Carbon-silica dual phase filler application to passenger tread compounds.

Silica has been used widely, either alone or in blends with carbon black for high performance and OE tire applications in the European market (ref. 1). The silica-based tires feature reduced rolling resistance and enhanced wet traction performance. However, silica-based compounds are more expensive in comparison with conventional carbon black-based compounds, due to the higher cost of the filler and the requirement for a high level of expensive silane coupling agents. Precise controls of the mixing conditions and multistage mixing procedures are also needed to ensure sufficient silanization and good dispersion of the silica filler in the compound (ref. 2). In terms of tire performance, silica-based tires exhibit, in general, lower wear resistance than carbon black-based tires (ref. 3) and suffer from relatively lower dry traction performance. Due to the non-conductivity nature of silica, tires made of silica tend to accumulate static electrical charge. More complex methods of tire production are therefore needed to increase the overall electrical conductivity of tires (ref. 4).

To meet the ever-increased performance requirements for tires, Cabot has introduced a new class of reinforcement material, the CSDPF 4000 series product, a second generation carbon-silica dual phase filler (CSDPF), using a proprietary process technology (ref. 5). The new reinforcement filler features high surface activity of the carbon domain and high silica surface coverage, i.e., the amount of silica at the surface of the aggregate. Owing to the increased surface activity and optimized silica surface coverage, the CSDPF 4000 series filler demands less than half of the silane coupling agent loading that is typically used for silica-based passenger tread compounds. The unique surface characteristics and morphology of the silica and carbon black domains are expected to lead to a step improvement in the wet traction, rolling resistance and abrasion resistance compromise over conventional reinforcement fillers such as carbon black and silica. In this article, the general characteristics of the new reinforcing material will be reviewed briefly. The compounding techniques, properties of compounds and potential of the CSDPF 4000 filler for passenger tire applications will be discussed in detail. CSDPF 4210, commercially known as CRX 4210, from the new technology will be used as an example for discussions.

Experimental

Materials

Three reinforcing fillers were used in the study: CSDPF 4210, silica (Zeosil 1165MP from Rhodia) and carbon black (N234 from Cabot). The analytical properties of the fillers are listed in table 1. Two types of silane coupling agents were used, one being the tetrasulfide type, bis(triethoxysilylpropyl) tetrasulfide (TESPT), and the other being the disulfide type, bis(triethoxysilylpropyl) disulfide (TESPD).

A 70/30 SBR/BR blend was used in the compound. Both solution and emulsion SBRs were used for the CSDPF 4210 study. The non-oil extended version of the solution SBR is used in combination with the oil extended version when lower total oil loading is needed to maintain constant compound hardness. The properties of the elastomers used in the study are listed in table 2.

Compounding

Typical formulations used in the study are listed in table 3. The following variables were used to further investigate the property/performance of the CSDPF 4210 filler:

* Filler loading;

* silane coupling agent types and dosages; and

* DPG level.

A three-stage mixing procedure, as described in table 4, was in general used to mix the compounds. However, variations from the three-stage mixing procedure were introduced to investigate the effect of mixing conditions on properties of CSDPF 4210-based compounds. The variations include numbers of mixing stages (two vs. three stages) and heat treatment time/temperature during the first stage of mixing. A laboratory scale internal mixer with a 1.57-liter chamber was used in compound mixing.

Testing procedures described elsewhere were used to determine the properties of compounds, both cured and uncured, such as Mooney viscosity, cure characteristics, bound robber content, stress-strain properties, rebound, abrasion resistance and dynamic properties (ref. 6). A modified British Portable Skid Tester (BPST) was used for the assessment of wet skid resistance of compounds (ref. 7). The extrusion quality of compounds was evaluated based on the extrudate appearance per ASTM D2230-96.

Results and discussion

Compound mixing procedure

CSDPF 4210, as a silica-modified carbon black, would need a certain amount of a silane-coupling agent to further enhance the interaction between filler surfaces and elastomer. Owing to the unique combination of carbon black and silica on the same filler aggregate and the usage of coupling agents, the mixing procedure for CSDPF 4210-based compounds should be different from a traditional one used for carbon black-based compounds. This lies in the tact that a silanization process needs to be accomplished during compound mixing in order to promote the interaction between the coupling agent and the CSDPF 4210 surface. However, as will be discussed later, due to the active nature of the CSDPF 4210 surface and a much lower level of coupling agent compared with silica-based compounds, the mixing procedure for CSDPF 4210-based compounds could potentially be less intensive than for silica-based compounds. For CSDPF 4210-based compounds, some caution needs to be exercised in controlling the temperature to avoid excessive heating and to prevent significant gelation during mixing.

