2220
INDUSTRIAL AND ENGINEERING CHEMISTRY
immediately present, the n hite crvstals formed on long standing. A relatively sharp melting (130.7” to 131-2” C.) sample of the white crystals showed an elementary composition of 64. lSyo carbon, 7.3SYc hydrogen; neutral equivalent 192; molecular weight erratic due to low solubility. Test, for aldehyde was negative. The viscous red oil appeared to be a mixt,ure, giving a positive aldehyde test. ACKKOWLEDGRIEST
The authors of this paper are indebted to I). A. Sicewander and Clark H. Ice, both formerly of Phillips Petroleum Company Research Department, who carried out much of the experimental work on the condensation of butadiene with furfural and identification of ‘the synthetic products isolated. The authors thank Phillips Petroleum Company, The Quaker Oats Company, and Office of Rubber Reserve for permission to publish this paper.
Vol. 40, No. 11
LITERATURE CITED
(1) Buell, C. K., and Boatright, R. G . , IND. ENG.CHEM.,39, 6% (1947). (2) Dunlop, A . P., andPeteIs, F. N., Ibid.,32, 1639 (1940). (3) Dunlop, A. P., Stout, P. R., and Swadesh, S., I b i d . , 38, 705 (1946). (4) Happel, J., et al., Trans. Am. Inst. Chem. Engrs., 42, 189 (1946). (5) Hillyer, J . C., and Deutschman, A. J., Anal. Chem., in press. ( G ) Hudson, B. J. F., and Robinson, R., J. Chern. ~ o c . 1941, , p, 715. (7) Kistiakowsky, G. B., and Ransom, W.IT., J . Cham. Phus., 7, 725 (1939). ( 8 ) Robe\-. R.. Wiese, H. K.. and Morrell. C. E., IXD.ENG.CHCM., 36, 3 (1944). (9) Williams, D. L . , and Dunlop, A . P., Ibid., 4 0 , 2 3 9 (1948).
RECEIVED November 7 , 1947. Presented in part before the Organio Section at the Second All-Day Technical Conference of the Chicago Section of the ANERICAX CHBMICAL S o c r E T Y , Evanston, Ill., January 1947.
Ultimate and Actual Tensile Strengths of Type I11 atex Films S. H. I\I.ARON, BENJAnIIN RIADOW, AND J. C. TRINASTIC Case Institute of Technology, Cleveland 6 , Ohio
-4 comparative stud3 was made of the tensile strengths of raw polymer and gum vulcanizate films prepared from fifty-three Type I11 GR-S latices. The ultimate tensile strengths of the two types of films showed n o correlation with one another when the calculations were based on the original cross-sectional areas. O n the other hand, wvhen the calculations Were made on the actual areas at break, the tensiles of the raw polymer and ~ u l c a n i z a t efilms obtained from a given latex were found to be essentiallj the same, This identity of film tensiles obtained from a given latex indicates that here compounding and curing do not lead to any reinforcement of the polymer, nor to an> change in the nature of the bonds involted i n film rupture.
