Polvmolecularitv of Viscose J
J
Rayon and Rayon-Grade Pulps J
J
W. E. DAVIS Hercules Powder Co., Wilmington, Del.
I
N T H E manufacture of Tire-cord viscose rayons prepared from chemical cotton up sheet structure by stirring and wood pulps frequently differ in fatigue resistance and viscose rayon, one of the iri water, followed by deimportant variables controlother dynamic properties. This study was made to deterwatering with ethyl alcohol, mine whether or not this variation correlates with differling the physical properties and simultaneous drying and ences in molecular weight and molecular weight distribuof the finished product is the fluffing with a jet of comtion of the rayons and the original celluloses. type of cellulosic raw map r e s s e d a i r . T h e rayons It was found that fatigue resistance correlates fairly well terial used. In particular, were scoured twice with soap with the amount of low molecular weight material in the the resistance of rayon tire solution, washed thoroughly, rayon, while tenacity correlates with weight-average cord t o breakdown under reduced t o a short fiber length molecular weight. A strong correlation was found between cyclic stress, commonly by cutting a i t h scissors, dethe amounts of low molecular weight material in the pulps termed fatigue resistance, is watered, and fluffed as for and in the corresponding rayons. markedly affected. I t has the pulps. T h e p r o d u c t s The results emphasize the importance of controlling the generally been found that were completely frcc of amount of low molecular weight material in viscose rayon rayon prepared from chemical sulfur. for tire cord. The strong correlation between amounts of cotton is superior in this relow molecular weight material in the pulps and rayons spect to that made from wood PROCEDURES suggests that improvement in rayons from wood pulps pulp. The principal object might be obtained by more thorough steeping, unless there of this study vias to deterThe method used for deis a difference between wood pulp and chemical cotton in mine whether or not the two termination of degree of polythe rate of generation of low molecular weight material types of rayon and the cormerization distribution- was during aging of alkali cellulose. This last point is of responding starting materials fractional precipitation of fundamental interest in cellulose chemistry and should be showed a concomitant variacellulose nitrate prepared by examined further. tion in average degree of treatment of the cellulose polymerization and degree with a mixture of nitric of polymerization distribuacid, phosphoric acid, and ” tion. This paper describes the techniques of fractionation used phosphorus pentoxide. This choice of method raised two quesas well as the differences found among chemical cotton, wood t,ions: ( I ) Does t,he nitrate have the same degree of polymerizapulp, and the rayons. tion distribution as the cellulose? ( 2 ) Is the nitrate stable with The numerous methods which have been used t o determine respect, t o degree of polymerization for the time and under the degree of polymerization distribution have been reviewed by conditions involved in fractionation? Cragg and Hammerschlag ( 2 ) . For the present study, only The first quest’ion has never been a.nswered by direct test those based on differential solubility were considered, as they because it has not been possible to reconvert cellulose nitrate t o are most suitable for preparing fractions of relatively large size. cellulose without serious degradation. However, the indirect Of these, fractional precipitation was preferred over the extracevidence and the arguments adduced by Davidson ( 3 ) and by tion method, since in the latter it is difficult t o be sure t h a t Staudinger and Mohr (16) suggest very strongly that there is equilibrium has been reached, and the successive fractions are little if any decrease in degree of polymerization during nitration obtained as dilute solutions which are inconvenient to handle with the mixture of nitric acid, phosphoric acid, and phosphorus from the standpoint of recovery and refractionation. pentoxide. Sat,isfactory stability of the nitrates was demonWhile there is a well developed theory ( 7 ) of fractionation on strated experimentally, as described below. the basis of differential solubility, its detailed application in In an attempt to avoid these possible sources of error two methods for direct fractionation of cellulose were investigated practice is extremely tedious. However, the theory predicts briefly early in the course of the study. These were the cupriethylt h a t a high ratio of total volume to volume of precipitated phase enediamine method of Strauss and Levy ( 1 7 ) , and the “summais essential for good separation, and on this more general basis the guidance of theory was used in the work. tive” method of Coppick, B a t t i s h , and Lytton (1), employing 2 N sodium hydroxide as solvent. These methods were abandoned because good solution of cellulose in cupriethylenediamine SAMPLES The twelve cellulose samples investigated are listed in Table
