Reviewing C&C testing of OTR tread compounds.

Experienced compounders know that enhancing field performance for one service application may also produce an adverse result in another application. This is particularly true with OTR tires and the cut and chip (C&C) performance of their treads. The variety of degradation mechanisms in the field demands an in-depth understanding of the impact of each formulation change. With multiple applications, there is often no universal solution, and the ability to test in each environment is not economically feasible. The laboratory offers an alternative, but only if the results of the testing are predictable. Unfortunately, many of the methods used today to evaluate this property have had limited success. This program was designed to study the effectiveness of a commercial laboratory cut and chip tester and to evaluate the ability of several laboratory abrasion testers to discern differences in compounds.

To start a discussion on cut and chip testing, it is essential to first clarify terminology. The term "abrasion resistance" testing will be used in a very broad context to refer to a category of tests that includes cut and chip, abrasion and even tearing type tests. The five specific tests chosen for this evaluation were BFGoodrich cut and chip, rotary drum abrasion (DIN abrader), pico abrasion, rotary drum abrasion (footwear or NBS abrader) and tear strength. Each test has a unique degradation mechanism:

* cut and chip tester--impact and chipping;

* DIN abrasion--abrasion;

* pico abrasion--cutting and abrasion;

* NBS abrasion--abrasion; and

* tear strength, die B--tearing.

The mechanism of the C&C tester is closely related to its name; however, the cutting portion of this test has been characterized as "impact" to differentiate this type of mechanism from the cutting action of the pico abrader. Abrasion is the predominant mechanism for both the DIN and NBS tests, but even between these two methods, it is important to understand the differences. The DIN test is typically run with the specimen traversing across the rotating drum, while the NBS is a fixed position test.

The diversity and complexity of degradation mechanisms on these tests can yield unexpected results when data are viewed on a macro level and treated generally in a category of abrasion or even more broadly as stock toughness. Mirroring the field condition, a compound formulation change that improves the results tot one test often negatively impacts another. To predict abrasion performance, a compounder must rely on experience and an in-depth understanding of any change's impact on the specific mechanism unique to the subject test.

Experimental

Test methods

The following instruments and test measurements were chosen for this investigation:

* BFGoodrich cut and chip tester--a vulcanized rubber annulus is mounted onto a drive spindle and rotated at 78.5 rad/s. The test piece is impacted by a tungsten carbide knife of specified geometry that is mounted at the end of a beam lifted by an eccentric cam device driven at 1 Hz. The beam rebounds from the test piece by the action of the drive mechanism and the rebound resilience properties of the test piece. This action continues with each lift and drop cycle for the preset test duration. The loss of mass and reduction in diameter are then determined. Loss of mass was used in this study for comparative purposes.

* Pico abrader--a pair of tungsten carbide knives of specified geometry and sharpness abrade the surface of a circular test piece rotated under controlled conditions of speed, time and three on the knives. A powdered material is applied to the surface of the test piece to suspend the abraded robber particles. After testing is completed, the mass loss of the test piece is determined. ASTM D2228 details the procedure used.

* NBS abrader--square blocks of specified dimensions are run against abrasive paper of a given grit size mounted to a drum rotating at 4.71 rad/s. A downward force on each test piece of 22 N maintains this contact. The test piece is abraded until 2.5 mm of thickness is removed, as measured by a dial indicator mounted above the test piece. The number of revolutions is then recorded and compared to a reference standard to produce an abrasive index as specified in ASTM D1630.

* DIN abrader--in accordance with ASTM D5963, a cylindrical test piece in inserted into a holder that controls the depth of sample exposure. The assembly is positioned normal to the surface of a rotating drum at 4.19 rad/s, covered with abrasive paper of specified grit. The assembly is then driven at a controlled rate under constant load along the axis of the rotating dram while rotating about its own axis. At the end of this single pass, the sample is removed mid volume loss and abrasion index values are calculated. The index values were used for comparative purposes.

* Tensile properties--tensile properties measurements for tensile stress at break, tensile strain at break and tensile stress at 300% strain are detailed in ASTM D412.

