A NEW PLASTIC MATERIAL-
AXF S. D. SHINKLE, A. E. BROOKS,AND 0 . H.CADY
U. S. Rubber Products, Inc., Passaic, N. J.
R
UBBER technologists are familiar with the aromatic compound, 1 to 3 moles of ethylene dihalide, and increasing number of uses to which rubber up to 1 mole of aluminum chloride. By suitable control the has been put in recent years through modireaction product can be vaned from a very soft plastic with fications and adaptations effected by skilful compounding. a shearing plasticity a t 65.6" C. (150" F.) of 20intheMooney At the same time, however, active research has been carried shearing plastometer (6) to a material having a shearing out, stimulated by the desire for new materials to meet still plasticity of more than 150. Products with milling, tubing, more exacting requirements-for example, greater resistance and calendering properties resembling those of rubber show to oils and solvents and to oxidation. In general these ina shearing plasticity in the range 40 to 80. This series of vestigations have taken one of two directions; they have plastics has been given the designation AXF. been directed to a search for new synthetic rubber-like maAXF does not react with sulfur, even after heating for a n terials or t o a study of new derivatives of rubber. hour a t 164" C. (327.2" F). This indicates the absence of I n both of these fields of research, achievements of outaliphatic unsaturation. The structure of the products is standing importance have been disclosed. Whitby and Katz unknown, but i t seems probable that they comprise extensive (9)reviewed and summarized the development work on synchains and networks of benzene groups, each linked to a t least thetic rubber from its early beginnings. The announcement two ethylene groups. Analysis for carbon and hydrogen of poly-chloroprene or DuPrene by Carothers (2) and his shows 92.2 per cent carbon and 7.8 per cent hydrogen, and associates was soon followed by recognition that this product thus the empirical formula gives a 1: 1 atomic ratio for is a synthetic rubber-like material with physical properties carbon and hydrogen. Such a formula fits a polymer comnot only rivaling those of rubber but superior in many parposed of H2CC&H&H2 units or of (H2C)2.CGH2.(CH~)z units ticulars in which rubber is most deficient. Various olefinas already suggested. sym-Diphenylethane has been isopolysulfide reaction products have been described by Patrick lated as a product from the earlier stages of the reaction. (6) and, under the trade name of Thiokols, have been presented to the industry. Other synthetic products which have attracted the attention A new class of elastic plastic materials which are very reof rubber compounders include the sistant t o the action of many solvents and chemical reagents glyptal resins (IO), flexible phenol resinoids, and the recently announced may be prepared by reacting an ethylene dihalide in the Koroseal (I). A paper by Thies and presence of aluminum chloride with an aromatic hydrocarbon Clifford (8) has s u m m a r i z e d the having the general formula RCaH4R1. Certain of these products reactions of the rubber hydrocarbon, with a shearing plasticity at 65.5" C. of 40 t o 80 (as measured apart from oxidation and vulcanization reactions. by the Mooney shearing plastometer) have been designated
Method of Preparation A new class of elastic plastic materials, recently discovered (?), is prepared by reacting ethylene dihalide in the presence of aluminum chloride with an aromatic hydrocarbon having the g e n e r a l f o r m u l a RCsH4RIwhere R and R1 each represent hydrogen or a saturated aliphatic hydrocarbon radical containing more than one carbon atom. Aromatic hydrocarbons with only one carbon atom in the side-chain radical (as toluene or xylene) do not undergo this reaction to give plastic products. Suitable proportions of reactants include 1 mole of
"AXF." The properties of the plastic make it especially interesting as a compounding ingredient for use with natural or synthetic rubber. The resistance t o ozone cracking, the flexibility, and the breaking elongation of oil- and gasoline-resistant and semihard rubber stocks containing 15 to 20 parts of sulfur per 100 of rubber may be increased by the addition of A X F t o the compound. A moderate amount of flexibility and stretch is possessed by hard rubber made from equal weights of rubber and AXF. As a compounding material with DuPrene, A X F is superior t o factice in several ways. A X F has an excellent plasticizing action both on DuPrene and on the ethylene polysulfide plastics known as Thiokol. With the latter, its inertness causes it to be preferred t o rubber for use in this capacity. 275
INDUSTRIAL AND ENGINEERING CHEMISTRY
276
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i i i i x i e intcrest to
comment on its general processing propertie$. Gradesof AXFhavingaMooneyshearingplasticityat 65.6OC. (150" 17.) in the range 40 to 80 may be milled, calendered, nnd tubed in the same manner as well broken down rubber. Similar products of greater plasticity are more tacky and liaridle with greater difficulty.
