INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 194.4
INSTAWUTY IN D611LLAllON
From the foregoing the extent of polymerbation a t the elvated tempemturea of dietillation can be predicted with considerable certainty. However, a more hassrdous form of instability may be e n w u n t e d . An pointed out above, them is a tendency for peroxidea to accumulate 88 “bottoms”. Distillation in batch to low bottoms, for example, may mult in active oxygen wncentnrtions in the reaidue 80 high that further heating produces an
1
explosive aukmidation. Tbe danger involved in distilling peroxid i d butadiene to very low bottoms is emphasized by the followh g experiment: The psmxidized butadine pmdneed in the 50’ C. test was permitted to evaporate under rmm conditions. After sll of the liquid hydmcarbon had disappeared from the flask and only a residue remained, the vessel wea wvered lightly and heated on a eand bath 80 tbat the temperature rose a t the rate of 10’ to 12’ C. per minute. when 125’ C. was reached, violent d e wmposition took plsoe within the flask, the wver of the flask was diapheed, and lsge volumes of white fumes were evolved. Further heating to 250’ C. d t e d only in the charring of the trace of reaidual material. Experience indicates that the explosion h a r d may be eliminsted by distilling in the presence of an adequate amount of pemxide-de8tmying substance and p r e venting air from returning to the distillation vessel after the heat is removed. In the ca8e of batch distillation of butadiene-wntaining materialn of high pemxide content, it is desirable that$he pemxides be deatruyed by the antioxidant before distillation is sterted. Since most peroxides q u i r e appreoiable time for de composition by antioxidants, the elimination can be c o n d e n t l y efiected by baating under pressure until the abeence of pmmidea is indicated by chemical tent. In distillation the addition of a b y d m w t a n b o i i higher than butadiene is an added factor ot. aafety since auch a p d u r e limitsthe degree to which the wroxidea can be concentrated during a aingle distillation. SUMMARY
1
activated and does not appear to be catalyzed by perondes or by steel &-. 2. Butadiene is also ca &le ul independent polymerization to bigh-rnolee$ar-weigbt but in the absen? of peroxided this reachon is insimfioant w m ~ a r e dta dimeriaation. Tbe ef-
tioe
4. The addition of suibble antioxidant inhibits the lormation of high-moleoular-weight polymer but hss no appreoiable effect on the rate of dimer formation. 5. The rata of high-moleoular-we’ t polymerization is directly proporhonal to the square root o the concentrshon of pmoxides (active oxygen). 6. Butadiene is readily peroxidized by air, but thisperoxidation may be inhibited for a time by the preaance of anhoxidanta. 7. The peroxides are not readily volatile and tend to accumulate in the residne if the diene is evaporated or distilled away. Concentration beyond a certain point yields an unstable reaidue which may decarnpose with violeuce whan heated. Recautiona for distillation of such peroxidid material are given.
‘8”
The authors wish to thank t h e among their wllesguea, prticu-
larly M. W. .Swaney and I. 8. Rice, who aided with the experimental work and manuscript, also the Standard Oil Develop ment Company for permission to publish. UTERANRE aM
(1) Kiatiakowaky. 0. B.. and Rsluam, W. W..J . CMn. Phna., 7. 7!2%% (1939). (2) ~ebsdev,8. st. ol.. sints(. KWW, 1938. N ~ 1.. a. tal 8. 8. R.. 11. 751-86 . . M e d d e v . 8.. st d.. A& phu&&im. (1939).
v.,
v.
(4) h t t , D.A., New Bd. (Am.C h . &.), 18,404 (1040). (6) Youm C. A.. Vast, R. R., and Nisuvland. J. A.. h. EUQ. CHmU.,Ax-. ED.,8, 18&8 (1938).
