Elastomers from Fluoroprene W. E. ILIOCHEL, L. F. SALISBURY, A. L. BARNEY, D. D. COFFMAN, AND C. J. MIGHTON E'. I . du Pont de Nemours & Company, Wilmington, Del. Fluoroprene homopolymer and copolymers have been prepared in emulsion systems and examined critically to evaluate their possibilities. Vulcanizates of fluoroprene rubbers, in general, have good sunlight resistance, aging characteristics, and oil resistance like the other polyhaloprenes-e.g., neoprene-and they have excellent freeze resistance as well. Copolymers of fluoroprene have been prepared and those involving acrylonitrile, dimethyl(vinylethinyl)carbinol, or styrene have shown particularly attractive rubberlike properties.
S THE first member of the haloprene (1-3) or halogensubstituted butadiene series, fluoroprene (2-fluoro-1,3butadiene) occupies a position between butadiene and chloroprene in most of its properties and characteristics. For example -it polymerizes a t a rate approximately twenty-five times that of butadiene under comparable conditions but it is somewhat slower than chloroprene in polymerization rate. However, fluoroprene resembles butadiene in that i t copolymerizes readily in wide proportions with most 1,3-dienes and many monovinyl compounds, whereas chloroprene copolymerizes only incompletely with many monomers. In sharp contrast with the other haloprenes, fluoroprene polymers, like those of butadiene ( I I ) , have an amorphous rather than crystalline structure in the stretched state and they require reinforcement with fillers t o develop high tensile properties in their vulcanizates. Polyfluoroprene rubbers obtained in 85 to 90% conversions using selected emulsion systems have exhibited tensile strengths of 2800 to 3200 pounds per square inch at 400 to 500y0 elongation in tread stock type vulcanizates. These vulcanizates are highly freeze resistant and have the good oil resistance of corresponding chloroprene polymers. The resilience of the vulcanizates is excellent and their resistance to ozone and sunlight is good, although not as outstanding as that of corresponding polychloroprene products. Polyfluoroprene vulcanizates, unlike those of polychloroprene, propagate a flame when ignited but they burn at a much slower rate than GR-S or natural rubber. I n electrical properties they are superior to polychloroprene vulcanizates, approaching natural rubber in resistivity and power factor. CopoIymerization of Auoroprene with methyl methacrylate, dimethyl(vinylethinyl)carbinol, styrcne, or acrylonitrile, in particular, proceeds smoothly and yields rubbers which are generally superior to polyfluoroprene in processing characteristics and tensile properties. Usually small proportions (3 to 15%) of monovinyl compounds have been found to promote improvements, which in the case of butadiene are realized by copolymerization with much larger proportions (25 to 40%) of the monovinyl compound. I n particular, the copolymers containing 5% of dimethyl(vinylethiny1)carbinol or 10% of styrene have shown good mill behavior and, in tread type vulcanixates, have exhibited tensile strengths as high as 4400 pounds per square inch rat 54070 break elongation while other vulcanizate properties such as resilience, freeze resistance, oil resistance, and resistance to ozone and sunlight appear similar to those of polyfluoroprene. Rubbers of excellent oil resistance have been obtained readily in SO to 90% yields by copolymerization of fluoroprene with acrylonitrile. B y the use of 15% of acrylonitrile, polymers are obtained whose
vulcanizates have a particularly attractive combination of freeze and oil resistance. Copolymerization with larger amounts-e.g., 30 to 40%-of acrylonitrile yields highly oil-resistant products but a t appreciable sacrifice in freeze resistance. Tread type vulcanizates of these rubbers generally have high tensile strengths -Le., 4500 to 5000 pounds per square inch. POLYMERIZATION
