off-road vehicle).

Source: Voith

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The raw fiber material is polymerized fromtwo components (P-phenylene diamine andterephthalyl dichlorine) and is then spun as an

endless fiber from a sulfuric acid solution. Fig. 1 shows the composition and the variousforms of aramid fibers.

Aramid fibers – characterization1.

Chemical structure of aramid fibers:para-aramid (poly-p-phenylene terephthal amide)

Microscopic structure of aramid fibers:Diameter approx. 10 µmLength: endless filament

Microscopic structure of aramid fiber pulp:Length approx. 1-2 mm Diameter: core/fibrils 10 µm/100µmSpecific surface: approx. 14 m2/g

Visual appearance of fiber pulp:felted fluffs, yellowish mass

Aramid staple fibers

Fig. 1: Aramid fibers - chemical structure and manifestations

From these high-quality endless fibers, the short fibers are obtained by cutting them to the required length (chopped or staple fibers).

Fiber pulp is then produced from these short fibers by means of special mechanical processing.

Source: Teijin Aramid (4)

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Range of Rhenogran® aramid pulp products2.

■ 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

The processing of the smooth short fibers toform highly fibrillated pulp does not changethe above-mentioned properties of the materi-al. In fact, this fibrillation leads to outstandingmechanical anchoring of the pulp fibers in thepolymer network and gives strength withoutthe use of adhesion promoters. A precondition for this is, however, good dis-persion of the pulp in the rubber compound.This is achieved by the use of specially pro-cessed Rhenogran® AFP and Rhenogran® P91short fiber pulp master batches.

To make use of the outstanding properties ofthe aramid short fibers, in particular the pulpfibers, for improvement of the technical effi-ciency of rubber compounds as well, it is nec-

essary to process these highly fibrillated fibersby complete separation to distribute individualfibers in the compound. This is only possiblewhen predispersing the fine bundles of fibers.

These fibers have outstanding technologicalproperties:

Pulp%

Product

Tab. 1: An overview of the Rhenogran® aramid short fiber pulp types

Bindingsystem

Appearance

Rhenogran® P91-40/EPDM

Rhenogran® P91-40/NR

Rhenogran® P91-40/CR

Rhenogran® P91-40/NBR

40

40

40

40

EPDM

NR

CR

NBR

light yellow chips

yellowish granules

yellowish granules

yellowish granules

40

40

EPDM

NR

light yellow chips

light yellow granules

Development products

Rhenogran® AFP-40/EPDM (GE 1909)

Rhenogran® AFP-40/NR (GE 1910)

Special types e.g. EVA, TPO, HNBR on request.

Productexamples:

Rhenogran® AFP-40/EPDM:light yellow chips, approx. 2-6 mm long

Rhenogran® P91-40/EPDM:light yellow chips, approx. 30x10x5 mm

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The products from the Rhenogran® AFP and the Rhenogran® P91 series are suitable foruse in mixtures of the common polymer typessuch as for example NR, IR, BR, SBR, EPDM,CR, NBR, HNBR. Rubber mixtures can be opti-mized for specific applications by addingRhenogran® AFP or Rhenogran® P91. Similarimprovements can be found in all types of rub-ber mixtures. An important factor here is the

anisotropic orientation of the fibers, that is, ori-entation in the direction of flow. In the directionof flow, the improvement in the properties isnormally significantly more pronounced than atright angles to the direction of flow. For individ-ual properties such as wear behavior, it maymake sense to align the fibers perpendicular tothe stress level.

Typical applications3.

Significant property improvement Component

Tab. 2: Applications and improvements in properties

V-belts, toothed belts, power trans-mission belts, conveyor belts

service lifewear, reduced running noiseincreased 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 (emergencyrunning properties), cross-dimensional stability, apex and beadfiller reinforcement

rollers, roller coverings

stability under load, apex resilience, cut resistance, modulus increase

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In the test compounds, 10 and 20 phrRhenogran AFP-40/EPDM and Rhenogran®

P91-40/EPDM respectively were used. In thecompounds with Rhenogran®, the content of

carbon black was reduced by 10 phr and 20phr respectively compared with control 01 with150 phr carbon black N 550, in order to achievean approximately comparable hardness level.

