INDUSTRIAL AND ENGINEERING CHEMISTRY
1380
of the mixture was heated and agitated for several hours prior to feeding into the pump. The introduction of a gear-type oil pump to agitate the coal-oil paste by recirculation and to feed the paste under positive pressure to the Hills-McCanna pump made the paste-pumping operation much smoother and eliminated the frequent loss of “prime” of the paste pump. It was found, however, that the gear-type oil pump would occasionally cause a “gelling” of the paste. This can be avoided by lowering the temperature of the paste and reducing the speed of the oil pump. Recently several hundred pounds of paste were made from Bruceton coal and centrifuged heavy oil from the earlier coal hydrogenation runs. With this paste there was little tendency for coal to settle out. It pumped readily and hydrogenated without difficulty. HEAVY-OILDISCHARGE.The erosion of ordinary highpressure valves is very rapid in discharging the heavy oil plus solid residue of the first hydrogenation stage. A long coil of narrow-bore copper tubing A , Figure 7, has been found to be a satisfactory discharge apparatus. LIGHT-OILDISCHARGE.Clogging of the light-oil discharge line by solid ammonium carbonate caused interruption of a recent run. This was avoided by steam-jacketing the discharge line and, when necessary, continuously injecting a small amount of water just ahead of the discharge valve. HYDROGEN RECIRCULATION. Injection of hydrogen along with the coal-oil paste is the only means of mechanical agitation that is readily available. It has been found that the
VOL. 29, NO. 12
amount of cold hydrogen that can be recirculated is limited to about 200-300 cubic feet per hour (measured a t atmospheric pressure and temperature). Larger amounts of cold hydrogen remove an excessive amount of heat from the converter and vaporize too much of the pasting fluid. The introduction of a heat exchanger inside the top section of the converter so that the light-oil vapors and hydrogen off-gas will preheat the incoming hydrogen will probably solve this problem. Such a heat exchanger fabricated of aluminum/tubing is now being tested.
Acknowledgment The writers wish to thank C. H. Fisher and Abner Eisner of .this laboratory for the distillation of the products and determination of tar bases, phenol, carboxylic acids, neutral oil, etc. They also wish to thank T. E. Warren of the Canadian Bureau of Mines, Fuel Testing Laboratory, and F. S. Sinnatt, Director of Fuel Research, Department of Scientific and Industrial Research, Great Britain, for the advice and help given in the design and operation of the experimental coal hydrogenation plant.
Literature Cited (1) Storoh, H. H., and Pinkel, I. I., IND. ENQ.CHEM., 2 9 , 7 1 5 (1937). (2) Warren, T. E., and Gilmore, R. E., Ibid., 29, 353 (1937).
RECEIVED July 22, 1937.
Resistance of Neoprene HOWARD W. STARKWEATHER AND HERBERT W. WALKER E. I. du Pont de Nemours and Company, Inc., Wilmington. Del.
UPERIOR water resistance of well-cured neoprene, like that of natural rubber, depends upon the absence of water-soluble ingredients and agents that are capable of absorbing water. It has been shown (1, 9, 8,6) that the water resistance of neoprene varies greatly with different activating agents. This paper includes a more detailed study of the water absorption of neoprene-magnesia-zinc oxide compounds and describes certain loaded stocks with improved water resistance. The water absorption was determined by the method already outlined (6),using slabs 0.20 cm. thick.
S
Calculation of Water Absorption The water absorption can be calculated from the increase in weight or from the increase in volume of a stock during immersion in water. A difference between these values is an indication of chemically combined water. This is based upon the assumption that water undergoes no significant change in volume during absorption but that there is a change in volume during a chemical reaction. The two methods of calculating the absorption of water are shown by the equations: a= a-b (c
x 100 = % vol. increase by weight method, W - d ) - (a - b) x 100 = % vol. increase by vol. method, V a - b
where a
= original weight in air, grams b = original weight in water, grams c = weight in air after immersion in
d
=
water, grams weight in water after immersion in water, grams
If there is no change in volume of the water, 6 = d and both methods give the same result. If, however, there is a decrease in volume, d > b and the calculated results by the weight method will be greater than those obtained by the volume method. The weight method gives, within the limits. of the experimental error, the volume of water absorbed per 100 volumes of sample, and the volume method gives the percentage increase in volume of the sample.