The polymerization of fluoroprene monomer may be carried out in different ways as described for chloroprene and other haloprenes (4, 5, l a ) . It is affected markedly by the presence of certain impurities such as monovinylacetylene or peroxides, which should be kept a t as low a concentration as possible. Various emulsion systems may be used with fluoroprene, but in general systems based on sodium oleate as emulsifying agent have given rapid emulsion polymerization and the resulting products have exhibited good physical properties. For the polymerizations reported here the aqueous system was prepared by dissolving 1.05 grams of U.S.P. sodium hydroxide in 140 ml. of water and adding 4.0 grams of crude oleic acid (red oil). One gram of potassium persulfate and 1 gram of Daxad 11 (a condensation product of a naphthalenesulfonic acid and formaldehyde) were dissolved in the aqueous mixture and the solution was frozen in the bottom of a 400-ml. capacity pressure bottle. Then 10 ml. of a 1% solution of potassium ferricyanide were added and .likewise frozen. T o the cold tube was added 0.4 gram of dodecyl mercaptan (commercial product known as DDM) and 100 grams of fluoroprenc. The tube was flushed with nitrogen and capped with a bottle cap having a thin polythene liner. Polymerization was effected by rotating the sealed pressure tube end over end in a constant temperature bath at 30" C. for 5.5 hours. T o the resulting latex was added 2% of a phenyl-l-naphthylaminediphenylamine (55 to 45) liquid eutectic mixture dispersed in water, and the latex was coagulated with acetic acid and brine. The product was washed with warm water on a corrugated rubber mill for 10 minutes and then milled to dryness on warm smooth rolls. There were obtained 96 grams of light brown, smooth milling, plastic polymer. The same polymerization procedure was used with only 90 ml. of water in place of the 140 ml. given above to prepare polyfluoroprene for latex applications. VULCANIZATION
Polyfluoroprene and its copolymers were readily vulcanized in gum or filled stocks. The compounding formula for the tread type stock used for polyfluoroprene throughout this investigation is as follows: Tread Type Stock A Polyfluoroprene, g . Medium processing channel black, g . Phenyl-I-naphthylamine, g . Stearic acid, g . Zinc oxide, g. Magnesia, extra light calcined, g . Sulfur, g .
100 40 2
1 10 10 2
Various modifications of this formula are possible to enhance different properties. The optimum cures in press-cured slabs were generally obtained with this formula in 60 minutes at 153" C.
2285
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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TABLE I. TREAD TYPEVULCAKIZATE COMPOSITIONS Neoprene Type G N Neoprene T pe F R Hevea (smoged sheets) GR-S Butadiene-acrylonitrile
B 100
l?i/36ll
B;t~~ie~e-acrylonitrile (60/40) M P C black Extralieht calcined magnesia Zinc oxrde Phenyl-1-naphthylamine Stearic acid Sulfur Mercaptobensothiazolr 2-Mercaptothiazoline Accelerator 80W Benzothiasyl disulfide
...
. . . .
. . . .
C
100'
D
:::
. . . . 100 . . . . . . . . . . . . . . . . . . .,.
36 4 5 2 0.5
40 4 6 2 0.5 1
E
48
F
G
.. .. .. .. .. .. .. .. .. lob'' ...
. . . . . .
......
100
.._ 50
.
I
.
47
...
100 45
.5 ~ . 2
1.5 1.25
,.. . . . . . . . . . . . . ,,. ,..
... ...
...
. . . . . .
1.25
a Butyraldehyde-aniline condensation product.
TREAD TYPEVTJLCAXIZATE TABLE 11. POLYFLTJOROPRESE PROPERTIES
of its original tensile strength after 48 hours' immersion in kerosene and water, respectively, a t 100' C. Tread stock type vulcanizates of polyfluoroprene generally exhibit 5 to 6% volume increase in water after 48 hours' immersion a t 100 C. OZONE AND SUXLIGHT RESISTANCE.Outdoor exposure tests of tread stock-type vulcanizates stretched 150% of their original length have shown that polyfluoroprene is better than Hevea, GR-S, Neoprene Type FR, and a butadiene-acrylonitrile (60/40) copolymer in sunlight resistance but is inferior to Neoprene Type GX (Table V). A polyfluoroprene vulcanizate containing 1% of a mixture of microcrystalline waxes used as a sun-checking inhibitor appeared as durable as neoprene in outdoor tests. I n ozone resistance, polyfluoroprene is markedly supcrior to Hevea or GR-S but is much inferior to Neoprene Type GN (Table VI). This test is based on exposure of sharply bent vulcanizates to ozone of a given concentration and determination of thc length of time before cracks develop. COPOLYMERS OF FLUOROPRENE
(Cure, 60 minutes a t 153' C.) Tensile 5trengt.h at.25'
Durometer hardness (Shore A) Rebound (Schopper) Tear resistance b
2900 Ib./sq. in. 400 56 1650 ib./so. in.
FLUOROPREXE-DIMETHYL(VIXYLJTTHI~TYL)CARBIXOL COPOLYMERS
( 7 ) . With as little as 570 of dimethyl(vinylethiny1)carbinol
72
44 % 210 lb./in.