I. The most pmr?ine?t IFexiaation of pure butadiene in the absence of pemadee M %enration. Thia reaction rn the>
*
NATURAL AND SYNTHETIC RUB6
*
..,LEONARD H. COHAN AND MARTINSTEINS@ 1 . 1
bntln.n(.l Grbon Company, Chlugo, 111. .’,
N THE last few years many applicstions have been found for Semiwnductiw r u b . In automobile and trolley bus tka,
I
a i r p l u n e ~ ~ t i ahoesolesformunitionworkers,etr., m,
where it is desirable to dlaeipate annoying and hasardous accumulations of Static eleCtrieity, emiwndncting rubber bas beeh found useful. Fhtmcally conducting rubber stocks can be prepared by inoorpomting powdered graphite or other carbon pigments in the rubber formula To obtain conductivity without black piwnenta eacri6cing other desirable physical pmpexties,~ prepared from e i t i m m t y l e n e or natural gaa have generally been
d. Recent investigations (4) in this labomtory have been directed toward diawverhg what fundamentalpropertiee of carbon blacks determine the electrical conductivity of rubber stocks. The rad t a ahow that in a typical tread stool, conductivity depends primarily on crystal structure, particle &e, and mufmstructure
Y
r
of the carbon black. Crystal structur more importmt properti&; &soe structure is leas wportmt. since crystal structure is pin& 8imilar for ciwn&bon blacks (S,6), the principal factor in deOrpdudvity in a wries of channel blacks is prticle aim. Reanlta included here show that this is true for natural rubber, reclaim, Buns 8, Thiokol N, Neoprene GN, and Butyl (GRI). mMEMODs
Reeietgnee measurements were made on cured Wile sheeta (approximahl 6 X 6 X 0.075 inch) laced between oircukr hms el& . ) 4 ( An !pparatua using the vol+etexammeter method o measmistgnCB w employed (Fyue 1). The u p g r electrode, E, ls connected through m e t e r A and battery to the lower electrode, C. Rubber test sheet T ia plaoed between the electrodes. To o b + p contgct +Ween the electrodes and test sheet, cimlea ahgh y l q e r m diameter than the upper electrode were painted on both sides of the .$at
(3
INDUSTRIAL A N D ENGINEERING CHEMISTRY
8
sheet with Aquadag colloidal graphite. The test sheet was subjected to a pressure of 36 pounds per square inch by a lever (not shown) attached to the upper electrode. Voltmeter V indicated the potential drop across the sample. Guard ring G was used to prevent leakage currents around the edge of the sample. Measurements were made a t about 15 volts d.c. for most StOCKS. Samples having specific resistances greater than 107 ohm-cm. were examined a t higher potentials; for stocks having resistances less than 3 X 102 ohm-om., lower potentials were employed t o prevent excessive heating. The Bashore resiliometer was used to measure rebound on three plies of tensile sheets. Abrasion tests were made with 8 du Pont abrader, using a Norton Crystolon wheel (No. 3746-15). All other rubber tests were made under standard conditions unless otherwise specified. Results of rubber tests in the tables or fi ures are given a t or near the indicated optimum cures except w%ere otherwise noted. PROPERTIES
OF
C A R B O N BLACKS
Table I gives the physical properties of the carbon blacks studied. Continental R-20, R-30, and R-40 are channel blacks developed particularly for preparing conducting rubber stocks. Continental A, D, and F are standard rubber-grade channel blacks; Continental AA and AAA are easy-processing-type channel blacks. Acetylene black is prepared by the decomposition of acetylene gas. The color index, obtained from a rub-up of carbon black in lithographic varnish, is essentially a measure of surface area. Particle diameters were estimated from electron microscope (IS) and adsorption measurements (11) on similar blacks.
TABLE I. PHYSICAL PROPERTIES OF CARBON BLACKS In Adsorption,
Estd. Av. %" Color Particle A B Index Diam.,mp 96 230 10 76 96 13 45 73 90 190 15 55 70 160 YO 90 23 50 50 80 25 45 50 75 85 49 26 85 70 Continental A 4.5 40 46 33 65 60 Continental AA 5.0 35 44 35 55 65 30 Continental AAA 4.5 43 34 60 Shawinigan aoetylene 0.9 11 OA = iodine adsorbed by 1 gram of black (to which 10 co..o! 10% HzSOa ha. been added) from 100 cc: of iodine solution in KT oqntaining 2.7 rams iodine and 4.05 grams KI per liter of solution. B = 01 iodine adsorbed ?as in A ) by a black from which the volatile content had t e e n removed in the volatile test (8). Black
Volatile Matter (S), DPG
%
(0,%
...
k
Iodine adsorption ( A ) is a rough measure of bare carbon surf a d (11); therefore, the devolatilized iodine adsorption ( B ) may be considered a rough measure of surface area of carbon black since particle size is not changed appreciably in the devolatiliza,'tion process. Per cent D P G is a measure of certain carbon-oxygen complexes on the surface of the black. It has been found that conductivity decreases with increased ,DPG adsorption for blacks of a given particle size (4). However, the effect of particle size is so much greater than any change in conductivity that can be ascribed to variation in DPG that the latter may be ignored in considering the conductivity of a series of blacks such as those listed in Table I. Figure 2 illustrates the variation of channel black properties with particle size.
