Incorporating Silica into Natural Rubber · Rubber compounding: chemistry and applications, 2nd ed....
Transcript of Incorporating Silica into Natural Rubber · Rubber compounding: chemistry and applications, 2nd ed....
Incorporating Silica into Natural Rubber
Suyanti Hersanto1, Joachim Bertrand², Wisut Kaewsakul1, Wilma K. Dierkes1, Anke Blume1
1 2
December, 2018
Content
INTRODUCTION QUESTIONS EXPERIMENT RESULTS &
DISCUSSION
ANSWERS
1. 2. 3. 4. 5.
1. INTRODUCTION
Natural Rubber (NR)
• Renewable material
• Good dynamic properties
(high fatigue resistance, low
hysteresis, low heat build-up)
Applications: anti-vibration mountings,
heavy duty tires, conveyor belts, etc.
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NR network
Protein: bonds with ω-end, acts as
a crosslink point (hydrogen bonds)
Phospholipids: branching point
(hydrogen and ionic bonds)
Repeating unit:
cis-1,4-polyisoprene
ω-end
S. Amnuaypornsri, et.al. Rubber Chem. Technol., 81 (2008), 753.
B. Rodgers. (2016). Rubber compounding: chemistry and applications, 2nd ed. CRC Press.
Silica
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Granulated Powder
Applications: tires and automotive products
Improved performances compared to carbon black filled
tire tread compounds:
• Tear resistance
• Wet traction
• Low rolling resistance
• Low heat build-up
Functional groups
Isolated and geminal silanol groups most
reactive, highly polar
Problem: NR is non-polar, whereas silica is polar.
Difficult to disperse the silica
Use of silane supports compatibility to polymer
M.D. Bair, J.G. Dorsey. J. Chromatogr. A 1220 (2012), 35.
Y. Li, et.al. Rubber Chem. Technol., 67 (1994), 693.
Coupling Mechanisms
Requirements for coupling
TESPT to silica:
• Temperature >130oC
• Sufficient reaction time
By-product: Ethanol
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RO
RO
ROtriethoxysilyl-
group
organo functional
group
propyl spacer
XSi
RubberSilica
surface
OH
Silica
coupling
Rubber
coupling
Coupling during
mixing
Coupling during
vulcanization
Silica
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Granulated Powder
Applications: tires and automotive products
Improved performances compared to carbon black filled
tire tread compounds:
• Tear resistance
• Wet traction
• Low rolling resistance
• Low heat build-up
Functional groups
Isolated and geminal silanol groups most
reactive, highly polar
Problem: NR is non-polar, whereas silica is polar.
Difficult to disperse the silica
Use of silane supports compatibility to polymer
But even after reacting with silane ca. 75% of all
Si-OH remain
Presence of silane decreases viscosity which
results in worse dispersion
M.D. Bair, J.G. Dorsey. J. Chromatogr. A 1220 (2012), 35.
Y. Li, et.al. Rubber Chem. Technol., 67 (1994), 693.
Dispersion Mechanisms
8Palmgren, H., Processing Conditions in the Batch-Operated Internal Mixer. Rubber Chem. Technol., 1975. 48: p. 462-494
Presilanized silica
ALTERNATIVES
Presilanized silica in a masterbatch
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Conventional Mixing and the Alternatives
Mixing constraints:
• High temperature for the coupling reaction (T>130oC)
• NR starts to degrade at this temperature
Conventional or dry mixing
rubber silica silaneStage 1
Stage 2 re-mixing: coupling reaction
Stage 3 compound curing agents
time-consuming, ethanol emission,
mixing + chemical reaction at the
same time
rubber Pre-silanized
silica
compound curing agents
2nd step required?
• Second mixing step might not be necessary save time
• No ethanol emission
• Silica is already dispersed in the masterbatch
compound curing agents
rubber with presilanized silica
2nd step required?
NR-Silica Masterbatch
Y. Gui, et.al. Composites Part B 85 (2016): 130-139.
S. Parasertsri, N. Rattanasom. (2011). Polym. Testing, 30,515.10
2. NR latex is
added
3. After
coagulation1. (Presilanized) silica
slurry
4. NR-silica masterbatch (dried &
compacted)
SEM observation of
NR / 30phr silica / 3phr TESPT:
Silica is better dispersed in a masterbatch
NR Dry mix
NR/silica/TESPT
Masterbatch
NR/silica/TESPT
*)TESPT was
added during
mixing
2. QUESTIONS
Questions
Mixing time
3 mixing cycles were applied: long (L), short (S) and very short (VS).