* Hardness--indentation hardness is determined using an A scale durometer according to ASTM D2240.

* Tear strength--tear resistance is measured using an ASTM D624 die B test piece that has been razor nicked to the appropriate depth. Tear strength is reported as the maximum force divided by the sample thickness.

* Rebound resilience--in ASTM D1054, the pendulum rebound procedure is detailed in Method B. A cylindrical sample is mounted in a holder and impacted by a free falling pendulum of specified length, mass and attached indentor geometry. As the indentor rebounds after impacting the test piece, the angle of rebound is measured and used in calculating rebound resilience.

* Crosslink density--crosslink density (CLD) is primarily a measure of the extent of vulcanization. This can be affected by the time of vulcanization and the type and amount of chemicals used in the process. By utilizing a solvent swelling technique, the crosslink density can be indirectly measured. CLD is measured by swelling the vulcanized sample in solvent, drying and calculating mass changes before and after immersion.

Compound design

A total of 12 compound formulations was developed, mixed and tested for this study. The formulas are shown in table 1. The recipes were designed in an attempt to create significant differences in expected abrasion properties and thus be able to measure the ability of the test methods to discern differences. It was accepted that generating significant differences meant developing formulations that were not always representative of treads used in actual OTR tires.

Base compound or control

The recipe used for the base compound is shown in table 2. SIR-10 was used as the polymer for this 100% natural rubber compound. N121 carbon black was chosen due to high reinforcing properties and high abrasion resistance. It is recognized that this black might not be used traditionally in some OTR treads due to high cost and difficulty in processing, but for the purpose of this study, it was decided that N121 was an appropriate choice. Aromatic oil, to aid processing, was added at a low level. Typical levels of zinc oxide and stearic acid were used along with TMQ/6PPD for degradation protection. The cure package included OBTS and rubbermakers sulfur. OBTS was used as it traditionally is in products having relatively thick sections, such as OTR tires.

Base compound with modified cure system

Two compounds were mixed with the cure system modified. A compound with the sulfur and accelerator doubled and a compound having the sulfur and accelerator reduced by 50% were prepared. Results of these mixes are compared to the control compound.

Base compound with addition of resins to improve abrasion resistance

Two compounds were mixed with a controlled level of different resins added to the base compound. These reinforcing resins have been promoted to improve abrasion and cut and chip resistance. The first product evaluated was a reactive processing aid, UltiPro 100 from Indspec Chemical. This material was used at a level of three parts per hundred of polymer, and HMT was added at 11% of the UltiPro. The second resin, SP-6701, a phenolic resin from Schenectady International, was also used at three parts per hundred of polymer. Hexamethylenetetramine, HMT, was added at 33% of total resin. Results of these mixes are compared to the control compound.

Compound with a 50/50 blend of NR/BR

A compound was designed to include a 50/50 blend of natural rubber and high cis polybutadiene, BR. The carbon black and oil levels remained the same, and the cure system was not modified, with the exception of a slight increase in OBTS. This compound was included to investigate the effect of BR, which normally changes the compound's rebound characteristics, thus affecting C&C properties. Results of this mix are compared to the control compound.

Compound with SBR

This compound contained 100% non-oil extended emulsion styrene butadiene rubber (SBR 1502). The carbon black type and level were unchanged. The oil level was increased to accommodate a 100 phr synthetic compound. Additionally, the curative levels were adjusted and a secondary accelerator, DPG, was added. Results of this mix are compared to the control compound.

Base compound with precipitated silica replacement of CB

Two compounds were mixed with precipitated silica replacing 100% of the carbon black at the same loading level. The first compound also included a designated level of polyethylene glycol, PEG 3350, to prevent the absorption of the accelerator by the silica. The second compound included the use of an organo-silane coupling agent (X50S, 50/50 blend of N330 and Si-69) and a different mixing procedure to react the silane with the silica and provide a higher level of reinforcement to the compound. Differences between the two compounds and a comparison to the base compound are reported.