T
HE present, practice for computing the ultimate tensile strengths of elastomcric films is to divide the breaking load by the cross-sect,ional area of t>hefilms bcforc elongat.ion. Such a calculation does not, yield the actual force per unit area required to break the film, nor does it take into consideration the elongation of the film and the reduction in cross-sectional area which the film undergoes on stretching. The values for ultimate tensiles t,hus arrived a t are not very indicative of t,lie atrengt,h of t.he polymers involved, nor are the elongation measurements much more than numbers to accompany tensile results. This difficulty was recognized as early as 1915 by Eaton and Grantham (2) when, in seeking to obtain a function dependent on both stress and strain, they expressed their results as a “tensile product”-i.e., the tensile calculated on the basis of cross-sectional area a t break. Wiegand (9) and others ( 1 , 3, 8) have also used the “tensile product” or “molecular tensile” to compare gum vulcanizates and loaded stocks to ascertain whether the use of fillers led to reinforcement of rubber arid to what’ extent. A revieu of some of this work is given by Shepard ( 6 ) and by Shepard, Street), and Park ( 7 ) . During the past several years this laboratory has had the task of preparing satisfactory latex films and testing them for tensile strength. Involved have been films cast directly from straight latex and films of gum vulcanixates cast from coni-
pounded latices. During this work no coiinection could be established between the ultimate tensiles of uncompounded arid conipounded films when these were calculated on the basis of the original cross-sectional areas. On the other hand, when the tensiles Tvere calculated on the basis of area a t brealc-i.e., the force actually required t o break a film per unit area-the tensiles of the Uncompounded and conipounded films, obtained from the same latex, were found to be essentially the same within the relatively large experimental errors involved in tensile testing. The purpose of this paper is to present the film tensile results obtained on fifty-three Type 111 GR-S latices, both uncompounded and compounded, and to show that the tensiles, when calculated on the basis of the area at break, are unaffected by the compounding and curing processes. CALCULATION OF ACTUAL TEXSILE STRENGTH
Tensile strengths calculated on the basis of the original area mill be referred to here as ultimate tcnsilc strengths, T, and tensiles calculated on the basis of the area a t break as actual tensile strengths, S . Ordinary tensile measurenients include the determination of the original area of the test specimen, A,, the original length between bench marks, I,, the load, L , at break, and the distanct between bench marks at break, l j . From these data the ultimate tensile strength is calculated as 1 = L!A.
,I
(1)
and the percentage elongation, E, is taken as
From the same data it is possible to calculate the actual tensilc strength of the specimens ’on the assumption that the volume between bench marks remains unaltered on stretching. T h a t this assumption is justified for unloaded rubbers was shown by Schippel ( 5 ) ,who found that the change in volume of unloaded natural rubbers on stretching does not amount t o more than about
November 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
0.15%. For the shapes of specimens ordinarily employed in testing, the assumption of constant volume leads to the equality,
A.1, = A&
(3)
where A/ is the area at break; hence
A/ = A o l o / l /
(4)
From Equation 4 actual tensile S follows as
=
On substitution of
T(i)
(5)
(3
from Equation 2
Equation 6 shows that the actual tensile can be calculated from the ultimate tensile and the percentage elongation, and is the relation used to evaluate the actual tensile strengths reported. This relation for S is identical with Eaton and Grantham's definition of tensile product and Blake's definition of molecular tensile. EXPERIMENTAL PROCEDURE
The uncompounded films were cast from straight and standard Typc I11 GR-S latices by the carbon dioxide-moisture technique deve!oped in this laboratory (4).The set films, removed from the molds, wcre dried in every instance for 24 hours at 100" C. in forced-draft circulation ovens. After drying, the films were cooled for one hour in a n air-conditioned room kept at 70" I?. (21.1 O C.) and 50% relative humidity. Test strips were then died out from the sheets of film, marked with half-inch bench marks, and tested. The use of smaller test strips with half-inch bench marks is necessitated in testing uncompounded latex films by the very high elongations shown by such films. Standard one-inch test strips will not break within the length of the testing machine even when it is modified as described below. T o obtain gum vulcanizate films from the same latices, the latter were first compounded with the following formula suggested by the American Anode Company (in parts by weight): 100.0 parts rubber as latex 2.0 parts sulfur 3 . 0 parts zinc oxide 2 .O parts Stalite 1 . 0 part piperidine pentamethyiene dithiocarbamate (Pip-Pip) 1.O part Nacconol 0 . 3 6 part monoethanolamine