Example recipes with test results4.

Tab. 3: EPDM mixture approx. 70 Sh A with 10 phr and 20 phr Rhenogran® AFP aramid fiber batches

1Control 01

100

150

70

3

1

1

4

5

0

0

EPDM

carbon black

plasticizer

activator

dispersing aid

antioxidant

antioxidant

peroxide

aramid pulp

aramid pulp

BunaTM EP G 8450

CB N-550

Paraffinic oil

Rhenofit® TAC/S

Aflux® 42

TMQ

Rhenogran® ZMMBI-50

Poly-Dispersion® VC-60P

Rhenogran® P91-40/EPDM

Rhenogran® AFP-40/EPDM

2Control 02

100

140

70

3

1

1

4

5

0

0

3P91,10

100

140

70

3

1

1

4

5

10

0

4AFP, 10

100

140

70

3

1

1

4

5

0

10

1P91, 20

100

130

70

3

1

1

4

6

20

0

2AFP, 20

100

130

70

3

1

1

4

6

0

20

In the control compounds 01 and 02, the addi-tional polymer content of the mixtures withadded Rhenogran® AFP-40/EPDM was notcompensated. In the compounds with 20 phr

Rhenogran®, the peroxide Poly-Dispersion®

VC-60P was increased from 5 phr to 6 phr inorder to compensate for the higher content ofpolymer binder.

With higher carbon black content, the mixturesshow correspondingly higher viscosity levels.

A higher fiber content, by contrast, does notlead to an increase in viscosity.

Mooney, scorch and rheometer measurements4.1

140

120

100

80

60

40

20

00 6

min.

ME

Fig. 2: Viscosity, Mooney ML 1+4/100°C

Control 01

Control 02

P91-40/EPDM,10 phr

AFP-40/EPDM,10 phr

P91-40/EPDM,20 phr

AFP-40/EPDM,20 phr

1 2 53 4

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120

100

80

60

40

20

00 45

min.

ME

Fig. 3: Scorch behavior (121°C)

Control 01

Control 02

P91-40/EPDM,10 phr

AFP-40/EPDM,10 phr

P91-40/EPDM, 20 phr

AFP-40/EPDM,20 phr

5 10 15 20 25 30 35 40

No systems show any scorching at 121°C curing temperature.

1,6

1,4

1,2

1

0,8

0,6

0,4

0,2

00 18

min.

Nm

Fig. 4: Rheometer test

Control 01

Control 02

2 4 6 8 10 12 14 16

P91-40/EPDM,10 phr

AFP-40/EPDM,10 phr

P91-40/EPDM, 20 phr

AFP-40/EPDM,20 phr

The rheometer curves are similar in terms ofcross-linking speed as well as in terms oftorque maximum. With an increased carbonblack content as well as a higher content of

Rhenogran® AFP-40, however, the torque max-imum achieves a higher level than controlcompound 02 (10 phr carbon black).

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HardnessAn increase of carbon black content of 10 phr(control 02 versus control 01) results in an in-crease in hardness of 3 ShA units. The additionof 10 and 20 phr Rhenogran® AFP-40/EPDMand Rhenogran® P91-40/EPDM respectivelyleads to an increase in hardness of

approximately 7 to 9 ShA units, independentfrom fiber load. Basically the same picture arises after aging(14 days/125°C). Aramid short fiber pulp thushas a considerable reinforcing effect even atrather low dosage.

