Effects of zinc soap on TESPT and TESPD treated silica compounds on processing and silica dispersion in polyisoprene rubber.

Processing additives are materials used at relatively low dosage levels, which improve processing characteristics without significantly affecting physical properties. In the early years, the classic additives such as mineral oil, bees wax, stearic acid and palmitic acid, etc., were used as natural raw materials, which are not constant as regards composition and quality. In recent years, they maintained a high standard through an appropriate purification process. The growth rate of additives such as homogenizers, peptizers and lubricants increased about four times between 1980 and 1995 (ref. 1). The chemical structures of the processing agents are classified as hydrocarbons, fatty acid derivatives, synthetic resins, low molecular weight polymers and organic thio compounds, as shown in table 1. Their effects are subdivided as peptization, dispersion, flow, homogenization, tack, high hardness and release, etc., as shown in table 2. Several additives such as fatty acid esters act as lubricants and dispersing agents. Sulfur containing bifunctional coupling agents have been studied since the 1970s to improve the processability at the mixing stage and to improve the chemical bonding between silica and the rubber chain at the vulcanization stage (refs. 2 and 3).

Bifunctional organosilanes such as TESPT and TESPD have been used in the green tire tread compound as processing aids during mixing and acted as chemical bonding agents at the vulcanization stage between silica and the rubber matrix due to their bifunctional characteristics. One end of the alkoxy group reacts with the silanol group on the silica surface via a hydrolysis mechanism (refs. 4-7). The other end of the sulfur reacts with the rubber chain at the vulcanization stage (ref. 8) and covalently bonds between silica and the rubber chain (ref. 9). Studies on green tire compounds using silane were mainly based on the SBR/BR compounds (refs. 10-17). Green tires exhibit low rolling resistance plus good wet and snow traction (ref. 18), which improve gas mileage and good grip on the road surface. However, the silica is more difficult to process and disperse in the rubber matrix than other particles (refs. 13, 19 and 20) due to its polar and hydrophobic character (refs. 21 and 22). There have been works to disperse the silica agglomerates mechanically, chemically and physically, etc., (refs. 14 and 23-31), however, there were no researches of polysulfidic silane treated silica compound in the NR matrix.

The NR compounds have been used in airplane tires, winter tires, fork lift tires, and medium and heavy duty truck tires due to their abrasion-, cutting-, tear- and rolling resistance and adhesion to a steel surface. They are also used for vibration absorption during earthquakes in buildings (ref. 32). The NR is non-polar and has more double bonds than the SBR.

Various zinc soaps such as zinc stearate, zinc laurate, zinc tallowate, zinc naphthenate, zinc resinate and zinc 2-ethylhexanoate are currently used in 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 (Cx) increased longer than C10. Unsaturated zinc soap such as zinc tallowate improves dispersibility. Even though large amounts of additives are used in the industry now, there were few systematic theories or research (ref. 33) on the zinc soap illustrated above.

We present the effects of the ZB (a class of zinc soap), which was developed in our lab, on TESPT and TESPD treated silica compounds in the NR compound during mixing and after vulcanization. Processability, silica agglomerate dispersion and mechanical properties of each compound were compared.

Experimental

Materials

The silanes used in this study were the TESPT and the TESPD tradenamed SCA98 and SCA985. The ZB used in this study is in commercial evaluations. The polyisoprene rubber was a Goodyear product, SIR-20. The silica used was Ultrasil VN3, which is precipitated silica with BET area 175 ([m.sup.2]/g) supplied by Degussa. Information on the materials used in this study is summarized in table 3.

Mixing

A BR 1600 internal mixer was used for compounding the rubber and additives and a data acquisition computer was attached to the mixer to obtain the data at the time of mastication. Two stage mixings were carried. The first stage was the compounding of the rubber, filler's and additives. In the second stage, sulfur and other accelerators were added into the compound. The fill factor was fixed at 0.7 and the starting operation temperature of the mixer was set to 65.5[degrees]C. The rotor speed was set to 77 rpm.

