INDUSTRIAL AND ENGINEERING CHEMISTRY
1066
TABLE J'.
.
~IECHASICAL A S D A C I D TREATY~NTY OF STEEL SURFACES ox EASEOF OIL R~aror.41, EFFECT O F
(Medium-viscosity mineral oil of 472 seconds Saybolt Universal viscosity a t 100' F.: cleaner, 1.5% sodium orthosilicate 0.15% of sodium keryl benzenesulfonare: conditions, 60' C., 10 r.p.nl,, 5 minutes) Cleaning St:xnd;trtl It113 Treatment of Steel Surface Index 1)eviatioii Value l a . Smooth-rolled n o t pickled 86 1 6 l b . Smooth-rolled', pickled 44 2 2s. Smooth-rolled, not pickled 88 1 19 2b. Smooth-rolled, pickled 17 3a. Rolled with rougher surface, no: pickled 97" 7 31 3b. Same as 3a, pickled 47 4 8 4. Same as 3h h u f e d Sl 1; .~ 6 ; Same as 4, pickled 67 .. 6. Panels covered R i t h black iron oxide 72 > 7. Same as 6, pickled 11 Ground n i t h fine grain grinding 8. rr heel c, J 83 Same as 8, pickled 30 9. 8 Ground with medium-grain grind10. ing a h e e l 62 9 Ground with coarse-grain grinding 11. ~"
+
A light s:iridblabting treatmciit gave aurse cleaniiig than any of the otlwr treatments. These surfaces gave neither xvorse rcsults on pickling uor better results on passivation. P u t of this may bc due to the fact that the level of results was in the range that is 1eaFt sensitive. I t seems to be established, hu\vevcsr. that pa4v:Ltioii docs iiot C:IUYC any improvemcIlt a.hen the surfaces are quiti, rorigh.
,,
[. of o i l removal from metal surfaces is grwtly inis probably metal oxide
may tic different for dif.ed far more readily wlien containing considerable quantities oE fntc fatty arid is removed more readily when it, is absent. 3. 'The I J W S ~ I ~ C Iuf : tlie cold-rolled or worked s u r f x e condition seeins t o be more iniportarit in determining cleaning performance than gross surface roughness n-ithin a limited range. 4. Ease of cleaning diminishes as the roughness of the surface iiicreascs. After a certain level of considerable roughness. the effects apparciitly clue to the oxide film are lost.
17. 18.
Sandblasted lightly 14 SRme a8 15.pickled 16 Same aa 19, passivated concd. "Os 9 a Removal of sulfurized fatty base, deposited from 1: 9 solution in toluene gave value of 14 for Bame conditions as 3a and 55 for same condition a d 3b:
ACKNOWLEDGJIENT
19.
20.
The effect of other mechanical variations of steel surfaces WI? also studied to some extent, and the data are presented in Table V. Surfaces that were obtained by grinding with a fine-grnirietl grinding Thee1 gave rather good cleaning-for example, a clemiing index of 83 in the removal of medium mineral oil. Surfnce!: ground Fvith a medium and Kith s coarse Ivheel gave valucLs that were worse than those ground x i t h a fine n~lieel-62 arid Zi, respectively. As in the case of the cold-rolled panels, cleaning index decreased with pickling and increased with subsequent passivation, although the changes Tere smaller with the coarse ground surfaces than with those obtained with the fine grained wheel. Surfaces prepared with a shaper using a fine fecd gave conbidcsrably worse cleaning than those ground Kith a coarse wheel. This cleaning was made tvorse by pickling. Hon-ever, cleaning of t h i ~ iurface was not improved by passivation.
