Advanced Silica Characterization and Its Importance for In- Rubber Performance

Advanced Silica Characterization and Its Importance for In- Rubber Performance Asia RubTech Expo 2018 27-29 September 2018, Bengaluru, India J. C. Nian, Andre Wehmeier, Dr. Jens Kiesewetter 1

Content 1. Introduction Production of precipitated silica Analytical characterization and in-rubber dispersion of silica 2. General considerations CTAB SSA in-rubber data BET SSA in-rubber data 3. Morphology control Silica fingerprint & fine tuning In-rubber data 4. Summary & outlook 2

Introduction Production of Precipitated Silica Production step Main parameter Product property mainly influenced ater Glass ulfuric Acid Precipitation ph, temperature, concentration, time, dosage, mixing Specific surface area (SSA), particle size distribution (PaSD / nm), initial structure, surface activity (silanol groups) ter Cleaning Filtration Waste Water Treatment Filling, time, solid content Conductivity, initial structure, ph Drying Type of dryer, temperature, solid content, time Moisture content, initial structure, SSA, PaSD (nm mm) Milling / Granulation Packaging Feeding rate, pressure Sieve residue / fines, initial structure, PaSD (µm mm) 80 % of final silica properties are generated within the precipitation 4

Introduction Analytical Characterization Method Norm Description Influence on BET specific surface area ISO 9277 CTAB specific surface area ISO 5794/1G Adsorption of nitrogen: internal & external surface area Adsorption of CTAB: external surface area Green compound & vulcanizate properties LSA silica CTAB = 120 m²/g DBP / DOA number ISO 19246 Void volume: ability to absorb dibutyl phthalate / dioctyl adipate Initial structure important for dispersion Loss on drying (2 h / 105 C) ISO 787/2 Content of volatile components ph ISO 787/9 H + / OH - in aqueous solution Silica/Silane reaction; vulcanization Silica/Silane reaction; vulcanization HSA silica CTAB = 190 m²/g Conductivity ISO 787/14 Sieve analysis (Rotap) ISO 5794/1F Conductivity in aqueous solution: corresponds to the salt content Particle size distribution (µm mm) of granules Transparency of the compound Balanced granule stability (conveying) / guarantee good dispersion tapped density (ISO 787/11); ignition loss (2 h / 1000 C) (ISO 3262/11); SiO 2 content (ISO 3262/17); Fe, Mn, Cu (ISO5794/1 A-C); 5

Introduction Initial Structure Measured by Void Volume Void Volume test method in development status Reproducible & differentiating results First good correlations to OAN No. s Information about particle stability Soft- & hardware had to be improved Evaluation has to be different to ASTM norm for carbon black cover sample transmitted pressure sensor filler between cylinder & piston compressing sample measuring pressure calculating void volume cylinder piston applied pressure sensor 6

In-Rubber Dispersion of Silica Discussion: RPA 2000 - Dynamic Mechanical Rheological Tester Method Dynamical mechanical compound analysis Strain & frequency sweeps or single measurements at different temperatures on green compound & vulcanizates Preparation & time Sample preparation 30 sec. per sample automatically scanning Measurement time in dependency of the program Picture / device Information received Analyzing the Payne-effect & reinforcement mechanism Limitations Not useful for general dispersion measurements, since results are in dependency of the whole compound & different characteristics of it Value Sensitive tool for quality control & product development 7

In-Rubber Dispersion of Silica EVONIK Topography Method Method Mechanical surface scanning based on ASTM D 2663 Scanned area 5 mm² (1 mm x 5 mm) 100 profiles scanned in direct contact to the surface Height resolution 0.5 µm Transversal vs. longitudinal resolution 10 µm x 6.25 µm Preparation & time Sample preparation 2 to 3 min per sample 2 times 5 mm² => 2 times ca 30 min scanning Information received Macro-dispersion Topo defect / peak area Peak number in different height classes 2 µm 15 µm & > 15 µm Limitations Sticking could occur for very soft samples, especially when measuring green compounds Picture / device Value Independent of fillers used Independent of operator Independent of optical properties of the compound Quantitative, reproducible, differentiating Automated system for up to 80 samples 8

