Macromolecular Materials and Engineering Full Paper Filler Wetting in Miscible ESBR/SSBR Blends and Its Effect on Mechanical Properties Hai Hong Le,* Katrin Reincke, Amit Das, Klaus-Werner Stöckelhuber, Swen Wiessner, Tung Pham, Quang Khang Do, Xuan Tung Hoang, Wolfgang Grellmann, Gert Heinrich, Hans-Joachim Radusch The selective wetting behavior of silica in emulsion styrene butadiene rubber (ESBR)/solution styrene butadiene rubber (SSBR) blends is characterized by the wetting concept, which is further developed for filled blends based on miscible rubbers It is found that not only the chemical rubber–filler affinity but also the topology of the filler surface significantly influences the selective filler wetting in rubber blends The nanopore structure of the silica surface has been recognized as the main reason for the difference in the wetting behavior of the branched ESBR molecules and linear SSBR molecules However, the effect of nanopore structure becomes more significant in the presence of silane It is discussed that the adsorption of silane on silica surface constricts the nanopore to some extent that hinders effectively the space filling of the nanopores by the branched ESBR molecules but not by the linear SSBR molecules As a result, in silanized ESBR/SSBR blends the dominant wetting of silica surface by the tightly bonded layer of SSBR molecules causes a low-energy dissipation in the rubber–filler interphase That imparts the low rolling resistance to the blends similar to that of a silica-filled SSBR compound, while the ESBR-rich matrix warrants the good tensile behavior, i.e., good abrasion and wear resistance of the blends Introduction “Green” passenger car (PC) tires were first introduced in the 1990s by using silane-treated silica instead of the Dr H H Le, Dr A Das, Dr K.-W Stöckelhuber, Prof S Wiessner, Prof G Heinrich Leibniz-Institut für Polymerforschung Dresden e.V., D-01069 Dresden, Germany E-mail: le-haihong@ipfdd.de Dr H H Le Institut für Polymerwerkstoffe D-06217 Merseburg, Germany Dr K Reincke, Prof W Grellmann, Prof H.-J Radusch Polymer Service GmbH Merseburg D-06217 Merseburg, Germany Prof S Wiessner, Prof G Heinrich Technische Universität Dresden Institut für Werkstoffwissenschaft D-01062 Dresden, Germany 414 Macromol Mater Eng 2016, 301, 414−422 © 2016 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim traditional carbon black as reinforcing filler in tread compounds As a result, significant reduction of the tire rolling resistance could be achieved.[1–6] Regarding the rubber part in PC tire treads, synthetic rubbers like butadiene Prof T Pham Hochschule Albstadt-Sigmaringen D-72458 Albstadt-Ebingen, Germany Prof Q K Do Institute of Chemistry Vietnamese Academy of Science and Technology Hanoi, Vietnam Dr X T Hoang University of Technology National University Ho Chi Minh City, Vietnam wileyonlinelibrary.com DOI: 10.1002/mame.201500325 Macromolecular Materials and Engineering Filler Wetting in Miscible ESBR/SSBR Blends and Its Effect on Mechanical Properties www.mme-journal.de rubber (BR), emulsion styrene butadiene rubber (ESBR), and solution styrene butadiene rubber (SSBR) represent the indispensable polymer matrix ESBR is the most widely used rubber in the world, representing about 30% of the synthetic rubber market This kind of rubber polymer has an excellent balance of properties and cost performance as well as processability For tire application, important properties like tensile strength, tear resistance, and abrasion resistance, as well as aging resistance can be achieved by use of ESBR Furthermore, ESBR is typically known for its broad molecular weight distribution that makes the processing easier Its biggest disadvantage is related to a very high rolling resistance and poor filler interaction Recently, SSBR with linear molecular structure and narrow molecular weight was found to give the tire tread compounds the better grip on snow and ice as well as much lower rolling resistance.