N
d
, 1%
b used to determine swell in hexane, bemane, wtone, and alcohol at mom temperature and in Circo lightpmopss oil at 180’ F. Freering charact8riatiea are determined on the en& of the broken dumbbellsfor the 30- and &minute OUIPB. With this information it is possible to tell wbther or not the product b worth further development. In f a d it b possible to make a fairly good estimate of ita commercial poesibilities. Advantegr and Disadvantages ot the kdun DIUDVANTAQES. The moat obviow disadvantage of this pmedure ie the repeated we of single test 6pechem. Kth a singlespecimen them is no chance to check d t a , and socidentd dafecte may spoil the test. The UBB of the asme mimen for measuring hardnw, rebound, and wmprpssiovl set may alter the results somewha& Another objedion is the probable presemce of calender grain in the tensile stripe. F’mbably the greatest objection, particularly in ita application to natural rubber, is the e x k v e breakdown obtained in the milling of d batches. h w e synthetic rubbers do not break down to the extent that natural rubber does this hss not bean a &ow problem, provided it WBB remgaiped. With natural rubber it in to we a warm mill and mix the batch rapidly. It haa been W b l e to adoptthe d mill p r o d u r e to the we of natural rubber batdm containing Bomewhere between 10 and 50 grams of rubber.
ADVANTAGES. The outatanding advanhgw of this p m cedure are the small mounta of material required and the speed with which the work can be done. Another advantage ia the accurate w n h l of mill and batoh temperatures. This make8 paesible the obssrvation of milling behavior at qmi6ed h p e r s t u ~ which ~ , is din predicting faatory proc&bhsrscteristies. A number of compsrisoIlshave shown that conclwiow b d on experimenta on the &inch mills agree well with those b d on eorperimente run on the standard 12-inch exp~aimentdmilla While the rapid adoption of a new material into fadory production depende primarily on the skill of the factory operstora, considerable wn6dence in this lOgram p d u r e haa been gained from the fadthat on more than one &on it haa bean possible to go frum 1Wam operations to factory production in a very short time. The predictions made from the small*ale evaluations have been in large meaBuTB ful6Ued in production.
Litemtun Cited (1) A. 8. T.M. Btandud. on Rubber produota, D412-41, Fig. 3-D (1941). (2) Ibid.. Das6-4(yT. Method B (1941). (a) hylink c. F.,~npubli.bed W X ~ (4) Garvey, B. E., A. 8. T. M.E&. 109, 18 (1941). 16) E.T..IND. ~mra.h. ANAL. . ED.. 9. 682 figan
w.
Unsatursaion of Synthetic * c * Rubberlike Materials * *
. Xeller-
La Verne E. Cneynoy The Goodyear Ti+%
Rubb
*
n,
+
Ohio4
*
he unsaturation of three ynthetj( butadiene Tpolymers hds been determined by a modified. tion of the Kemp-Wijs method. The reaction proceeds much more slowly than with rubber, 24 hours at 30” C. being required t o complete the addition reaction. The iodine values obtained vary somewhdt w i t h thesolvent employed, but in general are in the range of 85 t o 90 per cent of the theoretical values for straight linear polymers. The difference i s attributed to cross linkage.