Latices thus compounded were cast into films by the same technique used with uncompounded films ( 4 ) ; the set sheets of rubber were removed from the molds, cut into a number of smaller portion3 and vulcanized for l/2-, 1-, ll/z-, and 2-hour periods at 100°C. The vulcanized sheets were then cooled for one hour in t h e air-conditioned room, died out into standard test strips witlh one-inch bench marks, and tested. T h e results corresponding t o optimum cures were taken as the gum vulcanizate tensiles. All the break tensiles were measured in the constant temperature-humidity room on a special Scott tensile machine fitted n i t h lo-, 25-, and 50-pound heads and a spark recorder. For the data given here, only the 10-pound head was used. This machine was modified t o increase the distance between specimen gripi: so as t o allow measurement on half-inch test strips up t o 3300% elongation. The rate of pull was the standard 20 inches per minute used in rubber testing. RESULTS AND DISCUSSION
Table I summarizes the data obtained on the fifty-three Type I11 latices tested. Any conclusion drawn only from the observed T,/T, ratios would suggest that compounding and vulcanization of the latices increases the tensile strength of the polymer films by factors ranging anywhere from 1.6 t o 5.3 fold. However, the ratios of S, to S , indicate that, generally, uncompounded and compounded vulcanisate films give the same actual tensiles, and, hence, t h a t the compounding and curing do not lead to any rein-
2221
TABLEI. ULTIMATEA N D ACTUALF I I ~ TENSILES OF UNCOMPOUNDED AND COMPOUNDED TYPE111 LATICES' Sample No. NS-1 NS-2 NS-3 NS-4 NS-5 NS-6 NS-7 NS-8 NS-8 NS-10 NS-11 NS-12 NS-13 NS-14 NS-15 NS-16 NS-17 NS-18 NS-19 NS-20 NS-21 NS-22 NS-23 NS-24 NS-25 NS-26 NS-27 NS-28
FS-1
FS-2 FS-3 FS-4 FS-5 FS-6 FS-7 FS-8 FS-9 FS-10 FS-11 FS-12 FS-13 FS-14 FS-15 FS-16 FS-17 FS-18 FS-F FS-3014 TS-A TS-B
Tu 310 490 480 700 390 560 380 580 530 400 750 560 590 ' 560 430 630 540 500 580 420 640 790 650 840 680 600 720 830 900 360 670 520 510 650 360 350 500 510 460 410 140 300 580
El
To
Eo
3100 2500 2450 2000 2300 2200 2650 1500 1750 2300 1150 1700 2400 2450 2250 2300 2400 2450 2050 2300 2100 2000 2050 1970 2200 1900 2050 2050 1710 3100 1900 2200 2100 2050 2500 2700 2400 2100 2250. 2100 3100 1900 1650 1950 2600 2200 1700' 1600 2000 2200 3000 1900 1750 2100
1630 1740 1680 1230 1660 1750 1240 1280 1210 1370 1670 1140 1050 1610 1730 1970 2480 1930 1870 1080 1350 2130 1760 2320 2000 1710 2250 1660 2350 1800 2920 2530 1440 2100 1090 1770 1350 1880
590 560 600 600 580 650 570 570 500 540 580 580 530 730 640 590 650 600 630 680 620 680 580 670 660 630 650 680 630 660 610 610 620 600 550 590 550 600 600 580 500 520 620 510 600 600 810 640 610 570 580 530 550 610
TC __ Tu 5.26 3.55 3.50 1.76 4.26 3.13 3.26 2.21 2.28 3.43 2.23 2.04 1.78 2.88 4.03 3.13 4.59 3.86 3.22 2.58 2.11 2.70 2.71 2.76 2.94 2.85 3.13 2.00 2.61 5.00 4.36 4.87 2.82 3.23 3.03 5.06 2.70 3.69 3.48 4.06 4.43 3.86 3.52 2.43 3.30 3.80 2.00 2.64 4.28 2.99 3.76 1.65 1.63
Su 9,900 12,700 12,200 14,700 9,400 12,900 10,400 9,300 9,800 9,600 9,400 10,100 14,700 14,300 10,100 15,100 13,500 12,700 12,500 10,100 14,100 16,600 14 000 17:400 15,600 12,000 15,500 17,800 16,300 11,500 13,400 12,000 11,200 14,000 9,400 9,800 12,500 11,200 10,800 9,000 4,500 6,000 10,200 11,900 10,800 11,500 19,400 12,400 9,200 15,400 10,500 14,400 13,500 12,200
So 11,200 11,500 11,800 8,600 11,300 13,100 8,300 8,600 7,300 8,800 11,300 7,800 6,600 13,400 12,800 13,600 18,600 13,500 13,600 8,400 9,700 16,600 12,000 17,900 15,200 12,500 16,900 12,900 17,200 13,700 20,700 18,000 10,400 14,700 7,100 12,200 8,800 13,100 11,300 11.300 3,700 7,200 14,700 8,600 9,200 13,300 19,600 11,800 13,300 13,400 8,700 7,500 7,700 11,900
s. % 1.13 0.91 0.97 0.59 1.20 1.01 0.80 0.93 0.74 0.92 1.20 0.77 0.45. 0.94 1.27 0.90 1.38 1.06 1.09 0.83 0.69 1 .oo 0.86 1.03 0.97 1.04 1.09 0.72 1.06 1.19 1.54 1.50 0.93 1.05
0.68 1.24 0.70 1.17 1600 1.05 1660 1.26 0.82 620 1.20 1160 1.44 2040 1410 580 0.72 1320 0.85 400 1.16 1900 500 2160 1080 1.01 0.95 1850 730 440 1880 1.45 670 2000 0.87 TS-C 340 1280 0.83 SS-271 720 1190 0.52 SS-291 , 730 1190 0.57 Average 557 1680 ... 0.99 t0.20 a Columns 2 and 3 give ultimate film tensiles TU (in pounds yer square inch) and elongations Eu (in per cent) of the uncompounded latices. columns 4 and 5 give the same quantities for compounded latices, TCan'd Ec. Columns 7 and 8 give actual tensiles of uncompounded and compounded films Suand So, as calculated by Equation 6.