[7,8] However, SSBR is more expensive and difficult to be processed than ESBR Concerning the interest of tire manufacturers, i.e., lowering the rolling resistance by maintaining the wet grip and wear resistance and improving the processability one can propose ESBR/SSBR blends filled with silica, which can combine the advantages of ESBR and SSBR It is well known that the dynamic properties of tire tread compounds are strongly influenced by the filler– polymer interaction and consequently by the structure of the polymer–filler interphase.[9] According to Heinrich and Vilgis,[10] the differences in microstructure between ESBR and SSBR cause differences in polymer–filler interphase, which leads to the different dynamic behavior of their silica-filled compounds Indeed, silica represents a structure having pores on its surface in the nanometer region.[11] Due to its branching structure, ESBR does not effectively penetrate the silica nanopores leading to a weak polymer–filler interaction The weak interlocking might be responsible for a much larger amount of dissipated energy during dynamic-mechanical excitation of the rubber tread compound during rolling of the tire In contrast, the easy wetting of linear SSBR inside nanopores during mixing leads to a tight rubber–filler interlocking This kind of strong polymer–filler interaction causes a low contribution to energy dissipation during dynamicmechanical excitation Owing to this knowledge, the synergetic effect of the ESBR/SSBR blends can be achieved only if a special structure of the blend is formed, i.e., a structure comprising an SSBR-rich polymer–filler interphase and ESBR-rich matrix In our previous works we developed a wetting concept for quantifying the selective wetting behavior of filler in binary and ternary blends containing immiscible rubbers.[12–15] In this work, the wetting concept is further developed for characterization of the selective silica wetting in miscible ESBR/SSBR blends The correlation between the microstructure of filled ESBR/ SSBR blends and mechanical properties will be discussed www.MaterialsViews.com Experimental Section Materials and Sample Preparation: ESBR used was BUNATMSB 1500—Schkopau (Trinseo Deutschland GmbH) with a styrene content of 23.5% Mooney viscosity ML 1+4 (100 °C) is 50 MU SSBR used was SPRINTAN SLR4602 (Trinseo Deutschland GmbH) with a styrene content of 21% and vinyl content of 63% Mooney viscosity ML 1+4 (100 °C) is 65 MU Silica used was Ultrasil 7000 GR (Evonik) with specific surface area CTAB = 160 m2g−1 and BET = 170 m2g−1, pH-value 6.8 Bis(triethoxysilylpropyl) polysulfide (TESPT) Si69 (Evonik) and 3-Octanoylthio-1-propyltriethoxysilane NXT (Crompton) were used as coupling agents Silica-filled SBR compounds and blends with and without silane were prepared in an internal mixer Plasticorder PL 2000 (Brabender) according to Table Rotor speed of 50 rpm and fill factor 0.7 were chosen for all the mixtures Initial chamber temperature TA was varied and the corresponding dumping temperature TE was recorded A package of curing additives containing stearic acid, zink oxide (ZnO), sulphur, N-cyclohexyl2-benzothiazole sulfenamide (CBS), and diphenylguanidine (DPG) was used in all the mixtures In all formulations, the content of rubber, filler, and ingredients was given in phr (parts per hundred rubber) Samples were taken out during the mixing process at different times for further investigation Samples taken out at 30 mixing time were compression-molded at 150 °C and 100 bar for t90 to obtain a sheet used for mechanical testing Tensile Test: Stress–strain measurements were performed according to ISO 37 using a tensile tester Z005 (Zwick/Roell) with a cross-head speed of 200 mm min−1 at room temperature The test specimens had a thickness of mm and an initial gauge length of 50 mm All data presented are the average of five measured specimens for each sample Dynamic Mechanical Analysis (DMA): DMA was performed by means of a mechanical spectrometer Eplexor 150 N (Gabo) Temperature sweep measurements were carried out from −100 to 100 °C at a heating rate of K min−1 and at a frequency of Hz The specimens of size 25 × 10 × mm3 were stamped out from the cross-linked samples Fracture Toughness Characterization: The materials were characterized regarding their crack toughness by using the instrumented tensile-impact test (ITIT) Principal details on this test can be found in.