Wear Resistance of Vulcanized Elastomers

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Wear Resistance of Vulcanized Elastomers J. C. BURNS AND E. B. STOREY Polymer Corp., Ltd., Sarnia, Ontario, Canada

'

T h e lack of a satisfactory laboratory measure of the ANY laboratory test tion of other variables in the wear resistance of vulcanized elastomers has hindered machines have been field of b u t a d i e n e - s t y r e n e the development and acceptance of new elastomers for designed to estimate the wear elastomers. 'Chis, then, was use in tire treads. On an abrasive paper test surface, resistance of vulcanized elasmade the primary objective tomers. Although a few 'of comparable 41" and 122' F. OR-S tread wulcanizates of the present investigation. were ranked in the reverse order of that observed in road these machines were deTEST PROCEDURES tests, even after the extraction treatment described by veloped for special types of Oriffith et al. When a steel screen was used as the test rubber products, such as Except where noted, the surface on a National Bureau of Standards abrader, the coated fabrics, the greater GR-S-10, 41" F. GR-S, and 122" F. GR-S were commer41" F. OR-S vulcaniaate showed the higher wear resistnumber have been designed cial polymers produced by ance. The effects of state of cure, type and quantity of to assess the wearing qualiCanadian Synthetic Rubber, carbon black, and softener were similar to that reported ties of vulcanizates intended Ltd., Sarnia. The elastofor road tests. The screen provided a uniform test surface for use in footwear or automeric compounds were prepared on a 6 X 12 inrh whose wearing action was maintained over long periods mobile tires. The large laboratory mill following the of service. The lower rate of wear on this surface resulted number of new elastomeric compounding schedule outin an increase in the sensitivity of the determination, materials and reinforcing piglined in the specifications for ments introduced in the past g- o v e r n m e n t synthetic decade has increased the need rubbers. The test strips were vulcanized in a four-cavity mold which of a reliable method for selecting promising combinations in the produced a concave test surface having the same radius of curvalaboratory before submitting these to expensive performance ture as the test drum of the National Bureau of Standards abrader. tests under simulated service conditions. The determination of the abrasive resistance on garnet paper Present laboratory methods involve rubbing the vulcanized was carried out according to the -4.S.T.M. Designation D 394-47, Method B. compound over a surface composed of abrasive particles, such as The ethanol-toluene extraction treatment was carried out in emery, carbomndum, or silica particles, which may be affixed a Soxhlet extraction apparatus using a 31/2-inch length of test to a paper backing or bonded in a solid matrix. I n one method, strip. The treatment consisted of 96 hours extraction with a relatively flat surface of the specimen is caused to slide over the ethanol-toluene azeotrope, 48 hours extraction with ethanol (during which the solvent was changed three times), followed b> abrasive surface, and there is a continuous contact between these air-drying for 24 hours a t 77" F. t n o surfaces throughout the test. This is the method employed The acetone extraction procedure consisted of placing a 2 * / r Rith the Du Pont (9) and the National Bureau of Standards inch length of test strip in 300 ml. of acetone in a sealed pint can abraders (6). I n later types of test machines, the test specimen for 48 hours at 77" F. The strip was removed and allowed to dry in the dark for 24 hours in air a t 77" F. is a wheel of vulcanizate that is driven over a bonded abrasive I n all the tests carried out on abrasive paper, the specimen was sur'are, usually a t an angle to the direction of rotation of the abracemented to a piece of vulcanized fiber backing, by which it was sive disk. The Lambourn (3)and Vogt (7) machines, examples fastened to the test arm. of this method, are classed as discontinuous tests, since the rotation The.bal1 penetration was measured at an ambient temperature of 77" F. using a minor load of 30 grams and a major load of 1030 of the specimen produces an intermittent contact between any grams, on a '/&nch ball bearing. area of vulcanizate and the abrasive surface. In all these methods The 30-mesh stainless steel screen was cut parallel to the wire the abrasive surface tends to become clogged with the abraded to give a sheet 6 inches wide, This sheet was formed over the product and an air blast is employed to remove this mawial. surface of the drum so the cut, ends overlapped by about 3/4 inch and the wires ran around the circumference of the drum In one instance (9)the viscous smear produced on the abrasive parallel to the edge of the test specimen. The screen was fixed surface was so pronounced that the vulcanizate was extracted in this position by means of metal straps. The metal surface of with ethanol-toluene azeotrope in an effortto eliminate the source the test drum was coated with a commercial reclaimed rubber of this contaminating material. cement to prevent the screen from slipping during a test run. The test was carried out in a conditioned room a t an ambient The majority of such abrasion methods do give a reasonable temperature of 77" F. and relative humidity of 50%. A stream rorrelation with service performance when different types or of air was blown onto the screen through the air duct of the Kaquantities of carbon black or other fillers are compared with one tional Bureau of Standards abrader so that it was directed at elastomer. However, they are most unreliable when employed right angles to the axis of rotation of the drum. An air pressure of 10 pounds per square inch gage was used at the entry to the to compare the wear resistance of vulcanizates of different elasair duct. tomers. This deficiency has hindered the development of new The test specimen was cut from the molded test strip to give a types of elastomers and has prolonged the investigation of pos1 X 1 inch sample. A metal frame was bolted to the underside of the various polymerization factors on the wear sible effects of .the test arm of the abrader in which a 1 X 1inch opening was resistance of the vulcanized product. cut in the '/pinch thick metal. The surface of the specimen was Extensive road tests (8) have established that tires of the roughened with sandpaper and then fitted into the frame, holder on the test arm. The specimen was broken in for 2000 to 2500 commercial butadiene-styrene polymer (GR-S) polymerized revolutions of the drum a t a speed of 40 r.p.m., removed, cleaned at 41 ' F. will provide 23% greater mileage for equal wear than of loose particles of vulcanizate, and weighed. that prepared a t a temperature of 122" F. A laboratory method The drum was allowed to revolve with the air blast directed that would demonstrate this superior wear resistance for a 41 F. onto the screen in order to reduce the temperature of the metal GR-S vulcanizate might be expected to yield a qualitative evaluawire to 77 O F. before the start of the next test run. The specimen O

