EFFECTS OF ZINC SOAPS ON TESPT AND TESPD-SILICA MIXTURES IN NATURAL RUBBER COMPOUNDS

Transcription

1 STP0219 Paper No. 70 EFFECTS OF ZINC SOAPS ON TESPT AND TESPD-SILICA MIXTURES IN NATURAL RUBBER COMPOUNDS By Kwang-Jea Kim* John VanderKooi Struktol Company of America Polymer Processing & Additives R&D Stow, OH Presented at a meeting of the Rubber Division, American Chemical Society Pittsburgh, PA October 8-11, 2002 *Speaker

2 EFFECTS OF ZINC SOAPS ON TESPT AND TESPD-SILICA MIXTURES IN NATURAL RUBBER COMPOUNDS Kwang-Jea Kim* and John VanderKooi Struktol Company of America, Polymer Processing & Additives R&D Stow, OH ABSTRACT A zinc ion containing surfactants (ZB47 and ZL) were added into the TESPT (bis(triethoxysilylpropyl) tetrasulfide)/silica and the TESPD (bis(triethoxysilylpropyl) disulfide)/silica and their effects in the NR (isoprene rubber) compounds were investigated based on processability, rheology, and mechanical properties. The zinc surfactants improved the mechanical property, torque between maximum and minimum, modulus of the compounds, and reduced the cure time; and lowered the viscosity, tanδ values, heat generation during mixing in the internal mixer, reverting cure behavior, ODR minimum torque, viscosity, maximum tensile stress, and maximum elongation%. The modulus of long time cure specimens exhibited lower than that of the regular ones. The most significant improvement was found from the blowout experiment with the addition of the zinc surfactants. The ZB47 added compounds (S4/ZB47, S2/ZB47) exhibited lower heat generation during mixing, lower Mooney viscosity, and longer BO time than the ZL added compounds (S4/ZL, S2/ZL). * Corresponding author. Ph: ; Fax: ; kkim@struktol.com 1

3 INTRODUCTION The processing agents are classified as hydrocarbons, fatty acid derivatives, synthetic resins, low molecular weight polymers, and organic thio compounds depending on their chemical structures. Their effects are subdivided into as peptization, dispersion, flow, homogenization, tack, high hardness, and release etc. 1. Several additives such as fatty acid esters act as lubricant and dispersing agents. Bifunctional organosilanes, which containing sulfur have been studied to improve the processability at the mixing stage and to improve the chemical bonding between silica and rubber chain at the vulcanization stage 2,3. Silanes such as TESPT (bis(triethoxysilylpropyl)tetrasulfide) and TESPD (bis(triethoxysilylpropyl)disulfide) had been used in the green tire tread compound as a processing aids during mixing and acted as a chemical bonding agent at the vulcanization stage between silica and rubber matrix due to their bifunctional characteristics. On the one end of the alkoxy group reacts with the silanol group on the silica surface via hydrolysis mechanism 4-7. The other end of the sulfur reacts with the double bond of the rubber chain at the vulcanization stage 8 and covalently bonds between silica and rubber chain 9. Studies on green tire compounds using silane were mainly based on the SBR/BR compounds Green tire exhibits low rolling resistance, good wet and snow traction 10,18, which improves low gas mileage, good grip on road surface, respectively. However, silica particle exhibited more difficult to process and disperse in rubber matrix than other particles 13,19,20 due to their polar and hydrophobic character 21,22. There have been works to disperse the silica agglomerates mechanically, chemically, and physically etc. 14,23-31, however, there were few researches of polysulfidic silane treated silica compound in the NR matrix. The NR compounds have been used in the area of airplane tire, winter tire, fork lift tire, and medium and heavy-duty truck tire industries due to their abrasion, cutting, tear, rolling resistance, and adhesion on steel surface. They also used in the area of building s vibration absorption against earthquake 32. Zinc soaps such as zinc stearate, zinc laurate, zinc tallowate, zinc naphthenate, zinc resinate, and zinc 2-ethylhexanoate are currently used in the rubber compounds as additives. Depending on their structure such as carbon chain length, chain length distribution, polarity, and branching, their final product property varies. Most zinc soaps act as an intermolecular lubricant because they are rubber soluble. They improve surfactant action as their hydrocarbon chain length increased longer than ten-carbons. Unsaturated zinc soap such as zinc tallowate improves dispersibility. Even though large amount of zinc containing additives are used in the industry now, there were few systematic theory or researches 33 on the zinc soap illustrated above. We present the effects of the zinc soaps (ZB47 and ZL) on TESPT and TESPD treated amorphous precipitated silica compounds in the NR compound during mixing and after vulcanization. Processability and mechanical properties of each compound were compared. 2