The effect of mixing procedures on properties of CSDPF 4210-based compounds is investigated by varying the mixing condition (heat treatment duration) and numbers of mixing stages from the base mixing procedure described in table 4 using formulations listed in table 3. A heat treatment/dump temperature of 150 [degrees] C was used during the first stage of mixing (temperature measured from a thermocouple inside the mixer. The actual temperature of dumped compounds measured from a temperature probe is about 8-10 [degrees] C higher). Silica and carbon black reference compounds were mixed using the base mixing procedure.

The effects of mixing conditions on hysteresis at 70 [degrees] C and abrasion resistance of CSDPF 4210-based compounds are summarized in figure 1. Clearly, lower dynamic hysteresis at high temperatures (tan [[delta].sub.max] at 70 [degrees] C, the maximum loss tangent from the strain sweep measurement) is achieved when some heat treatment is performed or a three-stage mixing procedure without heat treatment is used to mix CSDPF 4210-based compounds. The abrasion resistance of CSDPF 4210-based compounds, as measured from the Cabot abrader, however, does not seem to be significantly affected, unless a two-stage mixing procedure without any heat treatment is used to mix the compounds. It appears that a two-stage mixing procedure combined with some heat treatment or a three stage mixing procedure without heat treatment would be sufficient to achieve good abrasion resistance. It should be noted that even with a two-stage mixing procedure combined with some heat treatment or a three stage mixing procedure without any heat treatment, CSDPF 4210-based compounds exhibit more than 40% reduction in hysteretic loss in comparison with carbon black-based compounds. Less intensive mixing procedures could therefore be used for CSDPF 4210-based compounds with only a minor compromise in the hysteretic performance.

[FIGURE 1 OMITTED]

Lowering the heat treatment/dump temperature to 140 [degrees] C results in CSDPF 4210-based compounds with slightly higher tan [[delta].sub.max] at 70 [degrees] C, similar to what has been reported for first generation CSDPF-based compounds (ref. 8). The processability of compounds, rated from the extrudate appearance from the Garvey die extrusion, does not seem to be significantly affected. Such results seem to suggest that no significant gelation occurs at temperatures lower than 150 [degrees] C for heat treatment duration shorter than two minutes. To obtain compounds with good dynamic properties without compromise in processability, heat treatment/dump temperatures between 140 and 150 [degrees] C seem to be appropriate for CSDPF 4210-based compounds when tertrasulfide-type silane coupling agents are used. Higher mixing temperatures could potentially be used with disulfide type silane coupling agents due to higher thermal stability of this type of silane coupling agents, as with silica-based compounds (refs. 9 and 10).

One of the unique characteristics of the CSDPF 4210 filler, in comparison with silica, is the fast incorporation of the CDSPF 4210 filler during compound mixing. Overall, when temperature is used as a criterion for compounding mixing/dumping, the total mixing time for CSDPF 4210-based compounds is about one minute shorter compared with silica-based compounds during the first stage of mixing when the mixing procedure listed in table 4 is used. It is generally believed that the incorporation process is the wetting of the filler with the rubber matrix and the displacement of the entrapped air (ref. 11). Silica, being hydrophilic in nature, has poor wettability with the SBR/BR matrix. Even in the presence of a silane coupling agent, a certain amount of time is still needed for the silanization process to occur such that the compatibility of silica with the elastomer matrix is enhanced. In the case of the CSDPF 4210 filler, close to 50% of the aggregate surface is carbon in nature, and the carbon black phase has a high activity towards non- or low polar polymer molecules as suggested by results from the inverse gas chromatography (IGC) measurement of the CSDPF 4210 tiller. The presence of the carbon phase and its high activity towards polymer will therefore enhance the wettability of the CSDPF 4210 filler with the SBR/BR polymer matrix, resulting in reduced incorporation time. Such a unique feature of the CSDPF 4210 filler will make possible increased mixing efficiency, hence, reduced total mixing cost for CSDPF 4210-based compounds in comparison with silica-based compounds.