In-Rubber Dispersion of Silica EVONIK Topography Method Determination of silica dispersion by surface analyzer Correlation Evonik topography method / light optical method roughness / % 35 30 y= - 0.34 x + 34.7 R 2 = 0.96 25 20 15 10 5 Peak Area A def 0 20 30 40 50 60 70 80 90 100 DI / % 9

General Considerations CTAB SSA In-rubber Data 1 st stage phr Buna VSL 4526-2 TDAE / Oil-extended S-SBR 96,25 Buna CB 24 Nd-BR; cis1,4 > 96 % 30,00 Silica variable Si 266 5,80 ZnO RS RAL 844 C ZnO 3,00 Edenor ST1 GS Stearic acid 2,00 Vivatec 500 TDAE 10,00 Vulkanox HS/LG TMQ 1,50 Vulkanox 4020/LG 6PPD 1,50 Protektor G 3108 Wax 1,00 2 nd stage Batch 1 st stage 3 rd stage Batch 2 nd stage Rhenogran DPG-80 80 % DPG 2,50 Richon TBZTD OP TBzTD 0,20 Vulkacit CZ/EG-C CBS 1,50 Sulfur 80/90 Soluble sulfur 2,10 11 1 st stage Silica I 54 phr 0,0 GK 1.5 N, fill factor 0,74; 70 rpm; chamber temp.: 70 C 0,0 0,0 0,0 0,0 0,0 15,5 20,0 40,0 60,0 80,0 min:sec batchtemp.: 145 C - 155 C Silica II 120 phr 0,0 20,0 40,0 60,0 80,0 0,0 0,0 0,0 0,0 0,0 0,0 00:00-00:30 polymer Silica III 160 phr 80,0 60,0 40,0 20,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 00:30-01:30 1/2 silica; silane; ZnO; stearic acid; TDAE Silica IV 187 phr 0,0 0,0 0,0 0,0 0,0 80,0 64,0 60,0 40,0 20,0 0,0 01:30 clean; aerate Filler Volume phr 80,0 80,0 80,0 01:30-80,0 03:30 1/2 80,0 silica; 80,0 wax; 6PPD; 79,5 TMQ 80,0 80,0 80,0 80,0 Filler SA phr * m 2 / g 12800 12000 1120003:30 10400 clean; 9600 aerate 14960 12805 12300 9640 6980 4320 1 st stage GK 1.5 N, fill factor 0,74; 70 rpm; chamber temp.: 70 C min:sec batchtemp.: 145 C - 155 C 00:00-00:30 polymer 00:30-01:30 1/2 silica; silane; ZnO; stearic acid; TDAE 01:30 clean; aerate 01:30-03:30 1/2 silica; wax; 6PPD; TMQ 03:30 clean; aerate 03:30-05:00 keep temp. at 150 C by adjusting rpm 05:00 dump & check weight 45 s on open mill (4 mm nip), sheet out weigh compound for 2 nd step; storage 24 h / RT 2 nd stage GK 1.5 N, fill factor 0,71; 80 rpm; chamber temp.: 80 C min:sec batchtemp.: 145 C - 155 C 00:00-02:00 batch stage 1 CTAB m²/g 02:00-05:00 keep temp. at 150 C by adjusting rpm 05:00 dump & check weight 45 sec. on open mill (4 mm nip), sheet out weigh compound for 3 rd step; storage 4 h / RT 3 rd stage GK 1.5 N, fill factor 0,68; 40 rpm, chamber temp.: 50 C min:sec batchtemp.: 90 C - 110 C 1 2 3 4 5 6 7 8 9 10 11 03:30-05:00 keep temp. at 150 C by adjusting rpm 05:00 dump & check weight 45 s on open mill (4 mm nip), sheet out weigh compound for 2 nd step; storage 24 h / RT 2 nd stage GK 1.5 N, fill factor 0,71; 80 rpm; chamber temp.: 80 C min:sec batchtemp.: 145 C - 155 C 00:00-02:00 batch stage 1 02:00-05:00 keep temp. at 150 C by adjusting rpm 05:00 dump & check weight 45 sec. on open mill (4 mm nip), sheet out weigh compound for 3 rd step; storage 4 h / RT 3 rd stage GK 1.5 N, fill factor 0,68; 40 rpm, chamber temp.: 50 C min:sec batchtemp.: 90 C - 110 C 00:00-02:00 batch stage 2; accelerators; sulfur 02:00 dump batch; process on open mill 20 sec. with 3-4 mm nip cut 3 x left, 3 x right with 3 mm nip roll up & pass through a 3 mm nip 3 x sheet off; store for minimum 12 h before vulcanization