The stock temperature changes during mixing were recorded in the computer and the data were analyzed. The mixing formulations and vulcanizations are included in table 4.

Steady shear viscosity measurement

Shear viscosity was measured in a pressurized rotational rheometer with a biconical rotor. This was the instrument described by Montes et al (ref. 34), which measures the viscosity at various speeds. The shear rate and shear stress were given by (refs. 35 and 36):

(2.1a, b) [gamma] = [OMEGA]/[alpha]

[sigma] 12 = 3M/4[pi][R.sup.3]

where [OMEGA] is the angular velocity, [alpha] is the cone angle, M is the torque and R is the cone radius.

Mooney viscosity measurement

Following ASTM D1646, Mooney viscosities were measured as a function of apparent shear rate at 0.7 (I/s) (0.2 rad/sec, 2 rpm) and ML1+4 at 100[degrees]C using a shearing disc. The rotor diameter of the shearing disc rheometer is 38.1 mm and the thickness of the rotor is 5.54 mm. The machine we used was a MV 2000. The shear rate at the outer radius of the shearing disc may be expressed as follows:

(2.2) [gamma](R) = R[OMEGA]/H

where R is the radius of the rotor, [OMEGA] is the rotor rotation angle and H is the distance between the disc surface and the stationary housing.

Reversion test

An oscillating disc cure meter was used for measuring the vulcanization and reversion resistance properties of the compounds following ASTM D 2084 at 160[degrees]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 100 cycles/min. (1.66 Hz) with amplitude of 3[degrees]. Minimum torque ([M.sub.L]), maximum torque ([M.sub.H]), scorch time (Ts2), cure time (Tc50, Tc90) and reversion resistance time (T-2) were measured.

Viscoelastic property (tan [delta]) before and after vulcanization

The unvulcanized rubber compounds after second stage mixing were characterized using an RPA 2000, which uses biconical dies in a pressurized sample chamber. The tip of each convex center of the two cones is facing each other (ref. 35).

Vulcanized materials were characterized using the Mechanical Energy Resolver (MER-1100B). This instrument measures oscillatory input of axial tension/compression response of the cylindrical specimen, as shown in figure 1b. Oscillatory tension/compression signal responses depending on material were measured as follows (ref. 37):

[FIGURE 1 OMITTED]

(2.3a,b,c,d) E'([omega]) = E * cos[delta]

E"([omega]) = E * sin[delta] = [omega][[eta].sub.el]

[sigma] = (E' + iE") [epsilon] = E * [epsilon]

E * = [([E'.sup.2] + [E".sup.2]).sup.1/2] = E'[[1 + [(tan[delta]).sup.2]].sup.1/2]

where [omega] represents oscillation frequency, [E.sup.*] is the complex dynamic modulus, [delta] is the phase angle, E'([omega]) is the real dynamic modulus, E"([omega]) is the imaginary dynamic modulus and [[eta].sub.el]([omega]) is the tensile viscosity.

Tensile test

The tensile test curves were obtained from dumbbell shaped specimens measured following the ASTM D 412-87 method. The tensile stress maximum (Pa), elongation at 100, 200 and 300%, and modulus (Pa) of each compound were measured. The thickness and the width of the specimens were average 2.2 mm and 6.3 mm, respectively.

Heat build-up (HBU) and blowout (BO) test

The Firestone Flexometer (ref. 38) was used to measure heat build-up and blowout of the sample per ASTM D 623. This is a testing apparatus for applying a uniform circulatory oscillating action under compression. The test specimen is located between the fixed upper part and the moving bottom part. 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 compression pressure applied 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 tests, the inside temperature of each specimen was probed after 45 minutes running. For BO tests, the dimensions of the center part of the sample were measured, and their deformation ratios (%) deviated from before tests were presented. The BO samples were further tested until the sample blowout and the blowout time were measured.