Apprwiatioii is espressed t o C. C. 1;:iivcett arid E. It, Itechel of the Frankford Arsenal Laboratory for their cooperation, and to the Ordnance Department for permission t o publish this paper. Special thsiiks :ire due J. ;\Iitclic.ll for helpful review of the manuscript m d to Adele Goldsteiri fiir performing a considerable amourit of tlic: experimental work. LITERATURE CITED
( I ) Brudi Ilcvcloyiiierit Co., "Surface Finish Xomenclature", 1945. ( 2 ) Harris, J . C., and Mesrs, li. R.,A S T M Bull. 120, 33 (Jan., 1943); 121, 33 (March, 1043); 129, 21 (May, 1944). ( 3 ) Herschman, H. K., J . Research S u l l . Bur. Stondards, 34, 26 (1945). (4) Sclilesinger, G., "Surface Finish", p. 152, London, Inst. of Production Engrs., 1942; Am. SOC. Mech. Engrs., .imcricen d., 11 (1942). (6) Spring, S., Forman, II. I., and Pede, L. F., IXD.Eso. CHEM.. .\x.\I,.ED.,18, 201 (1946). PRESENTED before the Division of Industrial and Engineerine Chemistry a t the 109th hZeeting of the AXERICAN C ~ I E M I C SOCIETY, AL Atlantic City. N. J.
Correlation of Tensile Strength with
Brittle Points of Vulcanized Diene Polvrners d
A. 81. BORDERS 4x1)R. L). .JLVE The Cood3eur Z'ire & Rubber Compurrj, fhrort 16, O h i o
F
OR several years work has been carried on here to evaluate a large number of diene polymers and copolymel's as rubberlike materials. The writers have observed that changes-in polymer composition vhich result in improved tensile strength and crack-growth resistance of the wlcanizate cause an increase in low temperature stiffness and a rise in brittle point. This generalization seems to apply for tensile values measured at elevated temperatures as well as for those a t room temperature. For example, a butadiene copolymer of dichlorostyrene can be made n-hich, as a tread type vulcanizate, exhibits a tensile
strength of over 1500 pounds per square inch a t 93" C., in comparison with 800 to 1000 pounds per square inch for GR-S in the same test tread formula a t the same temperature. The brittle point of the butadiene-dichlorostyrene rubber, however, is -35" C. or higher. GR-S treads in the same test have brittle points b e t w e n -55' and -60" C. Probably of greater practical importance is the fact that the vulcanizate with the higher brittle point is stiffer at temperatures well above the brittle point. The purpose of this investigation was to determine to what extent the maximum tensile strength of tread stocks of several
October, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
1067
number of butadiene and isoprene copolyniers were prepared by emulsion polrmerization with varying ratios of styrene, vinylpyridine, acrylonitrile, mono- and dichlorostyrenes. Stress-strain measurements at 27" and 93" C. and brittle tests were made for tread rulcanizates of each copolymer. To illustrate the dependeuce of tensile strength upon the brittle point, the maximum tensile strength ohser~edfor each rubber was plotted against AT. A s AT decrease%,the tensile strength of the isoprene and butadiene copolymers increases. Thus, those polymers with the higheqt brittle points hale the highest tensile strengths, at both of the teniperaturcs cwnsideretl. Points forall the butadiene polymers formone hand upon this plot. Those for isoprene rubhcrs fall 5liphtly lower; that is, the!
A
ha>e lower strength for a giren brittle point. Polydienes made in emulsion were found superior in their balance of tensile strength to brittle point to the diene rubbers prepared by other methods of polymerization. Tensile balues of Helea tread compounds at several temperatures are included; they show a marked superiority to the synthetic polymer tulcanizates in tensile strength at a giten AT. Similar measurements of Neoprene GU and Butyl compounds loaded with black furnished yalues of tensile US. AT falling within the band for but$diene polymers. A comparison of the effects of temperature upon the tensile of IIwca and GR-S tread compounds illuitrates the fact that the low hot tensile strength of GR-S is not the result of an ahrupt weakening at higher temperatures.
