Factors Affecting Rate of Vulcanization of Chloroprene Plastic Polymers E. R. BRIDGWATER AND E. H. KRISMANN, E. I. du Pont de Nemours & Company, Wilmington, Del.
T
HE preparation of chloro-
All t h e s e c o m p o u n d s conThe rate of culcanization of chloroprene plastic prene plastic polymers tain 10 per cent total weight of polymers and the range of cure and physical and their vulcanization m e t a l l i c oxides based on the properties of the culcanizates are profoundly weight of the polymer. Physito produce elastic rubber-like affected by Ihe addition Of carious cal p r o p e r t i e s of these comp r o d u c t s have a l r e a d y been oxides, suwur, certain acid sqfleners, and other p o u n d s c u r e d 20, 45, and 90 d e s c r i b e d . ' The purpose of minutes a t 141" C. are shown in this paper is to show the effect organic compounding ingredients. These effects Of various are, in general, not produced except when the TablellThe polymer used for these ingredients, 'lone and in 'Omabove mentioned materials are used in speciJic Can be vulcanized withb i n a t i o n w i t h one another, combinations with one another. out the addition of any other on t h e r a t e of vulcanization ingredients, but the vulcanizate of chloroprene plastic polymers and their effect on the physical properties of the vulcanizates. is weak, having a maximum tensile strength of approximately All tests reported herein were made on a modified chloro- 35 kg. per sq. em. when cured 60 minutes a t 141" C. (the prene plastic polymer (known commercially as DuPrene optimum cure). The tests shown in Table I1 demonstrate Type F), containing 94.5 per cent of polymerized chloro- the beneficial effect of adding metallic oxides but in no case prene, 5 per cent of a mineral oil known commercially as does the vulcanizate have satisfactory physical properties. Certain compounds were mixed and cured to show the medium process oil, and 0.5 per cent of phenyl-p-naphthylamine. This modified plastic polymer will be referred to effect of adding grade FF wood rosin (Hercules Powder Comhereafter in this paper, for the sake of brevity, as polymer. pany) of the following composition: melting point, 177" F. All compounded stocks were mixed on a 15 X 30 em. experi- (81' (2.); acid number, 153; and saponification number, 169. mental rubber mill, the temperature of the rolls being main- The composition of these compounds is shown in Table 111. tained a t 50" C. Mixed stocks were slabbed off the mill about 0.22 cm. thick and cured in a mold 0.20 cm. thick. All cures TABLE111. COMPOSITION OF COMPOUNDS 511-516 AXD 518 were made a t 141" C. (286" F.)-the actual temperature of the COMPOUND511 512 513 514 515 516 518 mold itself. Polymer Rosin Light calcined MgO ZnO Sublimed litharge
EFFECTOF METALLICOXIDES The compounds of Table I were mixed and cured. TABLE I. COMPOSITIOSOF COMPOUNDS 504-509
---
Pol mer LigKt calcined M y 0
504 100 10
Sublimed litharge
. ..
ZnO
...
505 100
. .. 10 ...
COMPOUND---506 507 100 100 ... 5 5 ... 10
...
508 100 5
...5
509 100
...
5 5
COMPOUND
AT
141'c.
Min. 504
505
506
507
508
509
20 45 90
STRESS AT ELONGATION OF: 300% 500% 700% Kilograms per sp. cm. 5.3 19.3 43.9 7.0 19.3 43.9 8.8 28.1 58.0
TESSILE STREXCTA
K g . / s q . em. 80.9 75.6 93.2
...
100 5
100 5
... ...
.. . . 10 ..
10
100 5 5 5
.. .
100 5 5
... 5
100 5
... 5 5
100 5
... ... ...
Compound 512 scorched during mixing to such an extent that it was impossible to obtain good cures. Physical tests on the other compounds are shown in Table IV. TABLE IV. PHYSICAL TESTS ON COMPOUNDS 511, 513-516, AND 518
TESTS ox COMPOUKDS 504-509 TABLE 11. PHYSICAL CURE
100 5 10 ..,
COMPOUND
ELONG.4TION AT
BREAK
AT
c.
Min .