Scanning electron microscope (SEM) characterization

A Hitachi S-2150 SEM was used to characterize the order of agglomerate particle size. The prepared compounds were fractured in liquid nitrogen and coated with silver using a sputter coater. The SEM pictures of agglomerate particles were characterized using an image analyzer (IA) system. The individual particle diameters were converted to mass average particle diameter. Average agglomerate sizes were generally represented in terms of higher averages because of the problem of subjectivity in dealing with small particles. Specifically, we have used the mass average (refs. 35 and 36).

Abrasion loss test

The abrasion loss of each cured compound was measured using the APH-40 abrasion tester. An abrasive paper P-60 (DIN 53512) attached to the 150 mm diameter was rotating at the speed of 40 rpm. The cylindrical sample (diameter 16 mm) with 10 mm thickness inserted into the sample holder traveled over the surface of the abrasive paper at a rate of 0.32 m/sec. under a loading of 10 N for a distance of 40 m. After the abrasion test, the test sample was removed, and weighing and calculation determine its volume loss. The debris collected from the abrasion test was converted to volume loss from the density of each compound using the following relation:

(2.4) A = [DELTA]M * [S.sub.0]/[rho] * S

where A is the abrasion ([mm.sup.3]), [DELTA]m is the loss (mg), [rho] is the density (g/[cm.sup.3]), [S.sub.0] is the normal abrasion grade (200 mg) and S is the abrasive grade (mg).

Results and discussion

Temperature and power changes during mixing

The stock temperature changes during mixing were presented in figure 1. The addition of the ZB into the S4 compounds lowers the stock temperature as well as the S2 compounds. As the concentration of the ZB increased from 0 to 1 wt % (two parts) and 3 wt % (five parts), the slope of the temperature rises on the S4 compound decreased from 1.276 to 1.236 and 0.176 each during mixing, and that of the S2 systems decreased from 1.336 to 1.288 and 1:184. The S2, S2Z2 (1 wt % ZB) and S2Z5 (3 wt % ZB) compounds generated more heat and consumed more power (not shown) than that of the S4, S4Z2 (1 wt % ZB), and S4Z5 (3 wt % ZB) compounds during mixing, respectively.

[FIGURE 2 OMITTED]

Steady shear viscosity

The shear viscosity of each compound from the internal mixer is summarized in figure 2. The addition of the TESPT and the TESPD reduced the viscosity of the NR, thus the S4 and the S2 compounds exhibited lower viscosity than that of the NR. The addition of the ZB in the S4 and the S2 compound further lowered the viscosity of the S4 and the S2 compound each, thus the NR/silane/silica/ZB compounds exhibited lower viscosity than the NR/silane/silica compounds. As the concentration of the ZB increased in the compounds, the viscosity of each compound decreased, i.e., S4 > S2, S4S2 > S4S5 and S2Z2 > S2Z5. It is a common trend that the viscosity increases as the filler concentration increases due to large filler surface area contacting polymer chains (refs. 20, 31, 33-35, 39 and 40). The viscosity reductions of the silane treated silica compounds were reported previously (refs. 31 and 40). The oil lubricates between the oleophilic silica (treated silica) and the rubber matrix, and between the rubber-rubber chains (ref. 39). The oil effects on emulsification of the calcite and talc particles were also discussed in the polystyrene matrix (ref. 40).

[FIGURE 3 OMITTED]

Overall, the addition of the ZB reduced the shear viscosity of the S4 and the S2 compounds and they were proportional to the ZB concentration.

Mooney viscosity

The Mooney viscosity dependence on the ZB concentration at 0.2 rad/sec, and 100[degrees]C is represented in figure 3. As the concentration of the ZB increased, the complex viscosity of the S4 and the S2 compounds decreased. The Mooney viscosity of the S4 and S4Z2 compounds exhibited higher levels than that of the S2 and S2Z2 compounds, respectively. The addition of the ZB reduced the viscosity of the S4 and the S2 compounds, i.e., S4 > S4Z2 > S4Z5 and S2 > S2Z2 > S2Z5, which exhibited the same trend of the steady shear and the complex viscosities measurement as shown above. At higher ZB concentration, the viscosity of the S4Z5 and the S2Z5 compounds exhibited close to each other.