Magnesia Stocks There is a contraction in total volume during absorption of water by stocks containing magnesia. This contraction varies with the amount of magnesia used but is independent of the zinc oxide content. It is apparently due to hydration of magnesia. The amount of magnesia hydrated can be calculated from the change in weight in water of a specimen after immersion. in water as follows: MgO Hz0 MgO Ha0 MdOHh
+
Gram Mol. Vol., M1. 3.20 12.60 18.02 18.02 1.00 30.62 5i:34 2:36 24.72 Contraction per gram mole 6.90
Mol. Wt. 40.32
SI).Gr.
-
40.32
Wt. MgO hydrated = (d - b) X 6.90 Parts MgO hydrated per 100 parts neoprene ( M ) = stock formula wt. with 100 neoprene 40.32 (d
- b) x 5.90 X
a
DECEMBER, 1937
The results obtained with f o u r d i f f e r e n t stocks a r e shown i n Table I. Most of the hydration occurs during the first 24 hours; it i n c r e a s e s only slightly as the immersion is continued for 420 hours, even though the water a b s o r p t i o n continues to increase substantially as shown by the values in the W and V columns of Table I. The average amount of m a g n e s i a h y d r a t e d i s 68 per c e n t of t h e t o t a l a m o u n t which w a s supposedly added. The magnesia actually used had been on hand f o r s o m e t i m e . It analyzed as follows:
Y y1
P
1381
INDUSTRIAL AND ENGINEERING CHEMISTRY
Since the determinations of both the degree of hydration and the composition of the m a g n e s i a involve indirect c a l c u l a t i o n s , these results are in as good a g r e e m e n t a s might b e e x p e c t e d . Leaching c a n n o t a c c o u n t for the difference, since water in which s a m p l e s h a d been exposed a t 100' C. contained only traces of m a g n e s i u m a n d zinc. Sim i 1a r determinations with three stocks which did not contain magnesia, as given in Table 11,did not show this change in weight in water even after an appreciable amount of w a t e r h a d been absorbed. T h e h y d r a t i o n of magnesia can account for only a small part of the water a b s o r p tion, and t h e r e s u l t with sample 7 shows t h a t t h e replacement of magnesia by magnesium hydroxide does not improve the water resistance. S i n c e i t seemed possible that some of this high abs o r p t i o n m i g h t be
The contraction in total volume during absorption of water by neoprene compounds containing magnesia is attributed to hydration of the magnesia. Neoprene compounds with a water resistance exceeding that of smoked sheet rubber compounds may be obtained by compounding with litharge and such additional activators as zinc sulfide and catechol. Rosin improves the water resistance of neoprene compounds at elevated temperatures. Sulfur decreases the water resistance of magnesia-zinc oxide and litharge-neoprene compounds in proportion to the amount used. The influence of temperature on the water absorption of both magnesia-zinc oxide and litharge compounds has been determined.
due to small amounts of magnesium chloride formed during cure, silver abietate and silver stearate where included in a series of compounds to convert the soluble chloride into insoluble silver chlaride. These stocks failed to show any improvement over the controls.
TABLE11. ABSORPTION OF WATERBY NEOPRENE WITHOUT MAGNESIA Formula No. Neoprene Type E
6" 100 20
PbO
ZnO Mg(0H)o Hours in Water at 1000
c.
0
24 48 120 186 48 5
100
70 100
...
5 10
6a
...
20 10
... ... r---
r
-
-
v
C
d
4.607
1.427
4.628
1.643
4:762
1:425
41866
1:642
...
