INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1948
at ’
or
The velocity of the gas is G/m, so that the time required for the gas to travel from inlet to cross section x is mx/G. Then the time, e’, a t which the gas passes the inlet section is 8’ = 0
mx -Q
-
where e is the time a t which it passes section x. Note that e‘,
of course, is always positive. [f we make the change in time variable 8’ =
e - mx - -that G
if we measure time a t inlet instead of a t distance x-the equation is simplified. It becomes
is,
above
and the heat exchange system is h (t‘
c&’
- t)
=
at’ - cd -,ae
which is identical to system 1 and is solved in the same manner. The resulting dimensionless graph is the same; the time correspondence, however, is 8’ = cd -8and
h
e
= cd -8
h
G
NOMENCLATURE
c
= mass velocity of gas
= known temperature difference shown in Figure 1 = specific heat of solid
c.
= specific heat of gas
d
= apparent density of bed
coefficient of heat transfer per unit volume of bed for the bed coefficient of heat transfer per unit volume of bed for the container coefficientof conductivity n-ithin the granules coefficient of conductivity for the bed weight of gas occluded between granules per unit volume of bed finite increment of dimensionless distance finite increment of dimensionless time ratio h’/h temperature of gas temperature of gas a t start-up a t inlet outside temperature temperature of solid temperature of solid a t start-up a t inlet dimensionless temperature of gas dimensionless outside temperature dimensionless water temperature dimensionless temperature of solid linear velocity of gas distance from inlet dimensionless distance from inlet(numberoftransferunits) time dimensionless time dimensionless function of T and X dimensionless function of T’ and X LITERATURE CITED
t- m - x
For dynamic cooling of adsorbent beds, the velocity m / G is very large, so that the time differential m / G becomes rapidly negligible compared to e and it is indifferent whether time is measured a t inlet or at distance x. For this reason, system 1 was established with the condition m = 0. In the case of heat transfer between a bed of broken solids and a liquid the time differential may not be negligible.
G a
1977
Furnas, C. C., Trans. Am. Inst. Chem. Engns., 24, 142 (1930). Gamson, B. W., Thodos, G., and Hougen, 0. A., I b i d , 39, No. 1 (1943). Ledoux, Edward, “Adsorption des Gas e t Vapeurs,” Paris, Lib. Poly. Ch Beranger, 1948. Ledoux, Edward, Chem. Eng., 55, No. 3, 118 (1948). Ledoux, Edward, “Vapor Adsorption. Industrial Applications,” Brooklyn, N. Y., Chemical Pub. Co., 1945. Ledoux, Edward. “Graphical Solution of Heat and Vapor Tranefer Problems” Brooklyn, N. Y., Chemical Publishing Co.. 1949 (in press). Saunders, 0. A,, and Ford, H., J. Iron Steel Inst. (London), No. 1, 291 (May 1940). Schumann, T. E. W., J . Franklin Inst., 208,405 (1929). Sherwood. T. K., and Reed, C. E., “ADDlied Mathematics in Chemical Engineering,” New York, MEGraw-Hill Book Co., 1939. RECEIVED August 4, 1947.
Accelerated Aging of EFFECT OF COPPER L. R. MAYO, R. S. GRIFFIN, AND W. N. KEEN Rubber Laboratory, E. I . d u Pont de Nemours & Company, Wilmington, Del.
T
HE catalytic effect which copper has on the oxidation of natural rubber vulcanieates is a matter of serious concern to the rubber technologist. As little as O . O O S Y , of copper (based on the rubber hydrocarbon) can cause the complete deterioration of a conventional rubber compound within a very few days in the 70 O C. oxygen pressure test, whereas comparable copper-free compounds remain in serviceable condition after several weeks of bomb aging (9). These effects of copper are substantially overcome in rubber stocks which are compounded for superior resistance to aging. Stocks of this type usually contain high a m w n t s of antioxidants, row concentrations of sulfur, and selected accelerators. The addition of a metal inhibitor to any stock is
decidedly advantageous. Nevertheless, in many applications, the only satisfactory solution is the careful avoidance of all oontact or contamination with copper in any form. For example, the insulated wire industry has prevented direct contact between a copper conductor and the rubber insulation by the use of a fibrous covering or a tin coating over the conductor. Keoprene compounds have been in use for several years as protective jackets for rubber insulated wires, but only recently have they been used to any extent as insulations. In such use they may come into direct contact with the copper conductor unless a separate layer such as a fibrous wrapping or tin coating is used. Since it has been shown that neopreneis less susceptible
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
1978
Neoprene conipounds having antioxidant protection are resistant to oxidation cataljsed bj copper and are made more resistant by the presence of a copper inhibitor in the compounds. A neoprene insrilatiort extruded and cnred over a bare copper conductor m a y age inot'e rapidly under severe conditions than the same compound on tin coated wire. The addition of a copper inhibitor to the eornpotind on bare copper. howei en-, improves insulation aging so that it is equal to thak of the original compo~md on tinned Mire made? a11 conditions. Therefore, it was coneluded that the tinning o f conduettors or the t19eof copper inhibitors is necessar? opldp where rxtremel) sei el e aging conditions pretail, The g.esdts on wire insulation are i n agreement with aiipplermentarg work emplo>i n g copper in other forms, such as ccapper stearatr.
