I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
November 1949
(6) Kuckler, L., and Thiele, H., 2. physik. Chem., B42, 359-79 (1939). (7) Marek, L. F., and McCIuer, W. B., INn. ENQ.CHEW,23, 878 (1931). (8) Norton, C. L., Jr., J . Am. Cerum. SOC.,29,187 (1946). (9) Pease, R. N.,J. Am.C h .SOC.,50,1779(1928). (IO) Pease, R.N., ttnd Durgan, E. S.,Ibid., 50,2715(1928). (11) Sacheae, Hans, 2. physik. Chen~.,B31,79-86,87-104 (1935). (12) Steaoie, E.W.R., C h m . Rev., 22,311 (1938). (13) Steacie, E. W.R., and Shane, G., Can. J. Research, 18B,203-16 (1940).
2535
(14) Storoh, H.H., and Kassel, L. S., J. Am. Chem.Soc., 59, 124&6 (1937). (15) Travers, M. W.,and Hawks, J. A., Tr5w. Faraday Soc., 35, 864 (1939). (16) Travers, M.W.,and Pearce, T. J. P., J . SOC.C h m . Ind., 53, 321T (1934). (17) Tropsch, H., and Egloff, G., IND. ENG.GIIEY.,27,1063 (1935). I~BICEIYED January 7, 1940. Presented before the fourth Southwest Nngional Meeting of the AMERICAN C A ~ M I C ASOCIETY, L Shreveport, La.. December 1948.
Low Temperature Behavior of Butadiene-Styrene Copolymers
x
EFFECT OF COMPOUNDING VARIABLES R. D. JUVE AND J. W. MARSH The Goodyear Tire & Rubber Company, Akron, Ohio
S
YNTHETIC rubbers and natural rubber increase in stiffness at low temperature and tend to lose their elastic characteristics. This stiffening and hardening phenomenon occurs in varying degrees with various elastomers. Natural rubber and certain synthetic rubbers crystallize during extended exposure at lorn temperature, whereas other synthetic rubbers such as G R S remain amorphous (7). I n a general review of the low temperature properties of synthetic rubber, Liska (6) has shown that decreased styrene in butadiene-styrene copolymers improves the flexibility at low temperature. The low temperature flexibility of vulcanized articles made from any particular rubber or synthetic rubber is influenced by the compounding ingredients admixed with the elastomer. In this paper results are shown of some studies of the effect of these compounding ingredients upon the low temperature serviceability of butadiene-styrene copolymers. Somewhat similar work on the effect of a large number of plasticizers in GR-S has been conducted at the Rubber Laboratory, Mare Island Naval Shipyard (8) with particular emphasis on compression set at low temperature. EXPERIMENTAL PROCEDURE
For the evaluation of plasticizers in GR-S,the following campounding recipe was used: Parts by Weight
GR-S EPC black
Zinc oxide Steario acid Sulfur Mercaptobenzothiazole Diphgny lguanidine Plasticizer
100.00 50.00
3.00 1 .oo 1.60
reducing the tendency for butadiene-styrene copolymer vulcanizates to stiffen during service at low temperature. Compounding variables which affect the behavior at low temperature include type and amount of plasticizer, particle size of the carbon black, and extent of vulcanization.
Tensile and elongation values at 27 ' C. were measured on the Goodyear autographic machine (I), tests at 93 C. were made on a standard L-2 Scott tester equipped with a heating jacket. The same machine was used for the tests at -57" C. A standard Bcott L-13 tester was placed in a -41 ' C. room for tests at that temperature. Standard A.S.T.M. dumbbells, 1 X 0.25 inch, were used on the Scott tester. Rebound values were determined on thn Goodyear-Healy rebound machine. Hot cut flex-life determinations were made on the Goodyear fleving machine using a rectangular sample 5 1 / ~inches long and 0.90 inch wide cut from a standard test sheet. A 6/32-inchcross wire cut wa8 made at the center. During the flexing, the samples are stretched to 20% elongation. The method for measuring dynamic properties has been described by Gehman et al. (3). Compression set test was conducted by a modification of A.S.T.M. D 395-471' method B. The per cent compression set was taken as the per cent set remainin after release from 30% compression for 168 hours at -57" Volatility is recorded ae the weight loss after 48 hours in an air oven at 100' C . O
6.
