Vulcanization 0%. utvl Ru ber with uinonedioxime a erivatives J
J. P. HAWORTH Standard Oil Development Company, Elizabeth, N. J . DISCUS SIQS
T h e compound p-quinonedioxime has been found to be an extremely active vulcanizing agent for Butyl synthetic rubber polymers in the presence of an oxidizing agent. The vulcanizing activity is the result of the oxidation of the p-quinonedioxime to p-dinitrosobenzene, this latter substance being the active vulcanizing agent. The activity of p-quinonedioxime can be aItered appreciably by being esterified with an aromatic acid, such as benzoic acid. The vulcanizates resulting from the described reaction are useful where extreme heat resistance is required and in applications where the extremely rapid vulcanization of some of the compounds can be utilized.
.
IIE term vulcanization is applied to any process whereby raw rubberlike materials are converted from a plastic, highly extensible mass t o a strong nonplastic product with good elasticity. The discovery by Charles Goodyear that rubber could be vulcanized by sulfur marked the beginning of the use of natural rubber in ever-.ividening channels. However, until the discovery by Ostromislensky (9) t h a t rubber could be vulcanized by polynitro derivatives of benzene, no other means for its vulcanization than Rith sulfur or sulfur chloride had been found. I t mas only natural, thercfore, when Butyl synthetic rubber v a s discovered, that sulfur should be tried as a vulcanizing agent. When comparing Butyl synthetic rubber ipith natural rubber, one of the major differences found is in the lower chemical reactivity v i t h sulfur in the presence of accelerators. This results, as would be expected, in a slower rate of vulcanization. While not slom enough t o prevent its use in practical applications, i t m-ould be desirable t o improve this rate. I n the course of studies on methods of vulcanization, it was found that Butyl synthetic rubber is rapidly vulcanizcd, in the presence of oxidizing agents, by nitrogen-containing derivatives of quinone (6),such as quinonedioxime and its esters. Previous work (3) had shown t h a t certain of these compounds would vulcanize natural rubber also.
TABLE 1,
The first chemical compound found in the laboratory to give vulcanization in Butyl synthetic rubber was p-quinonedioxime (known in the trade as GRIF). This, and a considerable portion of subsequent work being reported, was carried out with a Butyl synthetic rubber prepared by low temperature copolymerization of isobutylene with a small proportion of isoprcne ( 1 1 ) . This product had a viscosity-average molecular weight of approximately 450,000, and a diolefin content of about 0.6 mole yo (10) of the structural units. Since it was of extreme interest to know what sort of physical properties resulted from this type of vulcanization, it was characterized by comparison 1% ith a compound vulcanized by means of sulfur and accelerator. This comparison \%illbe found in Table I. From these data, it is immcdiately obvious that the rate of vulcanination obtained with p-quinonediovime in the presence of an oxidizing agent (lead dioxide) is very much faster than .irith sulfur and tetramethylthiuram disulfide. I n addition, a stock of verj much higher modulus having improved hysteresis properties results. It is of interest t o discuss the poqsible mechanieni of the reaction or reactions involved in this vulcanization process. It was found t h a t n hen vulcanization with p-quinonedioxime was carlied out in the presence of a channel type carbon black, an oxidation agent was not needed. This is shown by the data presented in Table 11. I n the range of coiicentrations tested, there is apparently no difference to be noted. If, on the other hand, a furnace black or a mineral filler is used, the evidence indicates that little or no vulcanization occurs as the result of the application of heat. The products resulting from this treatment are characterized by the absence of tensile strength and by the ability f o be dissolved by hydrocarbons. I n order t o cause the vulcanization reaction to proceed in this case, it has been necessary to use an oxidizing agent such as lead dioxide. The channel type carbon blacks have present on the particle surface some oxygen, probably in the form of peroxides, as opposed to the absence of such material in the furnace blacks and mineral fillers.
COXlPARIsOX O F SULFUR WITH p - ~ U I S O S C D I O X I > f E\'ULCASlz.4TION
Compound No. 9-7
Compound No. 9-1 ' Cure, min. a t
307' F.
Tensile strength Ib./sq. id.
hfodulus a t 200%
Elongation, 7%
Tear resistanoe, lb./in. ( 1 )
Heat buildups, C.
Cure, min. a t
240" F.
Tensile strength, lb./sq. in.
XIodulus a t 2007,
Recipes
9-1
Compound No.