April 1952

INDUSTRIAL AND ENGINEERING CHEMISTRY

825

TOMERS-Compounding was replaced in the frame holder in exactly the same position as before, and a test run was carried out for exactly 2500 revolutions. The specimen was cleaned, weighed, and the wear resistance calculated as the number of kilorevolutions required to remove 1 cc. of vulcanizate, indicated as krev./cc. EXPERIMENTAL

The initial tests were carried out on the National Bureau of Standards abrader using No. 21/% garnet abrasive paper. The GR-S elastomers were compounded in the specification recipes prescribed by the Office of Rubber Reserve; 122" F. GR-S in recipe A and 41' F. GR-S in recipe B (Table I). With the standard weight of 0.328 kg. on the test arm, the abrasive resistance of the 122' F. GR-S vulcanizate was found to be 79% greater than that of the 41' F. GR-S. The consensus

-

I

0

I

I

lz Y

* 2

GR-S

0

122'F. G R - S

0

41OF.

11

01 0

I

0.25

I

0.50

i

I

1

Y1

I

I

0.75

1.00

I

I

1.25

1.50

m

a WEIGHT ON TEST A R M (Kgrn.) Figure 1. Effect of Test Load on Abrasive Resistance

containing 30, 40, and 60 parts of EPC carbon black per 100 parts of rubber. This time consuming procedure takes 7 days and, concurrently, duplicate specimens were immersed in (a) acetone and ( b ) ethylene dichloride for 48 hours a t 77" F. All these immersion treat,ments produced a drop in the hardness of the vulcanizate (Table 111). The specimens treated with ethanoltoluene azeotrope suffered the greatest loss in abrasive resistance and even those immersed in acetone showed a substantial decrease in this property. The percentage decrease in abrasive resistance was remarkably constant for each solvent. The vulcanizates of three synthetic elastomers (Table IV) showed about the same percentage decrease in abrasive resistance after acetone immersion. The GR-S-10 vulcanizate, however, produced a heavy black smear on the abrasive paper in the original condition, and this abnormally high value was reduced to a "normal" level after treatment with acetone. This was the only contamination of the abrasive paper observed during this test program. The acetone treatment reduced the abrasive resistance of the GR-S-10 vulcanizate and, then, it showed the same qualitative rating with respect to GR-S as has been reported for road tests (1). The two 41" F. GR-S elastomers, however, had a lower abrasive resistance than that of 122' F. GR-S, both in the original and treated conditions. The comparative abrasive resistance of 41" and 122" F GR-S had not been unduly influenced by the state of cure of the vulcanizates since it was found that this factor had only a minor effect on the abrasive resistance of the acetone-treated vulcanizate (Table V). Newton and Scott ( 4 )have reported that significant difference8 in relative abrasive resistance may be obtained by using different sizes of abrasive grit in tests with the Du Pont abrader. The vulcanizates of 41 O F. and 122" P.GR-S were tested on various grades of abrasive paper (Table 17,Figure 2). The two vulcani-

