CONDUCTIVE ELASTOMERS PARAMETERS AFFECTING THEIR PROPERTIES AND CONDUCTIVITY

CONDUCTIVE ELASTOMERS: PARAMETERS AFFECTING THEIR PROPERTIES AND CONDUCTIVITY C. Mangone, W. Kaewsakul, W. K. Dierkes, A. Blume Elastomer Technology and Engineering, Department of Mechanics of Solids, Surfaces and Systems, Faculty of Engineering Technology, University of Twente, The Netherlands M. Klein Gunnewiek, L. A. E. M. Reuvekamp Apollo Tyres Global R&D B. V. , Enschede, The Netherlands presented at Tire Technology Conference, Hannover, Germany March 06, 2019

1. INTRODUCTION MARKET TREND – NEW TYRE LABELLING European Regulation no. 1222/2009 Fuel Efficiency. Wet grip Ø The difference between F and A could reduce fuel consumption up to 7. 5%. Ø The difference between G and A could be up to 30% shorting braking distance. Ø For A class the proposed RR labels for C 1, C 2 and C 3 tyres are below 5. 4, 4. 4 and 3. 1 Kg/t respectively. Ø For A class the proposed WG labels for C 1, C 2 and C 3 tyres are above 1. 68, 1. 53 and 1. 38 respectively. . Noise Levels Snow and Ice grip 2 TERMA's position on the review of the Tyre Labelling proposal, 2018.

1. INTRODUCTION MARKET TREND – INFLUENCE OF FILLERS Magic Triangle High vinyl S-SBR / BR HR-Silica / Silane ü ü Higher wet grip (~7%) Lower rolling resistance (~30%) Reduced fuel consumption (~5%) Improved winter properties × Low conductivity E-SBR / Carbon Black The CB can promote the conductivity to rubber compounds! 3 EVONIK industries, Customer seminar, 2009.

1. INTRODUCTION IMPORTANCE OF THE CONDUCTIVITY FOR A TYRE A safer drive 1016 1014 1012 Diamond Carbon blackfilled polymer 108 106 104 102 Silicon 1 10 -2 10 -4 10 -6 Birla Carbon, Rubber Carbon Black Technology, 2017. Pank H. et al. , Prog. Polym. Sci. , 39, 2014. Glass 1010 Conductive Discharged static electricity for a tyre while rolling Electrostatic/ Dissipative Conductivity of a tyre Insulative Volume Resistivity (Ω∙cm) Gold, Copper, Silver 4

1. INTRODUCTION CONDUCTIVE MECHANISM - ELECTRON TUNNELING EFFECT Carbon black network Gaps for the electrons 10 -30 nm Fritzsche J. et al. , J. Phys. : Condens. Matter, Vol. 23, 11, 2011. Orion Engineered Carbons, 2012. 5

2. FACTORS INFLUENCING ELECTRICAL CONDUCTIVITY OVERVIEW CB properties CB loading CB filled rubber Polymer & processing CB = Carbon black Dispersion 6

2. FACTORS INFLUENCING ELECTRICAL CONDUCTIVITY CARBON BLACK LOADING Percolation theory Volume Resistivity (Ω∙cm) Percolation zone 1014 - 1018 Ω∙cm Insulating Zone 108 Ω∙cm <102 Ω∙cm Conductive Zone ϕc Liu X. , Ph. D thesis, Friedrich-Alexander University of Erlangen-Nurnberg, Germany 2016. ϕ (wt%) 7

2. FACTORS INFLUENCING ELECTRICAL CONDUCTIVITY CARBON BLACK PROPERTIES Morphology of carbon black Structure of carbon black particles Spheroidal Branched Ellipsoidal Linear Araby S. et al. , Nanotechnology, Vol 26, 23 2015. Martinez R. F. , Comput. Mater. Sci, Vol 91, 2014. 8

2. FACTORS INFLUENCING ELECTRICAL CONDUCTIVITY DISPERSION OF CARBON BLACK Possible structure and surface area of carbon black dispersed in an elastomeric matrix Requirements and challenging: - Very good dispersion of carbon black - Low amount of conductive carbon black is needed - High structure and high surface area of CB are required to minimize its amount used - Very efficient technique to mix the compound is challenging 9 http: //www. cabotcorp. com/solutions/applications/industrial-rubber-products/dispersion

2. FACTORS INFLUENCING ELECTRICAL CB PROPERTIES - PARTICLE SIZE AND STRUCTURE OF CARBON CONDUCTIVITY BLACK CB/EPDM composites Volume Resistivity (Ω∙cm) 1016 Basic properties of carbon blacks used 1014 1012 1010 108 D C 106 104 A B C D E CTAB [m 2/g] 23 23 24 31 40 DBP [ml/100 g] 90 102 114 130 121 Mean agg size [nm] 362 343 339 295 240 A B E - Sulphur cure - Internal mixer with dump temperatures at 100 -160 o. C 102 100 50 140 70 80 90 100 110 120 130 140 ϕ, phr 10 Niedermeier W. et al. , KGK Kautschuk Gummi Kunststoffe, 2003.