-
r______l
than natural rubber t o the effects of copper ( d ) ] cjuesiionu a h ; as to the limitations of neoprene compounds in (*ontactwith copper QP neoprene-soluble copper compounds. This paper describes preliminary xvork that was c,arried out to provide sonle of the answers to these questions. EXPERL\IENTK E PHOCEDURB
A neoprene product map come in contact with coppei either. through direct contact with the metal 01 by the presence of copper ~ o ~ i p o u n dwithin s the stoc!c. A neopi,ene-soluble compound, copper stearate (10% copper), !vas used as a source of cont,amina-. tion during the initial phase of Lliis work, This compound has s of this been used as a source of contaminalion in p ~ w i o u studies nature with both natural rubber and neoprene (3,Q, 6). I d e r , standard copper xire conductors n w e used for obtaining contacl with the mctal. Ta,bles I and II describe the neoprme cornpounds used in this investigation, 4'h.e experimental data vere obtained by the determination of the physical properties of the neopwnc vulcanizates after sewral
1
2
3
Compound- 7.i4 5 partn
I__._
_ _ I I _
Neoprene, t y p e G X 0 Accelerator 552 ij Stearic acid Extra-Light calcixicd
0
b 0
d
6
7
8
___-----__I
100 100 100 100 I00 100 IC0 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.5 0.5 0.j 0.5 0 , 5 0.5 0.5 0.5 4 4 4 4 4 4 4 4
100
Identical with GR-LI. Piperidinium pentarnethylenedithiocarbarnatt. Phenyl-%naphthylamine. Disalicylal ethylenediamine (50% actix-e ingredient).
TABLE
11.
BASIC N E O P R E X E C O O S IYIRS JSSUL.4TIOii
(Preae cure, 10 minutes at l 5 3 O 63.; insulation cure, 22 seconds a t 203' C.) Coniuound 7.4-9, Parts LOO
Clay EPC carbon black Paraffin Petrolatum Zinc oxide Permaluxb Identical with GR-M-10. b DOTG salt of dicatechol borate.
.oo
2.00 4.00 36.00 35.00 38.00 10.00 6.00 3 .00 10.00 I .25
Vol. 40, No. 18
periods of accelerated aging. Most of the aging was carried out, in air a t 70" c. and atmospheric pressure or in oxygen at 70' C. and a pressure of 300 pounds per square inch. The compounds shown in Table I were aged as tensile test specimens. The insulation compounds (Tables 11,VI, and I'II) were extruded t o a Tall thickness of 3 / ~ 4 inch on both bare and t'inned solid copper conductor (KO. 14 AWG) and cured in a high pressure vulcanizer for 22 seconds a t a steam pressure of 225 pounds per square inch (203 ' C ~ ) " Specimens stripped from aged and unaged asselriblies were tehted. These methods are essent,ially those outlined in A.S.T.M. procedures ( 1 ) . In the graphic presentation of data elongation at breali, expressed in per cent, is used extensively as an index of retained physical properties. Per cent elongation is a physical. property of neoprene vulcnnizates highl), sensitive to change on aging arid therefore the one most, likely to reveal small Pignificant differ:?ncc:P (6). USE OF
.4wrmwmw
Tht: superior resistance of neoprene stocks to oxidation exish to a high degree ciniy n-hen compounding has included an effective antioxidant (3,I O ) . Since the deteriorating action of copper on elastomers is generally attributed to a catalysis of oxidation, it follows that the need for an antioxidant is essential where contamination with copper is anticipated. Table 111 gives data on the effect of copper stearate on the Fetention of physical properties of several basic neoprene compounds after several periods of aging in the oxygen preesure test. These data also are plotted in Figure 1. It will be seen that the addition of 1.0 part of c,opper stearate (0.1 part copper) to the stock unprotected by any antioxidant caused deterioration to occur ,so rapidly that no physical tests were possible after 5 days. Ho~vever,the addition of only 1 part of a standard antioxidant, S eozone D (plienyl-8-naphthylaniine) to -thiscompound effocts an outst anding improvement. USE OF COPPER INAlBlrOW