[16,17] The tests were carried out on double edge notched specimens (DENT) with dimensions length L = 64 mm, width W = 10 mm, thickness B = mm and initial notch depth a = mm.[18] The instrumented pendulum device RESIL IMPACTOR Junior (CEAST) was used with a pendulum hammer with a maximum working capacity of 7.5 J at maximum falling angle (150°), corresponding to a test speed of 3.7 m s−1 The initial gauge length was 30 mm For each vulcanizate, the load (F)–extension (l) diagrams of 10 specimens were recorded and analyzed As a result, Jd values were determined, which describe the materials resistance against crack propagation Surface Tension Measurements: Sessile drop contact angle measurements on a sheet of lightly cured rubber were conducted with the automatic contact angle meter OCA 40 Micro, DataPhysics Instruments GmbH, Filderstadt, Germany The surface energies were calculated from the results of these wetting experiments For this purpose a set of test liquids with different Macromol Mater Eng 2016, 301, 414−422 © 2016 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim 415 Macromolecular Materials and Engineering H H Le et al www.mme-journal.de Table Mixing regime of silica-filled SBR compounds and blends Mixing time Ingredient Content [phr] Mixing conditions ESBR or SSBR or ESBR/SSBR blend with varied ratios 100 TA = 50 °C Silica 50 n = 50 rpm Silane or ZnO 2.5 Stearic acid Step 10 Stopped and dumped: batch Dumping temperature TE = 90 °C Step 10 15 TA = 140 °C n = 50 rpm Batch Stopped and dumped: batch Dumping temperature TE = 152 °C Step 15 Batch 25 Sulfur 1.5 TA = 50 °C CBS 1.4 n = 50 rpm DPG 1.4 30 Stopped and dumped: batch surface tension (and polarity) was used: water, formamide, dodecane, and ethanol Surface energy calculations were performed by fitting the Fowkes Equation.[19] Experimental Determination of Filler Wetting in Rubber Compounds and Blends: For the investigation of the rubber–filler gel of the compounds and blends, 0.1 g of each raw mixture was stored for seven days in 100 ml toluene at room temperature The rubber–filler gel was taken out and dried up to a constant mass The rubber content in the gel LESBR and LSSBR as well as LB(ESBR/SSBR) as a measure for the wetting behavior of silica surface by ESBR and SSBR as well as ESBR/SSBR blend, respectively, is determined according to Equation (1)[12] L= m2 − m1 ⋅ c F m2 (1) The mass m1 is corresponding to the rubber compound before extracting m2 is the mass of the rubber–filler gel, which is the sum of the undissolvable rubber part and the mass of silica cF is the mass concentration of silica in the single rubber mixture or binary blends For ESBR/SSBR blend the rubber layer LB(ESBR/ SSBR) is the rubber part in the rubber–filler gel and consists of two contributions according to Equation (2) LB(ESBR/SSBR)(t ) = LB(ESBR)(t ) + LB(SSBR)(t ) (2) LB(ESBR) and LB(SSBR) can be determined by means of a calibration curve For creation of the calibration curve, blends with different ESBR/SSBR ratios were prepared and investigated by FTIR FTIR spectra were recorded by use of an FTIR spectrometer S2000 (Perkin Elmer) equipped with a diamond single Golden Gate Figure a) FTIR spectra of the neat ESBR and SSBR and b) correlation between the surface ratio AESBR(964)/ASSBR(907) and the mass ratio ESBR/ SSBR 416 Macromol Mater Eng 2016, 301, 414−422 © 2016 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim www.MaterialsViews.com Macromolecular Materials and Engineering Filler Wetting in Miscible ESBR/SSBR Blends and Its Effect on Mechanical Properties www.mme-journal.de ATR cell (Specac) Two neat rubbers show clearly a strong peak at 964 cm−1, which is assigned to vibration trans-1,4 butadiene unit, and a peak at 907 cm−1, which is attributed to vibration of vinyl1,2 butadiene unit (Figure 1a) Taking a closer look at the spectra, it is clear that the intensity of the peak at 964 cm−1 is stronger in ESBR than in SSBR, while the peak at 907 cm−1 is weaker in ESBR than in SSBR The difference in intensity of these two peaks can be used for identification of ESBR and SSBR in their blends The correlation between the peak area ratio AESBR(964)/ASSBR(907) and the given mass ratio ESBR/SSBR presented in Figure 1b is not described by a straight line as we often observed for other systems containing immiscible rubber components reported in our previous works.