4 EXPERIMENTAL Materials The silanes used in this study were the TESPT and the TESPD trade name SCA98 and SCA985, which were a product of Struktol. The zinc blends used in this study were ZB47 and ZL. The ZB47 and the ZL are commercial product from Struktol Co. America, which is a class of zinc soap blend 33. The elastomer used was natural rubber (polyisoprene rubber), which was a Goodyear product by the brand name of SIR-20. The silica used was ZS 1165MP, which is amorphous precipitated silica with BET area (m 2 /g) supplied by Rhodia Silicas. Various additives including activator, processing aids, anti oxidant, homogenizer, WB222, Stanplas 2000, curing agent, and accelerators were used. The information on the materials used in this study was summarized on Table I. Mixing The mixer used for compounding of rubber and additives was Banbury internal mixer (BR 1600), which equipped with a data acquisition computer to obtain the data at the time of mastification. Two stage mixings were carried. The first stage was master batch (MB) mixing, compounds rubber, silica, and additives. At the second stage, sulfur and other accelerators were added into the MB compound. The fill factor was fixed at 0.7 and the starting operation temperature of mixer was set to 65.5 o C. The rotor speed was set to 77 RPM. The stock temperature changes during MB mixing were recorded in the computer and the data were analyzed. The mixing formulations and vulcanizations are included in Table II. Mooney (Shearing Disc) Viscosity Measurement Shearing Disc Rheometer; Following ASTM D1646, Mooney viscosities were measured as a function of apparent shear rate at 0.7 (1/s) [0.2 rad/sec, 2rpm] and ML1+4 at 100 o C. The viscosity was measured in a pressurized rotational rheometer with a shearing disc rotor. The rotor diameter of the shearing disc rheometer is 38.1mm and the thickness of the rotor is 5.5mm. The machine we used for measuring Mooney viscosity was brand name Mooney Viscometer 2000 (MV 2000) manufactured from Monsanto Co. The shear rate and shear stress were given by 34,35 γ ( R) = RΩ H 3M σ 12 = (2.1a,b) 3 4πR 3

5 where R is the shearing disc radius, Ω is the angular velocity, H is the distance between the disc surface and the stationary housing, and M is the torque. The viscosities of each compound after 90 days mixing were measured and compared with each compound after 1 day mixing, respectively. Reversion Test Rheometer ODR (oscillating disc cure meter) 2000 manufactured from Monsanto Co. was used measuring vulcanization and reversion resistance property of the compounds following ASTM D 2084 at 160 o C. This instrument measures the vulcanization characteristics of vulcanizable rubber compounds at a constant speed in a pressurized rotational biconical rotor. The oscillation frequency was 1.66 Hz with amplitude of 3 o. Minimum torque (M L ), maximum torque (M H ), torque rise (M H -M L ), scorch time (Ts2), cure time (Tc90), and reversion resistance time (T-2) were measured. Viscoelastic Property (Tanδ) After Vulcanization Vulcanized materials were characterized using Mechanical Energy Resolver (MER-1100B) manufactured by Instrumentors, Inc. This instrument measures oscillatory input of axial tension/compression response of the cylindrical specimen. The average dimension of the cylindrical specimen was diameter 17.5mm and length 25.5mm, respectively. The temperatures and frequency measured the specimen were 23 o C and 100 o C, and 1Hz, respectively. Oscillatory tension/compression signal responses depending on material were measured as follow 36 σ = (E +ie ) ε =E* ε E (ω) = E* cosδ E (ω) = E* sinδ = ωη el E* = (E 2 + E 2 ) 1/2 = E [1 + (tanδ) 2 ] 1/2 (2.5a,b,c,d) where E* is the complex dynamic modulus, E (ω) is the real dynamic modulus, E (ω) is the imaginary dynamic modulus, δ is the phase angle, ω is the oscillation frequency, and η el (ω) is the elongational viscosity. Tensile Test Instron Universal Testing Instrument (Model4201) was used obtaining tensile data. The tensile test curves were obtained from the dumbbell shaped specimens measured following ASTM D method at 23 o C. The cross-head speed of the moving part was set to 50.8cm/min and the tensile stress maximum (Pa), elongation at 100, 200, and 300%, and modulus (Pa) of each compound was measured. The thickness and the width of the specimens were average 2.2mm and 6.3mm, respectively. Longtime cure specimen (Tc90x4) and short-time cure specimen (Tc90x1) were prepared and compared. 4

