SYNTHETIC RUBBER AND
ROLLAND WASHBELTUSEDIN FIGURE 1. FREBZE
THE
SEMIWORKS DEVELOPMENT
Plasticization of Neoprene Type G HOWARD W. STARKWEATHER AND MORTIMER A. YOUKER 1
E. I. du Pont de Nemours & Company, Inc., Wilmington, Del.
HE fact that natural rubber can be converted from a tough, essentially elastic, nonplastic form to a soft plastic material by mechanical working in the presence of air is well known to every one who has handled rubber. Earlier forms of synthetic rubberlike materials have not been comparable to natural rubber in this respect. In fact, some of them are actually rendered less plastic by prolonged milling. By polymerizing purified chloroprene in emulsion under carefully controlled conditions, it is possible to convert it into a type of neoprene which more closely resembles natural rubber in its ability to be plasticized, as well as in other respects. This Neoprene Type G is not an interpolymer or copolymer but is made without the use of other polymerizable materials. This discovery is of considerable commercial importance,
T
1
1 The group of papers on pages 934 t o 968 were presented before the Division of Rubber Chemistry a t t h e 97th Meeting of t h e Amerioan Chemioal Society, Baltimore, Md.
since it now becomes possible to make a synthetic material which can be handled in a manner similar to that used in processing smoked sheet or pale crepe. This product can be plasticized to almost any desired degree by the manufacturers of rubber goods. From the viewpoint of the production of a synthetic rubberlike material, this is also a decided advantage. The fact that polymerization occurs in emulsion simplifies the problem of temperature control and makes an entirely continuous process more practical. It has been found possible to polymerize continuously chloroprene in emulsion and to coagulate the polymerized emulsion by freezing on a rotating chilled drum. The continuous thin film formed in this way can be removed by means of a “doctor knife,” washed with water or other liquids on a moving belt, and dried by passage through an oven of suitable design. This passage through an oven serves to remove not only water, but also volatile polymers and other odoriferous materials. A product which can be thus formed in a thin tough sheet readily lends itself to this thorough washing and drying. A freeze 934
ELASTIC POL tion is appreciably more rapid in the presence of water on a suitable wash mill. Williams (4) and his eo-workers have found a number of chemicals which will accelerate the plasticization or peptization of natural rubber. It has also been found possible to accelerate the plasticization of Neoprene Type G by the addition of a number of different chemicals during milling. Materials which have a definite alkaline reaction are especially effective. Magnesia used as a compounding ingredient renders the neoprene more plastic. Starkweather and Wagner (2) have found that the cements made from Neoprene Type G containing magnesia are less viscous than corresponding cements made from the uncompounded neoprene, even when the neoprene has been plasticized by milling. Sodium hydroxide or even ammonia will have a similar effect, although the stronger sodium hydroxide may unfavorably influence the stability of the product. Data obtained with a number of different alkaline materials, milled 10 minutes on a 50" C. mill, are given in Table I. There appears to be a definite relation between the ionization constant of the chemical and its effectiveness as a plasticizing agent. I n general, the compounds with an ionization constant greater than 1 x 10-6 are the more effective. In many cases the neoprene is more plastic after 24-hour aging than it was when first treated. This initial softening may be followed by a decrease in plasticity upon longer aging. The rate of this change is greatly influenced by temperature and the type of plasticizing agent. The data indicate that the plasticized material can be kept for many weeks or months a t room temperature before it becomes nonplastic, although it can still be cured by suitable compounding and heating to elevated temperatures. The addition of materials such as piperidine and ethylenediamine, which are the most rapid plasticizing agents, results in the least stable product. The
Neoprene Type G, made by the polymerization of chloroprene in emulsion under carefully controlled conditions, can be plasticized to any desired degree by milling, especially under water, or by means of suitable chemicals. Alkaline materials such as di-o-tolylguanidine are especially effective plasticizing agents. Data are presented on the degree of plasticization and the stability with various amounts of the agents. A considerable number of chemicals commonly used in the rubber industry are effective plasticizing agents, but a few of them have a deleterious influence on some of the properties of the cured neoprene. The use of the guanidines, especially di-o-tolylguanidine, is recommended. Data obtained with two different modifications of this type of neoprene are shown. The more readily plasticized, Neoprene GCX, is recommended for water plasticization or for chemical plasticization when an especially plastic material is desired. Neoprene GCR can readily be softened chemically to the range of plasticity which is desirable for many practical processes.
roll and wash belt used in the semiworks development are shown in operation in Figure 1. Figure 2 shows the exit end of a continuous semiworks drying oven with one section of the side wall removed.
