INDUSTRIAL AND ENGINEERING CHEMISTRY
2914
ACKNOWLEDGMENT
The authors wish to express their appreciation to Klaus Hofmann of the University of Pittsburgh for his advice and cooperation in this work. to Gilbert Thiessen of the Komers . _ Co. for his gift of quantities of the methylnaphthalenes, and to R. A. Friedel of the Bureau of Mines for the spectroscopic nyork. LITERATURE CITED
Vol. 44, No. 12
(8) Griswold, J., IND. ENG.CHEY.,35, 247 (1943). (9) Horsley, L*H., Anaz.Chem., 1 9 , 5 0 7 (1947); 21, 831 (l949). Mair, B. J., and Streiff, A. J., J . Research Natl. Bur. Standards,
(10)
2 4 , 3 9 5 (1940).
(11) Morgan, G. T., and Coulson, E. d.,J . SOC.Chem. I n d . ( L o n d o n ) , (12)
53, 72T (1934). Morton, R. A,, and de Gouveia, A. J. A , , J . Chem. SOC.,1934,
(13)
Myles, RI., Feldman, J., Wender, I., and Orchin, bl., IXD.ENG.
(14) (15)
Othmer, D. r.,and Ten Eyck, E. II., Jr.,Ibid., 41, 2897 (1949). Thompson, R. B., in "Organic Syntheses," Vol. 20. p. 94, New York, John miley & Sons, Inc., 1940.
916.
CREM.,43, 1452 (1951).
Aun-ers,K. yon., Ber., 58, 154 (1925). Cosciug, T., Petroleum Z.,34, No. 16, 3 (1938). (3) Coulson, E. A, J . SOC.Chem. I n d . ( L ~ n d o n )60, , 123 (1941); 62,
(1) (2)
177 11943). (4)
Feldman, J.; Myles, M., Wender, I., and Orchin, M., IND.ENG.
(5) (6)
Fenske, M. R., I b i d . , 24, 482 (1932). Gilman, A., and Moore, F. TI'., J . Am. Chem. SOC.,65, 2086
CHEM.,41,1032 (1949). (1943).
(7) Glasgoy, A. R., Jr., Streiff, A. J., and Rossini, F. D., J . Research Xatl. Bur. Standards, 3 5 , 3 5 5 (1945).
J
(16) Krewski, hI.
S.,J . Buss. Phys Chem. Soc.,
44, 1739 (1912).
RECEIVED for revieff April 14, 1952. ACCEPTED August 15, 1952. Presented before the Division of Petroleum Chemistry at the 118th Meeting of the AMERICAN CHEMICAL SOCIETY, Chicago, Ill., September 1950. This work is a portion of the thesis of Julian Feldman which was presented t o the Graduate School, University of Pittsburgh, in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
J
M. H. REICH, R. E. SCHNEIDER, AND W. IC. TAFT G o v e r n m e n t Laboratories, University of Akron, Akron, Ohio
S
ODIUM has been utilized as the catalyst in the polymerization of butadiene in the liquid phase (9, 17') and it also has been suggested as a catalyst in the copolymerization of butadiene and styrene for the preparation of Buna 85-type copolymers (4) In 1946, Marvel (16) of the University of Illinois reported the successful copolgmeiization of 75 parts of butadiene and 25 parts of styrene a t 86" F. n i t h sodium sand as the catalyst. The factors affecting the rate of polymerization weie stated to be temperature of polymerization, typc of diluent, catalyst concentration, and impurities in the butadiene. Since sodium-catalyzed polybatadiene was thought to possess physical properties that ~5 ere different from those of emulsionpolymerized polybutadiene, probably hecause of the higher percentage of 1,a-addition units in the former, Juve and lfeyer ( 1 2 ) undertook the evaluation of the sodium-catalyzed 75/25 (charge ratio) butadiene/styione copolymer piepared by Marvel. These investigators stated that this new type of copolymer was considerably superior in niill processing characteristics and similar in stress-strain properties mhen compared to GR-S. In addition, the sodium-catalyzed polymer possessed R much better hysteresis-flex life relationship than did GR-S However, the low temperature properties of the experimental elastomer* were poorer than those of GR-S vulcanizates, as evaluated by brittle point values and Young's modulus determined at Ion temperature. -4n independent study of the proccssing and physical properties of sodium-catalyzed 75/25 butadiene/styrene copolymer by Schulze and coworkers (27) confirmed these results. T o r k a t the Government Laboratories ( 7 , 8) showed that sodium-catalyzed polymers prepared a t 86' F. in 8-ounce bottles had extremely low hysteiesis-temperature rise values, in the neighborhood of those of natural rubber. Use of the standard compounding recipe employed to mix GR-S-10 or X-624 (polymers 3-ithout stearic acid) yielded stocks vith high rates of cure. The hysteresis curves were unlike those of other synthetics (see Figure 1). It is evident that the sodium-catalyzed polymer behaves differently. The authors &ish to bring out that possibly tests should be conducted with these polymers under conditions
different from those found useful for current elastomers. The correlation between laboratory tests and tire results may not be the same for these polymers as for the other polymers. These earlier studies suggested the possibility of using this type of polymer as a tread and/or carcass stock; however, insufficient material was prepared by the bottle polymerizations and an extensive compounding study and evaluation of the synthetic elastomer could not be made. Therefore, the Government Laboratories, a t the request of the Synthetic Rubber Division after a conference in April 1949, prepared reasonably large quantities of sodium-catalyzed polvmers (monomer charge ratios of 100/0, 90/10, 85/15, and 75/25 butadiene/styrene) a t 86" to 188" F. on a pilot plant scale (25, 2 6 ) . Some of the factors, such as polymerization temperature, styrene content of polvmer, raw viscosity, and compounding ingredients, which affect the physical properties of the synthetic polymers when compounded as tread or carcass stocks. are discussed herein. PROCEDURE