Rubber Reserve recipe: 21/$ g a r n e t paper

of opinion is that when service conditions are more severe, the 41' F. GR-S shows a greater margin of superiority over 122" F. G R S . When the load on the test arm (Table 11, Figure 1) was increased the abrasive resistance of both vulcanizates decreased and that of 41 O F. GR-S approached the value shown by the 122 ' F. GR-S vulcanizate. However, there was no clear indication of a change in the relative abrasive resistance of the two elastomers, at least up to a load which produced excessive vibration of the specimens during the test. The effect of a prior extraction of the vulcanizate with ethanoltoluene azeotrope was examined for 122 ' F. GR-S vulcanizates

Table I. F. GR-S 41O F. GR-S

A 100

E P C carbon black Zinc oxide Stearic acid AI tax Sulfur

...

40

B

...

100 40

5

5

1.75 2

1.5 3 2

...

Conditions: 122' F. GR-S in recipe A Press cure, 70 min. a t 292' F. Abrasive surface, 21/e garnet paper E P C Black, l/a-Inch Ball Abrasive Pnrts/lOO Penetration, Resistance, Mils Rubber Treatment Krev./Cc. None 30 86 0.65 40 70 0.88 60 43 1.10 Ethanol-toluene 30 9s 0.27 Azeotrope 40 77 0.39 60 55 0.51 Acetone 30 106 0.48 40 86 0.60 60 80 0.80 Ethylene dichloridob 30 104 0.74 40 85 0 99 60 64 1.05

Table 11. Effect of Test Load on Abrasive Resistance (So. 21/z garnet paper) Abrasive Resistance, Krev:/Co. 41' F. GR-SQ 122' F. GR-Sb 1.10 0.67 0.154 1.00 0.60 0.200 0.47 0.84 0.328 0.65 0.40 0.481 0.35 0.53 0.655 0.42 0.24 0.987 0.32 0.16 1.295 Polysar Krylene compounded in recipe B ; press cure 60 minutes st Load on Test Arm,

Kg.

292' F. b Polysar 9 Compounded in recipe A ; press cure 50 minutes a t 292" F.

826

%

100 100

too

41 44 46 73 69 73 114 113 96

a Compared t o untreated vulcanizate of the same EPC carbon black loading. b Allowed to air-dry for 5 days a t 77' F.

Table IV. Relative Wear of Elastomers o n 2 1 / 2 G a r n e t Paper Elastomer Polymerization temp.,

a

Abrasive Ratinga,

*

Test Recipes Parta

122O

Table 111. Effect of Various Solvents o n Extracted Abrasive Resistance

' F.

Test recipe Press cure a t 292' F., min.

122' F. GR-S

GR-S-10

41' F. GR-S

X-485

122 A

122 B

41 B

41 B

60

60

60

60

A.brasive resistance,

krev./cc. Original Acetone treated Treated index (original = 100)

71

14

84

Ball penetration, mils Original dcetone treated Change

74 91 +17

83 100

70 86 4-16

a

1.02 0.72

3.750 0.61

f17

0.54 0.45

0.56 0.45 8@J

71 87 +I6

Produced a smear on the abrasive paper.