Base compound with changes in carbon black levels

Two compounds were mixed with variations in the carbon black. In the first compound, the carbon black level was increased 10 phr over the base compound. The second compound reduced the carbon black level by 10 phr. Results of these mixes are compared to the base compound.

Base compound with industry reference carbon black

A single compound was mixed with Industry Reference Black #7, replacing N121. This carbon black is actually a select grade of N330. Results of this mix are compared to the control.

Discussion of results

A somewhat non-traditional approach will be taken in reviewing the results of the study. Instead of simply presenting the results and discussing the findings, this article will contrast the anticipated outcome to what was found upon completion of the work. In the initial treatment, all abrasion tests are placed in a single group in terms of the anticipated result, and thus any compound change is predicted to have the same impact on each test. The predictions will be based on the anticipated impact a change will have on stock "toughness." This approach is taken specifically to highlight the difficulty one might encounter when abrasion testing is viewed without consideration as to the uniqueness of each test protocol. It is recognized that predictions, by their nature, are subject to debate. The anticipated results presented within are made from the perspective of a rubber compounder, but one with possibly limited experience. Certainly a compounder with 25 years of lab and field experience in this area would have gained insight that could make their anticipations for each individual test different than those offered here.

First, a few mechanical/physical test results will be reviewed to determine if the formula change had the intended impact on typical properties used to characterize compounds. Second, the abrasion results will be reviewed in a similar manner. To simplify the review of the abrasion properties, a summary table will be presented detailing the anticipated test result versus the actual test result. In these tables, the test data will be shown as either a plus (+), minus (-) or equal (=), with the comparative basis being the control stock. The anticipated results in the table are projected based upon what is likely to happen to stock toughness with the change to the formula. Stock toughness is a very broad term and is used only to provide a starting point for the discussion. Actual results for the abrasion testing highlight the possible counterintuitive findings when toughness is used as the sole predictor. "Unusual" findings from this cursory review are then discussed in more detail with consideration given to the specific degradation mechanism of the subject test and the specific change to the formula.

At the end of this section, the results from a simple linear regression analysis are discussed as an attempt was made to correlate the results from the BFG C&C tester were attempted to be correlated to the other abrasion tests.

The test results for all 12 stocks are shown in table 3. However, to review the results in more detail each type of compound change will be discussed individually.

Cure system changes

Two changes were made to the base stock. For the first change, the levels of sulfur and accelerator (OBTS) were doubled; and for the second change, the levels of each were halved. Table 4 highlights the changes specific to the cure system.

Assuming a relatively optimized conventional cure system for the base stock, the anticipated result from these two changes is that both should have a negative impact on stock toughness. First, in reviewing the base physical/mechanical properties for both stocks (table 3), it is evident that the anticipated change was achieved. The double cure package resulted in significantly decreased tensile and elongation, and an increase in hardness, rebound and crosslink density. The half cure package resulted in a significant decrease in tensile, elongation, modulus, hardness, rebound and crosslink density.

The data of table 3 can be reviewed to determine if for all five tests the abrasion results are negatively impacted as predicted. The test results are color coded--with green for desirable results and yellow for poorer results--compared to the base stock. A condensed summary is shown in table 5.

The tear strength test result is as expected, with both the more tightly crosslinked or more loosely crosslinked stock showing a negative impact. The BFG C&C tester yielded an interesting, but explainable, result. The double cure result is as anticipated, but the haft cure result showed better performance as compared to the base stock. Although unexpected, if simply viewing the formula change in terms of toughness, it is likely the half cure compound result was more influenced by the modulus, hardness and rebound characteristics of the stock. With the stock being significantly softer and lower in resilience, the degradation of the impact portion of the test was probably lessened. The stock could deflect and absorb the energy better without cutting. The three tests that have abrasion degradation mechanisms yielded counterintuitive results for the double cure, and the hardness and crosslink density increases are likely drivers.