The sodium-catalyzed polymers were prepared on a pilot plant scale a t 86" t o 188" F. The raTv polymer was soaked in methanol t o destroy the free sodium. Then about 1.5% of phenyl-2naphthylamine and 2% of stearic acid or 3.5'34 of acetic acid viere added to the polymers on a xvash mill or in a pelletizer. The polymers were subsequently dried a t 140" F. and tested. The sodium elastomers xvere compounded according to various test recipes (shomn in Table I ) , GR-S or GR-S-100 elastomer or natural rubber served as controls. Processibility mas judged by the time required for the stock to break dolw on the mill. compounded ilfooney viscosity, mill shrinkage, roughness of subsequently milled samples, and extrusion through a Garvey die b v means of a No. 1/2 R o ~ d eextruder. The cxtruded specimen was rated according to the method described by Garvey, Whitlock, and FreeFe ( 5 ) . The stress strain tests were conducted a t 77" or 212" F. on specimens (A.S.T.M. dumbbell strips, 0.075-inch thick) that had been cured
December 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
2915
1,2-isomer decreases with corresponding increases in 1,4-isomers as the temperatures for the alkaliType of Recipe catalyzed polymerizations are increased. The other Ingredients Tread Carcass properties of the polybutadiene did not appear to Cold rubber or XP-148 100 .. .. 100 .. be affected. GR-S 100. .. .. .... Natural rubberb .. .. 100 .. 100' Since none of the evaluated properties deterioSodium-catalyzed rubber .. .. 100 ' .. 100'. rated with an increase in polymerization temperaCarbon black 40C 40C 400 40d 30d 30d 30d Zinc 5 0 5 0 5 .0 5 5 .. 00 ture and t h e low temperature characteristics imSulfuroxide 2 .. 0 2 .. 0 3.0 2 .. 00 25 .. 00 2 25 .. 00 Altax (benzothiazyl diproved, polymerization temperatures of 168' F. 3.0 1.75 .. 1.25 1.75 .. 1.4,1.75 sulfide) or higher appear most advantageous. The polyParaflux 8.2016 (asphaltic resin) .. .. .. .. 5.0 o,056 o,056 5.0 o,056 5.0 mers discussed in the following sections of this DPG,(diphenylguanidine) .. .. .. Stearic acid 1.5 .. 3.0 3:O 3.0 3.0 3.0 paper therefore were made at high temperaPBNA (phenyl-2-naphthylamine) .. .. 1.5 .. .. 1.5 .. tures. Captax (mercaptobenzoAttention should be called to t h e method of thiazole) .. .. 0.5 .. .. 0.5 .. determining the amount of "combined styrene" as 5 Variations in the recipe are shown in the applicable sections of this paper. b Compound was cured a t 280' F. shown in Table 11. T h e relationship established 0 An easy processing channel black (Wyex) was employed unless noted otherwise in the by Schulze and coworkers (68) for sodium stocks discussion. d A high modulus furnace black (Statex 93) was employed unless noted otherwise in the made at 860F. to looyo conversion was applied to discussion. the refractive index measurements for determination of the percentage combined styrene. No attempt was made to correct for conversion or polymerizaa t 292' F., unless noted otherwise, as described in the Synthetic tion temperature. Although it is suspected t h a t these values Rubber Division Specifications (10). Strain tests were condo not represent the precise styrene content of the polymers, ducted a t 77" F. in accordance with t h e method outlined by Roth they are included to indicate t h a t the polymers are relatively similar with respect, to this constituent. and Stiehler (63). The value of 1, was calculated as suggested by Schade (64). EFFECT OF STYRENECONTENTO N PHYSICAL PROPERTIES Hysteresis was determined with a Goodrich flexometer (16) (TREADRECIPE). The physical properties of sodium-catalyzed a t 212" F. using a constant stroke of 0.175-inch and a load of 145 polymers of different styrene contents made a t a nominal tempounds per square inch; t h e percentage rebound was determined perature of 168" F. and compounded by the test recipe are shown with the Goodyear-Healy rebound pendulum, and the cut growth in Table 111. The maximum tensile strength at 77" F. of the at 212' F. on the DeMattia flexometer (a). The quality index, a stocks decreased as the amount of styrene in the charge formula relationship between the hysteresis-temperature rise and cut growth, was calculated as advocated by Juve and Schroeder (IS). The low temperature tests were conducted by the method proposed by Gehman, Woodford, and Wilkinson (6). RECIPES~ (PARTS) TABLE I. BASICCOMPOUNDING
I
.
R E S U L T S AND DlSCUSSION
The discussion of the results deals separately with the effects of varying the polymerization temperature, the styrene content, the viscosity of t h e polymers, and the compounding ingredients, The contributions of the several variables t h a t were considered in each of these major divisions are presented herewith.