0.62
0.78 As shown
In the study of the effect of carbon black particle size on low temperature properties, the recipe which follows was used: Polvbutadiene Paraflux Zinc oxide St.aric acid Sillfur Mrrcsptobensothiaeole DIr)hnnyluiianidine Carbon black
Elastomers lose elasticity and tend to become stiff at
low temperature. A study has been made of means of
Parts by Weight 100.00
6.00 3.00
1 .oo
2.10
0.83 1.04
As shown
The test for low temperature flexibility has been described by Gehman et al. (4). The tc~mrsraturesat which the relative moduli are 2, 5, 10, and 100 times the modulus at 25' C. are designated as Tt,Ts,T,o, and Ttw.
EFFECT O F PLASTICIZERS UPON LOW TEMPERATURE FLEXIBILITY
Twenty-six plasticizers, including those shown in the literature to have very low freezing points, were studied in G R S . Both 10 and 20 parts of each per 100 parts of GR-S were tested. GR-S was selected for the plasticizer study because it stiffens a t a higher temperature than butadiene-styrene copolymers of lower styrene content, thereby allowing a more critical examination of the plasticizing effect. Typical data from which the stiffness values shown on Table I were taken are plotted on Figure 1 for GR-S containing Flexol TOF (trioctylphosphate) and Para Flux (saturated polymerized hydrocarbon). The relative modulus curves clearly describe the flexibility of the stocks.
2536
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
IOC
Vol. 41, No. 11
2c
pate and F ex01 TOF were superior to the others tested. Ten, parts of di(n-hexy1)adipate and 10 parts of Flexol T O F were approximately equivalent to 20 parts of RIonoplex DOS (dioctyl sebacate) and 20 parts of Kapsol (methoxyethyl oleate). T h e noticeable hardening of GR-S containing 20 parts of di(n-hexyl) azelate and 20 parts of Monoplex DBS (dibutyl sebacate) probably can be explained by changes in the solubility of the plasticizers in the rubber.
IO
COMPARISON OF EASY PROCESSING CH4UNEL (EPC) AND FINE THERMAL BLACKS I S POLYBUTADIENE
5c
PAR A F LUX
cn
T R E A D STOCK)
2 5
f
k
G
az 2 Q
v,
ELI 0 Iw
The stiffening a t low temperature of polybutadiene stocks with 50 parts E P C black, 50 parts of thermatomic P-33 black, and without any black was compared. With the exception of a slightly higher Tz temperature, P-33 did not seem i o change the low temperature stiffening characteristics exhibited by the gum stock. The presence of 50 parts of E P C black caused the polybutadiene to increase in stiffness somewhat more rapidly. The freezing point of the stock, however, was the same as that of the stock which contained no black. Torsion stiffening data are listed in Table 111.
1 c-
HIGH BLACK AND HIGH PLASTICIZER I S GR-S
4
IO PARTS
w E
FLFXOL TOF-
J
The low temperature flexibility of GR-S can be improved by increasing the amounts of carbon black and plasticjzer without too great a deterioration of physical properties. The compounded stocks with increased black and plasticizer were of Rfooney viscosity similar to that of the control stock which contained 50 parts of EPC black and 10 parts of Flexol TOF. Moduli a t 300% elongation were also similar to that of the control
Figure 1. Effect of 10 Parts of Flexol TOF upon Relative Torsional iModulus of GR-S Tread Stock a t Low Temperatures
