1Silica in rubberSilica in rubber ––Possibilities and ChallengesPossibilities and Challenges

Joint seminar Joint seminar

KumiKumi--instituutti & MOLinstituutti & MOL

2

Wilma K. DierkesTampere University of Technology

Department of Material ScienceLaboratory of

Plastics and Elastomer Technology 33720 Tampere

Finland

University of TwenteDepartment of

Elastomer Technology and Engineering7500 AE EnschedeThe Netherlands

Tampere

Enschede

Silica in rubber –Possibilities and Challenges

3

Visiting Professorship

University Twente, Department of Rubber Technology, Enschede (Netherlands), PhD: ‘Economic mixing of silica-rubber compounds’

1991 1993 2005

University of Hanover (Germany): ‘Diplom Chemie’

Fondation Universitaire Luxembourgeoise, Arlon (Belgium), postacademical education: European Environmental Sciences

Education

Rubber Resources, the Netherlands: R&D, Technical Service

1991 1993 2001

Degussa Belgium: Researcher

Robert Bosch Produktie (Belgium): R&D, Production

University Twente, Enschede: Ass. Professor

Tampere University of Technology, Finland: Visiting Professor

1999 2009Profession

4

Particle size

distribution

Silica in rubber

Silica/silanes in rubber

Challenges

Dual phase silica

Surface modification

Coupling agents

In-situ Silica

Possibilities

Summary

Contents

5Silica in rubberHistory

1950 1970 1990 2010

Silica and silicates as replacement of carbon black

Precipitated silica (lower costs than pyrogenic silica)

First applications: shoe soles (colored, transparent)

?Silica in heavy-service tires (improvement of cutting and chipping resistance, better adhesion to textile and metal), 10-25 phr silica

Silica-silane technology for passenger car tire treads

Rolling resistance

Abrasionresistance

Wetgrip

Current silica consumption in rubber:

app. 0,5 mill. tons/year

6Silica/silanes in rubberHistory

1970 1990

Introduction of bifunctional silanes as coupling agents

Organofunctional silanes as adhesion promoters for glass fiber –polymer systems

F. Thurn, S. Wolff (KGK 28, 733ff, 1975): best silanes for highest reinforcing effect and minimal influence on scorch

-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

Combinations:sulfur- silane-

moieties

Bis-(triethoxysilyl propyl)tetra- and disulfides as coupling agents

Bis(triethoxysilylpropyl)disulfane

7

Particle size

distribution

Silica in rubber

Silica/silanes in rubber

Challenges

Dual phase silica

Surface modification

Coupling agents

In-situ Silica

Possibilities

Summary

8

Challenges

Polymer 1 Silica

Silica filled rubber blend

Polymer 2

Dispersion

Compatibility & polarity match

16.4

EPDM

16.6 17.5 19.7

SBR NBR NR Carbon black

Silica

70.0

Surface tension [mJ/m2]

Polymers Fillers

Particle size distribution & structure

Compound stability

Time

Good dispersion

Floccu-lation

Torq

ue

9

T.A. Vilgis, Polymer,

46(12), 4223 (2005)

A. Schröder, M. Klüppel, R. H. Schuster and J. Heidberg, Kautsch. Gummi Kunstst., 53, 257 (2000).

ChallengesDispersion & particle size distribution

Filler dispersion depends on: Polymer: Type, molecular weightFiller: Particle size distribution,

structure, surface activityBlend: Interphase transfer of fillers

10

Image size: 2,5 µ

EPDM with untreated silica

ChallengesDispersion

S-SBR with untreated silica

NBR with untreated silica

(H5C2-O)3Si – C3H6 – Sn – C3H6 – Si (OC2H5)3

Silane treatedsilica reinforced NBR

C2H2-plasma treatedsilica reinforced NBR

11

16.4

EPDM

16.6 17.5 19.7 20.4 21.8

SBR NBR NR CBS DCBS

22.5

MBT Carbon black

Silica

70.0

Surface tension [mJ/m2]

Polymers Curing agents Fillers

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

ChallengesPolarity & compatibility match

12

Re-agglomeration of the filler

(Viscosity) changes during storage

ChallengesCompound stability

Time

Good dispersion

Floccu-lationTo

rque

13

Particle size

distribution

Silica in rubber

Silica/silanes in rubber

Challenges

Dual phase silica

Surface modification

Coupling agents

In-situ Silica

Possibilities

Summary

14

SilicaSilica particleparticle

SilicaSilica: :

hydrophilichydrophilic

Rubber: Rubber:

hydrophobichydrophobic

E

SiOSiO

SiO

Si

OSi

OSi

O

O

O

OH

O

OH

Si

Si

O

tO(CH2)3

(CH2)3

Si

O

(CH2)3OEt

SS

Si

OEt

EtO (CH2)3 S

S

S

S

S

S

Possibilities: Coupling agentPolymer-filler incompatibility

15

Structure of different coupling agents

(EtO)3Si - (CH2)3 - S - (CO) - (CH2)6 - CH3

Blocked silane

S-[3-(triethoxysilyl)propyl]ester of octanethionic acid

Possibilities: Coupling agentDifferent types of coupling agents

Rhenofit 1715, Rheinchemie, Mannheim, Germany

Oligomeric silane (+ activator)