General Considerations CTAB SSA In-rubber Data 160 160 140 120 140 Mooney 2 nd stage / MU Mooney 2 nd stage / MU 110 100 90 Mooney 3 rd stage / MU Mooney 3 rd stage / MU 68 66 64 Shore - A Hardness / SH Shore-A-Hardness / SH 100 120 80 80 70 60 62 60 60 100 Active silica surface area (m 2 ) 40 0 2000 4000 6000 8000 10000 12000 14000 16000 140 80 130 60 120 DIN - Abrasion / mm 3 DIN Abrasion / mm³ 50 40 0 55 50 45 Active silica surface area (m 2 ) 2000 4000 6000 8000 10000 12000 14000 16000 Ball Rebound @ 23 C / % 58 Active silica surface area (m 2 ) 56 0 2000 4000 6000 8000 10000 12000 14000 16000 80 75 Ball - Rebound 70 C / % Ball Rebound @ 70 C / % 110 40 100 90 Active silica surface area (m 2 ) 80 0 2000 4000 6000 8000 10000 12000 14000 16000 Active silica surface area (m 2 ) 0 2000 4000 6000 8000 10000 12000 14000 16000 40 35 Active silica surface area (m 2 ) 30 0 2000 4000 6000 8000 10000 12000 14000 16000 70 65 Active silica surface area (m 2 ) 60 0 2000 4000 6000 8000 10000 12000 14000 16000 12

General Considerations CTAB SSA In-rubber Data 11 E* @ 60 C 10 (50 +/- 25 N; 16 Hz) 9 8 7 6 Active silica surface area (m 2 ) 5 0 2000 4000 6000 8000 10000 12000 14000 16000 0,15 0,13 tan d @ 60 C (50 +/- 25 N; 16 Hz) 106 104 102 100 98 96 LAT 100 wet skid rating @ 24 C / % Active silica surface area (m 2 ) 94 0 2000 4000 6000 8000 10000 12000 14000 16000 LAT 100 abrasion rating mean value / % Keeping the silane loading constant, the CTAB SSA & the filler loading are the key parameters for rubber reinforcement 102 100 98 96 94 92 90 88 Necessity for silane adjustment! 86 Active silica surface area (m 2 ) 84 8000 10000 12000 14000 16000 0,10 0,08 Active silica surface area (m 2 ) 0,05 0 2000 4000 6000 8000 10000 12000 14000 16000 13 Especially for high SSA silica it is necessary to adjust the silane content in order to ensure getting the full reinforcing potential & finally for the best abrasion resistance

General Considerations BET SSA In-rubber Data 77 Mooney-viscosity / MU 67 81 80 71 69 47,4 MDR M H / dnm 49,9 50,0 65 Static in-rubber data 79 77 67 67 80 20,5 22,0 22,0 CTAB SSA BET SSA 111 109 109 190 155 136 ML(1+4) at 100 C; 2nd stage ML(1+4) at 100 C; 3rd stage Dynamical in-rubber data 89 87 70,2 68,6 68,9 90 CTAB SSA 111 109 109 14,0 12,0 10,0 BET SSA 8,0 6,0 4,0 2,0 190 155 136 MH 160 C; 3 MH 160 C; 0.5 310 Tensile test (3 rings) 11,5 295 12,7 12,9 2,7 3,0 3,1 280 340 320 300 280 260 240 220 CTAB SSA BET SSA 111 109 109 190 155 136 Shore-A-hardness / SH DIN-abrasion / mm³ At constant CTAB SSA the BET SSA has an slight impact on the X-link density due to high accelerator affinity CTAB SSA BET SSA 111 109 109 190 155 136 Ball-Rebound, 60 C / % HBU; Flexometer, 0.225 inch, 25 min @ RT / C 0,0 200 CTAB SSA BET SSA 111 190 109 155 109 136 Modulus 100 % / MPa Modulus 300 % / MPa Elongation at break / % 14