...
...
...
...
...
d
C
...
...
% Volume Absorption 8.2
8.1
---
d
C
4.842 5.372 5.582 5.981
6.260
1.251 1.258 1.255 1.255
1.258
20.6
Press-cured 30 minutes at 1 5 3 O C.
.
Litharge Gum Stocks
Previous work (3, 6) showed that a litharge compound (Eagle-Picher sublimed litharge) containing zinc oxide, rosin, and sulfur had high water resistance. A disadvantage of this combination is the instability of the uncured compound and the processing difficulty it presents. The stability may be improved if the sulfur is omitted, but its activating influence is lost and the zinc oxide does not activate a litharge compound in the absence of sulfur. Possible activators for use in a litharge compound have been evaluated in a gum stock, and the results are summarized in Table 111. Litharge alone gives a fairly stable stock, and the cured slabs have good water resistance but low modulus and tensile strength. The addition of magnesia raises the modulus but decreases the stability in the absence of rosin and lowers the water resistance.
1382
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 29, NO. 12
-
. . :a .m.
h
2 8% : :
m
5% .: :. .:o. 3
2
bi (D
3432 lCOOO
.: s. .: :. :. :. :.:.:
asi"gg2
z (D
r-' coco
[ p m
V 9d
d
W
r
!4 s
e
-0
2a
.e
2
L
5
m N
... ... .*.. ......... ... h
m
m
. .. ,..
0 0 0 . .
O N - . 3
m o o . . . .
....
O N . . . . i
ci 0
d
5
u
e a
DECEMBER, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
to 0.08 cm., respectively. The apparent absorption of similar rubber samples (compound 15) under identical conditions increased from 1.92 to 3.02 to 5.65 per cent. The water resistance of neoprene compounded with a high amount of soft carbon black, with and without softening agents, was measured to determine the advantage in water resistance to be gained by high loading and the influence of the softening agents on the water absorption. The compounds prepared and the test data obtained are given in Table V. The results show that, although the use of an increased amount of carbon black by itself increases the water resistance, the selection of the softening agent employed to produce a stable and processable stock may decrease the water resistance considerably. This is illustrated by compound 22 in which cottonseed and mineral oils were used. An agent such as Barrett No. 10 oil gives a compound (23) witk a plasticity and stability comparable to those of the compound containing cottonseed and mineral oils. During the first 24-hour immersion period a t 100" C., Barrett No. 10 oil volatilizes, and the net result is an apparent shrinkage rather than a swelling. After the first 24-hour period compound 23 containing the Barrett No. 10 oil shows a definite swelling, due to water absorption. Upon prolonged exposure, especially a t elevated temperatures, the apparent water absorption of all the samples is influenced by loss of material due either to leaching or volatilization.
FIGURE I 8 0-
-
WATER ABSORPTION OF CARBON BLACK STOCKS
15 RUBBER 16 NEOPRENE
+ PbO
1383
IS NEOPRENE+ P b O + Z n O + S
I9 N E O P R E N E + P b O + Z n S
70- 17 N E O P R E N E t P b O t M P
0 6.0c a
* 5.0-
i
54
K W
5 4.0-
f
W
5 3.0 d 5 2.0 W
a 1.0
D A Y S AT 30%
Zinc oxide without sulfur in the presence of litharge has no significant effect on the stability or water absorption but actually retards the cure and lowers the modulus. Zinc sulfide is a mild activator in combination with litharge, although less effective than magnesia; it has little effect on the stability or water resistance. Catechol is effective in giving a high-modulus gum stock with good water resistance but low tensile strength. In fact, the tighter cure obtained with catechol gives a litharge compound with improved water resistance. Although catechol itself is water soluble, the small amounts used probably exist in the cured compound as an insoluble lead salt.