Vol. 36, No. 1
Appreciable amounts of semiconducting rubber are required for those war applications where it i s desirable to dissipate static electricity, such as shoe soles and flooring in explosive plants, landing gear on planes, etc. The present shortage of acetylene black makes it necessary to use other types of carbon black for this purpose. In other cases it is desirable to have a low-conductivity or high-resistance stock. The conductivity of typical trerd type stocks of natural rubber, reclaim, Buna S, Neoprene GN, Thiokol N, and Butyl (GR-I) is reported. The conductivity depends primarily on the carbon black used in the tread stock. For all the rubbers, the resistance decreases sharply as the particle size of the channel black decreases.
with acetylene black. Resistivity, the inverse of conductivity, drops off rapidly as the particle size decreases. These results are in agreement with the hypothesis (7, 9 ) that Conductivity in rubber-carbon black stocks occurs through chains of carbon black particles, and that as the particle size decreases, conductivity increases as a result of the formation of a sufficiently greater number of chains per unit weight of carbon. The conductivity of channel black R-40 nearly approaches , that of acetylene black. Heat of combustion measurements (IO) and x-ray photographs (9, 6) show acetylene black to have a more graphitic structure than the channel blacks. Acetylene black, therefore, is not plotted according t o its particle diameter which is about 43 m p ( I S ); it is represented in the figures by S and its properties appear as single points next to the results for R-40 which approaches it most closely in conductivity. Figure 3 shows that, as particle size decreases, rate of cure decreases. Tensile strength is maximum for grade D with a particle diameter of 25 mp. Modulus is essentially constant except for blacks R-30 and R-40 which have somewhat lower values than the standard rubber-grade blacks. The decrease in tensile and modulus for the small-particle-size blacks is due possibly to poor dispersion. Poor dispersion would cause fine-particle-size blacks to behave like blacks of larger particle size. Rebound a t 25" C. increases with increasing particle size and is lower for all of the channel blacks than for acetylene black; rebound at 100' C. follows the same trend but is about 40 per cent higher on the average. Williams plasticity increases rapidly
N A T U R A L RUBBER T R E A D STOCKS
Tests were made in the following formula, cured at 280" F.: Smoked sheet Zinc oxide Pine tar Bteario acid
100 7.85 3.00 3.ao
Sulfur Meroaptobenzothiazole Carbon black
2.81 0.743 50.5 (25.8 v01./100 vol. rubDer)
I n Table I1 and Figure 3, resistivity and other physical properties of stocks prepared with channel blacks are compared
Figure 1,
Electrical Resistivity Apparatus
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1944
with decreasing particle size; the addition of softeners to the better-conducting channel black stocks to obtain plasticities comparable to acetylene black greatly reduces the conductivity of the stocks and further decreases the already low rebound. Abrasion loss on the du Pont abrader is approximately constant for all the blacks except R-40 which has a greater loss probably due to the poor dispersion.
-
CARBON BLACK R-40 61
R d O R-20 I
I
I
I
F I
A
AA AAA
D A 1 1
I
I
I
1250
I
I
i
I
VOLATILE I
I
9
I n actual service, rubber compounds often come in contact with tar, oils, or solvents which swell the rubber and affect the conductivity as well as other properties. An exaggerated case of such swelling action is obtained by immersing the stock in naphtha (Table 111); the effect is to increase the resistance markedly. The acetylene black stock is affected even more drastically than the channel black stocks. EXPERIMENTAL BLACK. An experimental channel carbon black, R-40E, was made up which has a conductivity essentially equal to that of acetylene black. I t s particle size is similar to R-40 (10 mp). The rate of cure is sufficiently rapid to make an increase in acceleration unnecessary. Behavior of R-40E, with and without extra stearic acid, is shown in Table 111. The additional stearic acid increased tensile strength, modulus, durometer hardness, and abrasion resistance of R-40E, as it did with R-40, but the rebound of R-40E was decreased. The increased dispersion increased the conductivity of the cxperimental black. R-40E has better tensile, modulus, and abrasion resistancethan R-40 but resistance to aging is not so good. Both tensile. and conductivity of R-40E deteriorate more on aging than in t h e case of R-40. ALL-RECLAIM TREAD STOCKS
I IODINE
(%) I Z5lL
Figure 2.