For the half cure, the results for the DIN and pico abraders were as anticipated. It is interesting to note that the softness and resiliency changes of the half cure compound did not affect the knife-cutting of the pico test in the same way as the impact-cutting of the C&C test, and the results produced are opposite. Finally, the half cure compound is soft enough that on a fixed position abrasive paper test, like NBS abrasion, abraded compound can gum the paper and produce results better than expected.

Polymer changes

Natural rubber is generally considered to be very tough, and has excellent cut and chip characteristics. Although compounders can modify formulas to provide similar or even better C&C resistance utilizing other general purpose polymers, it can be assumed that simply dropping in other polymers with minor compound modifications may have a negative impact on stock toughness. As demonstrated previously with the cure package study, stock toughness does not always translate into abrasion resistance, and this can be particularly true for polymer changes. Two compound variations were included in this study (table 6). First, 50% of the NR was replaced with polybutadiene (BR). In the second variation, all of the NR was replaced with SBR. In both cases, appropriate modifications were made to the cure system. In the case of the SBR, more process oil was added.

Table 3 shows the base physical/mechanical properties of the NR/BR stock as compared to the 100% NR of the base stock. Tensile and elongation are negatively impacted, while modulus and hardness are not significantly changed. The good hysteretic properties of BR are evident in the increased rebound. A crosslink density comparison on stocks with two different polymer blends is difficult. Overall, the impact on stock toughness of this compound change is expected to be negative.

For the 100% SBR stock, the hardness is similar to the control, and the modulus is slightly higher. All other base properties are downwardly affected. A negative impact is expected on stock toughness, and a summary is shown in table 7.

The tear strength and C&C tester produced the anticipated results. Interestingly, the variations in resilience of these stocks did not produce counterintuitive results, as in the case of the previously discussed half cure compound. It is possible to assume that the compound hardness, essentially equivalent for all the polymer variations, was more of a driver for the half cure stock results. The abrasion test results for all three compounds were opposite of the prediction based on stock toughness, but in terms of industry usage of BR and SBR in passenger tire tread compounds for good wear resistance, the findings are not out of line.

Reinforcing resin addition

The third type of compound formulation change was to add reinforcing resins to the base compound, as shown in table 8. Two resins were chosen, and in both cases the resin along with the appropriate amount of hexa were added as a curative for the resin.

Reinforcing resins typically add toughness to a stock. They act to chemically reinforce the polymer matrix, and in doing so, can reduce elongation properties. Measuring the change in abrasion resistance of this type of change in the lab is very dependent upon the type of test. The unique degradation mechanisms for each test can be impacted differently. Both resins have similar and expected impacts on the base mechanical/ physical properties (table 3). The tensile strength is only slightly affected. The elongation, in both cases, is off by a little more than 10%. The modulus and hardness are both higher, a little more so in the case of resin A. Rebound is only slightly higher. The only large difference in the two resins is in the crosslink density measurements; as there was no change for resin B and a significant increase for resin A, indicating a more tightly bound polymer network. It was anticipated that stock toughness would be increased for both resin additions, although the overall impact might be less than what was seen for the cure and polymer changes. The test results are summarized in table 9.

There were no counterintuitive results for either of the reinforcing resins. The resin addition was expected to have a positive impact on the C&C results, but some of the results were less than 10% and judged to not be significant. Of note is that the tear strength, cut and chip and pico testing produced changes with the least positive gain, and these tests are likely more affected by the reduced elongation. The DIN and NBS abrasion test results showed the most increase, and the obvious drivers for these were the increased stock hardness and modulus.

Silica replacing carbon black

Having the base stock being a highly reinforced natural rubber stock, it was anticipated mat Rill replacement of the carbon black with silica would have a significant negative impact on the base properties and the stock toughness. The first variation was the full 100% replacement, and then the second variation included the addition of a coupling agent to provide additional chemical reinforcement. Both formula changes are shown in table 10.

Both silica-reinforced stocks were expected to have significantly decreased toughness. The coupling agent in the second variation was expected to recover some of the loss in mechanical properties. The base mechanical/physical properties for both stocks show properties of much less reinforced stocks, with the tensile, modulus and hardness being lower, and the elongation and rebound being higher. The crosslink density decrease for both stocks shows the "looseness" of the polymer matrix. The addition of the coupling agent had only a small impact. The individual cut and chip test results are summarized in table 11.