Overall, the addition of the ZB reduced the Mooney viscosity of the S4 and the S2 compounds and it depended on the ZB concentration.

Viscoelastic properly (tan [delta]) before and after vulcanization

Figure 4 represents the tan [delta] value changes at different temperatures and at different ZB concentrations before vulcanization at 60[degrees]C and 100[degrees]C. The addition of the ZB increased the tan [delta] values of each compound, i.e., S4 < S4Z2 < S4Z5 and S2 < S2Z2 < S2Z5. As the temperature increased from 60[degrees]C to 100[degrees]C the tan [delta] values of the S4, S4Z2 and S4Z5, and the S2, S2Z2 and S2Z5 compounds increased. The tan [delta] values of the S4, S4Z2 and S4Z5 compounds exhibited lower levels than that of the S2, S2Z2 and S2Z5 compounds at both temperatures, and they increased as the ZB concentration increased.

[FIGURE 4 OMITTED]

Figure 5 represents the tan [delta] values (E"/E') as a function of the ZB concentration of each compound after vulcanization at 23[degrees]C and 100[degrees]C. As the test temperature increased from 23[degrees]C to 100[degrees]C, the tan [delta] value of each compound decreased, which was the opposite trend compared with the unvulcanized systems. The tan [delta] values of the TESPT treated silica compounds exhibited lower levels than that of the TESPD treated silica compounds at both temperatures, and they were decreased as the ZB concentration increased which was also the opposite trend compared with the unvulcanized systems. The lower tan [delta] 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 same ZB concentration were almost zero (not shown), which was similar to unvulcanized systems (figure 7) respectively. The addition of the ZB decreased the tan [delta] values and further decreased them as the ZB concentration and the temperature increased, which was the opposite result compared with the unvulcanized systems. At higher ZB concentration, the tan [delta] value differences between S4Z5 and S2Z5 became close together.

[FIGURES 5 & 7 OMITTED]

Overall, before vulcanization, the addition of the ZB increased the tan [delta] value of each compound, and this further increased them as the ZB concentration increased due to lower G'. Thus, the addition of the ZB increased the processability during internal mixer mixing. After vulcanization, the ZB acted as a lubricant during mixing and increased the degree of crosslinking as the ZB concentration and the temperature increases after vulcanization.

Reversion test

Figure 6 shows the vulcanization curve of the S4, S4Z2 S4Z5, S2, S2Z2 and S2Z5 compounds with respect to time increment at 160[degrees]C for 30 minutes. The addition of the ZB increased the reversion time. As the concentration of the ZB increased, the reversion time of each compound (S4Z2, S4Z5, S2Z2 and S2Z5) increased. At the same ZB concentration, the S4, S4Z2 and S4Z5 compounds exhibited higher maximum and minimum torque than those of the S2, S2Z2 and S2Z5 compounds, respectively. The S4Z5 and S2Z5 compounds exhibited no reversion torques for 30 minutes at 160[degrees]C. As the ZB concentration increases, the torque rise from minimum to maximum increased, which implies a higher degree of three-dimensional network formed. The S4, S4Z2 and S4Z5 compounds exhibited higher minimum torque, higher maximum torque and faster cure time than those of the S2, S2Z2 and S2Z5 compounds, respectively. The higher minimum torque of the S4 compound matches with the shear viscosity data and the Mooney viscosity as previously shown. The high torque of the S4, S4Z2 and S4Z5 compounds might result from the higher amount of sulfur level than those of the S2, S2Z2 and S2Z5 compounds, respectively. At the same weight, the TESPT compounds (S4, S4Z2 and S4Z5) have a higher sulfur level than those of the TESPD compounds (S2, S2Z2 and S2Z5). We summarized the maximum and minimum torque, scorching, cure, reversion and maximum torque time in table 5.

[FIGURE 6 OMITTED]

Overall, the addition of the ZB increased the reversion time and the degree of crosslinking and they were proportional to the ZB concentration.