6 Heat Build Up (HBU) and Blowout (BO) Test The Firestone Flexometer 37 was used measuring HBU and BO of the sample as of ASTM D 623. This is a testing apparatus for applying a uniform compressive circulatory oscillating action onto specimen. The test specimen is located between the fixed upper part and the moving bottom part. While the upper part pressurizes the specimen, the bottom part is circulatory oscillating at a constant speed of 13.1 Hz (787 RPM). The amplitude of the lower moving part was 7.62 mm. The applied pressure was 0.78 MPa on the HBU and 1.73 MPa on the BO sample. The test specimen was in the shape of a frustum of a rectangular pyramid with dimensions; base, 54 by 28.6 mm; top, 50.8 by 25.4 mm; and altitude, 38.1 mm. For HBU and BO test, the inside temperature of each specimen was probed after 45 min. running. The BO samples were further tested until the sample blowout and the blowout time were measured. RESULTS AND DISCUSSION Temperature and Power Changes During Mixing The master batch (MB) temperature changes during mixing were presented in Figure 1. The addition of the zinc soaps (ZB47 and ZL) into the S4 and the S2 compounds lowered the MB temperature, respectively. The addition of the ZB47 and the ZL into the S4/Cont compound decreased the MB drop temperature from 141 o C to 128 o C and 132 o C each and that of the S2/Cont systems decreased from 148 o C to 128 o C and 133 o C each, respectively. Comparing the ZB47 (S4/ZB47 and S2/ZB47) and the ZL (S4/ZL and S2/ZL) compounds, the ZB47 added compounds generated less heat than the ZL compounds in the mixer, respectively. Over all, the addition of the zinc soaps into the S4/Cont and the S2/Cont compounds generated less heat during MB mixing, respectively. The ZB47 added compounds generated less heat than the ZL added compounds, respectively. Mooney Viscosity The Mooney viscosity of each compound measured is represented in Figure 2. The addition of the ZB47 and the ZL decreased the Mooney viscosity of the S4 and the S2 compounds. The Mooney viscosity of the TESPT added compounds (S4/Cont, S4/ZB47, S4/ZL) exhibited higher than that of the TESPD added compounds (S2/Cont, S2/ZB47, S2/ZL), respectively. Comparing long time storage (LTS) and short time storage (STS) compounds, while the Mooney viscosity of the LTS compounds of the S2/Cont(LTS) and the S2/Cont(STS) exhibited close to each other, and that of the S4/Cont(LTS) exhibited higher than the S4/Cont(STS). The Mooney viscosity of the LTS compounds exhibited lower than that of the STS compounds on the zinc soaps added compounds. The viscosity reductions of the silane treated silica 31 and zinc soap 1 compounds were reported previously. The oil present in the compound lubricate between the silane treated silica and the rubber matrix, and between the rubber-rubber chains 38. The emulsified calcite and talc particles with oil were also discussed in the polystyrene matrix 39. 5