Effect of Wood Rosin
Litharge-Carbon Black Stocks A comparison of carbon-black-loaded neoprene, compounded with litharge and additional activating agents, with a practical water-resistant rubber compound showed that the neoprene compounds, except that containing magnesia, have superior water resistance a t 30" and a t 100" C. Since two soft carbon blacks (P-33 and Thermax) were used in the rubber stock, both were used in the same proportion in the neoprene to give the same volume loading. The compounds and test data are included in Table IV. The water absorption values a t room temperature and at 100" C., as calculated from the gain in weight, are plotted against time in Figures 1 and 2. I n each case the water resistance of the loaded neoprene stock is appreciably better than that of the corresponding gum stock (Table 111). The effect is greater than that which can be attributed to the dilution of the neoprene by carbon black. At both room temperature and a t 100" C. the water resistance of the stock containing zinc oxide and sulfur is slightly inferior to that containing only litharge as activator. The addition of zinc sulfide has little effect, whereas the addition of catechol actually improves the water resistance. These conclusions regarding the influence of compounding ingredients on water absorption of the 0.2cm. slabs were substantiated by measurements made with thinner slabs. The thinner t h e s a m p l e , t h e greater the apparent water absorption of any given compound, especially during the shorter periods of exposure. For example, the apparent volume per cent absorption of compound 16 during 48-hour immersion in water at 100" C. increased from 0.64 to 0.85 to 1.07 as the thickness of the samples varied from 0.21 to 0.14
The effect of the addition of 5 parts of rosin per 100 parts of neoprene to both magnesia-zinc oxide and litharge stocks
FIGURE 2 WATER ABSORPTION OF CARBON BLACK STOCKS 18 NEOPRENE t PbO t ZnO t S
15 RUBBER
E
20
3 2 I
5
ID
20
30 40 DAYS AT 100 C.
50
60
70
1384
INDUSTRIAL AND ENGINEERING CHEMISTRY
is shown by the data plotted in Figure 3. The addition of rosin makes no difference on the water resistance of neoprene a t room temperature, but it appreciably improves the resistance a t elevated temperatures. The litharge stock containing rosin actually appears to be more resistant a t 100” C. than a t some intermediate temperatures. Amounts of rosin greater than 5 parts per 100 parts of neoprene do not improve the water resistance; 10 parts are no more effective than 5 parts, but 20 parts of rosin decrease the water resistance.
VOL. 29, NO. 12
’
J
TABLEV.
EFFECTOF SOFTENINGAGENTS ON LITHARGE-CARBON BLACKSTOCKS
Formula No. Neoprene Type E FF wood rosin Litharge Carbon black (Thermax) Cottonseed oil Mineral oil Barrett No. 10 oil
21 100 5
20
150
. . ... ,
22
23
100 5
IO! 0
20
20
150
150
...
5 5
...
...
..
10
Stability, Plasticity-Recovery Numbers Aged a t 50° C., Hr. 0 24 48 96
Effect of Sulfur
200-14 250-46 285-61 352-116
130-14 162-7 189-27 238-69
130-5 173-8 202-30 270-89
Stress-Strain Data”
M. A. Youker of the du Pont Company observed that the water absorption of a magnesiazinc oxide gum stock was increased from 16.1 to 26.7 per cent by increasing the sulfur content from 1 to 3 parts per 100 parts of neoprene. The influence of sulfur was less marked in the case of carbon black stocks. N. L. Catton of the du Pont Company investigated in more detail the influence of sulfur and observed not only this effect on the water resistance of magnesia-
Cure at
153’ C.,
,
Min. 10 20 40 60
56( 800) 83 1175) 9011275) 90(1275)
Days qf Immersion 4 16 32 32
121(1725) 121(1725) 139 1975) 13411900)
330 180 230 210
28 400) 97(1375) 260 421600) 121(1725) 290 40(575 121(1725) 290 42(600] 125(1775) 250
37(525) 54 776) 541776) 53(750)
114 121 121 121(1725) 240
Stress-Strain Data after Immersion in Water a t loOD C.