The results from the testing were very close to expectations. All of the tests, with the exception of NBS abrasion, showed significantly lower results as compared to the base stock. The NBS testing produced very small differences and, similar to the half cure results, it must be concluded that the softness of both silica stocks produced unusually good results because of this being a fixed position sandpaper abrasion test.

Carbon black changes

Changing carbon black loading or grade can significantly impact stock toughness. This study looked at three variations, including higher loading, lower loading and less reinforcing. In table 12, the three changes relative to the control formulation are shown.

Changing the carbon black loading in this manner was anticipated to create a tougher stock with higher loading and a less tough stock with lower loading and less reinforcing. However, the results of the mechanical/physical testing shown on the base properties (table 3) highlight some unexpected findings from the compound changes.

The increase in carbon black loading, which typically is expected to increase the tensile strength had the opposite impact. A decrease in carbon black loading usually produces lower tensile values, but in this instance yielded virtually equivalent numbers. Both of these results indicate a base stock that is very highly reinforced, and one in which more reinforcing can overload the stock. The results from the less reinforcing black continued to support this finding, as the change had only a minimal impact on the mechanical properties. The summary of results in table 13 lists the predictions as forecasted from the original assumptions.

None of the results, either for a specific compound change or lot a specific type of test, yielded results completely as expected. The tear strength results further highlighted the base stock's very highly loaded nature. Increasing black loading overloaded the stock and decreased tear properties. Decreasing the black loading had very little effect. The lower reinforcing black did produce expected results, with a significant decrease in tear. The C&C and DIN testing were not very sensitive to the carbon black changes. The pico testing provided results closest to expectations, with the increased carbon black showing no impact, but with lower black loading and less reinforcement yielding lower results.

Correlation of tests

An attempt was made to correlate the test results of the C&C test results to results from the other abrasion tests. A simple linear regression analysis yielded very low R square values, indicating little relationship. This is not surprising, as the test is unique and was specifically designed to be so. An attempt to correlate the C&C test results to the other stock properties also yielded results showing little correlation.

Further analysis in an attempt to correlate other abrasion tests to each other or to the other stock properties found only a couple of relationships. Again, using a simple linear regression, the best correlation obtained was between the pico test and 300% modulus--with an [R.sup.2] value equal to 0.878. Correlating the two abrasive paper tests, DIN and NBS, gave an [R.sup.2] of 0.759.

Conclusions

The individual abrasion tests in this study all have unique degradation mechanisms. Although compounds can be very broadly categorized in terms of their stock toughness, the specific compound changes employed to affect the desired properties can produce unexpected results on certain tests. It is important to understand the compound change being made, the type of test being utilized to measure the change, and, hopefully, how the mechanism of degradation for that particular test relates to the field condition.

From the testing in this study, it is evident that tear strength testing should typically be included as a measure to characterize cut and chip resistance. Overall, it gave the best results, as compared to the expectations, but even with this measure, it gave counterintuitive results for one of the carbon black loading tests. A number of the tests is impacted by compound hardness and caution should be the word when trying to compare results from stocks with differing hardness values. Specifically, the BFGoodrich C&C and NBS abrasion tests yielded better results than expected when the stock was soft. Conversely, all three abrasion tests (DIN, pico and NBS) produced unexpected good results when the compound became harder. Polymer changes are always difficult for direct comparisons, and when it comes to degradation mechanisms, these changes highlight the differences between impact, cut, chip and tear versus abrasion.

Predicting abrasion results is a challenge. Experience and in depth knowledge of exposure conditions and degradation mechanisms, in the field or in the lab, are essential.