Content 1. Introduction Production of precipitated silica Analytical characterization 2. General considerations CTAB SSA in-rubber data BET SSA in-rubber data 3. Morphology control Silica fingerprint & fine tuning In-rubber data 4. Summary & outlook 15

Morphology Control Silica Fingerprint & Fine Tuning Silica characterization by disc centrifuge measurements after strong US treatment Excerpt of a presentation of CPS Instruments Europe; with the permission of L.O.T.-Oriel GmbH & Co. KG Germany 16

Morphology Control Silica Fingerprint & Fine Tuning In principle several thousands of different precipitations can be done These can be abstracted to some very basic precipitation routes Two of these are shown in the following slides Precipitation type I Highly dispersible silica with moderate PaSD Standard silica high reinforcement potential Precipitation type II Highly dispersible silica with broader PaSD Improved RR & high reinforcement potential 17

Morphology Control Silica Fingerprint & Fine Tuning CTAB 85 m²/g CTAB 110 m²/g 1,0 relative weight 1,0 relative weight 0,8 0,8 0,6 0,6 0,4 0,4 0,2 CTAB 85 PPT I CTAB 85 PPT II 0,2 CTAB 110 PPT I CTAB 110 PPT II diameter / µm diameter / µm 0,0 0,0 0,0 0,1 1,0 10,0 0,0 0,1 1,0 10,0 Broader particle size distribution (PaSD) in the nm µm scale for precipitation PPT II 18

Morphology Control Silica Fingerprint & Fine Tuning 1,0 relative weight CTAB 160 m²/g 1,0 relative weight CTAB 200 m²/g 0,8 0,8 0,6 0,6 0,4 0,4 0,2 CTAB 160 PPT I CTAB 160 PPT II 0,2 CTAB 200 PPT I CTAB 200 PPT II diameter / µm diameter / µm 0,0 0,0 0,0 0,1 1,0 10,0 0,0 0,1 1,0 10,0 Broader particle size distribution (PaSD) in the nm µm scale for precipitation PPT II 19

Morphology Control Silica Fingerprint & Fine Tuning 1,0 0,8 relative weight Precipitation type I increasing CTAB 1,0 0,8 relative weight Precipitation type II increasing CTAB 0,6 CTAB 85 m²/g CTAB 110 m²/g 0,6 CTAB 85 m²/g CTAB 110 m²/g 0,4 CTAB 160 m²/g CTAB 200 m²/g 0,4 CTAB 160 m²/g CTAB 200 m²/g 0,2 0,2 diameter / µm 0,0 0,0 0,1 1,0 10,0 diameter / µm 0,0 0,0 0,1 1,0 10,0 For all silica a good correlation of SSA CTAB & BET (MP) is given PaSD in nm µm scale after strong US treatment good correlation to SSA The lower the SSA the broader the peak (d 75 ) & the higher the Mode 20

Morphology Control Silica Fingerprint & Fine Tuning Relative values / % (no rating); PPT II vs. PPT I (= 100 %) for different performance indicators 87 94 79 94 94 96 96 96 92 88 83 91 85 100 97 PPT I = 100 % CTAB stays to be the most important parameter, but fine tuning is possible via the PaSD 61 Processing & hysteresis loss can be improved by a broadened PaSD CTAB 85 m²/g CTAB 110 m²/g CTAB 160 m²/g CTAB 200 m²/g ML(1+4) at 100 C 2nd stage ML(1+4) at 100 C 3rd stage Payne-effect tan d (max) 21

Morphology Control Silica Fingerprint & Fine Tuning Relative values / % (no rating); PPT II vs. PPT I (= 100 %) for different performance indicators 112 107 96 83 101 98 94 99 98 97 97 98 97 99 101 100 PPT I = 100 % CTAB stays to be the most important parameter, but fine tuning is possible via the PaSD CTAB 85 m²/g CTAB 110 m²/g CTAB 160 m²/g CTAB 200 m²/g Shore-A-hardness Modulus 300 % Elongation at break DIN-Abrasion, 10 N Abrasion indicators might be improved by a narrower PaSD 22