EARLY in the development of Il'eoprene Type G, it was found possible to isolate polymers which were essentially nonplastic but which could be converted into plastic usable material by milling on a laboratory mill, especially in the presence of water. For example, an early charge milled 20 minutes on a 12-inch laboratory mill had a plasticityrecovery of 178-81. A similar sample which had first been milled under water for 15 minutes on a laboratory 12-inch wash mill had a plasticity-recovery of 84-2. The plasticity-recovery numbers in 0.001 inch were determined a t 80" C. on a 2-cc. pellet with the Williams parallel plate plastometer (3). Although it is possible to plasticize this type of neoprene by dry milling, especially on a cold mill, the rate of plasticiza-
FIQTJRE 2. EXITENDOF 935
A
CONTINUOUS SEMIWORKS DRYING OVEN
160160 -
100
TABLEI. INFLUENCE OF ALKALINE MATERIALS ON PLASTICITY-RECOVERY OF NEOPRENE TYPEG" -Plasticity-RecoveryIonization Parts per aged at 70' Constant, 100 Parts --Hr. K8, at 25' C . Neoprene 0 24 ,~ 180-82 ...... 156191 156-31 ...... 1 .'O 127-95 85-1 1 . 2 x 10-8 0.5 1 18-47 115-6 1 x 10-3 0.5 100-0 4 . 4 x 10-4 108-6 0.25 147-22 105-3 0.19 4 . 4 x 10-4 124-7 102-4 ...... 0.35 114-2 95-5 8 . 6 X 10-6 0 36 95-1 0.5 4058 . 5 X 10-5 138-12 117-15 0.25 0 . 1 x lo-: 110-1 1 131-8 0.41 113-2 112-4 0.82 130-12 112-3 4 . 7 x 10-5 0.46 132-46 ...... 100-2 0.52 139-19 ...... 100-6 0.41 141-22 ...... 98-2 0.58 131-82 1 . 7 X 10-8 152-73 0.5 142-24 117-39 ...... 1.0 154-24 106-6 0.2 7 . 6 x 10-7 7 x 10-7 0.5 158-35 119-20 152-18 0.5 1 . 2 x 10-8 170-144 i 5 i - i o 9 1 . 4 X 10-8 0.5 ...... 144-95 162-91 0.5 158-117 123-59 0.5 177-148 151-109 0.5
Di-o-tolylguanidine Oleylamine Dimethyllorolamine Dimethylstearylamine Quinine Diethanolamine Brucine p-Phenylenediamine Pyridine a-Piooline a-Aminopyridine Dibenzylaniline
......
......
Aged 5 weeks at28'C.
C.48
.
Agent None MgO Piperidine Diethylamine Dibutylamine Cyclohexylamine Dioyolohexylamine Tributylamine Ethylenediamine Diphenylguanidine
Q
VOL. 31, NO. 8
INDUSTRIAL AND ENGINEERING CHEMISTRY
936
igO1i30 205166-165 135-90 160-132 130-75 133-87 i3Ki25 150-140 183-80 144-142 225-189 118-49 119-49 177-178 164-162 145-99 139-109 15iGi49 185-144 148-155 150-132
\\
-
6 140 3 130 > 120 -
eg 110" -
I . .
92-0 102-1 95-0 95-0
y 100 :-:
90-
...
0
5 60-
... ... ... .
\
4 n
.. .. .. ...
I
170
2 70-
.
40 eo
99-0 91-6 95-0
60
...
-
30-
10411
... ... ...
eo 10
...
...
PLASTICITY
_------_PLASTICITY+ RECOVERY
-
I
1
I
0.6
1.0
2.0
4.0
Many of these results were obtained by H. W. Walker.
plasticizing action in these cases is apparently due to the free amines since the hydrobromides or hydrochlorides of several of these amines, such as dibutylamine, cyclohexylamine, and dicyclohexylamine, had little or no plasticizing action.