The plasticizers are listed in Table I in order of the ascending 2'10 values of the stocks containing 10 parts of plasticizer. It should be observed, however, that in some cases the stocks containing 20 parts plasticizer rate better than the chosen tabulating method would appear t o rate them. As an example, tributyl tricarballylate is placed low on the list, but 20 parts of this material resulted in a stock with a Tio value a t -57' C. which would place it high on the list in comparison to 20 parts of the other plasticizers. Marked differences in the flexibility of GR-S were caused by the various plasticizers. For example, the substitution of 10 parts of butyl Cellosolve pelargonate for 6 parts of Para Flux lowered the Ti", the temperature a t which the relative modulus is ten times the room temperature modulus, from -42" to -56" C. I n Table I1 js given a list of the sources from which plasticizer samples were obtained and a description of the compositions Plasticizers for which data are given in Table I but which are not described in Table I1 were prepared in the Goodyear Research Laboratory. I n selecting a plasticizer for low temperature applications, i t is necessary to consider, in addition to low temperature flexibility, the volatility and water extraction. Also important are the effects upon the processability and the physical properties of the rubber. These effccts upon the final products are not considered herein. For the purpose of this investigation, all of the plasticizers included in this report were miscible with GR-S. The test results shown in Table 1 were obtained by rapidly bringing the stocks to test temperature and evaluating them. Some of the best plasticiLers from the preliminary screening test were then subjected to long time exposure tests a t low temperature. Figures 2 and 3 describe the increase in relative modulus during 2 weeks' exposure at - 57" C. Di(n-hexy1)adi-
~-
~
TABLEI. P L A ~ T I C I Z INEGR-S R~ Plasticizer Butyl Cellosolve pelargonate Di (n-hexylladipate TP-SOB Flexol TOF Di(n-hexy1)aselate Tributyl aconitate
plasticizer Parts of per 100 Parts GR-S 10 20 10 20 10 20 10 20 10 20 10 20 10
Monoplex DBS
20
10
Di (2-ethy1hexyl)azelate
20
10
Monoplex DO9
20 10
Plasticizer XP-3
20 10
Octyl diphenyl phosphate
20 10 20 10 20 10 20 10 20
Mixed octyl adipate Kapsol Dibutyl phthalate Tributyl phosphate
10
Tributyl tricarballylate
20
10
Di(mixed octy1)succinate
20
10
Tetrabutyldiglycol carbamate
20
10
Flexol 3 G 0
20
10
Di(2-ethylhexy1)adipate
20
10 20 10
KP-140 Butyl butoxyethyl phthalate
20 10 20
Plasticizer SC Dioctyl phthalate
10 20
Baker P-4C
10 20 6
Para Flux (control tread stock)
.,.
Torsion Stiffness Values, 0
Tz
Ts
-38 -53 -37 -48 -41
-51 -60
-51
-42 -49 -40 -45 -36 -43 -34 -32 -36 -4
-32 -34 -33 -38 -30 -38 -26 -37 -28 -31 -28 -32 -34 -42 -35 -39 -30 -34 -30 -37 -27 -33 -19 -42 -30 -38 -27 -35 -29 -33 -25 -31 -25 -30 -18
-50 -58 -52 -58 -51 -56
-50 -55 -49 -51 -63 -49 -47 -47 -47 -50 -47 -51 -45 -46 -45 -52 -44 -45 -44 -48 -46 -47 -45 -52 -44 -46
-43 -49 -44 -49 -42 -52 -43 -48 -43 -46 -41 -46 -42 -45 -40
-4B -39
c.
T ~ Q TIDO -56 -61 -63 -76 -54 -62 -6'2 -69 -53 -61 -61 -67 -53 -60 -58 -64 -52 -56 -57 -65 -52 -57 -54 -63 -51 -60 -57 -66 -50 -58 -51 -62 -50 -57 -55 -63 -50 -55 -54 -60 -50 -54 -48 -55 -49 -55 -54 -60 -48 -58 -51 -59 -48 -53 -51 -58 -48 -53 -49 -57 -47 -56 -57 -64 -47 -55 -51
-47 -52 -4i -51
-47
-55 -46
-51 -46 -49 -45 -49
-45 -47 -44 -48 -42
-59
-55 -60 -54 -55 -55 -62 -51 -55 -50 -54
-51 -55 -50
-54
-51 -54 -50
November 1949
, TABLE11.
lor IDENTIFICATION OF PLASTICIZERS
Plasticizer Source of Sample Composition Plasticizer XP-3 Advance Solvents & Chemical {Methyl Ceiidsolve Baker's P-4C Baker Castor Oil Co. Acetyl ricinoleate Barrett Division. Allied Chemi-
L
-
KEY 0-10 0-10PARTS DI(N-HEXYL)ADIPATE a-70 e-20
A-IO A-20
2
P 41 L I Corp. Columbia Chemical Division, Pittsburgh Plate Glass Co. Commeroial Solvents Corp. C. P. Hall Co.
i
Para Flux
C. P. Hall Co.
Plasticizer SC
Harwick Standard Chemical co. Monsanto Chemical Co.