forcement of the latex polymer. I n fact, the average value of SJS, for all fifty-three latices is 0.99 =+= 0.20. The deviation of 2070 from unity is not excessive when the uncertainties inherent in film casting and testing are considered. The reason for the misleading conclusions given by the T,/T, ratios lies in the fact that, in ultimate tensile calculations, the large reduction in area attendant on stretching to the break point is disregarded. This reduction in area may be greater than 30 fold for uncompounded films but only 6 t o 8 fold for gum vulcanizates. Consequently, the low break loads observed with the former, when referred to the original cross-sectional area, give low uncompounded ultimate tensiles, whereas the higher break loads observed with gum vulcaniaates give higher ultimate tensiles. However, actually, the break loads with uncompounded films, where the elongations are very high, are low only because the cross-sectional area at break is so small. With gum vulcanizates the area at break is much higher, and so is the break load. Still, in both types of films the actual force per unit area at break is cssentially the same. The only effect of the compounding and vulcanization appears to be, therefore, a stiffening of the polymer which prevents excessive elongation and area reduction on stretching. I n vie% of these results tensile data in general, and film tensile data in particular, should be expressed on a n actual tensile basis in order to arrive at a true index of the polymer
INDUSTRIAL AND ENGINEERING CHEMISTRY
2222
.
strength of rubbers and latex films. The present practice of expressing the results on an ultimate tensile basis is totally misleading and tends to give the impression that compounding and vulcanization of Type I11 latices, at least, leads to reinforcement, when no reinforcement may actually take place. Since the actual tensile of compounded and uncompounded latex films was found to be the same in this study, i t must follow also, if there is no difference in chain packing in the two types of films, that the same links, and the same number of links per unit mea, are broken in both compounded and uncompounded films. If the breaking of carbon-to-carbon bonds is involved in film rupture, these facts must mean that the same bonds are broken In both films, and that sulfur cross linking on vulcanization does not contribute to polymer strength but only to its stiffening as reflected in extensibility. Another conclusion apparent from the data is t h a t Type 111 latices may differ widely in the strength of the polymer films. If the very low result for sample FS-13 is omitted, the spreads between maximum and minimum values amount to a factor of 3.6 in Tu, of 2.8 in Tc, and of 2.9 in S. The highest value of X observed, 20,700 pounds per square inch, compares not unfavorably Kith the actual tensiles of natural rubber vulcanizates, which range from about 25,000 to 35,000 pounds per square inch. tf the influences responsible for film tensile variation in Type TTT latex could be ascertained, and if these could be controlled
Vol. 40, No. 11
so as to yield consistently the high tensiles occasionally observed with films of this latex, we would have a polymer approaching fairly closely natural rubber latex films in strength. ACKNOWLEDGMENT
This study was sponsored by the Office of Rubber Reserve, Reconstruction Finance Corporation, as part of tho Government Synthetic Rubber Program. LITERATURE CITED
(1) Blake, J . T., IND. ENQ.CHEM.,20, 1084 (1928). (2) Eaton, B. J., and Grantham, J., J. SOC. Chem. I n d . , 34, 989 (1915). ( 3 ) Greidor, H. W., J. IND. EM. CHEM.,14, 385 (1922); 15, 604 (1923). (4)Maron, S.H., and Madow, B., IND. ENQ.CHEW,ANAL.ED.,20 545 (1948).