II
II
I5
20
1 25
ESTIMATED PARTICLE
I
I 30
DIAMETER
(mp)
35
Physical Properties of Channel Carbon Blacks
ShuLL-PARTIcLE-SIzE BLACKS. Blacks as fine in particle size as R-40are difficult to disperse and retard cure excessively. Increased dosage of stearic acid and accelerator tend to overcome these difficulties (Table 111). The above formula was varied as indicated. Increased dosage of stearic acid markedly increases tensile strength, modulus, durometer hardness, and abrasion resistance of stocks containing R-40 but does not have any particular effect
Whole tire reclaim was used. The manufacturer provided the following analysis of this material: Parts Rugber er 100
Per Cent 55.19 Rubber hydrocarbon 17.22 Carbon black 13.86 Ash 10.49 Acetone extract 0 16.6 volumes per 100 volumes rubber.
10% 31 25 10
The following test formula was cured a t 287' F.: Reclaim Zinc oxide Stearic acid Sulfur
175.0 4.0 2.0 3.25
Diphenyl uanidine Mercapto%ennothiaiole Carbon black
0.2 0.5 29.0 (14.6 vol./ 100 vol. rubber)
The total carbon black loading in the above stock is 60 parts per hundred rubber hydrocarbon by weight (30.2 by volume). The reclaim stocks have a much lower conductivity than similar rubber stocks; this can be attributed chiefly to the presence of oils and inert fillers. Moreover, the carbon black already present in reclaim is likely to be standard carbon black which does not have a particularly high conductivity.
OF NATURAL RUBBER STOCKS T A B L11. ~ PROPERTIYJS
Acetylene Black Cure for best tensile a t 280' F.,
min.
Modulus a t 4 0 0 7 Ib./sq. in. Tensile a t break,'ib./sq. in. Elongation a t break,, 70 Aged tensile, lb./sq. 1n.U % of original, tensile Aged elongation, % Durometer hardness Abrasion loss, cc./hp.-hr. Rebound a t 25' C % Rebound a t 100" 6.. % ' Williams plasticity, in. Resistivity, ohm-em. X 103 a
Oxygen bomb, 16 hours a t 80'
30 1925 3400 565 2700 80 515 63 164 54 71 0.162 0.22
R-40
R-30
K-20
90 1600 3700 650 2000 54 480 65 317 33
90 1950 4125 625 2400 58 490 65 165 38 50 0.206 1.0
90 2076 3950 625 2700 68 470 64
48
0.273 0.53
171
2;
0.180 1.6
Channel Blacks I? D 70 2150 4150 610 2800 67 510 63 186 40 56 0.170 200
65 2125 4200 615 2900 69 500 62
15s
40 57 0.172 600
A
65 2100 4100 630 2950 72 480 63 158 41 57 0.177 400
AA
AAA
60 2100 3800 570 3 140 83 480 63 159 43 59 0.168 6000
60 2125 3725 590 3200 86 530 60 148 44 60 0.152 10,000
C. and 50 lb./sq. in.
on the physical properties of acetylene black which was apparently well dispersed and had adequate stearic acid in the base formula. The resistivity of R-40 is not decreased by the increased dispersion. The inclusion of both extra stearic acid and accelerator with R-40 increases the rate of cure and tensile strength over that of the stock containing additional stearic acid only. Resistivity increases only slightly when the stocks are aged.