In case the neoprene is to be plasticized by mastication in the presence of water, it is more practical to use Neoprene Type GCX. Data for plasticity and recovery plotted against time of milling are shown in Figure 4 (data obtained in Neoprene Plant under the direction of N. C. Somers). The results are to be considered only approximate since they vary greatly with the type of mill, the size of the batch, the temperature of the mill, and the temperature of the water. I n this case 100-pound batches were run on a two-roll wash mill, having a smooth front and a corrugated back roll each 60 inches long and 20 inches in diameter, and running a t a surface speed ratio of 1 to 1.33. The temperature of the water was about 40" C. a t the start of the milling but was lowered to 20 O C. towards the end of the milling. The samples were dried by running a few minutes on this mill without water and then milled to dryness on a smooth mill. Since, with experience, the operator soon becomes able to judge the plasticity of the neoprene from its appearance on the wash mill, there is less
BY SUITABLE control of the polymerization it is possible to vary the ease with which the product can be plasticized. Data obtained with two modifications of Neoprene Type G are shown in Figure 3. Both of these samples were milled with varying amounts of di-o-tolylguanidine for 10 minutes on a 6 x 12 inch laboratory mill, the rolls of which were heated with water circulating a t 50" C. The plasticityrecovery numbers are for samples aged 48 hours a t room temperature. It is apparent that Neoprene GCX (Commercial n'eoprene Type G that is prepared to be softened by water washing) is more readily plasticized than Neoprene GCR (Neoprene Type G that is prepared to be softened by chemical plasticization) ; but there is also considerable danger of over-plasticization to a material which is too soft and tacky for practical use.
170
160
I60
-
I
I
I
I
130 -
',i I
I
I
I
I
I
I
I
-* 0-----0
&.-A
ORIQINAL AQEO 24 HRS. AT 50OC. AGCO 4 0 HRS. AT SO'C.
200
140 Y
; 120a
=> 110 B 100
-
a
;6 0 -
I-
5
70-
f
00-
1801
50-
40
-
200
2o --
-
30
PLASTICITY
160
PLASTICITY t RECOVERY
I-----
1401
10
I
I
,
,
I
I
I
I
,
I
I
I
,
@ \
..-- -.-
I20 loo
Om260.6
1.0
---_ ...... c
os
I
1 4
2
U OOTQ
FIGURE 5. INFLUENCE OF DIBUTYLAMINE, BARAK, AND DI-0-TOLYLGUANIDIN ON PLASTICITYRECOVERY OF NEOPRENE GCR (MILLED 10 MIN.AT 50 C.)
+
O
INDUSTRIAL AND ENGINEERING CHEMISTRY
AUGUST, 1939
NEOPRENE GCX
937
Neoprene Extra light calcined magnesia Semireinforcine carbon blacka Zinc oxide Gastex was used.