W
60
3
b-
a (X-6241
D:
2
0
50
(OR-S-IO1
w
2
POLYMERlZATlON VARIABLES
40
a
*
EFFECTOF POLYMERIZATION TEMPERATURE ON PHYSICAL > PROPERTIES (TREADRECIPE). Since emulsion polymers pre-
30
pared a t low temperature exhibit better stress-strain and flex life properties than do those made at 122" F., physical properties 20 0 10 2 0 30 of sodium-catalyzed elastomers of 75/25 (charge ratio) butadiene A L T A X , PARTS PER 100 PARTS O F POLYMER styrene made at nominal temperatures of 86' to 188' F. and mixed according to a test recipe with 40 parts of Wyex E P C black, 2 Figure 1. Effect of Altax on Hysteresis-Temperature Rise parts of sulfur, and 1.25 parts of Altax per 100 parts of polymer were investigated (7, 8) and the results are shown in Table 11. TABLE 11. EFFECT OF POLYMERIZATION TEMPERATURE O N THE PHYSICAL PROPERTIES No significant change in most of the OF SODIUM-CATALYZED 75/25 BD/Sa COPOLYMERS physical properties of the polymers of this ~ ~ Hysteresise ~ ~ i l ~ Gehman monomer ratio was obtained by increasTemp. Reboundf, Yo Values, Poly. Combined Strength ing the polymerization temperature. The Temp.b, Styrenec, Viscosity, a t 77O F Set, rise, At At Minus C., F. % ML-4 Lb./Sq. 1d:d % ' F. 77' F. 212' F. Freezing Pt. Gehman low temperature properties im86 31.0 63 3100g 16.5 48 31 66 13 proved from a freeze point of -13" C. 104 31.2 66 3180Q 10 3 40 32 68 11 for a copolymer made at 86' F. to -29' C. 122 27.9 54 2800 65 16 13.6 51 31 168 32.6 46 2830 35 48 68 25 9 . 3 for one prepared at 188' F. Improvements 188 31.3 49 2910 11.3 39 50 66 29 of -13' C. were also obtained in the Butadiene/styrene. freeze points of sodium-catalyzed polyb Nominal values Determined from refractive index measurements. butadiene (19) with a n increase in the d Maximum values for vulcanizates cured a t 292' F. e Cured 90 minutes polymerization temperature from 86" to I Cured 60 to 70 mi 168' F. Meyer, Hampton, and Davison Q Determii (18) have shown t h a t the amount of O
- I
2916
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 44, No. 12
butadiene and of 90/lO and 75/25 butadiene/styrene polymers are compared in Table IV. All of the stocks were [Tread Recipe: 40 parts of Wyex (EPC) black and 1.25 parts of Altax] compounded by a carcass-type recipe Hysteresisd with 20 or 30 parts of the H M F black Combined 300% Tensile Temp. per 100 parts of polymer. The maxiBD/Sa Styrene, Viso., Modulusb, Strengthc, Set, rise, DeMatti? Quality yo ML-4 Lb./Sq. In. Lb./Sq. In. O F. Flexures Index6 Ratio mum tensile strengths of the stocks SODIUM-CATALYZED POLYMERS improved at each carbon black loading 100/0 44 1280 1860 4.5 31 1,000 0.8 when the amount of styrene in the charge 14:s 45 1020 90/10 2340 5.3 33 5,000 3.9 formula was increased from 0 t o 25 parts. 43 980 85/16 19.1 6.3 36 2,000 1.3 2400 58 1290 2.5 75/25 31.0 5.6 30 3,000 2820 The additional carbon black markedly XP-148 EJIULSION POLYBUTADIEXE M A D EAT 1 2 2 O F. increased the tensile strength. 100/0 31 800 1750 13.0 60 5,000 1.5 Although polybutadiene and 75/25 butadiene/styrene stocks exhibited simiX-539 GR-S lar hysteresis values when compounded 71.5/28.5 23.5 52 1080 3440 5.6 41 5,000 3.0 by t h e tread recipe with 40 parts of NATURAL RUBBERf Wyex EPC black, these results with 86 1220 4610 6.0 26 710,000 710 t h e H M F black show t h a t t h e 90/10 60 minutes. and 75/25 butadiene/styrene stocks apvulcanieates cured at 292O F. parently had lower temperature rise 120 minutes. 90 minutes. values a t the 20- and 30-part loadings of carbon black than did the polybutadiene Dolvmer. However. insuffi. " cient carcass stock data are available to establish this without question. The values for the styk* 201 rene specimens are consistent with other data. The sodiumcatalyzed stocks had hysteresis values t h a t were lower than those of GR-S-100 but not so low as those of natural rubber. EFFECT OF RAWVISCOSITY ON THE PROCESSING AND PHYSICAL PROPERTIES(TREAD RECIPE). The processing and physical characteristics of sodium-catalyzed polymers of 75/25 butadiene/styrene made at a nominal temperature of 168' F. to various viscosities and compounded by the tread recipe are shown in Table V. Generally, the mill processing, extrusion, rebound, and hysteresis properties appeared to be essentially independent of G,w 201 raw viscosity in the range of 12 to 95 ML-4. The polymer of 95 ML-4 gave somewhat higher tensile strength and higher modulus values than did stocks of lower viscosity when measured 32001 a t 77 O F. (CARCASS RECIPE). The effect of raw viscosity, from 12 to 95 bIL-4, on the physical properties of sodium-catalyzed polymers of
TABLE111. EFFECTOF STYRENE CONTENT ON PHYSICAL PROPERTIES OF SODIUMCATALYZED POLYMERS MADE AT 168' F.
..
..
..
