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9/26/2016
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“Rubber Process Analyzer – RPA.
Bridging the gap between polymer and
compound rheological properties and true
material processing on the shop floor”.
Henri G. Burhinwww.polymer-process-consult.be
TA Rubber testing SeminarGreenville SC, September 2016
Copyright TA Instruments, USA
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Rubber Process Analyser, presentation outline
• Instrument design and history
• Testing scope• Elastomers (pure gum).
• Rubber compounds
• Polymer case studies• AMW, MWD and LCB
• Compound case studies• Mixing
• Extrusion (surface aspect, output and green-strength).
• Thixotropy
• Silica mixing
• Advance curemeter• Cure fundamental parameter and cure simulation
• Sponge compounds.
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Rubber Process Analyser
• History and market position• Development: late 80ies early 90ies
• Commercialization: 1992
• Aim: address rubber processing problems
• Original design: Moving Die Rheometer
• Retain MDR curemeter capability• Isothermal and non isothermal cure
• Monitoring of sponge compound blowing
• Became soon popular at large rubber factories (tire
manufacturers)
• Much less popular at small to medium size companies who
found it:• Far too complex to operate and to understand
• Expensive
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Limitation of Standard Tests (Mooney viscosity)
0,01 0,1 1 10 100
0,01
0,1
1
.
η
shear rate, γ
vis
co
sity
ML1+4
0.0
16.0
32.0
48.0
64.0
80.0
0.0 1.6 3.2 4.8 6.4 8.0
Moo
ne
y-V
isko
sitä
t [M
U]
Zeit [min]
SCARABAEUS GMBH - [email protected] - Tel.:+49 (0) 6403/9034-0
Polymer C1
Polymer C1
Polymer B1
Polymer B1
Polymer A1
Polymer A1
SCARABAEUSMooneyprüfung
Entwicklung
Mooney Viscosity ML1+4:
Shear rate 1.6 s-1 (2 rpm)
But a torque rather than a viscosity.
Conversion factors for MU to
Nm and RPM to true shear
rate in s-1.
1 MU = 0.083 Nm
2 RPM = 1.58 s-1 ( )
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•Standard test•Isotherm •Anisotherm•S‘ and S‘‘ -> TanDelta
• Rheometer• Biconic dies• closed die system• 100cpm /1.67 Hz• 0.5° / 7% strain
one point method
It is important to getmore information to helpthe developer
0.0
1.0
2.0
3.0
4.0
5.0
0.0 2.0 4.1 6.1 8.2 10.2
Ela
stische
r A
nte
il [dN
m]
Zeit [min]
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
2.00
Tan
De
lta
SCARABAEUS GMBH - [email protected] - Tel.:+49 (0) 6403/9034-0
Scarabaeus GmbHMeß- und Produktionstechnik
SIS V50
Amplitude
Frequenz
Abbruchkriterium
2.79%
1.67Hz
Curemeters design and limitations.
Moving Die Rheometer “MDR”Improperly called rheometer
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TA Instruments – RPA, a true rheometer
Zeit
γ
-1 .5
-1
-0 .5
0
0 .5
1
1 .5
0 5 10 15 20 25 30 35 40
ω 1
ω 2
Zeit
γ1
-3
-2
-1
0
1
2
3
0 5 10 15 20 25 30 35 40
γ2Viscosity is measured with various
types of viscometers and rheometers. A
rheometer is used for those fluids which
cannot be defined by a single value of
viscosity and therefore require more
parameters to be set and measured than
is the case for a viscometer
https://en.wikipedia.org/wiki/Rheometer
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Ω,ϕ θ
α
M
R
Zeit
γ
-1.5
-1
-0.5
0
0.5
1
1.5
0 5 10 15 20 25 30 35 40
ω1
ω2
Frequency:
RPA 0.001…50.0 Hz
Step 0.001Hz
RPA Rheometer (Closed boundary DMA)
Open boundary DMA
ARES – ARES G2
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Dynamic testing typical output from frequency sweep
In a single test,
frequency sweep
provides several
outputs
• Dynamic viscosity
(η*)
• Dynamic modulus
(G’ and G”)
• Tangent δ
One single test
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Effect of Molecular Weight Distribution (MWD) on compound extrusion behavior
Surface defect as
« shark skin »on
extrusion
Tentative conclusion
Shark skin effect in extrusion is due to
MWD effect and not LCB effect.