Tensile test

Figure 7 represents the modulus changes depending on ZB concentration at 100% elongation, which were measured from the dumbbell shaped specimens following ASTM D 412-87 method. At 100, 200 and 300% elongation, as the ZB concentration increased from zero to one and three wt % ZB, the modulus of each compound increased. As the concentration of the ZB increased, the maximum elongation % and the maximum tensile stress decreased. The TESPT treated compounds exhibited lower maximum elongation % and the maximum tensile stress than that of the TESPD treated compounds, respectively. We presented various tensile properties measured from dumbbell shaped specimens in table 6.

Blowout (BO) and heat build up (HBU)

Figure 8 represents the photograph of the BO specimen after BO testing following ASTM D 623 using a Firestone Flexometer The deformation ratios measured from each specimen were plotted in figure 9. The addition of the three wt % ZB into the S4 and the S2 compounds lowered the deformation ratio from 8% to 1% and 6% to 2%, respectively. In comparing the S4 and the S2 compound, the S2 compound exhibited less deformation than that of the S4 compound. However, after addition of the ZB, the S4 compound exhibited less deformation than the S2 compound, which showed the opposite result compared to without the ZB addition. This will be discussed later in this section. These samples were further tested under the same condition with the BO test until the sample blowout, as shown in figure 10. The addition of the three wt % ZB into the S4 compound increased the BO time from 84 minutes to 9,900 minutes, and that of the S2 compounds increased from 81 minutes to 8,600 minutes. The S4, S4Z2 and S4Z5 compounds exhibited higher BO time than the S2, S2Z2 and S2Z5 compounds, respectively. The temperature generated by the circular oscillation movement from each sample was measured. The addition of the three wt % ZB into the S4 compound decreased the HBU temperature from 118[degrees]C to 107[degrees]C and that of the S2 compounds decreased from 121[degrees]C to 106[degrees]C.

[FIGURES 8-10 OMITTED]

Overall, the addition of the ZB lowered the deformation ratio, lowered the HBU temperature and extended the BO time, and they were proportional to the concentration of the ZB. The addition of the ZB into the TESPT and TESPD compounds formed a stronger three dimensional network, and the TESPT network was stronger than that of the TESPD compound. The ZB seems more interactive with the TESPT than with the TESPD. The concentration of the sulfur existing in the TESPT compounds is higher than that of the TESPD. The excessive sulfur existing in the TESPT compounds might have increased the three-dimensional network in the compound more than in the TESPD.

Scanning electron microscope (SEM) characterization

Figure 11 represents typical SEM photographs of the TESPT, TESPD and ZB treated silica dispersion in the NR after vulcanization. The silica agglomerates in the S4 and the S2 compounds were well dispersed. However, the SEM photographs of the ZB added compounds exhibited several large silica agglomerates. The polydispersites of the vulcanized S4, S4Z2 and S4Z5 compounds calculated from image analyzer data were 0.741, 0.790 and 0.796, and that of the S2, S2Z2 and S2Z5 compounds was 0.708, 0.716 and 0,749, respectively. The addition of the ZB increased the polydispersity of each compound. The S4, S4Z2 and S4Z5 compounds exhibited wider distribution of the silica agglomerates than the S2, S2Z2 and S2Z5 compounds, respectively. The silica agglomerate diameter before vulcanization was larger than after vulcanization. The ZB effects on the size and dispersion of silica agglomerates in the NR compounds are summarized in table 7.

[FIGURE 11 OMITTED]

Overall, the vulcanization reduced the silica agglomerate sizes and the addition of the ZB shifted the distribution of the silica agglomerate into mixtures of big and small agglomerates.

Abrasion resistance

The addition of the three wt % ZB into the S4 and the S2 reduced the abrasion loss ([mm.sup.3]) from 143 to 128 and 133 to 131, and increased the compound density (g/[cm.sup.3]) from 1.18 to 1.19 and 1.17 to 1.19, respectively. The S4 compound exhibited more abrasion loss than the S2 compound, however, the addition of the ZB reduced the abrasion loss and depended on the concentration of the ZB. The ZB effects were more significant on the S4 than on the S2 compound. The results of the abrasion resistance and the density of each compound are represented in table 8.