aynthetic rubbers varies with the trniperat iir(' tliffcrcnce betEecn tlie brittle point and the tensile testing temperature of each rubh(,r. These data can thcii he used t o judge the validity and extcnt of the general obscrvtttion tti:it cliangcs in copolymer composition vi11ic:h incrcases strcngtli :tlso r:tisc: t he hrittlt point.
n-ith A T valucs bctn-een 40" and 101)" C., and the second is the hot tensile rvith A T from 110" t o 180" The points form a continuous band for the butadiene polymers, although the room-temperature tensile points for rubbers of loiv brittle point. and t h r hot tensile values for polymers of high brittle point do not quite ovrrlap. I n representing rubbers of several ratios of trro conionomer8, no distinction was made in tlie symbol. Thus, in Figure 1 butadicne/styrene copolymers from charged ratios of 90/10 t o 50./50 are all represented by open circles. E:ach may be identi-
PROCEDURE
Since many of the data presented here m r c rollected over a period of several years, the compounding used for the tread test stjock was not identical for all of the ruhbern. Tl1r.y were alike, however, in that all contained either 45 or 50 parts of easyprocessing channel black. The loading for each rubber is indicated in the tables. Tensile values rcported by Tcner, Kingsbury, and Holt (11) for Hevea over a wide range of temperatures and used here for cornparison w r c for a t,rc*ad containing 40 parts of a n unspecified channel black. 0 t h ingredients in the 50-part-hlack cornpoun diene and isoprene copolymers (except those with were incorporated according to the Rubber Reserve test formula. The compound containing 45 parts of black is similar except that a combination of Captax and D P G is used in place of Captax alone, and sulfur is rcduced from 2.0 t o 1.6 parts. I n the cases of rapid-curing copolymers of vinylpyridine and in the cases of Butyl and Seoprenc, t l c other ingrrxknts wcre markedly different for prnper curing. Tensile values were measured over a range of c u m for each compound on t,hc Goodyear autographic machine a t 27" C. II). Tests a t higher temperatures were made on a standard 1,-2 Scott tester equipped Kith a heating jackct. Standard A.S.T.11. dumbbells, 1 X '/, inch, m r e used on the Scott , \vas t l i c highest tester. The tciisile value uscd in thc. ~ i r c w i istudy observed over the range of c u r e s Brittle point was determinctl liy nieans of ail impact tcst. Test specimens. 0.95 X 2.45 em., are riit from standard test sheets 1.8 to 2.5 mm. thick. One end of the w n p l e is clamped in the holder, and a piston is brought down sharply on the suspended end of the piece. T h e strips are tcTstet1 in air in a n aluminum cy1indt:r surroundcd by a dry ice-acetone hath. Temperaat the rat,e of approximately 1 ' per minute, and t,ure is lon~erc~d t,he blow is applied after each 5' C. change. Temperature a t which piece shatters is recorded as britde temperature. The comparison in Table I of brittle points obtained by this method with those reportctl hy Liska ( 6 ) s h o w satisfactory agrecment.
c.