Compounding Material with Rubber In Figure 2 ace shown comparative stress-strain curves for a pure gum type rnbher compound with 3 parts of sulfur and for the same rubber compound with 40 parts of AXF added. The cures are for 5 minntes at 191' C. (286" F.). These curves sliow that tlie addition of this amount of AXF has but. slight effect on tensile strength and ultimate elongation, and caiises a small reduction in modulus. The com-
c
B
I
FIQUR~PI 1. SWELLINR OF AXF IN GASOLINE AND IN OIL A.
B. C.
N o t immersed. Immeraplt in geedine 6 dsye at room tempeisturo. Immersed i n mindle oil 5 days at 70' (2.
Physical Properties The general physical properties of AXF plastic are outlinpd as follows:
l.M
spcoifio Pi.Vi1." Ash % Co1&
Odor Hardening t e n w
" C. Tenaile stiength.'by./sq. o m ril>./sq i o ) Elongation. % Action oi acids and alkalies after immeiaion for 1 week irt room temp.: Coned. HCI Coned. IiIS08
I.? hrkbrwn Piaotienily none
0 U p to 82 (4501 Cp t o 600
I o nctiun
Swell8 and hardens slight!) N" actinn
AxI" shows very low swelhg in Such solvents as ethyl alcohol, acetone, gasoline, kerosene, and light lubricating oils. Figure 1 gives a comparison of a sarnple of AXF hydrocarbon with other AXF sampIes which have been immersed for 5 days in gmoline at room temperature or for 5 days in spindle oil at 70" C. There is some penetration of gasoline into the AXF as evidenced by the hlister formation. Thc volume increase is fi.3 per cent for the sample immersed in easoline and 3.4 oer cent for the samule in oil. On the basis of'these properties, &F has been investigated as a compounding material for use with rubber, DuPrene, or Thiokol. It will be shown that AXF may be combined with these plastic!: in proportions such as both to improve their processing characteristics and to give products with properties capable of withstanding more severe serviceconditioiir of certain types.
FIOURE 2. STRES~S-STRAIN CURVES FOR PURE GUM RUBBER AND FOR AXF RUBBER
pounding of rubber with large amounts of AXF does lower the t e n d e strength of the stock. It is well known in therubberinduatryt~hatthecomponnding into a low-sulfur nlbber stock of the various new oil-resistant synthetic rubbers has not heen an effective means of developillg an oil-resistant compounded rubber, AXFis accordingly not recommended as a compounding agent to promote oil resistance in a low-sulfur rubber compound. There are, however, interesting effects of .4XF in low-sulfur rubber compounds. For example, a compouiid having rubber and AXF in the p.oportion 70:30 shows a reduction in rate of diffusion of air of more than 40 per cent as compared with the sanie conlpouild without AXF.
*.
Processing Properties Although AXF is generally used i n connect.ion with other pla;t' -i ics as an auxiliary e om po u n d i ng m a t e r i a l , i t m a y h e of
4 P
3 PERCENTC ~ ~ * i n a r i o ~ PERCEHT eLaroRIlon FIGURE 3. STRISS-~TRAIN CURVESFOR RUBBERAND RUBBER-AXFConspouNns
INDUSTRIAL AYD EZCINEf%llY(; CHI3MlSTRY
MARCH, 1936
277
A more interesting application of AXF is in the development of flexible semi-hard rubber compounds of excellent oil resistance. Rubber compounds containing 15 to 20 parts of sulfur combined per 100 of rubber are known to have high resistance to swelling in gasoline or motor oils. However, such cornpounds have a sufficiently low breaking elongation so that they do not meet the requirements of flexibility for many types of service. Figure 3 shows comparative stressstrain curves of semi-hard ruhher compoimds with and without AXF. The higher breaking elongation of the AXF stocks is to be noted, particularly in the compound with 15 parts of sulfur per 100 parts of rubber. Figure 4 shows a comparison of the effect of gasoline immersion for a period of 3 years of a semi-liard ruhher AXF compound as compared with that. for a heavily loaded rubher stock designed for service as an oil-resistant compound. Table I gives the formula for a typical AXF-rubber compound of the type nuder discussion and indicates the percentage swelling of this compound in gasoline and in spindle oil. TABLEI. EFFECT OF IMMERSINO SEMI-HARD RUBRER-AXF COMPOUND IN SWELLING MEDIAFoa ONER'EEK Rubber AXF Zine oxide Csrban blaek M?~gnesiumoxide
(Cured 75 minutes at 153' C.) Chloium oxide IO0 75 Diphenyl guanidine Sulfur 30 Antioridsnl
Gwelling Medium
10 4
20 2
20
Temp. of Test 0
Mat0Cg:nde gapoilme Light spindle o i l
c.
