2496
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
paring hydroxylamine. Yet it does include “Hydroxylamine, Organic,” in class 260, subclass 563, which was searched. However, the searcher did not desire to find patents on organic-substituted hydroxylamine processes since he ignored them. There is no search note to class 23, subclass 190, included with the definition of subclass 563 of class 260. It is recognized that there are instances where reference to the alphabetical index and use of the methodical procedure for outlining a field of search do not produce the desired results. Often but one or two patents of interest exist and may not merit mention in the index, subclass titles, or definitions. Under such circumstances, location of the sought subject matter may often be accomplished by searching where analogous subject matter having like fundamental characteristics may be found. For instance, the process limited to placing molten sealing compound between the sides and tops of storage battery cells has no well-defined place in the classification, but by analogy the search for this subject matter would be in class 18, “Plastics,” subclass 59, as a molding and uniting operation, rather than with the art in class 136, “Batteries,” subclass 175, “Assembling Processes.” If it becomes impossible to attain a proper field of search, assistance may be obtained by stating the search problem specifically in writing to the Commissioner of Patents, Washington 25, D. C. A field of search will be prepared for you, but the value of this service depends largely on the adequacy of the request. With the classes and subclasses designated, there will ordinarily
Vol. 43, No. 11
be included the number of original and cross-reference patents and the number of sheets on which the patent numbers are listed, 100 to a sheet. These lists are available a t a cost of 20 cents per 100 numbers or fraction thereof, and the patents listed may be inspected a t libraries which have patents bound in numerical order. The search may also be made in the public search room in the Commerce Building in Washington, where all U. S. patents are in classified as well as in numerical arrangement. LITERATURE CITED
(1) Bjorksten, Johan, Chem. Eng. News, 26, 1216 (1948). (2) Deller, A. W., “Patent Law for Chemical and Metallurgical Industries,” New York, Chemical Catalog Co., Inc., 1931. (3) Dickerson, Donald L., “Socony-Vacuum Patent Manual,” New York, Socony-Vacuum Oil Co., Inc., 1944. (4) Hoar, R. S., “Patent Tactics and Law,” 3rd ed., New York, The Ronald Press Co., 1950. (5) Litton, James B., presented before the Division of Chemical Literature, 117th Meeting, AMERICAN CHEMICAL SOCIETY, Houston, Tex. (6) Palmer, A. M., “University Patent Policies, Practices, and Procedures,” American Council on Education, January 1948. (7) Rosa, Manuel C., J . Patent Ofice Soc., 29, 241 (1947). (8) Thomas, Edward, “Chemical Inventions and Chemical Patents,” New York, Clark Boardman Co., Ltd., 1950. (9) U. S. Patent Office, “Classification of Patents,” 2nd rev., Washington 26, D. C., U. S. Govt. Printing Office, 1946. RECEIVED July 20, 1951.
The second p a r t of the symposium, “Evolution of a Patent,’’ was published in Chemical and Engineering News a s follows: October 22: “Dynamics of Patent Practice,” W. L. Cheesman, U. S. D e p a r t m e n t of Agriculture. “Chemical Patent Practice,” Pike H. Sullivan, S t a n d a r d Oil Co. (Indiana). October 29 : “Handling Chemical Patent Applications,” Earl P. Stevenson a n d F r a n k N. Houghton, A r t h u r D. Little, Inc. “The Corporate P a t e n t Department,’’ A r t h u r B. Bakalar, Shell Development Co.
Butadiene Polymers for Low Temperature Service J
ROSS E. MORRIS, JOSEPH W. HOLLISTER, AND FRANK L. SHEW Rubber Laboratory, Mare Island Naval Shipyard, Vallejo, Calif.