INDUSTRIAL A N D ENGINEERING CHEMISTRY

VOl. 44, No. 4

dLASTOMERS-Compundhg Table V. Effect of Time of Cure on Abrasive Resistance of Extracted Vulcanizate Polymer x-485 Recipe B Immersion treatment 48 hours in acetone at 77' F. 24 hours in air at 77' F. Drying treatment Abrasive material 21/z garnet paper 35 50 Press cure at 292' F., min. 58 58 No. tents Abrsscve resistance, krev./co. 0.374 0.383 Mean value Standard deviation of individual test 0 041 0 037

showed a higher wear resistance on the 30-mesh screen than that of the 122" F. elastomer and the same relative order of wear resistance was found on 10-mesh and 100-mesh stainless steel screens. The ideal test surface might consist of a series of wires, uniformly spaced, whose length ran a t right angles to the direction of rotation of the drum. Indeed, such a test surface

70 58

r

I

1

I

I

I

0.385 0.040

Table VI. Effect of Abrasive Grit Size on Relative Abrasive Resistance of 41 O and 122" F. OR-S Abrasive Paper Mesh

Abrasive Resistance, KrevJCc. 41°F. 122'F. Grade of grit GR-Sa GR-Sb 0.79 2 1/a 30 0.52 0.43 0.62 80 1 /o 0.69 100 0 . 5 6 2/0 120 0.64 0.66 3/0 180 1.00 0.94 4/0 180 1.37 1.26 5/0 a Recipe B; press cure, 60 minutes at 292' F. b Recipe A; prem cure, 50 minutes at 292' F.

GR-S = 100) 66 69 81 97 106 109

0

I

0

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4I0E O R - S

0 122OF GR-S

/'

1'

0

03

a tx Ql a .

MESH SIZE OF ABRASIVE GRIT 100

50

;$

I50

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0

210

310

410

I ,

510

GRADE OF ABRASIVE PAPER Figure 2. Effect of Abrasive Grit Size on Abrasive Resistance In an effort to determine the cause of this reversal in the relative resintance of the two polymers, a measurement was made of the temperature of the specimens during a test on 2l/1 garnet paper. A copper-constantan thermocouple was cemented between the specimen and the vulcaniaed fiber backing material, and the temperature a t this point was noted during a test run (Figure 3). The temperature of the 41 O F. GR-S vulcaniaate was found to be about 8" F. higher than that of the 122" F. elastomer, even at a distance of about 0.2 inch from the plane of abrasive action. A search was made for a test surface that would produce a lower rate of wear of the vulcaniaate and, preferably, allow a more rapid dispersion of the heat generated during abrasion. A steel screen might offer some advantages as a test surface. A test run was made using a 30-mesh 8tainless steel screen, and it was found that the vulcaniaate was worn by movement over the screen m d at a rate considerably lower than that observed on an abrasive grit surface. The 41" F. GR-S vulcaniaate

April 1952

.02

.04

.06

.OB

.IO

ABRASION LOSS (INCH)

a

,

I

"0

w cn a

sates showed an equal abrasive resistance on 4/0 garnet paper and the 41' F. GR-S vulcanizate was somewhat superior on a 5 / 0 garnet paper. Unfortunately, there was excessive vibration of the specimen on this h e grit, and it was difficult to obtain reproducible test values. 1.5

i

Comparative Rating of 41' F. GR-S (122O F.

s1m

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4loF OR-S o 122OF GR-S 0

2

0

0.2

0.4

0.6

0.8

1.0

ABRASION PERIOD (KR,) Figure 3. Temperature Rise at Base of Test Specimen Rubber Reserve recipe: 2 1 / a garnet paper; ambient temp., '11' F.