[12–15] Thus, the ratio LB(ESBR)/LB(SSBR) in the rubber–filler gel can be determined manually using the calibration curve presented in Figure 1b The selective wetting of silica in ESBR/SSBR blend can be calculated according to Equation (3) and (4): S B(ESBR)(t ) LSSBR LB(ESBR)(t ) P = ⋅ S B(SSBR)(t ) LESBR LB(SSBR)(t ) P (3) S B = S B(ESBR)(t ) + S B(SSBR)(t ) (4) SB(ESBR) and SB(SSBR) are the silica surface fractions wetted by ESBR and SSBR component of blend, respectively t is the mixing time SB is the total filler surface wetted in blend LPESBR, LPSSBR and LPB(ESBR/SSBR) are the saturated rubber contents in the gel of the single compounds and blend, respectively They can be determined from extraction experiments of the samples taken out at 30 mixing time Results and Discussion 3.1 Theoretical Prediction and Experimental Determination of the Selective Wetting of Silica in ESBR/SSBR Blends When silica is mixed into a rubber blend, both rubber components compete with each other to wet silica On the basis of the Z-model proposed in our previous work [20] the filler surface fraction wetted by blend components of a binary ESBR/SSBR blend at an equilibrium state can be predicted using Equations (5) and (6) B(ESBR) ⎛ γ SSBR + γ F − γ SSBRγ F ⎞ Seq B(SSBR) = nESBR/SSBR ⎜ ⎟ Seq ⎝ γ ESBR + γ F − γ ESBRγ F ⎠ B(ESBR) B(SSBR) S B = Seq + Seq (5) (6) SeqB(ESBR) and SeqB(SSBR) are the filler surface fractions wetted by each blend component at an equilibrium state nESBR/SSBR is the mass ratio of the rubber phase ESBR to SSBR, respectively γESBR, γSSBR, and γF are the surface tension values of the blend components and filler, respectively Setting the surface tension values γESBR = 24.3 mN m−1 and γSSBR = 24 mN m−1 of rubber components, which were www.MaterialsViews.com Figure Prediction of the selective wetting of silica by ESBR in 50/50 ESBR/SSBR blend experimentally determined, into Equations (5) and (6) with nESBR/SSBR = for the investigated blend, a Z-shaped master curve demonstrating the filler surface fraction wetted by ESBR component in dependence on the filler surface tension can be created as seen in Figure By fitting the surface tension γF = 73 mN m−1 of the nonmodified silica[21] to the master curve a surface fraction of silica wetted by ESBR phase SeqB(ESBR) = 0.517 was predicted for 50/50 ESBR/SSBR blend Upon the silanization process the surface tension of silica reduces to a value γF = 45 mN m−1[15] because of the hydrophobization of the silica surface Fitting this value to the master curve, a value SeqB(ESBR) = 0.52 was determined Based on this result, it can be obviously predicted that ESBR and SSBR show the same affinity to silica surface and the same wetting behavior An addition of silane will not show any effect on the wetting behavior of both rubbers The kinetics of silica wetting in 50/50 ESBR/SSBR blends was experimentally characterized by the wetting concept according to Equations (3) and (4) According to Equation (1), the plateau values of rubber layer LPESBR and LPSSBR were determined from the extraction experiment for filled ESBR and SSBR compound collected at 30 LPESBR = 0.27, LPSSBR = 0.52 were determined indicating that ESBR forms a thin rubber layer on the silica surface, while SSBR presents a thick rubber layer bound to silica surface As seen in Figure 3a the silica surface fractions SB(ESBR) and SB(SSBR) wetted by ESBR and SSBR molecules, respectively, increase immediately after adding 50 phr silica into 50/50 ESBR/SSBR blend without silane It is clear that SSBR wets silica faster than ESBR in the first mixing stage (up to 15 min) The branching structure of ESBR may be the reason for its slow filler wetting due to Macromol Mater Eng 2016, 301, 414−422 © 2016 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim 417 Macromolecular Materials and Engineering H H Le et al www.mme-journal.de Figure Kinetics of silica wetting in 50/50 ESBR/SSBR blend in a) absence and b) presence of silane the steric hindrance In the second mixing stage