fied by reference to the values in Table 11. One of the butadienezjt,yrene points represents data for a tread stock of German Buns S-3; it falls within the normal spread of the styrene rubbers. With increase in the amount of vinyl compound present in the butadiene copolymers, maximum tensile strengths increase and brittle points are higher. For a given weight proportion, some vinyl monomers are more effective than styrene in improving tensile, b u t it is apparent t h a t the sacrifice in brittle point ie similar for a given degree of rensile improvement, regardless of the comonomer. The batid of points for butadiene polymers may be compared 111 Figure 1 with a curve for tensile values of a Hevca compound over a wide temperature range, reported by Tener, Iiingsbury, and Holt ( 1 1 ) . TKOadditional points on this curre represent values obtained in this laboratory for a test compound containing 50 parts channel black (9). The marked superiority of tensile of Hevea over any butadiene rubber of comparable brittle point is apparent. The spread between the band of points for the butadiene rubbers and the curve for Hevea'inclicates that, over a certain temperature range, Hevea exhibits tensile values 500 to 1400 pounds per square inch higher at the same A T than any of the synthetic rubbers tested. Values for But,yl and Keoprene G S are similar to those of the hutadicne rubbers. Since these two polymers are funda~rient~ally different, they are included in Figure 1 only for comparison. Figure 2 represents a similar plot of tensile and AT values for a series of isoprene copolymers. I n general, the points fall below t h v for tlir huta.diene rubbers. and form a similar but broader
UISCUSSION O F RESULTS
The data ohtained, together with those of othvr workers used for compitrison, arc recortletl in Table 11. These data can hc plotted on ttvn ?cparate graphs, ror~ni-tcmpc'ra.t,uretensile against brittle point and hot tcrisilc against brittle point. It rvas considcrcd prefmiblt;, ho\vcver, to combinc thcse two i n onc diagram to permit, a tcst of the hypotlicsis that, maximum tcnsilo strengths of certain dicne copolymcrs inerrasc with a drcrcaw in the tcmpcrature spread, A T , between the brit,tle point and thc tcmperature a t \vliich the tensile measurement is madc. Figure 1 shows this comparison for butadiene polymers. I n most instances there arc txvo points for each polymcr: One tenailc value was dct,ermincd a t room tcmperaturc and, hence,
TABLEI . COMPARISON THOSEI~1:PORrEDBY
O F BRITTLEP O I S T RESELTST I T B LISIi.4 (6)FOR TREAD COUPOl3DS
Brittle Point. O C. Goodyear Liska S a t u r a l ruhber - 53 53 Polybutaaiene - 80 Below - 72 75/29 hutadiene:'styrene -570 - 63" 60/40 butatiwneistyrene - 40 42 Keoprene G S -40 - 39 Butyl -40 39 a Our d a t a for t h e copolymer containing approxiniately 24% combined styrene; t h a t of Liska probably a n earlier sample containing 21-22% atyrene.
-
-
10-68
Vol. 38, No. 10
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLE11. SUMM.4RY Black Loading, Parts/100 Rubber 45
Rubbero
45
50 50 B utadiene/styrene, 90/10 85/15 80/20 75/25 75/25 75/25 75/25 75/25
50 45 50 45 45
2110 2320 2310 2600 2370
...
...
75/25
68/32 ( B u n s 6-3) 65/35 65/35 65/35 65j35 55/45 50/50 50/50 Butadiene/acrylonitrile, 90/10 85/15 80/20 80/20
1020 (93; C.) 940 (93; C.) 715 (93" C.) 982 (86' C.) 840 (930 C.) 557 (1190 C.) 1030 (93" C.) 1125 (93" C.) 1010 (930 C.) 1410 (93' C.)
...
...
2920
70130 . ., ~
... ...
~
70/30 70/30 70/30 60/40 65/45 50/50 Butadiene/dichlorostyrene, 75/25 65/35 Butadiene/m-chlorostyrene, 75/25 70/30 67/33 65/35 65/35 65/35
60/40
OF
TESSILE AND BRITTLE P O I N T VALUES
Maximum Tensile Strength, Lb./ Sq. In. A t room ht BrittlQ temp. other point, (27' C.) temp. c. 1625 765 (93' C.) - 73 I500 700(93°C.) -73 1800 ... - 73 1870 ... - 73
... 1855
(bkb C.)
-68 - 65 - 60 - .57 - 57 - 37 - 57 -57 57 - 37 - 45 - 45
-
- 45 - 43 - 35 - 30 - 30 - 57 - 54 - 50 - 50 - 30 - 30 - 30 - xn __ - 25 - 20 - 15
50 50
3275
3200
1365 (82' C.) 1493 (82' C.)
-45 - 30
50 50 50 50 50 50 50
2500 2975 2800 3000 2730 3375
1110 (93" C.) 1205 (93" C.) 1175 (93' C.) 1095 (93' C.) 1155 (93' C.) 1445 (930 C.) 1865 (82'' C.)