I n Figure 4,resistivity and other physical properties of the reclaim stocks are plotted against particle size of the blacks (Table IV). The standard rubber-grade channel blacks have particle diameters of 23 mp and more have resistivities greater than 10'0 ohm-em. which could not be measured with the apparatus employed. However, Figure 3 shows the logarithm of resistivity increases linearly as particle size increases for R-40, R-30, and
INDUSTRIAL AND ENGINEERING CHEMISTRY
10 CARBON )
R-30 R-20
BLACK F
Vol. 36, No. 1
CARBON BLACK D A
S
R-40
R-30 R-20
F
AA AAA 50 I
-
1
40
Y m 6 r
-g m
30
!? 3
z
20
_-
I5 20 ESTIMATED PARTICLE
25 DIAMETER
(mp)
30
35
15
20
ESTIMATED PARTICLE DlAMt
IR
IO 35
(mp)
CARBON BLACK
CARBON B L A C K
S R-40
2500
I
laop
1000
R-30 R-20 I
I
F
D A
I
I
I
AA AAA I 400
m r 0
I
I
I
6
0
u
+ -
m
0 MODULUS AT 200 %E
U
I) 100
RECLAIM
500
‘ IO
I5 20 ESTIMATED PARTICLE
25 DIAMETER
30
(mp)
A A AAA
0.25
REBOUND
44 P ASTICITY
ESTIMATED PARTICLE
Figure 3.
Properties of Natural Rubber Stocks
Figure 4.
DIAMETER
(mb)
Properties of Reclaim Rubber Stocks
35
0
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1944
11
R-20. I n this instance, acetyS'TOCKs CONTAINING SXALL-SIZE BL.4CKs TABLE 111. P R O P E R T I E S O F N A T U R l L RUBBER lene black has a conductivity Acetylene Acetylene --Channel Blacks between R-40 and R-30. Aging Black Blacka R-40 R-40a R-40anb R-40E R-40EQ decreases the resistivity of the Cure for best tensile a t 280' F., min. 30 30 90 90 65 45 45 reclaim stocks. The effect of 1950 2000 2400 1600 1975 1850 Modulus a t 4 0 0 % , lb./sq. in. 1925 4100 4450 4050 4325 3350 3700 Tensile a t break Ib./sq. in. 3400 aging here is larger and in a E l o n a t i o n a t b;eak % 565 575 650 630 660 610 595 1700 1850 Agecftensile, lb./sq.'in. 2700 2700 2000 2600 2600 different direction from that 54 63 58 42 43 To of original tensile 80 noted in rubber. 528; 480 475 460 400 390 Aged elongation, % 515 65 68 67 66 68 Durometer hardness 63 80 All of the channel black Abrasion loss, cc./hp.-hr. 164 184 317 234 211 27 1 224 34 35 34 30 25O C. Y o 54 54 Reboiind a t stocks required the same time Rebound a t 100' 6.. 7% 71 71 48 33 50 51 52 50 to reach maximum tensile Williams plasticity. in. 0,162 0,164 0.273 0.280 0.258 0.244 0.260 Resistivity, ohm-em. X 103 strength. Modulus and tensile 0.22 0.21 0.53 0.52 0.58 0.32 0.25 Original 0.24 0.21 0.54 0.50 0.68 0.57 0.48 Aged c are approximately constant for After naphtha immersiond 115,000 ... 3,300 1,940 1,390 , .. ... the large-particle-size blacks Increased steario acid from 3.30 t o 5.00 parts per 100 rubber. but decrease with decreasing b Increased accelerator from 0.743 t o 0.95 part per.100 rubber. c Oxygen b o m b , 16 li?ui-s a t 80' C. and 50 lb./sq. in. particle size for the finer blacks, d Immersed 72 hours in 70' BB. naphtha a t 25' C. possibly because of poor dispersion as in natural rubber. Aeed tensile increases with increasing particle size as does per cent of original tensile retained. the conductivity o f small-particle-sizc R-40 approaches that of Acetylene black has lower abrasion loss on the du Pont abrader acetylene black. Aging slightly increases the resistivity of the than the channel blacks of which AAA has the lowest and Buna S stocks, but all increases are within the limits of error R-40 the highest loss. of this test. Most Buna S stocks exhibit poorer conductivity than similar rubber stocks excrpt, for those rt'inforced with acctyB U N A S T R E A D STOCKS lene black and R-40. Tensile and modulus both go through maxima for channel The following formula (cured a t 307" F.) was used; the blacks of particle diameters between about 23 and 26 mp, The physical properties of the Buna S stocks are listed in Table 5' and faIling off of these properties for smaller-diameter blacks mag be Figure 5. caused by poor dispersion, and variations in compounding and Bun8 S (Buton S) 100 Sulfur 2 milling might change this behavior. Abrasion loss shows a Zinc oxide 5 Mercaptobenaothiamole 1.5 Pine tar 5 Carbon black 50 (26.0 vol./ slight minimum in Table V for grades D and F having particle Stearic acid 2 100 vol. Buna S) diamctcrs of 25 and 23 mH, respectively. I n Rima S stocks, acetylene black has a higher abrasion loss t,han most, of the channel The logarithm of the resistivity increases linearly with parblacks. ticle size for the range of channel blacks studied. As in rubber, 0
5
I
TABLE 117. llcetylene Black 30 1125 1350 260 1075 80 150 63 170
Cure for best tensile at 287' F.. min. 3lodulus at ZOO%, lb./sq. in. Tensile at break, lb./sq. in. Elongation at break %G Aged teysjle, lb./sp.'in. yo of original tensile Aged elongation % Durometer h a r d k s Abrasion loss (60-min. cure), co./hp.-hr. Rebound (60-min. cure), 7% 28 A t 25' C. 51 A t 100' C. 0.199 Williams plasticity, in. Resistivity, ohm-om. X 103 Original 680 Ageda 380 a Oxygen bomb, 16 liours a t 80' C. and 50 lb./sq. in.