Butvl B-1.45
100 5 3 60 1
Zinc oxide Stearic acid E P C black Tetramet hylthiuram disulfide Sulfur p-Quinonedioxime Lead dioxide ~
E
1.5
.. .. -.
9-7 100 5 3 GO
...
.
I
.
2 6
Goodrich Flexometer (6); load, 148 Ib./sq. in.; stroke, 0.125 in.; speed, 1800 r.p.ni.; and temperature, 40' C.
2314
Elongation, 7,
Tear resistance, 1b.b
Heat buildup", O
c.
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1948
2315
TABLE 11. VULCANIZATION ACTIVITY OF p-QUINONEDIOXIME TABLE, OF BUTYL SYNTHETICRUBBER 111. VULCABIZATION Cornpound No. 431-1
Cure Tensile Modulus IvIin ;t Strength at 287" F. Lb./Sa. 1 .; 300%
15 30 45
60
75 90 120
Elongation, %
1290 1950
430 660
720 670
ziio ..
810
600
1970
740
...
..
Scorch Tests Tensile strength Elongalb./sq. in'. tion, %
450 1150 1230 1210 1460 1540
...
..
640
WITH
Compound S O .
1100+ 970 860' 800 810 760
977-1
llOO+
977-2
p-DINITROSOBENZENE
p-Dinitrosobenzene, Concn. 0 1
Cure, Min. a t 227' F.
15 30 45 287' F. 30
830 800 800 750
1480 2000
490 760
750 670
1960
700
670
... ...
..
2040
1%
...
860
..
620
227' F. 15 30 45 287' F. 30 00
0.7
977-3
1100+ 980 860 860 760 750
320 1130 1230 1370 1460 1560
227' F. 15
1.0
947-1
Base Recipe Compound No. Butyl B-1.45 Zinc oxide Stearic acid E P C black p-Quinonedioxime
431-1 100 5 3 60
4
431-3 100 5 3
431-2 100 5 3 60
Butvl B-1.45
These results would seem to indicate that oxidation of the p quinonedioxime to some intermediate product is the first step in the vulcanization reaction. It has since been shown by Flory and Rehner (4) that the active ingredient involved in the vulcanization reaction is p-dinitrosobenzene which results from the mild oxidation of p-quinonedioxime (8).
H O =~ = N O H
+ [OI -+
390 530
1100' 1040 930
450 490
890 830
820 680 730
750 750 680
1010 880
710 630
o=N-=-N=o
Data in Table 111illustrate the vulcanizing activity of p-dinitrosobenzene. Here i t will be seen that as the proportion of vulcanizing agent is increased, ultimate tensile strength is likewise increased. However, the optimum state of cure is reached in a very short time at a relatiyely low temperature. Those compounds containing the higher proportions of p-dinitrosobenzene are very difficult to handle, as vulcanization often sets in before the mixing operations can be completed. The physical propert2es of p-quinonedioxime stocks containing fillers other than channel type carbon blacks have been studied.
30 45 287' F. 30
1i8o
..
400 .,
1370
60
1280
550 540
227O F. 15 30 45 287' E'. 30 60
3.0
947-2
60 2
3
+
220
60
..
15 30 45 60 75
70
1100' 1100+ 1100
1100+ 1100-
227' F. 1B 30 45 287' F. 30
0.4
Elongation,
60 60
60
..
960
431-2
Tensile Strength, Lb./Sq. In. 0 60 60
li90
..
..
1270 1470
260
330
Base Recipe
&&ic
acid EPC black p-Dinitrosobenzene
100
3 60
As noted
These properties are summarized in Table IV. Tensile strengths of all these compounds are somewhat lower than would be obtained from a comparable compound vulcanized with sulfur. Compounds vulcanized with p-quinonedioxime can best be characterized by comparing them with similar compounds vulcanized with sulfur. Generally speaking, they are lower in tensile strength, particularly those compounds containing a relstively small amount of black or mineral filler. At the same time, stocks having considerably higher modulus characteristics result. Tear resistance is generally poorer. Resistance to aging at elsvated temperatures is considerably improved by this type of vulcanization. Rate of vulcanization, obviously, has been tremendously improved.