from 15 to 30 min, the fraction SB(ESBR) gradually increases, while SB(SSBR) remains unchanged and at 30 silica is wetted homogeneously by both blend components This result is well corresponding to the prediction and attributed to the fact that the same chemical affinity of silica to both rubbers is essential for filler wetting at longer mixing time, while the differences in rubber microstructure (branching and linear) influence the kinetics of filler wetting at short mixing period It is well known that the absorption of the non-rubber impurities of ESBR to silica surface may contribute to the wetting behavior of silica by rubbers However, the wetting of silica by both rubbers investigated is the same at the end of the mixing process that leads to the conclusion that in our investigation the silica wetting is insignificantly influenced by the nonrubber impurities of ESBR As the compatibility between silica and rubbers is low, a reduction of the polarity difference can commonly be achieved by silane coupling agents such as NXT and Si69 as done in this work The effect of NXT and Si69 on the kinetics of selective silica wetting in ESBR/SSBR blend is obviously seen in Figure 3b The silica surface fraction SB(ESBR) increases and reaches a plateau value of 0.32 after mixing time, while SB(SSBR) continuously increases up to 15 and reached a plateau value of 0.68 A preferential wetting of silica by SSBR in presence of silane cannot be explained by taking into consideration the chemical rubber–filler affinity, because the chemical affinity of silica to both rubbers is similar For explanation of this feature, the behavior of linear chains (SSBR) and branched chains (ESBR) in silica pores should be taken into consideration When a polymer molecule is forced into a small pore and the space available for the polymer is restricted, a minimum pore size hmin through which the branched polymer is able to pass through was introduced by Heinrich and Vilgis[10] according to Equation (7) hmin ≈ N ( D−1)/2 ≡ M ( D−1)/2 D 418 (7) where M ∼ ND is the mass of the branched polymer The spectral dimension D was introduced for a natural generalization of the stretched length of a branched polymer object.[22] The minimum pore size for linear polymers is independent of the molecular weight, i.e., linear polymers (D = 1) pass through a very small pore if hmin is of the order of the Kuhn segment radius For branched polymers (1 < D < 2) the minimum pore size hmin becomes larger Based on the wetting behavior of silica in ESBR/SSBR blend in the absence and presence of silane, the effect of silane can be explained as illustrated in Figure It can be postulated that in the case of the absence of silane the pore size is larger than the hmin and the space filling by ESBR is nearly not disturbed (Figure 4a) By addition of silane the silica surface is covered by a thin layer of silane, which constricts the pores to an extent that the branched polymers cannot penetrate the pores as seen in Figure 4b In other words, the unaccessible space for ESBR becomes larger, when silane is used In contrast, the linear SSBR molecules can easily penetrate the small pores and wet silica inner surface well even in presence of silane, i.e., the presence of silane does not enlarge the unaccessible space for SSBR As a result, the presence of silane will reduce the silica surface fraction wetted by ESBR and increase the silica surface fraction wetted by SSBR in their blends Figure 5a represents the silica surface fraction SB(ESBR) and SB(SSBR) by variation of ESBR fraction in ESBR/SSBR blends It is obvious that in all blends the silica surface is dominantly wetted by the SSBR component The structure of the blends investigated can be illustrated in Figure 5b showing morphology with a SSBR-rich interphase and ESBR-rich matrix DMA of silica-filled ESBR/SSBR blends with varied blend ratios was performed The tanδ-temperature curves of different blends with NXT are presented in Figure 6a ESBR shows a glass transition at the temperature TG = −41 °C and SSBR at TG = −11 °C All ESBR/SSBR blends show only one transition peak that indicates the Macromol Mater Eng 2016, 301, 414−422 © 2016 