STRESSAT ELONGATIONS OF: TENSILE 300% 500% 700% STRENGTH Kilograms per sq. em. Kg./sq. cm. 7.0 24.6 61.5 170 12.3 36.9 86.1 174 17.6 45.7 118 172
511
20 45 90
513
20 45 90
10.6
7.0 8.8
17.6 24.6 33.4
47.5 79.1
% 920 900 900
CURE
141'
...
ELONGATION AT BREAK
% 1000 900 800
110 79.1 65.0
860 700 620
20 45 90
10.5 8.8
8.8
33.4 26.4 26.4
73.8 68.5 93.2
116 144 93.2
800 900 700
514
20 45 90
5.3 5.3 8.8
19.3 15.8 26.4
47.5
31.6 36.9 40.4
84.4 94.9 102
257 230 179
950 900 820
42.2
780 900 700
15.8 17.6 17.6
61.5
58.0 91.9 61.5
20 45 90
515
20 45 90
3.5 5.3 7.0
12.3 21.1 26.4
33.4 47.5 56.3
75.6 79.1 96.7
1000 880 920
20 45 90
7.0 10.6 15.8
19.3 29.9 38.7
51.0 87.9 105
167 158 123
980 830 740
516
20 45 90
3.5 5.3 10.5
10.6 14.1 33.4
29.9 31.6 63.3
56.3 75.6 77.5
920 960 780
20 45 90
7.0 8.8 12.3
12.3 17.6 31.6
33.4 65.0 93.2
118 123 93.2
930 830 700
518
60 120
....
7.0 8.8
12.3 15.8
43.9 58.0
1000 1020
20 45 90
5.3 5.3 8.8
14.1 14.1 21.1
33.4 33.4 45.7
84.4 86.1 118
960 980 960
1 Nieuwland, Calcott, Downing, and Carter, J . Am. Chem. Soc., 53, 4197 (1931).
The effect of adding rosin has been in every case to increase improve the physical the rate Of cure and properties of the vulcanizate. Its beneficial effect is greatest 280
March, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
in the compounds containing magnesia, either alone or in combination with other oxides, and is particularly great in the case of compound 514 which contains the combination of zinc oxide and magnesia. That this beneficial effect of rosin is due to its interaction with the metallic oxides is shown by compound 518 which contains rosin alone, and which cures no faster and has no better physical properties than would be obtained from the polymer itself without addition of any compounding ingredient. Tests on compound 514, which is the best by far in this series, are shown in Table T’ over a range of cures from 10 to 120 minutes a t 141 O C. TESTSON COMPOUSD514 TABLEV. PHYSICAL STRE66 AT ELONGATION OF: 300% 500% 700% Kilograms per sq. em. 38.7 15.8 8.8 84.4 31.6 15.8 91.9 17.6 35.2 36.9 94.9 17.6 40.4 98.4 17.6 102 17.6 40.4 19.3 43.9 107
CURB AT
141’ C. Min. 10 20 30 45 60 90 120
TFNSILEE L O N G A T I O N STRENGTH A T B R E A K K g . / s q . em. % 160 1080
950 900 900 860 820 830
257 220 230 190 179 189
The effect of metallic oxides on this polymer may be summarized as follows: 1. Magnesia, zinc oxide, and litharge all accelerate the vulcanization of the polymer and greatly increase the stiffness of the vulcanized products. 2. This effect is much more marked in the presence of rosin or its equivalents. uivalents of rosin R-ill be discussed later under the head!?: ‘;Softeners.”) 3. The use of zinc oxide alone is impractical since it promotes vulcanization at low temperatures and hence causes scorching. This is especially true in the presence of rosin. 4. The best results are obtained by using magnesia in conjunction with zinc oxide in the presence of rosin. The combination of these two oxides has far greater effect than either of them alone.
cure and to increase greatly the stiffness of the vulcanized compounds. It has materially shortened the range of cure of the compound containing magnesia and zinc oxide (compound 538), but this effect is less marked in the case of compounds 535 and 539. However, none of these stocks can be regarded as satisfactory, and even the compounds containing magnesia, either alone or together with zinc oxide or litharge, have some tendency to scorch during mixing. When sulfur is added to compounds containing the metallic oxides plus rosin, its effect is quite different. I n the compounds containing magnesia it has practically no tendency to cause scorching on the mill. It does tend to cause scorching in the compounds containing zinc oxide or litharge alone or the combination of the two but this effect is much less marked than in the compounds containing no rosin. These facts were observed during mixing of formulas (Table VIII) which are the same as those of Table I11 excepting that 0.5 part of sulfur has been added. TABLEVIII. COMPOSITION OF COMPOWDS 542-547
Formulas were mixed and cured (Table VI) to show the effect of adding 0.5 part of sulfur to the compounds of Table I. TABLEVI. COMPOSITION OF COMPOUNDS 537-540
FKmer ZnO ig t calcined
Lig& calcined YgO ZnO Bublimed litharge Sulfur
535 100 10
... ...