f
W
*
16001
0
5
10
15
20
25
30
COMBINED S T Y R E N E , %
Figure 2. Effect of Styrene Content on Low Temperature Flexibility, Tensile Strength, and Hysteresis of SodiumCatalyzed Polymers
TABLEIV. EFFECT OF STYRENE CONTENT ON PHYSICAL PROPERTIES OF SODIUM-CATALYZED POLYMERS MADE AT 168" F. [Carcass recipe:
Statex 93, Parts
Statex 93 (HMF black) with 2.0 parts of sulfur and 1.4 parts of Altax] Tensile Hysteresisb Strength T%mp. a t 77' F." Elongationb, Set, rise, Lb./Sq. In: % % F. POLYBUTADIEXE
was decreased from 25 to 0 parts. The hysteresis values of the sodium-catalyzed polymers were essentially similar regardless of the styrene contents, and slightly higher than t h a t of natural rubber but superior to those of GR-S and emulsion polybutadiene prepared a t 122' F. T h e rebound values a t 212' F. were alike (700/0), whereas those a t 77" F. tended to decrease (irom 58 t o 500/0) with increases in styrene content. Of the sodium stocks, the polybutadiene possessed t h e poorest flexing characteristics and quality index. Although the Gehman low temperature properties of these polymers improved when the quantity of styrene in the charge formula was decreased, only the freeze point of the polybutadiene elastomer was comparable to t h a t of GR-S; t h e other stocks were poorer in this respect (see Figure 2). Copolymers made from 90/10 or 85/15 (charge ratios) butadiene/styrene appeared t o possess the best balance of physical properties. (CARCASS RECIPE.) The physical properties of sodium poly-
20 30
4.0 3.4
19 24
20 30
90/10 BD/S (14.9% COMBINED STYRENE) 880 370 2.9 1230 380 3.5
15 18
20 30
75/25 BD/S (31,070 COMBINED STYRENE) 1180 390 3.3 1830 400 3.4
19
GR-S-100 820 750
2.9 3.5c
22 29 c
1.9 1.6
10 13
20 30
580 830
1770 2970
300 350
16
SATURAL RUBBERd 20 30
3980 690 4000 640 4 Maximum values for vulcanizates cured at 292O F. b Cured a t 292O F.for 9 0 minutes. C Data for X-624, a polymer similar t o X-478. d Cured at 280° F.
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1952
2917 COMPOUNDING INGREDIENTS
EFFECT OF RAWVISCOSITYON PHYSICAL PROPERTIES OF SODIUM-CATALYZED 75/25
TABLE V.
BD/Sa COPOLYMERS
Visc., ML-4 Raw Compd. 05 .. 66 59 48 32 26 12
L
86 68 61 52 40 32 19
[Tread recipe: 40 Parts of Wyex (EPC) black and 1.25 parts of Altax] 300 ? '' Tensile Tensile Hysteresis Mod.8, Strengtho, Strengthb Temp. DeMattia Extru- Lb./Sq. Lb./Sq. Lb. Sq.' E1ong.b. Set, rise, Flexures Quality sion In. In. in. % % F. X 10-1 Index Index A t 77' F. A t 212O F. Cured a t 292' F. for 90 minutes 10.0 9.0
12.5 10.0 9.0 13.0 14.5
1360 960 1290 1360 1320 1280 1080
3360
800 _. .
260 300 310 300 280 300 3 10
..
7:3 11.4 8.7 12.0 13.8
32 36 35 37 38
X-539 GR-8 POLYMER 3440 930 290 10.3
49
3n70 ....
2810 3000 2830 2660 2140
51 57 10.0 1320 Butadiene-styrene. b Cured a t 292' F. for 60 minutes. 0 Maximum values for vulcanizates cured at 292O F.
810 840 770 740 740 580
..
.. 4 4 5 6 6
3.'6 3.1 4.0 4.5 4.4
3
1.4
a
TABLE VI. EFFECT OF VISCOSITY ON PHYSICAL PROPERTIES OF SODIUM-CATALYZED 75/25 BD/S COPOLYMER^ (Carcass recipe: Viscosity,
ML-4
Raw Compd.
95 70 61 55 38 26 12
65 43 44 39 30 25
Gel,
%
11 I9 4 5 2 3
DSV
1.75 parts of Altax, cured a t 292O F. for 60 minutes) 300% Tensile Tensile Modulus Strengthb Strength Elong., sulfur, Lb./Sq. 1;. Lb./Sq. 1;. Lb./Sq. 1;. % Parts At 77O F. A t 212O F.
STOCKS COMPOUNDED WITH 30 PART^ OF STATEX 93 (SODIUM-CATALYZED POLYMERS) 3.25 2 1460 2360 530 2 3.06 860 1430 290 2 2.90 760 1500 270 2 2.69 820 1440 320 2.45 2.5 1010 1330 360 1.85 2.5 1420 300 860 1.40 3.0 1410 960 180
210 170 170 180 170 170 120
Hysteresis Temp.
orlT
4.3 3.9 3.8 5.5 5.9 5.1 7.2
22
19
EFFECTOF VARIATIONIN AMOUNTS OF SULFUR, ALTAX, AND D I PH E N Y L G u A N I D I N E (CARCASSRECIPE). A study was made of the effects of varying the amount of sulfur, Altax, and diphenylguanidine in a compounding recipe with 30 parts of H M F black per 100 parts of polymer on the physical properties of sodium-catalyzed 75/25 butadiene-styrene polymers prepared a t a nominal t e m p e r a t u r e of 168" F. As shown in Table VII, increasing the amount of the curative generally increased the modulus and lowered the hysteresis properties to a slight extent, but did not affect the maximum tensile strength substantially.
