2384
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 LITERATURE CITED
Albert, O.,2. phyaik. Chem., A182,421 (1938). Althouse, P. RI.,thesis, Pennsylvania State College, 1943. Ilthouse, P. M., Hunter, G . W., and Triebold, H. O., J . Am. Oil Chemists’ SOC.,24, 257-9 (1947). (4) Althouse, P. M., and Triebold, H. O., IND.RING.CREM.,AKAI,. ED.. 16. 605-6 (1944). . , ( 5 ) American ‘Society for Testing Materials, “Rook of A.S.T.M. Standards,” p. 983, Philadelphia, 1942. (6) Bried, E. H., Kidder, H. F., Murphy, C . M., and Zisman, W. n., IND. ENG.CHEW,39,484-91 (1947). ( 7 ) Gill, A. H., and Dexter, P D., Ibzd., 26,8810-2 (1934). \81 Gould, C., Holzman, G., and Niemann, C., Anal. Chem., 19, 204 6 (1947). 9) Hoback, J. H., Parsons, D. O., and Baitlett, J F., J. A m . Chem. Soc., 65, 1606 (1943). (10) Hunter, G. W., thesis, Pennsylvania State College, 1946. (11) Msttil, K. F., and Longeneckn, H. E , Oil & Soap, 21,16 (1944).
Vol. 40, No. 12
(12) Natelson, S., and Zuckerman, J. L., IND.EXG.CHEM.,ANAL. ED.,17, 739 (1945). (13) Norris, F. A., and Terry, D. E., Oil & Soup, 22, 41 (1945). (14) Rossini, F. D., Natl. Bur. Standards, A.P.I. Research Project 44, private communication, 1945. (15) Ruhoff, J. R., and Reid, E. E., J. Am. Chem. Soc., 55, 3827 (1933). (16) Schiessler, E. W.,Pennsylvania State College, private cornmunication. (17) Schneider, F., New York, John Wiley & Sons, 1946. (18) Stull, D. R., IND. ENG.CHEM., 39, 517 (1947). RECEIVED July 23, 1947. Presented before the Division of hgricultural and Food Chemistry a t the 112th Meeting of t h e AMERIcAh- CHEMICAL SOCIETY,New York, N. Y . Authorized for publication aa Paper 1381 in the Journal Series of the Pennsylvania Agricultural Experiment Station. Condensed from a thesis submitted b y Carl W.Bonhorst t o the faculty of the Graduate School of Pennsylvania State College in partial fulfillment of the requirements for the degree of mapter of science.
Low NONSTAINING SUPER10
OCESSING- TYPE
J. C. MADIGAN, L. H. HOWLAND, E. K. BURNS, AND C. V. BAWN I’nited S t a t e s Rubber Company, Naugatuck, Conn.
a
previous paper (1) described the development, manufacture, and use of GR-S-65, a low water absorption copolymer designed for wire and cable insulation. This material was shown to possess electrical properties superior to those of GR-S types in production a t t h a t time. Since then two new Copolymers have bean designed, developed, and produced. The first of these two materials is designated X-392 SP; it varies from standard GR-S in t h a t acid-glue coagulation is used to minimize water-solubles and improve electrical stability, and a new nonstaining, mondiscoloring stabilizer is substituted for the conventional antioxidant. The other is ralled X-393 SP; i t varies
from standard GR-S in the above two features, but i n addition contains a controlled amount of built-in gel which is obtained b y the use of a cross-linking agent. The copolymer possesses extremely good processing properties and is used in blends with rubber, GR-S, GR-$65, or X-392 SP to obtain the balance of processing and physical properties required for a given process and product. X-392 SI’ and X-393 SP were outgrowths of the development of GR-S-65 and GR-S-60 b u t they are usefulgwherever nonstaining, low water absorbing, or superior processing qualities are important. Evaluation data and description of the processes are given*
REVIOUS papers have described improved processing obtained by inducing gel into GR-S (6) and the improved electrical properties obtained by acid-glue coagulation ( 1 ) . Two bulletins distributed by the Office of Rubber Reserve describe GR-S-60 (5) and GR-S-65 (a), the polymers developed from the above two processes, in the order named. The purpose of the present work was to combine these two developments with a third-namely, the use of a nonstaining stabilizer-and to produce a polymer or group of polymers having improved processing and electrical properties, as well as no tendency to stain. These polymers were to be designed primarily, but not exclusively, for use in wire and cable insulation. The resulting copolymers were X-392, which is acid-glue coayulated and contains a nonstaining st.abilizer, and X-393, which, in addition to the X-392 variations, is cross linked with divinyl benzene to increase gel or benzene-insoluble content and thereby improve processing. The nonstaining stabilizer now used for these copolymers is a cresylic sulfide type. An intermediate step between GR-S-66 and GR-S-60 on the one hand and X-392 and 393 on the other consisted in the manuiacture of a pair of polymers containing a similar stabilizer.