0.5
536 100
... 10 ...
0.5
537 100
... ...
538 100 5 5
0.5
0:5
10
539 100 6
...
5 0.5
TABLEVII. PHYSICAL TESTSON COMPOUNDS 535, 538, AND 539 COM-
CURE AT
STRES3 A T E L O N Q A T I O N O F :
POCND
141’C.
300%
535
20 45 90
10.6 17.6 19.3
49.2 59.8 58.0
96.7 111 123
538
20 45 90
10.6
42.2
98.4
21.1
73.8
20 45 90
8.8 8.8 12.3
38.7 40.4 54.5
539
17.6
500%
66.8
700%
ELONGATENBILE T I O N AT STRENGTH BREAK 121 142 123
A00 800 700
... ...
98 4 134 94.9
700 680 560
82.6 94.9 123
82.6 149 146
700 860
760
By comparing Table VI1 with Table I1 i t will be seen that the effect of sulfur has been in each case to accelerate the
... ... 5
0.5
543 100
544 100
5 0.5
10 5 0.5
... 10 ...
... ...
645 100 5 5
546 100 5
0.5
5 0.5
...5
...6
TABLEIX. PHYSICAL TESTSON COMPOUNDS 542 COMPOUND
CCRE AT
141’ c. Min. 20 45 90
STRESS AT E L O N G A TOIFO : ~ 30070 500% 100% Kilograms p e r sq. em. 10.6 28.1 63.3 12.3 33.4 77.3 19.3 51.0 132
544
20 45 90
8.8 7.0 10.6
17.6 15.8 22.9
45.7 47.5 66.8
545
10 20 45 90 120
8.8 17.6 19.3 19.3 19.3
21.1 40.4 42.2 45.7 45.7
646
10 20 45 90 120
7.0 8.8 10.6 15.8 14.1
547
20 45 90
7.0 8.8 12.3
5 0.5
The most striking effect of the addition of this small amount of sulfur is that the compounds containing sulfur all have a marked tendency to scorch during mixing. Compound 536 scorched so badly in spite of all precautions that it was impossible to obtain satisfactory cures. Compounds 537 and 540 were almost as bad as 536 in this respect. Physical tests on the compounds containing magnesia alone and in combination with zinc oxide and litharge are shown in Table VI1 .
542 100 10
547 100
...
5 5 5 0.5
Stress-strain data on these compounds, cured a t 141’ C., are shown in Table IX. Compound 543 is omitted because, in spite of all precautions, it scorched during mixing to such a n extent as to make a physical test of little value.
540 100
...5
MgO
Sublimed litharge Rosin Sulfur
COMPOUND---
Pol mer
COMPOCNDS
r
542
EFFECTOF SULFUR
281
AND
544-547
ELONGAT E N S I L ~T I O N OF STRENGTS BREAK Ko./sq. cm. % 221 1000 190 940 169 760 98.4 176 153
900 1000 880
47.5 98.4 102.0 116 118
204 232 232 190 185
1080 920 900 840 800
14.1 19.3 29.9 36.9 36.9
28.1 47.5 68.5 91.9 102
121 181 183 227 223
1160 1030 990 930 870
14.0 15.8 24.6
36.9 47.5 68.5
120 174 162
950 960 880
Compound 542, which contains magnesia but no zinc oxide or litharge, has fairly satisfactory physical properties, but the elongation drops off relatively rapidly on the overcure (90 minutes). Compound 544, which contains litharge alone, is a rather soft and tender stock, but compounds of this type may have commercial value for such purposes as insulated wire where the presence of zinc and magnesia may be objectionable. Compound 546, containing magnesia and litharge, has fairly satisfactory physical properties and an excellent range of cure. Compound 545, containing magnesia and zinc oxide, is stiffer throughout the range of cures, has a flat curing curve, and exhibits high tensile strengths and no tendency toward reversion. Higher percentages of sulfur produce an even greater increase in the rate of cure and in the stiffness. Tests have been conducted on the compounds of Table VI11 with sulfur increased to 2.0 and further to 5.0 parts. The addition of as much as 5.0 parts of sulfur causes the elongation to drop off on overcures. Increasing the sulfur in compound 545 (Table VII) from 0.5 t o 2.0 parts causes a slight increase in the rate
Ii Y D U S T R I A L A N D E N G I X E E R I N G C H E M I ST R Y
282
of cure, the correct cure being reached between 10 and 20 minutes a t 141" C., with tensile strength of 3500 pounds per square inch and a n elongation of 900 per cent.