7 Over all, the addition of the ZB47 and the ZL reduced the Mooney viscosity on both the S4 and the S2 compounds. The ZB47 added compounds exhibited lower Mooney viscosity than the ZL added compounds on both the S4 and the S2 compounds. The LTS compounds exhibited lower viscosity than the STS compounds on the zinc soaps added systems. Reversion Test Figure 3 represents the result of the reversion test of the S4/Cont, S4/ZB47, S4/ZL, S2/Cont, S2/ZB47, and S2/ZL at 160 o C for 30 min. The highest order of minimum-torque (M L ) was the S4/Cont(14.7MU) compound, and then decreased to S2/Cont(14.1), S4/ZL(10.6), S4/ZB47(10.1), S2/ZL(9.7), and S2/ZB47(9.5), respectively. Comparing between the S4 and the S2 compounds with respect to the Cont, the ZB47, and the ZL systems, the S4 compounds exhibited higher M L than the S2 compounds, respectively. Comparing among the Cont, the ZB47, and the ZL compounds with respect to the S4 and the S2 systems, the Cont systems exhibited highest M L, then the ZL, and then the ZB47 added systems. The order of M L consistently matches with the Mooney viscosity measurement shown in Figure2. The order of torque-rise ( Torq) between minimum and maximum torque (M H - M L ) exhibited the highest at the S4/ZL(81.0) compound, and then decreased to S4/ZB47(79.8), S2/ZL(79.7), S4/Cont(78.0), S2/ZB47(76.1), and then S4/Cont(75.5), respectively. Comparing between the S4 and the S2 compounds with respect to the Cont, the ZB47, and the ZL systems, the S4 compounds exhibited higher torque-rise than the S2 compounds, respectively. Comparing among the Cont, the ZB47, and the ZL compounds with respect to the S4 and the S2 systems, the ZL systems exhibited the highest torque-rise, then the ZB47, and the ZL added systems, respectively. The order of scorch-time (Ts2) of each compound exhibited the highest at the S2/ZB47(4.1min) compound, and then decreased to S2/ZL(4.0), S4/ZB47(3.6), S4/ZL(3.5), S2/Cont(3.5), and S4/Cont(3.0), respectively. Comparing between the S4 and the S2 compounds with respect to the Cont, the ZB47, and the ZL systems, the S2 compounds exhibited higher scorch-time than the S4 compounds, respectively. Comparing among the Cont, the ZB47, and the ZL compounds with respect to the S4 and the S2 systems, the ZB47 systems exhibited the highest scorchtime, then the ZL, and the Cont systems, respectively. The order of cure-time (Tc90) of each compound exhibited the highest at S2/ZL (9.9min), and then decreased to S4/ZL(9.9), S2/ZB47(9.9), S4/ZB47(9.5), S2/Cont(8.1), and S4/Cont(7.7), respectively. Comparing between the S4 and the S2 compounds with respect to the Cont, the ZB47, and the ZL systems, the S2 compounds exhibited higher cure-time than the S4 compounds, respectively. Comparing among the Cont, the ZB47, and the ZL compounds with respect to the S4 and the S2 systems, the ZL systems exhibited highest cure-time, then the ZB47, and then the Cont systems. The order of reversion-time (T-2) of each compound exhibited the highest at the S2/ZB47(28.5min) compound, and then decreased to S2/ZL(26.2), S4/ZB47(22.1), S4/ZL(21.2), S4/Cont(12.8), and S2/Cont(12.2), respectively. Comparing between the S4 and the S2 compounds with respect to the Cont, the ZB47, and the ZL systems, the S2 compounds exhibited higher reversion-time than the S4 compounds, respectively. Comparing among the Cont, the ZB47, and the ZL 6

8 compounds with respect to the S4 and the S2 systems, the ZB47 systems exhibited the highest scorch-time, then the ZL, and the Cont, respectively. Comparing between the ZB47 and the ZL compounds with respect to M L and Torq, ZB47 exhibited lower M L than the ZL; however, ZL exhibited higher Torq than the ZB47. The high torque of the TESPT compounds (S4/Cont, S4/ZB47 and S4/ZL) might result from the higher amount of sulfur level than those of the TESPD compounds (S2/Cont, S2/ZB47, and S2/ZL), respectively. At the same weight, the TESPT compounds have higher sulfur level than those of the TESPD compounds. We summarized the maximum, minimum, and torque rise and scorch, cure, and reversion time on Table III. Over all, the addition of the ZB47 and the ZL increased the processability and the degree of cross-linking. While the ZB47 compounds exhibited better processability, than the ZL the ZL compounds exhibited stronger 3-dimensional cross-linking than the ZB47 on both the S4 and the S2 systems. Viscoelastic Property (Tanδ) After Vulcanization Figure 4 represents the tanδ values (E /E ) as a function of the ZB47 concentration of each compound. As the test temperature increased from 23 o C to 100 o C the tanδ value of each compound decreased, which was the typical trend 36. The tanδ values of the TESPT treated silica compounds exhibited lower than that of the TESPD treated silica compounds at both temperatures and they were decreased as the ZB47 and the ZL added systems, respectively. The lower tanδ values of the TESPT treated compounds result from the higher elastic properties (E ) of the TESPT treated compounds while the loss modulus (E ) differences of the ZB47 and the ZL were almost zero (not shown), respectively. The addition of the ZB47 and the ZL decreased the tanδ values and the differences of the ZB47 and the ZL systems were not significant on both temperatures. Over all, the addition of the ZB47 and the ZL increased the processability during mixing and increased the degree of cross-linking after vulcanization. Tensile Test Figure 5 represent the modulus of each compound at 100% elongation with respect to long time (Tc90x4) and short time cure (Tc90x1) specimen. The addition of the ZB47 and ZL increased the modulus on both the Tc90x4 and Tc90x1 specimen. The Tc90x4 compounds (S4/Cont, S4/ZB47, S4/ZL, S2/Cont, S2/ZB47, and S2/ZL) exhibited lower modulus than the Tc90x1 specimen, respectively. The modulus of the ZB47 and ZL treated compounds with Tc90x4 exhibited same or higher modulus than the Tc90x1. This trend matches with the reversion curve data as shown on Figure 3. As the vulcanization time increased the modulus of each compounds decreased. The TESPT treated compounds exhibited higher modulus at 100, 200, and 300 elongation and exhibited lower maximum elongation% than the TESPD treated compounds, respectively. We presented tensile properties measured from dumbbell shape specimen on Table IV. 7

