Silica systems to modulate the compromise reinforcement / hysteresis for the silica filled elastomers

Transcription

1 Silica systems to modulate the compromise reinforcement / hysteresis for the silica filled elastomers S. Daudey, L. Guy (Rhodia) Introduction / General silica review The main functions are : Absorption : as carrier or anti-caking for feed / food nutrition Abrasion / thickening : as active ingredient for toothpaste, paper, cement, etc. Reinforcement : as reinforcing filler for rubber applications (shoe sole, technical goods and.green tire) 2 1

2 Introduction / Highly Dispersible Silicas as reinforcing filler In the 9 s, the modification of the PC Tire Tread using the combination of a highly dispersible silica, a coupling agent, a specific elastomer and an adapted rubber process technology enabled the development of the Green Tire RR Environmental benefits and Energy saving: -5% on fuel consumption (around -1 g saved CO2 / km) 8 WR 6 WG CB (1 index) Std SiO2 HDS The higher the better 3 Agenda Chemistry of the high performance silicas Precipitated silica, the main criteria impacting reinforcement. Precipitated silica, the main criteria impacting hysteresis. Perspectives and Conclusions 4 2

3 Chemistry of the high performance silicas FORMING MORPHOLOGY INTERFACE 5 Chemistry of the high performance silicas Amorphous Precipitated Silica types Mainly processed from sand and sodium carbonate, With no specific hazard for Human Health and no significant toxicity for Environment. 6 3

4 Chemistry of the high performance silicas Chemical Reaction First step of the process x SiO 2 + Na 2 CO 3 (SiO2) x,na 2 O + CO 2 SAND SODIUM CARBONATE SODIUM SILICATE Second step of the process (an acido-basic reaction) (SiO2) x,na 2 O + H 2 SO 4 x SiO2 + Na 2 SO 4 + H 2 O SULFURIC ACID PRECIPITATED SILICA SODIUM SULFATE 7 Chemistry of the high performance silicas precipitation Sulfuric Acid Process Sand Sodium carbonate slurry mixing chamber Dilution filtration washing Vitrous Silicate Furnace 14 C Liquid Silicate Cake liquefaction grinding compacting micronisation Finished product: amorphous precipitated Silica Dissolution Spray Drying storage 8 4

5 Chemistry of the high performance silicas Precipitated silica can be proposed under different physical forms : Powder, which is the classical and primarily form, obtained by classical drying Granule,, which is a compacted powder. Makes handling much easier Micropearl,, which is obtained directly using a specific drying process. 9 Chemistry of the high performance silicas Aspect, granulometry and morphology ASPECT granulate 5 µm to few mm micropearl agglomerate to break under high shear stress Morphology aggregate mechanically unbreakable = Reinforcing filler elementary particule 5 to 3 µm grinded particule 1 to 1 µm 1 to 5 µm 5 to 4 nm 5 to 4 nm COMPOSITION SiO2 (amorphous), hydrated surface 1 5

6 Chemistry of the high performance silicas Filler - Aggregates morphology, - Elementary particle size, - Inter-aggregat distance, - Level of dispersion. Rubber(s) matrix - Tg, Mw, Mn, MMD - Fonctionnalisation, - Level of reticulation. Interface (matrix / filler) - Surface activity of the pure filler, - Nature of the interfacial molecule (coupling or not), - Nature of the rubber composition. The management of the Silica nature is possible with variations in : 1 Morphology (aggregate size, porosity,..), 2 Surface activity (specific surface area, energy surface,.). 11 Chemistry of the high performance silicas One important characteristic for the reinforcing object: aggregate size linked to the rubber matrix. Morphology Aggregates size Zeosil 185 GR Aggregate size - dw (nm) by XDC) Zeosil 1115 MP Zeosil Premium 2 MP Zeosil 1165 MP ZHRS 12 MP Specific Surface area - CTAB (m²/g) - Possibility to get a compromise between the aggregate size and the specific surface area. 12 6