factice and p-coumarone resin (Cumar RH) to compound 514 (Table 11): TABLE XII. COMPOSITION OF COMPOUNDS 588, 589, 591-593, ASD
The effect of sulfur on this polymer may be summarized as follows: 1 . It has a marked tendency to cause scorching in the absence of rosin or its equivalent. 2. Even in the presence of rosin, sulfur tends to cause scorching in compounds containing no magnesia, but compounds containing sulfur in conjunction with both magnesia and rosin have hardly any tendency to scorch and can be mixed without difficulty. 3. In compounds containing no rosin, sulfur tends to cause the elongation to drop off rapidly on overcures, but in the presence of rosin, and especially in the presence of rosin plus magnesia plus zinc oxide or litharge, it does not shorten the range of cure and materially improves the strength and toughness of the vulcanizates over the entire range of cures.
EFFECT OF SOFTESERS The formulas shown in Table X were mixed and cured to show the effect of certain pine products commonly used in rubber compounding. COMPOCND Pol mer LigKt calcined X g O ZnO Rosin oil Medium pine tar Rosin Pine oil
Polymer Light calcined SlgO ZnO Rosin Brown factice p-Coumarone Sulfur
CCRE AT
141'C.
Mi%
... ...
7
592
593
100
100
: ...
2 ...
...
...
5
...
0.5
5
5
20
595 100 5 5 5
...
20 0.5
Compounds 591 and 595 should be compared with compound 545 (Table VIII). Stress-strain data on these compounds are shown in Table XIII. TABLEXIII. PHYSICAL TESTSos COMPOUNDS 588,589, 591593, AND 595 COM-
CURE AT
POUND
141OC.
588
.Win. 20 45 90
ELOSO~-
STRESSAT ELONGATIOK OF: T E X ~ I L ET I O N A T 300% 500% 700% STRENGTHBREAK .. .Kiloyrams per sq. cm. Kg./sq. cm. % 12.3 33.4 75.6 229 960 17.6 45.7 109 22 1 880 19.3 45.7 112 195 850
589
20 45 90
15.8 21.1 22.9
35.2 49.2 52.7
75.6 116 134
186 163 158
960 790 740
59 1
20 45 90
17.6 22.9 22.9
38.7 52.7 59.8
84.4 121
...
170 162 135
880 780 690
592
... ...
... . .5.
20 45 90
12.3 14.1 14.1
28.1 33.4 35.2
70.3 86.1 86.1
216 216 213
980 920 910
5
593
20 45 90
5.3 10.6 10.6
17.6 24.6 24.6
38.7 54.5 54.5
165 193 167
1080 1000 970
595
20 45 90
8 8 10 6 10 6
19.3 24.6 26.4
45.7 56.3 61.5
206 197 193
1130 1000 980
... ... ...
...
PINETAR
ROSINOIL
68.0 53.4 68.2 1.0341
52.7 10.8 63.6 0.9655
TABLEXI. PHYSICAL TESTSON COMPOUNDS 582-585 Coai-
... ...
591 100 5 5 5 20
585 100 5 5
Stress-strain data on these compounds after curing a t 141" C. are shown in Table XI.
POUND
5
589 100 5 5 5 20
584 100 5 5
The rosin oil and pine tar used for these tests analyzed as follows: Acid number Saponification value Iodine number Specific gravity at 25O C.
588 100 5 5 5
583 100 5 5
...5
... ... ...