Overall, the addition of the ZB into the S4 and the S2 compounds increased a stronger 3D network structure. The ZB effect was more significant on the S4 than the S2 compound.

Conclusions

The addition of the ZB into the TESPT and the TESPD compounds improved the processability, and they were proportional to the ZB concentration. The TESPT compounds exhibited higher viscosity than the TESPD compounds during mixing. The addition of the ZB also increased reversion resistance time of the compounds proportional to the ZB concentration. After the vulcanization, the BO time of the ZB added compounds exhibited significantly higher than without the ZB compounds. It also improved the tensile modulus at elongations, increased the compound density and lowered the abrasion loss of the compound. The silica agglomerate sizes were reduced after vulcanization. Addition of the ZB increased the polydispersity of the agglomerate sizes.

The addition of the ZB increased the strong three-dimensional network structure in the TESPT and the TESPD treated silica filled NR compound. The zinc in the ZB seems related to the vulcanization mechanism, and the free sulfur and the functional sulfur level exists in the organosilane also related to the degree of cross/inking of the compounds, thus affecting the processability and properties of the final compounds.

The S4 compounds were less stable during mixing and more reactive after vulcanization than the S2. However, the addition of the ZB changed their character. The ZB improved the stability of the TESPT more than the TESPD compounds during mixing and improved the degree of crosslinking after vulcanization. The mechanism of the ZB is not clear at this stage. We presume the addition of the ZB affected the role of sulfur reaction mechanism in the compound, including the breaking of the sulfur in the silane, and the efficiency of the coupling is still under investigation. This will be discussed in a future work with chemical reaction experiments.

Table 1--basic chemical structures of processing
additives

Group                           Examples

Hydrocarbons                    Mineral oils
                                Petrolatum
                                Paraffin waxes
                                Petroleum resins
Fatty acid derivatives          Fatty acids
                                Fatty acid esters
                                Fatty alcohols
                                Metal soaps
                                Fatty acid amides
Synthetic resins                Phenolic resins
Low molecular weight polymers   Polyethylenes
                                Polybutenes
Organo thio compounds           Peptizers
Table Table 2--the effect of processing additives

Effects          Examples

Peptization      2.2'-Dibenzamidodiphenyl disulfide
                 Pentachlorothiophenol
                 Zinc soaps
Dispersion       Fatty acid esters
                 Metal soaps
                 Fatty alcohols
Flow             Metal soaps
                 Fatty acid esters
                 Fatty acid amides
                 Fatty acids
Homogenization   Resin blends
Tack             Hydrocarbon resins
                 Phenolic resins
High hardness    High styrene resin-rubber masterbatches
                 Phenolic resins
                 Trans-polyoctenamer
                 Organo silicones
Release          Fatty acid esters
                 Metal soaps
                 Fatty acid amides
Table 3--materials used in this study

                           Tradename

Rubber                     SIR 20
Peptizer                   A86
Filler (silica)            Ultrasil VN3
Activator                  Zinc oxide (ZnO)
Processing aid             * Titanium dioxide (Ti[0.sub.2]),
                             stearic acid
Antioxidant                TMQ
                             [poly(trimethyl dihydro quiniline)]
Inhibitor, antioxidant,    Sunolite 240
  antiozonant
Lubricant, activator       Carbowax 3350;
                             (polyethylene glycol)
Homogenizer                60 NS flakes
Processing aid,            WB 222
  dispersing agent
Plasticizer, softener      Stanplas 2000
Bonding agent              SCA 98
                             [bis(triethoxysilylpropyl)tetrasulfane]
                             SCA 985
                             [bis(triethoxysilylpropyl)disulfane]
Activator                  ZB
Vulcanizer                 Sulfur
Accelerator                * MOR
                             Vanax A (4,4'-dithiodimorpholine),
                             DPG (diphenylguanidine)