Bound rubber content

Bound rubber content has long been recognized as an important factor for rubber reinforcement and is, in general, considered to be a measure of the surface activity of the filler (refs. 12 and 13). Bound lubber formation in carbon black-based compounds can also be affected by other factors, including the morphology of the filler, polymer composition and mixing conditions (ref. 14). In rubber compounds containing a silane-coupling agent, bound rubber formation is further complicated from the enhancement of the interaction between polymer and filler surfaces by the coupling reaction, especially when the mixing temperature is high (ref. 15). To use bound rubber content as an assessment for the surface activity of the CSDPF 4210 filler, coupling agents were excluded from the formulation and the same mixing procedure was followed to mix all compounds. The mixing procedure as described in table 4 and formulations listed in table 5 were used for the bound rubber study. The total filler weight loading (silica plus carbon black) is adjusted such that equal volume filler loading is maintained in all compounds. The DPG loading was adjusted slightly to reflect the silica content in the compounds.

Figure 2 shows the bound rubber content of CSDPF 4210-based compounds without silane coupling agents in comparison with compounds containing silica, carbon black and their blends. Clearly, the bound rubber content for silica/carbon black blend-based compounds decreases linearly with increasing silica content, indicating that the total bound rubber content in silica/carbon black blend-based compounds is an additive function of contributions from the individual fillers in the blend. However, the bound rubber content of CSDPF 4210-based compounds does not follow such an additive function generated from carbon black and silica, showing a value even higher than carbon black-based compounds. The result is quite surprising, considering the fact that about 50% of the CSDPF 4210 aggregate surface is covered by silica (ref. 5). In general, the bound rubber content for silica-based compounds without silane coupling agents is much lower than that of compounds containing carbon black with a similar surface area (ref. 12). The bound rubber content of compounds would then be expected to reduce when the surface of the filler aggregate is covered by silica. The high bound rubber content in CSDPF 4210-based compounds therefore clearly suggests that the surface of the carbon black phase in the CSDPF 4210 filler is much more active than that of conventional carbon blacks.

[FIGURE 2 OMITTED]

The bound rubber content of CSDPF 4210-based compounds is further increased when a coupling agent is introduced, as shown in figure 2. In contrast to the case without a silane-coupling agent, the bound rubber content of silica/carbon black-based compounds in the presence of the coupling agent increases with silica content in the compound. This can be attributed to the reaction of the coupling agent with silica and polymer, forming some chemical bonds between silica and elastomer molecules and between elastomer molecules, since TESPT is also a sulfur donor. The coupling agent could also react with functional groups and active sites on the carbon black surface as suggested in the literature (ref. 16).

The high surface activity of the CSDPF 4210 fillet" is also confirmed from the measurement of free energies of adsorption of low molecular weight analogs of rubber molecules using IGC (ref. 17). The free energy of adsorption of heptane, which is taken as a model molecule for nonpolar polymers (ref. 18), on the CSDPF 4210 filler is found to be higher than that of its carbon black counterpart, N234, and much higher than that of a 50/50 silica/carbon black blend. Such a result clearly demonstrates that the CSDPF 4210 filler has strong interaction with polymer molecules in rubber compounds.

It has been well recognized that the energetic center of the carbon black surface is related to the defect of the crystal lattice, edges of crystallites or their basal planes, and/or less organized carbon atoms in the quasi-graphitic structure (refs. 19 and 20). The fact that higher free energies of adsorption are achieved with non-polar probes in the CSDPF 4210 filler suggests that the presence of the silica phase in the filler aggregate increases the numbers of surface-active centers of the carbon phase. This may be due to an increased population in the crystal defects and reduced size of the basal planes (ref. 17). The high surface activity of the CSDPF 4210 filler is expected to have a significant implication on the physical properties of CSDPF 4210-based compounds.

Processing characteristics of compounds

The processing characteristics of compounds are listed in table 6. The Mooney viscosity of CSDPF 4210-based compounds is influenced by silane coupling agent dosages. It is worthwhile to mention that the Mooney viscosity of silica-based compounds is much higher than that of CSDPF 4210 based compounds when no silane coupling agent is present (160 Mooney units for silica-based compounds vs. 120 Mooney units for CSDPF 4210-based compounds).