I
N T H E course of preparing naval vessel8 to maneuver in the Arctic, the problem has arisen of providing rubber gaskets which recover rapidly from compression a t temperatures as low as -35’ F. The task of developing a suitable gasket stock was assigned to this laboratory by the Bureau of Ships. Previous work (9,10) has shown that regular GR-S is generally satisfactory for this application because its vuIcanizates do not crystallize or undergo second-order transition a t -35” F. Furthermore, this rubber is low in cost and is readily available. During the past several years the Office of Rubber Reserve and, to a lesser extent, the Phillips Petroleum Co. have made experimental polybutadienes and butadiene-styrene copolymers for evaluation by Defense Department laboratories. These rubbers have differed in polymerization temperature and, in the case of the copolymers, in styrene content. Since regular GR-S, the prototype of these rubbers, has been found to be suitable for use in the manufacture of gaskets for service a t temperatures as low as -35” F., it is desirable to ascertain whether any of the experimental rubbers are better than GR-S for this purpose. Some information on the low temperature properties of polybutadienes and butadiene-styrene copolymers has been pub-
lished. Beu et al. ( 1 ) found by x-ray studies on unvuloanized rubbers that polybutadienes polymerized a t 86” F. and a t lower temperatures crystallized to some extent when stretched 300% a t 32’ F. and cooled to -22” F. Polybutadiene polymerized a t 104”F. did not crystallize. A 90/10 (charge ratio) butadienestyrene copolymer prepared a t 4’ F. and containing 6.8% bound styrene crystallized under these conditions, but an 80/20 co~~
~
The purpose of this investigation was t o d e t e r m i n e whether o r not butadiene-styrene copolymers with a different ratio of these constituents and/or a different polymerization t e m p e r a t u r e t h a n standard GR-S a r e better rubbers for the m a n u f a c t u r e of gaskets for low t e m p e r a t u r e service than s t a n d a r d GR-S. The butadiene-styrene copolymers tested totaled 34. T h e cold compression set test performed a t -35” F.wasused t o evaluate the suitability of these rubbers for gasket service. Six copolymers yielded vulcanizates having stable compressioh sets considerably lower t h a n the compression
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 1951
TABLE
ON EXPERIMENTAL I. TESTRESULTS
249'1
STOCK&
?$$% Pusey and Jon-
Rubber
Charge Ratio
B/W'
Polym.
,."T
Combined styrene,
vo
Moone Tensile Ultimate Elonation ML-P S t m h, Elongation, I%./& at I;.$. % Inch 212O F.
690
0.67
0.67
100.2 100.2 98.2 56.6
430 420 410 590 640
1.41 1.48 1.43 1.26 1.28
0.35 0.41 0.82 0.91 0.74
0.28 0.35 0.48 0.82 0.78
98.5 97.1 70.6 49.4 60.9
99.8 98.3 94.5 65.5 60.4
360 440 410
700 650
660
1.20 1.28 1.29
1.00 1.07 0.96
0.94 0.99 0.92
45.1 42.9 44.9
61.0 51.5 48.1
660 770 880 920
300 370 310 430
540 610 680 610
2.26 1.19 1.26 1.30
0.92 0.87 1.12 1.10
0.69 0.88 0.95 0.98
50.7 43.6 38.4 41.3
81.8 50.6 41.4 43.0
790 820 810
340
650 600 660
i:% 1.31
1.06 1.08 1.05
1.05 1.03 0.98
32.4 32.6 35.4
38.0 35.9 37.0
680
460 410 320 430 620 370 390 360
380 360 670 370 370
1.38 1.42 1.16 1.50 1.42 1.11 1.17 0.79 0.89 0.80 0.68 0.44 0.04
1.18 1.16 1.16 1.50 1.35 1.03 1.03 0.81
