Silica in rubber –
Possibilities and Challenges
Joint seminar
Kumi-instituutti & MOL
1
Silica in rubber –
Possibilities and Challenges
2
Tampere
Wilma K. Dierkes
Tampere University of Technology
Department of Material Science
Laboratory of
Plastics and Elastomer Technology
33720 Tampere
Finland
University of Twente
Department of
Elastomer Technology and Engineering
7500 AE Enschede
The Netherlands
Enschede
3
Visiting Professorship
Education
1991
1993
2005
Fondation Universitaire
University of
Hanover (Germany): Luxembourgeoise, Arlon (Belgium),
postacademical education:
‘Diplom Chemie’
European Environmental Sciences
University Twente, Department
of Rubber Technology,
Enschede (Netherlands), PhD:
‘Economic mixing of silicarubber compounds’
Profession
1991
1993
1999
2001
Degussa
University Twente,
Rubber Resources,
Robert Bosch
Belgium:
Enschede:
the Netherlands: R&D, Produktie
Researcher Technical Service
Ass. Professor
(Belgium):
R&D, Production
2009
Tampere
University of
Technology,
Finland: Visiting
Professor
4
Contents
Silica in rubber
Silica/silanes in rubber
Challenges
Possibilities
Coupling
agents
Surface
Dual phase
modification
silica
Summary
In-situ
Silica
Particle
size
distribution
Silica in rubber
5
History
1950
Silica and
silicates as
replacement
of carbon
black
1970
Precipitated silica
(lower costs than
pyrogenic silica)
First applications:
shoe soles
(colored,
transparent)
1990
Silica in heavyservice tires
(improvement of
cutting and
chipping
resistance, better
adhesion to textile
and metal), 10-25
phr silica
2010
Silica-silane
technology
for passenger
car tire treads
?
Rolling
resistance
Abrasion
resistance
Wet
grip
Current silica
consumption in rubber:
app. 0,5 mill. tons/year
Silica/silanes in rubber
6
History
1970
Organofunctional
silanes as
adhesion
promoters for
glass fiber –
polymer systems
Introduction of
bifunctional
silanes as
coupling
agents
1990
F. Thurn, S. Wolff
(KGK 28, 733ff, 1975):
best silanes for
highest reinforcing
effect and minimal
influence on scorch
Bis-(triethoxysilyl
propyl)tetra- and
disulfides as
coupling agents
Combinations:
sulfursilanemoieties
-SCN
-S-CS-OR
-S-CS-NHR
-S-C(NH)(NH2)
-SH
-S-S-S-S-S-S-S-S-S-
-Si(OCH3) 3
-Si(OC2H5) 3
-Si(i-OC3H7) 3
-Si(n-OC3H7) 3
-Si(CO4H9) 3
-Si(OC8H17) 3
Bis(triethoxysilylpropyl)disulfane
7
Silica in rubber
Silica/silanes in rubber
Challenges
Possibilities
Coupling
agents
Surface
Dual phase
modification
silica
Summary
In-situ
Silica
Particle
size
distribution
8
Challenges
Dispersion
Particle size
distribution
& structure
Compound stability
Torque
Silica filled rubber blend
Flocculation
Good dispersion
Polymer 1
Time
Silica
Polymer 2
Compatibility & polarity match
Polymers
Fillers
EPDM SBR
NR
NBR
16.4 16.6
17.5
19.7
Carbon
black
70.0
Surface tension [mJ/m2]
Silica
Challenges
9
Dispersion & particle size distribution
Filler dispersion depends on:
Polymer: Type, molecular weight
Filler:
Particle size distribution,
structure, surface activity
Blend:
A. Schröder, M. Klüppel, R. H. Schuster and J.
Heidberg, Kautsch. Gummi Kunstst., 53, 257 (2000).