TABLETIL
Tensile tests conducted according to A.S.T.X. specifications D412-41. b A.S.T.M. designation, D624-44.
Q
The density of polyfluoroprene is 1.13, about 10% less than that (1.23) of the next higher polyhaloprcne, neoprene. Other elastomers used for comparison were compounded as indicated in Table I. POLYFLUOROPRENE PROPERTIES
T'ulcanizates of polyfluoroprene have TENSILE PROPERTIES, exhibited tensile strengths of 2800 to 3200 pounds per square inch in tread type stocks (Table 11) but generally only 800 to 900 pounds per square inch at 1000% break elongation in pure gum stocks. Latex films in gum vulcanizates (100 polymer solids, 5 zinc oxide, 2 sulfur, and 1 sodium dibutyldithiocarbamate, cured 120 minutes a t 141 C.) have shown somewhat higher tensile strengths than milled polymers, and the highest gum vulcanizate tensiles, 1300 to 1500 pounds per square inch, have been obtained from latexes prepared at low temperatures-i.e , 5" to 10' C. None of the fluoroprene polymers has shown crystallinity in x-ray diffraction measurements even at elongations of 1 0 0 0 ~ o . The tensile properties and resilience of polyfluoroprene vulcanizates are, in general, equal or superior to those of GR-S in comparable vulcanizates, but are inferior to those of Hevea rubber or Xeoprene Type GN (a polychloroprene identical with GR-M currently manufactured by the Office of Rubber Reserve, Reconstruction Finance Corporation a t Louisville, Icy.). Polyfluoroprene has approximately half the tear resistance of Neoprene Type GN but is similar in this respect to GR-S. FREEZEAND OIL RESISTANCE.Polyfluoroprene exhibits better resistance to both stiffening and embrittlement a t low temperature than Iieoprene Type FR, the most freeze-resistant neoprene (Table 111). I n general, polyfluoroprene vulcanizates are comparable t o those of Hevea or GR-S in freeze resistance and are much superior t o those of commercial oil-resistant rubbers. The oil resistance of the fluoroprene rubber compares favorably with that of Neoprene Type GN, as indicated by volume increase after 48 hours' immersion in kerosene a t 100 C. (Table IV). A polyfluoroprene vulcanizate (tread type, cured 60 minutes at 153 C.) which had an original tensile strength of 3080 pounds per square inch at 530y0 break elongation, retained 69% (TB/EB = 2130/520%) and 75% ( T B / E B= 2310/570%) O
Vol. 40, No. 12
Test Tioa, ' C. Fsob, C. Bent loopc,
FREEZE RESISTANCE FOR TREADTYPE STOCKS
Polyfluoroprene. Stock A , Cured 60 Min. a t 153' C. - 48 48 C. 62
--
Neoprene Type TR Hevea Stock GR-8 Stock Stock C, Cdred D, C&ed 30 E , d r e d 45 20 Min. a t X n . at hfin. a t 1 4 1 O C. 141" C. 141' C. 39 - 44 49 -45 - 53 - 47 -GZ Below -62 57
-
-
-
a Temperature a t which a stretched vuicanizato cooled t o -70' C. and released shows 10% retraction. Tao tests (6). Temperature a t which vulhanizate exhibits Shore hardness midway between 100 and the room temperature value (15). C Breaking temperature after 1-hour exposure. Modified A.S.T.M designation D736-43T.
TABLE IV. COMPARISON OF FREEZE AND OIL RESISTANCE
Vulcanizate Stock Polyfluoroprene Neoprene Type F R Neoprene Type G N Butadiene-acrylonitrile (75/25) Butadiene-acrylonitrile
Vulcanizate Composition
Cure
F
Min. 60 20 30 30
C. 153 141 141 141
Tna O C.' -48 -39 -24 -26
G
40
153
- 12
.4
C B
(60/40)
Volume Increase after 48 Hours in Kerosene a t 1000
c., %
70 to 75 90 to 95 65 to 70 24 12
GR-5 E 45 141 -51 Temperature a t 10% retraction in Tso test (6).