PROPERTIES OF RECLAIM
RUBBER STOCKS Channel Blacks
,
F
185 66 219
R-20 45 1000 1600 335 1150 72 200 66 243
45 1050 1750 335 1250 71 190 66 253
D 45 1100 1750 305 1400 80 210 66 235
A 45 1100 1800 325 1450 80 215 66 245
AA 45 1100 1750 315 1350 77 200 65 248
AAA 45 1150 1750 310 1400 80 195 65 203
23 40 0.324
24 41 0.325
24 45 0.289
24 48 0.268
24 48 0.283
24 49 0.251
25 50 0.243
25 50 0.241
130 105
2100 1900
27,000 19,000
> 10'
>io7 ,..
> 107
>io7
R-40 45
875 1475 345 1000 68 190 66 293
R-30 45 1050 1600 325 1100 69
...
...
1 . .
>io7
...
OB BUNA S STOCKS TABLE V. PROPERTIES
Acetylene Black 45 1400 1900 550 11375 88 350 a8 205 38 52 0.211
Cure for best tensile a t 307' F., inin. hIodulus a t 4 0 0 7 lb./sq. in. Tensile a t break,'ib./sq. in. Elongation a t break, % Aged tensile, lb./sq. in.a % of original tensile Aged elongation, Yo Durometer hardness (at 30 aec.) Abrasion loss (150-min. cure), cc./hp.-hr. Rebound a t 25' C.. % Rebound a t 100' C., 41, Williams plasticity, in.. Resistivity, ohm-cm. X 10% 0.14 Original 0.17 Aged5 Air bomb, 16 hours a t 126' C. and 60 Ib./sa. in. -
,
Channel Blacks--R-40 90 1300 2800 590 2475 88 440 66 28 40 0,292
R-30 90 1450 2950 570 2500 85 400 65 195 29 43 0.266
R-20 90 1400 2900 600 2500 86 400 64 180 31 44 0.246
0.31 0.33
2.0 2.2
2.9 3.0
...
__-
A
F
D
65 1600 3100 600 2700 87 430 65 160 30 47 0.223
65 1660 3150 605 2800 89 410 65 150 31 47 0.218
0.204
0.200
1000
4400
1000
280,000 280.0 0 0
...
______
...
__
A.4
65 1400 3200 640 2900 91 490 66 190
66 1380 2900 595 2400 83 375 63 2113 33
32 48
...
49
~
...-.
AAA 65 1500 2630 600
2300 87 390 63 206 33 49 0,203 2'90,000
...
12
INDUSTRIAL AND ENGINEERING CHEMISTRY CARBON
CARBON BLACK ~~
R-40
S IO
R-30 R - 2 0
F
D A
A A AAA
8
S R-40
Vol. 36, No. 1 BLACK
F
R-30 R-20
D A
A A AAA
60
8
6
45
6
4
30
4
2
15
0
2
10
15 20 ESTIMATED PARTICLE CARBON
S
5000
R-40
R-30 R-20
25
BLACh F
D A
I
I
I
35
30
DIAMETER
(mp)
10
IS ESTIMATED
20 PARTICLE
25 DIAMETER
30
(my)
35
0
AA AAA l
700 m
6
z
-0
SP
X
-. 4000 Z
qm
~L
X
x TENSILE
v)
3000
>:600
A
x*-'
v) . . I
"2 0 z
ELONGATION
2
500 /i
Lh
BUNA S
2000
g
MODULUS AT 400 %E.