TABLE IV. FILLERS IN ~-QUINONEDIOXIME BUTYLSYNTHETIC RUBBER COMPOUNDS Stook
No. 1038-1 1038-2 1038-3 1038-4 1038-5 1038-6 1038-7 1038-8 1038-9 1038-10 1038-11 1038-12
Filler None M T black F T black Suprex clay Silene Celite 270 slineralite Zinc oxide Kalvan Hydrated alumina Zinc aulfide Pyrax
Cured 15 Min. at 287' F. Tensile Modulua strength at Elongalb./sq. id. 300% tion, % ... 860
190 240 210 160 110 110
720 710 650 660 740 690
110
810
50 110 110 160
860 810 770 690
Cured 30 Min. a t 287" F. Tensile Modulua strength, at ElongaIb./sq. in. 300% tion, %
Cured 60 Min. a t 287O F. Cured 120 Min. a t 287O F. Tensile Modulus Tensile Modulus strength at Elonga- strength, at ElongsIb./sq. it;. 300% tion, % Ib./aa. in. 300% tion, % 750 590 60 1180 620 290 1420 750 260 600 1300 310
1140 640 550 1390 1120 900 710 660
Base Recipe Butyl synthetic rubber B-1.45 Zinc oxide Stearic acid Sulfur E-&uinonedioxime ' ead tetroxide Filler
.
100
5 3 1.5
2 8
30 volumes
7. -. in
670 660
730 810 680
710 640
2316
INDUSTRIAL AND ENGINEERING CHEMISTRY
Aromatic E s t e r s Aliphatic Esters V.I-57 p-quinonedioxime diVA-21 p-quinonedioxime benzoate (scorch reduced) VS-29 &acetate (trans a n d VA-89 p-quinonedioxime dic i s ) (scorchy) io-chlorobenaoate) (scorch V.4-42 n-ouinonedioxime dicaprdate (acorchy) VA-82 p-quinonedioxirne dilaurate (scorchyj VA-95 p-quinonedioxime distearate (scorchy) VA-100 o-auinonedioxime di(scorch reduced) c r o t o i a t i (scorchy) VA-104 p-quinonedioxime di- V.4-93 di (3,s-clinitrobenzoate) (scorcby) naphrhenate (scorch>-) \-A-96 di(p-methoxybenzo;AJ.IPHATIC DIBABICACIDS ate) (scorchy) V A S 7 di(n-amoxybenzoate) VAI-68p-quinanedioxime (scorchy) succinate (sluggish, lorn VA-103 di(m-broinobenzoate) cure) (scorch reduced) VA-69 p-qninonedioxime adipate (sluggish, low - k R O X A T I C DIBASICACIDS cure) VA-70 p-quinonediosinie phthalate (no cure) VA-99 p-quinonedioxime dihydrogen phthalate (no cure) ~~
~ Q U I N O N E D I O X I(VB-1) ME Aromatic 3Iodified Aliphatic Esters \'A-94 p-quinonedioxime di(phenylacetate) (scorchyj PA-109 p-qninonedioxinie di (n-phenylcarbamate) (scorchy) V I - 1 16 p-quinonedioxime dicinnamate (reduced scorch)
Ethers Vh-47 bisethoxymethyl rther of auinonediosimo iverv low cures) Vh-48 monoethoxymethj-l ether of quinonedioximc (no cure) I.&-54 dimethyl ether of quinonedioxime (no curcT* VA-108 p-quinonedioxime diFURPCROL DERIVATIVE benzyl ether (no eure) PA-114 p-quinonediosinie \-.I-88 p-quinonedioxime didi:2,4,6 - trinitsoplienyi) furoatc (scorchy) ether (no cure)
Vol. 40, No. 12
Metallic Derivativeb VA-22 monosinc salt of quinonedioximo (SliEht scorch inediuin tensiles) VA-23 dizinc salt of qninonediosiiiie (slirht cure) V.4-24 zinc chloride doublo salt of quinonedioxime (slight cure) V.4-25 rnononiercury salt of guinonediosirne (scorcliy) V.4-26 dimercuric salt of qiiinoncdioxime (loiv tensilcs) VA-27 mercuric chloride double salt of yuinoncdioxime VA-30 monoferric salt of quinonedioxime (no cure) VA-31 monobarium chloridc double salt of quinoncdioxime (low tensiles) V.4-32 monocupsic salt of q~uinonedioxime (low tensilcs) VA-37 mono-lead salt of nuinonedioxime (med. tensilcs) VA-38 mono-barium salt of [ruinonedioxinie (med. tensilea) VA-BY mono-milgnesium salt of quinoncdioxime (101,- tensi!eij VA-41 mono-calcium salt of quinoriedioxirne (low tensilci) VA-64 c11ver halt of p-quinoncdioxime (very scorchy)