670
2.00 2.19 1.66 2.08 1.94 1.43 1.42 1.37 1.61 1.46 1.47 1.44 1.38
0.84 0.68 0.40 0.05
47.1 48.6 41.4 38.8 38.8 38.1 40.8 54.3 66.8 69.1 68.8 81.7 101.2
65.3 65.8 47.7 44.4 40.6 39.8 40.6 56.1 58.7 59.0 70.1 82.6 100.3
430 420
2.07 1.90
1.65 1.37
1.41 1.34
39.1 40.5
49.2 42.1
x-453 XP-145 X-454 XP-139 X-478
100/0 95/5 90/10 86/16 71/29
41 41 41 41 41
0
4.1 8.3 13.4 23.6
22 34 42 b4
38
900
810 1010 980 1400
480 460 580 430 670
80 P H 80 PJ 80 P K
90/10 85/16 80/20
68 68 68
10.0 12.2 15.2
52 37 39
870 990 990
100/0 90/10 86/15 80/20
86 86 86 86
8.0 14.0 16.0
0
34 35 48 88
80 PC 80 P D 80 PE
BO/ 10 86/15 Sol20
104 104 104
8.1 12.4 16.8
36
XP-148 XP-156
100/0 100/0 96/5 90/10 85/16 86/15 80/20 71/29 71/29 70/30
122 122 122 122 122 122 122 122 122 122 122 122 122
0 0 3.8 1f:A 12.0 15.6 23.5 22.9 22.8 27.4 32.9 43.0
27 24 67 41 26 43 39 43 62 31 33 33 38
770 860 880 740 1040 680 710 790 1110
145 145
0 8.7
27 37
690 620
XP-140 XP-138 80 PB 80 P A GR-8 QR-8 10 XP-61 XP-60
x
49 &If3 40 AC XP-171 XP-I76
" Butadiene-atyrene
66/sS
g$g
100/0 90/10
F.
100.6 100.2 96.4 62.4
90/10 72/28
290 270 430 380
x-4068P
at
-35'
0.27
E%:
720 610 970 800
85
F.
0.18 0.17
40 41 85 62
86
at
-35'
0.20 0.18 0.38
0 0 9.6 22.6
X$-170 X -173 80 P F 80 PG
... ... 600
F,,
Compression Set, % After After 5 hours 94 houra at at -35' F. -35' F.
1.21 0.97 1.21 1.02
14 14 14 14
XP-169 Philprene B XP-172 XP-137
At
82"
Indent., Mm. After After 5 hours 94 hours
660
770 660
aso 360
500
370 870 400 460
380 390
660
630 620 550 640 660 680
0.66
charge ratio into reaction vessel. on uncompounded rubber
b Mooney viscosity measured
polymer prepared at 4 ' F. and containing 16.0% bound styrene did not, Lucas el al. (7) showed by dilatometric measurements on unvulcanized rubbers that polybutadienes prepared at SO', 1 4 ' -4', and -27' F. crystallized unstretched at 14' F. Crystallization waa so rapid in specimens made at the lower temperatures that it was largely complete &thin 5 minutes after starting to cool the specimens to the test temperature. A 90/10 copolymer prepared a t 14' F. crystallized at -13' F., but a 70/30 copolymer prepared at the same temperature did not. Johnson and Bebb (6)found, by measuring the Young's modulus of vulcanized specimens, that polybutadienes prepared a t bO* F. and a t -40' F. crystallized rapidly below 0' F. D'hnni, Naples, and Field ( 8 ) observed that the torsional stiffness a t low temperaturea of vulcanizates obtained from polybutadiene and butadiene-styrene copolymers prepared a t 109' F. increased as the combined styrene inoreased. Crystallization was not indicated in this case. Juve and Marsh (6) compared a polybutadiene vulcanizate with aa 86/16 copolymer vulcrtnizate for cold compression set set of the standard GR-S vulcanizate. T h e polymerization temperatures of these copolymers ranged from 86" to 145" F. and their contents of combined styrene from 8.7 to 16.0%. The polymerization temperature of standard GR-S is 1Z2' F.and its combined styrene content is 23.5%. All six experimental copolymers, except possibly the copolymer prepared at 146' F., would be better than standard GR-S for manufacturing gaskets for low temperature mrvice. Thus, reduced styrene content is beneficial in a copolymer for this application, which is fortunate in view of the present short supply of styrene.