Table 1--compound design matrix

                CCP-1    CCP-2    CCP-3    CCP-4    CCP-5
                 Base      2 x    112 x    NR/BR      SBR
                stock     cure     cure

Ingredient
SIR10          100.00   100.00   100.00    50.00
Taktene 1203                               50.00
SBR 1502                                           100.00
N121            60.00    60.00    60.00    60.00    60.00
IRB7
HiSil 210
X50S
PEG3350
Aromatic oil     5.00     5.00     5.00     5.00    20.00
ZnO              5.00     5.00     5.00     5.00     3.00
Stearic acid     2.00     2.00     2.00     2.00     2.00
TMQ              1.50     1.50     1.50     1.50     1.50
6 PPD            2.00     2.00     2.00     2.00     2.00
UltiPro 100
SP-6701
Hexa
OBTS             0.70     1.40     0.35     1.00     1.80
DPG                                                  0.10
Sulfur           2.50     5.00     1.25     2.50     2.00
Total          178.70   181.90   177.10   179.00   192.40

                CCP-6    CCP-7    CCP-8      CCP-9
                Resin    Resin   Silica   Silica +
                    A        B                X50S

Ingredient
SIR10          100.00   100.00   100.00     100.00
Taktene 1203
SBR 1502
N121            60.00    60.00
IRB7
HiSil 210                         60.00      60.00
X50S                                         12.00
PEG3350                            2.00
Aromatic oil     5.00     5.00     5.00       5.00
ZnO              5.00     5.00     5.00       5.00
Stearic acid     2.00     2.00     2.00       2.00
TMQ              1.50     1.50     1.50       1.50
6 PPD            2.00     2.00     2.00       2.00
UltiPro 100      3.00
SP-6701                   3.00
Hexa             1.00     0.33
OBTS             0.70     0.70     0.70       0.70
DPG
Sulfur           2.50     2.50     2.50       2.50
Total          182.70   182.03   180.70     190.70

                CCP-10    CCP-11        CCP-12
               + black   - black   - Reinforc-
                                           ing

Ingredient
SIR10           100.00    100.00        100.00
Taktene 1203
SBR 1502
N121             70.00     50.00
IRB7                                     60.00
HiSil 210
X50S
PEG3350
Aromatic oil      5.00      5.00          5.00
ZnO               5.00      5.00          5.00
Stearic acid      2.00      2.00          2.00
TMQ               1.50      1.50          1.50
6 PPD             2.00      2.00          2.00
UltiPro 100
SP-6701
Hexa
OBTS              0.70      0.70          0.70
DPG
Sulfur            2.50      2.50          2.50
Total           188.70    168.70        178.70

Table 2--control-base stock formula

Material        RHC

SIR10          100.00
N121            60.00
Aromatic oil     5.00
ZnO              5.00
Stearic acid     2.00
TMQ              1.50
6 PPD            2.00
OBTS             0.70
Sulfur           2.50

Total          178.70

Table 3--test results

                            CCP-1      CCP-2      CCP-3      CCP-4
                             base   2 x cure   1/2 cure      NR/BR
Tensile                     stock

Stress @ break, MPa          26.5       20.1       16.7       20.9
  % change                    par       -24%       -37%       -21%
Strain @ break, %             499        282        442        365
  % change                    par       -43%       -11%       -27%
Stress @ 300%, MPa           16.0        n/a       10.7       17.1
  % change                    par        n/a       -33%         7%
Hardness, dur. A               72         78         61         73
  % change                    par         8%       -15%         1%
Rebound resilience, %        40.0       43.9       35.5       48.0
  % change                    par        10%       -11%        20%
Crosslink density,
    moles/[cm.sup.3]     6.66E-06   1.71E-05   1.58E-06   9.22E-06
  % change                    par       157%       -76%        38%
Tear strength, Die B,         144        116         71        119
  kN/m                        par       -19%       -51%       -17%
  % change
Cut and chip test
  Loss in mass, gm           2.66       4.44       1.81       2.92
    % change                  par        67%       -32%        10%
  Loss in diameter, cm       0.53       0.89       0.33       0.58
DIN abrasion
  Abrasion loss,
      [mm.sup.3]              114         94        167         45
    % change                  par       -18%        46%       -61%
  Abrasion resistance         137        166         94        350
    index, %
Pico abrasion
  Loss in weight, mg         18.8       16.0       45.6       12.2
    % change                  par       -15%       143%       -35%
NBS abrasion
  Abrasive index, %         2,202      4,509      2,703      5,953
    % change                  par       105%        23%       170%