~ Q U I ~ T O S E D I O X( T IM A -E1 )
S u c l e a r JIodification \'.I-33 1,4-naplithoquinonedioxime (cures) PA-34 1,2-naphthoquinonedioxime (no cure) VA;49 chlorornethylquinonedioaime \'A-67 ethyl p-quinonedioxirne carboxg-late (slight cure) Vh-73 , 2,6-dimethyl-1,4-quinonedioxime (scorchv) (lorn
Sulfur Derivatives Phosphorus Derjvatives Miecellancous VA-71A p-quinonediorime di- PA-79 p-quiiionediorime phos- P d - 2 2 pllloroglucinol trioxime benzene sulfonate (no cure) phito ( n o cures) (very diwht cure wit11 no \'A-110 sodiiim benzoquinone- TA-80 p-cjuinonediosirne phosPbO., with PbCL only fair dioxime xanthate (no cure) phochloride (reduced scorch tensiles) VA-111 benzoquinone requires lead) TAL-582,5-dinitsoso-4-ijoVA-112 dierhglxanthoiiiiine propyltoluene (scorchy) (no cure) POLYXC: p-dinimosoberizene iscorches pn mill: DERIVATIVES OK T1I.il10VA-72 o-quinonedioxime (no QUINOSEDIOXISIE cure) VA-65 o-dinitsosobenzene (no cure) VA-123 m-dinitsosobenzene (scorches on mill) Base Recipe Butyl B-1.45 Zinc oside Stearic acid EPC black Viilcanizing agent\ Oxidizing agent I
oxime (no cure) VA-28 thymoouinonedioxime (very lorn -cure without Phon, hiqh tensile and scorchy with PbOr)
The vulcanization obtained with p-quinonediosime and an oxidizing agent, although of interest in specific applications, is too scorchy to be of practical interest for t,he great majority of general applications. It is of prime importance, therefore, to have some means whereby the rate of cure may be retarded a t procec;sing temperatures to such a point that it becomes of practical value. It was found in the early stages of t'his ~ o r k that other bifunctional compounds of the quinone type, such as quinone, tetrachloroquinone, and quinone d i a d , had no vulcanizing action. This forces one to the conclusion that' either the theories of Fisher (3) and Farmer ( Z ) v i t h respect to the rulcanizatioii of natural rubber are not correct 90 n or the mechanism of the reactions of these materials in natural rubber is not operable in Butyl synz 0 LJ thetic rubber. k? 82 Since diiiitroso compounds are so active, the < principal rate-determining reaction would appear >W to be the initial oxidation of the dioxime. The obz 0 0 served rate would probably also be dependent upon I74 the particular dinitroso compound formcd, provided the latter exists, as believed, in hydrocarbon media as an equilibrium mixture of t,he mono- and bimolec66 ular species (4). To substantiate thesc view., a series of compounds based on the parent compound, p-quinonedioximc,
e
_1
100
3"
60
Varied
r a s synthcsized and then evaluated in a Butyl synthetic rubbcr compound. They may be classified into major groups a i shown in Table 1 '. Of all the classes, the aromatic csters of p-quinonedioxime most nearly approach the aim of good physical propertice accompanied by reduction in scorch tendencies.
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1948
TABLE VI.