after conditioning 168 hours at -71" F. They found that the polybutadiene had a somewhat higher set after 30 minutes' recovery than the 85/15 copolymer, and that the set of the polybutadiene decreased less than the set of the copolymer when the recovery time was Bxtended to 7 days. Thie indicated that the polybutadiene crystallized to a greater extent than the copolymer. The polymerization temperatures of these rubbers were not stated. COMPOUNDING
The 34 rubbers investigated in the present work included regular GRS and GR-S 10 as well aa the experimental rubbers. All of these rubbere except Philprene B were made under the d i c t i o n of the Office of Rubber Reserve. Philprene B was made by the Phillips Petroleum Go. The polymerization temperatures ranged from 14" to 146' F. and styrene contents ranged from 0 to 43%. Each of the rubbers was compounded and cared as follows: Rubber. 100 6 Zinc oxide High elongation furnace blaok" 40 Tetramethylthiursm monasul5de 2 Di henylguanidine 0.4 supfur 0.7 Cures. 20 minutes at 310° F. for O.O&inoh thickness 26 minutes at 310" F. for 0.60-inch thickness
Sterling K.
This is not a practical recipe but wm intended to permit differentiation of the rubbers from the standpoints of hardness and oompreasion set at -35' F. without interference from carbon blaok structure or rate of cure of the rubber. The high elongation furnace black, Sterling K, has little structure as judged by its low oil adsorption factor (11). Strong acceleration and low sulfur content were used in an attempt to bring the rubbere t o approximately the same state of cure notwithstanding any inherent differencea in rate of cure.
2498
INDUSTRIAL A N D ENGINEERING CHEMISTRY TESTS PERFORMED
The properties of the wlcanizates which were of the most interest were hardness and rate of recovery from compression a t -35" F. Hardness W M measured with the Pusey and Jones Irtstometer described in ASTM Test Method D 531-49. of recovery from compression was determined by the cold cornpression set test (9, IO). The specimens for both tests were disks 0.50 inch thick and 1.129 inches in diameter. The readings on the Pusey and Jones plastometer were actually measurements of softness, and therefore were inversely related to hardness.
kte
IO0
90
d 9 o ul ")
80
I
t
10
2
8o
6 0
t3 50
40
_.
0
-
~~
IO
20
30 COMBINED
40 STYRENE,
0
IO
20
To
Figure 1. Relations between Cold Corn ression Set and Combined Styrene Content for Rubbers % d n g Different Polymerization Temperatures
The hardness of the vulcanizates was measured at 82" F. and also a t -35' F. after conditioning specimens for 5 hours and for 94 hours in methanol at this temperature. For the measurementa a t -35" F., the plastometer wrts mounted on a platform above the cold methanol bath, while the specimen bein tested rted on a table which was located a t least 1 inc% below $% : &e of the methanol. A 6/Finch length of Lucite rod waa installed between the indentor shaft and the indentor for the pur ses of lengthening the shaft and reducing the flow of heat to tE",indentor and thus into the specimen. The values obtained for hardness were in terms of millimeters indentation of the specimen by the '/-inch diameter hemispherical indentor acting under a load of 1 kg. The indentation measurements were made exactly 1 minute after applying the load to the indentor. The cold compression set test followed the procedure of the hot compression set test described in M T M Test Method D 395-49T (method B), except for time intervals and temperatures of conditionin and recovery. In the cold compression set test, specimens ofeach vulcanizate were comprewed a t room temperature between chromium-finished plates using spacer bars to restrict the deflection to 403. The clamped specmens were immersed in methanol at -35 F. within 5 minutes after compression. After 5 hours' conditioning, two specimens of each vulcanizate were released from the clamps without removal from the cold methanol. The specimens were allowed to recover for exactly 30 minutes and then rapidly measured for thickness with a dial micrometer ga e. The other two specimens of each vulcanizate were releasecf after 94 hours' conditioning and given the same treatment. The Mooney viscosity of the raw rubbers was measured at 212' F. in the viscometer after 4 minutes' running. The large rotor was used. The tensile properties of the vulcanizates at 82' F. were also determined. RESULTS
The results of all the tests appear in Table I. The rubbers are listed according to polymerization temperature and charge ratio. These data and the values for combined styrene were furnished by the suppliers. The cold compression set data are plotted in Figure I against these combined styrene values.