Morphology Control Silica Fingerprint & Fine Tuning Equal PaSD fingerprint & analytical data, but different silanol group density 1,0 relative weight low Sears high Sears Specific Surface Area 0,8 CTAB m² / g 159 161 BET (MP) m² / g 169 170 Initial Structure ml / (100 g) DOA (Silica orig.) 195 201 0,6 0,4 low Sears ph -- 6,4 6,8 Moisture % 4,3 5,8 Sears No. 8,1 13,9 Amount KOH (moisture cor.) ml / (1,5 g) 8.1 13.9 high Sears 0,2 0,0 0,0 0,1 diameter / µm 1,0 Silanol group density varied to a great extent PaSD very close All other parameters are quite similar 23

Morphology Control Silica Fingerprint & Fine Tuning Equal PaSD fingerprint & analytical data, but different silanol group density 20 MDR isotherme @ 165 C; strain: 0.5 50 RPA isotherme @ 165 C; strain: 3 123 122 Mooney-viscosity / MU low Sears high Sears 18 16 14 torque / dnm Cure time: 20 min 45 40 35 torque / dnm Cure time: 20 min 12 30 67 64 10 25 50 49 8 6 Low Sears High Sears 20 15 Low Sears High Sears 4 10 ML (1+4) at 100 C 1st stage ML (1+4) at 100 C 2nd stage ML (1+4) at 100 C 3rd stage 2 5 0 time / min 0 10 20 30 40 0 time / min 0 5 10 15 20 25 Processing seems not be improved, but isotherms are effected @ low & high strains 24

Morphology Control Silica Fingerprint & Fine Tuning 3,5 3,0 2,5 G* / MPa Equal PaSD fingerprint & analytical data, but different silanol group density RPA strain sweep 0,3 42,0 %; 1,6 Hz 2 nd strain sweep 0,25 0,20 tan δ 2 nd strain sweep 18,2 20,3 18,2 20,3 Zwick, 16 Hz, 50 N +/- 25 N Zwick, 16 Hz, 50 N +/- 25 0,475 0,472 low Sears high Sears Zwick, 16 Hz, 5 low Sear high Sea 2,0 0,15 1,5 1,0 Low Sears 0,10 Low Sears High Sears 8,5 7,7 0,163 0,153 0,5 High Sears 0,05 8,5 7,7 0,0 strain / % 0 1 10 100 strain / % 0,00 0 1 10 100 E*, 0 C E*, 60 C Strain & force controlled measurements show a slightly increased stiffness & hysteresis loss for high Sears number silica tan d, 0 C tan d, 60 C 25

130 Morphology 125 Control Silica Fingerprint & Fine Tuning 120 115 110 LAT 100 WET rating / % Equal PaSD fingerprint & analytical data, but different silanol group density LAT 100: Wet rating / % LAT 100: Dry handling rating / % 105 100 95 90 Low Sears 85 High Sears 80 75 ambient temperature / C 70-10 10 30 50 70 Low Sears High Sears SFC 100 98 µ 100 102 Cornering 100 96 Handling 100 98 sfc = mean value of all side force coefficient ratings µ = maximum of the polynom of the 2 nd order cornering = gradient in the range of slip angles -3 to 6 handling = rel. rating(cornering stiffness)* rel. rating(friction coefficient) R 100 Wet & Dry behavior: Both silica behave within the error of measurement the same 26

Summary & Outlook Evonik is able to control the morphology of precipitated silica to a great extend The CTAB SSA stays to be the most important analytical parameter for in-rubber data The BET SSA has a slight impact on the X-link density due to the high accelerator affinity In-rubber dispersion can not be predicted by analytical parameters alone Only hints can be obtained by correlations to reference materials The silica fingerprint & fine tuning of it can be obtained by different precipitation routes At given conditions (type of polymer, other ingredients (esp. silanes), mixing equipment & curing) a broadened PaSD can improve processing & hysteresis loss a narrower PaSD can improve abrasion resistance indicators the silanol group density seems to have only slight influence New precipitation routes are in development to further adjust & improve in-rubber properties 28