7 Chemistry of the high performance silicas Morphology Hg porosimetry Case of Z1165MP 3.5 INTRAPARTICULAR POROUS VOLUME INTERPARTICULAR POROUS VOLUME cumulated porous volume (ml/g) pore diameter (µm) For reinforcement, only the second step (pores below 1 µm) is interesting. 13 Chemistry of the high performance silicas Interface Surface chemistry Silica surface modelling (Rhodia) 6 x 6 nm 2 TGA silanols condensation free and physically adsorbed water moisture 5 C/min Temperature ( C) loss of weight (%) A surface chemistry based on : -water, - hydrophylic species (silanols) 14 7

8 Chemistry of the high performance silicas Interface Surface chemistry- exemples 1 Low OH silica Z1115MP Z1165MP 95 Loss mass % 9 free and physically adsorbed water moisture silanols condensation Temperature C Correlation with dielectric measurements see M Kluppel, L Guy Macromolecules (28) 15 Chemistry of the high performance silicas A surface chemistry useful for surface properties management Interface Surface chemistry Silica surface modelling (Rhodia) Chemical species on the Silica surface From A Legrand, «The Surface Properties of Silicas», Wiley ed. Which means : - absorption of ingredients (like vulcanization system), - use of an interfacial agent in order to interact with the hydrophobic media. 16 8

9 Chemistry of the high performance silicas Interface Silanols characterization NMR- 29 Si - MAS FT-IR Low OH silica Z1165MP SiOSi network Si Isolated Silanols Terminal Silanols Internal Silanols Vicinal Silanols OH Si Single silanol Pyrogenated silica Z 1165MP Low OH silica HO Si OH Geminated silanol <> (ppm) The nature and the amount of the silanols groups at the silica surface permit to manage the interface with the rubber matrix. 17 Chemistry of the high performance silicas Interface Energetic approach Define the chemical structure of the silica is not sufficient, we NEED to have information about the energy surface due to the interactions with the elastomers (containing alkene, aromatic groups) «simple» approach like dispersive component or wetting angle more interesting way : energetic site distribution even after silane grafting. 18 9

10 Chemistry of the high performance silicas 35 3 The value of the surface energy γ s, that explains the capacity of the filler surface to interact with a defined molecule, can be decomposed in : γ s D : dispersive component (related to the filler / rubber interaction), γ s P : polar or specific component (related to the filler or polar molecules / filler interaction). The Inverse Gas Chromatography at infinite dilution (IGC-ID - Papirer / Donnet) permits to obtain the corresponding values with several probes (only high energetic sites). Dispersive components (mj/m2) at 11 C for Silicas and 22 C for CB Dispersive 4 35 Interface Dispersive energetic data Polar (acid/base) Specific interaction parameter or ISP (kj/mol) - Acidic nature of the filler surface : Ether - Basic nature of the filler surface : Chloroform N234 Z1115MP Z1165MP N234 Z1115MP Z1165MP CHCl3 - Acidic probe Ether - Basic probe 19 Chemistry of the high performance silicas Interface Distributions energetic data From IGC at finite dilutions, a distribution of the energetic sites can be obtained : to compare fillers (precipitated silicas vs carbon black), to evaluate the impact of a surface treatment (interfacial agent,...). CBET (n.u.) BET constant : Interaction probe / surface Probe : alkane Probe : alkene Probe : Isopropanol Z1165MP N234 Z1115MP Z1165MP / TESPT Distribution of energetic sites (µmol/(kj/mol)) Energetic site distributions N234 Z1165MP Z1115MP Z1165MP/TESPT,16 PROBE : ALCENE,14,12,1,8,6,4,2, Activation Energy (kj/mol) Interaction between dienic elastomer & free silica surface even after grafting. 2 1