HE quantitative determination of rubber unsaturation has concerned numerous investigators. The use of iodine chloride aa a reagent for this purpose (the well-known Wijs method) has achieved favor in recent years (S, 9, ld, 19, 16, 16, 26, 27). Under the proper experimental conditions, the addition has been shown to be quantitative, and substitution rmtions can be kept at a minimum (16,18). This procedure has likewise been rather extensively employed aa a measure
T
of the residual unsaturation of various rubber derivative (6, 7,8, SO,SI, Sd). This reagent docs not, however, add quantitatjvely to all unsaturated compounds, regardless of structure (16). The presence of a negative substituent on one or more of the unsaturated carbon atom inhibits the reaction; in fact, it may entirely prevent it, as in the cases of maleic or fumaric acids or dichloroethylene (9, 19). In other compounds extensive substitution may occur along with addition, aa in the case of the unsaturated terpenes ( 1 6 ) . The unsaturation of the polymerized d i o l e h should be of considerahle interest, especially in comparison with natural rubber. It should he of special interest to study the comparative reactions with iodine chloride, which has become practically a standard reagent for rubber. Kemp and Mueller (16) mention that polychloroprene, to which they erroneously refer as polyvinyl chloride, adds iodine chloride to only 30 per cent of theory. This could be due to two causes-the negative inhence of the chlorine attached to an unsaturated carbon, and/or possible cross linkage between chains (cyclization). It is well established that polychlorcprene is much less reactive chemically toward other reagents than is natural rubber (4). It is unfortunate that Kemp and Mueller did not state with more detail the history of the sample studied, as such a result might have shbwn some intereating correlation with the experiments reported in this paper. a m a s et 01. (5’4) report that the unsaturation of the class of materials known as butyl rubber is between 1 and 2 per
1324
******
INDUSTRIAL A N D ENGINEERING CHEMISTRY
centof thatofnaturalrubber,asdetarminedbyiodinenumber. €'mumbly some modification of the Wijs method may have been employed, although no experimental details are given. The polymers and copolymers of butadiene have been and are achieving industrisl and militmy significance, both in this country and in Enrope. It was therefore deemed of interest to study the chemicsl unsatwation of some of the other typical examples of this group of materisla. Thornhill and Smith ($6)reported the unsaturation of a typical commercial sample of this type. Since the exact composition was not known, the reeulta are not indicative of much, other than the fact that some sort of value can be obtsined by the general application of the standard method. Rubberlike materials of the butadiene class have been shown by the work of M a ~ and d others to possess a lower degree of linearity and regularity than thoae polymers produced by "polycondensation" (88). Pummerer (86) studied the ozonolysis cleavage produds of sodium butadiene rubber, and failed to find succinic dialdehyde and S U C C ~ ~acid, ~ C which would be the pmducta from a strsigbt linear polymer of the 1,4 type. Hia work mma to indicate that there is a considerable amount of 1,2 polymerization, as well 88 1,4, and that both may occur in the same Unit, giving rise to crow Links@ or cyclisation. This cyclization seems to occur spontaneously in storsge with all the butadiene polymers, and stabilizers such ea phenylgnaphthylamine are ususlly incoprated with the polymer to prevent this ($3). Experimental Procedure Three polymers were employed: a sodium butadiene polymer and emulsion copolymers of butadiene-styrene and butadiene-acrylic nitrile, in which the weight ratios were 4 butediene to 1 styrene and 7 butadime to 3 acrylic nitrile, respectively (If, 17, $6, $7'). The copolymers may be regarded as typical of the commercial American products, while the odium polymer is an example of one type of Enropean svnthetic rubber. The actual w t u r a t i o n of these materials is a function of meral variables. For instmce, there is as yet n~&quate during measure of the actnal extant of cyclization occu polymerization or during storw. Other ingredienta present during polymerization undoubtedly maturation in the polymer; in fact, added for this purpose (81). Further, there is de6nit- -?of that the two monomers do not alwaya combine in m proportions added, and that the ratio varies, at 1ea1 some conditions of polymeriaation, wi@e yield to d o n is taken (92). The ratios sssumed for pr calculation are those which are believed to represen approximation of the actual struct~re,as revealed teaisls balance" (84). F O ~ p q m w of calculation, the poljkmation L mnmed to proceed in an orderly hear fashion. For the butadiene polymer, then, there would be one double bond per C,Eb unit, corrwponding to an iodine 469.3. In contrjbthe styrene copolymer one tifth of the ute no unnatwation, the remainder being C.6 unita. icdine value is therefore four 6ftb of the above, or Likewise, the theoretical uneaturation of the acrylic nitrile copolymer is seven tenths of 469.3, or 328.5. The s~mpleswere sheeted on a mill, extracted 8 hours with alcohol to remove the inhibitor, dried, and stored in a vncnum desiccator until we. The sheeted eample was cut into 8 d pieceu before we. Under these conditions of storage the cyclizing effect did not seem to be rapid, but samples storad for periods longer than one month showed progreaSve &nution of iodine value. Wherever p d b l e , determinations were madeontheoriginslmasterbatcbolpurifiedeample,toprevent any possible variationa due to difference in sample history.