had a considerable w,earing effect on the vulcaniaate, and the 41 O F. GR-S vulcaniaate, again, showed more resistance to wear than that of the 122 O F. GR-S. The test data are shown in Figure 4, which also gives a schematic representation of the various test surfaces. The differences in the value of wear resistance obtained on the various screens would seem to be a function of the area of contact of the vulcaniaate and steel during each revolution of the drum, and, perhaps, of the spacing of the wire. The 30-mesh screen produced the largest difference in the wear resistance of the two elastomers and was adopted for use in subsequent tests. This screen consisted of a 28 X 30 mesh, angle-crimped, having a wire, 0.0135 to 0.015 inch diameter, of Type 304 stainless steel. The profile of the screen, then, would be different in the directions of the wa+ and shoot wires; this is illustrated in Figure 5 I n the warp direction ( B )the 122°F. GR-Svulcanizate was found to have a wear resistance some 30% of that in the direction of the shoot wires ( A ) . In each case the surface of the specimen wa8 worn to produce a series of alternate ribs and grooves. The grooves were formed by the points a t which the warp and shoot wire crossed in the screen. The A direction was selected for use in subsequent tests. Three screens were cut in the A direction and the average wear resistance of the 122' F. GR-S vulcanizate was found to be 16.00, 16.13, and 15.40 kilorevolutions per cubic centimeter loss of vulcaniaate. One screen was heated in a muffle for 5 minutes a t 550" C. in order to burn off any organic material and, after a short break-in period, a value for wear resistance similar to that of the original test was obtained. One of these screens was used in various tests for 750,000 revolutions of the test drum and, after this time, further specimens of the 122" F GR-S vulcanizate gave a wear resistance some 3% lower than in the original tent. One might assume that continued wear of the screen would flatten the top of the wires, thus increasing

INDUSTRIAL AND ENGINEERING CHEMISTRY

827

-ELASTOMERS-Compounding further test where the air stream was directed a t the spccirilcsn itself resulted in a slight decrease in wear resistance. This effect would seem to result from the difficulty in causing the air t o reach the interface of the specimen and the screen. The surfare of the screen itself became warm during a test run, and it m i proliable that the air blast served to reduce the temperature of tlie screen and the test surface of the specimen. The data (Table X I I ) indicated that the maxiSCREEN SCREEN WIRE WIRE WEAR RESISTANCE RELATIVE: mum wear resistance was obtained a t an air MESH DIAMETER SPACING (KR,/cc.) RATING pressure of 10 pounds per square inch gapt. SIZE (INCH) (INCH) 41'F. 122OF. (122'F. G R - S Possibly a still higher value would be obtaincd GR-S GR-S 100) at higher air pressures, but the change in wear A IO 0.0470 00530 4.05 2.55 I59 resistance, using air pressures of 7 and 10 pounds per square inch gage did not indicate that, t h w e B 30 0.0130 00203 9.95 5.82 171 would be any substantial gain a t higher air C 100 0.0045 0.0055 5.05 3.46 146 pressures. A comparison of 41' and 122" 17. GR-,S D 0.0330 0.0670 7.94 5.72 I39 vulcanizates was made in tread-type recipes COLItaining 0, 1, 2 5, and 5 parts of Paraflux per 100 parts of rubber. For any one compound. the wear resistance increased with the time of cure and leached a maximum level a t cure tinic somewhat longer than the optimum ten& cure t (Table IX). The relationships of tensile strcngtli, modulus a t 300%, and wear resistance with t l i p time of cure are illustrated in Figure 6. .fL(11 A B C D of these test values increased with an increnw in the state of cure of the vulcanizate. Figure 4. Wear Resistance o n Various Wire Surfaces The maximum wear resistance valueq vrt estimated from the data given in Table I X aiid In the previous tests on the 30-mesh screen a period of 2500 the values for 41 and 122' F. GR-S vulcanizates arc conirevolutions of the test drum (about 1 hour) had been adopted pared in Figure 7. At all levels of softener, up to 5 paits per 100 parts of rubber, the 41 F GR-S vulcanizates ahowed on an arbitrary basis; a depth of about 0.01 inch of the vulcanizate was removed in one test. It seemed pertinent to determine superior wear resistance to the corresponding 122" F. GK-S vulcanizate. The wear resistance of the vulcanizates d e c r e a d if the test value calculated from such a small loss of vulcanizate with an increase in the loading of softener, but a greater chanae would be reproducible between tests of the same specimen. The test data (Table VII) show that a good reproducibility was produced in the wear resistance of the 41" F. GE-9 th:m was obtained for one test specimen in a series of consecutive the 122" F. GR-S. wear periods. Under the test load the vulcanizate is deformed around t h e wires of the screen and, thus, a stiffer vulcanixate would rub over a smaller area of wire during one revolution of the test drum Table VII. Consecutive Tests of One Specimen If the modulus at 300% is proportional to the deformation of (30-mesh screen) the vulcanizate, the wear resistance of these two polymers should Loss, Wear Resistance, vary directly with the modulus of their vulcanizates. A relationTest Revolutions Grain Krev./Cc. ship (Figure 8) was indicated between these two propcrtirs 1 2000 0.0633 36.4 for each cure, a t each softener loading. From these curves 2 2000 0.0624 36.9 the area of contact between the steel and vulcanizate during each revolution. This should result in an increased rate of wear of the vulcanizate and is the direct opposite of that which occurs with an abrasive paper. Here the abrasive grit is rapidly worn or rubbed off the backing material with an accompanying rapid increase in the apparent abrasive resistance of the vulcanizate.