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Effect of Molecular Weight Distribution (MWD) on compound extrusion behavior
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1 1 10 100 1000 10000 100000
Tan
ge
nt δδ δδ
(-)
Frequency (Rad/s)
50°(EPDM3)
125°EPDM3)
50°(EPDM1)
125°(EPDM1)
Crossing 1
Crossing 2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
3.5 4.5 5.5 6.5
Log MW (Daltons)
dw
t/d
(lo
gM
)
Production line 1
Production line 2
Maximum extrusion speed for no surface
defect
Production line 1: 25 m/min
Production line 2: 2 m/min
• LCB contend of both polymers was
very similar
• The extrudability problem (shark skin)
was found in the large reduction of
small molecules in the problem
polymer
• Very small molecules act in compound
as excellent processing aid
• The higher tangent δ value at high
frequency for the good processing
polymer confirmed this result.
Ligne 1 Ligne 2
LCB Index 4.39
LCB Index5.47
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Zeit
γ1
-3
-2
-1
0
1
2
3
0 5 10 15 20 25 30 35 40
γ2
Strain:RPA 0.005…360.0 °
Step 0.01°
RPA Rheometer Strain sweepFrom small strain to large strain (SAOS to LAOS)
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Instrument: RPA flex
Company: TA Instruments
Sample A) : Synthetic Butyl
Edbrisic - BK
B) : Synthetic Butyl
Exxon
Film: Dartek - polyamid film
Comparison of Butyl IIR (RPA) Technical information
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Comparison of Butyl (RPA) Test Program
MethodTemperature
[°C]Frequency
[Hz]Strain
[°of arc]
Frequency-Sweep 150 0.05 - 50 0.5
Strain-Sweep 150 0.2 0.5 - 90
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Comparison of Butyl (RPA)
Frequency - Sweep, 150°C, 0.5°of arc, G’, G”
Crossover Point at different Frequencies
=> Different Molecular Weight
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Comparison of Butyl (RPA)
Frequency - Sweep, 150°C, 0.5°of arc, tan δδδδ
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Comparison of Butyl (RPA)
Frequency - Sweep, 150°C, 0.5°of arc, ηηηη” (Log-Scale)
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Comparison of Butyl (RPA)
Frequency - Sweep, 150°C, 0.5°of arc, ηηηη” (Lin-Scale)
15.4%
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Comparison of Butyl (RPA)
Strain - Sweep, 150°C, 0.1 Hz, G’, Tan δδδδ
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Comparison of Butyl (RPA)
Strain - Sweep, 150°C, 0.1 Hz, Long Chain Branching
Different Branching Index
LCB index typical repeatability
95% confidence
±0.09
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Rubber compound process troubleshooting
Rubber compound extrusion.
Serious processing problem in production
Summary of observations:
• All batches passed standard QC tests.
• QC test involves rheometer only (MDR).
• One batch gave higher extrusion head pressure and temperature,
higher swell and surface defect (“Orange skin”) suggesting possible
scorch in the extruder.
• The faulty batch was compared to a trouble free batch.
Good
Bad
160° C
GoodBad
Both compounds have identical or almost identical ML and
MH.
The faulty compound exhibits a lower cure rate (?)
The faulty compound exhibits a significantly LONGER
scorch time (??????)
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Rubber compound process troubleshooting
Good
Bad
Non isothermal cure test (80° C – 180° C)
Some differences in
the uncured state
Non isothermal cure test confirms
identical ML and MH and longer
cure time for the faulty batch
Some differences are observed on
G’ and Tangent δ before cure
suggesting that viscoelastic
properties of uncured compounds
being different.