***
Vol. 34, No. 11
Kemp has indicated some of the variables affecting the reaction, such as temperature, excees of reagent employed, time of reaction, and e5ect of solvent. In general, he found that shorter reactions at room temperature gave the same values as longer reaction at 0' C., but that after periods of the order of 20 hours, substitution began to be evident, The e5ect of solvent is also worth noting; in general, carbon disulfide mmed to be the most satisfactory. The choice of solvent was dictated to some extent by the characteristics of the polymer under study. &me thirty solvente were inveatigated as potential media for the reaction; with a few exceptions they were not of much value. Carbon disul6de to function fairly e5ciently for the butadiene polymer and the styrene copolymer, but is valuelees for the acrylic nitrile copolymer. To compare the three polymers, a series of determinations was d e in chloroform,which 8eem8 to be a fairly efficient solvent functioning acma the entire series. None of these polymers were soluble to the same extent as rubber. Furthermore, it was preferred to avoid heating the ~ o l ~ t i ~since n s , heat has bean shown to exert a cyclizing d e c t on theae polymers (I, IO,8496'). A 0.l-grsm sample was dowed to swell in 50 ml. of solvent ~~ overnight and then shaken to break up the S W O I I lumps. The solution and subsequent treatment were carried out in a SO&mI. widdipped ssssy hk,which was coated black to avoid any substituting e5ect of light upon the reaction. Twenty-five milliliters of 0.2 N iodine chloride, prepared according to Kemp, were then added. Although Kemp states that for rubber the solution should be clean and free of precipitate after the addition, this condition could not be realized in these eamples, since the solubility of the polymer de6nitely decreased by the addition of the acetic acid solution of the reagent; consequently the polymer precipitated in small particles throughout the solution. The glaea stopper was moistened with 15 per cent potaasum iodide solution and -led with par&. This precaution was necessary in order to prevent lom of reagent. The hk wza then placed in a &tant-temp+rature bath for the requisite time. Expe ' enta at Oo C. indicated that a sati8factory reaction . in a reasonable time at this temperacould n% e obtamed ture. For this reaeon most of the reactions were run at 30' C. hk from the bath, a portion of 25 ml. iodide solution was poured in p of the Bask before the seal was broken. In this ny liquid tending to escape was absorbed in the ed to the thk. The remainder of
*
*
tion was titrated immediately
4
-
4 as zatisfacbry. The d t a varied somewhat with h e rata of titration,which was as rapid 88 possible. The B M W d B N method ~ of solution in pdichlorobensene (S),which is of s p e d d u e for vulcanised m b h les, was investigated and found to be of no value here. t, it has sevefal distinct dieadvantagea for thee polymers, such as tendency toward cyclization during the long heating nemsary and precipitation of the polymer when the solution is diesolved in another solvent. The anslytical multa are 8ummBRBed ' in Table I. For comparison the iodine numbers are expre8sed in tarma of the theoretical dues for the specific polymers. In general, the most zatkfactory behavior was obtsined with the carbon disulfide mlutions. The chief dieadvantage of carbon disulfide as a solvent is ita high vapor pressure at the temperature employed. Chloroform, although a better uniform solvent for the three polymen, gives ~01~ti0ns which show more tendency
1942
N&,
Table 1.