200
TABLE V. SUNLIGHT RESISTANCE OF TREAD TYPE TrULCANIZATESa
(After exposure t o summer sun a t Wilmington, Del., o n 45'* south racks) Vulcanizates Checked, Days Cracked, Days GR-S 2 10 Hevea 2 10 Butadiene-acrylonitrile (60/40) 10 19 Neoprene Type F R 19 10 Polyfluoroprene 16 24 Neoprene Type G N 218 a Same stocks and cures as given in Table IV; Hevea, stock D, cured 30 minutes a t 141" C.
...
TABLE 1'1.
OZOKE
RESISTANCE OF TREAD TYPEVULCANIZATBS"
Vulcanizate
Time to Failure of Sharply Bent Vuloanizatc in Presence of Ozone, Min. 4 4
12
18 48
Same stocks and cures as given in Table IV; Hevea, stock D, cured 30 minutes a t 141O C. (I
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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tion of the hydroxyl group in these polymers TABLEVII. FLUOROPRENE-DIMETHYL(VINYLETHINYL)CARBINOLdecreases the water resistance somewhat. COPOLYMERS~ FLUOROPRENE-STYRENE COPOLYMERS (9). Composition 97/3 95/5 90/10 85/15 80/20 75/25 50/50 Highly freeze-resistant rubbers which exhibit DDMa, % 0.25 0.25 0.30 0.10 0.10 0.10 0.10 greater tensile strength and better processing Product yieldb, % 93 90 84 84 89. 86 85 Mill behavior fair good good good fair excel. good characteristics than polyfluoroprene have also Tread tvDe vulcanizate ~. DroDertiis been obtained by copolymerization of fluoroprene Cure, min. a t 153O C. 30 60 100 50 40 50 30 with small amounts of styrene but, on the whole, 1450 1560 1420 1820 1560 2020 1930 Modulusat300% lb./sq.in. Tensile, lb./sq. ik. 3660 3410 3530 3640 3610 2950 2530 the styrene copolymers do not process so satisElongation a t break, Yo 500 475 520 440 480 380 350 70 70 65 75 73 70 78 Hardness (Shore A Durfactorily as corresponding dimethyl(vinylethiny1)ometer) 46 46 36 43 R e b o y d (Schopper), % 35 31 10 carbinol compositions and they are somewhat in-48.0 -46.9 -40.2 -39.0 -33.5 -27.0 -1.5 T L Q ~C. . ferior in oil resistance (Table VIII). In order t o 76.0 74.5 69.5 66 .O Vol. increase in k'erosene, 61.3 48.6 26.7 rnl /o obtain significant improvements in the copolymer, Vol. increasein water, Y o d 4.5 4.8 15.2 . . . 2 0 . 3 20.2 10% styrene is needed and the resulting vula Polymerization was carried out in 4% sodium oleate emulsion a t 30' C. using the indioated amounts of dodecyl mercaptan (DDM) as modifier. canizates are not so resistant t o the swelling acb Total yield of produot (containing soaps and antioxidant) divided by amount of monomer and multiplied by 100 to convert to per cent. tion of kei-osene as those of polyfluoroprene. The Temperature a t 10% retraction in T60 test (6). fluoroprene-styrene copolymers are slightly inferior d Volume increase after immersion for 48 hours a t looo C. t o polyfluoroprene in resistance to stiffeninga t low temperatures but they appear to be equal in their resistance to embrittlement in the cold. They are better than polyfluoroprene and the fluoroprene-vinylethinylI 1 I I carbinol copolymers in electrical properties. FLUOROPRENE-ACRYLONITRILE COPOLYMERS.Copolymerization of fluoroprene with acrylonitrile leads to rubbers having outstanding oil resistance. The most attractive compositions L F R E E Z E RESISTANCE from the standpoint of both oil and freeze resistance appear to be those containing 3 to 20% of acrylonitrile since they yield vulcanizates having the best over-all combinations of properties (8) (Table I X and Figure 1). The introduction of 30 to 40% of acrylonitrile leads t o products having high oil resistance but a t appreciable loss in freeze resistance. I n Figure 1 the curve of KEROSENE RESISTA~Z kerosene resistance shows only slow change below approximately 80% fluoroprene. These products tend to be dry and somewhat difficult to process without softeners.