-55 -46 -45 -43 - 43 -43 -35
3400
Monomer ratio indicated is t h a t charged into t h e polynierization reaction. b S R F black.
band. Thus for a given brittle point, the isoprene rubbers are weaker than the butadiene polymers. Effects of vinyl comonomers upon tensile and brittle point are the same as for the butadiene rubbers. Preliminary data for polymers of 2-methyl-1,3-pentadiene from this laboratory and that reported by AIcMillan, Bishop, Marple, and Evans (7) show that these rubbers have still higher brittle points than butadiene or isoprene polymers, but are similar or inferior in tensile strength. I n the Rubber Reserve test formula a methylpentadiene rubber had a tensile strength of 2150 pounds per square inch and a brittle point of - 1' C. Hence the methylpentadiene rubbers tested are inferior with respect t o $he balance of tensile and brittle point properties. METHOD OF POLYMERIZATION
All of the diene polymers and copolymers described here were made in emulsion. Polybutadienes and polyisoprenes formed by sodium-catalyzed mass polymerization have, in general, much higher brittle points than polymers of the same composition made in emulsion. This difference is illustrated in Table 111, which also includes data for polybutadienes reported by Conant and Liska ( 4 ) ; they observed the higher brittle point of sodiumpolymerized polybutadiene rubber. Since these mass polymers of higher brittle point do not exhibit better tensile strengths than emulsion polydienes, their position on the graph of tensile against AT is below the bands shown in Figures 1 and 2. Polydienes prepared by other workers in this laboratory with organometallic catalysts were found t o represent an improvement over sodium-catalyzed polydienes with respect
Rubbern Butadiene/mixed o- and p-chloros tyrenes, 80/20 75/25 7O/XO 65/35 Butadiene / vinylpyridine. 7 5 / 2 5 75/25 75/25 75/25 65/35 55/45 Polyisoprene Polvisoprene Polyisoprene Isoprene/styrene, 7 5 / 2 5 75/23 (j) 73/23 50150
50/50 (6) Isoprene/acryloniirile, 80/20 70/30 67/33 60/40 Isoprene,/methyl methacrylate, 75/25
Iaoprene/vinylpyridine, 80/20 80/20 75/25 75/23 75/25 Hevea (9) Hevea (11 ) Hevea (I 1 ) Hevea ( 1 1 ) Hevea (I 1 ) Hrvea ( 2 f ! Hevea (1 1 ) Hevea ( I I , Keopreue G N Seoprene G N Butyl (GR-I)
Black Lcading, Pnrts/100 Rubber 50 50
p0 a0 45 45 45 45
50 45 45 46 50 45 50 50 45 50
50
Maximum TenGle Strength, Lb./ Sq. In. At Brittle temp. other point, (27' C . ) temp. c.
A t room
2605 2975 2890 3000
1030 (93' C.) 1130 (93' C.) 1125 (930 C.) 1430 (93' C.)
2750 3150
1320 (93" C.) 130.5 (93' C.) 1437 (Bfj' C.) 903 ( I 19' C.) 1340 ( ~ c.) 0 1675 (93' C.)
...
... ...
3075 1300 1.550 1230 2200 2500 1640
2600 2700
45
1960
730 (93' C.)
4B 45 45
2420 2460 2495 2380 2200
50 40 40 40
4000
990 (930 C ) . 1100 (930 C.) 1010 (930 C.) 1110 (930 C.) 1200 (93" C . ) 5730 (93' 2500 (-40' C.)C.)
40 40 40
40 4.5 45 45
... ...
... ...
...
2770 3400 2800
- 5; - 30 - 5_5- 40 - 23 - 57 - 67 -s7 - 29 - 29 - 29 I d 0
-1
- 1
- 29 - 12
650 (93: C.) 850f93 C.)
1640 1950 2630 2240
45 45
-
54.5 (930 C.) 780 (93' C.) 480 (93' C.) 855 (93" C.) I050 (93" C . ) 555 (930 C.) 1065 (93' C.) 1440 (93' C.)