( 5 ) Schippel, H. F., J. IND. ENQ.CHE;~.,12, 33 (1920). (6) Shepard. N. A., in Alexander’s Colloid Chemistry,” Vol. I V , pp. 312-16, New York, Reinhold Pub. Gorp., 1932. (7) Shepard, N. A , , Street, J. N., and Park, C. R., in Davis and Blake’s “Chemistry and Technology of Rubber.” ChaD. XI. Kew York, Reinhold Pub. Gorp., 1937. (8) Stevens, H. P., J . SOC.Chem. I n d . , 35, 874 (1916) (9) Wiegand, W. B., Can. C h e m J.,4,160 (1920). RECEIVED October 3,1947. PreRented before the Division of Rubber Chem. istry a t the 112th Meeting of the AMERICANCHEMICAL SOCIETY,New York, N. Y.
FRITZ S. ROSTLER AND ICATHLEEN S. ROSTLER Golden Bear Oil Company, Oildale, Calif.
T
HE advantages of using premixed preparations of fillers
and plasticizers in compounding rubber have been discussed (8). These advantages are, primarily, a saving in milling time, even power consumption during milling, elimination of dust in handling dry fillers, and elimination of the inconveniences involved in handling highly viscous plasticizers. In this previous study it Ras found that a fixed ratio of filler to plasticizer exists for each filler-plasticizer pair limiting the amount of plasticizer vhich can be premixed with a filler without impairing dispersion of the filler in a rubber mix. When a premixed preparation was used having plasticizer proportion below this limit, the resulting rubber compound had the filler dispersed at least as well as when the ingredients were incorporated separately, as evidenced by the physical properties and by microscopic observation of the vulcanized compound. If, on the other hand, this plasticizer limit was exceeded, dispersion mas poor and the physical properties of the vulcanized compound were lower than those obtained by separate incorporation of the two ingredients, and microscopic observation of the torn surface of the compound showed filler present in lumps instead of evenly dispersed. An attempt was made to relate the limit of plasticizer content of the premixed preparation t o the relative effect of the filler and the plasticizer on the plasticity of the masticated rubber ( 2 ) . tt was found t h a t in a number of cases the limiting amount of plasticizer coincided with the mixture in which the softening effect of the plasticizer was equivalent to the stiffening effect of the filler. I n other words, the concentration of plasticizer in the premixed preparation had to be low enough so that the plasticity of the rubber mix either remained constant or decreased when the premixed preparation was incorporated into rubber. A plas-
ticizer concentration high enough so that the premixed preparation had a softening effect on the rubber gave poor dispersion. The proportion of plasticizer t o filler in which softening effect of plasticizer is equivalent to stiffening effect of filler was called the “constant plasticity ratio,” for when incorporated into masticated rubber in any amount, the plasticity of t h e rubber matrix remains constant. With carbon blacks this general rule t h a t the constant plasticity mixture was the limit of plasticizer for good dispersion was found t o apply approximately t o the thermal blacks and to the furnace blacks; hon-ever, there were two d+ cided exceptions to the rule. With the structure blacks, lampblack, and acetylene black, good dispersion of the filler could be achieved by incorporating i t in the form of premixed preparations containing proportions of plasticizer high enough t o soften the batch considerably. With the channel blacks, the limit t o the amount of plasticizer which could be successfully premixed with the black was much lower than would be expected, so that for successful filler dispersion a premixed preparation had to be used with considerable stiffening effect ( 2 ) . SCOPE OF INVESTIGATION
Although the previous study had shown that the effect of 8 premixed plasticizer-filler preparation on the plasticity of the rubber mix was of importance, it was obvious t h a t other factors must enter into the picture. The purpose of the present study was t o find some rule applicable to all carbon blacks correlating other specific properties with the proportions of black and plasticizer which could be premixed for incorporation into rubber. I n order to arrive at the correlation sought in the form of a quantitative expression, the previously measured data were