SUBSTITUTION OF REDLEAD ZINC OXIDE (TREAD
FOR
RECIPE). The physical properties of s o d i u m - c a t a1yz e d 75/25 butadiene/styrene copolymer of 53 ML-4 viscosNATURAL RUBBER ity compounded with 0 to 5 86 .. *. 2 740 3920 2170 750 3.3 13 parts of red lead are sumWITH 30 PARTS OF PHILBLACK 0 STCCKSCOMPOUNDED marized in Table VIII. The (SODIUM-CATALYZED POLYMERS) stocks mixed with 3 parts 95 61 11 3.25 2 1450 2860 550 210 4.8 21 of red lead cured rapidly. 48 38 2 2.31 2.5 1540 2500 410 170 5.2 20 35 32 2 2.21 2.5 1480 2160 470 180 7.3 24 A reduction or an increase NATURAL RUBBER of the amount of red lead 86 58 .. .. lowered the rate of cure. To 2 1100 4280 2370 710 2.7 17 Combined styrene varied from 30 to 34%, as determifled from the refractive index measurements, with the lower the rate of cure to a p exception of polymers of 55 and.12 ML-4 which had combmed styrene contents of 26.6 and 25.5%, respectlvely. proximately t h a t of GR-S or Maximum values for vulcamzates cured a t 292OF. GR-S-100, it was necessary to lower the cure temperature to 260" F. or to decrease 75/25 butadiene/styrene made a t a nominal temperature of the quantity of curing agents. Elimination of red lead 168 F. and compounded according to a carcass-type recipe with from the compounding recipe lowered appreciably the rate H M F black is shown in Table VI. The modulus and tensile and level of cure, but the maximum tensile strength was strength a t 77" and 212" F. were not substantially affected by decreased. Increases in the amount of Altax for stocks changes in viscosity from 12 to 70 ML-4. On the other hand, without metallic oxide improved the tensile strength moderately. polymer of 95 ML-4 viscosity exhibited a higher compounded viscosity and better tensile strength a t 77" and 212' F. The other properties of the high TABLE VII. EFFECT OF SULFUR, ALTAX,AND DIPHENYLGUANIDINE ON PHYSICAL PROPERTIES viscosity stock were comparable OF SODIUM-CATALYZED 75/25 BD/Sa COPOLYMER to those of the lower viscosity [Carcass recipe: 30 parts of ( H M F black) Statex 93; cured a t 292O F. for 60 minutes] polymers. 300% Tensile Tensile Hysteresis Similar s o d i u m - c a t a l y z e d Modulus Strength Elong., Strength, Elong.. Te.mp. Sulfur, Altax, DPGb, Lb*/Sq. Ih. Lb./Sq. . ;1 % Lb./Sq. In. % stocks of 35, 48, and 95 ML-4 Set, % ?? Parts Parts P a r t A t 77' F. At 212O F. viscosity were compounded by a 3.0 1.40 0.056 1120 1410 163OC 350 340 150 4 . 7 2.3d 16 14d carcass recipe with 30 parts of a 2.5 1.40 0.056 1490 1610 1020 390 360 190 5 . 5 3.0 18 15 1.40 0.056 770 1390 1660 high abrasion furnace black. I n 2.0 450 320 200 5 . 9 3.8 23 22 2 . 5 2.25 0.056 1120 1340 1460 340 230 130 3.5 2 . 1 14 14 this seriesof tests, tensile strength 2.5 1.75 0.056 1070 1430 1540 370 160 4.1 2.5 15 14 tended to improve with increasing 330 190 5.5 3.0 18 15 2.5 1.40 0.056 1020 1490 1610 390 350 raw viscosity and was higher than 2.5 1.76 0.400 1140 1190 1440 320 290 150 1.9 1.9 14 14 2.5 1.75 0.250 1110 1350 1570 340 300 150 2 . 7 2.2 14 15 those of stocks of similar vis2.5 1.75 0.056 1070 1430 1540 370 330 160 4.1 2.5 15 14 cosity compounded with the a Butadiene-styrene. b Diphenylguanidine. H M F black a t both 77" and Figures in this oolumn are maximum values for vulcanisates cured at 292O F. 212" F. Hysteresis and rebound d Figures in this column are for cure a t 292O F. for 90 minutes. values were generally similar. 15 21 22 22 18
..
--
2918
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 44, No. 12
tics. Since sodium-catalyzed polymers do not contain any fatty acid after formation, the effect of adding stearic (Tread recipe: no zinc oxide but 3 parts of stearic acid; cured a t 292' F.) acid ( 2 2 ) to the raw polymer to react 300% Tensile Hysteresis with sodium and also during compoundRed Modulusb, Strengthc, Temp. Cure Lead, Altax, Sulfur, Lb./Sq. In. Lb./Sq. In. Setd, rised, Indexe, ing was determined. Methanol was 70 F. Min. Batch No. Parts Parts Parts At 77O F. not employed to neutralize the alkali 1 5 L25 1.5 1330 2450 .. .. .. in the controls. The stress-strain and 2 3 1,25 1.5 1510 2670 .. 16f 3 1.0 1.5 900 3170 6,'s 64 24 hysteresis properties of the resultant 17 3 0.5 1.5 1420 2580 .. .. stocks are shown in Table X. 22 3 1.25 0.5 740 2630 5.5 43 30 7 2 1.26 1.6 1.560 2830 .. , . Failure to neutralize the alkalinity 10 1 1.25 1.5 1390 2490 .. , . 9 None 1.25 1.5 620 2430 .. .. .. of the polymer apparently did not 12 None 1.25 2 0 690 2450 .. .. .. .. .. significantly h a r m t h e s t r ess- s t r a i n 13 None 1 .75 2 .. 