Although conventional antioxidants significantly improve rhe aging of neoprene vulcanizates in the presence of copper, they do not appear to offer complete protection. A special class of compounds which possesses no outstanding antioxidant propertiea but is specifically effective in counteracting the action of copper when used in conjunction with conventional antioxidants has been developed. The disalicylal diamines of propylene and ethylene are outstanding examples of these compounds and are referred to as copper inhibitors. The data in Table 111 show that copper inhibitor used without an antioxidant is relatively ineffectivein retarding degradation in the oxygen pressure test, regardless 01the presence or absence of copper stearate. However, the addition of 2.0 parts of copper inhibitor to a stock already containing Neozone D gives full protection against the 1 0 part of qopper stearate present. This is shown in Figure 2. EFFECT OF COPPER OY IWSUEATlOh TYPE STOCK
The extent to which an insulation compound may deteriorate and still be considered serviceable is a debatable question. I n this paper, a tensile strength of 1000 pounds per square inch and an elongation of 50% have been selected arbitrarily as the lower limits of insulation serviceability, To determine the effects of copper concentration on the rate of oxidation of a code wire stock, varying amounts of copper stearate (0.25 to 4.0 parts) were added to the base compound 7A-9 (Table 11). This resultedin compounds 7/1-10 to 14, inclusive. The data obtained during aging of test specimens (3 X 6 X 0.075 inch) in the oxygen pressure test for 49 days are presented in Table I T 7 Figure 3 i s a graphical analysis of this data. The
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1948
I
EFFECT OF ANTIOXIDANT
L\
1979
EFFECT OF COPPER
INHIBITOR
~ 7 0 0
COPPER BEARING STOCK WITH ANTIOXIDANT AND
NON-COPPER STOCK
NON-COPPER "400
COPPER BEARING
NEOZONE 0
$3001 lo ^
NON-COPPER STOCK N O ANTIOXIDANT
200
OL.
DAYS
I
I
L
'
5
I 21
10
DAYS
OXYGEN PRESSURE TEST
SO
OXYGEN PRESSURE TEST
Figure 2
Figure 1 ._____I_..__
linear relation between life in the oxygen bomb and the copper stearate content shows that the expected service life of a neoprene vulcaniaate contaminated by a copper compound is directly proportional to the amount of copper present. The curve indicates that it requires slightly more than 2% of copper stearate (0.2% copper) based on the neoprene to double the rate of aging and that the presence of 1% of copper stearate increases the rate of deterioration by approximately 25%. The effects of a copper inhibitor on the oxygen bomb aging of a neoprene code wire stock containing copper stearate were investigated, Copper inhibitor, varying from 0.25 to 4.0 parts, was added to compound 7A-12 which contains 1 part of copper stearate. This resulted in compounds 7A-15 to 19, inclusive, which are shown in Table V together with the physical test data obtained from their aging tests. Increasing amounts of copper inhibitor are shown to be beneficial, but from 1.0 to 2.0 parts appear sufficient to improve the aging characteristics of the copper-bearing stock to equal approximately those of a copper free control. Copper compounds vary in their ability to promote oxidation. In some compounds it has been shown that copper may be bound chemically in such a manner that i t no longer accelerates the oxidation of natural rubber vulcaniaates (8). It is logical to assume that different copper compounds also vary in their effects on neoprene vulcaniaates. The simplest explanation, therefore, for the effectiveness of a copper inhibitor in counteracting the deterioration caused by copper stearate is that the catalytically active copper of the stearate forms a complex or compound with the copper inhibitor and thus is rendered inactive.
CODE WIRE STOCK TIME TO REACH 50% ELONGATION
25
&.
50
20
IO
40
COPPER S T E A R A T E ( P U R T S PER 100 PARTS NEOPRENE )
Figure 3 CONTACT WITH METALLIC COPPER
Three assemblies were used to study the effects of metallic copper in direct contact with a neoprene code wire compound. In each case the neoprene compound was extruded and cured on a tinned or bare copper wire as designated in Table VI. No copper inhibitor was used in the compound placed on the tinned wire. This compound, with and without copper inhibitor (7A-9 and 20), was extruded also on bare copper wire. The data (Figure 4) show that, using the oxygen pressure test as a criterion, a neoprene insulation stock extruded directly on bare copper wire deteriorates somewhat more rapidly than when it is extruded on tinned wire. The use of 2y0 of a copper inhibitor, however,
TABLE 111. EFFECTOF COPPER STEARATE ox OXYGEN PRESSURE^ AGINGOF BASICNEOPRENE VULCANIZATES Compound 7A1
2 3 4 5
a
Copper Stearate, Parts .