...
C
Change i n freeze resistance and kerosene resistance with fluoroprene content in tread type vulcanizates
TABLE VIII.
FLUOROPRENE-STYRENE COPOLYMERS" 95/5
Composition
90/10
85/15
75/25
50/50
marked improvements in mill behavior and tensile strength are 0.4 0.3 0.3 0.3 0.3 DDM % Produbt yieldb, % 87 93 94 96 10.0 realized without any appreciable sacrifice in freeze or oil resistfair good good v. good fair Mill behavior ance. As the proportion of the carbinol is increased progresTreed type vulcanizate properties 50 GO 50 60 Cure, min. a t 153' C. sively from 5 to 50% there is a slight improvement in mill be1360 1590 1360 1730 . .50 . Modulus a t 300%. lb./sa. in. 3320 havior and kerosene resistance attended by a decrease in freeze Tensile lb /sq. in.' 3580 4090 3320 1450 425 Elongakion a t break 01, 500 520 500 290 resistance (Table VII). Copolymers of 95/5 composition pre1650 1700 Tensile a t 70' C. Ib:/sq. in. 1690 1700 ...85 68 70 70 Hardness (ShoreA Durometer) 67 pared under preferred conditions have yielded vulcanizates 48 34 34 14 46 Rebound (Sohopper), % (tread-type compound A) having tensile strengths as high as TioC,.' C. -46.0 -- 4 2 . 0 -- 3 8 . 0 -29.0 -1.4 Vol. increase in kerosene, % 102 100 97.3 92.8 104 4400 pounds per square inch a t 500y0 elongation. At 70" C. a Polymerization carried out in 4% sodium oleate emulsion for 5.5 hours the tensile strength of these tread type vulcanizates averages a t 30' C. using amount of modifier indicated. 1700 to 2100 pounds per square inch a t 300 to 400% elongation. 6 Total yield of product (containing sorqp residue and 2% antioxidant) divided by amount of monomer and multiplied by 100. The aging characteristics of Temperature a t 10% retraction in T60 test (6). these vulcanizates compare favorably with those of NeoTABLE IX. FLUOROPRENE-ACRYLONITRILE COPOLYMERS prene Type GN in convenComposition 95/5 90/10 85/15 80/20 75/25 70/30 60/40 50/50 tional tests. n D M a 01, 0.8 0.9 0.3 1.25 0.8 1 .o 0.3 0.9 The preferred (95/5) fluoro3 3 3 Hr. a t hOo C. 3 3 5 5.5 3 prene - dimethyl(vinylethiny1)Product yieldb, Yo 98 102 97 93 83 91 93 97 Mill behavior Poor V.poor Fair V.poor Poor Fair Poor Poor carbinol copolymers are similar Tread type vulcanizate properties to polyfluoroprene in sunlight Cure min. (" C.) 20(153) 60(153) lOO(141) lOO(141) 60(153) 30(153) 15(141) 30(141) Modblus a t 300%, lb./sq. in. 1900 1790 1480 1990 2590 1650 2270 resistance and not greatly in4090 4830 4460 4150 Tensile, Ib./sq. in. 3070 3440 iioo 2480 390 380 520 470 400 480 395 140 Elongation a t break, % ferior in resistance to cracking Tensile a t 70' C., lb./sq. in. . . . 2070 2020 2190 1680 1420 in ozone. They are superior t o 70 75 '73 Hardness (Shore A Dur70 70 80 ' 83 70 ometer) Neoprene Type GN in com40 33 32 30 Rebound (Schopper), % 47 46 16 12 -25.4 -23.0 -37.1 -32.6 -17.5 -10.2 ... TIQ C.C -46.0 pression set and abrasion resist23.9 18.0 15.0 9.6 6.8 6.1 Voi. increase in kerosene. ?& 68.5 31.1 ance as indicated by the D u Polymerization carried out in 401, sodium oleate emulsion a t 30' C. using indicated amounts of modifier. b Total yield of dry product (containing soap residue and antioxidant) divided by amount of monomer and Pont (American Society for multiplied by 100. Testing Materials, method A) 0 Temperature a t 10% retraction in TKO test (6). abrasion test. The introduc'
Q
2288
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 40, No. 12
- 50
wo e
-40
I? .u
2s W
- 30
w
f
-20
I 100
'Figure
80
2.