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Rubber compound process troubleshooting
Good
Bad
RPA testing “Payne” diagram – 100° C
Bad compound shows higher
modulus at both low and high
strain.
This suggest that filler
dispersion is not the cause of
the problem.
The problem therefore stays
in either polymer quality of
filler content.
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Rubber compound process troubleshooting
Frequency sweep at 100° C Strain sweep at 100° C
Bad and good batches show almost
identical viscoelastic properties in both
frequency and strain sweep.
Only some significant difference is
observed at very low shear rate
(frequency) on Tangent δ.
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Rubber compound process troubleshooting
W disp.
(J)
Good 168.94
Bad 177.11
ISO Standard method 4664-1
Where ε is the ellipse area or the energy lost per
oscillation
γ0 is the maximum strain
σ0 is the maximum stressε = π.γ0.σ0.sin δ
The bad compound has
been found to dissipate
almost 10% higher energy
per cycle in non-linear
conditions.
Premature scorch for this
compound is produced by
large heat generation in the
extruder.
LAOS test 100° C, 90° arc, 0.2 Hz
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Practical example, linear and branched Polymer
Keltan 6950 Nordel 5565
Mooney ML 1+4 [MU] 65 65
Ethylen [%] 48 50
ENB content [%] 9 7.5
Distribution medium medium
Degree of branching Branched Linear
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Practical example, linear and branched Polymer
Frequency Sweep
Shear - thinning
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Practical example, linear and branched Polymer
Frequency Sweep
Mooney
Low
Frequency
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Physical description of Polymers
Strain Sweep - LAOS
High Strain
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Physical description of Polymers
Strain Sweep - LAOS
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Recipe of Compounds
Keltancompound
Nordelcompound
phr phr
EPDM (LCB) 100
EPDM, linear 100
Fast Extrusion Furnace (FEF) carbon black 95 95
Chalk 50 50
Paraffinic Oil 65 65
ZnO 6 6
Stearic acid 1 1
Drying agent 9 9
Antiaging agent 0,5 0,5
Sulfur and accelerator 4,5 4,5
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Physical description of filled PolymersStrain Sweep - PAYNE
A.
R.
Pa
yn
e,
Ru
bb
er
Pla
st.
Ag
e 4
2,
96
3 (
19
61
)
Pic. 2.2.: schematic representation of the composition of the dynamic modulus
of various proportions by Payne [16]
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0.1 1 10 100 1000
Strain (%)
0
100
200
300
400
500
G* (kPa)
10 phr
20 phr
40 phr
60 phr
Variation of G* of
reinforced rubber
compound in the strain
domain
Henri Buhrin, "Visco-elasticity Properties of Polymers and Compounds. From Linear to Non Linear Visco-elasticity, Benefit and Potential”
Payne diagram, increasing filler content
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0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
0.01 0.1 1
Sch
ub
mo
du
l G
* [k
Pa
]
Amplitude [Grad]
SCARABAEUS GMBH - [email protected] - Tel.:+49 (0) 6403/9034-0
10357
10359
10361
10363
10365
Scarabaeus GmbHMeß- und Produktionstechnik
SIS-V50
Prüftemperatur 100 °C
Delay time before start test
0.5, 1.0, 2.0, 4.0, 8.0 min
Delay time before start test
0.5, 1.0, 2.0, 4.0, 8.0 min
Compound, Reinforcing fillers
RPA Rheometer
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Uncured compound thixotropy in
DMA measurements.
0
200
400
600
800
1000
1200
1400
1600
1800
0.01 0.1 1 10 100
G'
(kP
a)
Strain (%)
Compound property
change after instrument
CLOSURE!
Non stationary conditions
Instrument closure
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Uncured compound thixotropy in DMA measurements.