0 770 2510 20 None 3.00 1.5 1030 2620 .. .. .46. properties. Utilization of stearic acid 23 58 1.25 2.0 1070 2810 9.7 33 as an additive to the raw polymer None 1.75 2.0 1230 3370 9.0 51 51 X-603 GR-Sk Butadiene-styrene. did not appear to affect the flex life b Cured for 50 minutes. or hgst,eresis properties to any marked Maximum values for vulcanizates cured a t 2 9 2 O F. d Based on strain data; optimum cure plus 43 minutes. extent. The use of stearic acid in e Cure index = 6 (cure point - scorch point) + scorch point. f Cured a t 260" F. with 1.5 parts of stearic acid. compounding resulted in stocks with Mixed with 5 parts of zinc oxide and 3 parts of stearic acid. tighter cures and thus lower hyst,eresish Mixed with 5 parts of zinc oxide but without stearic acid. temperature rise values. EFFECT O F TYPEO F C.4RBON BLACK. TABLE IX. EFFECT OF SANTOCURE ON PHYSICAL PROPERTIES (TREADRECIPE). Sodium-catalyzed OF SODIUM-CATALYZED 75/25 BD/Sa COPOLYMER 75/25 butadiene/styrene copolymers w r e compounded with (Tread recipe: 1.5 parts of sulfur: cured a t 292' F.) 1.5 or 2 parts of sulfur and 0.93 or 1.25 parts of Altax and Stearic hfodulusb 300% Tensile Strength, Cure with different types of carbon black (HhIF, EPC, and HBF) Santocure, Acid, Lb./Sq. In'. Lb./Sq. In. Index, andthephysicalpropertiesof thecuredstockswereexamined(Table Parts Parts a t 77O F. A t 77O F.C A t 212O F.6 RIin. XI). The tensile strengths - of stocks mixed with either PhilSODIUM-CATALYZED POLYMER black 0, a high abrasion furnace black, or Wyex, an easy proc1.25 3.0 1410 2870 .. .. essing channel black, were similar, and superior to those of the ., .. 1.25 1.5 1300 2840 1.00 3.0 1190 2750 .. .. polymers compounded with Statex 93, a high modulus furnace 1.00 1.5 1170 2730 920 52 black. Lowering t h e HAF black loading to 35 parts did not 1.25die 3.0 1070 2810 840 46 harm the teneile strength, although the modulus values decreased. X-603 GR-S COSTROL 3370 930 51 At similar levels of sulfur, AItax, and black, the H M F black 1,75d,e .. 1230 specimens usually had lower hysteresis values than did the other a Butadiene-styrene. b Cured for 50 minutes. specimens. Further improvement in the hysteresis of the HAF C Maximum values for vulcanizates cured a t 292O F. d Altax. black vulcanizates was obtained a t a 35-part black loading e 2 parts of sulfur. by raising the amount of stearic acid from 1.5 to 3.0 parts. ) Sodium-catalyxed75/25 butadiene/st'yrene (CARCASS RECIPE. The hysteresis temperature rise of red lead stocks cured at Were parts Of and parts noted otherwise? and Of A1tax per looparts Of polymer, 2600 F. was lower than that of stock mixed with a low loading of with different brands of carbon black (Statex 93, acetylene, the curing agents and of stocks nithout oxide. Gastex, myex, Philblack A, and Philblack 0) and the physical Incorporation of red lead into the polymer decreased the cure properties of the stocks were examined (Table XII). 4 t a loadindex (an inverse measure of scorch) from approximately 64 t,o30 ing of EO parts of carbon black, stocks containing the HAF black minutes. (Philblack the best tensile strength a t 77" F.; those -kLTax ( T R ~ ~ ~ ~ ~ ~~ ~ ~ 0) ) exhibited . s~~~~~~~~~~~ OF sANToCURE for the HhIF black (Statex 93) and Gastex (a semireinforcing The phgsical ploperties of sodium-catalyzed 75/25 butadiene/black) specimens were as low as 1650 pounds per square inch. styrene stock of 53 3IL-4 viscosity compounded TTith different When the specimens x-ere tested a t 212" F., Philblack 0 and amounts of Santocure (reaction product of cgclohexylamine and Philblack B (a high modulus furnace black) stocks appeared to mercaptobenzothiazole) in place of Altax are shovn in Table IX. One part of Santocure and 1.5 part's of stearic acid per 100 parts of polymer yielded a sodium stock xith a 300% ACIDO K THE PHYSICAL PROPERTIES OF SODIUMTABLE X. EFFECTOF STEARIC modulus versus time-of-cure curve someCATALYZED POLYBUTADIEKE mThat similar to t h a t for X-603 (all data (Tread recipe: 40 parts of Philblack 0, 1.23 parts of hltax, and 2.6 parts of sulfur) not shown), although that of the forme1 Hyfiteresisc Stearic Acid flattened out a t higher cures. The tensile In ra,v Added o n ~ e n s i i eStrength, Temp. DeMattia strengths of specimens with 1.25 parts of polymer, miil, ~Lb./Sq. In. pE!~Li& Set, rise, FlexuresC % parts At77O F.Q At212'F.b At 77' F.a -4t212'F.b % F. X 10-8 Santocure were slight'ly higher than those Sone 1410 580 360 210 11.4 39 1 Noned Noned 3.0 1460 710 330 230 7.8 35 1 mith 1.00 part: both were poorer than 360 220 12.8 42 2 1460 560 0.6 h-one that of GR-S. The scorch properties of 0.5 360 220 8.3 34 1 3.0 1500 440 10.2 40 2 1480 590 380 210 1.0 None the sodium stocks were in the same range 9.2 36 1 1660 550 410 200 1.0 3.0 340 210 10.2 44 2 1470 560 2.0 None as those of GR-6. 7.6 34 2 1610 490 350 190 3.0 2 .o &kDDITION O F STEARIC ACID (TREAD a Values a t optimum cure based on 300% modulus versus time-of-cure curve. b Arrerage for 60- and SO-minute cures. RECIPE). It is generally recognized t h a t c Samples were cured for 30 minutes longer than the optimum cure, based on 300% modulus. fatty acid may be added to rubbers to d Polymers were not soaked in methanol. decrease variations in curing characteris-
TABLE VIII. EFFECT OF REDLEADO N PHYSICAL PROPERTIES OF SODIUM-CATALYZED 75/25 BD/Sa COPOLYMER
O
I
.