Vol. 43, No. 11
The tensile properties and hardness a t 82" F. of the vulcanieates were influenced by the temperature of polymerization, the Mooney viscosity, and the styrene content of the respective raw rubbers; but the relations between these properties of the vulcanizates and the characteristics of the raw rubbers were not well defined. When polymerization temperature was the only variable, low polymerization temperature correlated fairly well with high tensile strength and increased hardness, When Mooney viscosity or styrene content was the only variable, a high value of either of these characteristics also correlated fairly well with high tensile strength and increased hardness. The relations between compression set a t -35" F. and polymerization temperature and combined styrene were better defined. Figure 1 shows that smooth curves were obtained when the compression sets of rubbers having the same polymerization temperature were plotted against their contents of combined styrene. Sufficient point8 were obtained on some of these curves to show that compression set passed through a minimum as styrene content increased. Hardness at -35" F. was not as amenable to treatment in this way because this property was found to be affected by Mooney viscosity as well as by polymerization temperature and combined styrene. Inspection of the data in Table I and the curves in Figure 1 shows that the lowest compression sets which were fairly stable were obtained with the rubbers listed in Table 11. These rubbers contained from one half to two thirds as much combined styrene as regular GR-S. They had considerably lower compression sets than regular GR-S. Other rubbers also had low compression seta but the values were less stable-Le., they increased too much when the conditioning interval wai lengthened from 5 hours to 94 hours. This is shown in Figure 1 by the greater vertical d i e tance bet,ween the dashed curve and the solid curve for rubbers having the same polymerization temperature.
TABLE 11. VULCANIZATES OUTSTANDING FOR Low COMPRESSION SETAT -35' F.
Polym. Rubber
80 PF
80 PG 80 PD 80 PE XP-138 80 PB 80 PA XP-175
T$m& 86
86 104 104 122 122 122 145
Combined Styrene, % 14.0 16.0 12.4 15.8 11.0 12.0 15.6 8.7
Compression Set at -35O F. After After 94 hours. 5 hours,
%
%
38.4 41.3 32.6 35.4 38.8 38.1 40.8 40.5
41.4 43.0 35.9 37.0 40.6 39.8 40.5 42.1
Not all of the rubbers listed in Table I1 would be suitable for use in manufacturing gaskets. For example, the tensile strength of the XP-175 vulcanizate was so low that it might be impossible to develop a suitable gasket stock from this rubber. DISCUSSION
The rise of compression set with time of conditioning is attributed to crystallization ( I O ) . Crystallization of the rubber in a gasket is particularly undesirable since it causea partial or complete loss of sealing ability (9). Crystallization also hardens the rubber as evidenced by the indentation data in Table I. It will be noted that those rubbers which experienced a considerable rise in compression set when the conditioning time wan extended also showed an increase in hardness. The rubbers which underwent a rise in compression set between 5 hours' and 94 hours' conditioning, indicating crystallization, were polybutadienes and copolymers of low styrene content. However, not all of the polybutadienee and copolymera of low styrene content behaved in this manner even though they crystallized. Some of those prepared a t 14' and 41' F.-namely XP-169, Philprene B, XP-172, X-453, and XP-145-had very
INDUSTRIAL AND ENGINEER1NG.CHEMISTRY
November 1951
high Compression sets after 5 hours' conditioning, and the values were raised only a small amount, if a t all, by lengthening the aonditioning time to 94 hours. One of the polybutadienes, XP169, attained high compression set in shorter times than 5 houra and a t higher temperatures than -35" F., aa shown in Table 111. The very rapid crystallization of these rubbers is in agreement with the observations of Lucaa and coworkers (7) and Johnson and Bebb (6)on similar rubbers.