COMPARISOX OF DERIVATIVES OF p-QUINONEDIOXIME
Cure Temp.,
Formula F. 1 Tetramethyl307 thiuram disulfide, 0.5 mercaatobenzothiazole, 2 sulfur 2 VB-lb, 6 PbOz 240
6 VA-570, 10 PbaOP
Temp. Rise, Tensile Modulus C., Cure, Strength, at Elonga- Cured Min. Lb./Sq. In. 300% tion, % 60 MinSa 15 70 30 2460 240 866 60 2525 440 780
287 ,
6.3 VA-QZd, 10PbaOa
287
6 VA-906, 10PbaOa
287
15 30 60 15 30 60 15 30 60 15 30 60
1900 2240 2170 1830 1880 1720 1860 1820 1630 1870 1850 1650
1410 1700 1920 960 1230 1170 1400 1410 1250 1120 1220 1290
420 440 350 450 440 390 420 400 400 490 460 400
2317
in flow characteristics a t 250" F. in which both of the nonsulfur type vulcanizates excel. The first step in the vulcanization of Butyl synthetic rubber b y . an ester of quinonedioxime, such as quinonedioxime dibenzoate, is believed to be given by
N I/ O C O C S )
NO
kO.OC(_I)
NO
I
41 45 40
1
The reactions following the formation of the dinitroso compound apparently proceed in the same manner as previously indicated. Subsequent to the original work, Butyl synthetic rubber polymers of higher unsaturation have become available. The present commercial product can be characterized as follows:
43
Base Recipe
300,000 to 350,000 0.8 to 0.9 mole %
Viscosity-average molecular weight Diolefin content Goodrich Flexometer a t room temperature, 0.125-inch stroke, 148 lb./sq. in,. load, 30-minute test. b p-Quinonedioxime. 0 p-Quinonedioxime dibenzoate. d p-Quinonedioxime di (m-nitrpbenzoate). e p-Quinonedioxime di (0-chlorobenzoate). a
The behavior of quinonedioxime (VB-1) and quinonedioxime dibenzoate (VA-57) in such a polymer is shown by the data in Table VIII. These data can be compared directly with those of the first three compounds of Table V to determine the effect of increased unsaturation. Such a comparison reveals that the major change is an increase in the modulus of the polymer of
TABLE VII. INNER TUBEC o m o u m s
Formula 1.0 Tetramethylthiuram disulfide. 1 . 3 sulfur
2 VB-lb, 10 PbO, 1.5 sulfur 6 VL4-57b, 10 PbuOa, 1.5 sulfur
Scorch Cure 30 Min. a t 227O F. Tensile Elongation, % (Ib./sq. ih.) 0 llOO+ 1390 500
730 810
Hot Flowa a t 250O F. Cure Temp., F. 307 287 287
Cure Min.' 40
Tensile, Modulus Lb./Sq. I n . a t 300% 2090 160
15
Lb./sq. in. Elongatq 75% tion, % elongation 740 64
60 30
1440 1390 1350
690 660 690
240 290 180
48 47 44
15 30 60
1170 1160 1020
560 550 530
350 490 400
63 73 70
1 hr.
220
Elongation after 3 hr. 5 hr. 300 390
136 142 152 192 156 167
163 167 167 236 186 189
175 178 186 268 198
202
7 hr. 420 185 155 158 28 217 211
Base Recipe Butyl synthetio rubber B-1.45 100 Zinc oxide 5 Stearic acid 3 SRF b1,apk 50 Vulcanizing agents As noted a Dumbbells loaded over a period of 30 minutes a t room temperature to a n elongation of 76%. Dumbbells then placed in a circulating air oven maintained at 250" F. and elongations noted a t indicated time intervals. b See Table VI for composition.
Three representatives of this class were chosen for comparison with p-quinonedioxime. The results obtained with respect to physical properties are shown in Table VI. It is obvious that physical properties of the vulcanizates compare favorably with those of p-quinonedioxime. Lead tetroxide (red) has been used with the aromatic esters, since there was some evidence that the action of lead dioxide was too severe, resulting in actual oxidation of the dinitrosobmzene to unreactive dinitrobenzene. In addition, the comparisons are made on cures at different temperatures in order that they may be made a t the same times of cure. To show the actual reduction of scorch, samples were run in the Mooney viscometer operating a t 227" F. ( 7 ) . This information is shown in graphical form in Figure 1. Of these three, the dibenzoate ester has been studied most thoroughly, as it appears the most practical from the standpoint of availability of raw materials. Some data are summarized in Table VI1 comparing p-quinonedioxime dibenzoate with the parent compound, p-quinonedioxime, and with a sulfur vulcanizate. The improvement in scorch characteristics is again obvious. M o s t important is the vast improvement obtained
TABLE VIII. COMPARISON OF SULFUR AND ~-QUINOXEDIOXIME VULCANIZATION Formula 1 Tetramethylthiuram disulfide, 0.5 mcrcaptobenzothiazole, 2 sulfur 2 VB-la, 6 PbOz 6 V A - L ~10 ~ ~PbsOi ,
Cure Tensile Temp., Cure, Strength, Modulus O F. Min. Lb./Sq. In. a t 300% 350 307 , 15 2320 570 30 2600 690 60 2610 240
287
15 30 60
2250 2200 1960
1960 2150
..