What is thixotropy ? – Viscosity time dependence
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Heinrich, dN/dt=kN2 ,1995
xx:yy
0.0
100.0
200.0
300.0
400.0
500.0
600.0
700.0
800.0
0 .0 6.0 12 .0 18.0 24.0 30 .0
Sch
ub
mo
du
l G
' [kP
a]
Zeit [m in]
SCARABAEUS GMBH - info@scarabaeus -gmbh.de - Tel.:+49 (0) 6403/9034-0
0.05° 5744
0.05° 5747
Scarabaeus GmbHMeß- und Produktionstechnik
SIS V50
Compound, Reinforcing fillers
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Physical description of filled PolymersStrain Sweep - PAYNE
Tensile Strength [Mpa]
Keltan cmp. 9.25
Nordel cmp. 8.32
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Kinetic description of filled Polymers
Vulcanisation
Keltan compound
Nordelcompound
S' Min [dNm] 1.21 1.4
S' Max [dNm] 20.44 23.17
ENB content [%] 9 7.5
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Physical description of filled Polymers
Frequency Sweep
Shear thinning
15%
5%
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Extrusion – Machine parameters
Extrusion Keltan compound Nordel compound
Temp. extruder [°C]70 70
Pressure die [bar]91.3 102
Current [A]111.5 124
Speed [m/min]10.5 10.5
Temp. Mass [°C]
114 114-125
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Additional use of Payne diagram
Tread compound formulation
Ingredient PHR
Buna VSL 4020-1 103.1
Buna CB 10 25.0
Ultrasil 3370GR 80.0
Silane X50S 12.5
High aromatic oil 5.0
ZnO 2.5
Stearic acid 1.0
6 PPD 2.0
Wax 1.5
Patent Application EP 0501 227, Michelin, R. Rauline, February 25th, 1991
Silica compound
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TESPT (Si69 DEGUSSA)Bifunctional organosilanes
C2H5O
C2H5O
C2H5O
OC2H5
OC2H5
OC2H5
Si-(CH2)3-S-S-S-S-(CH2)3-Si
Oligosulfane Group
Alkoxy Groups
(Varying from 2 to 7 sulphur atoms)
Silica "silanisation"
Mixing from 140°C to 160°C
C2H5O
C2H5O
C2H5O
OC2H5
OC2H5
OC2H5
Si-(CH2)3-S-S-S-S-(CH2)3-Si
-O-Si-O-Si-O-
OH OH
-O-Si-O-Si-O-
OH OH
SILICA
0.01 0.1 1 10 100 1000
Lo
g (G
*)
Strain (%)
G*0
G*∞
Polymer AMW
Hydrodynamic effect (Filler loading)
Occluded rubberBond rubberPolymer/Filler strong interactions
Filler/Filler weak interactions
Van Der Waals Interactions (Carbon
Black)
Hydrogen bonding (Silica) given by
Hydroxi group
Silica silane chemistry
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Time (mins) Addition Temp (°C) Energy (W.h)
0 Add polymers 65 0
½ Add ZnO, ¾ silica, ¾ X50S and stearic
acid
? 20
Add rest of silica, rest X50S, wax, 6PPD and oil
? 550
Sweep ? 700
Dump at 750 W.h ? 750
Remill
0 Add masterbatch 65 0
Dump at 650 W.h ? 650
MASTERBATCH MIXING PROCEDURE
Internal mixer: 3 L Tangential
Masterbatch mixing procedure
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MIXING CYCLE IMPROVEMENT (Payne Diagram)
0.101.00
10.00100.00
1000.00
Strain (% SSA)
10
100
1,000
G' (KPa)
No 1 (65 RPM)
No 2 (55 RPM)
No 3 (45 RPM)
No 4 (65&45 RPM)
100° C, 0.1 HzUncured
Increasing reaction SiO2 > Silane increased silane
degradation
Mixing conditions and Payne diagram
Mixer speed step 1
Mixer speed step 2
Dump tempstep 1
Dump tempstep 2
Total mixing energy
CPD 1 65 65 155 180 4.123
CPD 2 55 55 145 161 4.076
CPD 3 45 45 146 146 4.067
CPD 4 65 45 153 155 4.133
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MS(1+4)100°C
G’@1% strain (kPa)
S’@450% strain (dNm)
CPD 1 68.7 448 27.69
CPD2 65.4 568 23.75
CPD3 68.1 754 19.75
CPD4 60.5 448 19.04
Mooney viscosity versus visco-elasticity
At first, Mooney viscometer was used for QC of silica
compounds
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G' vs. StrainTESPT vs. TESPD (Masterbatch & Remill)
0.101.00
10.00100.00