11 Chemistry of the high performance silicas Interface Free silica interface Observations about the silica surface From the calculus on 6-8 Si-OH / nm2, 1.2 at Si /nm2 functionalized by the silane, From Inverse Gas Chromatography (Blume - IRC25) after OTES grafting, 7% of free silica surface From Molecular Modelling of the Silica Surface (6 * 6 nm 2 ) functionalized by the silane (Rhodia), the free silica surface could be accessible to the polymer chains. Even after grafting with a silane, around 5-7% of the silica surface remains free to be in interaction with the elastomeric chains (isoprene / styrene / butadiene / vinyl-1,2) 21 Chemistry of the high performance silicas Conclusions Filler - Aggregates morphology, - Elementary particle size, - Inter-aggregat distance, - Level of dispersion. Rubber(s) matrix - Tg, Mw, Mn, MMD - Fonctionnalisation, - Level of reticulation RR Interface (matrix / filler) - Surface activity of the pure filler, - Nature of the interfacial molecule (coupling or not), - Nature of the rubber composition WR 6 CB (1 index) Std SiO2 HDS WG 11

12 Chemistry of the high performance silicas Perspectives The impact of the morphology / interface parameters for the silica will be explored to modulate the duality : reinforcement versus hysteresis WITH 5 SILICAS Very low SSA Low SSA Reference HDS High SSA High aggregate size High SSA Name Zeosil 185Gr Zeosil 1115MP Zeosil 1165MP Zeosil Premium 2 MP ZHRS 12MP Characteristics TYPICAL ANALYSIS* CTAB (m2/g) 8 11 Amorphous precipitated BET (m²/g) Agenda Chemistry of the high performance silicas Precipitated silica, the main criteria impacting reinforcement. Precipitated silica, the main criteria impacting hysteresis. Perspectives and Conclusions 24 12

13 Precipitated silica, the main criteria impacting reinforcement. Rubber / Filler reinforcement : 1- High level of the dispersion / distribution of the filler 2- High level of interactions between the rubber and the filler Case of the Silica Filler 1- Reduction of the defects => Interest of highly dispersible silicas 2- Improvement of the affinity between silica (hydrophilic / polar) and elastomer (ssbr non polar) : - Creation of a covalent link => Use of a coupling agent (silane like TESPT, ) - Optimization of the number of links => Specific surface area / Morphology (aggregate size and shape). 25 Precipitated silica, the main criteria impacting reinforcement / Dispersion The dispersion of the silica impacts greatly the reinforcing behavior of the vulcanized rubber tread compound First rubber/filler disruptions Z1165MP+CA Conventional silica 16 m²/g + CA 2 4 deformation direction 21µm 21µm The dispersion of the silica impacts greatly the reinforcing behavior of the vulcanized rubber tread compound. 13

14 Precipitated silica, the main criteria impacting reinforcement / Impact of the silica polymer coupling During compounding, silica has to be compatibilized with the polymer. A coupling agent (silane - CA) is required to keep a strong interaction at high strains. 8 Secant Modulus N 347 Z 1165MP Z 1165MP + TESPT Strong interface Low debounding 3 Weak interface 2 1 Formation of Vacuoles Strain 27 Precipitated silica, the main criteria impacting reinforcement / Specific surface area The specific surface area will drive : the total surface of the filler in contact with the polymer. Total surface using BET N 2 Accessible by the rubber, AND by some rubber polar ingredients. External surface using CTAB Accessible by the rubber Target : BET N 2 surface CTAB surface To reduce the trapping and the absorption of the chemicals 28 14

15 Precipitated silica, the main criteria impacting reinforcement / Specific surface area At the same volumic fraction, a higher specific surface area silicas gives more covalent bonds between filler and elastomer through the coupling agent: More efficient stable links between filler and matrix (Z1165MP > Z185GR), Z1165MP (8 phr) / TESPT Z185GR (8 phr) / TESPT CTAB = 16 m2/g CTAB = 8 m2/g Stress (MPa) N33 (8 phr) Strain (%) 29 Precipitated silica, the main criteria impacting reinforcement / Morphology The shape and the size of the objects (aggregates) will, as far as they are well coupled, play a major role onto the final rubber properties: Zeosil 185 GR Aggregate size - dw (nm) by XDC) Zeosil 1115 MP Zeosil Premium 2 MP Zeosil 1165 MP ZHRS 12 MP Specific Surface area - CTAB (m²/g) - The new family (Z Premium 2 MP), obtained with an original morphology allowing to achieve a high specific surface area together with high dispersibility associated to bigger aggregates. 3 15