100 7 28.8 5
I
0
COMPOUNDED
The influence on Neoprene Type GCR of three different plasticizing agents used in approximately equimolecular quantities is shown UNCOMPOUNDED 5o in Figure 5. The dibutylamine was added 111 I Ill I 111 1: I I Ill Ill 250n as a 25 per cent solution by weight in a light 200 mineral oil. "Barak" (dibutylamine oleate) ,50 NEOPRENE GCR has the advantage that it also reduces the 100 COMPOUNDED *t 5 0 tackiness of softened neoprene, which may 0 assist the processing of the more plastic samG If 2 0 0 ples. Since di-o-tolylguanidine is a solid, it n 150 is somewhat easier to add on the mill and UNCOMPOUNDED is less apt to be lost by volatilization during milling. There is a marked difference in the 25 0.5 I 2 0.5 I 2 4 rate at which the three materials act. Di% DIBUTYL AMINE % DI-ORTHO-TOLYLGUANIDINE butylamine acts much more rapidly than di-oFIGURE6. INFLUENCE OF DIBUTYLAMINE AND DI-0-TOLYLGUANIDINE ON tolylguanidine, and the effect is apparent PLASTICITY RECOVERY AND STABILITY OF NEOPRENE TYPEG , AGED0, within a few minutes. Barak is interme24, 48, 96, AND 120 HOURSAT 50" C. diate between the other two materials in this rate of action. If the sample is removed from the mill as soon as the di-o-tolylguanidine has been thorTABLE11. WATER-PLASTICIZED NEOPRENE GCX oughly incorporated, it will still appear decidedly tough; Time Water-Milled but if after standing for a few hours at room temperature it Time Aged at 70' C. 0 min. 30 min. 90 min. is replaced on the mill, it will be found to be much more plastic. HOUTE The initial plasticity data given in this report were obtained Plasticity-Recovery 0 309 91-7 58-3 on pellets which had been aged for one day at room tempera48 ... 100-5 63-2 ture, unless otherwise stated. In one case in which 1 per ... 96 101-7 65-1 cent di-o-tolylguanidine was added and the sample milled Modulus (300Y0), Lb. per Sq. In. Time Cured at 141' C. for 15 minutes, the plasticity-recovery determined within 20 Min. minutes was 151-114; after 2 hours at room temperature it 7 ... 400 425 had dropped to 120-22 and after 3 days a t room temperature, 15 ... 925 1000 30 ... 1125 1175 to 110-9. Since the compounded stocks plasticized with Tensile Strength, Lb. per Sq. In. Barak were less stable than those containing dibutylamine 7 ... 1150 1300 15 ... 2275 2300 or di-o-tolylguanidine, its use has not been generally recom30 ... 2450 2475 mended. Per Cent Elongation at Break
B
200
100 -
IllI
Ill
'
+
7 15 30
...
600 800 680
...
...
danger of overplasticizing Neoprene Type GCX by this method of softening than when chemical agents are used. The tensile properties of the compounded and cured stocks, made from the GCX plasticized to a plasticity-recovery of 58-3, were almost identical with those obtained with the sample plasticized to only 91-7, as Table 11shows. For the purpose of this investigation, stocks were compounded with twenty volumes of a semireinforcing carbon black. This amount of carbon black was not sufficient to obscure variations in the samples of neoprene, but the results were more practical than those obtained with a gum stock. The compounding formula used throughout this report was as follows :
800 760 700
RESULTS obtained with varying amounts of dibutylamine and di-o-tolylguanidine with both Neoprene Types GCR
TABLE111. PHYSICAL TESTDATAON CHEMICALLY PLASTICIZED KEOPRENETYPEG Dibuty1amine:a
$ D!-q-tolylguanidine: : Plasticity-recovery :
-Neoprene 0.25
,...
2
Type GCR-
....
....
....
Min. Cure,at 141' C. 10 30 60
1125 1275
10 30 60
2975' 3075
Tensile Streneth. Lb. aer Sa. In. 2650 2925 3225 3000 3100 3200 2950 3175 3125 3125 3000
10
.. . .
1
1
1
-
.
,...
1350 1325
675 950 1075
1125 1300
1000 1275 1275
2275 2425 2475
2950 2950
2900 2875 2825
620' 560
750 600 550
Hardness (Shore Durometer TvDe A) 51 55 57 .. 55 60 59 62 60 60 65 58
54 59 61
10
....
30
52
30
Absorption in 48 Hr. at 100' C., Vol. Per Cent Water 12.6 13.0 13.2 8.7 16.5
30
Kerosene 69
70
__
Per Cent Rebound (Sohopper) 52 51 46
58
011.
....
4 64-4
.. ..
~~
Per Cent Elongation at Break 810 870 640 660 610 620 630 580 600
Added as a 2 5 per cent solution in light mineral
....
0.5 92-5
1125' 1350
~
1100
Type GCX-
61-3
620' 550
60 61
2
....
96-5
30 60
30 60
a
141-34
4 105-6 Der S o . In.
-Neoprene 0.25
0.5 92-8 150-65 Modulus 300%. Lb. 625 750 1000 1176 1175 1375
0
57
48
68
640 ' 560
. ..