However, compounds of these copolymers, 362 and 363, were found to be somewhat scorchy because of the activation imparted by the stabilizer. The modification used in X-392 and X-393 does n o t m u s e scorch. METHOD OF MANUFACTURE
I n general, X-392 and X-393 are made in the same fashion as standard GR-S. T h a t is, they are emulsion copolymers of 76 to 77 parts butadiene and 23 to 24 parts styrene on fatty acid soap, coagulated to yield dry polymer after 70 to 80% hydrocarbon conversion at about 121 ’ Fa The cross-link agent for X-393, divinyl benzene, is added with the initial charge and dissolved in the styrene; it enters the polymerization in such a manner as to cause branching and/or cross-connection among polymer chains. The cresylic sulfide stabilizer for both X-392 and X-393 is added to the latex, after removal of unreacted hydrocarbons, as the watcr-solublc sodium salt. Direct solution in the latex ensures a uniform distribution and intimate admixture of the stabilizer with the polymer on coagulation. Coagulation is accomplished in a continuous process, by pouring the stripped
December 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY WATERABSORPTION, RAWSTOCK
TABLEI. Immersion Time 20 hr. 7 days 14 days 21 days
I
n
2385
Absorption, Mg. per 8s. Cm. GR-S SP GR-S-65 SP X-362 X-363 X-392 4.45 0.94 1.11 1.01 0.93 11.9 2.97 1.33 3.66 2.53 4.83 ... 19.1 7.'06 7:86 8:38
X-393 0.92 2.72 6.81
..
..
70" C. The purpose of introducing the data of Table I1 is to show that the electrical properties of X-392 and X-393 are similar to those of X-362 and to relate these polymers t o the familiar GR-S-65, by,the use of Table I.
0
i
21
1 4
TABLE 11.
Imniersion Time, Days
Figure 1. Water Absorption
Days
X-362 5.6 7.3 11.1 12.5
1
and stabilized latex into a water solution of 0.25% sulfuric acid and 0.05% glue (no brine is use&). From this point on, the process differs considerably from that of the standard plant described in the paper on GR-S-65 (I). The next sequence of operations is: Dewatering (on Dorr separator) to about 50:50 water t o polymer ratio. Reslurrying with water t o abdut 5% solids slurry. Dewatering (on gyratory screen) to about 50:50 water to polymer ratio. Reduction of water to about 30% on the rubber (in Louisville squeezer). Straining through 16-mesh screen, which cleans and reduces to 10% wateror less; Drying t o specification moisture of 0.50%. Straining dry through 16-mesh screen. Sheeting out on 60-inch mill to approximately 0.25 inch. Packaging.
2 5 7
ABSORPTION, CURED STOCK
Absorption, Mg. per Sq. In. X-363 X-392 4.5 5.2 6.0 6.9 8.7 10.4 10 .o 13.0
x-393 4.9
6.5 10.0 11.7
ELECTRICAL TEST PERFORMANCE OF X-362
An outline of the compounding formula used in making these tests (as reported by American Steel and Wire Company, Worcester, Mass.) is as follows:
xaa GR-s
45.00 45.00 4-00 1.40 1.50 0.20 0.40 1.50 1 .oo
Organic 611er Zinc oxide Black
wax
F a t t y acid Antioxidant Accelerator Sulfur
1Oq.0,l I.WO
Specific gravity
The main purposes of this exhaustive treatment are to provide maximum cleanliness, minimum residual water-soluble content, and an initial breakdown.