16 Precipitated silica, the main criteria impacting reinforcement / Morphology At the same volumic fraction, the modification of the aggregate size in association with a good level of dispersion allows a change in the reinforcing behavior: 25 2 Stress strain 8 phr CTAB = 2 m2/g CTAB = 2 m2/g 15 CTAB = 16 m2/g 1 Z1165MP 8phr 5 Z Premium 2 MP8phr ZHRS 12MP 8phr Precipitated silica, the main criteria impacting reinforcement. Rubber / Filler reinforcement : 1- High level of the dispersion / distribution of the filler 2- High level of interactions between the rubber and the filler Case of the Silica Filler 1- Reduction of the defects => Interest of highly dispersible silicas 2- Improvement of the affinity between silica (hydrophilic / polar) and elastomer (ssbr non polar) : - Creation of a covalent link => Use of a coupling agent (silane like TESPT, ) - Optimization of the number of links => Specific surface area / Morphology (aggregate size and shape)

17 tan d tan d Agenda Chemistry of the high performance silicas Precipitated silica, the main criteria impacting reinforcement. Precipitated silica, the main criteria impacting hysteresis. Perspectives and Conclusions 33 Precipitated silica, the main criteria impacting hysteresis When a filler is added in the rubber matrix, an increase of the dynamic sweep (,1% to 1%) deals to a reduction of the modulus (no-linearity Payne Effect) and the apparition of a maximum for the loss factor Tan δ max - Loss factor Tan δ Loss factor Tan δ Elastic modulus G 1,6 1,4 1,6 1, ,2,2 1,2 Elastic modulus (Pa) 1,,4,6 1,,8,8 1,,8 1 7,6,4,2-3,, -2,5-2, -1,5-1, -,5 Log (def), Température 1,2 1,4 1,6 Impact T/ε%,6,4,2-3,, -2,5-2, -1,5-1, log (def) -,5, température -3, 1 6-2,5-2, -1,5-1, -,5 Deformation amplitude , 8 Temperature - C - As the level of dynamic strains is representative of the Tire operating range (Rolling resistance / Wet Traction), need to go deeper in the understanding of the Payne Effect 34 17

18 Precipitated silica, the main criteria impacting hysteresis. Rubber / Filler hysteresis : 1- High level of the dispersion / distribution of the filler 2- Low level of interactions between the rubber and the filler Case of the Silica Filler 1- Homogenization of the distance between aggregates => Interest of highly dispersible silicas 2- Low level of energetic affinity between silica (hydrophilic / polar) and elastomer (ssbr non polar) : - Reduction of the total engaged surface btw silica / rubber => Specific surface area & Amount of silica - Limitation of the rubber layer with reduced mobility => Nature & Amount of the interface agent (silane,..) / Morphology (aggregate size and shape). 35 Precipitated silica, the main criteria impacting hysteresis / Low level of energetic affinity with Silica Storage modulus G' (MPa) Storage modulus and loss T = 4 C 2,5E+7 2,E+7 1,5E+7 1,E+7 5,E+6,E+,1,1,1,1 1 Strain CB 347 Z1165MP,5,4,3,2,1 Loss factor Storage modulus / surface contact area for 1g of rubber G / contact area for 1g of rubber 3 E E E + 3 E +, 1, 1, 1,1 1 S tra in C B Z M P Lower Payne Effect and hysteresis with Silica vs Carbon Black (without interface agent for Silica)