                           Supplier

Rubber                     Goodyear
Peptizer                   Struktol
Filler (silica)            Degussa
Activator
Processing aid             * DuPont
Antioxidant                Vanderbilt
Inhibitor, antioxidant,
  antiozonant
Lubricant, activator       Harwick
Homogenizer                Struktol
Processing aid,            Struktol
  dispersing agent
Plasticizer, softener      Harwick
Bonding agent              Struktol
Activator                  Struktol
Vulcanizer
Accelerator                * Harwick
Table 4--mixing formulations and procedure on NR
compounds

Formulation
1st stage             Control 1   Control 2   SCA98    SCA98
Material                (S4)        (S2)      (S4Z2)   (S4Z5)

SIR20                  100.00        --         --       --
A86                      0.25        --         --       --
Ultrasil VN3            57.00        --         --       --
Zinc oxide               4.00        --         --       --
Stearic acid             2.00        --         --       --
TiO2                     5.00        --         --       --
TMQ                      1.00        --         --       --
Sunolite 240             1.25        --         --       --
Polyethylene glycol      1.00        --         --       --
60 NS flakes             3.50        --         --       --
WB 222                   2.00        --         --       --
Stanplas 2000            4.00        --         --       --
SCA98 (S4)               2.50       0.00        2.50    2.50
SCA985 (S2)              0.00       2.50        0.00    0.00
ZB (ZB47)                0.00       0.00        2.00    5.00
2nd stage
Sulfur                   2.00        --         --       --
MOR                      2.00        --         --       --
Vanax A                  0.50        --         --       --
DPG                      0.50        --         --       --

Formulation
1st stage             SCA985   SCA985
Material              (S2Z2)   (S2Z5)

SIR20                   --       --
A86                     --       --
Ultrasil VN3            --       --
Zinc oxide              --       --
Stearic acid            --       --
TiO2                    --       --
TMQ                     --       --
Sunolite 240            --       --
Polyethylene glycol     --       --
60 NS flakes            --       --
WB 222                  --       --
Stanplas 2000           --       --
SCA98 (S4)             0.00     0.00
SCA985 (S2)            2.50     2.50
ZB (ZB47)              2.00     5.00
2nd stage
Sulfur                  --       --
MOR                     --       --
Vanax A                 --       --
DPG                     --       --

Mixing procedure

a. Add rubber and peptizer
b. Mix to 30 sec.
c. Add rest of additives
d. Mix to 121[degrees]C and sweep
e. Mix to 5 min. and dump
Table 5--the vulcanization characteristics of the
compounds at 160[degrees]C 30 min.

(Error = [+ or -] 2%)

Torque     Max.     Min.       [DELTA] torque        Ts2      Tc50
time      torque   torque   ([M.sub.H]-[M.sub.L])
(min.)     (MU)     (MU)            (MU)            (min.)   (min.)
System

S4         91.0     16.0            75.0             4.2       8.5
S4Z2       92.0     11.3            80.7             4.5      10.0
S4Z5       95.4      8.6            86.8             4.0       9.5
S2         89.5     14.2            75.3             4.8       9.2
S2Z2       87.2      9.2            78.0             5.2      10.5
S2Z5       90.7      8.4            82.3             4.8      10.4

Torque     Tc90    Reversion      Time
time                 (T-2)     ([M.sub.H])
(min.)    (min.)    (min.)       (min.)
System

S4         10.1      16.4         13.2
S4Z2       12.0      24.7         17.1
S4Z5       11.7       >30         19.7
S2         10.5      16.0         13.1
S2Z2       12.7      22.9         15.9
S2Z5       12.3       >30         19.8
Table 6--tensile properties of each compound

         Tensile     Elongation   Modulus   Modulus   Modulus
       stress max.      max.       100%      200%      300%
          (MPa)         (%)        (MPa)     (MPa)     (MPa)