TABLE 111. POWER FACTOR, X-362
WATER ABSORPTION TESTS
Days
That it is reasonable to assume close similarity in the electrical properties of X-392, X-393, X-362, X-363, and GR-S-65 is indicated by the data plotted in Figure 1 and shown in Table I. The water absorption of the raw stock in mg. per sq. cm. is given as a function of immersion time in distilled water a t 70 O C. In this test a specially prepared sheet of rubber is weighed before and after immersion to determine the absorption value. The detailed procedure is given in ( 4 ) . The data obtained in this laboratory show that the water absorption of all these polymers is essentially the same, and much better than standard salt-acid coagulated GR-S. I n a new method for testing water absorption the polymers were mixed with curatives and vulcanized before testing to eliminate the difficulties involved in testing the raw polymer. The test formula is as follows:
8 17 23 29
Polymer Zinc oxide Sulfur Tetramethylthiiiram monosulfide
WATER
Immersion Time,
1
ir,
Power Factor a t o o m Temperature inch 6/04 inch 0.642 0.770 0.745 0.816 0.743 0.743
8/84
... ...
... ...
yo Power Faotor 70' C.
inch 0.635 0.814
,/a4
0.840 0.854 0.882
PERCENT POWER FACTOR
Grams 500 25 12.5 1.25
These were mixed on a 6 X 12 inch mill and cured for 25 minutes a t 292" F. Mold cavities were 5 X 8 X 0.075 inch and test specimens were die cut t o 1 X 5 inches. Table I1 gives the results of the water absorption test in mg. per square inch a t
at
inch 0.649 0.801 0.856 0.844 0.902
6/84
Test Duration, Days
Figure 2. Power Factor X-362 Amerioan Steel t Wire Company, Worcester, Mass.
INDUSTRIAL AND ENGINEERING CHEMISTRY
2386 SPECIFIC INDUCTIVE CAPACITY
Vol. 40, No. 12
INDUCTIVE CAPACITY, X-362 TABLE IV. SPECIFIC
33
Days
A t Room Temperature inch S / i i inch
3/64
3/84
At 70° C. -. inch h / w inch
3.2
3.I
Test Duration, Days
Figure 3. Specific Inductive CapaciLg X-362 Arnericnn Steel
$r
Wire Company, Worcester, RIass.
Determillations wele made accoi ding to A\.S.T.M.D 470-461' with both 3/B4-in~h and 5/ca-inch insulation on KO. 14 ATVG coated solid copper (outside diameter, = 0.158 inch and 0.220 Inch, respectively) Figuie 2 and Table 111 give the power factor as a function of Immersion time a t two different temperatures. Figure 3 and Table IV give the specific inductive capacity over the same period. Capacihy increases with time are shown in Table V, and finally insulation lesistance, breakdown, and mrchanical water absorption in Table VI. These values are comparable to those obtained with other low water absorption types of GR-S, such as GR-S-65.
primarily a processing aid. Employing both GR-S and natural rubber compounds of various types, users have reported that with a 50L1, substitution of GR-S-60, a improvement in shrinkage and an equivalent reduction of swell at extrusion dies was obtained. For better results in using X-3Y3 or GR-8-60 with natural rubber, the GR-Sand the rubber should be compounded separately and the cures balanced before mixing the st,ocks. Wit.h the cross-linked copolymers, a reduction of sulfur of tlie ordw of 25% is recommended. Since t,he cross linkage results in a reduced solubility, plasticizers similar to those used with oilresisting synthetics probably would be more effective. One of the indirect advantages to be gained from the use of X-393 a3 a processing aid is that fillcrs which are sometimes used to improve processing may be reduced or omitted, with a resulting improvement in physical properties. Excellent retention of
GARVEYDIE VALWmb, o . ~ ~ o - I X C IDIE I 75 smoked sheet, 28 oarts X-393 GR-9-60 SP TubiGg rate, g./rnin. 109.5 100.5 Tubed thickness,
PROCESSING ADVANTAGES
in.