60 FLUOROPRENE, %
F l u o r o p r e n e - B u t a d i e n e - Aerglonitrile Copolymers
I 100
Figure
60 40 FLUOROPRENE.%
80
3.
20
0
Fluoroprene-Butadiene-iicry lonitrile Copolymers
C h a n g e in freexe resistance of tread type vulcanizates with fluoroprene content a t different acrylonitrile levels
Change in kerosene resistance o f tread tvpe vulcanieates with fluoroprene content at different ac&onitrile levels
Rubbers made' by the copolymerization of fluoroprene with 15y0of acrylonitrile have part,icularly good vulcanizate properties. I n tread type stocks cured 60 minutes at 153" C. such copolymers have exhibited tensile strcngt,hs of 3800 to 4800 pounds per square inch with 300% break elongation a t 25" C. and 2700 pounds per squarc inch with 400% clongation a t 70" C. Tear strengths in the A.S.T.3.I. test have varied from 235 t o 395 pounds per inch. These products arc inferior to the neoprenes in resistance t o oven aging ( T B I E B = 2270/160 after 2 days a t 121 C.) but are nearly equivalent in resilience and heat, buildup. They are superior to polyfluoroprene in sunlight resistance (checked on 19th day and cracked after 41 days, Table V) and ozone resistance (20 minutes, Table TI) but are still inferior t o Xeoprene Type GN. These copolymers have better compression set and abrasion resistance than Neoprene Type G S . The solvent resistance of the fluoroprenc-acrylonitrile (85115) copolymer is much superior t o that of Neqprene Type G S and is a t least equivalent to that of a butadiene-acrylonitrilc ( 7 5 / 2 5 ) copolymer in comparable vulcanizates, while in freeze resistance the fluoroprene copolymer is better t,hnn either Keoprcnc Type G S or the butadiene copolymer (compare Tables IT' and IX). A fluoroprene-acrylonitrile (85/15) copolymer tread type vulcanizate (cured 100 minutes at 141" C.) had an original tensile st,rengt,hof 4860 pounds per square inch and retained a tensile of 4000 pounds per square inch a t 520% elongat,ion after aging for 2 days in kerosene a t 100" C. Yulcanizates of the fluoroprene-acrylonitrile (70/30) copolymers (tread-type stock A cured 30 minutes a t 153" C.) are slightly better than those of a butadiene-acrylonitrile (60/40) copolymer (stock G of Table I cured 40 minutcs a t 153' C.) in oil resistance (8 t o 10% volume increase in kerosene a t 100 O C. in 2 days -us. 125% for thc butadiene copolymer) and arc appreciably better in freeze resistance according t o the Tlo valuese.g., Tlo = 17" and -12" C., respectively ( 6 ) , and FSo valuese.g., F;o = 19" and -11" C., respectively. Tl6 is the temperature at which a vulcanizate shows 10% retraction in the TSO test. F;, is the temperature a t which a vulcanizate exhibits a Shore durometer hardness midway between 100 and the room temperature value (13). Furthermore, the fluoropreneacrylonitrile copolymer is superior in resilience-e.g., the Schopper rebound is 24 to 30% in these tread type stocks 2's. 18% for the butadiene-acrylonit,rile (60/40) copolymer vulcanizate.
butadiene, and acrylonitrile in the same 4To sodium oleate emulsion has yielded rubbers ranging from highly freeze-resistant t,o highly oil-resistant products depending upon the conipoaition of the initial monomer mixture. The variations in these propert,ics obtainable as functions of the compositions are illustrated ill Figures 2 and 3, in vhich are plott'ed families 0 ) curves depicting the changes in 01'7 values and kerosene resistance v-ith changing fluoroprene content for nitrile contents of 0, 10, 20, 30, and 405; (the remainder in any given copolymer is butadiene). The vulcmizate properties of these thrce coniponen t copolymers vary with their compositions, of coiirse, but it is possihle to obtain good rubberlike properties.