5Ob 45
50
- 57 -51 -47 43
-- 12 7
1130 (b3'C.)
- 34 - 37
- 37 - 29 -29 - 29 - 53 - 53 - 53 - 53 - 53 - 53
5050 ( - 200 C.) 4600 (0' C.) 4100 (20' C.) 3300 ((io0 2.ioo ( i o n 0 c.) 1200 (140' C.) 1070 (93' C.)
c.)
- 53 - 53
- 40 - 40
- 40
1375 (93' C.)
to tensile-brittle point balance, but they were no better in this regard than rubbers made in emulsion. If polydienes containing no second monomer are considered, changes in brittle point with method of polymerization probably depend upon the structure of the polymer-eg., the number of side vinyl groups resulting from 1,2 addition of butadiene. Selker, Kinspear, and Kemp (IO) found that polyisobutylene of very low molecular weight had a higher brittle temperature than polyisobutylenes of higher molecular weight, but that there waa no significant change of brittle point for polymers beyond molecular R-eight of about 10,000. Although polymers tested in the present investigation differ in average molecular weight and in molecular weight distribution, none were extremely low in molecular m i g h t . The AIooney viscosity of the most plastic rubber included in this study was 26 (large rotor, 4 minutes, 100" C.). I n view of other experience in this laboratory and the discussion of Boyer and Spencer (g), it appears that structure rather than molecular weight must explain the differences in brittle point between mass and emulsion polydienes.
TABLZ111. BRITTLEPOINTS O F E314rvLSIOX POLYDIEXES Rubber
Compound GR-S Tread Sodium butadiene/styrene5 Tread Emulsion polybutadiene Tread Sodium polybutadiene Tread Gum Emulsion polybutadiene ( 4 ) Gum Sodium uolvbutadiene ( 4 ) a Same bu&diene/styrene ratio a s GR-S.
b N D 1IASS
Urittp Point, C. - 67 - 26 73 -51 74
-
- 40
INDUSTRLAL A N D ENGINEERING CHEMISTRY
October, 1946
1069
EFFECT OF PLASTICIZERS
TABLEIV. TENSILE AND BRITTLE POIXTVALUES OF PLASTICIZED BUTADIEKE-STYRENE RUBBER TREAD COMPOUNDS
Flexibility of rubber compounds may be improved by addition of suitable plasticizers. Although no thorough study has been made of the effect of plasticizers upon the tensile-brittle point relation of the various rubbers, the data in Table I V summarize results of experiments in which dibutyl sebacate was added to a 50/50 butadiene/styrcne copolymcr. Twenty parts of plasticizer lowered the brittle temperature from -30" to 45" C., still 12" higher than t h a t for unplasticized GR-S. Maximum tensile strength of the plasticized 50/50 butadienejstyrene rubber had fallen t o only 1650 pounds per square inch in comparison with 2320 for the GR-S control. Similarly the tensile of a tread stock of GR-S t o which 20 parts of the same plasticizer had been added was only 1150 pounds per square inch. If values for these plasticized compounds are placed on the graph of Figure 1, the points fall below the band for butadielie polymers. Thus, this particular plasticizer vas less effective in loivering brittle temperatures with minimum loss of tensile than was a suitahle change in copolymer composition.
Rubber RO/5O butadiene-styrene 50/50 butadiene-styrene GR-S GR-S
Plasticizer. Parts Dibu:yl Sebacate Sone 20 None 20
Maximum Tensile Strength, Lb./Sq. I n . 2650 16.50
2320 1150
Brittle Pyt, C.