Inoreape in Yo1
%
25
32.5
70
58.0
The oxygen aging characteristics of rubber compounds are not changed in any substantial degree by the presence of AXF in the compound. The use of a good rubber antioxidant, in the proportions ordinwily recommended in rubber compounding, affords adequate protection. The ozone resistance of semi-hard rubber compounds such asdescribed inTable I, with and without AXF, was compared. Very deep cracks formed iii the rubber compound while practically none appeared in the AXF-nibber compound which received the same ozone exposure. By compounding AXF in a hard-rubber stock in a 1: 1 ratio with the rubber present, it is possible to combine moderate flexibility with the characteristic chemical inertness of hard rubber. A typical wlcanite compound is compared with a similar stock containing 100 parts of AXF (both cured 7 hours at 145' C.): Compound: Rubber dXF
Zino oxide
Magnsaium oxide Sulfur Diphenyl wanidine Tensile strength: I(g./sq. cm. Lb./ep. in. Elongation st brock. %
OD 1W
....
OF
1w
The black rin8.i~aomi-hsrd rubber wbioh eontains AXF: t h e white ""E is a highly pigmented rubber compound. Lelk rings 88 molded; righi, after eoskins in gasoline for 3 y'8ra.
Inasnmch as facbice is recomiriended as a processing ageiit for improving the handling properties of DuPreno, a number of direct, comparisons of AXE' and factice have been m d e in various types of compoonds. Figure 5 shows a comparison of the cliangi+.in plast.icity during storage of a DuPrcne-fact,ice compound and a Di~PreiieAXF compound, Although the shearing plasticities of the txo compounds 24 hours after mixing were 69 and 62, respectively, t,he DuPrene-factice compound renched a plasticity of 105 in 14 days, whereas the AXF compound required 39 days to reach a plasticity of 109. Mil1;ng t,est,s were made daily 011 a sample of each compound, and t.he final plasticity measurements were made on the (late oii which the compound had so set up that it was impracticahle to mill it again. Both of the stocks are conventional compoimds containing both zinc oxide and magnesium oxide within the range of amounts recommendcd for DuPrene stocks. Thr conipoimds differ only in the presence of factice or AXP. The excellent plasticizing action which AXE shows in Dul'rene stocks reduces the temperatures developed during milling, promotcs smoothness of finish of calendered stocks, reduces calender shrinkage, and improves the tubing properties. Figures 6 and 7 show the effectsongasolineand oil resistance of a typical DuProne oil-resistant. conipoiind which may be
100
5 5 45 4
5 5 45 4
476.4 7060 5.5
176.4 2510 15.0
I
I
I
4
8
12
I
I
I
I
I
I
16
20
24
28
32
36
Compounding Material with DuPrene The investigation of the behavior of AXF as a compounding material with DuPrene has had the point of view of determining the possibility of improving the handling properties of the latter as well as of studying the effectupon the physical properties of the compounds. In connection with processing behavior, the milling, batch storing, calendering, and tuhing properties were considered while the gasoline and oil resistance mere examined carefully in connection wit11 physical tests
1
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INDUSTRIAL AND ENGINEERING CHEMISTRY
278 25.