S4        26.2          581         2.8       6.2      10.6
S4Z2      24.6          554         2.9       6.4      10.7
S4Z5      23.2          480         3.3       7.6      12.7
S2        27.0          606         2.5       5.6       9.8
S2Z2      25.4          562         2.8       6.2      10.5
S2Z5      24.9          537         2.8       6.5      11.1
Table 7--the ZB effects on the size and dispersion
of silica agglomerates in the NR compounds

                Compound     Number        Mass      Polydispersity
                            average      average           Pd
                           ([micro]m)   ([micro]m)

                S4           0.694        1.006          0.780
                S4Z2         0.527        0.707          0.577
Before          S4Z5         0.550        0.877          0.609
vulcanization   S2           0.783        1.706          0.966
                S2Z2         0.577        0.692          0.613
                S2Z5         0.503        0.644          0.546
                S4           0.422        0.608          0.741
                S4Z2         0.443        0.973          0.790
After           S4Z5         0.451        0.870          0.796
vulcanization   S2           0.400        0.452          0.708
                S2Z2         0.301        0.725          0.716
                S2Z5         0.391        0.677          0.749
Table 8--density and abrasion loss of vulcanized
s4 and S2 compounds

          Density       Abrasion loss
       (g/[cm.sup.3])   ([mm.sup.3])

S4          1.18             143
S4Z2        1.18             128
S4Z5        1.19             128
S2          1.17             133
S2Z2        1.18             136
S2Z5        1.19             131

References

(1.) "Rubber Handbook," Struktol Co. (2001).

(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. Gorl, A. Muller, M. Knaack and T. Gobel, Kautsch. Gummi Kunstst., 50, 881 (1997).

(5.) A. Hunsche, U. Gorl, H.G. Koban and 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. 1985.

(10.) Europe Patent EP0501 227, (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. 811, 1996. Paper No. 75.

(12.) A. McNeish and J.T. Byers, "Low rolling resistance tread compounds--some compounding solutions," ACS Rubber Division meeting, Anaheim, CA, May 1997.

(13.) 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. 1999.

(15.) C.R. Stone, K.H. Menting and D.M. Hensel, "Optimizing the use of disulphide silane in a silica 'green tire' tread compound," Schill & Seilachet, ACS Rubber Division meeting, Cincinnati, OH, Oct. 2000.

(16.) P. Cochet, "Highly dispersible reactive silica for low-rolling-resistance tires," Rhodia Silica, ITEC-2000 (No 22A), Akron, OH, Sept. 2000.

(17.) 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," ACS Rubber Division meeting, Providence, RI, Apr. 2001.

(18.) 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 and M.P. Wagner, Rubber Chem. Technol., 32, 1,286 (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).

(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 General des Establissement Michelin & Cie).

(30.) H.-D. Luginsland, J. Frohlich and A. Wehmeier, "Influence of different silanes on the reinforcement of silica-filled rubber compounds'," ACS Rubber Division meeting, Providence, RI, Apr. 2001.

(31.) 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, 1988.

(33.) J. VanderKooi, "Zinc soaps for improved vulcanizates: Part II," ACS Rubber Division meeting, Louisville, KY, Oct. 1996. Paper No. 2.

(34.) S. Montes, J.L White, and J. Nakajima, Non-Newtonian Fluid Mech., 28, 183 (1988).

(35.) J.L. White, "Principle of polymer engineering rheology," Wiley Inter-Science, New York (1990).

(36.) J.L. White, "Rubber processing: Technology materials, and principles," Hanser Publishers, Cincinnati, OH (1995).

(37.) A.N. Gent, "Engineering with rubber: How to design rubber components," Hanser Publishers, New York (1992).

(38.) U.S. Patent (filed June 9, 1931) 02,048,314 (July 21, 1936), R. W. Allen (Firestone Tire & Rubber Co.).

(39.) K.J. Kim and J. VanderKooi, "Comparative studies on effects of TESPT and TESPD treated silica compounds on processing and silica dispersion during mixing in natural rubber," ACS Rubber Division meeting, Cleveland, OH, Oct. 2001. Paper No. 93.

(40.) K.J. Kim and J.L. White, Polym. Eng. & Sci., 39, 2,189 (1999).