Kapsol KP-140
Ohio-Apex, Inc. Ohio-Apex, Inc. Ohio-Apex, Inc. Charles Pfizer & Co. Charles Pfizer & Co.
Monoplex DBS
TP-SOB
Resinous Products Division, Rohm & Haas Co. Resinous Products Division, Rohm & Haas Co. Thiokol Corp.
Tz
-GO
Monoplex DOS
2537
INDUSTRIAL AND ENGINEERING CHEMISTRY
Trioctyl phosphate Tetrabutyldiglycol carbamate Tributyl phosphate Butyl Cellosolve pelargonate Saturated polymerized hydrocarbon Glycol ester of vegetable oil fatty acid Octyl diphenyl phosphate Methoxyethyl oleate Tributoxyethyl phosphate Dioctyl phthalate Tributyl aconitate Tributyl trioarballylate Dibutyl sebaoate
U
-I W
1) 1)
FLEXOL TOF *I
'1
2i
a IO
2
TIME 4 IN DAYS
Figure 2. Increase in Torsional Stiffness during Long Time Exposure at -57' C. for GR-S Containing Di(n-Hexy1)Adipate and Flexol TOF
Dioctyl sebacate
polybutadiene it was increased to 2.1 parts per 100 parts by weight of polymer. The physical test data shown in Table V indicate that the increased sulfur and acclerator had no significant effect upon the OF PARTICLE SIZE OF CARBONBLACKON torsion stiffening results a t low temperature. It was also found TABLE111. EFFECT FLEXIBILITY OF POLYBUTADIENE AT Low TEMPERATURES that when the four stocks described in Table V were exposed for Gum Stock Thermal 14 days a t -57" C. no increase in the relative modulus occurred. (No Carbon Black Black Black) P-33 EPC The permanent set under static compression a t low temperature was investigated using a method similar to that described Parts by wt. ' ... 60 60 Average particle size of carbon by Morris et al. (6). The compression set a t -57" C. was lower black (@),89. m./g. ... 23 80 Torsion stiffening C cured for both the polybutadiene and the butadiene-styrene (85/15) 40 Min. a t 13'5O C:' 7'6
Tla Tioo
- 67 70 --76
High molecular weight pol yether
-51 67 -70 74
-
-
-44
-GO 64 -74
-
stock. Tensile strength appeared to be increased slightly as black and plasticizer were increased. Although the increase to BO parts of black and 15 parts of plasticizer did not change the rebound significantly, the further increase to 75 parts black and 20 to 25 parts plasticizer lowered the rebound a t both room temperature and a t elevated temperature. Increasing black and plasticizer did not seem t o change the flex life. With 60 parts of black and 15 parts of Flexol TOF, the dynamic characteristics were very similar t o those of the control. With 75 parts of black and 20 to 25 parts of Flexol TOF, the dynamic resilience waq lower and the internal friction was somewhat greater. The stock containing the combination of 60 parts black and 15 parts Flexol TOF had a 4' C. lower freezing point ( T I Othan ~) the controls. It also had lower compression set a t -57" C. Further improvement in low temperature flexibility was caused by increasing black t o 75 parts and plasticizer to 20 to 25 parts. . The volatility a t 100O C. did not seem t o be increased significantly by increased black and plasticizer. Physical test data are tabulated in Table IV. INFLUENCE OF EXTENT OF VULCANIZATION
Polybutadime and butadiene-styrene (85/15) copolymer, both prepared by emulsion polymerization in a GR-S-type recipe a t the Goodyear pilot plant, were compounded in a conventionaltype tread recipe a t two levels of cure. The two Ievels wed included control stocks with the amount of sulfur and accelerator normally used for GR-S, as well as stocks with sulfur and accelerator increased approximately proportionally to the theoretical increase over GR-S in unsaturation. For the butadiene-styrene (85/15),the sulfur was increarled from 1.6 to 1.8 parts, and for
KEY -
0 - 2 0 PARTS MONOPLEX DBS XMONOPLEX DOS
v-
11
It
*I
"
KAPSOL
2ww I
10
4
TIME IN DAYS
Figure 3. Increase in Torsional Stiffness during Long ~i~~ E~~~~~~~at -570 C. for GR-S Containing various Plasticizers
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
2538
TABLE IV. HIGHBLACK-HIGH PLhRTIClZER Base StocL
TABLU V. ADJUSTEDS u w m AND ACCELERATORIN POLYBUTADIENE AND BUTADIENE-STYRENE (65/15)
GR-S
Pasts 100.00 3.00
GR-S
Zinc oside Stwric acid Sulfur
IN
VOl. 41, No. 11
Rase Btoak
1.BO Black and Plasticizers Added to Basic Recipe, Parts .__I______ 30.00 60.00 75.00 75.00 10.00 15.00 20.00 25.00 0.55 0.62 0.62 0.62 0.78 0.78 0.78 --0.64..