The high Mooney viscosity of silica-based compounds without a silane-coupling agent is generally believed to be due to the tendency of silica to form a strong filler-filler network in the green compound (refs. 21 and 22). The high Mooney viscosity of silica-based compounds is in agreement with the large Payne effect of cured compounds when no silane-coupling agent is present (refs. 5 and 23). The high Mooney viscosity of CSDPF 4210-based compounds without a coupling agent is, however, quite surprising, since, as will be discussed later, CSDPF 4210-based compounds exhibit a very low Payne effect even when no coupling agent is present. It appears that while filler networking may result in higher Mooney viscosity, high bound rubber content in CSDPF 4210-based compounds may also contribute to the increased Mooney viscosity when no coupling agent is used. The formation of bound rubber would immobilize the molecular chains around the filler particles and the entanglement of the immobilized molecular chains would give rise to increased compound viscosity.

The cure characteristics of CSDPF 4210-based compounds were found to vary with CSDPF 4210 filler loading when the same cure package was used. The t'90, for example, increases with CSDPF 4210 loading. The change in cure kinetics could be explained from the acidity of silica and by the adsorption of curatives on the silica domain. It is well recognized that silica tends to adsorb a significant level of curatives, causing delay in the onset of the vulcanization process and the reduction of the crosslinking density in compounds (ref. 24). Since about half of the surface of the CSDPF 4210 aggregate is silica, the presence of silica at the surface of the CSDPF 4210 aggregate would therefore be expected to influence the cure kinetics of CSDPF 4210-based compounds. The cure kinetics of CSDPF 4210-based compounds can be adjusted, for example, through variations of the level of a secondary accelerator, such as DPG. It should be noted that in comparison with silica-based compounds with similar filler loading, a much lower DPG level is needed in CSDPF 4210-based compounds to achieve desirable cure characteristics.

Stress-strain properties

The tensile and other physical properties of compounds are listed in table 7. There is about a four-unit difference in the room temperature hardness between carbon black- and CSDPF 4210-based compounds. Without silane coupling agents, CSDPF 4210-based compounds would exhibit similar hardness at room temperature as silica/coupling agent- and carbon black-based compounds when roughly equal volume loading is used. The reduction in the morn temperature hardness when a coupling agent is introduced can be explained from a further reduction in filler-filler interaction in CSDPF 4210-based compounds. The tensile properties of CSDPF 4210 based compounds are, in general, similar to those of silica- and carbon black-based compounds.

Dynamic properties

The storage modulus at both 0 and 70 [degrees] C of CSDPF 4210-based compounds without silane coupling agents is compared with that of silica/carbon black blend-based compounds in figure 3. As can be seen, the small strain (0.1%) storage modulus of silica/carbon black blend-based compounds does not increase linearly with silica content at both low and high temperatures. Rather. a minimum in the storage modulus is achieved at certain silica content. The minimum is especially well defined when compounds are tested at low temperatures. A similar trend is seen when the difference in storage moduli between small strain (0.1%) and large deformation (60%) ([DELTA]G' = [G'.sub.o] - [G'.sub.[infinity]], where [G'.sub.o] is the storage modulus at 0.1% and [G'.sub.[infinity]] the storage modulus at 60% strain) is plotted against silica content, as shown in figure 4. The dependence of the storage modulus on the strain level under dynamic deformation is referred to as the Payne Effect (ref. 25). The observation that [DELTA]G' does not increase linearly with silica content is a clear indication that a less developed filler-filler network is formed in silica/carbon black blend-based compounds when no silane coupling agent is present (ref. 23). This phenomenon can be explained from a theoretical model developed by Wang by taking into consideration the filler-polymer and filler-filler interactions when two fillers with different characteristics (surface free energies, both dispersive and polar components) are present and different interactions (hydrogen bonding and acid-base interaction) are involved in compounds (ref. 23). First of all, the interaction between silica and carbon black aggregates is weaker than that between any of these two filler aggregates. Secondly, the mean distance between the same types of aggregates which have a higher attractive potential are larger in the blend than for any of their single filler counterparts, hence less flocculation of the aggregates would be expected in the blend. From the consideration of thermodynamics and kinetics of filler network formation, a silica/carbon black blend-based compound would be expected to show lower Payne effect than what would be predicted from the additive function of the two single filler-based compounds.