***
INDUSTRIAL A N D E N G I N B a R l N G CHEMISTRY
Summnry of Analvtiul R a r k at 30° C. Lblr.nt
C&
a*
ca
Chlmoform Chloroform Chloroform
Chlmofmm l3enmne
&I-
B
71.8
8
400.0 420.8
88.8
a88
486.7 479.7 a18.a
22.6 .48 188
a
4 a2 48
188
we
4 4 2
4
24
c8r
I8
lea
&.m
Chlomfmm Chloroform
Chloroform Chloroform
chtmcdorm Chlmofm Chlmofmm
Chlorofmm ExPdnwlLt ,Nrried out .t 0.
886.4 881.0
4
CSl C& C& CSl Chloroform chloroform
.
2
a
1
22
48
188
836 2 4
za
48
188 836
w.o
428.6 8M.4
&.a
M.6 408.7 468.0 454.0 166.0 p88.8
2m.a 887.8 887.8 m.4 201.1
m6.z
884.1 884.8 aio.6
8i.a 82.4 86.2 91.8 85.1 102.2 74.1 76.4 M.2
67.0 67.1
87.8
W.9 88.0
ea.8 77.0
89.8 88.8
88.7 64.8
78.2
88.8
89.0 83.6
281.8
74.8
am.? 288.0 278.8 ass.0 288.7 871.1
81.2 81.4 84.1 87.0
90.7
******
1325
The resulte in chloroform give dehite indication of cyelisstion on long reaction for both the copolymers, but the polybutadiene 8 e 8 m ~to have undergone mhetitutiy At shorter periods of time, the results in chloroform are 8hghtly lower than those in carbon &&de, the d 8 e . m being ~ ~ most pronounced for the polybutdene. The experimental m o r is decidedly larger when chloroform is employed, 80 that on the whole the results in the' two solventsmay be regarded ea showing reasonably @ agreement. The acrylic nitrile copolymer ahom leas consktenoy in ita behavior. If the %hour value alone in conaidered, we might conclude that the presence of the negative nitrile group bad r e p 4 the reaction. However, this polymer shows the but most rapid initial rate of reaction, followed by a BWY very 8 1 0 ~ rise to a maximum value after a reaction period of 188 hours. After this, the value again dmps. It is Weved that probably the valw obtained in 2 to 4 horn actually give a truer picture of the addition reaction for this polymer than do the values OW in longer periods of resotion. The single result obtained in bensene can be regarded only 88 an indication of a possible direction of future investigation. It wan obtained after most of the other work had been completed, and therefore a more extended study in thin aolvcmt WBB not made.
88.4
c.
to form emulsion^ during titration. Mthough benzene gave the highest value and the neareat to theoretical in a comparative series, ita solubility characteristicsand general behavior are not entirely satisfactoryand it cannot be recommended. Attempts to determine suMtution in these reactions met with little succees. The method employed wea that of Mcllhenny (a0) ea modified by Learie and McAdrcm (18). Fugitive and nomeproducible end pointa were obtained in both carbon disul6de and chloroform. Some of the ditsculty may have bean due to hydrolysis of the iodochloride, 88 suggested by Kemp and Mueller (le). Although substitution may have occurred during some of the reactions, there WBS no satisfactory memure of it. far ea natural rubber is concerned, Kemp and Mueller feel that the combination of a glsoial acetic acid solution of iodihe chloride and carbon did d e BS a solvent for the rubber exerts a powerful repressive in9uence on side reactionssuch ea substitutionand hydrolysis (Z4,18). Furthermore,the relatively long flat portion of the curve is tab ea sdditionsl evidence that little substitution had occurred; th~issupportforthisaseumptionintheaomewhat higher values obtained with very long reaction periods. Discussion of Results Several conclusions may be reached by a study of the data included in Table I and plotted in Figure 1. The reaction
Y
10
30 TIME IN HOURS
ZO
40
Figure 1. Iodine Values of Polymers V.I Time
.