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim www.MaterialsViews.com Macromolecular Materials and Engineering Filler Wetting in Miscible ESBR/SSBR Blends and Its Effect on Mechanical Properties www.mme-journal.de Figure Illustration of the wetting of silica pores by ESBR and SSBR molecules a) without and b) with silane miscibility of them in molecular level The tanδ value at °C, which is a measure for wet grip of a tire, is determined by the glass temperature of the matrix The tanδ at °C of all the blends lies between those of ESBR and SSBR component The tanδ at 60 °C is considered as a measure for the rolling resistance of a tire and is mainly determined by the internal friction caused in the polymer–filler interphase This discussion is related to hindered dynamics of polymer segments in the vicinity of filler surfaces, leading to the formation of a coating layer of immobilized glassy polymer.[23–28] Gusev[9] used a finite element method and showed that both storage and dissipation energies are strongly localized in these coating layers Wang et al[29] also stated that the tanδ strongly depends on the interfacial layer Due to the loose interlocking between branched ESBR molecules and silica surface a high internal friction is generated in the rubber–filler interphase during cyclic deformation that leads to a high value of the tanδ at 60 °C as seen in Figure 6a.[10] The tight interlocking between linear SSBR and silica surface is the reason for the low value of tanδ at 60 °C and internal friction of silicafilled SSBR compound (Figure 6a) With increasing ESBR fraction in the blend up to a fraction of 0.4, the value of tanδ at 60 °C of blends remains unchanged at the level Figure a) SB(ESBR) and SB(SSBR) in dependence on the ESBR fraction in blends and b) the suggested morphology of silica-filled ESBR/SSBR blends showing an SSBR-rich interphase and ESBR-rich matrix www.MaterialsViews.com Macromol Mater Eng 2016, 301, 414−422 © 2016 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim 419 Macromolecular Materials and Engineering H H Le et al www.mme-journal.de Figure Temperature dependence of a) tan δ of blends with different ESBR/SSBR mass ratio in presence of NXT and b) tan δ at 60 °C in dependence on the ESBR fraction in blend of that of the SSBR single compound (Figure 6b) That is related to the fact that the silica surface is mainly wetted by the SSBR with a tight interlocking Passing the ESBR fraction of 0.4, the silica surface fraction SB(ESBR) wetted by ESBR starts to increase and contribute markedly to the increase of tanδ at 60 °C Both silanes used, NXT and Si 69, show the similar effect on the tanδ at 60 °C, however, the extent made by Si69 is stronger than that of NXT Without silane, ESBR and SSBR compound present higher values of tanδ at 60 °C The tanδ at 60 °C of unmodified 50/50 ESBR/SSBR blend is the average value of those of ESBR and SSBR compound (Figure 6b), i.e., no synergetic effect was achieved in the absence of silane According to Figure 3a, in this blend, silica is wetted homogeneously by ESBR and SSBR Thus, the internal friction generated in the rubber– filler interphase results from contributions by both rubbers This finding again emphasizes the role of the interfacial phenomena and the selective wetting of the filler surface in the dynamic properties of filler rubber compounds The tensile behavior of ESBR and SSBR compounds as well as of the 50/50 ESBR/SSBR blend is presented in Figure 7a The stress and strain at break of the SSBR compound are much lower than those of the ESBR compound The result is related to the narrow molecular weight distribution of linear SSBR compared to the broad molecular weight distribution of branched ESBR The 50/50 ESBR/SSBR blend presents a tensile behavior, which approaches the level of ESBR and much better than that of SSBR The stress at break and strain at break of ESBR/SSBR blends with different blend ratios are presented in dependence on ESBR fraction in Figure 7b With increasing ESBR fraction up to 0.5, the stress at break of blends increases strongly and reaches the level of ESBR at an ESBR fraction of 0.5 After that the stress at break remains unchanged with increasing ESBR