- 30
- 45 - 57 ,..
pair of rubbers. Difficulties in obtaining reliable stress-strain data for the weak gum compounds necessitate further measurements before valid conclusions are made. Butyl and Seoprene, which fortuitously fell Tvithin the tensile-brittle point band for butadiene rubbers in the case of black compounds, have much higher gum tensile strengths than any butadiene or isoprene polymer of similar or even higher brittle temperature. T h u s the three rubbers, IIevca, Butyl, and Seoprene, which can crystallize t o some degree upon cxtension, excel the noncrystallizing butadiene and isoprene rubbers in the tensile-brittle point balance of their gum compounds. Of these three, only Hevea exhibits such a superiority in the tread compounds.
GUM STOCKS
So far consideration has been given only t o tread type compounds containing 45 t o 50 parts of channel black. It is appreciated that from a fundamental point of view, it, would be preferable to base this type of study on gum compounds or a t least on stocks with lower loadings. Brittle temperatures of gum compounds differ only slightly from those reported here for black compounds. As is ~v-ellknown, however, tensile values of gum compounds of GR-S aud other emulsion hydrocarbon diene polymers ttnd copolymers are very low. Preliminary data indicate a rchtion between tensile and brittle point for the gum stocks which is similar to t h a t observed for the loaded compounds. Again the vinyl monomers n-hich increase rubber strength raise the brittle temperature, although the increase in strength may be from 220 t o 450 pounds pcr square inch in a particular pair of gum compounds in comparison with a jump from 2400 t o 2900 pounds for the loaded compounds of the same
CORRELATION O F OTHER PROPERTIES W I T H BKITTLE TEMPERATURE
A possible correlation Tvith brittle temperature of test properties other than tensile strength reveals interesting general observations, b u t several difficulties arise in attempts t o make quantitative comparisons. For example, the same changes in copolynier conipositioii that increase tensile strength and raise the brittle tempcrature ordinarily improve the resistance t o crack growth of tread compounds of the copolymers. Since resistance to crack growth varies markedly with degree of cure, it is difficult to choose values a t a comparable state of cure for a srries of different synthetic rubbers t o permit a test of crack-growth relation to low temperature flexibility. Further study of both crack-growth rcsistance and tear resistance is planned. I n general, the emulsion polymers of highcst resilience are those with the lowest brittle tempcratures. .kcidition of a second monomer t o butadiene, or increase of the amount of the second monomer, ordinarily lowers resilience and raises the brittle point of the copolymer. Such general observations hold for resilience measured a t room temperature. At higher temperatures resilience of the copolymcrs increases and differences observed at room temperature betweeii rubbers are reduced.
\
EFFECT O F TEAIPERATURE OX TENSILE
The low tensile strength of GR-S compound.; a t temperatures near 100" C. is well known. This observation has led to generalizations, such as t h a t made by Parliiuson ( 8 ) ,t h a t "tensile and tear of carbon loadcd GR-S comDounds fall off much morc rapidly with incrcas-
-
V-BUTYL 7-NEOPRENE C N
0
those of Figure 1; GR-S xalues are from this laboratory for the compound containing
INDUSTRIAL AND ENGINEERING CHEMISTRY
1078
Laboratories in preparing the polymer? arid ~i the Compound Dei elopment Departnleni in corcpounding and evaluation. Particular thanks are due J. D. D'Ianni, J. H. Fielding, E. S.Teed, and R. 11.Pierson. The permis.ion of T h e Goodyear Tire Bt Rubber Company to publish :hi, x o r k I C p r ~ t ~ f i i l acknon ly ledged.
I
4000
Vcl. 38, No. lfi
-
LITERATURE CITED (1) .Ilbertoni, G . J., TXD. ENQ.CHEM.,A s . 4 ~ ED. . 3, 236 (1931); Rubber Chem. Tech., 4, 591 (1931).
3ooo3
z
0
-
0'
3 m
Cam0
( 2 ) Boyer, R. F., and Spencer, R . F., J . d p p l i e d Phys., 16, 594 (1945). (3) Bur. of Standards, to Office of Rubber Director India Rubber W o r l d , 108, 573 (1943). (4) Conant, F. 3.. and Liska, J. W., J . d p p l i e o Phys., 15, T67 (1944). (5) Hoyer, H. W., U. 9. Rubber Co., private
0. I
-
I
a
e e
8
communication.