. I
I
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1952 2400 2200
-
4.0 PARTS
- 2000 i
I
0
ISOO.
m
A 1600-
2 I400 3'1200-
a
g 1000-
ae soo0
$
600-
25
50
76
100
I25
150
TIME OF CURE, MINUTES
Figure 3. Effect of Sulfasan R on 300% Modulus Values of Sodium-Catalyzed Polymers have higher tensile strengths than did the other stocks. Rebound results a t 77" and 212" F. for the stocks with Statex 93, Philblack 0, and Wyex were usually similar; those for Gastex and acetylene (a conducting furnace black) were higher. The Philblack 0 specimen exhibited a hysteresis-temperature rise value t h a t was equal to those for most of the stocks; that of the Wyex stock was the highest, probably caused by the relatively low state of cure as shown by the high set value. The results shown in Table XI11 where various levels of sulfur and Altax were used, coupled with those obtained in the study of raw viscosity and accelerating ingredients, indicate that Philblack 0 or Philblack A stocks might yield the best balance of hot tensile and hysteresis properties. COMPOUNDS OF SODIUM-CATALYZED POLYMERS WITH VARIOUS LOADINGS OF OIL AND CARBON BLACK. Work a t the Government Laboratories (SO), Phillips Petroleum Co. (69),and Firestone Tire and Rubber Co. ( 1 ) has shown t h a t sodium-catalyzed polymers exhibit better hysteresis properties than does emulsion GR-S made a t 122' F. The Phillips Petroleum Co. has reported (2, 20) that the use of polybutadiene of low molecular weight in low temperature GR-S improves the hysteresis property, and studies a t the Government Laboratories (14) have
indicated that the addition of oil to 41" F. butadiene/styrene copolymer of high viscosity also aids the hysteresis characteristics. Thus, a study (81) was made of the effects of adding 0, 10, and 20 parts of a processing oil (Circosol-2XH) per 100 parts of polymer, during compounding upon the stress-strain and hysteresis properties of 75/25 butadiene/styrene sodium-catalyzed polymers of 66 ML-4 average viscosity. These oil levels were utilized a t carbon black loadings of 30,40, and 50 parts of Philblack 0 and Statex 93 per 100 parts of polymer. Summarized average stressstrain and hysteresis results for both polymers are given in Table XIV. GR-S-100 polymer (X-624) and natural rubber, both compounded without softener a t carbon black loadings of 30 and 40 parts, served as controls. The levels of the curing agents were varied for control polymer X-624 and for the sodium-catalyzed polymers to yield similar rates and levels of cure a t each carbon black loading, as judged by the 300% modulus versus time-of-cure curve. An increase in the amount of the processing oil, added on the mill, from 0 to 20 parts lowered the tensile strength of the sodium-catalyzed polymers a t 77" F., but deterioration of this property was minimized a t the higher carbon black loadings. At a test temperature of 212' F., 20 parts of oil caused a drop in the tensile strength. When the quantity of Philblack 0 or Statex 93 was increased from 30 to 50 parts, the tensile strength a t 212' F. was improved a t each oil loading. To obtain hysteresis values on the flatter portion of the hysteresis time-of-cure curve, the hysteresis specimens were cured for 45 minutes beyond the optimum cure time, as determined by constant-load elongation (strain) data. The hysteresis properties of the sodium polymers improved with increased amounts of oil. Although the moduli curves a t the various carbon black loadings were similar, the percentage set values of the hysteresis specimens generally decreased with increased amounts of the oil, indicating t h a t stocks mixed with 20 parts of oil were cured tighter than the others. When the oil stocks had similar or higher set values (data not shown), the improvement in hysteresis with Circosol2XH was not quite so pronounced.
3200k
i
A
SI00
TABLE XI. EFFECTOF VARIOUS ,CARBON BLACKSMIXEDWITH SODIUM-CATALYZED 75/25 BD/Sa STOCKS (Tread recipe: Altax, Parts
Sulfur, Parts
1.5 parts of stearic acid; cured a t 292O F.6) Hysteresise 300% Tensile Temp. ModulusC Strengthd Set, rise, Lb./Sq. In'. % F. Lb./Sq. In'. 40
1.25 0.93 1.25 0.93 1.25 1.25 0.93
2.0 2.0 2.0 2.0 1.5 2.0 2.0
93 2560 2210
910 680 40 P A R T 8 1010 760 910
8.1 12.2
39 48
40 PARTSOF PHILBLACX 0 1640 3080 1290 2840
35 P A R T 8 OF PHILBLACK 0 0.93 2.0 1120 2940 1.25 2.0 1340 3130 1,25f 2.0 1300 2920 a Butadiene/styrene. b Optimum cure determined from strain data. Cured for 50 minutes. d Maximum values for vuloanizates oured a t 292O F. e Cured for 45 minutes. 1 Compounded with 3 parts of stearic acid.
15.2 18.8 22.3
48 56 52
10.2 11.5
45 50
22.3 9.8 9.0
59 39 36
-
45 76 82 0 Phenyl-2-naphthylamine was added on the basis of the amount of natural rubber present in the blend. b Cured for 120 minutes. 0 Compoundin ingredients added t o 90/10 BD/S copolymer, then natural rubber was addef. d Compoundin ingredients added to natural rubber, then 90/10 B D / S copolymer was acfded.