-

-

O

O

3

4

5 6 7 8 9

10

2000 2000 2239 2097 2600 2002 2145 2195

0,0596 0.0672 0.0679 0.0628 0.0779 0.0581

0.0611 0.0666

38.7 34.3 38.1 38.6 38.7 39.9 39.9 38.1

DI RECT I O N

WEAR RESISTANCE ( KR ,/c c.)

CROSS-SECTION

16.0

A

In all these tests an air blast had been directed a t tlie screen, using an air pressure of 7 pounds per square inch gage a t the entry to the distribution duct of the National Bureau of Standards abrader. Since any contaminating material derived from contact with the vulcanizate could easily be swept off the wires into the interstices of the screen, it seemed desirable to determine what effect, if any, was now being produced by the air blast. Accordingly, a 122" F. GR-S tread vulcanizate, containing 5 parts of Paraflux per 100 parts of rubber was tested on the 30mesh screen using an undercure and a cure approximating the optimum tensile cure. The data (Table VIII) show that there is considerable increase in the wear resistance of the vulcanizates when an air stream was directed onto the screen a t right angles to the axis of rotation of the drum. The wear resistance increased as the air pressure a t the entry to the distribution duct was increased from 7 to 10 pounds per square inch gage. A a28

'

s

m

6.6

A Figure 8. Cross Section of Screen and Specimen

INDUSTRIAL AND ENGINEERING CHEMISTRY

Vol. 44, No. 4

-ELASTOMERS-ComgauadingTable VIII.

Effect of Air on Wear Resistance (30-mesh screen) Wear Resistance, Krev./Cc. CureQ, Cure, 35 min. 70 min. 2.39 4.34

K O air

Air directed at screen 7 Ib./sq. 10 Ib./sq. Air directed 10 lb./sa.

inch gage inch gage a t specimen inch gage

Relative Wear Resistance, % Cure, Cure, 35 min. 70 min. 100 100

3.03 3.34

6.28 6.86

127 140

145 168

3.10

5.65

130

130

r I-

(3

-

5000

50

E-

0

Y

40

4000

z

4

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20

2000 0

IO

1000

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a= u)

2% -I

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25

35

CURE

I

50

I

70

100

I

140

0::

E

292°F (MIN.)

AT (LOG,,

-- -

SCALE)

----

Figure 6. Wear Resistance , Modulus at at 3OQ% ; and Tensile Strength of 41 ' and 122" F. OR-5 Vulcanizates _ I

the wear resistance of the 41 F. GR-S vulcanizates was calculated to be about 160% of that shown by a 122' F. GR-S vulcanizate of the same modulus a t 300%. This is an approximate value, since the two test values were measured on test pieces which were cured at different times in mold cavities having different dimensions. It does suggest, however, that a good correlation would be obtained if both tests could be carried out on the same vulcanized specimen. The presence of a maximum in the wear resistance-time of cure curve was more evident in compounds showing a high wear resistance, such as those containing an HAF carbon black, and, in this case, the effect of state of cure was found to be more critical. As illustrated by the data in Table X and Figure 9, the 30-mesh screen may also be employed to evaluate the wear resistance of soling-type compounds. Up to at least 90 parts of Silene EF per 100 parts of rubber in a 41" F. GR-S compound, the wear resistance was proportional to the filler loading. The effects of quantity and type of carbon black, and of softener on the wear resistance of 122' F. GR-S compounds (Table X I ) were found to be similar to that reported for road wear tests (6). It is apparent that tests with the 30-mesh screen are very sensitive to variations in elastomer characO