[FIGURES 3-4 OMITTED]

It is worthwhile to note that CSDPF 4210-based compounds without a silane coupling agent show very low [DELTA]G' values that approach the lowest exhibited by the silica/carbon black blend system, a clear indication of weak filler-filler interaction in CSDPF 4210-based compounds. The weak filler-filler interaction in CSDPF 4210-based compounds can be explained by the reduced probability for the aggregate surface to face the same category of surfaces of the neighboring aggregate when the carbon black aggregate is partially covered by silica. In addition, the higher bound robber content in CSDPF 4210-based compounds would prevent or reduce the flocculation of the filler, further reducing the filler network formation.

Filler-filler interaction is further depressed and filler-polymer interaction enhanced in CSDPF 4210-based compounds when a coupling agent is introduced as revealed, from an even lower Payne effect, as shown in figure 5. The coupling agent would react with silanol function groups at the surface of the CSDPF 4210 filler and with polymer chains. The chemical bonding via the coupling agent between filler surfaces and elastomer chains would strengthen filler-polymer interaction, thereby effectively reducing filler-filler interaction.

[FIGURE 5 OMITTED]

Weak filler-filler interaction and strong filler-polymer interaction via strong adsorption of elastomer molecules on the CSDPF 4210 surface and through strong coupling reaction would be expected to lead to compounds with low hysteretic loss at high temperatures. Indeed, that is the case as is shown in figure 6 where the dynamic hysteretic characteristics of CSDPF 4210-based compounds are compared with those of silica-, carbon black- and silica/carbon black blend-based compounds. Clearly, the hysteretic loss curve from CSDPF 4210-based compounds, when a loading level of 2.7 phr TESPT is used, virtually matches that of silica-based compounds with 6.4 phr of TESPT. In fact, as shown in figure 7, a minimum in tan [[delta].sub.max] at 70 [degrees] C seems to be reached for CSDPF 4210-based compounds when the TESPT level is about 3.5 to 4.0 wt.% (of CSDPF 4210 filler loading, i.e., 2.5 to 2.9 phr of TESPT for 72 phr CSDPF 4210-based compounds), i.e., less than half of the level needed for silica-based compounds.

[FIGURES 6-7 OMITTED]

As is with other types of reinforcing fillers, the high-temperature hysteretic properties of CSDPF 4210-based compounds are influenced by filler loading. However, as shown in figure 8, the dependence of high-temperature hysteretic loss on filler loading is less for CSDPF 4210-based compounds compared with carbon black-based compounds. Such results seem to suggest that optimization of filler loading could be achieved with the CSDPF 4210 filler to enhance other desirable tire performances such as abrasion resistance and traction performance without sacrificing much of the hysteretic performance of CSDPF 4210-based compounds.

[FIGURE 8 OMITTED]

It has been well recognized that rolling resistance of a tire is correlated with hysteretic loss at high temperatures (tan [delta] at 50-70 [degrees] C) of compounds (ref. 26). The close match of hysteretic properties between CSDPF 4210- and silica-based compounds indicates CSDPF 4210-based compounds would give rise to tires with rolling resistance performance comparable with silica-based tires.

Wet skid resistance

The prediction of wet traction performance based on laboratory results has been proven to be more difficult than with rolling resistance. This is understandable considering the complexity of the interaction between tires and road surfaces under wet conditions. Many factors could influence such interaction, such as the roughness of road surfaces, testing speed, temperatures, ABS vs. non-ABS and vehicle load. Dynamic properties of compounds, such as hysteretic loss at low temperatures (tan [delta] between -15 [degrees] C to 5 [degrees] C), have been found, to a certain extent, to correlate with the wet skid performance of tires (refs. 27 and 28). High hysteretic loss at low temperatures is considered to be beneficial for enhanced wet skid resistance of tires, considering the high frequency associated with the braking of tires. As is shown in figure 6, CSDPF 4210-based compounds exhibit high hysteretic loss at low temperatures (<0 [degrees] C), similar to silica-based corn pounds. Clearly, based on the consideration of absorption of energy during tire braking, CSDPF 4210-based compounds would be expected to show good wet traction performance.