FI,COROPRENE-BUTADIENE-ACRYLOP~ITRILE COPOLYMERS.Copolymerization of three component mixtures of fluoroprene,
MQYOMER SYNTHESIS
Fluoroprene monomer was prepared by the gas phase addition of anhydrous hydrogen fluoride to monovinylacetylene (IO). Yields of 50 to 707,, a t approximately 40% conversion, wcre ohtained during the first 12 to 14 hours, after which there was a gradual decrease in conversion to about 10% after 40 hours of operation. The reactor employed consisted of a 6-foot lcngth of 1.5-inch black iron pipe arranged vertically with a u-ater-heated jacket and packed with a charcoal-supported catalyst. To prcpare the catalyst, charcoal was impregnated with mercuric nitrate solution equal to 100 gra.ms of mercuric nitrat'e pcr liter of charcoal and roast.ed a t 100' to 135' C. in a stream of dry air until free mercury appeared in the exit t,ube from the roaster. Commercial, anhydrous hydrogen fluoride and monovinylacetylene, mixed Kith equal volumes of nitrogen, were passed into the reactor bJseparate entry ports. Alixing of the reactants must take plane over the catalyst or in a large space connected directly to the catalyst bed by a wide passage. The mixture of monovinylacetylene and hydrogen fluoride was adjusted to a mole ratio of 1 to 1.2 and, with the 2 volumes of nitrogen diluent, was passed through the catalyst bed with a contact time of 40 t o 50 seconds and a temperature of 50' to 100 C. The product, was led directly from the bottom of thc reactor into soda lime in an iron container to absorb the excess hgdrogcn fluoride. The gas stream was then dried with calcium chloride and passed through a condenser cooled to -80" C. to obtain thc crude product. Careful fractional distilla,t,ion of the crude yielded pure fluoroprene boiling a t 11.8' to 12.0" C. (at 760 mni., correcting 0.1" for each 3-mm. variation in pressure) (densit'y = 0.849 and ng = 1.401). The residue contained a srnall amount of 3,3-difluoro-l-butene boiling a t 24.5 C. (densit,y = 0.951 and n; = 1.330). Fluoroprene so obtained behaved normally in Diels-Alder reaction with 1,4-naphthoquinone, giving 2-fluoro1,2,3,ltetrahydroanthraquinoneconvertible to 2-fluoroanthi-aquinone by oxidation. The fluoroprene was kept under an atmosphere of nit,rogen t o prevent the formation of peroxides and waq stored over hydroquinone t o inhibit polymerization. Fluoroprene and t,he fluoroprene elastomers described in tliiv O
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1948
paper represent a laboratory development only. materials described are commercially available.
Sone of the
ACKNOWLEDGMENT
The authors gratefully acknowledge the assistance of staff members of the Organic Chemicals Department of this company in testing some of tho vulcanizates doscribed in this paper. LITERATURE CITED
(1) Carothers, W. H., and Collins, A. M., U. S. Patent 1,950,431 (1934). \----,
(2) Carothers, W. H., Kirby, J. E., andcallins, A . M . , J.Am. Chem. SOC., 55,789-95 (1933). (3) Carothers, W. H., Williams, Ira, Collins, A. M., and Kirby, J. E., Ibid., 53,4203-25 (1931).
2289
(4) Collins, A. M., U. S. Patent 1,967,861 (1934). (5) I b i d . , 2,264,173 (1941). (6) Fornian, D. B., and Radcliff, R. R., IND.ENG.CHEX..38, 1048-52 (1946). (7) Mochel, W. E., U. S.Patent 2,426,560 (1947). (8) I b i d . , 2,429,838 (1947). (9) Salisbury, L. F., U. S. Patent 2,416,456 (1947) (10) I b i d . , 2,426,792 (1947) ; other pending patent applications. (11) Sebrell, L. B., and Dinsmore, R. P., I n d i a Rubber W o r l d , 103, 37 (1941). (12) Starkweather, H. W., and Collins, A . &I., U. S. Patent 2,227,517 (1941). (13) Yerzley, F. L.. and Fraser, D. F. IND.ENG. C H E M ,34, 332 (1942). RECEIYED March 6, 1948. Contribution No. 226 from t h e Chemical Department, Experimental Station, E. I. du Pont de Nemours & Company, Wilmington. Del.