l
2922
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 44, No. 12
LITERATURE CITED
TABLE XVI. CHEMICAL TESTDATAFOR SODIUM A N D EMULSION POLYMERS FOR USE IN WIRESTOCKS
(1) Adams, H. E., et al., private communication to Synthetic
Rubber Division, Reconstruction Finance Corp., Washington, D. C. (2) Alexander, J. W., et al., I b i d . Polymer iYo. % % (3) Am. 900.Testing Materials, Committee D-11, "A.S.T.M. Standards on Rubber Products," Designation D 394-40, PhiladelEXIJLSIOSGR-S POLYHERS phia, Pa. 3.30 0.04 0.8 0.90 0.23 GR-S-AC alum) (4) Ebert, F., Heidenbrack, R., and Orth, P., U. S. Patent 2,209,746 GR-S-65-SL (acid glue) 0.29 0.13 5.03 0.04 0.6 5.39 Nil 0.7 0.63 0.04 X-674-SP (acid glue) (July 30,1940). (6) Garvey, B. S., Jr., Whitlock, M. H., and Freese, J. A., Jr., SODIUM-CATALYZED 75/25 BD/S P O L Y M E R S IND.ENG.CHEM..34. 1309-12 11942). 78P Blend 7 0.56 0.12 Nil 0.17" 1.2 (6) Gehman, S. D., Woodford, D. E., and Wilkinson, C. S., Jr., 78P 62 Blend 3 0.32 0.31 Nil 0.185 1.2 I b d . , 39, 1108-15 (1947). 78P 63 Blend 2 0.38 0.25 Nil 1.6 S R D Specifications, Max. ... 0.45 . . . 0.175 .. 3.6 (7) Goldsmith, H.. private communication to Synthetic Rubber a Reported as sodium acetate. Division, Reconstruction Finance Corp., Washington, D. C. (8) Goldsmith, H., and Labbe, B. G., Ibid. (9) Harries, C., Ann., 383, 157 (1911). (10) I n d i a Rubber World, 109, 375-9 (1944); 111, 446 (1945). (11) Juve, A. E., B. F. Goodrich Co., private communication. XVI, and the processing, stress-strain, and electrical properties (12) Juve, A. E., and Meyer, A., IND.ENQ. CHEM.,39, 1490-93 for stocks compounded by a typical wire recipe containing 135 (1947.1. parts of clay and whitings, 28 parts of zinc oxide, 40 parts of hard (13) Juve, A, E., and Schroeder, C. H., private communication to hvdrocarhon, and 5.5 parts of mixed accelerators are shown in Synthetic Rubber Division, Reconstruction Finance Corp., Table XVII. Washington, D. C. (14) Laundrie, R. IT., and Labbe, B. G., Ibid. (15) Lessig, E. I.,IND. ENG.CHEM., ANAL.ED.,9, 582-8 (1937). TABLE XVII. PHYSICAL PROPERTIES OF SODIUM AND EMTJLSIOX POLYMERS FOR USE IN (16) Marvel, C. S.,et al., J . PoEyWIRE STOCKS mer Sci., 1,275-88 (1946). Resistivitya 117) Mathews. F. E.. and Stranee. a t 75' F. Ohm-Cm. E. H., Brit. Patent 24,750 Viscosity, MI11 ExtruCure 300% Tensile x 1014 (1910). ML-4 Shrinkage, Roughsion Index a t Modulus", Strengths At At (18) Meyer, A. W.,Hampton, R. Polymer No. Raw Compd. % ness Index 250° F. Lb./Sq. In. Lb./Sq. In'. 30 sec. 1 min. K., and Davison, J. A., J . Am. Chem. SOC.,74, 2294 E n f n L S I o N GR-S POLYMERS (1952). GR-S-AC 52 42 44 12 13 21.0 430 950 1.19 1.36 (19) Mills, E. O., Reich, M. H., 53 41 48 8 13.5 480 1020 4.1 4.6 GR-S-65-SP and Goldsmith, H., private X-674-SP 69 60 35 10 13 16:5 720 1130 0.85 1.05 communication to SynSODIUM-CATALYZED 75/25 BD/S COPOLYMERS thetic Rubber Division, Reconstruction Finance 78P Blend7 56 54 33 17 15.0 630 1150 10.5 15.7 78P 62 Blend 3 53 55 30 4 14.5 zi:o 520 1030 12.3 16.8 Corp., Washington, D. C. 60 31 11 13 26.0 590 1110 9 8 130 78P 63 Blend 2 49 (20) Phillips Petroleum Co., Ibid. (21) Reich, M. H., Moss, B., and a Cured for 10 minutes a t 292' F. Schneider, R. E., Ibid. ( 2 2 ) Reich, M. H., and Sohneider, R. E.. Ibid. Roth, F. L., and Stiehler, R. D., India Rubber World, 118, The sodium-catalyzed raw polymers met the Synthetic Rubber 367-71 (1948). Division specifications for polymers t o be used in wire and cable Schade, J. W., Ibid., 123, 311-14 (1950). stocks, namely, maximum water-soluble ash of 0.45% and maxiSchneider, R. E., and Goldsmith, H., private communication to mum water absorbed of 3.5 mg. per square em. T h e RaterSynthetic Rubber Division, Reconstruction Finance Corp., Washington, D. C. soluble ash content and the amount of water absorbed for t h e Schneider, R. E., and Reich, M. H., l b i d . sodium polymers compared favorably to those for typical wire Schulee, TV. A, et al., IND. ENG.CHEM.,41, 414-16 (1949). and cable polymers, GR-S-ilC, GR-S-65-SP, and X-674-SP. Schulze, W-.A,, and Crouch, J., J . A m . Chem. SOC.,70, 3891-3 (1948). The mill processing, extrusion, and stress-strain characteristics Svetlik, J. F., and Howard, W. S.,private communication to of the sodium polymers were similar to or better than those for the Synthetic Rubber Division, Recon8truction Finance Corp., emulsion stocks. The resistivity of t h e sodium polymers was Washington, D. C. definitely superior to t h a t of the emulsion polymers, averaging Taft, W.K., et al., I b i d . 10.9 X 1014 and 2.05 X 10'4 ohm-cm. a t room temperature in 30 A~CCEPTED July 28, 1952. RECEIVED for review May 20, 1952. seconds (11). On the basis of these results, sodium polymer This work was sponsored by the Synthetic Rubber Division, Reconstruction Finance Corp., in connection n i t h the government synthetic rubber program. should be suitable for wire and cable stock$. Ash, % Water Total soluble
~
Fatty Acid,
Fatty Soap,
Water Abaorbed Mg./Sq. Crh.
~
~I