To further assess wet skid resistance of CSDPF 4210-based compounds, other than low-temperature dynamic properties, a modified British Portable Skid Tester (BPST) was used to measure the friction force between rubber compounds and a sandblasted glass plate considered to be a model road surface under wet conditions. As shown in figure 9, the wet skid resistance of CSDPF 4000 series filler-based compounds is a linear function of the surface area of the silica portion oil the filler aggregate. The surface area of the silica portion is defined as the product of silica coverage, i.e., the amount of silica at the surface of the filler aggregate and the total surface area of the CSDPF 4000 series filler. It should be noted that in comparison with the first generation CSDPF 2000, enhanced wet skid resistance is achieved with CSDPF 4000 series filler-based compounds when the same amount of silica is present in the aggregate. Apparently, silica is used very efficiently in the CSDPF 4000 technology to enhance wet skid resistance of compounds. Such enhancement in wet skid resistance is made possible by significantly increasing the silica coverage at the surface of the CDSPF 4000 aggregates.

[FIGURE 9 OMITTED]

It has been shown that there is some correlation between the wet skid resistance value as measured from the BPST and the wet traction performance of tires (ref. 29). With a substantial increase in wet skid resistance as measured by BPST, CSDPF 4210-based compounds can be expected to exhibit much enhanced wet traction performance.

It has been recognized through our extensive work on wet traction mechanisms that, while the low-temperature hysteretic loss of compounds is important, other factors are equally, if not more, critical in determining the wet traction performance of tires (ref. 30). Those factors include the elasto-hydrodynamic lubrication (EHL), especially micro elasto-hydrodynamic lubrication (MEHL) and boundary lubrication (BL). When a tire is in contact with a wet road surface, the contact area can be divided into three zones (ref. 31):

* A squeeze-film zone is located in the front where the water film is progressively squeezed out under the action of inflation. EHL and MEHL are of importance for friction in this zone.

* A transition zone occurs where the tire element, having penetrated the squeeze film, begins to drape dynamically about major asperities of the road surface and to make contact with lesser asperities.

* A traction zone occurs where water film has been almost totally removed. BL plays a more important role in governing the skid resistance in this zone. In the squeeze-water and transition zones, silica-based compounds would show a significant advantage over carbon black-based compounds with respect to wet skid resistance. However, in the traction zone where boundary lubrication is important, carbon black-based compounds would exhibit better skid resistance. The CSDPF 4210 filler, having characteristics of both silica and carbon black within the same aggregate, would then be expected to result in compounds with good skid resistance under both EHL and BL conditions.

Abrasion resistance

A Lambourn abrader type machine was used to assess the abrasion resistance of compounds. As shown in figure 10, the abrasion resistance of CSDPF 4210-based compounds in general increases with TESPT loading until a level of about 4 wt. % (of filler loading) is achieved, Clearly, CSDPF 4210-based compounds exhibit higher abrasion resistance than silica-based compounds, even though only half of TESPT silane coupling agent is used. However, the abrasion resistance of CSDPF 4210-based compounds does not quite reach the level of N234-based compounds when the same filler loading is used. Nevertheless, as pointed out previously, due to the low hysteretic loss at high temperatures and less sensitivity of the hysteretic loss to filler loading variations in CSDPF 4210-based compounds, an optimized loading can potentially be achieved with the CSDPF 4210 filler for enhanced abrasion resistance.

[FIGURE 10 OMITTED]