19 Precipitated silica, the main criteria impacting hysteresis / Low level of energetic affinity with Silica Inverse Gas finite dilution (probe = alkene) N234 Z1165MP Z1115MP Z1165MP/TESPT Probe : alkane Probe alkene,16 6 Distribution of energetic sites (µmol/(kj/mol)),14,12,1,8,6,4,2 PROBE : ALCENE CBET (n.u.) ,4 49,1 Interaction between the filler surface and the alkene ("rubber") is divised by a factor of 3 as observed for the values of tan d and G'. 15,4 15,9 14,4 4,7 5,2 5,4, Activation Energy (kj/mol) N234 Z1115MP Z1165MP Z1165MP / TESPT The more dissipative interface for the CB vulcanizates (related to the silica ones) could be due to the existence of much higher energetic sites on the filler surface, For the silica, the absorption of the alkene/alkane probes is not perturbed by the addition of a coupling agent (1.2 atom of Si from TESPT / nm2). 37 Precipitated silica, the main criteria impacting hysteresis / Reduction of the total engaged surface btw silica / rubber Loss factor at 4 C (T > Tg + 5 K) in function of the Silica Engaged Surface (SSA_CTABxQ) Tan d max at 4 C for the same amount of CBS (2 phr),6,5,4,3 Z1165MP/TESPT Z1115MP/TESPT N234 No filler,2, Engaged surface x (d_silica/d_silica or d_carbonblack) in m2 The filler amount variation has a very negative impact for CB compounds while for silica there is a small change in the tan δ value

20 Precipitated silica, the main criteria impacting hysteresis / Reduction of the total engaged surface btw silica / rubber Tan δ at 4 C Payne effect (G ) at 4 C,3 1,E+7,25 CTAB = 16 m2/g Z1165MP (8 phr) + TESPT Z1115MP (8 phr) + TESPT Tan d,2,15,1 CTAB = 8 m2/g Z1165MP (8phr) + TESPT Elastic modulus - G' (Pa) Z185Gr (8 phr) + TESPT,5 Z1115MP (8phr) + TESPT Z185Gr (8phr) + TESPT,,1% 1,% 1,% 1,% Dynamic strain (%) 1,E+6,1% 1,% 1,% 1,% Dynamic strain (%) The SSA decrease (Z1165MP > Z1115MP > Z185GR ) induces a reduction of the Payne Effect & tan δ. 39 Precipitated silica, the main criteria impacting hysteresis / Reduction of the total engaged surface btw silica / rubber PARADOXE : At the same total surface (2 x 8), Z Premium 2 MP reduces hysteresis and Payne Effect at 4 C compared to Z HRS12MP. Tan δ at 4 C Payne effect (G ) at 4 C,3,28 1,E+8 8 phr CTAB = 2 m2/g 8 phr,26,24,22,2,18,16 CTAB = 16 m2/g CTAB = 2 m2/g Elastic modulus (Pa) 1,E+7,14,12,1 Z1165MP Zeosil Premium 2MP Z HRS12MP % 1% 1% 1% Dynamic Strain 1,E+6 Z1165MP Zeosil Premium 2MP Z HRS12MP % 1% 1% 1% Dynamic Strain WHY? 4 2

21 Precipitated silica, the main criteria impacting hysteresis / Limitation of the rubber layer with reduced mobility Loss factor at 4 C (T > Tg + 5 K) in function of the Silica Engaged Surface (SSA_CTABxQ),5 Tan d max- 4 C - 1 Hz - Shear from 5 % to.1 %,45,4,35,3 Z1165MP Z1115MP Z Premium 2 MP,25,2,15,1,5, SQ With Z Premium, the SxQ criteria is no longer a good predictor for the tan δ max. Is it possible to find a criteria able to align std HDS and Premium? 41 Precipitated silica, the main criteria impacting hysteresis / Limitation of the rubber layer with reduced mobility d min Φ = dw Φ 1/3 M agr agr 1 Filler,5,45 Tan d max- 4 C - 1 Hz - Shear from 5 % to.1 %,5,45 Tan d max- 4 C - 1 Hz - Shear from 5 % to.1 %,4,35,3 Z1165MP Z1115MP Z Premium 2 MP,4,35,3 Z1165MP Z1115MP Z Premium 2 MP,25,25,2,2,15,15,1,1,5,5, SQ,, 5, 1, 15, 2, 25, 3, dmin _ aggregat-aggregat(nm) Taking into account the pseudo-fractal shape, a master curve is obtained whatever the silica family. The minimal distance between aggregates seems to play a major role