.
Neozone
D,
Parts
Copper Inhibitor Parts
...
I
1
... 1 ...
... 1 1
, . I
6 ... 7 . 1. . 1 8 1 1 A.S.T.M. Designation D572-42.
TABLE Iv. EFFECTO F Compound 7A9 10 11 12 13 14
Copper Stearate, Parts
...
0.26 0.50 1.00 2.00 4.00
COPPER
Original 1650 1475 1575 1560 1625 1800
. . I
,.. .
.
I
... 2 2
;
Tensile Strength, Lb./Sq. In 10
21
Original 2400 2400 2625 2375 2625
days 1650 Welted 2475 2350 1700
days 1600
day,. Melted
2i00 2126 1675
2225 1676 1425
2376 2625 2350
1700 2475 2425
Melted 2325 2250
2225 2075
STE.4RATE CONCENTRATION
ON
OXYGEN
Tensile Strrngth, Lb./Sq. In. 7 14 21 26 42 days days days days days 1390 1180 1230 1200 1425 1330 1180 1190 1230 1210 1260 1190 1130 1120 1230 1130 1190 1030 1040 1000 1210 900 790 790 Melted 700 740 Melted ...
...
...
30 days
...
...
2075 Melted Resinous and blistered
...
2125 2025
Original 600 675 720 720 585 660
635 670
PRESSURE A C I N G O F A
4s
days 1280 1010 940 Melted
... t . .
Orisinal
Elongation a t Break, % 5 10 21 days days days 480 310
...
666
b66
630 430
585 340
480 560 640
520 580
...
510 365 100
. . ~ 470 ... 510
a0 days
... ... . .. ..~ ... 445 44.5
465
NEOPRENEINSULATION STOCK
Elongation 7 14 days days 425 300 415 300 405 275 400 260 505 255 205 30
at Break, % 21 28 days days 270 206 200 200 180 200 160 150 100 80
...
.. .
42 days 120 90 90 70
...
...
49 days 100 60 60
... ... .*.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1980
TABLEv. EFFECT OF
COPPER INIlIBITOR COXCENTRATIOS ON OXYGEN PRESSURE AGING O F A NEOPREXE
CONTAINKG COWERSTEARATE
Copper Inhibitor X-872-La. Parts
Copper Stearate. Part8
Compound
7A-
-
Tensile Strength, Lb./Sq. 7 14 21 28 days days days 1180 1230 1200 1190 1030 1040 1120 1110 1010 io90 1100 io50 1190 inso 1060 1180 1151 io50 1200 1090 io30
Original days 1650 1390 9 I .do 1550 1130 12 1 00 1575 1310 16 0.25 1.00 1675 1320 16 0.50 IGOO 1425 17 1.00 i on 1525 1400 i .no 18 2.00 I .no 1650 1390 19 4.00 Disalioylal propylenediarnine (80% active ingredient).
... 1 . .
5
VOl. 40, No. 18
In. 42 49 days days 1425 1280 1000 Melted 1025 Xelted 920 1130 1120 950 1090 1080 LZIO 1220
INSULATION STOCK
_______Elongation a t Break, Original
7
days 425 400 475 470 500
;oo nno
14
days 255 250 300 300 365 390 415
21 days 270 160 185 185 185 305
m
%
28 days 205 150 105 200
'
42
49 dayk 101,
zoo
120 70 70 90 110
235 230
160 190
days
... ... 50 BO 90
ion
TABLEVI. OXYGENPRESSURE AGISG OF KEOPRCSG Corm KIRKImr L ~ T I O Uos BARECOPPERA N D TIN COATED CQNDT-CTORP Copper
Compound 7A9 tin coated) 9 [bare copper) 20 (bare copper) TABLE
R O V E N A G I N G O F XEOPREXE C O D E \TIRE
Copper Inhibitor X-872-L. PartF
Compound 7A9 (tin aoated) 9 bare copper) t o )bare copper)
Original lG00 1650
2 .'do
1600
TYSLLATIOS
Tensile Strength, Lb./Sq. I n . 7 21 GO 90 days day8 days days 1600 lG00 1575 1550 1650 GOO GOO 1575 1600 1575 m o 137~
more than offsets this catalytic effect and results in a stock Thicii is more resistant to deterioration on bare copper wire than the oontrol stock on a tinned conductor. At the end of 49 days' aging in the oxygen pressure test, all of the assemblies could be flexed through 180"with no cracking of the neoprene insulation. Rather than rely solely on one type of accelrrated aging, additional samples of thc same insulated wires were aged in the 70" C itir oven Rwuliing data. Table VTI. obtained over a n
to Break, % _______ 21 28 35 42 49 days days days days dayp 90 GO 220 175 140 50 30 20 170 100 280 200 170 100 80
Elongation __.______
7
2 00
70" c. h
VTI.