595
COMPOUND-
TABLEX. COMPOSITION OF COMPOUNDS 582-585 582 100 5 5 5
5-01. 25, No. 3
ELONGA-
STRESSA T ELONGATION OF: TESSILE TION AT 300% 500% 700% STRESGTH BRE.AK Kzlograms per sq. cm. Kg./sq. cm. % 7.0 21.1 45.7 151 1080 12.3 31.6 73.8 179 930 17.6 45.7 112 162 800
582
20 45 90
583
20 45 90
7.0 14.0 19.3
22.8 43.9 52.7
52.7 96.7 118
137 185 155
1000 890 780
584
20 45 90
15.8 17.6 17.6
31.6 36.9 40.4
84.4 94.9 102
237 230 179
950 900 820
These tests show that rosin oil materially increases the rate of cure and stiffness of the cured stocks. Pine tar has a similar but somewhat greater effect. Rosin still further increases the stiffness and rate of cure, whereas pine oil has no appreciable effect. Further tests, not reported in detail in this paper, have shown that turpentine and other pine products, consisting largely of terpenes, have, like pine oil, little or no effect. However, abietic and certain other aromatic acids are, like rosin, powerful accelerators and stiffeners. On the other hand, stearic and other fatty acids have little or no effect.
EFFECTOF FACTICE AND CUMAR RESIX The formulas shown in Table XI1 were mixed and cured to show the effect of adding various proportions of brown
Comparisons of these tests with those on compound 514 (Table IT') and with the tests on compound 545 (Table IX) show that brown factice has but little effect on the rate of cure, with a slight tendency toward acceleration. Similar compounds containing white factice were also run but are not reported here since the results were substantially the same, excepting that white factice has slightly greater accelerating effect. The addition of 0.5 part of sulfur to the compound containing 20 parts of brown factice (compound 591) increases the rate of cure to about the extent that would be expected from the effect of sulfur in the absence of factice. Coumarone resin has a distinct softening effect but does not retard the cure even when used to the extent of 20 per cent based on the weight of the polymer. Coumarone has the effect of increasing the elongation and preventing the elongation from dropping off on overcures. The addition of 0.5 part of sulfur had but little effect on the rate of cure of the compound containing 20 parts of coumarone. I n spite of their high elongations the coumarone compounds have quick recovery from extension and low permanent set. Coumarone is a valuable compounding ingredient for this polymer since it increases the tackiness of the uncured stocks. Factice has the opposite effect, and for this reason it should prove to be beneficial to use these two ingredients in combination with each other. Further tests on the effect of adding coumarone, factice, and other organic fillers, in combination v i t h one another, to chloroprene polymers n-ill be reported in a subsequent paper. SUMMARY
These tests h a r e clearly shovn the desirability of compounding this polymer with zinc oxide, magnesia, and rosin, and h a r e demonstrated that these three ingredients when used together have a desirable effect that cannot be obtained with, or even predicted from, the results obtained with any
March, 1933
Ii Y D U S T R I A L A I\; D E N G I
one of them alone or the combination of any t\vo of them. It has been shown further that, although it is possible to obtain good vulcanized products from this polymer Tvithout the addition of sulfur, a great increase in the rate of cure and substantial improvement in physical properties of vulcanized from the use Of as little as O'' per cent Of products It is further shoWn that Of the polymer' On the pine tar and rosin oil may be substituted for rosin but that
N E E R I N G C H E M I ST R Y
283
they are somewhat less efficacious. The authors postulate that the value of rosin, pine tar, and rosin oil is probably due to the organic acids that they contain. Coumarone resin and brown factice are shoivn to be desirable compounding ingredients for chloroprene polymers. RECEIVEDAugust 29, 1932. Presented before the Dlvlsion of Rubber Chemistry a t the 84th Meeting of t h e .$mencan Chemical Society, Denver, cola, August 22 to 26, 1932.