fraction The Jd-values, which are a measure of the crack resistance of the investigated blends, are presented in Figure in dependence on the ESBR fraction For both blend series modified with NXT and Si69, respectively, Jd increases with increasing ESBR fraction and it reaches the high Figure a) Stress–strain curves of silica-filled ESBR and SSBR compound as well as 50/50 ESBR/SSBR blend, and b) stress and strain at break of ESBR/SSBR blends with varied blend ratios 420 Macromol Mater Eng 2016, 301, 414−422 © 2016 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim www.MaterialsViews.com Macromolecular Materials and Engineering Filler Wetting in Miscible ESBR/SSBR Blends and Its Effect on Mechanical Properties www.mme-journal.de the good tensile behavior, i.e., good abrasion and tearing resistance of the blends Acknowledgements: The authors wish to thank the Deutsche Forschungsgemeinschaft (DFG) (Project Nr LE 3202/1–1) and Vietnam National Foundation for Science and Technology Development (Nafosted) (Grant number 104.02–2014.90) for the financial support Received: September 9, 2015; Revised: November 9, 2015; Published online: January 29, 2016; DOI: 10.1002/mame.201500325 Keywords: mechanical properties; rubber blends; selective filler wetting Figure Jd values of silica-filled ESBR/SSBR blends with varied blend ratios level of the ESBR compound at a ESBR fraction of 0.5 The similar dependence of the fracture behavior of blends on the blend mass ratio when compared with the tensile results would lead to a conclusion that the tensile and fracture properties of the filled blends are determined mainly by the matrix, while the dynamic properties are significantly influenced by the rubber–filler interphase The tensile and fracture behavior is strongly connected also to other important properties for such as tearing and wear resistance as well as abrasion resistance Therefore, a combination of high strength and high crack toughness should be given as for such materials as a pre-condition for the use in tire treads Conclusions In this work, the wetting concept was further developed for experimental determination of the selective wetting behavior of silica in miscible rubber blends It was found that in non-silanized miscible blends made up by ESBR and SSBR the silica surface is wetted by the linear SSBR molecules faster than ESBR molecules as a result of the branching structure of ESBR molecules However, after long mixing time both rubbers wet silica surface in the same extent In this case, the nanostructure of silica surface with nanopores influences only the kinetics of rubber wetting in the early state of mixing but not the end state In contrast, in silanized blends the adsorption of silane on silica surface constricts the nanopores, thus their space filling by ESBR is significantly hindered due to its branching structure The dominant wetting of silica surface by the tightly bonded SSBR molecules imparts the blends the low rolling resistance compared to silica-filled SSBR compound, while the ESBR-rich matrix warrants www.MaterialsViews.com [1] B T Poh, H Ismail, K S Tan, Polym Test 2002, 21, 801 [2] P Sae-oui, Ch Sirisinha, T Wantana, K Hatthapanit, J Appl Polym Sci 2007, 104, 3478 [3] H Ismail, B T Poh, K S Tan, M Moorthy, Polym Int 2003, 52, 685 [4] L Qu, G Yu, L Wang, Ch Li, Q Zhao, J Li, J Appl Polym Sci 2012, 126, 116 [5] Y C Ou, Z Z Yu, A Vidal, J B Donnet, Rubber Chem Technol 1994, 67, 834 [6] N Suzuki, M Ito, F Yatsuyanagi, Polymer 2005, 46, 193 [7] S Thiele, S Rulhoff, (Styron Europe GmbH), W O Patent No 2011/079922A1, 2011 [8] S Thiele, S Knoll, S Rulhoff, (Styron Europe GmbH), W O Patent No 2011/076377A1, 2011 [9] A A Gusev, Macromolecules 2006, 39, 5960 [10] G Heinrich, T A Vilgis, Kautsch 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KGaA, Weinheim www.MaterialsViews.com Macromolecular Materials and Engineering Filler Wetting in Miscible ESBR/ SSBR Blends and Its Effect on Mechanical Properties www.mme-journal.de ATR cell... Weinheim www.MaterialsViews.com Macromolecular Materials and Engineering Filler Wetting in Miscible ESBR/ SSBR Blends and Its Effect on Mechanical Properties www.mme-journal.de Figure Illustration