0
KEY: 0-ISOPRENE- STYRENE 0-EMULSION FCLYISOPRENE P-ISOPRENE-VINYLPYR!DlNE I B-ISOPRE NE- ACRYLONITRILE h-ISOPRENE- METHYL METHACRYLATE
od
o; TEST
Figure 2.
4b
'
Id0
do
$0 s'o o;, TEMPERATURE MINUS BRITTLE POINT
@.)
IkO
ab
!&
Tensile-Brittle Point Comparison of Tread Stocks of Hevea and Synthetic Isoprene Polymers
(6) Liska, J. W., ISD. ENQ.CHEM.,36, 44 ( 1 9 4 4 1 : Rubber Chem. Tech., 17, 421 (1944). ( i )3lcMillan, F. M.,Bishop, E. T., Illarple, K. E . ~ and Evans, T. IT., India Rubber World, 113 663 (1946). ( 5 ) Parkinson, D., Trans. Inst. Rubber Ind., 21. s o . 7 (1945); Rubber Chem. Tech., 19, IO(! (1946). (9) Rebrell, L. B., IXD.ESQ. CHEY.. 35, 735 (1943). (10) Eellcer. Ill. L.. WinsDear. G . G.. and Kemu A. R.,Ibid., 34, 157 (1942;: Rubba? Chem Tech., 15, 243 (1942).
(11) Tener, R. F., Kingsbury, 8. S.. and Holt, K. L. Bur. Standards, Tech. Paper 364, 22 (1926):
Dawson, T. R.. and Porritt. B. D.. "RubberDirector (3). I t appears t h a t the rate of tensile decrease with increase of temperature is more rapid for the GR-S tread compounds than for Hevea at lon temperatures. The cur\ c for GR-S Battens a t higher temperatures; t h a t for H e l e a begins t o drop more rapidly near 120 C. Statements concerning the more rapid loss of tensile of GR-9 a i t h increase in temperature are often based on percentage loss of the room-temperature tensile value Ekcn i f the slope. of the two curves of Figure 3 mere the same, the pel centage loss of roomtemperature strength would be greater for GR-S because of t h e low values a t the low temperature. From a practical point of view the higher strength of Herea compounds in the temperature range 70' t o 120" C. is the important consideration, rather than the rate of change of tensile over a pai ticular range
Physical and Chemical Properties", p. 231, Cro?-don. Reaearcb Assoc. of Brit Rubber Slfrs., 1935. PRESENTED b d o r e t h e Division of Rubber Chemistry at t t c ;(,gin Meetinn of the AXERICAXCEFXICAL SOCIETY.Atlantic City K J ,
'
THEORY
It is possible t h a t the structural features wliich restrict chain mobility at low temperatures also contribute t o a n embrittlement or hardening of the rubber upon elongation a t the temperature of stress-strain measurements. Thus. those polymers of highest brittle point may harden most readily or to the greatest extent when they are stretched at room temperature. Since hardening might he expected to limit longitudinal slipping of chain segments, one might then predict a better distribution of stress and, hence, greater strength. Experimental studies t o determine whether hardening actually occurs upon stretching of the noncrystallizing, synthetic butadiene and isoprene rubbers will be of interest.
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c
ACKNOW LEDGRIE3T
The work reported here as done in i-oriiiection nit11 the Government Research Program on Synthetic Rubber under contract with the Office of Rubber Reserr e, Reconstruction Finance Corporation. The authors are glad t o acknon ledge the cooperation of seieral members of the Goodyear Research
01
-20
I 0
I 20
I I I I 40 60 80 I00 T E S T TEMPERATURE (OC)
I
20
I
14C
Figure 3. Effect of Temperature on Tensile Strength of Heiea and G R - S Tread Stocks