380 310 290
15 30 60
1820 1770 1710
1300 1410 1350
430 390 380
Base Recipe Butyl B-2.5 Zinc oxide Stearic acid ' EPC black Vulcanizing agents See Table V I for composition.
Elongation, % ' 870 800 740
100 5 3 60 As noted
INDUSTRIAL AND ENGINEERING CHEMISTRY
2318
Vol. 40, No. 12
Tensile-Modulus
TABLE IX. RETARDERS FOR ~ Q U I N O N E D I O X I M E Conoentration, pts./ Cured 60 Min. a t 2 2 i 0 F. Compound Control Aidehvde amine reaction product -4ldehyde amine reaction prod+ Phenolic amine compound Reaction product of acetone and diphenylamine N-p-tolyl-N'-p'-tolylsulfonyl- p - phenylene diamine Phthalic anhydride Cndisclosed p-P henylp henol Ditolylguanidine salt of dicatechol borate Dibutylammonium oleate Mixture of aryl meroagtans Lead dimethvldithiocarbamate . Lead (phenyldiaminoethy1)phenyldimethyldithiocarbamate Di-o-tolylguanidine Diphenylthiourea Aldehyde amine Octadecylamine 8 - N a.~ h t h. v lmercaptan Xylyl mercaptan Phenyl-a-naphthylamine,) 92.5% m-Toluylenediamine,
Trade Name Trimene base Butene
100 Butyl Tensile, Synthetic lb.! Rubber sq. in. 420 0.25 190
.. .
0.25
290
Albasan BLE
0.25 0.23
280 810
...
290
1100 890
LIUF
0.25
680
260
860
ESEN UTB Parazone Permalux
0.25
600
0.25 0.25
690 710 420
170 270 160 110
980
0.26
910 990 1010
Barak R P A No. 4
0.25 0.25
850 700
190 130
1070 1070
680
Ledate
0.25
520
._.
1100
SPDX
0.25
420
,..
1100
200 130 110
1100 1100 1100
140
liO0
160
1100
...
1100
DOTG
0.5 260 0.5 420 0.5 280 AM-1180 1.5 No cure RPA No. 2 0 . 5 480 (active) RPA No. 3 0.55 420 (active)
"808"
170
7. . - 5 % I , ,
Polymerized trimethyldi-' hydroauinoline Dibenzylamine Butyraldehyde aniline condensation product Undisclosed
Mod., Elonga500% tion, % 120 1000 . . . 1100
Agerite resin D DB.4 Antox Flectol vhite
...
0.5
170
0.5 0.5
No cure GO
... .. . .. .
0 .5
400
130
Base Recipe Butyl synthetic rubber (GR-I) Lead tetroxide p - uinonedioxirne 9% black Retarder
100 5 1 50 As indicated
Min. a t 227O F. 20 40 60
Control 1080-450-860 1340-710-800 1460-810-730
a t 500~'-Elongation N o Stearic Acid 940-450-840 600-580--950 1260-680-780 800-350-8N! 1310-680-780 900-380-880
pl'o Zinc Oxide
No Zinc Oxide or Stearic Acid 350-140-1070 490-170- 980 570-210- 960
The results obtained in a study of variom materials t o determine their effectiveness as retarders of this type of vulcanization are shown in Table IX. From thcsc data it is obvious that not many of these materials have an appreciable retarding effect. However, two amines, octadecylamine and dibenzylamine, d e appear to be of interest. Subsequently, octadecylamine proved to be of most interest. I t s effect both at processing temperatures and a t curing temperatures is shown by the data in Table X. The practical utility of this type of vulcanization has been demonstrated in several fields of application. One of these fields is that of tire-curing bags. These bags are subject to extreme aging conditions and vulcanizates obtained from quinonedioxime or its derivatives have provided greater resistance to this type of aging than has a sulfur vulcanizate. Such a comparison ip shown in Table XI. Included in this comparison are compoundc vulcanized with p-quinonedioxime dibenzoate and with p quinonedioxime retarded with an aliphatic amine.
TABLE X. OCTADECPLAMINE AS RETARDER Base Recipe
1100
iioo 1100
Butyl synthetic rubber (GR-1) Zinc oxide Sulfur E P C black S R F black p-Quinonedioxime PbaO4 Process oil Ootadecylamine
Recipe I
Cure, Min. 60 4
6 8 10 30
Cure Temp.,
E'. 227 312
Tensile Strength, Lb./Sq. In. 380 710 1030 1270 1400 1800
I
I1
10;
100 5 2 20 30 I 5 4 0.5
J
2 20 30 1 6 4
... Modulus at 300%
...