l'lie prooessiiig advantages that are obtained when 10 to 507;
of GR-S-60 SI' is used in blends with either natural or synthetic rubber have been described in (3,5 ) and are well known to the rubber trade. The advantages consist of reduction of calender shrinlrage and swell a t extrusion die and increased smoothness of extruded, calendered, or molded goods. A relut,ion b e h e e n X-393 and GR-S SP, established as an Iridicalioii of t.he performance of the new polymer, is provided in Figure 4. The processing improvement imparted to a smoked sheet, noiil)laclr compound by the utle of 25 parts X-393 is compared t,o t,he same effect with 25 parts GR-6-60 SP. The formula used i i i I)reparing this compound was as follows: Slasterbatch Pinoked sheet Tetramethslthiuram monosulfid? Total Sinolwii slieet 1\Iant,elbat,ah
X-393 or '211-S-60 Ziric oxide Clay
SP
W l i i Ling Medium process oil Stkarir acid Mercaptobenzothiozole Sulfur
0.260
0.263
CALENDEH PRoCEsrilNQ
Rugosity of calendered sheet 0.095 Shrinkage of calendered sheet 11.0
0.130 10.0
Press Cured Nonblack Stock
Figure 4.
Processing Comparison of X-393 and GR-5-60 SP
90.0
_1_0 . 0
100 0
74.1 1.0 28.0
5.0 75.0
40.0 18.0
2.5 1.0 1.6
Froin k'igure 4 it is apparent that X-393 is the full equivalent of GR-S-60 SP with regard to processing advantages. The information relating t o the use of GR-S-60 SP given in the Rubber Reserve bulletill (3) applies also to X-393. Keither of these materials is designed for use as 10070 of the elastomer, but is
No
Stabilizer
Figure 5.
Cresylic Sulfide Stabilizer
Standard Stabilizer
Staining
Plasticized nitrocellulose lacquer. 15-day window exposure; compounds of GR-S
nhite
.
December 1948
TABLE V. Period, Days 1-8 8-15 1-29
INDUSTRIAL AND ENGINEERING CHEMISTRY
CAPACITY INCREASE, X-362 yo Increase yo Increase
at Room Temperature 8/64 inch 6/84 inch
0.18 0.18
TABLE VI.
..
a t 70° C . 8/04 inch 6/04 inch 3.93 3.68
0.68 0.46
10:40
5:26
OTHERELECTRICAL TESTS,X-362
Test Insulation resistance (megohms per 1000 feet a t 60° F.) K Immediate breakdown (volts) Breakdown average, (volts per,mil) ”Mechanical moisture absorption (mg. per sq. inch) I n water 7 days a t 70’ C. I
TABLE VII.
8/64
Inch
6/04
Inch
30,000 76,200 38,700-40,000 825-855
62,000 115,000 45,000-46,000 576-590
19.0
18.9
tensile and elongation are characteristic of compounds containing t,he cross-linked copolymers.
2387
COMPARISON OF FOUR COPOLYNERS IN TIRETREAD
RECIPE
(Representative control test resultsa, Xaugatuck Plant f GR-S-65 X-392 GR-S-60 X-393 Test SP SP SP SP Volatile matter, yo 0.16 0.22 0.37 0.30 0.21 0.20 Ash total % 0.16 0.07 Ash’ watek-ooluble, % 0.06 0.07 0.06 ETA extract, % 6.70 6.10 ?:58 6.90 5.01 5.12 5.13 F a t t y acid, % 5.64 nil 0.01 0.04 nil Soap, % 1.33 Stabilizer, % 1..18 1.70 1.29 Bound styrene, % 23.1 24.8 24.2 23.1 Raw viscosit Mooney 48.7 49.0 61.8 85.7 CompoundeBhscosity, Mooney 62.3 134.4 66.5 125.0 Williams plasticity a t 10 min., 4.25 mm. 4.20 6.13 5.90 Williams recovery, at 10 min., 5.95 6.00 mm. 7.50 7.20 Water Absorption, mg. per s q . om. at 20 hrs., 70° C . 1.84 0.71 1.1 1.00 Tensile & t 50 min. cure, lb. per sq. in. 2895 2790 2072 2170 Elongation at 50 min. cure! % 701 690 424 370 300% modulus, lb. per sq. in. 2.5 min. cure 379 400 746 720 1319 60 min. cure 1230 885 880 90 min. cure 1710 1276 1310 1701 Averages of recent months’ production; ipecifioation recipes.