Physical properties4.2

76

74

72

70

68

66

64

62

6001 02 P91, 10 P91, 20AFP, 10 AFP, 20

ShA

Fig. 5: Hardness ShA, vulcanization (13 min, 180°C)

96

94

92

90

88

86

84

82

8001 02 P91, 10 P91, 20AFP, 10 AFP, 20

ShA

Fig. 6: Hardness ShA, after aging (14 d/125°C)

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9 ModulusCarbon black leads to a slight modulus in-crease. Compared with carbon black, shortfiber pulp leads to a significant modulus in-crease in the direction of the fiber orientation,and depending on the amounts added (20 phrRhenogran® AFP-40/EPDM) can cause themodulus to increase fourfold (20% elongation)(Fig. 7). In cross direction (at right angles tofiber orientation) the level of modulus 100

remains widely unchanged (Fig. 8).This is of major significance for componentswith an uniaxial direction of stress (e.g. powertransmission belts). Ideal fiber orientation isachieved by calendering or extruding the com-pounds. Laboratory mixes are prepared on anopen mill.

5

4.5

4

3.5

3

2.5

2

1.5

1

0.5

001 02 P91, 10 AFP, 10 P91, 20 AFP, 20

MP

a

Fig. 7: Modulus at low elongation levels, longitudinal

Modulus 20%

Modulus 50%

Modulus 100%

2.5

2

1.5

1

0.5

001 02 P91, 10 AFP, 10 P91, 20 AFP, 20

MP

a

Fig. 8: Modulus at low elongation levels, transverse

Modulus 20%

Modulus 50%

Modulus 100%

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10 Tear strengthTear strength increases when Rhenogran®

aramid short fiber pulp types are used. This effect becomes particularly clear afteraging.

Dynamic performance and flex crack stabilityThe dynamic lifetime of fiber reinforced elas-tomers is highly dependent on fiber dispersion.While evenly dispersed fibers exhibit equivalentlifetime of comparable carbon black filled com-pounds. When rating Rhenogran® AFP in com-

parison to Rhenogran® P91 elastomers con-taining AFP-dispersion showed the best flexcrack stability as a result of further dispersionimprovement.

Visual characterization of the fiber dispersionThe dispersion of the fibers plays a significantrole in the property profile of the material, inparticular with respect to uniaxial reinforce-ment, as well as in the dynamic service life ofthe component. As can be seen from Fig. 10,

when pure aramid pulp is mixed into EPDMmixtures, large, undispersed agglomerates ofpulp remain, and these can reach a length ofseveral millimeters in diameter.

50

45

40

35

30

25

20

15

10

5

001 02 P91, 10 AFP, 10 P91, 20 AFP, 20

N/m

m

Fig. 9: Tear resistance after vulcanization and after hot air aging

vulc. 9 min/180°C longitudinal

vulc. 9 min/180°Ctransversal

aging 14d/125°Clongitudinal

aging 14d/125°Ctransversal

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11 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 physicalproperties and can lead to premature failure ofthe component. From the photos in Fig. 10 it can clearly be seen that correct dispersing isachieved with conventional mixing methods

when using predispersed aramid short fiberpulp, parallel as well as perpendicular to thedirection of fiber orientation. Pure pulp fiber re-sult in large undispersed structures that resistprolonged mixing even at high shear.

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12 Summary5.

■ Aramid short fiber pulp is characterized by unusually high strength, under static and dynamic load. In particular at low elonga-tion, extremely high moduli can be achievedin the direction of fiber orientation.

■ Aramid short fibre pulp is extremely resist-ant to thermal load and chemical influ-ences.

■ Aramid short fiber pulp only achieves prac-tical dispersibility when predispersed quali-ties are used, such as for example Rhenogran® AFP-40/EPDM or Rhenogran®

P91-40/EPDM.

■ In terms of the level of strength, dynamic resist-ance and the morphological evaluation of the quality of distribution, Rhenogran® AFP-40/EPDMproves 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 with-out warranty, and this also applies where proprietary rights of third parties are involved. It does notrelease you from the obligation to test the products supplied by us as to their suitability for the in-tended processes and uses. The application, use and processing of the products are beyond ourcontrol and, therefore, entirely your own responsibility. Should, in spite of this, liability be estab-lished 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 Condi-tions 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.

Images by courtesy of Gates Power Transmission Europe BVBA, Belgium, Teijin Aramid BV, TheNetherlands and Voith Paper Holding GmbH & Co. KG, Germany.

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