0
0 1000
' IO
15 ESTIMATED
20 PARTICLE
CARBON
25 DIAMETER
30
imp)
35
BLACK
CARBON BLACK
ESTIMATED PARTICLE
Figure
5.
Properties of Buns S Stocks
Figure 6.
DIAMETER
Properties of Thiokol
(mp)
N Stocks
..
PROPERTIES OF THIOKOL N STOCKS
TABLE VI. Cure for best tensile a t 287' F.. 111111. Modulus a t ZOO%, lb./sq. in. Tensile a t break, lb./s . i n Elongation a t break, ' Aged tensile, Ib./s,q. in.a % of original tensile Aged elongation, % Durometer hardness Abrasion loss (60-min. cure), c c . / h p . - h ~ . Rebound a t 25O C 7 Rebound a t 80' C:: Williams plasticity, in. Resistivity, ohm-om. X 103 Original Aged"
3
%
5
Acetylene Black 30 925 1200 320 1075 90 150 80 232 25 50 0.168 0.031 0.063
I
R-40 55 350 1050 500 900 85 320 64 720 17 36 0.181
R-30 55 600 1300 530 975 75 245 63 396 17 37 0.150
R-20 55 GOO 1250 520 975 78 220 63 369 18 37 0.152
0.21 0.24
1.51 1.00
2.39 3.24
60 72
133 169
4
BAA 45 800 1200 320 700 58 120
AA 45 800 1250 380 800 64 115 66 274 19 40 0.138
68 286 20 42 0.141
33.0 49.5
2400
...
4100
A
AAA 65 1900 2950 605 2410 82 510 63 213 36 56 0.099
45 700 1300 405 900 69 190 65 3 14 18 39 0.140
*..
PROP~RTIES OF NEOPRENE GN
Acetylene Black 40 1600 2200 590 1850 84 600 64 260 36 54 0.104
Cure for best tensile at 307' F., min. Modulus st 400%, Ib./sq. in Tensile a t break lb./sq. in. Elongation at b;eak, % Aged tensile, lb./sq. in.= yo of original, tensile Aged elongation, 3' % Durometer hardness Abrasion loss, cc./hp.-hr. Rebound at 25' C. % R?bpund at l q O p d.! % Williams plasticity, in. Resistivitv. ohm-om. X 103 Originai Aged0
0.320 0.280
Channel Blacks
R-40 65 2000 4100 675 3550 86 540 66 228 31 52 0.113 81 50
J?
D
90 2075 3875 650 3150 81 570 66 222 33 51 0.107
R-20 90 1975 3550 665 3100 87 540 65 226 33 52 0.099
65 1800 3478 670 2750 79 550 64 227 33 52 0,100
65 1900 3300 660 2640 80 530 64 220 34 53 0,100
66 2000 3175 605 2690 85 540 64 230 34 54 0.099
AA 65 1900 3100 640 2875 83 505 64 234 35 55 0,099
2000 630
28,000 6,000
47,000 12,000
130,000 50,000
20,000 6,000
250.000
R-30
108
108
...
Air bomb, 24 hours at 126' C. and 60 lb./sq. in.
TABLE VIII. PROPER TIE^ Cure for best tensile a t 307O F., min. Modulus a t 400%, lb./sq,. in. Tensile at break, lb./sq. in. Elongation at break % Durometer hardness',(at 30 see.) abrasion loss (180-min. cure), cc./hp.-hr. Rebound at 100; C.! % Williams plasticity, in. Resistivity, ohm-om. X 10% a
Channel Black F D 45 45 650 700 1300 1250 470 435 950 900 73 72 205 200 63 64 306 318 19 18 39 40 0.145 0.141
Air bomb, 16 hours at 126O C. and 60 lb./sq. in.
TABLE VII.