TABLE^ 111. EFFECTSOF TIMEAND TEMPERATURE ON COMPRESSION SET OF XP-169 VUI~CANIZATE Temperature of Methanol, F. 35 -35 -35 -35 20 0 0
Conditioning Interval, Hours 10 niin. 2 5
-
Compression Set, % 100.0 100.2 100.5 100 2 98.5 93.3 96.5
94 I 1
-
72
It was surprising to find that the compression set of polybutadienes and copolymers of low styrene content prepared a t 104', 122O, and 145' F. increased with lengthened conditioning time, indicating that thew rubbers crystallized to Rome extent. It has been generally assumed that rubbers polymerized a t these higher temperatures would not crystallize because of their nonuniform structure (8). Apparently the severe stresses induced by compression caused crystal nuclei to develop which would never have formed spontaneously. This was also the conclusion of Gehman and coworkers (3) after comparing the cold compression set test with the Gehman torsion test. The 5-hour and 94-hour curves for the 122" F. rubbers in Figure 1 pass through n minimum for compression set and then rise to slightly over 100% set when the combined styrene reaches 43%. None of the other curves pass through such a definite minimum for compression set, but they probably would do so if they were carried to higher values for combined styrene. All of the 5-hour curves lie below the corresponding 94-hour curves to the left of the respective inflections; those curves which inflwt tend t o coincide to the right of the inflections. The differences in level of the &hour and 94hour curves to the left of the inflections are due to crystallization. The remainder of this discussion deals with the behavior of the rubbers identified by points on the curves to the right of the inflections. Internal viscosity is responsible for the cold compression set of rubbers which do not crystallize. The effect of internal viscosity on set is practically independent of time; the set of a specimen rises to its final value soon after the compressed specimen reaches temperature equilibrium (10). Thus, the 5-hour cold Compression set values were equal to, or almost equal to, the 94-hour values in the cam of the 122' F. rubbers containing more than 16% combined styrene (we Figure 1). It has been shown that excessive internal viscosity is just as detrimental to the sealing ability of gaskets as crystallization ( 9 ) .
2499
Internal viscosity is a direct function of combined styrene if other characteristics are the eame. This explains the rise of compression set with combined styrene beyond the inflections of the curves in Figure 1. If it were not for crystallization, these curves would not inflect but would start at a low value of compression set a t 0% combined styrene and s l o p upward with increasing combined styrene. The GR-S 40 AC vulcanizate with 43.0% combined styrene had slightly more than 100% set after 5 hours' conditioning due to its high internal viscosity and thermal shrinkage. Such behavior suggested that this vulcanizate was near, or had passed through, its second-order transition. This inference was confirmed by performing a brittle point test with the American Cyanamid apparatus (4). Strip specimens broke when tested a t -35" F. after conditioning for 7 days a t this temperature. In contrast to the brittleness of the GR-S 40 AC vulcanizate at -35" F., specimens of the XP-169 vulcanizate did not break when tested under similar conditions although it also reached 100% set a t this temperature. Thus crystallization does not make a rubber brittle even though it results in 100% compression set. COMPARISON IN PRACTICAL STOCK
Vulcanizates prepared from the low-styrene copolymers listed in Table I1 have faster recovery from compiassion a t -35" F. than similar vulcanizates prepared from GR-S and GR-S 10. As previously pointed out, these vulcanizates were prepared using a special recipe which was not practical for most gasket applications. It was therefore of interest t o compare thew rubbers using a practical recipe. For this purpose a recipe R a h used which had been developed for manufacturing medium-soft gaskets from GR-S 10 to comply with a military specification ( I d ) . This recipe is given below. Rubber Zinc oxide Medium abrasion furnace blacko Fine furnace blackb Blended wax Tri-2-0th lhexyl phon hate Tetramet%ylthiuram $isulfidv Sulfur " Philblaok A. Stater B. Heliozone.