Logarithmico-Normal Distribution in Breakage of Solids BENJAMIN EPSTEIN Coal Research Laboratory, Carnegie Institute of Technology, Pittsburgh, P a .
In this paper a statistical model. is constructed for breakF,(x); a second step of the age mechanisms and a breakage process is conceived of as process operating on Fl(x) under investigation in depending on two basic functions: P,(y), the probability will lead to F&) and so on this laboratory is the characof breakage of a piece of size y in the nth step of the breakterization of the strength of with the nth step of the breakage process; and F ( x , y ) , the distribution by weight of coke, or more precisely, the age process operating on particles of size x less than or equal to y arising from the F " - ~ ( z )and leading t o F n ( z ) , factors affecting the resistbreakage of a unit mass of size y. Under certain hyance of coke to size degradathe size distribution after n potheses about P,(y) and F(x,y) it can be proved that the tion. The study of these steps. Basically the equadistribution function F,(x) after n steps in the breakage questions has led in a natural tions describing the effect of process is asymptotically logarithmico-normal, a form of any given step of the breakway t o the consideration of distribution frequently observed. the mechanism of the breakage process express the fact t h a t t h e change in the cumuage of solids in general. It lativeweight finer than a given is the purpose of this paper size, r, is given by the amount of material of size less than or to report some of the results found thus far. I n the course of this work it has become increasingly evident equal t o x which arises from the breakage of material of size that certain types of crushing and grinding operations lead t o greater than or equal to x in the given step under consideration. I n addition t o the concept that a breakage process can be the logarithmico-normal distribution (6)-that is, a distribution which plots as a straight line on probability paper. This has considered as a succession of discrete events, two basic functions which are essentially statistical in nature are introduced. These been recognized empirically in the literature on the grinding and crushing of solids-for example, Austin (1) who gives an extensive functions will determine the progress of a breakage process. literature, and Hatch and Choate (9)and Hatch (8). However, no They are: (A) P"(y), the probability of breakage of a particle of attempt has been made in these articles t o give physical reasons size y in the nth step of the breakage process; and (B) F(z,y), which would make the occurrence of logarithmico-normal size disthe cumulative distribution by weight of particles of size x 5 y tributions plausible. Indeed, the only published attempt t o conarising from the breakage of a unit mass of size y. struct theoretical breakage mechanisms basedon thetheory of probThe introduction of these basic functions, coupled with the ability which will lead t o logarithmico-normal distributions seems underlying assumption that a breakage process can be broken to be due t o the Russian mathematician Kolmogoroff ( I d ) . up into steps, gives a framework within which the changes in the This paper, however, is relatively inaccessible and sketchy and is particle size distribution can be studied as a function of the based on the introduction of a number of complicated functions. number of steps in the process. It is recognized that consideration of the size (in the linear DESCRIPTION O F A THEORETICAL BREAKAGE MECHANISM sense) or dimension of the piece is not strictly justified except when dealing with essentially one-dimensional solids such as Any breakage process may be conceived of as composed of discrete steps and therefore it makes sense to talk of a breakage thin rods. In actual practice the pieces are three-dimensional event which will consist merely of a single step in the degradaand of irregular shape. I n this case the logical procedure would tion process. Viewed in this way, it is clear that the breakage be' to classify pieces according to volume because the principle process can be studied logically after any finite number of steps: of mass conservation then could be applied t o each piece broken. n = 1,2,. , N , . More precisely, if the original cumulative Unfortunately there are practical difficulties involved in measursize distribution by weight-that is, the per cent by weight less ing volumes accurately and quickly, and therefore it is common than or equal t o size x-is F,(z), then the operation of one step practice 60 divide a sample into linear size compartments by of the breakage process will give rise to a new distribution sieving through a series of wire-mesh screens of decreasing square
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