9 Over all, the ZB47 and the ZL added compounds exhibited higher modulus than the compounds without them on both Tc90x4 and Tc90x1 systems. The Tc90x4 system exhibited lower modulus than the Tc90x1 systems. Blowout (BO) time and Heat Build Up (HBU) Figure 6 represents the BO time of each specimen tested following ASTM D 623 using Firestone Flexometer. For short time storage (STS) specimen, the addition of the ZB47 and the ZL into the S4 compound increased the BO time from 5min to266 min and 234min and that of the S2 compounds increased from 1min to 251min and 228min, respectively. Comparing the ZB47 and the ZL compounds with respect to the S4 and the S2 systems, the ZB47 compounds exhibited higher BO time than that of the ZL compounds, respectively. For long time storage (LTS) specimen, the addition of the ZB47 was reduced the BO time compared to the STS specimen as well as the S2/ZL(LTS) compound. The S4/Cont and the S2/Cont compounds of the LTS exhibited higher BO time than of the STS compounds. Figure 7 shows the heat generated by BO and HBU test. The BO test exhibited higher heat generation than the HBU test. The addition of the ZB47 and ZL into the S4 and the S2 compounds decreased the BO and HBU temperatures on each systems and BO test exhibited significant temperature changes than the HBT test. Over all, the addition of the ZB47 and the ZL extended the BO time and lowered the BO and the HBU temperature. Those represent the addition of the ZB47 and the ZL into the TESPT and TESPD compounds form stronger 3-dimension network. Comparing the S4/Cont and the S2/Cont with and without zinc soaps (ZB47 and ZL), they seem more interactive with the TESPT than with the TESPD because the temperature drop of the S2 compounds was more significant than the S4 compounds. This might be related to the 16% higher level of the sulfur exists in the TESPT compounds than that of the TESPD 38, which is believed to increase the 3-dimensional network in the compound. 8

10 CONCLUSIONS The addition of the zinc soaps (ZB47 and ZL) into the S4/Cont and the S2/Cont compounds lowered the heat generation in the MB mixing and the ZB47 compounds (S4/ZB47 and S2/ZB47) generated less heat than the ZL compounds (S4/ZL and S2/ZL), respectively. It also improved the processability of each compound (S4/Cont and S2/Cont). The viscosity of the ZB47 compounds (S4/ZB47 and S2/ZB47) exhibited lower than that of the ZL compounds (S4/ZL and S2/ZL), respectively. The TESPT compounds (S4/Cont, S4/ZB47, and S4/ZL) exhibited higher viscosity than the TESPD compounds (S2/Cont, S2/ZB47, and S2/ZL), respectively. The addition of the zinc soaps also increased the reversion resistance time of each compound. After the vulcanization, the BO time of the zinc soaps added compounds exhibited significantly higher than without the zinc soaps ones. It also improved the tensile modulus at 100, 200, and 300% elongations of the compound. The over cured compounds at Tc90x4 exhibited lower tensile modulus then the Tc90x1. The addition of the zinc soaps increase the strong 3-dimensional network structure in the TESPT and the TESPD treated silica filled NR compound. However, the ZB47 added compounds with the LTS exhibited significant decrease in BO time. The zinc ion in the zinc soaps seems related to the vulcanization mechanism and storage time. The free sulfur and the functional sulfur level exist in the organo silane also related to the degree of cross-linking of the compounds. Thus affecting the processability and properties of the final compounds. The TESPT treated compounds were less stable during mixing and more reactive after vulcanization than the TESPD. However, the addition of the zinc soaps changed their character. The zinc soaps improved the stability of the TESPT more than the TESPD compounds during mixing and improved the degree of cross-linking after vulcanization. The mechanisms of the zinc soaps are not clear at this stage. We presume the addition of the zinc soaps affected the role of the sulfur reaction mechanism in the compound including the breaking of the sulfur network in the silane. The efficiency of the coupling with different kind of zinc soap, which includes aromatic functional group, is under investigation. ACKNOWLEDGMENTS The authors would like to express appreciation to Mrs. Barbara Eikelberry for support on the experiment. Special thanks are extended to Struktol Company of America for permission to publish this paper. 9