April 1952

50

teristics and test recipe. The Rubber Reserve Co. specification test recipe, which contains only 40 parts of EPC carbon black per 100 parts of rubber shows about the same relative wear resistance for 41 F..and 122" F. GR-S as one containing 50 parts of EPC or HAF carbon black per 100 parts of rubber. Thus, the properties of a small quantity of an experimental elastomer may be compared with those of a commercial elastomer using the Rubber Reserve recipes, and it would not be necessary to prepare a special test compound for this purpose. As promising as this method may appear, i t has one characteristic in common with the other abrasion tests-namely, it would indicate that a natural rubber tread vulcanizate has a wear resistance considerably lower than that of a comparable GR-S vulcanizate (Table XII). In this test, the abraded surface of the natural rubber vulcanizate was somewhat'sticky and a slight

*

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3000 I-

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a:

w

cn z w

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PARAFLUX (PHR) Figure 7. Effect of Paraflux on Relative Wear Resistance of 41" and 122" F. OR-S Vulcanizates

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Table IX. Effect of Paraflux on Wear Resistance of 41" and 122" F. OR-S Base recipe:

Polymer E P C black Paraflux Stearic acid

Parts 100 50 As shown 2

Zinc oxide Santocure Sulfur

Parts 3 1.26 1.80

41" F. GR-S 122' F. GR-S Wear Modulus Tensile Wear Modulus Tensile resistance, a t 300% strength, resistance at 300%, strength, krev./co. Ib./sq. inoh lb./sq.inch krev./cc.' lb./sq. inchlb./sq. inch Cure5 without Paraflux, min. 35 50 70 100 140 Cure with 1 part Paraflux, min.

8.0 27.4 44.3 48.3 47.8

2 -.5 _

8.8 50 23.6 70 39.7 100 43.8 140 36.8 Cure with 2.5 oarts Paraflux, miti. 35 Undercured 50 17.2 70 100 37.2 140 37.9 Cure with 5 parts Paraflux, min. 35 Undercured 50 10.2 70 18.2 100 25. I 140 28.3 .

.

I

730 1320 1750 2030 2220

3820 4480 4680 4400 4600

21 4 36 8 39.3 40 6 42 5

750 1350 1610 1870 2010

3800 4820 4545 4310 4470

20.8 31.4 38.3 41.9 37.6

590 1100 1450 1680 1780

3915 4460 4370 4635 4420

15 0 30.3 30 7 41.1

520 880 1170 1340 1460

3755 4380 4340 4510 4420

11.1 18.0 22.0 28.8 25.3

, .

1650 2100 2250 2350 2450

3650 3710 3430 3200 3315

3730 3505 3740 3210 3220 1315 1580 1740 1820 1835

3830 3625 3265 2890 3140

1185 1540 1675 1755 1860

3610 3800 3650 3720 3220

All cures a t 292O F.

INDUSTRIAL AND ENGINEERING CHEMISTRY

829

/ELASTOMERS-Compounding 3.5

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3.0

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30

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10

w

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500

1000

1500

A 2000

[rT

a

Paraflux, Parts/100 Rubber 0

41'

F.

GR-S

1220

tA

1.0

2.5 5.0

60

1.5-

1.0-

w

'

2500

MODULUS AT 3 0 0 % (PS.1.) Figure 8. Correlation of Wear Resistance and Modulus at 300%

0.5-

Olb

F.

1'5 io d5 i o 3 5 do o; C U R E AT 292°F. (MINS.) (LOG10

SCALE)

Figure 9. Effect of Silene EF on Wear Resistance of 41 F. G R - 8 Vulcanizates

V

O

smear waa produced on the steel screen. However, the presence of this contamination did not produce .a high wear resistance, and the low test value may be associated with a high coefficient of friction between a natural rubber vulcanizate and

Table X.