1000.00
10
100
1,000
10,000
G', KPa
6.00 phr TESPD Optimised mixing (65-45 RPM)
6.25 phr TESPT Optimised mixing (65-45 RPM)
6.00 phr TESPD High speed mixing (65 RPM)
6.25 phr TESPT High speed mixing (65RPM)
Masterbatch
Remil
TESPT versus TESPD
Silica silane reaction can essentially be measured
after mixing second stage
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Silica mixing test conclusion
Careful visco-elasticity measurements on masterbatch can rapidly and
easily:
• Fully characterize Payne diagram
• Payne diagram low strain elastic modulus provides essential
information of silica/silane chemical reaction
• Payne diagram high strain elastic modulus or better elastic
torque provides information on the uncured compound
processability
2 industrial uncured compounds
• Compound 1 can be processed
but won’t provide adequate
cured properties
• Compound 2 will provide
adequate cured properties but
cannot be processed.
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Physical description of filled PolymersStrain Sweep – Injection molding compounds
Highly variable mixing
Large difference in
Carbon Black
dispersion.
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Physical description of filled PolymersStrain Sweep
Energy dissipation in process
LAOS – 90° Arc – 100°C, 0.1 Hz
UNCONTROLLED
MIXING PROCESS
ε = π.γ0.σ0.sin δ
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•Instrument repeatability
•Additional mixing compound
•Sample number: 15
•CV (Std Dev/Mean) ≈ 0.75%
•Production compound homogeneity
•Batch number: 1
•Sample number: 12
•CV ≈ 0.75%
•Production variability
•Batch number: 18
•CV from 15.43% to 4.72%
Instrument repeatability, Compound homogeneity and production variation
Relevant QC Irrelevant QC
Poor material homogeneityMore variation within one batch than between
batches
Mean 1232.5
Std Dev 166.1
CV (%) 13.5
Mean 940.0
Std Dev 50.7
CV (%) 5.4
Complex modulus (G*)
@ low frequency
Within
batch
Between
batch
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Enhanced Calculation MDR: Cure Kinetic
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
22.0
24.0
0.0 5.0 10.0 15.0 20.0 25.0 30.0
Ela
stisch
er
An
teil [d
Nm
]
Zeit [min]
Copyright SCARABAEUS GMBH, Germany
180°C
170°C
160°C
150°C
140°C
SCARABAEUS GMBHPostfach 200 163
D-35399 Langgöns
Prüfdatum
Amplitude
12.12.2003
0.50°
Prüftemperatur
Frequenz
180 °C
1.67Hz
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Enhanced Calculation MDR: Cure Kinetic
PEX B, crosslink of silane modified PE with water (H2O)
kj/mole
Ea 63.7751
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Enhanced Calculation MDR: Cure Kinetic
-0.40
0.18
0.76
1.34
1.92
2.50
2.180 2.205 2.230 2.255 2.280 2.305 2.330 2.355 2.380 2.405 2.430
ln (ti) [min]
1/T *1000 [K]
-1.50
-0.90
-0.30
0.30
0.90
1.50
ln Uk(n) [1/min]
Copyright SCARABAEUS GMBH, Germany
SCARABAEUS GMBHReaktionskinetik
SIS V50
Teilenummer
Datum
ISOTHERM
18.12.2003
Ea (ti) [kJ/mol] 93.16
Ea (Uk) [kJ/mol]
a (ti) [min]
a (Uk) [1/min]
b (ti)
b (Uk)
R² (ti)
R² (Uk)
Anzahl Werte
Reaktionsordnung
97.29
-25.04
27.04
11.204
-11.702
0.999
1.000
5
1.00
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Cure simulation based on kinetics. verification
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
0.0 6.0 12.0 18.0 24.0 30.0
Ela
stis
che
r A
nte
il [d
Nm
]
Zeit [min]
0.00
16.00
32.00
48.00
64.00
80.00
96.00
112.00
128.00
144.00
160.00
176.00
192.00
Ist-
Te
mp
era
tur [°
C]
Copyright SCARABAEUS GMBH, Germany
SCARABAEUS GMBHPostfach 200 163
D-35399 Langgöns
Prüfdatum
Amplitude
12.12.2003
0.50°
Prüftemperatur
Frequenz