150 220 240 340 700
E:longation.
70
930 770 7 80 800 700 600
higher unsaturation. The work discussed in the following portions of this paper wm carried out using the polymer just described. Another means of preventing prevulcanieation during processing operations would be to use some material which would inhibit the vulcanization reaction occurring with p-quinonedioxime a t temperatures encountered during processing operations but which would have relatively little effect a t the higher temperature- used for vulcanization. I n an attempt t o TABLE XI. CURIXGBAGSTOCKS find such a material. a base recine was After Aginga _ _ chosen containing 50 parts of SRF Tensile lfodulus Tensile Modulus black with 1 part of p-quinonedioxime Cure, Temp., Strength, at Elonga- strength, at ElongaFormula Mill. O F. Lh./Sq. In. 300% tion, % lb./sq.in. 300% tion, % and 5 parts of lead tetroxide present 1 Sulfur, 2 selenac, 15 320 1470 390 730 660 290 550 2 Btearic acid, 5 30 1150 530 590 600 370 520 as vulcanizing agent. Vulcanization a t 60 970 540 490 600 350 220 process oil processing temperatures, or "scorch," 120 880 490 500 560 330 540 240 1040 400 710 460 220 580 was evaluated by examining physical 6 VA-57, 6 PbrOi, 15 320 1090 590 590 590 530 330 properties of stocks vulcanized for 2 sulfur, 10 proe30 1070 720 520 470 270 ess oil 60 1060 820 400 510 566 320 various times at 227" F. Materials of 120 1050 840 400 520 460 330 interest were subsequently vulcanized 240 990 820 360 390 .. 280 2 VB-1, 6 PbrO4, 13 320 660 380 450 480 350 400 at 312' F. in order better t o evaluate 2 sulfur, 1 octa30 990 590 440 580 410 410 their merit. 350 420 490 580 decylamine, 10 60 1420 860 1430 940 450 650 480 410 process oil 120 In a preliminary experiment using 1260 780 460 680 420 450 240 the above recipe, the influence on Base Recipe scorch of both zinc oxide and stearic Butyl synthetic rubber (OR-1) 100 Zinc oxide 25 acid was investigated. Both of the'se SRF black 60 materials were found t o contribute t o a Aging conditions: aged 8 hours in open steam a t 338O F.; then 8 hours in 80 lb./aq. in. air a t 260' F., scorch, as is illustrated by the following repeated three times f o r 48 hours' total. data:
December 1948
1NDU.STRIAL AND E N G I N E E R I N G CHEMISTRY
2319
ACKNOWLEDGMENTS
(4) Flory, P. J., and Rehner, J., Jr., IND. ENG. CHEM.,38, 500
The writer wishes t o thank L. A. Mikeska, S. B. Lippincott, and L. T. Eby for the synthesis of the many compounds required during the course of this study. H e is also grateful t o W. C. Smith and R. L. Zapp for carrying on much of the evaluation work involved, and t o others in the organization with whom it was his pleasure to discuss many of the points involved.
(1946). (6) Haworth, J. P., U. S. Patent 2,393,321 (1946). (6) Lessig, E. T., IND. ENQ.CHEM.,ANAL.ED., 9, 582 (1937) ; Rubber Chem. and Technol., 11, 249 (1938). (7) Mooney, M., IND.ENQ.CHEM.,ANAL.ED.,6, 147 (1934). (8) Nietaki, R., and Kehrmann, F., Ber., 20, 613 (1887). (9) Ostromislensky, I. I., J.Russ. Phys. Chem. SOC.,44, 204 (1912). (10) Rehner, J., Jr., and Gray, P., IND.ENQ.CHEM.,ANAL.ED.,17, 367 (1945). (11) Thomas, R. M., and Sparks, W. J., Australian Patent 112,876 (1941).
LITERATURE CITED (1) Am. SOC. Testing Materials, Standards on Rubber Products, D 824-411'. (2) Farmer, H. H . , Trans. Faraday SOC.,38,340 (1942). (3) Fisher, H. L., IND.ENG.CHEM.,31, 1381 (1939): U. S. Patents 1,918,328 (1933); 2,170,191 (1939).