0 Butadiene polymer in carbon disulfide 0 Butadiene polymer in chloroform Butadiene-styrene polymer in carbon disulfide A Butadiene-styrene pol er in chloroforn
0 Butadiene-acrylic n i t r i r polymer in chloroform
proceeds much more SIOWIY with all these polymers than with The d8erence between the experimentally datamined unrubber. There is a fairly rapid initial reaction, followed by a saturation and the theoretical values may be regarded ea due rapid leveling of the curve in all which indicates that to cycliration or c r a linking. It is inkeating to note the most of the addition bas occurred. The muease in iodine fairly narmw range in which these values fall. Accepting the value on prolonged reaction in the case of the butadiene polyobtaineed in carbon disulfide ea being somewhat more mer is undoubtedly the beginning of ~ ~ b ~ t iS t i ~ this t i ~ resulta ~ reliable, both the butadiene polymer and the styrene rn requirea nearly 2 weeks and since the curve is practically flat polymer contsin about 10 per cent of c m linkage,with the after24 hours, we may assume that the addition reaction has acrylic nitrile copolymer apparently being somewhat more resohd equilibrium after 24 hours at 30' C. Thin compsrss highly cyclized. with 16 minutes or less required for ruhber. The styrene copolymer in carbon disulfide bas Likewise reached equiliirium Acknowledgment in 24 hours. This marked d8erence in reactivity between these synthetic types and natural rubber egrees with their The authors are grateful to The Godyear Tire & Rubber well-known reeistance to aging and to the action of chemical Company for a fellowship grant to the junior author which made this study pomible and for f u n d i n g the eamples used = m t a (6,W Sa.
.
*** *
INDUSTRIAL A N D BNGINEERINQI C H E M I S T R Y
in thia investigation. They are also deeply indebted to L.B. Fabrell, A. M. CWord, and E. J. Osterhof of the Gwdyear organisation for advice,supgestions, and a r i t i b . Literature Cited
&.. 63.
4208 (1931). (E.) CheYneY. unPUbIiahw3 data. (6) -, IND. ENQ. CHIY.,19.18% (lean. 0 Finhm nod Gray. Ibid.. 18.414 (1926). (8) Fiahar and MoCoLn, Ibid.. 19,13% (1927). (9)Qorgaa, Kaukzhk, 4,258 (1828). (10) H w n , Ibid.. 14,208 (1938). (11) ~arriss.dnn., 383,208,ala (bn). (la) H s w r and Brown, IND. ENQ.Cnm~., 31.1226 (1929). (18) Hsllller and 8.e. J . Phw. CXm.. 46, 118 (1942). (14) Ingle. J . 9a. Chmm.Id.. ZS,4% (1904). (1s) Kemp, IND.ENO.CWY.,19,681 (1927). (16) Kemp nod Musller. IND.ENQ.(X~X.,ANAL.ED.,6,62 (1984). (17) gonrad and Taahunkur, U.8. Patent 1,973.oOO (Isa?).
c
t
Vol. 34, No. 11
leaia uld M o A b , IND. ENQ.CBm..12,678(19%). Leakodtaoh. "chemioa Teahnolom nod of Oila. Fsta, snd W-", New York, Maomillsn Co.. 1921. MoIlhenny. J . Am. CXm.Sac., 21, 1084 (1888). Mnrk and R d . "High Polymeria Resctiona", New York, Inte-en-
(1) Aleunder, Kmda&&, 14,203 (1888). (2) B U e d BN-, IND. ENQ.CH.Y..29.888 (1937). (a) Brown and Hauar. Ibid.. So, 1291 (1888). (4) Csmtbers. Willinma. C o b , and Kirby, J . Am. CXm.
* *
Publiahera. 1941.
M-I. J . Am. Ch&. &..So, 280,1045(1988); 61,3241 (1939). M d e r , "The &ienoe of Rubber", tr. by Dunbmk and Morris, New Yark, %&old Publishing Cerp., 1934. (24) Osterhof. E. J., private communoation.
Pummerer, Kautachuk. 10, 149 (1934). Runmerar and Msnn. Bsr.. 62,2876 (1928). Pummerer and BWk, IW., 64.826 (1W1): 67,292 (19%). Rsnim, KO&&. 16,138(laa0). Roth, Wirtb. and Berendt. Ibid., 17,31 (1941). Bbsdiumr and Geim,Haw. Chim. A&. 9,649 (.19%). Btaudin& snd Widmer. Ibid., 9,629 (1926). Btevena and Miller. P m . Rubbsr T d .C W . , Ladrm.1938,287.