Bis(triethoxysilyl)polybutadiene, n = 27

(EtO)3 Si - (CH2 -CH=CH -CH 2)n- Si(EtO)3

NXT Silane, GE Silicones, Wilton, CT, USA

[ ]n

Monomeric silane

Bis(triethoxysilylpropyl)disulfane (TESPD)

Si 266 Evonik (Degussa), Frankfurt, Germany(EtO)3Si - (CH2)3 - S-S - (CH2)3 - Si(EtO)3(EtO)3Si - (CH2)3 - S-S - (CH2)3 - Si(EtO)3

16

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 2 4 6 8 10 12 14Silanzation time [minutes]

fille

r-fil

ler i

nter

actio

nG

'(0.5

6%)-G

'(100

%) [

MPa

] TESPD, 145ºCblocked silane, 155ºC

Possibilities: Coupling agentDifferent types of coupling agents

Dierkes, W., University Twente, thesis: Economic mixing of silica-rubber compounds, ISBN 90-365-2185-8, 2005

Filler-filler interaction

Log

shea

r mod

ulus

Log shear deformation

Filler-filler interaction

Payne effect:

Destruction of the filler network

(filler-filler interaction)at strains > 1%

results in modulus decrease

17

0

30

60

90

120

150

1.0 2.5 5.0Silanization time [minutes]

ML(

1+4)

, 100

ºC [M

U]

TESPD

Viscosity

0.0

0.5

1.0

1.5

2.0

2.5

1.0 2.5 5.0Silanization time [minutes]

G'(0

,56%

) -G

'(100

%) [

MPa

]

Payne effect

135°C

145°C

155°C

165°C

Blocked silane0.0

0.5

1.0

1.5

2.0

2.5

1.0 2.5 5.0Silanization time [minutes]

G'(0

,56%

) -G

'(100

%) [

MPa

]

Silanization time [minutes]

0

30

60

90

120

150

1.0 2.5 5.0

ML(

1+4)

, 100

ºC [M

U]

Oligomeric silane0.0

0.5

1.0

1.5

2.0

2.5

1.0 2.5 5.0Silanization time [minutes]

G'(0

,56%

) -G

'(100

%) [

MPa

]

B

0

30

60

90

120

150

1.0 2.5 5.0Silanization time [minutes]

ML(

1+4)

, 100

ºC [M

U]

Possibilities: Coupling agentDifferent types of coupling agents

Die

rkes

, W.,

Uni

vers

ity T

wen

te, t

hesi

s: E

cono

mic

mix

ing

of s

ilica-

rubb

er

com

poun

ds, I

SB

N 9

0-36

5-21

85-8

, 200

5

18Possibilities: Surface modification Plasma polymerization: film characteristics

Tailored interphases between filler and polymer for better- compatibility - wettability

- dispersion - stability

Monomer Plasma-Polymer - highly crosslinked- two-dimensional network - disordered structure- thermally, chemically stable- very adherent- bulk properties preserved

19

Untreated silica

Polyacetylene-treated silica

M. Tiwari, University Twente, thesis; to be published in 2010

Possibilities: Surface modification Plasma polymerization: filler morphology

20Possibilities: Surface modification Plasma polymerization: Reduction in polarity

M. Tiwari, University Twente, thesis; to be published in 2010

Untreated silicaPolyacetylene coated silicaPolypyrrole coated silicaPolythiofene coated silica

Time (minutes)0 2 4 6 8 10 12 14 16

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

0 2 4 6 8 10 12 14 160,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

0 2 4 6 8 10 12 14 160,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

Wei

ght o

f wat

er p

enet

ratio

n (g

)

21Possibilities: Surface modification Plasma polymerization: Polymer blend recipe

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

Silane (TESPT) -- -- -- -- 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: 1.5SE:0.75

S: 1.5SE:0.75

S: 1.5SE:0.75

S: 1.5SE:0.75

S: 1.5SE:0.75

TMTD 0.4 0.4 0.4 0.4 0.4

ZBEC 0.75 0.75 0.75 0.75 0.75

Components

PPy: polypyrrole PTh: polythiophene

S: S-SBR

T: silane (TESPD)PA: polyacetylene

E: EPDM

22Possibilities: Surface modification Plasma polymerization: properties

SEU SEPA SEPPy SEPTh SET0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

G'(0

.56%

) - G

'(100

.04%

) [M

Pa]

Sample code

SBR

-EPD

M b

lend

M. Tiw

ari, University Tw

ente, thesis; to be published in 2010

SU SPA SPPy SPTh ST0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

G'(0

.56%

) - G

'(100

.04%

) [M

Pa]