                            CCP-5      CCP-6      CCP-7      CCP-8
Tensile                       SBR    Resin A    Resin B     Silica

Stress @ break, MPa          20.8       25.6       24.5       17.1
  % change                   -22%        -3%        -8%       -35%
Strain @ break, %             347        434        442        691
  % change                   -30%       -13%       -11%        38%
Stress @ 300%, MPa           18.0       18.8       17.1        3.6
  % change                    13%        18%         7%       -78%
Hardness, dur. A               70         80         78         61
  % change                    -3%        11%         8%       -15%
Rebound resilience, %        36.1       41.5       41.2       47.0
  % change                   -10%         4%         3%        18%
Crosslink density,
    moles/[cm.sup.3]     5.46E-06   8.42E-06   6.62E-06   7.80E-07
  % change                   -18%        26%        -1%       -88%
Tear strength, Die B,          49        142        130         62
  kN/m                       -66%        -1%       -10%       -57%
  % change
Cut and chip test
  Loss in mass, gm           3.05       2.77       2.50       3.82
    % change                  15%         4%        -6%        44%
  Loss in diameter, cm       0.61       0.51       0.46       0.74
DIN abrasion
  Abrasion loss,
      [mm.sup.3]               81         96        100        281
    % change                 -29%       -16%       -12%       146%
  Abrasion resistance         193        162        157         55
    index, %
Pico abrasion
  Loss in weight, mg         18.9       17.9       19.5       67.9
    % change                   1%        -5%         4%       261%
NBS abrasion
  Abrasive index, %         5,121      3,517      3,468      2,099
    % change                 133%        60%        57%        -5%

                            CCP-9     CCP-10     CCP-11        CCP-12
                         Silica +    +10 phr    -10 phr     CB - less
Tensile                      X50S      black      black   reinforcing

Stress @ break, MPa          16.0       22.1       27.6          26.1
  % change                   -40%       -17%         4%           -2%
Strain @ break, %             536        352        553           503
  % change                     7%       -29%        11%            1%
Stress @ 300%, MPa            7.1       19.2       13.2          15.6
  % change                   -56%        20%       -18%           -3%
Hardness, dur. A               57         77         66            69
  % change                   -21%         7%        -8%           -4%
Rebound resilience, %        45.1       35.2       40.9          43.8
  % change                    13%       -12%         2%           10%
Crosslink density,
    moles/[cm.sup.3]     1.89E-06   8.79E-06   4.74E-06      6.61E-06
  % change                   -72%        32%       -29%           -1%
Tear strength, Die B,          36         93        137           105
  kN/m                       -75%       -35%        -5%            --
  % change
Cut and chip test
  Loss in mass, gm           3.21       2.58       2.78          2.67
    % change                  21%        -3%         5%            0%
  Loss in diameter, cm       0.66       0.46       0.58          0.48
DIN abrasion
  Abrasion loss,
      [mm.sup.3]              231        122        126           114
    % change                 103%         7%        11%            0%
  Abrasion resistance          68        128        124           137
    index, %
Pico abrasion
  Loss in weight, mg         42.0       18.8       23.3          21.5
    % change                 123%         0%        24%
NBS abrasion
  Abrasive index, %         1,950      3,412      2,754         2,212
    % change                 -11%        55%        25%            0%

Table 4--formula changes to cure system

         Base    Double   Half
         stock   cure     cure

Sulfur   2.50     5.00    1.25
OBTS     0.70

Table 5--cure system changes anticipated vs. actual test
results

                   Double          Half
                    cure           cure

                 Pre-    Re-     Pre-    Re-
Test            dicted   sult   dicted   sult              Mechanism