Interphase transfer of fillers
T.A. Vilgis, Polymer,
46(12), 4223 (2005)
Challenges
10
Dispersion
EPDM with untreated silica
S-SBR with untreated silica
NBR with untreated silica
Silane treated
silica reinforced NBR
C2H2-plasma treated
silica reinforced NBR
(H5C2-O)3Si – C3H6 – Sn – C3H6 – Si (OC2H5)3
Image size: 2,5 µ
Challenges
11
Polarity & compatibility match
Polymers
Curing agents
EPDM SBR
NR
NBR CBS
DCBS
MBT
16.4 16.6
17.5
19.7 20.4
21.8
22.5
Fillers
Carbon
black
Silica
70.0
Surface tension [mJ/m2]
Incompatibility of the components (polarity, unsaturation)
Dispersion and wetting difficulties of the filler
Re-agglomeration of the filler
Low adhesion of polymer on the filler surface
Challenges
12
Torque
Compound stability
Flocculation
Good dispersion
Time
Re-agglomeration of the filler
(Viscosity) changes during storage
13
Silica in rubber
Silica/silanes in rubber
Challenges
Possibilities
Coupling
agents
Surface
Dual phase
modification
silica
Summary
In-situ
Silica
Particle
size
distribution
Possibilities: Coupling agent
14
Polymer-filler incompatibility
OH
Si
EtO
O
O
Si
O
Silica
(CH ) S S
23
Si
O
O Si (CH ) S S
23
particle
O
O
S
Si
O Si (CH )
S
O
23
Si
OEt
OEt
O
O
Si
Si
OH
(CH )
S
EtO
23
S
Silica:
hydrophilic
Si
Rubber:
hydrophobic
Possibilities: Coupling agent
Different types of coupling agents
Structure of different coupling agents
Blocked silane
S-[3-(triethoxysilyl)propyl]ester of octanethionic acid
(EtO)3Si - (CH2)3 - S - (CO) - (CH2)6 - CH3
NXT Silane, GE Silicones, Wilton, CT, USA
[
]n
Oligomeric silane (+ activator)
Bis(triethoxysilyl)polybutadiene, n = 27
(EtO) 3 Si - (CH 2 -CH=CH -CH 2 )n - Si(EtO)3
Rhenofit 1715, Rheinchemie, Mannheim, Germany
Monomeric silane
Bis(triethoxysilylpropyl)disulfane (TESPD)
(EtO)3Si - (CH2)3 - S-S - (CH2)3 - Si(EtO)3
Si 266 Evonik (Degussa), Frankfurt, Germany
15
Possibilities: Coupling agent
16
Different types of coupling agents
TESPD, 145ºC
blocked silane, 155ºC
3.0
2.5
2.0
1.5
Log shear modulus
G'(0.56%)-G'(100%) [MPa]
filler-filler interaction
3.5
Filler-filler
Filler-filler interaction
interaction
Log shear deformation
1.0
0.5
Payne effect:
0.0
0
2
4
6
8
10
Silanzation time [minutes]
12
14
Destruction of the filler network
(filler-filler interaction)
at strains > 1%
results in modulus decrease
Dierkes, W., University Twente, thesis: Economic mixing of silica-rubber
compounds, ISBN 90-365-2185-8, 2005
Possibilities: Coupling agent
17
Different types of coupling agents
90
60
135°C
30
0
1.0
2.5
5.0
Silanization time [minutes]
155°C
150
ML(1+4), 100ºC [MU]
145°C
120
165°C
90
60
Blocked silane
30
G'(0,56%) - G'(100%) [MPa]
TESPD
120
2.5
2.0
1.5
1.0
0.5
0.0
1.0
2.5
5.0
Silanization time [minutes]
G'(0,56%) - G'(100%) [MPa]
ML(1+4), 100ºC [MU]
150
2.5
2.0
1.5
1.0
0.5
0.0
0
1.0
2.5
5.0
Silanization time [minutes]
ML(1+4), 100ºC [MU]
150
B
120
90
60
Oligomeric silane
30
0
1.0
2.5
5.0
Silanization time [minutes]
G'(0,56%) - G'(100%) [MPa]
1.0
2.5
5.0
Silanization time [minutes]
2.5
2.0
1.5
1.0
0.5