It has been shown that overall good performance is achieved in silica-based compounds when solution SBR is used in combination with silane coupling agents (refs. 32 and 33). However, as shown in figure 11, silica-based compounds exhibit poor abrasion resistance when emulsion SBR is used. In contrast, better abrasion resistance is achieved when the same emulsion SBR is used with the CSDPF 4210 filler, even though the abrasion resistance of CSDPF 4210/ emulsion SBR-based compounds is not as good as their solution SBR-based counterparts. The reason for the poor abrasion resistance of silica-based compounds containing emulsion SBR is believed to relate with the tendency of silica to adsorb strongly polar ingredients in emulsion SBR similar to what is believed to happen ill the silica/NR compound system (ref. 34). In general, 5-7% of organic compounds with polar groups, mainly surfactants, is left in dry emulsion SBR (ref. 35). The adsorption of such polar components by silica would reduce the efficiency of the coupling reaction in the compound system, hence reducing the abrasion resistance of silica/emulsion SBR-based compounds. Similarly, the reduction of the abrasion resistance of CSDPF 4210-based emulsion SBR compounds compared with their solution SBR counterparts can be explained from the adsorption of the polar ingredients by the silica phase of the CSDPF 4210 aggregates. However, since a highly active carbon phase is also present simultaneously on the same aggregates, the carbon phase will contribute positively toward the abrasion resistance of CSDPF 4210-based compounds, hence better abrasion resistance in comparison with silica-based compounds when emulsion SBR is used.

[FIGURE 11 OMITTED]

Conclusion

Owing to the unique characteristics of the CSDPF 4210 filler, high filler-polymer interaction is demonstrated in CSDPF 4210-based compounds by high bound rubber content. CSDPF 4210-based compounds exhibit low hysteresis at high temperatures that is comparable with silica-based compounds with the additional benefit of lower silane coupling agent dosage. CSDPF 4210-based compounds can therefore be expected to offer low rolling resistance for tire applications. CSDPF 4210-based compounds also exhibit enhanced wet skid resistance as measured by BPST. Since carbon black- and silica-based compounds contribute differently to wet traction in different contact zones of tires with road surfaces, CSDPF 4210-based compounds would be expected to exhibit overall good wet traction performance under a wide range of conditions. Due to the dual phase nature of the CSDPF 4210 filler, CSDPF 4210-based compounds have better abrasion resistance than silica-based compounds and can therefore be expected to show enhanced treadwear performance. The CSDPF 4210 filler thus appears to be an excellent candidate for tread applications to accomplish an overall good balance among three critical performances - rolling resistance, wet traction and wear resistance.

Table 1 - analytical properties of fillers

Filler             Si         STSA         DBP      CDBP      Silica
                 content    (t-area)     ml/100g   ml/100g   coverage
                    %      [m.sup.2]/g                          %
Carbon black
  N234             N/A         118         125       100       N/A
CSDPF 4210        10.2         119         157       108        55
Silica (Z1165)    46.7         132         N/A       N/A       100
Table 2-analytical properties of elastomers

Polymer            Type       Extender oil   Bound styrene
                                  phr              %

SSBR, VSL 5025-1   Solution       37.5            25
ESBR, SBR 1712C    Emulsion       37.5           23.5
ESBR, SBR 1721     Emulsion       37.5            40
BR, Budene 1207    Solution        --

Polymer            Cis 1,4   Vinyl content    MV         Tg
                   content
                      %            %                 [degrees] C

SSBR, VSL 5025-1     --            50        40-50       -18
ESBR, SBR 1712C      --            --        43-53       -56
ESBR, SBR 1721       --            --        42-54       -35
BR, Budene 1207      98           1.5        50-60      -104
Table 3 - typical compound formulation

Ingredient                   Silica   N234   CSDPF
                                              4210

OE-SSBR (Buna VSL5025-1)       96.3   96.3    96.3
BR (Budene 1207)               30.0   30.0    30.0
Silica (Z1165)                 80.0
Carbon black (N234)                   72.0
CSDPF 4210                                    72.0
Coupling agent TESPT            6.4            2.7
Aromatic oil                    1.8    1.8     1.8
Zinc oxide                      3.0    3.0     3.0
Stearic acid                    2.0    2.0     2.0
Antioxidant (Santoflex 13)      1.0    1.0     1.0
Antioxidant (Wingstay 100)      1.0    1.0     1.0
Wax (Sunproof Imp)              3.5    3.5     3.5
CBS                             2.0    1.1     1.6
Sulfur                          1.4    1.4     1.4
DPG                             2.1    0.3     1.0
Table 4 - internal mixer 3-stage mixing procedure

Stage 1 (50 rpm walls at 50 [degrees] C, rotors at 60 [degrees] C,
fill factor: 0.70)
 0 sec.               Polymer
30 sec.               Filler and silane coupling agent
At  90 [degrees] C    Zinc oxide/stearic acid/antioxidant/wax
At 110 [degrees] C    Sweep and increase RPM to 80
At 120 [degrees] C    Add oil
At 150 [degrees] C    Heat treatment for 2 min.
                      Dump