Q
13
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1944
Acetylene Black 30 1000 1630 600 50 98 32 0.142 0.14
----
R-40 1so 590 1400 655 43 584 24 0.174 0.39
OF
BUTYL(GR-I) STOCKS Channel Blacks-
R-30 90a 800 2475 670 50 293 25 0.183 0.74
R-20 90 1000 3100 715 50 234 27 0.177 0.82
F
D
A
60 840 3000 730 47 228 25 0.173 26
60 930 2750 705 48 218 30 0.170 72
60 970 2800 700 46 2 07 30 0.169 91
AA 60 1000 2580 670 45 191 34 0.159 1200
AAA 60
1030 2750 700 46 183 32 0,158 735
Maximum tensile occurred a t 60 min., b u t other factors indicate t h a t 90 min. more closely approximates the best tensile cure.
N E O P R E N E GN T R E A D STOCKS
THIOKOL N R E C A P STOCKS
The formula and mill procedure used was recommended by the Thiokol Corporation ( 1 2 ) ; cure was 287" F. Thiokol. Type X Zinc oxide Stearic acid
100 10.00 1.OO
Beneothiazyl disulfide Diphenylguanidine Carbon black
0.46 0.10 40.00 (30.9 vol./ 100 vol. Thiokol N )
As in rubber, reclaim, and Buna S, the logarithm of resistivity decreases linearly with decreasing particle size (Table VI, Figure 6). The conductivity of acetylene black is six times greater than that of R40 in Thiokol N. For channel black stocks, Thiokol N has a little better conductivity than rubber; acetylene black stock, however, shows appreciable improvement over the conductivity in rubber. The comparatively high conductivity of Thiokol N stocks is in part due to the volume loading of carbon black, 30.9 compared to about 26 for natural rubber and Buna 8. Little difference in cure rate as determined by time to reach maximum tensile strength was observed; however, this method of determining state of cure is not very satisfactory as Thiokol N has a n extremely flat cure time-tensile curve. As particle size decreases, elongation increases and both modulus and durometer decrease. Furthermore, aged tensile and elongation increase as particle size decreases. This behavior may indicate that the coarse blacks have faster cure rates than the fine blacks. Abrasion loss increases with decreasing particle size in Thiokol N and is greater for the channel blacks than for acetylene black.
The following formula was cured a t 307" F.: Neoprene Type G N Zinc oxide Light calcined magnesia RPA No. 3 Light process oil
100 5
4 2 1
Stearic acid Phenyl-0-na hthylamine Beneothiazyrdisulfide Carbon black
1 2 0.75 31
(21.5 v01./100 vol. Neoprene GN)
In Table VI1 and Figure 7 the resistivity is shown to vary with particle size in the same way as in the other rubbers tested. Acetylene black has a conductivity 250 times that of R-40. The resistivity of the Neoprene GN stock studied is quite high, which can be attributed in part to the low carbon black loading of 31 parts by weight or 21.5 parts by volume. Grade A stocks appear to have a lower resistivity than would be expected from particle size alone. This behavior also applies to most of the other rubbers tested (Tables 11, IV, V, and VI). Whether the estimated value for particle size is too high for Grade A black or whether its low resistivity is due to other factors is not certain. Tensile strength increases sharply with decreasing particle size; there is a difference of more than 1100 pounds per square inch between AAA and R-40 stocks. This variation in tensile is considerably greater than that observed for the other polymers studied. Modulus and elongation are essentially constant; how-
INDUSTRIAL AND ENGINEERING CHEMISTRY
14 S R-40
10
CARBON
R-30 R-20 I
I
BLACK F D A I I
A A AAA # I00
S R - 4 0 R-30 R-20 8
1
Vol. 36,-No. 1
CARBON B L A C K F
I
D A
AA AAA
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I
200
x e
80
E
60
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R-40 R-30 R-20
F
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1
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15 20 25 ESTIMATED PARTICLE DIAMETER
I
30
35
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tmp)
CARBON BLACK
AA AAA
S R-40
4000
F
R-30 R-20
D A
AA A A A
3000
2000 w
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w
5
b
A
2000 +
k
F
F
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IOOOl
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c
1000
I
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I 30
(mp)
0
"
1300 35
10
15 20 ESTIMATED PARTICLE
CARBON BLACK S
60
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MODULUS AT 400 % E
0
NEOPRENE GN
15 ESTIMATED
-