0.0
1.0
2.5
5.0
Silanization time [minutes]
Dierkes, W., University Twente, thesis: Economic mixing of silica-rubber
compounds, ISBN 90-365-2185-8, 2005
Payne effect
Viscosity
Possibilities: Surface modification
18
Plasma polymerization: film characteristics
Monomer
Plasma-Polymer
- highly crosslinked
- two-dimensional network
- disordered structure
- thermally, chemically stable
- very adherent
- bulk properties preserved
B Tailored interphases between filler and polymer for better
- compatibility
- wettability
- dispersion
- stability
Possibilities: Surface modification
19
Plasma polymerization: filler morphology
Untreated silica
M. Tiwari, University Twente, thesis; to be published in 2010
Polyacetylene-treated silica
Possibilities: Surface modification
20
Plasma polymerization: Reduction in polarity
M. Tiwari, University Twente, thesis; to be published in 2010
Weight of water penetration (g)
2,0
Untreated silica
1,8
Polyacetylene coated silica
Polypyrrole coated silica
1,6
Polythiofene coated silica
1,4
1,2
1,0
0,8
0,6
0,4
0,2
0,0
0
2
4
6
8
10
Time (minutes)
12
14
16
Possibilities: Surface modification
21
Plasma polymerization: Polymer blend recipe
PA: polyacetylene
S: S-SBR
E: EPDM
PPy: polypyrrole
Components
T: silane (TESPD)
PTh: polythiophene
SEU
SEPA
SEPTh
SEPPy
SET
phr
phr
phr
phr
phr
S-SBR
50
50
50
50
50
EPDM
50
50
50
50
50
Silica
50
50
50
50
50
ZnO
2.5
2.5
2.5
2.5
2.5
Stearic acid
2.5
2.5
2.5
2.5
2.5
--
--
--
--
4
Sulfur
1.5
1.5
1.5
1.5
1.04
CBS
1.5
1.5
1.5
1.5
1.5
DPG
S: 1.5
SE:0.75
S: 1.5
SE:0.75
S: 1.5
SE:0.75
S: 1.5
SE:0.75
S: 1.5
SE:0.75
TMTD
0.4
0.4
0.4
0.4
0.4
ZBEC
0.75
0.75
0.75
0.75
0.75
Silane (TESPT)
Possibilities: Surface modification
22
Plasma polymerization: properties
60
0,4
0,3
0,2
0,1
0,0
10
Reinforcement parameter
0,6
Bound rubber content (%)
50
40
30
20
SPA
SPPy
SPTh
ST
SU
SPA
SPPy
SPTh
ST
0
SU
SPA
0,5
0,4
0,3
0,2
0,1
ST
8
50
6
40
30
4
20
2
10
0
0
SEU
0,0
SEPTh
SPTh
Reinforcement parameter
Bound rubber content (%)
0,6
SPPy
10
60
0,7
SEPPy
2
Sample code
70
SEPA
4
Sample code
0,8
G'(0.56%) - G'(100.04%) [MPa]
SBR-EPDM blend
Sample code
SEU
6
10
0
SU
8
SET
Sample code
Bound rubber:
Polymer chains are
adsorbed /
bond to the filler
surface
SEPA
SEPPy
SEPTh
Sample code
SET
SEU
SEPA
SEPPy
SEPTh
SET
Sample code
Smax − Smin
m
− 1 = αF F
0
0
S max − S min
mP
The lower αF,
Smax
Torque
G'(0.56%) - G'(100.04%) [MPa]
Straight SBR
70
0,5
Dispersion
Filler-polymer interaction
M. Tiwari, University Twente, thesis; to be published in 2010
Filler-filler interaction
0,7
the better the dispersion
Smin
Time
Possibilities: Surface modification
23
Plasma polymerization
Straight SBR
28
SU
SPA
SPPy
SPTh
ST
20
SEU
SEPA
SEPTH
SEPPy
SET
14
Stress (MPa)
24
Stress (MPa)
SBR - EPDM blend
16
16
12
12
10
8
6
8
4
4
2
0
0
0
100
200
300
400
Strain (%)
500
600
700
800
0
50
100
150
200
250
300
Strain (%)
M. Tiwari, University Twente, thesis; to be published in 2010
Possibilities: Silica-carbon black combinations
24
Dual phase silica
Silica domains distributed