I
I
0
V
-
a
A
DuPrene-factice compound is based on compound 236l described in the DuPrene Manual (5). The formulas are as follows : DuPrene Soft brown factice (hardness AXF Thermaxa Zinc oxide, Light-oaloined magnesia Rosin Soft oumarb Cottonseed oil Neozone D a A s ecial variety of carbon black. b p - d u m a r o n e resin.
DuPrene-Factice 100 150
...
370 10 10 1 10 5 2
DuPrene-AXF 100
...
150 370 10 10 1 10 6
2
The use of AXF in DuPrene is not recommended where the highest tensile strength and abrasion resistance are required. Tests have shown no evidence that either the oxygen or heataging of DuPrene compounds is impaired by the presence of ~~
TABLE 111. PHYSICAL TESTSOF AXF IN DUPRENE COMPOUNDS
COMPOUNDS TABLE11. DATAON OIL-RESISTANT [Cured 45 minutes a t 141.7' C. (287' F.)] Modified DuPrene D-1 Fillers replaced 70 DuPreneDuPrene D-1 by A X F 30 A X F Formulas 70 100 100 DuPrene 30 52 ... AXF 86 86 ..* Whiting 28.6 28.5 GastexO 11.5 , 11.6 11.5 Glue 10 10 10 Zinc oxide 10 10 10 Light-calcined magnesia 2 2 2 Cottonseed oil 5 6 5 Wood Neozone rosin 2 2 2 Neozone Db 1.5 1.6 1.6 Sulfur Properties Unaged Tensile strength: 72.9 91.4 98.1 Kg./sq. am. 1035 1301 1395 Lb./sq. in. 260 410 740 Max. elongation, % 19 46 17 Set, % Properties after 6-Day Immersion i n Spindle Oil a t 70' C. Tensile strength: 60.4 74.5 53.4 Kg./sq. cm. 716 1060 759 Lb./sq. in. 760 210 370 Max. elongation, % 16 7 10 33.7 45.4 49.6 %%g, % by vol. a A special variety of oarbon black. b Phenyl-&naphthylamine.
...
Figure 8 shows the stress-strain curves for the series of compounds described in Table 11-namely, DuPrene oilresistant compound D-1, a similar compound in which all of the fillers have been replaced by an equal volume loading of AXF, and another compound in which partial substitution (30 parts by weight) of AXF has been made for an equivalent amount of DuPrene. The replacement of fillers by AXF gives a compound of higher volume cost, but offers the possibility of combining the features of high breaking elongation with excellent resistance to gasoline and oil. Figure 9 compares the swelling changes after 5 days of immersion in spindle oil a t 70" C. of a DuPrene-AXE' and a DuPrene-factice compound. The dimensions of the test sample before immersion are also shown for comparison. The
Formula of Compound B P 60 Sulfur 0.6 DuPrene AXF 40 Cottoneeed oil 2 Light-calcined magnesia 5 Neozone D 2 Zinc oxide 5 Carbon black 42.8 Wood rosin 5 Tensile Strength 1 Week i n 96 Hr.i n 1 Week i n Spindle Oil Oxygen a t Gasoline at Room Temp. a t 70' C. Cure a t Unaged 70 C. 141.7' C. KO./ Lb./ Kg./ Lb./ Kg./ Lb./ KO./ Lb.1 Min. sq. cm. sq. m. sq. cm. sq. in. sq. cm. s q , in. sq. cm: 8q. i n . 15 112.1 1695 106.9 1520 108.3 1640 78.8 1120 115.8 1646 109.7 1560 111.8 1590 79.6 1130 30 46 116.8 1660 110.4 1670 111.1 1580 80.2 1140 60 119.6 1700 109.7 1560 113.9 1620 80.9 1150 75 116.8 1660 112.6 1600 106.2 1610 80.9 1150 90 117.4 1670 102.0 1460 108.3 1540 86.2 1210 Maximum Elongation, Per Cent 16 330 330 30 320 46 320 60 290 75 310 90 1 This particular compound modification was suggested by a member of the development staff of the Rubber Chemicals Division of E. I. du Pont de Nemours & Company, Inc.
FIGURE7.