Parts 100. no 50 no R no 3.00 1.00
Polymer EI'C blank Para Flux Zinc oxide Stearic acid
1.00
___I___
E P C hlack Flexol TOF ~~clercaptobenzothiazoio Diphenylguanidine
I__
Propcrties Componnded Mooney viscosity 51 Tensile, lb./sq. in. Cure min. at 135' C. 30 2075 .in 1850
Elorigation, % Cure niin. at 135' C. 30 40 fi0
Modulus a t , 3 0 0 % elongation, Ih./sq. in. Cure min. a t 135' C. 30 40
183CI
47>
375 :I 3
.">
C.
T,
?'IO
Tiao comprepsion set at -57' C. 'aftei 168 hour- recovery, cured 45 niin. a t 138O C. Volatility, % wt. lous, cured 45 min. a t 1 3 5 O C.
2290 2100 2000
2520
2270 2420
47'3 pz0 J80
485 446 395
2590 2380
470 440
57
58.0
58.0
55.5
55.5
69 6
09.0
67.9
68.5
40 37
33 31
"
o/o
24.2 24.3
103 0 107.8
09.3 102.1
113.6 116.5
97.3 98.3
50.4 49.6
50.6 60.3
64.2 65.3
53.2
Ti00
s o t after 168-hr. coniDression a t -57' c.,
cured 40 min. a t 1350 c. After 0.5 hr. recovery Aftei 2 hr. recovery After 24 hr recovery After 168 lis. recovery
TABLEVI.
-25 - 44 -51 - 58
- 34
: ;:
-3
-62
-65 - 63
-53 -58 -64
84.5
80.0
71.6
66.9
0.93
0.83
0.96
1.08
-40
copolymer stocks at the higher state of vulcanization. Tho compression set of polybutadiene was very high a t -57" C., even with the improvement. caused by increased sulfur and accelerator. No explanation is given for the fact that polybutadiene of excellent low temperature flexibility should have recovery from static compression inferior to that of a butadiene styrene (85/15) copolymer of higher freezing point. Since the polybutadiene showed no evidence of stiffening during extended exposure a t -57" C., crystallization does not appear t,o be the explanation. TENSILE ANI) ELONGATION CHARACTERISTICS AT LOW TEMPERATURE
Data are given in Table VI showing the tensile and elongation of several stocks a t -41 O and -57 C. These data show the GR-S, butadieneetyrene (85/15), and polybutadicne to have greater tensile strength a t both -41 and -67" C. than a t room temperature. Although the tensile strength of polybutadiene at room temperature is much lower than that of GR-S, a t -41 ' C. it is almost as good as that of GR-8. There seemed to be some eorrelation between the freezing point and the per cent change between room temperature elongat,jon and the elongation at, low temperahure.