22 Precipitated silica, the main criteria impacting hysteresis / Limitation of the rubber layer with reduced mobility Extension to the Payne Effect (elastic modulus) 1 8 Tan δ max 1,4 5, G (= G o G oo) at 4 C DGprim (MPa) - 4 C - 1 Hz - Cisaillement - 5 % <-->,1% G'o 1,2 4, Z1165MP_TESPT G (Pa) 1 7 1,,8 Tand 3, Z1115MP_TESPT Z Premium 2MP_TESPT,6 G' = G'o - G'oo G'oo,4 2,,2 1 6, 1E-3,1,1 1 Deformation amplitude 1,,, 5, 1, 15, 2, 25, 3, minimal distance btw aggregates (nm) At T = 4 C (T > Tg + 5K), existence of a critical minimal distance (d*min) where the amplitude of the Elastic Modulus G is close to. d*min near 25 3 nm (with ssbr525-1) (Similar to Tokita s results (KGK ) using Carbon Black rubber compounds) 43 Precipitated silica, the main criteria impacting hysteresis / Limitation of the rubber layer with reduced mobility The Z Premium 2 MP - a shifted product - allows to show interesting behavior in dynamic properties (linked to Rolling Resistance) : ❶ Minimal distance between aggregates (d min ) is a key factor to explain the variation of the dissipative energy component and leads to a full silica mastercurve, ❷ Obtention for the silica aggregates of a critical minimal distance (d* min ) at around 25-3 nm where the variation of the Payne Effect seems strongly reduced. Based on the approach of the rubber layer with reduced mobility due to silica interface, developed by F. Lequeux, D. Long, P Sotta, the existence of confined elastomeric segments between silica aggregates seems to plays as an additional dissipative energy source. e(t,ω) Tg( ω) e( T, ω) = δ T Tg( ω) γ 44 22

23 Precipitated silica, the main criteria impacting hysteresis. Rubber / Filler hysteresis : 1- High level of the dispersion / distribution of the filler 2- Low level of interactions between the rubber and the filler Case of the Silica Filler 1- Homogenization of the distance between aggregates => Interest of highly dispersible silicas 2- Low level of energetic affinity between silica (hydrophilic / polar) and elastomer (ssbr non polar) : - Reduction of the total engaged surface btw silica / rubber => Specific surface area & Amount of silica - Limitation of the rubber layer with reduced mobility => Nature & Amount of the interface agent (silane,..) / Morphology (aggregate size and shape). 45 Agenda Chemistry of the high performance silicas Precipitated silica, the main criteria impacting reinforcement. Precipitated silica, the main criteria impacting hysteresis. Perspectives and Conclusions 46 23

24 CONCLUSION - The control of the interface Rubber / Silica The chemistry of the precipitated silicas have been exposed, Used as reinforcing filler for the rubber compounds, the precipitated silicas with different specific surface areas allow to fine tune the mechanical and dynamic properties. With a high level of dispersion, the Z Premium 2 MP a shifted product - leads to improve our Payne effect understanding, with the introduction of the interaggregates minimal distance parameter. (see L. Guy, Ph. Cochet, Y. Bomal, S. Daudey KGK, 62 (7-8), 383 (29) & KGK, 58 (1-2) 43 (25), H. Montes, T Chaussée, A Papon, F Lequeux, L. Guy, Eur. Phys. J. E 31, (21)), A Papon, H. Montes, F Lequeux, L. Guy, J Polym Sci Part B Polym Phys, 48, (21), S. Merabia, P Sotta, D Long, J Polym Sci Part B Polym Phys, 48, (21)) 47 THANKS for your ATTENTION 24