100 5 30 15 1 20 1 1
Vulcanized test specimens were prepared from GR-S 10 and from each of the copolymers, except XP-138 and XP-175, listed in Table 11. XP-138did not process satisfactorily and its vulcanizates prepared in preliminary work had poor tensile properties. Preliminary vulcanizates prepared from XP-175 also had low tensile properties. The respective curing times for the test specimens, either 0.08 or 0.5 inch thick, were those curing times a t 290" F. required to attain a hot compression Jet of approximately 30%. The compression set test followed ASTM Test Method D 395-49T (method B), using a conditioning interval of 46 hours at 194" F. The vulcanized specimens were tested for tensile properties a t 82' F., Pumy and Jones hardness a t 82 O and -35' F., and com-
TABLE IV. TESTRESULTSON MEDIUM-SOFT GASKETSTOCKS
Rubber 80 PF 80 PQ
Charge Ratio B/Sd 85/15 80/20
80 P D 80 P E
85/15 80/20
Polym. Comb. Ttmz., Styrene,
%
86 86
14.0 16.0
104 104
12.4 15.8
%$$$EPusey and Jones Indent., Mm.
Moone ML-4Y
Cure Tensile Uitimate ElonMinutes, Stren th Elonation at at Lb./$q.' gation, ?!b./Sd. 212" F . 290OF. Inch % Inch 52 23 1760 460 1000 41 27 1710 440 1020 26 20
1630 1660
440 430
950 990
1.55
1.61
1.24 1.22
1.30 1.22
25 4 23.7
26.9 24.1
31.7 33.5
85/15 122 12.0 46 29 28 80/20 122 15.6 43 26 71/29 122 22.9 54 Butadiene-styrene charge ratio into reaction vessel. Mooney visoosity measured on uncompounded rubber.
1560 1620 1560
420 420 410
970 1040 1030
1.67 1.68 1.56
1.35 1.35 1.07
1.33 1.38 1.05
24.5 25.8 31.1
25.7 26.9 31.7
31.0 30.4 28.4
80 P B 80 PA
GR-5 10
37 38
At 82' F. 1.51 1.54
Compression Set, % After After After After After 5 hours 94 hours 5 hours 94 hours 46 hours at at at at at -35'F. -35' F . -35'F. -35" F . 194' F. 1 24 1.18 24.5 25 9 29.3 1.22 1 30 25.3 26.0 27.4
2500
INDUSTRIAL A N D ENGINEERING CHEMISTRY
pression set a t -35" and 194" F. The results of the tests are given in Table IV. The data show that all of the low-styrene copolymers were at least equal to GR-S 10 in tensile properties and a few excelled GR-S 10 in tensile strength. The low-styrene copolymers had about the =me hardness a t 82" F. as GR-S 10, but they were softer a t -35" F. They had lower compression set a t -35" F. than GR-S 10. The 30 to 50% lower cold compdssion sets of these practical stocks, in comparison with the compression sets of the corresponding experimental stocks described earlier in this report, were due to the presence of the ester plasticizer in the practical stocks. I t thus appears that butadiene-styrene copolymers containing less combined styrene than regular GR-S or GR-S 10, and possibly prepared a t a lower polymerization temperature than these rubbers, are a better choice for use in manufacturing gaskets for low temperature service. ACKNOWLEDGMENT
Much of the testing in this investigation was done by John M. Holloway.
Vol. 43, No. 11
LITERATURE CITED
Beu, K. E., Reynolds, W. B., Fryling, C. F., and McMurry, H. L., J. Polymer Sci., 3,465 (1948);Rubber Chem. and Tech-
nol., 22,356 (1949). D'Ianni, J. D., Naples, F. J., and Field, J. E., IND.ENG.CHEM., 42,95 (1950). Gehman, S. D.,Jones, P. J., Wilkinson, C. S., and Woodford, D.E., Ibid., 42,475(1950). Graves, F.L., Rubber WorEd, 113,521 (1946). Johnson, P.H.,and Bebb, R. L., IND.ENQ.CHEM.,41, 1577 (1949). Juve, R. D., and Marsh, J. W., Ibid.,41,2535 (1949). Lucas. V. E..Johnson. P. H.. Wakefield. L. R.. and Johnson. B. L,, Ibid.', 41,1269 (1949): Meyer, A. W., Zbid., 41, 1570 (1949). Morris, R. E.,Hollister, J. W., and Barrett, A. E., Ibid., 42. 1581 (1950). Morris, R. E., Hollister, J. W., and Mallard, P. A., Rubber wmia, 112,455(1945). United Carbon Co., Charleston, W. Va., "Today's Furnace Blacks," 1947. U. S. Military Specification MIL-R-900-4 (March 23, 1950). RECEIVED March 2 , 1951. Presented before the Division of Rubber Chriuistry of the AUERICAN CHEMICAL SOCIETY, Washington, D. C., 1951.