102(1430) 144(2050) 190 65( ’325) 127(1800) 200 86(1225) 132(1875) 200 118(1675) 135(1925) 130 93 1 3 2 ~ ) ? 128(1823) 180 104(1425) 127(la00) 160 lIl(1578) 140(2075) 160 071 95;) 130(1850) 180 93(1325) 127(1SOO) 160
% Loss of Material after Immersion in Water at looo C. 0.67
--
4.84
3.34
Apparent % Volume Water Absorption (Weight Method) av
NEOPRENE
foe
48
noun
PERIOD.
Days 2 4
100 NEOPRLNL T Y P E E , 10 HgO, 5 In0
S
I ROSIN 5 ROSIN
0
16 32 51 71 81
0
30°C. 0.14 0.23 0.29 0.33
100°C.
0:is
0.34 0.60 0.75 0.97 1.17 0.98 0.72
3OOC. 0.39 0.62 0.64 0.76
1 :26
1
100DC. 1.87 2.47 2.77 2.75 2.00 1.18 0.67
3OOC. 0.00
0.02 0.04 -0.09
....
-0.35
....
100°C. -3.76 -3.40 -3.25 -3.11 -2.32 -2.20 -2.53
....
0:iz .. 1:4 .. -0.72 The figures for each formula represent stress a t 100% elongation in kg. per sq. cm. (lb. er sq. in.), tensile strength in kR. per sq. om. (Ib. per sq. in.), and per cent elonpatlon at %reak.
0
shown in Figure 3. These results indicate that the hydration of magnesia occurs a t room temperature as well as a t elevated temperatures. They show clearly the superiority of the litharge stocks.
Literature Cited
1I-
I
10
so
40 80 so T E M P E R A T U R E ‘C.
70
no
so
(1) Bridgwater a n d Krisman, IND. ENG.CHEM.,25, 280 (1933). 100
(2) Clapson, Ibid., 29, 789 (1937). (3) E.I. du P o n t de Nemours and Co., Inc., D u Prene Manual, Aug.,
1934.
zinc oxide stocks but an even greater effect with lithargemagnesia stocks. I n a stock containing 20 parts litharge, 2 magnesia, and 5 rosin, as the sulfur was varied from 0, 1,3, 5 to 10 per cent the water absorption in 48 hours a t 100” C. increased from 7.53 to 11.09, 43.0, 76.2, and 96.5 per cent, respectively. Here again the effect was less marked in a carbon black stock than in a gum stock. This decrease in the water resistance in the presence of sulfur may be attributed to the formation of water-soluble products by reactions of the sulfur with neoprene. A greater activating influence of litharge as compared with magnesia and zinc oxide on these reactions would account for the greater impairment by sulfur of the water resistance of a litharge compound than of a magnesia-zinc oxide compound.
Variations with Temperature The water absorption for both magnesia-zinc oxide and litharge gum stocks a t temperatures from 30’ to 100’ C. is
(4) India Rubber World, “Compounding Ingredients for Rubber,”
1936. (6) Starkweather a n d Walker, IND. ENG.CHEM.,29, 872 (1937). REOEIVXID September 23, 1937. Presented before the Division of Rubber Chemistry a t the 94th Meeting of the American Chemical Society, Rochester, N. Y., September 6 to 10, 1937. Contribution 36 from Jackson Laboratory, E. I. du Pont de Nemours and Company, Inc.
Correction On page 968 of the September, 1937, issue of INDUSTRIAL AND ENGINEERINQ CHEMISTRY an error occurs in the very important definition of “Molecular Distillation.” The sentence which begins on the iifth line of the section on “Apparatus and Methods” should read: “The free path of the majority of the moleculen emerging is then greater than the distance between the surfaces, and distillation occurs at the lowest possible temperatures.” The word “less” was printed instead of “greater.” K. C. D. HICKMAN