Sample code

Stra

ight

SB

R

Filler-filler interaction

SEU SEPA SEPPy SEPTh SET0

10

20

30

40

50

60

70Bo

und

rubb

er c

onte

nt (%

)

Sample code

SU SPA SPPy SPTh ST0

10

20

30

40

50

60

70

Boun

d ru

bber

con

tent

(%)

Sample code

Bound rubber: Polymer chains are adsorbed / bond to the filler surface

Filler-polymer interaction

SEU SEPA SEPPy SEPTh SET0

2

4

6

8

10

Rei

nfor

cem

ent p

aram

eter

Sample code

SU SPA SPPy SPTh ST0

2

4

6

8

10

Rei

nfor

cem

ent p

aram

eter

Sample code

The lower αF, the better the dispersion

P

FF

min0

max0

minmax

mm1

SSSS α=−

−−

Time

Torq

ue

Smin

Smax

Dispersion

23Possibilities: Surface modification Plasma polymerization

SBR - EPDM blend

0 50 100 150 200 250 3000

2

4

6

8

10

12

14

16

0 50 100 150 200 250 3000

2

4

6

8

10

12

14

16

0 50 100 150 200 250 3000

2

4

6

8

10

12

14

16

0 50 100 150 200 250 3000

2

4

6

8

10

12

14

16

0 50 100 150 200 250 3000 50 100 150 200 250 3000

2

4

6

8

10

12

14

16

0 50 100 150 200 250 3000

2

4

6

8

10

12

14

16

0 50 100 150 200 250 3000

2

4

6

8

10

12

14

16

0 50 100 150 200 250 3000

2

4

6

8

10

12

14

16

0 50 100 150 200 250 3000

2

4

6

8

10

12

14

16

Stre

ss (M

Pa)

Strain (%)

SEU

SEPPySET

SEPASEPTH

M. Tiwari, University Twente, thesis; to be published in 2010

0 100 200 300 400 500 600 700 8000

4

8

12

16

20

24

28

0 100 200 300 400 500 600 700 8000

4

8

12

16

20

24

28

0 100 200 300 400 500 600 700 8000

4

8

12

16

20

24

28

0 100 200 300 400 500 600 700 8000

4

8

12

16

20

24

28

0 100 200 300 400 500 600 700 8000

4

8

12

16

20

24

28

Stre

ss (M

Pa)

SU

Strain (%)

SPPy

ST

SPA

SPTh

Straight SBR

24Possibilities: Silica-carbon black combinations 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

25Possibilities: Silica-carbon black combinations 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

26Possibilities: Silica-carbon black combinations Dual phase silica: rolling resistance (tan δ)

CSDPF: Carbon silicon dual phase filler distributed within carbon black (Cabot)

tan δ

Temperature, ºC

Meng-Jiao Wang, Ping Zhang, Khaled Mahmud, meeting of the Rubber Division, American Chemical Society, Dallas, TX, April 4 - 6, 2000

Abrasion

Low temperature properties Wet traction

Rolling resistance

Heat build-up

27Possibilities: In-situ silica 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

Max. in-situ silica concentration so far: 43 phr

(practical loading for e.g. tire compounds: appr. 80 phr)

TEOSTetraethyl orthosilicate

Particle size: appr. 10 nm to 40 nm

Y. IKEDA, Y. KAMEDA, J. Sol-Gel Sci. Technol. 31, 137–142, 2004

28Possibilities: In-situ silica In Natural Rubber

K. Murakami et al., J. Mater. Sci. 38, p. 1447 (2003)

Silica concentration: 33 phr

Surface treatment: 0,5 phr γ-MPS

NR-V: vulcanized1. NR-mix - V: mill-blended, vulcanized2. NR-mix - γ -V: mill-blended, with γ-MPS, vulcanized3. NR-in situ -V: in situ silica, vulcanized4. NR-in situ - γ -V: in situ silica, with γ-MPS, vulcanized

1 2 3 4

1

2

34

NR-V

γ-Mercaptopropyltrimethoxysilane

29Possibilities: Particle size distributionBlends with nano fillers

LILIANE BOKOBZA J. Polym. Sci. Part B: Polymer Physics, 46, 1939–1951, 2008

Improving filler-filler network formation with preservation of the strong filler-polymer interaction

by blends of conventional fillers + nano particles

Example: Carbon black + CNT’s

SBR compound

30

Possibilities of silica technologySummary

Silica/silane allowed to shift the magic triangle of tire performance

to a higher level: a promising start

Main functional difference with CB: strong (covalent) filler-polymer bond

Critical aspect: morphology (good distribution and dispersion,

strong polymer-filler interaction)

Challenge: Improved and stable polymer-filler network

Possibilities: + Surface modification of silica

+ Improved particle size distribution and structure

31

Acknowledgements

M. Tiwari

UT-ETE & Teijin Twaron

32

Thank you for your attention!Thank you for your attention!

Silica in rubberSilica in rubber ––Possibilities and ChallengesPossibilities and Challenges