Thornhill and Smith. Ibid., 34.218 (1942). Tmhunhv and Back. U. 8. Patent 1.936.7al (1933). %gl*r. chenh-.ztu., 62 I26 (1938).
.y
Effect of!'Afiiti ?point of Oil on Swelling .of fithetic Rubbers *
A. C.
Hrnron
Rock lrland Arsenal, Rock ldand, 111.
P
* *
*
The synthetic rubber samples were 1 inch in diameter and inch thick. Before immersion, the volume of each rubber disk was determined by A. S. T. M. method D47137T. The disks were immersed in Wcc. portions of the various oils and subjected to the conditions of the test. The volumes of the disks were determined periodically up to 130 days. Figure 1 shows the increase in volume plotted against the number of days at mom temperature for the three synthetics. Figure 2 is a plot of the logarithm of percentage increase in volume
REVIOUS Feports on correlating the swelling of synthetic rubbers in oils with the aniline points of the oils have heen made for the purpose of selecting a standard oil for immersion tests or an oil for use in compounding. This investigation was conducted for the purpose of determining the changes in volume to be expected with certain comTable 1. Composition 01 Synthetic Rubbers Used pounded materials in various oils of the hydraulic type used -Bun. - 100 in recoil mechanisms. --- Neoprene 1w.o Buns N The synthetic materiala used had the followingcompositions P x o G N 20 Dibutyl sebamte 30.0 loo.oo 1.65 76 P33 30.0 1.5 8te.rio Mid shown in Table I. The physical properties of the oils are 20 G.sts. 5.0 M.gn€& 4.0 1 8 h i e soid given in Table 11. Oils 1 to 6, inclusive, are of p a r f i c 3.0 40.0 Therms= 5 zim oxide 1.0 G.atel 5.0 origin; the others are undoubtedly naphthenic-base oils. 8 M.gna.h 1.5 2.0 NaomneD 2 Nsomne D Pu.Bn 1.0 The aniline points are the maximum cloud temperatures oh1 Ntax 5.0 Zinsaxide 2 tained on repeated additions of aniline. Five grams of oil 10 were placed in a teat tube, a small amount of aniline was cure,tao Ib./ 20 75 sa.m_.mm. 22 added. and the tube was heated in an oil bath to 10' C: above the expected aniline point. This was then allowed t& cool while being agitated. Teble II. Prop.r(irs of Oils The temperature at which a "cloud" formed was recorded, more aniline was added, and the Aniline POW Point, C. Point. process repeated until a maximum cloud temoil Gravity Max. M)% F. No. o A . P . I . Spai6e perature was reached. 130.6 122 30.9 100 +I8 +5 580 484.0 0.8850 26.6 1 Carmen et d. ( 1 ) and maser (3) noted that 128.9 121 104 +28 0.8844 450 215.8 18.9 28.5 2 ---2030 30 127.2 119.3 lOT +22 455 162.0 15.8 0.8805 3 29.2 the presence of polyolesnS gives a "pseudo m . 8 118.a 88.9 10.7 0,8718 446 30.8 4 aniline point". That is, a haze is formed due to -30 113.9 111.1 34.0 5.6 :B 33.3 0.8686 415 6 P a .? sa.7 +25 1.57 .. . + 2 : 276 4.6T 0.8208 38.8 6 the separation of the polyolefins before the 9z.a 87 -30 89.0 7.98 43 23.2 0.9147 395 4A 90.6 @.a < 36 2.83 81 +26 305 12.12 actual cloud point is reached. In the present 0.8718 31.0 5A 19.4 74.3 < 35 9.74 2.38 57 -8 29.3 0.8800 250 5B investigation only oil F A gave this haze. This 4a.a a5.3