11 1 REFERENCES K. J. Kim and J. VanderKooi, J. Ind. Eng. Chem., 8(4), 334 (2002). 2 F. Thurn and S. Wolff, Kautsch. Gummi Kunstst., 28, 733 (1975). 3 S. Wolff, Kautsch. Gummi Kunstst., 32, 760 (1979). 4 A. Hunsche, U. Görl, A. Müller, M. Knaack, T. Göbel, Kautsch. Gummi Kunstst., 50, 881 (1997). 5 A. Hunsche, U. Görl, H. G. Koban, T. Lehmann, Kautsch. Gummi Kunstst., 51, 525 (1998). 6 H. Ishida, Polym. Compos., 5, 101 (1984) 7 H. Ishida and J. L. Koenig, J. Colloid Interface Sci., 106, 334 (1985). 8 S. Wolff, Kautsch. Gummi Kunstst., 34, 280 (1981). 9 S. Wolff, The Role of Rubber-to-Silica Bonds in Reinforcement, paper presented at the first Franco-German Rubber Symposium, Obernai, France, Nov Europe Patent EP , (1991), R. Rauline (Michelin). 11 R. W. Cruse, M. H. Hofstetter, L. M. Panzer and R. J. Pickwell, Effects of polysulfidic silane sulfur on rolling resistance, ACS Rubber Division meeting, Louisville, KY, Oct. 8-11, Paper No A. McNeish and J. T. Byers, Low Rolling Resistance Tread Compounds-Some Compounding Solutions, Degussa Corporation, ACS Rubber Division meeting, Anaheim CA, May C. R Stone, M. Hensel, K.H. Menting, Kautsch. Gummi Kunstst., 51, 568 (1998). 14 C. R. Stone, K. H. Menting and D. M. Hensel, Improving the silica Green Tyre tread compound by the use of special process additives, Schill & Seilacher, ACS Rubber Division meeting, Orlando FL, Sept C. R. Stone, K. H. Menting and D. M. Hensel, Optimising the use of Disulphide Silane in a silica Green Tyre tread compound, Schill & Seilacher, ACS Rubber Division meeting, Cincinnati OH, Oct P. Cochet, Highly dispersible reactive silica for low-rolling-resistance tires, Rhodia Silica, ITEC-2000 (No 22A), Akron OH, Sept F. Yatsuyagagi and H. Kaidou*, N. Suzuki and M. Ito**, Relationship between secondary structure of fillers and the mechanical properties of silica filled rubber systems, *Yokohama Rubber Co., **Science Univ. of Tokyo, ACS Rubber Division meeting, Providence RI, Apr U.S. Patent (filed Feb. 20, 1992) 5,227,425 (1993), R. Rauline (Michelin). 19 H. Ismail and P. K. Freakley, Polym. Plast. Technol. Eng., 36, 873 (1997). 20 K. J. Kim and J. L. White, J. Ind. Eng. Chem., 6(4), 262 (2000). 21 J. A. Hockley and B. A. Pethica, Trans Faraday Soc., 57, 2247 (1961). 22 R. Bassett, E. A. Boucher, and A. C. Zettlemoyer, J. Colloid Interface Sci., 27, 649 (1968). 23 J. H. Bachmann, J. W. Sellers, M. P. Wagner, Rubber Chem. Technol., 32, 1286 (1959). 24 E. M. Dannenberg, Rubber Chem. Technol., 48, 410 (1975); 48, 558 (1975). 25 M. P. Wagner, Rubber Chem. Technol., 49, 703 (1976). 26 P. Vondracek, M. Hradec, V. Chvalovsky, and H. D. Khanh, Rubber Chem. Technol., 57, 675 (1984). 10