RECEIVED April 3, 1947. T h e work reported here was carried out during the past five years. Earlier publication was withheld in accordance with secrecy orders of the United States Patent Office.
RESIN-PLASTICIZER SYSTEMS Analysis of Log Stiffness-Temperature and Viscosity Characteristics G. J. DIENES AND F. D. DEXTER Bakelite Corporation, Bound Brook, N . J .
A
q u a n t i t a t i v e method of c o m p a r i n g resin-plasticizer
systems in t w o important temperature regions is de-
scribed. The characteristics in the temperature region of application are evaluated f r o m log stiffness-temperature curves, and those in the processing temperature region by parallel-plate plastometer measurements. A simple and practical empirical equation is developed w h i c h describes m a t h e m a t i c a l l y the inverted S-shape log stiffness-temperature curves. The equation is characterized by four physical constants: the limiting stiffness a t low and high temperatures, the temperature, T,, at w h i c h the slope of the log stiffness-temperature c u r v e has its m a x i m u m value, and the m a g n i t u d e , S,, of this m a x i m u m slope. This equation is s h o w n to be applicable to a l a r g e variety of materials. The variation of T, w i t h pbr cent plasticizer, w h i c h is approximately linear i n the 15-50qo concentration
I
N ORDER t o describe theessentialeffects of the addition of a plasticizer to a resin, it is necessary to consider the mechanical
and flow properties in two general temperature regions. The first, which covers a fairly extended range, is t h a t region in which the compounds may find ultimate use and is described as the application temperature region. The second is the region of processing temperatures. T o be useful such evaluation must be expressible in terms of some simple, physically meaningful constants which are indices of such important properties as plasticizer efficiency and temperature sensitivity. One of the most useful methods for evaluating the mechanical property of elastomers in the application temperature region is the determination of stiffness as a function of temperature. I n a stiffness measurement, usually carried out in flexure or torsion, a constant load is applied to the specimen for a given time interval ( 5 to 10 seconds), the resulting deformation is measured, and the stiffness calculated from well-known formulas of the theory of elasticity. Since for plastic materials the deformation, in general, is complex and contains elastic, delayed elastic, and viscous components, the resulting stiffness is but one point on the deformation-time or creep curve. The stiffness-temperature curve is, therefore, arbitrary but nevertheless useful. Log stiffness-temperature curves show a characteristic inverted S-shape. It is possible, in principle, to derive an equation
range, is s h o w n to be a good measure of plasticizing efficiency. The m a g n i t u d e of the slope, S,, w h i c h is approximately independent of the plasticizer concentration in the 15-50% region, measures the temperature sensitivity of the resin-plasticizer system. The most useful q u a n t i t y for c o m p a r i n g resin-plasticizer s y s t e m in the vicinity of processing temperature is the absolute viscosity obtainable b y parallel-plate plastometer techniques. It is s h o w n that the log viscosity-per cent plasticizer c u r v e is linear in the 15-50% concentration range. The slope of this c u r v e is a measure of the h i g h temperature plasticizer efficiency. Thus, t w o s u p p l e m e n t a r y analyses permit q u a n t i t a t i v e comparison of various resin-plasticizer systems in the t w o impofiant temperature regions-the general temperature region of application and the region of processing t e m p e r a t u r e . .
for these curves from a mathematical expression for creep deformation as a function of time and temperature. However, the theory of creep phenomena is not far enough advanced t o carry out such a treatment. Tuckett (6) obtained a stiffnesstemperature relation based on a simple mechanical model which predicts a curve of the correct general shape but does not describe the experimental data. Thus a need exists for describing the stiffness-temperature curves in terms of some simple function containing constants which can be easily interpreted and have physical meaning. The development of such a n empirical equation makes i t possible to describe quantitatively such propertim as temperature sensitivity of the resin-plasticizer system and concentration efficiency of the plasticizer. The effect of plasticizers at elevated temperatures is most conveniently evaluated by means of a previously developed parallelplate plastometer technique (4, 6). The principal feature of these tests is that elastic, delayed elastic, and viscous components may be separated and evaluated. Of these, viscosity is the most convenient constant t o employ in determining compound characteristics in the processing region of temperatures. The activation energy for viscous flow measures the high temperature sensitivity. T h e slope of the log viscosity-per cent plasticizer curve determines the high temperature plasticizer efficiency.