70
Y2 91
90 89
HS,%
IJOIY-
-39 - 60
B/S,
Normal 1.60 0.62 0.78
.-69
--30 53 - 5!j
91 87 84 81
90 81 82 75
-77
Stocka K o ~I Tested a t -57O 3800 500
+is
Stockb No. 2
?IS,
Adjuatwl 1.80 0.70 0.88 3::
I
-51
- 57
- 69
-70
STRESS-STRAIN CHARACTERlSTICS TEMPERATURE
Tenrile. lb./scl. in. Elongation, 70 Yo change from room tomp. elongation
-_ I I 72 (i3
57
AT
Stork KO. 36
Low Stock No. 4 d
C. 3150 335
3440 225
4840
-21
-41
- 100
0
c.
l'ensilc, Ib./sq. in. Elongation, % , % change from room t,emp. elongation
26.9 25~7
63.5
.-36
-58
- FE
I'lO
27 29
27.8 29.0
O
^
E..
29.4 31.9
- ?!
7'.
415
60
32 22
Sulfur Morraptohenzothiazole Diphenylenanidine Torsion stitfnesn values, C., wired 40 min. at 135' C. Ta
2250
53
50
TL
47
56
10 ___
7'01sion stiffening,
57
1200 1375 1435 75
k:PC black Flexol T O F
80
A2
1310 I510 1650 75 20
1510
40
_ I
1170 1275 1370 60 15
1080 1300
60
Haidness-Shore A , cured 40 min. a t 1 3 3 O C. Robouiid a t 27' C.. %, cured 5.5 inin. a t 135O C. Rebound a t 93' C., cured 55 inin. a t 135' C. Hot out-strip flex Iiie. min. Cure min. a t 135O C. 40 80 Dynamic resilience, % Cure rnin. a t 135O C. 40 80 Dynamic moduliis. kg./sq. cin. Cure min. a t 135O C, 40 80 Internal friction. kp. Cure min. a t 135" C.
I__
h i p
h t a d i e n c , butadiene. Normal Adjusted 1.60 2,10 0.62 0.88 0 78 1.04
Tested a t --.110 2485 3420 480 460
.-I- 6
-I-4
., . .. ~
2670 310
...
-29
Tested a t Room Teinperature Tensile, Ib./sq. in. 1420 1860 1930 2040 Elongation, % 42% 435 3 80 435 - 72 62 59 Freezing point, C. 82 a Polyhutadiene w i t h 6 part&of Floxol T O F i n tread-type recipe. Butadiene/styrene (85/15) with 6 parts of Floxol T O F in tread-typo recipe. 0 GR-S with 10 parts of di(n-hexyl) sdipate in tread-type recipe. d GR-6 with 6 parts of P a r s Flux in tread-typo recipe,
-
-
-
p
ACKNOW LEDGM ENT
The authors are grateful to The Goodyear Tire &. Rubber Company for permission to publish this work. The cooperation of S. Y.Gehman, P. J. Jones, W . D. Wolfe, J. D. D'Ianni, and other members of the Goodyear Research Laboratories in the preparation of experimental polymers and plasticizers and In the determination of physical properties is greatfully acknowledged. LlTERATURE CITED
Albertoni, G. J., IND.ENG.CEEM., ANAL. ED., 3, 236
(1931);
Rubber Chem. and Technol., 4,591 (1931).
Drogin, Isaac, "Developments and Status of Carbon Black," pp. 99, 104, West Virginia, United Carbon Co., Inc., 1945. Gehman, S. D., Woodford, D. E., and Starnbaugh, It. B., IND. EWC. CHEM.,33, 1032 (1941).
Gehman, S.D., Woodford, D. E., and Wilkinson, C. S., Ibid., 39, 1108 (1947).
Liska, J. W..Ibid., 36, 44 (1944) ; Rubber Chem. and Techml., 17, 421 (1944).
Morris, It. E., Hollister, J. W., and Mallard, P. A., India Rubber World, 112, 455 (1945); Rubber Chem. and Techml., 19, 151 (1946).
Sebrell, L. E.,and Dinsmoro, R. P., I n d i a Rubber World, 103, 37 (1941); Rubber Chem. and T'echnol., 16. 857 (1943).
United States Navy Department, Bureau of Ships, unpublislled report, Washington, D. C., Nov. 3, 1948. RECEIVEDNovember 16, 1848. Presented before the fall meeting of the Division of Rubber Chemistry of the A M ~ E R X CCHEMICAL AN SOCIETY,Dotroit, Mich., Novrmbpr 8 to 10, 1948. Contribution No. 164 from Tho Goodyear Tire & Rubber Company Research Laboratory.