throughout the aggregates
of the filler
(CRX2124, Cabot)
Carbon black with silica shell
on the particle surface
(CRX4210, Cabot)
http://www.cabot-corp.com/cws/businesses.nsf/8969ddd26dc8427385256c2c004dad01/
91da3d4fd303e09c85256c7a00502230/$FILE/CRX4000-012-FTF'01-Florida%20meeting%2001-01.pdf
Possibilities: Silica-carbon black combinations
25
Dual phase silica: filler-filler interaction (Payne effect)
Carbon black with silica on the particle surface (CRX4210, Cabot)
Silica domains distributed throughout the aggregates of the filler (CRX2124, Cabot)
OESSBR: oil extended S-SBR
M.-J. Wang, M. Morris: Recent Developments in Fillers for Tire Applications; in: Current Topics in
Elastomers Research, A.K. Bhomick (ed.), CRC Press, 2008
Possibilities: Silica-carbon black combinations
26
Dual phase silica: rolling resistance (tan δ)
Rolling
resistance
Heat
build-up
tan δ
Abrasion
Low
temperature
properties Wet traction
Temperature, ºC
CSDPF: Carbon silicon dual phase filler distributed within carbon black (Cabot)
Meng-Jiao Wang, Ping Zhang, Khaled Mahmud, meeting of the Rubber
Division, American Chemical Society, Dallas, TX, April 4 - 6, 2000
Possibilities: In-situ silica
27
Process
Sol-gel process with TEOS and n-butylamine as catalyst
- Swelling of thin rubber sheets in TEOS
- Immersion in an aqueous solution of n-butylamine
TEOS
Tetraethyl orthosilicate
Particle size: appr. 10 nm to 40 nm
Max. in-situ silica concentration so far: 43 phr
(practical loading for e.g. tire compounds: appr. 80 phr)
Y. IKEDA, Y. KAMEDA, J. Sol-Gel Sci. Technol. 31, 137–142, 2004
Possibilities: In-situ silica
28
In Natural Rubber
Silica concentration: 33 phr
Surface treatment:
0,5 phr γ-MPS
γ-Mercaptopropyltrimethoxysilane
NR-V
1
2
4 3
2
3
4
1
NR-V: vulcanized
1. NR-mix - V: mill-blended, vulcanized
2. NR-mix - γ -V: mill-blended, with γ-MPS, vulcanized
3. NR-in situ -V: in situ silica, vulcanized
4. NR-in situ - γ -V: in situ silica, with γ-MPS, vulcanized
K. Murakami et al., J. Mater. Sci. 38, p. 1447 (2003)
Possibilities: Particle size distribution
29
Blends with nano fillers
Improving filler-filler network formation with
preservation of the strong filler-polymer interaction
by blends of conventional fillers + nano particles
SBR
compound
Example:
Carbon black + CNT’s
LILIANE BOKOBZA J. Polym. Sci. Part B: Polymer Physics, 46, 1939–1951, 2008
30
Possibilities of silica technology
Summary
¾ Silica/silane allowed to shift the magic triangle of tire performance
to a higher level: a promising start
¾ Main functional difference with CB: strong (covalent) filler-polymer bond
¾ Critical aspect: morphology (good distribution and dispersion,
strong polymer-filler interaction)
Ö Challenge: Improved and stable polymer-filler network
Ö Possibilities: + Surface modification of silica
+ Improved particle size distribution and structure
31
Acknowledgements
M. Tiwari
UT-ETE & Teijin Twaron
Silica in rubber –
Possibilities and Challenges
Thank you for your attention!
32