Stage 2 (80 rpm, walls at 50 [degrees] C, rotors at 60 [degrees] C,
fill factor." 0.70)
 0 sec.               Stage 1 compound
At 150 [degrees] C    Dump

Stage 3 (50 rpm, walls at 50 [degrees] G, rotors at 60 [degrees] C,
fill factor: 0.60)
 0 sec.               1/2 compound, curatives, 1/2 compound
At 110 [degrees] C    Dump
Table 5 - compound formulation without a silane coupling agent

Compound No.                   A-1     A-2     A-3     A-4

OE-SSBR (Buna VSL5025-1)      96.3    96.3    96.3    96.3
BR (Budene 1207)              30.0    30.0    30.0    30.0
Silica (Z1165)                80.0    62.0    45.0    29.0
Carbon black (N234)                   16.0    30.0    44.0
CSDPF4210
Aromatic oil                   1.8     1.8     1.8     1.8
Zinc oxide                     3.5     3.5     3.5     3.5
Stearic acid                   2.0     2.0     2.0     2.0
Antioxidant (Santoflex 13)     1.0     1.0     1.0     1.0
Antioxidant (Wingstay 100)     1.0     1.0     1.0     1.0
Wax (Sunproof Imp)             3.5     3.5     3.5     3.5
CBS                            2.0     2.0     1.6     1.5
Sulfur                         1.4     1.4     1.4     1.4
DPG                            2.1     1.7     1.4     1.0
Total phr                    224.5   222.1   218.4   215.9
% silica                       100      80      60      40

Compound No.                   A-5     A-6     A-7     A-8

OE-SSBR (Buna VSL5025-1)      96.3    96.3    96.3    96.3
BR (Budene 1207)              30.0    30.0    30.0    30.0
Silica (Z1165)                14.0     7.0
Carbon black (N234)           57.0    63.0    69.0
CSDPF4210                                             71.0
Aromatic oil                   1.8     1.8     1.8     1.8
Zinc oxide                     3.5     3.5     3.5     3.5
Stearic acid                   2.0     2.0     2.0     2.0
Antioxidant (Santoflex 13)     1.0     1.0     1.0     1.0
Antioxidant (Wingstay 100)     1.0     1.0     1.0     1.0
Wax (Sunproof Imp)             3.5     3.5     3.5     3.5
CBS                            1.3     1.2     1.1     1.6
Sulfur                         1.4     1.4     1.4     1.4
DPG                            0.7     0.5     0.3     1.0
Total phr                    213.4   212.1   210.8   214.0
% silica                        20      10       0      22
Table 6 - processing characteristics of compounds

Compound    Filler         TESPT
ID          type            phr      min.      max.
A           Silica          6.4       7.9      35.4
B           N234            N/A       7.8      27.4
C           CSDPF 4210      2.7       9.1      28.7

                                              Mooney viscosity
Compound    Filler         ts-2      t'90         ML(1+4)
ID          type           min.      min.       Mooney units
A           Silica         3.95      13.21           73
B           N234           4.46      10.90           81
C           CSDPF 4210     3.44      12.62           86
Table 7 - physical properties of compounds

Compound   Filler       TESPT    [sigma] 100   [sigma] 300   [sigma] b
ID         type          phr         MPa           MPa          MPa
A          Silica        6.4        2.27          10.18        17.81
B          N234          N/A        2.08          9.29         19.13
C          CSDPF 4210    2.7        1.96          9.79         19.62

                                       [sigma] 300/     Tear
Compound   Filler       [epsilon] b    [sigma] 100      strength
ID         type             (%)           Ratio         N/mm
A          Silica           457            4.49         34
B          N234             542            4.48         36
C          CSDPF 4210       492            4.99         35

Compound   Filler       25 [degrees] C    70 [degrees] C
ID         type                %                 %
A          Silica             36                57
B          N234               26                41
C          CSDPF 4210         35                55

                        Durom. A hardness
Compound   Filler       25 [degrees] C    70 [degrees] C
ID         type
A          Silica             65                59
B          N234               65                57
C          CSDPF 4210         61                56

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