OIL SWELLING O F DUPRENEAND DUPRENE-AXFCOMPOUND
MARCH, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
279
AXF. There is evidence that the high ozone resistance of DuPrene is enhanced when AXF is added to a DuRene compound. DuPrene-AXF compounds show higher tensile strengths as the carbon black loading is increased. In a 60 DuPrene-40 AXF stock, as the volume loading of carbon black is increased from20 to40 volumes on 100volumes of DuPrene-AXF plastic, the tensile rises from approximately 100 to 150 kg. per square cm . Table 111 shows several physical properties over a range of cures of a typical Dufrene-AXF compound loaded with carbon black. AXF has also been found very resistant to the action of lithographic varnishes. The swelling of AXF in a commercial lithographic varnish after 5 days' immersion amounted to only 1.5 per cent. This feature has been used to advantage in compounding with DuPrene to prepare products which are particularly adapted to use in printers' blankets and inking rollers for some types of work. B c A RESISTANCE OF DnFIQURE9. SWELLING PKENE-FACTICE AND DUPRENE-AXF COMPOUNDS
Compounding Material with Thiokol Some studies on the effect of compounding AXF with the several commercial olefin polysulfide plastics have been made. With certain types of these plastics, it has been reconimended that small percentages of rubber be added to assist in processing operations. It has been found that amounts of AXF as high 89 20 per cent by weight may be compounded into these plastics to give products more readily processed, with somewhat higher breaking elongation and the same high resistance to gasoline and oils characteristic of the olefin polysulfide plastics when processed alone. Table IT' shows the physical properties of several Thiokol compounds with rubber and with AXF. A new type of olefin polysulfide plastic recently introduced (Thiokol D) is highly resistant to mill breakdown. It has been found that the introduction of approximately 20 parts by weight of AXF to 100 parts of Thiokol plastic effects a reduction in milling time of a standard Thiokol D compound from 40 to 15minutes for 8.500-gram mix on a laboratory mill. AXF reduces the shearing plasticity of Thiokol, as shown by the following data: Milling Time. blooney Plastloity Unit. Minutes st 100" C. 1 2 1 2 O F 40" 172 15 126
Standard Thiokol D Thiokol D 10 A X F Thiokol D 20 A X F 15 81 The longer millinp time with the standard Thiokol D compound -8s eeoe~saryto get the mix into aheet form.
+
+
100
I
I
I
I
I
I
1
TABLE IV. AXF vs. R ~ B B EINR TEIOKOL A COMPOUVDS (Cured 60 minutes at 141' C.) Formula 100 RQ Olefin rtolyadfide plmtio, Thiokol A Rubber 5 AXF Diphenyl guanidine 0.25 Tetramethylthiiiism disulfide 0.10 Zino oxide 10 stea,ric acid 0.5
....
CY
BR
1w
1W
20
_... 0.25 0.10
10
0.5
Tcnaile atrerath: Kg./m. om. 511.7 60.6 Lb./h. in. 764 862 Max. dongstion. % 220 a50 20 52 set, % Immeraed 7 Days i n Gaaoliiie at Room Tempeistuie Tensile strength: Ks./sa. om. 48.8 50.5 694 LE.786. in. 718 Max. elongation, % 290 220 22 26 Set % v i increase. % 25.8 0.0 Immerand 7 Dsva irI Spindle Oil at 70' C. Tenaile strength: rtg./sq. om. 47.7 43.8 Lb./sq. in. 623 678 Mar. eiongstion, 200 240
set %
20
voi.inorease,%
1.2
TABLE V. EPFECT OF AXF
IN
AXF
29.6
OH
1w
...
NZ
1W
55 10 0.5
0.3
60.7
864 470
1. , t. i lIrnmeised 7 Dam ill Geaoline a t Room Temperature 'rensiie strenilti>:
&t~ L7. ,"
Fz~cenr E ~ o ~ c a w m
FIQURE 8. STREBESTRAIN CURVES OF DUPRENE ASD D~'RENE-AXFCOMPOUVDS
0.25 0.10 10 0.5
49.0 697 290 43 46.2 657 270
35
0.0
42.8 608 230 24 0.0
141' C.)
Gas55 Zinc azide 10 Steario acid 0 5 Altar dibensothiawl disulfide 0.3 Properties Unsged Tannlle atrength: K d s s . cm. 72.3 Lb./sq. in. 1027 M a x . elongation, 7% 450
Kg./sq. em.