Tensile Strength, Lb./Sq. I n . 14 21 28 35 42 49 Original days days days days days days days 800 I G ~ O ~ G S O isno 1400 1320 1200 i n 4 0 1600 1500 1400 1200 1100 720 ieSo 150 1650 1750 1700 1650 1500 1400 1100 1150
Inhibitor X-872-1,. Partp
ON
Original 540 520 540
7 days 380 345 400
14 days 290
BAREC O P P E R
240
320
ASD T I N COATED
COXTIUCTORS
Elongation t o Break, % 1 7 r -________ 7 21 GO 90 days Original days days days day 1350 540 420 420 340 295 1400 520 435 435 305 250 1350 540 405 405 320 275
_ _ l _ l _
170 dayp 180 190 200
aging period of nearly 6 months (170 days) show that the phvsicd properties of the neoprene insulations do not decrease to a greater than normal extent as a result of contact with copper. This is illustiated clearly in Figure 5 in which only one curve is needed to represent the decline of elongation with aging. Although 170 days at 70" C.is not considered an extremely long aging period for neoprene vulcanizates, its failure to distinguish between insulation on bare and tinned copper is significant. It indicates that oxygen bomb aging is relatively more severe than oven aging in the presence of an oxidation catalyst such as copper A. similar relation betneen the 80" C. oxygen bomb and the 100' C. air oven was found in other work involving the aging of n neoprene jacket stork dusted with finelv divided copper ( 7 ) EXTENDED YATURAL AGING
9
DAYS
'
I El
14
7
OXYGEN
*2 8- -
Katural aging tests on the compounds discussed in this paper have not progressed sufficiently for comparison with the accelerated aging results. NoTYever, preliminary 6-month tests show no significant differences between the compounds on bare copper wire either with or without copper inhibitor. Thew tests are being conducted in direct sunlight in Florida. 35
EXTERATURE C I T E D
P R E S S U R E TEST
Figure 4
w
1
EFFECT O F T Y PAEI R OOF CONDUCTOR VEN
I 1
h a 0
o NEOPRENE ON TiNNED W I R E , N O COPPER INHIBITOR x NEOPRENE ON B A R E WIRE, NO COPPER INHiBiTOR o NEOPRENE O N RARE WIRE, W I T H COPPER iNH18iTOR XB72L I 90
I
7
21
60
DAYS
IN 70'0
A I R OVEN
Figure 5
i
Ani. SOC. Testing Mateiials, Standards for Rubber PioductR, Designations D412-41, D572-42, D573-43, D470-41 (1946). Bott, E. C. B., and Gill, L. C., Trans. J n s t . Rubber Ind., 19, 63 (1943). Catton, Fiaser, and Forinan, R u b b e r Chemicals Div., E. I. dii Pont de Nemours & Co., Eept. 42-2 (1942). Du Pont de Semours, E. I. &- Co., BZ Rept. ee (1941). rorman, D. B., ISD. EIFG.CHEM.,35, 1942 (1943). Jones, P. C., and Craig, D., Ibzd , 23, 23 (1931). Keen, IT. N., and Jones, 0. R., reported work, Rubber Laborntoiy, E. I. du Pont de Nemours & Co. (1946). Morely, J. F., J . Rubber Research, 16, 31 (1947). Neal, A. ST,,Rubber Chemicals Div., E. I. du Pont de Kemoure & Co., Rept. 38-1 (1935). hTeal, A. M,, Bimmeiman, H. G., and Vincent, J. R.,IND. ENG CHEW.,34, 1294 (1942).
I
I70
RECEIVED September 23, 1947. Presented before the Division of Rubber SorIFTT, Chemistry a t t h e 112th Meeting of t h e AMERICANCHBMSCAL New York, N. Y.