640 600 550
61 62
60 62 62
48
47.5
40.5
18.3
18.4
14.1
57
67
56
e
INDUSTRIAL AND ENGINEERING CHEMISTRY
938
VOL. 31, NO. 8
in the range of plasticity which is practical for the manufacKEROSENE 30 ture of molded goods IO or other articles that 800 are processed by ex%ELONGATION AT BREAK trusion or calendering. Data on cured slabs of samples with the STRESS&T300% Ieast and largest TENSILE STRENGTH amounts of chemical (WHOLE COLUMN) plasticizers are given LBS. PER sa. IN. CURE: 10,30 6 0 in Table 111. These MIN. AT 14IdC. results indicate that di-o-tolylguanidine acPLASTICITY-250celerates the rate of RECOVERY -I3 200COMPOUNDED 160 cure and that the use STOCK of the larger amounts AGED O,24,48HRS. loo50 AT 5OOC. lowers the swelling in PLASTICITY- I150solvents but somewhat RECOVERY - 0 decreases the resiliency UNCOMPOUNDED NEOPRENE of the cured stocks. AGE0 0 , 2 4 , 4 8 , 9 6 Data obtained with HRS. AT 5OOC. a considerable number d +i of different rubber ac0 d celerators are shown in Figures 7 and 8. In each case a 300gram sample of NeoOF VARIOUS RUBBER CHEMICALS ON PROPERTIES OF NEOPRENE GCR FIGURE 7. INFLUENCE prene GCR was milled for 10 minutes on a 6 X 12 inch laboratory mill; the rolls of this mill CHEMICALS AS PLASTICIZERS FOR NEOPRENE were heated with water circulating at 50°C. TABLE IV. RUBBER The agents TYPEG“ being tested were added as rapidly as possible. Four parts Active Less Active of the agent per 100 parts of neoprene were used in all exA-1 1 A-5-10 amples, except the first in Figure 6 in which 2 parts of di-oA-77 “Accelerator 808” tolylguanidine were used. It is apparent that many of the “Accelerator 49” “Accelerator 833” % VOL. INCREASE; 48 WRS. AT I00”C. WATER
#-111
“Accelerator 552” “Acrin” “Antox” “Barak” Captax
C-P-B
Age Rite resin Age Rite sirup Age Rite white Albason Aldehyde ammonia Altax
BLE BXA Flectol B Flectol H Formaldehyde resin Hexa Novex ‘ ‘Permalux” “RPA #1” ‘ ‘Solux” “Tetrone A” Thiocarbanilide ‘‘Thionex” Triphenylguanidine Trimene base Tuads Zimate O Chemical compositions are given in “Compounding Ingredients for Rubber” (1). D-E-A Di-Esterex Diphenylguanidine Di-o-tolylguanidine E. A. Hepteen base Ovac Phenex “RPA #2” “R & H 50 D” “RPA #3” Ureka “Vulcanex” “Vulcone” “X-872” (when heated)
and GCX are shown in Figure 6. The difference in the ease of plasticization of the two modifications is apparent. Here again, the materials which were plasticized least tended to become more plastic upon compounding or upon storage, whereas the samples which were plasticized to the greatest extent tended to become less plastic upon aging a t elevated temperatures. All of these samples were stable for several months at room temperature. The sample of Neoprene GCR that was softened with 2 per cent di-o-tolylguanidine is I
Y
.
PLASTICITY- I 250
PLASTICITY- I RECOVERY - 0 UNCOMPOUNDED 100 NEOPRENE 50 AGED 0.24,48,96 HRS.AT 5@C. N
!&g
$
;
7
1
#
0
x
p
”
a
u
d.z22gpat;r“ U : r T K U + : U O
C
U
P
o
0: I w I-
OF VARIOUS RUBBER CHEMICALS ON FIGURE 8. INFLUENCE PROPERTIES OF NEOPRENE GCR
INDUSTRIAL AND ENGINEERING CHEMISTRY
AUGUST, 1939
accelerators, especially of the aldehyde amine and mercaptan classes, are effective plasticizing agents. Several of the materials are as effective as the guanidines as plasticizers but give somewhat slower curing stocks. Most of the samples for the 30-minute cure had a Shore Durometer Type A hardness of 58-60. Several common rubber chemicals are classified according to their action as chemical plasticizers of Neoprene Type G in Table IV. This classification is only approximate, since there are appreciable variations in effectiveness among the different members of each class. The data show that Neoprene Type GCX may be plasticized to a greater extent than Neoprene Type GCR by either water washing or chemical means. Advantage of this is taken in the preparation of soft neoprene for the manufacture of sponge and in the compounding of soft raw mixes of ex-
939
cellent flow characteristics, where permanent softness such as results from the use of oils, factice, etc., cannot be tolerated. In certain cases it is advantageous to combine chemical plasticization with softening by water washing. For example, the time required to soften Neoprene Type GCR by water washing may be materially shortened by use of a small aniount of chemical agent.