2. FACTORS INFLUENCING ELECTRICAL CONDUCTIVITY CB PROPERTIES – SHAPE Multiwalled Carbon Nanotubes d=10 nm l=1. 5 mm - High surface area (250 -300 m 2/g) - High aspect ratio - Improvement of mechanical properties, especially strength - Excellent electrical properties Volume Resistivity (Ω∙cm) 1014 1012 • • 1010 108 106 104 100 0 Mensah B. et al. , International Journal of Smart and Nano Materials, Vol. 6 , 211, 2015. Sulphur cure Solution blending using a sonication process 1 2 4 5 6 ϕ (phr) 8 10 11

2. FACTORS INFLUENCING ELECTRICAL CONDUCTIVITY CB PROPERTIES – SHAPE Graphite 0, 14 nm • • - High surface area (2630 m 2/g) High aspect ratio (0, 188) Improvement of mechanical properties, especially strength Excellent electrical properties 1016 Log ρ (Ω∙cm) 0, 34 nm 1018 • 1014 SR Silicone rubber Room temperature curing agent Solution blending using a sonication process 1012 1010 108 0 1 2 3 4 5 ϕ, wt% 12 Sadasivuni K. K. Et al. , Progress in Polymer Science, 39, 2014.

2. FACTORS INFLUENCING ELECTRICAL CONDUCTIVITY POLYMER TYPE AND PROCESSING METHOD Percolation Threshold of MWCNT/elastomeric composites Rubber Processing Percolation threshold SBR Dry mixing (IM) 5 phr SBR/BR Dry mixing (IM) <3 wt% SBR/NBR Dry mixing (IM) ~1 wt% NR/NBR Dry mixing (IM) 2 phr IIR Dry mixing (IM) 6 -8 phr CR Dry mixing (IM) 5 phr CR Dry mixing (two-roll mill) 3 phr NR Dry mixing (two-roll mill) 9 -16 wt% NR Solvent 0, 5 -1 phr EPDM Solvent 4 phr SBR Solvent 2 -3 phr IM = Internal Mixer 13 Mensah B. et al. , International Journal of Smart and Nano Materials, Vol. 6, 211, 2015.

2. FACTORS INFLUENCING ELECTRICAL CONDUCTIVITY POLYMER PROPERTIES § Chemical similarity between carbon black surface and polymer chain o e. g. chemical nature, macrostructure of chain, surface energy distribution § Viscosity (preferably low) § Compatibility of polymer blend affects the migration of filler particles Mostafa A. et al. , Journal of Testing and Evaluation, Vol. 38, 347, 2010. Jiang Z. et al. , Colloids and Surfaces A: Physicochem. Eng. Aspects, Vol. 395, 105, 2012. Bokobza L. , ESPCI Paris. Tech, 2012. 14

3. ELECTRICAL CONDUCTIVITY UNDER STATIC STRAIN SETUP 15

3. ELECTRICAL CONDUCTIVITY UNDER STATIC STRAIN UNIAXIAL TENSION CB/NR composites Resistivity ρ, Ω∙cm • 70 phr CB Alignment of aggregates Breakdown of agglomerates Extension ratio Yamaguchi K. et al, Journal of Polymer Science: Part B Polymer Physics, Vol. 41, 2079, 2003. Breakdown of filler agglomerate structure under strain N 330 BET (m 2/g) 78 DBP (ml/100 g) 102 16

3. ELECTRICAL CONDUCTIVITY UNDER STATIC STRAIN LOADING/UNLOADING CB/NR composites 10 phr of CCB Log Resistivity ρ, Ω∙cm 50 phr CB N 330 Extension ratio N 330 CCB BET (m 2/g) 78 1000 DBP (ml/100 g) 102 370 Jha V. et al. , Journal of Applied Polymer Science 116, 2010. CCB = conductive carbon black 17

4. ELECTRICAL CONDUCTIVITY UNDER DYNAMIC STRAIN SETUP DMA Breadboard Voltage Power module Supply Voltage module Sample DMA Breadboard Power Supply 18

4. ELECTRICAL CONDUCTIVITY UNDER DYNAMIC STRAIN TIME SWEEP CCB/S-SBR composites S-SBR CCB 12 phr 25% vinyl - 25% styrene BET = 1000 m 2/g DBP = 420 ml/100 g • • Sulphur cure system Internal mixer Bhagavatheswaran E. S. et al. , 190 th Technical Meeting of Rubber Division ACS, 2016. CCB = conductive carbon black 19

4. ELECTRICAL CONDUCTIVITY UNDER DYNAMIC STRAIN TIME SWEEP Tan δσ-ε Tan δσ-R Sinusoidal trend of resulting stress (linear viscoelasticity) and resistance. 20 Bhagavatheswaran E. S. et al. , 190 th Technical Meeting of Rubber Division ACS, 2016.

4. ELECTRICAL CONDUCTIVITY UNDER DYNAMIC STRAIN TEMPERATURE SWEEP CCB/S-SBR composites □ 12 phr CCB ○ 13 phr CCB 21 Bhagavatheswaran E. S. et al. , 190 th Technical Meeting of Rubber Division ACS, 2016.

5. CONCLUSIONS § The electrical conductivity of a tyre promoted by carbon blacks can improve the dissipation of static charge accumulated on the tread surface § The factors influencing the electrical conductivity of an elastomer are: Ø Loading level of CB: above the percolation threshold Ø CB properties: high surface area and high structure Ø Filler dispersion: very good dispersion is desired Ø Polymers & processing: good affinity and interaction with CB, good technique to disperse the carbon black particles § The conductivity of carbon black-filled elastomer composites can be monitored under both static and dynamic circumstances 22

ACKNOWLEDGEMENTS § Apollo Tyres Global R&D B. V. (Enschede, The Netherlands) for the permission to present this work § Dr. Michel Klein Gunnewiek, Dr. Louis Reuvekamp and the other colleagues of Apollo Tyres for the scientific support § Dr. Wisut Kaewsakul, Dr. Wilma Dierkes, Prof. Anke Blume, Andries van Swaaij and the other colleagues of ETE

THANK YOU FOR YOUR ATTENTION Carmela Mangone c. mangone@utwente. nl carmela. mangone@apollotyres. com