Flow of Paper Pulps in Pipe Lines C. A. BRAUTLECHT AKD J. R. SETHI,University of Maine, Orono, hle. facilities for determining data U R I S G the rapid dePower required as a ,factor due to friction in i n v o l v i n g w a t e r and fluids. velopment of pulp and the pumping of paper p u l p s has been studied o n Usually, however, the equippaper mills of ever ina small scale experimentally. Power consumpm e n t f o r agitating pulps in creasing size, the need of pumption in p u m p i n g cellulose (screened unbleached s u s p e n s i o n , s h r e d d i n g , or ing and flow of pulp has been suljite p u l p ) in dilute suspensions through a breaking up pulps obtained as one of the most important facsheets or pressed laps, etc., is tors. Cost of capital invested, &inch centrifugal p u m p and varying lengths of not available. I n addition, the equipment , economy of operaone-inch p i p e have been determined. Seventeen i n t r o d u c t i o n of pulps i n t o tion in a highly competitive intests have been made with inrialions in concentanks, pipe lines, pumps, and dustry, and maintenance have tration of suspension, length of pipe line, and v a l v e s i n v o l v e s considerable led to an effort to select motors, introduction of ,fittings. Power required to lift cleaning costs or other difficulpumps, pipe lines, and storage ties. tanks of sufficient capacity, but one pound of water or p u l p suspensions, up to One objective of this simple w i t h o u t too large excess and 1.57 per cent concentration, per minute per 100 e x p e r i m e n t a l s t u d y was to corresponding waste in pome r feet is the same; rate of discharge into a weighing and in operation and maintestimulate l a r ge-s c a1 e studies box falls quite rapidly with a n increase in length o n t h e p a r t of organizations nance expense. Thus, engineerof pipe; with concentration constanf, increase in supplied mi t h the n e c e s s a r y ing data have been often sought without much of value b e i n g equipment, funds, etc., so that rate of floto increases velocity head and is proeventually complete data would found. Of the many types of reportional to the square of the velocity; friction be available for the h a n d l i n g ciprocating, rotary, and centrifuhead increases with rate o j discharge, which of suspensions of groundwood, gal pumps, the plunger, openraries with p i p e length; total actual effective impeller volute centrifugal, and sulfite, soda, kraft, a n d o t h e r head increases with increase in velocity; amount pulps in all commercial concenrotary pumps of the Sash type, are most used in the pulp industrations and for all pump and of power increases with rate of discharge; inpipe sizes. try. Conversation and c o r r e creased p i p e length decreases celocity of jlow in spondence with engineers having Scientific data wi!l be more in feet per second; and total actual head decreases to do with pulp mill design have demand in transporting paper with increased p i p e length because of the rapid indicated that little information pulps in the future because the decrease in celocily and velocity head. was available and that hydraulic "slush system" of moving pulp data were commonly employed in water suspension from pulp in connection with comtmtations to paper m i l l s i n v o l v e s : (I) or design for the pumping and flow of dilute suspensions decreased labor; (2) decreased waste, due to making laps, of pulp. The literature comprises only a few articles in rolls, sheets, or bales, and to transportation and the subsejournals and published data of pump manufacturers (4). quent resuspension of the cellulose; (3) decreased heat; Some companies pump pulps a considerable distance. and (4) decreased power. Every pulp mill using new wood The Fraser Company produces pulp in Canada and pumps it pulp logically should be associated with a paper mill, except across the St. John River to its paper mill in the IJnited States where a paper mill is in an old established locality where lorn a t Madawaska, hle. The Webster mill of the International taxes prevail, and where tariffs, embargoes, markets, pulp Paper Company involves the production of groundwood pulp costs, transportation, etc., do not act adversely. Pulp on one side of the Stillmater River, a t Orono, Me., and pumps mills with favorably situated timber holdings, or located a t it a t about 4 per cent concentration one-fifth of B mile to the the head or on navigable tidewater with rail facilities, will paper mill on the other side of the river. I n the control of always have a trade advantage with a n associated paper mill water power it is desirable for a pulp and paper company to a t the same location. own its dam and the property adjacent to the clam on both OBJECTOF STUDY sides of the river. This leads often to a consideration of a pulp mill on one side of a river and a paper mill on the other The chief objective of this study was to investigate some side, with the problem of a pulp pipe line to be solved. I n of the factors involved in pumping unbleached sulfite pulp many of the new large mills paper machines are also frequently through various lengths of pipe lines and also the effect of a a considerable distance from pulp grinders, screens, bleach few fittings. tanks, etc. (2, 7-9). The laws of flow of mater in pipe lines may be summarized hlany hydraulic laboratories throughout the world have as follows (5):
D