180 °C
1.67Hz
70.0
80.0
90.0
100.0
110.0
120.0
130.0
140.0
150.0
160.0
170.0
180.0
190.0
200.0
0.0 10.0 20.0 30.0
Temperatur [°C]
Zeit [min]
0
10
20
30
40
50
60
70
80
90
100
Reaktionsumsatz [%]
Copyright SCARABAEUS GMBH, Germany
Soll-Temperatur
berechnete Umsatz
gemessene Umsatz
SCARABAEUSHeizzeitrechnung
Temperaturprogramm
Datum 18.12.2003
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Cure simulation based on kinetic parameters
Cure
simulation
Rubber slab: 10 mm thick
155° C cure temperature
Compound initial temperature: 30° C
Arbitrary heat conductivity values
Edge
Mid-point
Center10 mm
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Cure simulation – Cure time optimization
Rubber slab: 10 mm thick
155° C cure temperature
Compound initial temperature: 30° C
Taking into account both heating
and cooling, cure time can safely be
reduced from 8 min. to 5 min., 35%
reduction
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MDR - Application on sponge rubber
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Use of kinetic analysis on different MDR curves
Conversion rate constant on pressure curve
Boyle Law: ∙ ∙ ∙
Pressure is linearly proportional to n so P can be used to calculate
conversion rate constant of gas formation in the compound.
Detection of dual decomposition reaction in silica compound based on
filler level
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Activation energy of blowing agent decomposition
TA Instruments
Confidential
Insulation foam
NBR-PVC blend with Cellogen AZ
Car door seal
EPDM compound with Cellogen OT
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Results – Different sample weight, same shape
Accurate cure and blowing agent decomposition testing prerequisite:
• Identical material quantity
• Identical shape with minimizing material flow in the test chamber.
Increasing compound sample size
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Effect different sample shape, same weight
Different sample high and different Diameter
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Results – Same sample weight, same shape
Optimum repeatability and accuracy can only be archieved on cure and
pressure with sample weight ±0.01 g and sample diameter ±1 mm
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RPA summary and conclusion
• Since its commercialization, the RPA has found a growing importance in rubber testing.
• At first, at big rubber manufacturers such as tire companies
• But these were the most reluctant to share useful information on how to use this novel
instrument.
• The level of complex physical properties of rubber compound and even pure polymers
have hindered wide and fast distribution
• Available literature may present some of RPA useful technique in showing how things
are different but often failed to explain why.
• In this presentation I tried to present some of critical RPA tests in connection to material
fundamental properties.
• These properties include processing related characteristics such as viscosity, green-
strength (sagging resistance), surface aspect, mixing etc.
• We have also seen precise relationship between RPA measurements and polymer
characteristics (AMW, MWD, LCB etc.) affecting compound processing.
• The RPA effective testing power remains essentially within it high and flexible
programmability thus offering a unique testing versatility.
• So the RPA is capable to replace a large amount of conventional techniques.
• It can as well considerably deepen rubber behavior understanding.
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