20
THIOKOL D COXPOWNDS
(Cured30 minutes at Formula Olefin polysulfide plmtio. Thiokol D
22
....
46.5
Lb./8q. i n . , 680 Mer. elongation. % 460 set 7% 20 v d inoreaae. % 2.1 Immersed 7 Days in Spindle Oil at 70Tenaile strength: Ka./sn. a n . 32.7 Lb./sq. in. 464 Mar. elongation, % 420 21 set, % voi. inorease, % 1.4
54.0
768
510
25 2.2
OA 100 20 55
I0
0.5
0.3
52.2 742 480 10 ..
40.8 577 520 34
2.R.
C. 45.4 646 520 23
2.8
33.0 489 530 31 2.8
280
INDUSTRIAL AND ENGINEERING CHEMISTRY
Table V shows the test data for a typical compounded olefin polysulfide plastic (Thiokol D) and for similar compounds to which 10 and 20 parts of AXF, respectively, were added. No attempt has been made in this paper to discuss all the possible applications of AXF as a compounding material. It is desired to point out that the process for preparing the material has been brought under such control as t o make possible the preparation of a type of material with uniform physical properties but capable of controlled variation as to hardness and viscosity. The material has been found to have interesting properties as a plasticizing agent and as a stabilixing agent for compounded DuPrene in storage. It also has distinct possibilities as a processing agent for polysulfide plastics and enhances some of their useful properties. More recent investigations which have not yet been concluded suggest that AXE’ may find important application in the wire insulation field. These features of AXF application include improvements in the oil and solvent resistance of cable coverings, and the still more important property of high resistance to electrical breakdown. Details of these
VOL. 28, NO. 3
developments will be reserved until such time as a more complete quantitative study has been made.
Literature Cited (1) Brous, S. L., and Semon, W. L., IND. ENQ. CHEM.,27, 667 (1935). (2) Carothers, W. H., Williams, I . , Collins, A. M., and Kirby, J. E., J. Am. Chem. Soc., 53, 4203 (1931). (3) Du Pont de Nemours, E. I., & Co., Ino., DuPrene Manual, Aug. 1, 1934. (4) Hayden, 0. M., and Krismann, E. H., IND. ENG.CHEM.,25, 1219 (1933). (5) Mooney, M., IND.ENG.CHEM.,Anal. Ed., 6, 147 (1934). (6) Patrick, J. C., and Mnookin, M., U. S. Patents, 1,854,423 and 1,854,480 (1932), and numerous subsequent patents. (7) Shinkle, S. D., British Patents 407,948 and 415,953 (1934); U. S. Patents 2,016,026 and 2,016,027 (1935). (8) Thies, H. R., and Clifford, A. M., IND. ENO. CHEM.,26, 123 (1934). (9) Rhitby, G. S., and Katz, J. R., I b i d . , 25, 1204, 1338 (1933). (IO) Wright, J. G. E., Chem. & Met. Eng., 39, 438 (1932). RECEIVED October 15, 1935. Presented before the meeting of the Division of Rubber Chemistry of the American Chemical Society, Akron, Ohio, September 30 and October 1, 1936.
The original of this, No. 63 in the Berolzheimer series of Alchemical and Historical Reproductions, is in the Museum and Art Gallery of Derby, England, the native city of the artist. It was painted about 1771, having been shown in the Exhibition of the Society of Artists of Great Britain of that year. Accordin to the artist, this painting represents $’The Alchymist, in search of the Philosopher’s Stone, discovers Phosphorus, and prays for the successful conclusion of his operation as was the custom,pf the Ancient dhymical Astrologers. Joseph Wright, commonly known as “Wright of Derby,” was born in 1734. His work was largely portraiture and landscape. He studied in London under Thomas Hudson, the teacher of Reynolds, and achieved his best results in the portrayal of artificial light. He was elected an A. R. A. in 1781, an R. A. in 1784, and died when 63 years old. W. Pether, the well-known engraver, executed a very fine engraving of this famous painting. A detailed list of the first sixty reproductions, together with full particulars for obtaining photographic copies of the originals, appeared in our issue for January, 1938, page 129, where also will be found Reproduction No. 61. Reproduction No. 62 appears on page 241 of our February issue.
The AlchyrnistB y Joseph Wright