Translucent Films of Acrylic Acid Esters-Acrylonitrile Copolymers J -
FRED LEONARD, IRVING CQRT, AND T. B. BLEVINS A r m y Prosthetics Research Laboratory, A r m y Medical Center, Washington, D . C.
Translucent elastomeric films in pastel shades, low pressure cast from polymeric emulsions, are required for the fabrication of skin-colored cosmetic gloves to be worn by amputees. In order to augment strength properties without unduly affecting translucency, investigationof the reinforcing effect of an isotropic silica was undertaken. Cast films containing the silica showed an enhancement in strength properties over uncompounded films, and films ' containing up to 40 parts of silica per 100 parts of dry COpolymer suffered only slight loss in translucency in the unstrained state. However, as the compounded films were strained they showed a marked increase in whiteness and opacity, as compared to uncompounded films. Possible explanations of this effect are given. Through this study it has been found possible to reinforce latex copolymers in emulsion form with an aqueous dispersed filler, which did not appear to increase the opacity of the cast film.
T
RANSLUCENT elastomeric films in pastel shades, cast a t low pressure from polymeric emulsions, are required for the fabrication of ski-colored cosmetic gloves to be worn by amputees. In the course of a study of the application of emulsion polymerized copolymers and tripolymers of ethyl acrylateacrylonitrile and ethyl acrylate-butyl acrylate-acrylonitrile for this purpose, it became necessary to investigate the possibility of increasing the tensile and tear strength of elastomeric films cast from emulsions of these polymers, through the use of reinforcing fillers that would impart neither color nor inordinately greater visual opacity. A survey of the refractive indexes of white and colorless inorganic compounds indicated that the refractive indexes of the
various silicas were of the same order of magnitude as the determined refractive index of an ethyl acrylate-acrylonitrile copolymer used in the investigation, and it was decided to test silicon dioxide as a reinforcing agent for these copolymers. Other workers have investigated silica of fine particle size as a reinforcingfiller in GR-S (6), natural rubber (I), and vinyl copolymers ( 4 ) . EXPERIMENTAL
MONOMER PURIFICATION. Ethyl acrylate and butyl acrylate (Rohm & Haas) were washed in a separatory funnel with a solution containing sodium hydroxide (5% w./v.) and sodium chlcride (20% w./v.), until the washings were colorlesa, and then with demineralized water, until the washings were neutral to litmus. Acrylonitrile (American Cyanamid) was fractionated through a 16-inch column packed with glass helices a t 10 to 1 reflux ratio (boiling point 77.3" C. a t 760 mm.). The monomers were stored at 0" C. until ready for use. POLYMER RECIPE Monomers Demineralized water Santomerse D Potassium persulfate C.P. Sodium thiosulfate pe'ntahydrate, C.P. Potassium chloride, C.P.
% 55 45
0.010 1.23
]
Based oonoentration on monomer
0.010 0.20-0.25
PREPARATION O F POLYMERS. To a three-necked flask immersed in an ice bath at 0" C. and fitted with a reflux condenser, stirrer, copper-constantan thermocouple in a stainless steel well, and nitrogen inlet tube was added a solution of Santomerse D (Monsanto Chemical Co.) in demineralized water containing the potassium chloride. After 5 minutes of stirring, oxygen-free nitrogen was bubbled through the solution, and continued throughout the course of the reaction. After 0.5 hour the mixed monomers in the desired concentrations were added. TWOhours later, the potaissum persulfate and sodium thiosulfate were introduced. The polymerization started after an induction period of 10 to 30 minutes (as determined by an approximately 0.5" temperature rise recorded on a 4-point Brown recorder). The reaction was allowed to proceed for 24 hours.