Q1. Which is the most suitable mixing cycle for each compound?
Mixing problems
2 processing aids were used: PA1 and PA2. Polarity: PA1 < PA2.
Q2. Does a processing aid supports the mixing?
Mixing procedure
Evaluations on the mixing behavior and the mechanical properties.
Q3. Which is the best solution: in-situ, presilanized or masterbatch?12
3. EXPERIMENT
Method DRY MIX (DM) PRESILANIZED (PS) MASTERBATCH (MB)
Mixing cycle L VS VS L VS L S VS
NR 100 100 100 100 100
NR-silica masterbatch 152.12 152.12 152.12
ULTRASIL VN3 GR 50 50 50
TESPT coupling agent 5 5 5
PS1: BM Silica COS 8569 MH 52.12 52.12
PA1 (Ultra-flow 700S) 2 2 2 2 2 2
PA2 (Ultra-DFR 900) 2 2
Compound number 1 2 3 4 5 9 10 11
Chemicals: ZnO, stearic acid, 6PPD, TMQ, wax, TDAE oil
Curatives: Sulfur, CBS, TBzTD
Amount in phr (part per hundred part of rubber)
Compound Formulation
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L: long
S: short
VS: very short
Mixing ProcedureMixer: Brabender 390 ml
Fill factor: 70%
Starting speed: 60 rpm
15
0.5
0.5
0.5
0.5
0.5
0.5
2
2
1
1
1.5
1.5
2
2
4
4
0 1 2 3 4 5 6 7 8 9 10 11
4
0 1 2 3 4
STAGE 2(T dump = 140oC)
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
1
1
1
1
0 1 2 3
STAGE 3(T dump < 100oC)
STAGE 1(T dump = 140oC)
Long (L)
Short (S)
Very short
(VS)
Very short
(VS) for MB
Add NR / ½ NR-silica masterbatch
Add silica, silane / ½ NR-silica masterbatch Add ½ NR-silica masterbatch and ½ PA2
Add chemicals and PA1 or PA2 Add chemicals and ½ PA2
Sweep (ram opened) Add previously mixed compound
Shearing (ram closed) Add curatives
18:50
14:20
10:20
10:20
Time (min)
Measurements
Mixed compound
(uncured)
Tensile
Hardness
Dispersion
Cure
characteristics
Mooney viscosity
Bound rubber
Filler-filler
interaction
Compound
(cured)Cure
Heat aging
70oC
Compression set
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4. RESULTS AND DISCUSSION
Mixing
NR-silica masterbatch tough material
• High silica content
• Absence of processing additives
• Higher mixing energy
Different incorporation times of the chemicals
• Presilanized silica has poor flowability
(DM: granulated; PS1: fluffy; MB: dispersed)
• Presence of silica between the mixer wall and
the compound slippage
00 01 02 03 04 05 06 07 08 09 10 110
50
100
150
200
250
300
350
400Torque Temp DM-PA1_L (1)
Torque Temp PS1-PA1_L (4)
Torque Temp MB-PA1_L (9)
Torq
ue [
Nm
]
Time [min]
0
20
40
60
80
100
120
140
160
Tem
pe
ratu
re [
oC
]
DM = dry mix
PS1 = presilanized
MB = masterbatch
LONG cycle
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Mixing
Similar profiles for different processing
additives in the dry mix (2) and (3)
00 01 02 03 04 05 06 070
50
100
150
200
250
300
350
400
Torq
ue [N
m]
Time [min]
Torque Temp DM-PA1_VS (2)
Torque Temp DM-PA2_VS (3)
Torque Temp PS1-PA1_VS (5)
Torque Temp MB-PA2_VS (11)
0
20
40
60
80
100
120
140
160
Tem
pera
ture
[oC
]
DM = dry mix
PS1 = presilanized
MB = masterbatch
VERY SHORT cycle
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Mooney Viscosity
DM-PA1_L (1
)
DM-PA1_VS (2
)
DM-PA2_VS (3
)
PS1-PA1_L (4
)
PS1-PA1_VS (5
)
MB-PA1_L (9
)
MB-PA1_S (1
0)
MB-PA2_VS (1
1)
0
20
40
60
80
ML (
1+
4)
100
oC
[M
U]
Dry mix: Longer mixing = higher viscosity:
• Better silanization expected (=lower viscosity)