Literature Cited (1) “Compounding Ingredients for Rubber,” New York, Bill Bros. Publishing Corp., 1936. (2) Starkweather and Wagner, IND.EXG.CHEM.,31, 961 (1939). (3) Williams, IND.ENQ.CHEM., 16, 362 (1924). (4) Williams and Smith, U. 5.Patents 2,018,643-4 (1935); 2,064,580 (1936); 2,132,505 (1938). CONTRIBUTION No. 41 from Jackson Laboratory, E. I. du Pont de Nemours & Company, Ino.
Effect of Modifying Agents on Vulcanized Neoprene Compounds The term “modifying agent” is used to designate materials which in rubber are normally considered as activators, accelerators, or vulcanizing agents. Their effect on the modulus, tensile strength, resistance to tear, hysteresis properties, and rate of cure in a neoprene tread type of compound are discussed. Included in the list of materials tested are various concentrations of catechol, @-naphthoquinone, Captax, triethanolamine, di-o-tolylguanidine, butyraldehyde monobutylamine condensate, zinc chloride, sulfur, and stearic acid.
-
T
HE term “modifying agent” is used to designate ingredients which when added to neoprene compounds before vulcanization change the rate of cure or alter the physical properties of the vulcanizate. In rubber technology, compounding ingredients having such effects would be termed accelerators, activators, retarders, or vulcanizing agents. The use of such specific terms has been avoided because it is not certain how the materials investigated should be classified. The effects of various modifying agents on the properties of Keoprene Type GW vulcanizates were studied in the following formula : Neoprene Type GW Extra light calcined magnesia Channel black Cottonseed oil Zino oxide
100 4 36 3 5
Modifying agents (some of which are shown in Table I) were added in varying amounts to this compound. Stress-strain properties were determined on a standard Scott tensile testing machine using dumbbell test specimens
MAYNARD F. TORRENCE AND DONALD F. FRASER Organic Chemicals Department, Rubber Chemicals Division, E. I. du Pont de Nemours L Company, Inc., Wilrnington, Del. (Die C, A. 8. T. M. Designation D412-36T) died from slabs, 3 X 6 x 0.085 inch in size, which had been press-cured 30, 45, 70, and 90 minutes a t 130.5’ C. (267’ F.). Tear resistance was determined by the Winkelmann method (3) with the ends of the test specimens modified to fit the ’ grips of a Scott testing machine. Heat build-up tests were run on a Goodrich Flexometer ( 2 ); a stroke of 0.125 inch, a load on the sample of 155pounds per square inch, and a frequency of 1800 cycles per minute were used on cylindrical pellets 0.75 inch in diameter and 1.00 inch high, press-cured 60, 90, 120, and 180 minutes at 130.5’ C. The results of these tests are shown by curves in Figure 1. Resistance to flex cracking was determined on a du Pont flexing machine (A. S. T. M. Designation D430-35T, Method C). It was found that all the neoprene vulcanizates tested had a resistance to flex cracking approximately ten times that of the best rubber vulcanizates of a tire tread type. In the interests of brevity the results of these tests are not reported. The results of the stress-strain and tear tests are shown in Table I. To show more clearly the effects of the modifying agents, the base neoprene compound contains 4 parts by weight (on 100 parts of neoprene by weight) of extra light calcined magnesia, rather than the 7 parts generally recommended in Neoprene Type GW compounds. The base compound contains 20 volumes of channel black per 100 parts by weight of neoprene (16 volumes channel black per 100 volumes of neoprene). The effects on the neoprene vulcanizate of various amines, including hexamethylenetetramine, triethanolamine, di-