Tear strength     -       -       -       -                  Tearing
Cut & chip        -       -       -       +      Impact and chipping
DIN abrasion      -       +       -       -                 Abrasion
Pico abrasion     -       +       -       -     Cutting and abrasion
NIBS abrasion     -       +       -       +                 Abrasion

Table 6--formula changes to polymer

               Base stock   NR/BR      SBR

SIR10              100.00   50.00
Taktene 1203                50.00
SBR 1502                            100.00
Aromatic oil         5.00    5.00    20.00
ZnO                  5.00    5.00     3.00
OBTS                 0.70    1.00     1.80
DPG                                   0.10
Sulfur               2.50    2.50     2.00

Table 7--polymer changes anticipated vs. actual test results

                       NR/BR                SBR

Test            Predicted   Result   Predicted   Result

Tear strength       -         -          -         -
Cut & chip          -         -          -         -
DIN abrasion        -         +          -         +
Pico abrasion       -         +          -         =
NBS abrasion        -         +          -         +

Test                      Mechanism

Tear strength               Tearing
Cut & chip      Impact and chipping
DIN abrasion               Abrasion
Pico abrasion   Cutting and abrasion
NBS abrasion               Abrasion

Note: change from base stock of less than
[+ or -] 10% is represented as =

Table 8--formula changes with resin addition

              Base    Resin   Resin
              stock     A       B

UltiPro 100    --     3.00     --
SP-6701        --      --     3.00
Hexa           --     1.00    0.33

Table 9--reinforcing resins anticipated vs. actual test results

                     Resin A              Resin B

Test            Predicted   Result   Predicted   Result

Tear strength       +         =          +         =
Cut & chip          +         =          +         =
DIN abrasion        +         +          +         +
Pico abrasion       +         =          +         =
NBS abrasion        +         +          +         +

Test                      Mechanism

Tear strength               Tearing
Cut & chip      Impact and chipping
DIN abrasion               Abrasion
Pico abrasion   Cutting and abrasion
NBS abrasion               Abrasion

Note: change from base stock of less than
[+ or -] 10% is represented as =

Table 10--formula changes with silica as filler

            Base Stock   Silica   Silica + X50S

N121          60.00        --          --
HiSil 210       --       60.00        60.00
X 50S           --         --         12.00
PEG3350         --        2.00         --

Table 11--silica replacing black--anticipated vs. actual test results

                      Silica           Silica + X50S

Test            Predicted   Result   Predicted   Result

Tear strength       --        --        --         --
Cut & chip          --        --        --         --
DIN abrasion        --        --        --         --
Pico abrasion       --        --        --         --
NBS abrasion        --        =         --         --

Test                       Mechanism

Tear strength                Tearing
Cut & chip       Impact and chipping
DIN abrasion                Abrasion
Pico abrasion   Cutting and abrasion
NBS abrasion                Abrasion

Note: change from base stock of less than [+ or -]
10% is representedd as =

Table 12--formula changes to carbon black

        Base   Increase   Decrease     Decrease
       stock    loading    loading   reinforcement

N121   60.00    70.00      50.00          --
IRB7    --        --         --          60.00

Table 13--carbon black changes--anticipated vs. actual test
results

                  More black     Less black

Test            Proj.   Act.   Proj.   Act.

Tear strength     +      -       -      =
Cut & chip        +      =       -      =
DIN abrasion      +      =       -      =
Pico abrasion     +      =       -      -
NBS abrasion      +      +       -      +

                 Reinforcing

Test            Proj.   Act.             Mechanism

Tear strength     -      -     Impact and chipping
Cut & chip        -      =                Abrasion
DIN abrasion      -      =       Cutting and abra-
Pico abrasion     -      -                    sion
NBS abrasion      -      =                Abrasion

Note: change from base stock of less than [+ or -]
10% is representedd as =

Reference

(1.) J.R. Beatty and B.J. Miksch, "A laboratory cutting and chipping tester for evaluating off-the-road and heavy duty tire treads," Rubber Chem. Technol. 55, 1,531 (1982).