• Pre-scorch by premature crosslinking of TESPT
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Presilanized silica and masterbatch:
• Silanization reaction shouldn’t have an influence
• Higher decrease of filler-filler network = better
dispersion
• Higher cleavage of NR chains
Payne Effect: Indicator for Micro-Dispersion
DM-PA1_L (1
)
DM-PA1_VS (2
)
DM-PA2_VS (3
)
PS1-PA1_L (4
)
PS1-PA1_VS (5
)
MB-PA1_L (9
)
MB-PA1_S (1
0)
MB-PA2_VS (1
1)
0
50
100
150
200
Sto
rag
e m
od
ulu
s (
G') [kP
a]
G'(0.56%) - G'(100%)
G'(100%)
• Shorter mixing cycle higher filler-filler network and less
cleavage of polymer chains
• Masterbatch compounds lowest filler-filler interaction
• PA1 leads to lower Payne effect than PA2
Peng, et.al. (2005). Polym. Adv. Technol. 16: 770-78221
Filler network
Filler-rubber and rubber
networks
Bound Rubber
DM and PS1: long cycle higher bound rubber content
• Higher coupling possibility?
• Premature crosslink
MB: long cycle lower bound rubber content
• Better dispersion of silica: release of occluded rubber
Processing aids
• PA2 is more polar than PA1: Supports PA2 silica – silane –
polymer coupling?
DM-PA1_L (1
)
DM-PA1_VS (2
)
DM-PA2_VS (3
)
PS1-PA1_L (4
)
PS1-PA1_VS (5
)
MB-PA1_L (9
)
MB-PA1_S (1
0)
MB-PA2_VS (1
1)
0
10
20
30
40
50
Bou
nd
rubbe
r [%
]
Physical BR
Chemical BR
22H.D. Luginsland, et.al. (2002). Rubber Chem. Technol., 75, 563.
Silica cluster
Cure Characteristics at 160oC
0 5 10 15 20 25 300
1
2
3
4
5
6
7
8
To
rque
[dN
m]
Time [min]
PS1-PA1_L (4)
DM-PA1_L (1)
MB-PA1_L (9)
MB-PA2_VS (11)MB-PA1_S (10)
PS1-PA1_VS (5)
DM-PA1_VS (2)DM-PA2_VS (3)
DM: very short mixing marching modulus (2) and (3)
• Long cure time
• Inadequate silanization
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DM, PS1: long mixing reversion (1) and (4)
• NR chain degradation
MB: close results regardless of their mixing cycles
DM PS1 MB
Long cycle (L)
& PA1
Very short cycle (VS)
& PA1
Very short cycle (VS)
& PA2
11 (98%)3 (97%)
4 (97%)1 (97%) 9 (96%)
5 (96%)2 (93%)
100 μm
10 (97%)Short (S) cycle
Macro Dispersion
Worse dispersion:
VS mixed dry mix with PA1
PA2 improves dispersion in
the very short mixing time
(by improved silica – silane
– polymer coupling?)
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5. ANSWERS
Answers
Q1. Which is the most suitable mixing cycle for each compound?
• Dry mix long mixing
• Pre-silanized and NR-silica masterbatch very short mixing cycle possible
Q2. Does a processing aid supports the mixing?
• Yes. PA2 (Ultra-DFR 900, higher polarity than PA1) is preferable for a shorter mixing time
• Supports the silica – silane – polymer coupling but leads to higher Payne effect in the green compound
Q3. Which is the best solution: in-situ, presilanized or masterbatch?
Overall, NR-silica masterbatch with very short mixing:
• In-rubber properties are as good as the conventionally mixed one but with shorter mixing time
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Answers
All in all, different influences have to be considered:
Level of
• dispersion
• silanization
• polymer degradation
• premature crosslink
• Polymer-polymer coupling
• Polymer – silane – silica coupling
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Challenging!
ACKNOWLEDGEMENT