STABILIZER
The stabilizer contained in X-392 and X-393 is a cresylic sulfide type. I n tests a t 212 O F. it protected GR-S against resinification longer than some of the present standard stabilizers of the amine type. Representative data give a time to resinification of 96 hours with the standard stabilizer and 144 hours with the cresylic sulfide stabilizer. The absence of staining in compounds using GR-S containing the cresylic sulfide type stabilizer as compared to those using a standard stabilizer is shown in Figure 5 , a photograph of three strips exposed in a window test for 15 days. The sample containing the cresylic sulfide type stabilizer is about the same as that containing no stabilizer, whereas the standard stabilizer sample shows a definite stain. The upper portion of each sample is untreated; the lower has been dipped in a special plasticized nitrocellulose lacquer, comparable with that frequently used on wire insulation. Close examination of the blank shows that lacquer tends to discolor slightly itself, probably because of the plasticizer it contains. However, the cresylic sulfide type stabilizer has imparted no further stain, whereas the standard stabilizer has. The compounding formula used in preparing’ these samples was as follows: Polymer Coumarone indene resin Sulfur Zinc oxide Titanium dioxide Light-colored hard clay Extra-light magnesium oxide Wax Mercaptobenzothiazole Tetramethylthiuram monosulfide
100
7.5 4.0 40 50 60
5 2 1.5 -0.25
This compound is press cured 60 minutes at 292 F. O
APPLICATIONS
Although these copolymers, X-392 and X-393, were outgrowths of the development of GR-S-65 and GR-S-60 (both used in wire manufacture) their usefulness is considerably wider
than that. Wherever nonstaining, low water absorbing, and/or superior processing qualities are important, they can be used beneficially. For example, their applications have included fabric coating, molded mechanical goods, and natural rubber footwear compounds. Table VI1 gives the average control test results of X-392, X-393, GR-S-65, and GR-S-60 in the WPB tread recipe. It has been found possible to combine into one pair of polymers the three major developments of glue-acid coagulation for low water absorption, cross linkage for improved processing, and a special stabilizer for elimination of staining. These polymers, X-392 and X-393, are being made for wire and cable insulation and other uses. ACKNOW LEDGhlENT
This investigation was carried out under the sponsorship of the Office of Rubber Reserve, Reconstruction Finance Corporation, in connection with the government’s synthetic rubber program. The authors wish to thank that agency for permission t o release this publication and the following persons who assisted in the development program and preparation of the paper: F. L. Holbrook, I. E. Cutting, and A. L. Rodde. LITERATURE CITED
(1) Madigan, J. C., Borg, E. L., Provost, R. L., Mueller, W. J., an6 Glasgow, G. U., IND. ENG.CHEM.,40,307 (1948). (2) Officeof Rubber Reserve, Reconstruction Finance Corp., Wash., D. C., Bull. GR-S-65 (January 1947). (3) Ibid., GR-S-60 (June 1947). (4) Ibid., “Specifications for Government Synthetic Rubbers,” sea. D-3, p. 31 (Jan. 1, 1947). (5) Schoene, D. L., Green, A. J., Burns, E. R., and Vila, G. R., IND. ENG.CHEM.,38, 1246-9 (1946). RECEIVED September 23, 1947. Presented before the Division of Rubber CHEMICAL SOCIETY, New Chemistry at the 112th Meeting of the AMERICAN York. N. Y.