12 27 Krysztafkiewicz, Colloid Polym. Sci., 267, 399 (1989). 28 S. Kohjiya, Y. Ikeda, Rubber Chem. Technol., 73, 534 (2000). 29 U.S. Patent (filed July 7, 1998) 6,169,137 (2001), Vasseur;Didier (Compagnie Genearl des Etablissement Michelin&Cie). 30 H.-D. Luginsland, J. Fröhlich and A. Wehmeier, Influence of Different Silanes on The Reinforcement of Silica-Filled Rubber Compounds, Degussa AG, ACS Rubber Division meeting, Providence RI, Apr K. J. Kim and J. L. White, Composite Interfaces, (in print). 32 A. D. Roberts, Natural Rubber Science and Technology, Oxford Science Publishers, New York, J. VanderKooi, Zinc Soaps for Improved Vulcanizates Part II, Struktol Company of America, ACS Rubber Division meeting, Louisville KE, Oct Paper No J. L. White, Principle of Polymer Engineering Rheology, Wiley Inter-Science, New York (1990). 35 J. L. White, Rubber Processing: Technology, Materials, and Principles, Hanser Publishers, Cincinnati (1995). 36 A. N. Gent, Engineering with Rubber: How to Design Rubber Components, Hanser Publishers, New York (1992). 37 U.S. Patent (filed June 9, 1931) 02,048,314 (July 21, 1936), R. W. Allen (Firestone Tire & Rubber Co.). 38 K. J. Kim and J. VanderKooi, Kautsch. Gummi Kunstst., 55,??? (2002). 39 K. J. Kim and J. L. White, Polym. Eng. & Sci., 39, 2189 (1999). 11

13 TABLE I MATERIALS USED IN THIS STUDY Trade name Supplier Natural Rubber SIR 20 Goodyear Peptizer A86 Struktol Silica ZS 1165MP Rhodia Activator Zinc Oxide [ZnO], Stearic acid Processing aid Titanium dioxide [TiO 2 ] DuPont Antioxidant TMQ Vanderbilt [poly(trimethyl dihydro quinoline)] Antioxidant, Antiozonant, Inhibitor Sunolite 240 [paraffin wax] Lubricant, Activator Carbowax 3350; Harwick [polyethylene glycol] Homogenizer 60 NS Flakes Struktol [mixture of aliphatic hydrocarbons] Processing aid, Dispersing agent WB 222 Struktol [ester of saturated fatty acids] Plasticizer, Softener Stanplas 2000 Harwick [naphthenic distillate oil] Bonding agent SCA 98 Struktol [bis(triethoxysilylpropyl)tetrasulfane] Bonding agent SCA 985 Struktol [bis(triethoxysilylpropyl)disulfane] Activator ZB47 2 ZL 3 Struktol Struktol Vulcanizer Sulfur Accelerator MOR*,4, Vanax A; [4,4 -dithiodimorpholine], DPG; [Diphenylguanidine] *Harwick 1 2,2-dibenzamido diphenyl disulfide/metal-organic complex/fatty acid ester on inorganic carrier. 2,3 O O R C Zn C R O O R=C 6 -C (morpholinothio)benzothiazol 12

14 TABLE II MIXING FORMULATIONS AND PROCEDURE ON NR COMPOUNDS 2.1 Formulation MB Stage Material Control 1 (S4/Cont) Control 2 (S2/Cont) SCA98 (S4/ZL) SAC985 (S2/ZL) SCA98 (S4/ZB47) SAC985 (S2/ZB47) SIR A ZS 1165MP Zinc Oxide Stearic Acid TiO TMQ Sunolite PEG NS Flakes WB Stanplas SCA98 (S4) SCA985 (S2) ZL ZB nd Stage Sulfur MOR Vanax A DPG Mixing Procedure a. Add rubber and A86 b. Mix for 30 sec c. Add rest additives d. Mix for 121 o C(250 o F) and sweep e. Mix for 5 min and dump. 13