2.0

Parts/100 rubber: Polysar Krylene, 100. Silene EF. as shown; Cumar M H 2Vz, 10: stearic acid,'2; zinc oxide. 5; Altax. 3 ; sulfur, 2

stainless steel or, possibly, a degradative softening of the vulcanizate accelerated by the high temperature generated at the vulcanizate-steel interface. SUMMARY

Wear Resistance of 41" F. GR-S with Various Loadings of Silene EF

The use of a stainless steel wire screen on the National Bureau of Standards abrader will produce a wearing action on a vulcanParts Parts ized elastomer and 41" and 122" F. GR-8 vulcanixates exhibit Recipe: 41' F. GR-S 100 Zinc oxide 5 the same relative order of wear resistance that has been observed Silene E F As shown Altax 3 10 Sulfur 2 Cumar MH2l/r in road tests. Stearic acid 2 The wear resistance determined on this test surface was sensiSilene EF, Parts tive to the state of cure of the vulcanizate, and a maximum value Cure 22.5 30 60 90 was obtained a t a cure slightly longer than the optimum tensile at 292' F., min. Wear resistance, krev./cc. cure. The method is very sensitive to the type and quantity 20 0.45 0.39 0.73 1 69 of carbon black and softener loading in the vulcanizate. These 25 0.45 0.63 1.35 2.38 factors are ranked. also in the same order as observed in road 0.72 1.64 2.68 30 0.55 tests. The method may be applied to footwear compounds as 3s 0.57 0.76 1.65 2.90 50 0.62 0.74 1.72 3.05 well as to tread vulcanizates of synthetic elastomers. 70 0.58 0.72 1.58 2.56 The use of a metal screen offers a uniform and reproducible test surface for a determination of wear resistance; it suffers little change during continued Table XI. Effect of Carbon Black and Softener Loading on Wear use; and the material is not affected by minor changes Resistance of 41" F. and 122" P. GR-S in the ambient temperature or relative humidity. (30-mesh screen) The reproducible nature of the wire screen great11 Polymer, GR-s 4i0 F. 122O F. 410 F. 1220 F. 1220 F. 1220 F. 1220 F. 1220 F. reduces the need for a reference standard and comparisons may be made between tests conducted at Carbon black HAF relatively long intervals of time on either the same SRF HAF EPC Type FPC EPC EPC EPC 40 00 Loadinea 40 50 50 50 50 50 or a duplicate screen. Softener Type Loading"

.. .. ..

.. ....

Wear resistance, krev./cc. 9.0 8.5 Parts/100 parts of rubber.

... ..I

22.5

...

... 17.5

Paraflux Paraflux Paraflux 5 5 5

.. .. ,.

ACKNOWLEDGMENT

3.0

39.4

The authors wish to thank Polymer Corp., Ltd., for permission to publish this investigation.

11.5

28.5

(I

LITERATURE CITED

XII-

Wear Resistance of Natural Fb~bberTread Vulcanizate

(30-mesh screen) Parts Recipe: Smoked sheet 100 Stearic acid H A F carbon black 50 Agerite HP Pine tar 5 Captax Zinc oxide 3 Sulfur Press Cure at 292O F., Wear Resistance, Blin. Krev./Cc. 90 10.5 25 10.8 35 12.2 50 11.8

0.6

(1) Amon, F. H., Trans. Inst. Bubber Ind., 26, 177 (1950). ( 2 ) Griffith, T. R., Storey, E. B., Barkley, J. W7.D., and McGilvray, F. M., Anal. Chem., 20, 837 (1948). (3) Lambourn, L. J., Trans. Inst. Rubber lad.,4 , 210 (1928). (4) Newton, R. G., Scott, J. R., and Willott, W. E., J. Rubber Research, 17, 75 (1948). ( 5 ) Sigler, P. A., and Holt, W. L . , India Rubber World, 82, 63 (1930).

2.8

(6)

Parts 3 1

Sperberg, L. R., Svetlik, J. F., and Bliss, L. A., IND. EXG.CHU.,

41, 1641 (1949). (7) Tronson, J. L., and Carpenter, A. IT7.,Am. SOC.Testing Materials, Proc., 31, 11, 908 (1936). (8) White, L. M., IND. ENG.CREM.,41, 1554 (1949). (9) Williams, I.,Ibid., 19, 674 (1927). RECEIVED for review September 17, 1951.

830

INDUSTRIAL AND ENGINEERING CHEMISTRY

ACCEPTBD January 28, 1952.

Vol. 44, No. 4