15 Torque Time (min) TABLE III VULCANIZATION CHARACTERISTICS OF EACH COMPOUND (160 O C 30 MIN. (ERROR=±2%)) Max Torq. Min Torq. Torq. Ts2 Tc50 Tc90 M H M L (M H -M L ) (MU) (MU) (MU) (min) (min) (min) Reversion (T-2) (min) System S4/Cont S4/ZL S4/ZB S2/Cont S2/ZL S2/ZB

16 4.1 Tc90x1 TABLE IV TENSILE PROPERTIES OF EACH COMPOUND Tensile Stress Max (MPa) Elongation Max (%) Modulus 100% (MPa) Modulus 200% (MPa) Modulus 300% (MPa) S4/Cont S4/ZL S4/ZB S2/Cont S2/ZL S2/ZB Tc90x4 Tensile Stress Max (MPa) Elongation Max (%) Modulus 100% (MPa) Modulus 200% (MPa) Modulus 300% (MPa) S4/Cont S4/ZL S4/ZB S2/Cont S2/ZL S2/ZB

17 150 S4/Cont S4/ZL S4/ZB47 Temp( o C) 100 Ram open 50 Ram open Time (sec) (a) 150 S2/Cont S2/ZL S2/ZB47 Temp( o C) Ram open Ram open Time (sec) (b) FIG. 1. Zinc soaps effect on temperature changes in MB for (a) S4 compounds, (b) S2 compounds. 16

18 65 Mooney Viscosity (MU) S4(STS) S2(STS) S4(LTS) S2(LTS) 35 0pbw(Cont) 2.5pbw(ZL) 2.5pbw(ZB47) ZB Concentration FIG. 2 Zinc soaps effect on Mooney viscosity for (a) storage times of the STS and the LTS compounds, (b) the S4 and the S2 compounds. 17

19 S4/ZB47 S4/ZL S4/cont Torque (MU) Time (min.) (a) S2/ZB47 S2/ZL S2/cont Torque (MU) Time (min.) (b) FIG. 3. Zinc soaps effect on reversion test for (a) S4 compounds, and (b) S2 compounds. 18

20 S2 23 o C S4 23 o C tanδ 0.05 S2 100 o C S4 100 o C pbw(Cont) 2.5pbw(ZL) 2.5pbw(ZB47) ZB Concentration FIG. 4. Zinc soaps effect on viscoelastic property (tanδ) on the S4 and the S2 compounds at 23 o C and 100 o C from MER (1 Hz, 3%). 19

21 4 100% Modulus (MPa) 3 S4(Tc90x1) S2(Tc90x1) S4(Tc90x4) S2(Tc90x4) 2 0pbw(Cont) 2.5pbw(ZL) 2.5pbw(ZB47) ZB concentration FIG. 5. Zinc soaps effect on tensile modulus of Tc90x4 and Tc90x1 at 100% elongation on the S4 and the S2 compounds. 20

22 Blowout Time (min.) S4(STS) S2(STS) S4(LTS) S2(LTS) 0 0pbw(Cont) 2.5pbw(ZL) 2.5pbw(ZB47) ZB concentration FIG. 6. Zinc soaps effect on the BO time on the S4 and the S2 compounds and the STS and the LTS compounds. 21

23 HBU/BO Temperature ( o F) S4(BO) S2(BO) S2(HBU) S4(HBU) 0pbw(Cont) 2.5pbw(ZL) 2.5pbw(ZB47) ZB Concentration FIG. 7 Zinc soaps effect on temperature rise of the HBU/BO test for the S4 and the S2 compounds. 22

24 Figure Captions Figure 1 Zinc soaps effect on temperature changes in MB for (a) S4 compounds, (b) S2 compounds. Figure 2 Zinc soaps effect on Mooney viscosity for (a) storage times of the STS and the LTS compounds, (b) the S4 and the S2 compounds. Figure 3 Zinc soaps effect on reversion test for (a) S4 compounds, and (b) S2 compounds. Figure 4 Zinc soaps effect on viscoelastic property (tanδ) on the S4 and the S2 compounds at 23 o C and 100 o C from MER (1 Hz, 3%). Figure 5 Zinc soaps effect on tensile modulus of Tc90x4 and Tc90x1 at 100% elongation on the S4 and the S2 compounds. Figure 6 Zinc soaps effect on the BO time on the S4 and the S2 compounds and the STS and the LTS compounds. Figure 7 Zinc soaps effect on temperature rise of the HBU/BO test for the S4 and the S2 compounds. 23