I. The rayons were all 1100-denier, 480-filament yarns. While TABLE I.
each pulp sample is representative of the type of material used in preparing the corresponding rayon, the sample of pulp was not necessarily taken from the specific lot used in preparing the rayon from which the rayon sample was taken. I n the absence of information on the variability of the pulps with respect t o degree of polymerization distribution, the extent of the error which may arise from this source is unknown. The pulp samples were used as received, except for breaking
CELLULOSE S I M P L B S FOR
Identifying Letter for Both Pulps and Rayons A B C D E
F
516
Pulp Type Wood pulp Wood pulp Wood pulp Wood pulp Chemical cotton Chemical cotton
FRACTIONATIOS Pulp Mfr. 1 1 1
2 3
4
Rayon Mfr. 1 2 3 3 1 3
February 1951
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INDUSTRIAL AND ENGINEERING CHEMISTRY
I N ACETONE AN0 HEXANE ADD HEXANE P
I
SOLUTION
R
E
C
I
,DISSOLVE I N ACETONE AND HEXANE TO 1 . 5 % CONCENTRATION. TREAT SAME AS S O L U T I O N A
S
1
1
ADD HEXANE
I
D I S S O L V E I N ACETONE AND HEXANE TO 1 . 5 % CONCENTRATION, TREAT SAME AS S O L U T I O N A
PRECIPITATE I
I N ACETONE AND HEXANE TO 1 . 5 % ,DISSOLVE CONCENTRATION. TREAT SAME AS S O L U T I O N A
ADD ~ E X A N E
SOLUT I ON
PREC I P I TATE
Figure 1.
Flow Sheet for Complete Fractionation
required a solvent saturated with cupric hydroxide, and this solvent was not stable; successive fractions precipitated from oupriethylenediamine by addition of 8 N sulfuric acid came down over a very narrow range of acid volume; the viscosity of cupriethylenediamine solutions of cellulose decreased markedly in the presence of air; and none of the cellulose samples were soluble in 2 N sodium hydroxide unless previously regenerated from solution--e.g., in cupriethylenediamine. Since the fractionation was being carried out on cellulose nitrate, this derivative was available for determination of degree of polymerization. Intrinsic viscosity was selected as the most easily determined measure of degree of polymerization, and a brief study was made of the intrinsic viscosity-degree of polymerization relationship.
*
+9
PREPARATION ANALYSIS,AND STABILITY OF NITRATES. The nitration procedure used was essentially t h a t of Davidson (3). At the end of the reaction the product was filtered off, pressed to remove a s much of the adhering acid as poossible, and stirred rapidly into a lar e volume of water a t 0 C. It was then filtered off, washe2 thoroughly with water, boiled with water for 3 hours, dewatered with ethyl alcohol, boiled three times for 5 minutes with ethyl alcohol, and stored wet with ethyl alcohol. As samples were needed they were removed from storage and airdried. All nitrates were analyzed for nitrogen by the nitrometer method; results ranged from 13.65 to 13.85’35, corresponding t o a degree of substitution of 2.8 to 2.9. Enough samples were analyzed for phosphorus content to make certain t h a t it did not exceed t h a t corresponding to one combined phosphate group per 400 glucose residues, and averaged only 1 per 800 residues. The method used for phosphorus involved digesting the sample with nitric acid, ashing, removing iron and silica, and determining the phosphorus by the Lamotte colorimetric method, which is based on reduction of phos homolybdate with stannous chloride as described by Denighs (67. The stability of these nitrates with respect to degree of polymerization is shown by the data in Table 11. The acetone solution was stored a t 25’ C. in a tightly sto pered glass flask which was exposed t o the diffuse light of the lagoratory. The alcoholwet nitrate was stored in a brown bottle under the same conditions used for all the other nitrates. The changes which are to be noted in Table I1 are all within experimental error; in no case do they exceed 3%. FRACTIONATION. The first stages of the fractionation procedure used for the rayon nitrates are shown in Figure 1. Throughout the process, whenever cellulose nitrate was dissolved in a mixture of acetone and hexane, the two were added alternately and in such proportions as just to avoid precipitation. Fractions were thrown down by adding hexane, warming to redissolve the precipitate, and cooling slowly. The twenty fractions produced by the scheme of Figure 1 were recovered by
evaporation as thin films (0.002 inch), which were soaked in water to displace residual solvent and air-dried. The air-dry yields were corrected for loss in weight a t 105’ C. I n some cases intrinsic viscosities were determined on these fractions and the information used to set up degree of polymerization distribution curves. Most of the samples, however, were also subjected to further fractionation by recombining the above fractions (in proportion to their yields) in grou s according to viscosity, dissolving in acetone and hexane (celglose nitrate concentration = 0.5’%), and separating into 3 to 5 fractions by the procedure described above. As a rule, about 28 fractions were obtained in the third stage. A shorter procedure, designed t o furnish only the low de ree of polymerization end of the distribution curve, was applief t o the nitrates prepared from the pulps. The techniques were as above, with the fractionation scheme shown in Figure 2. The precipitates marked A together amounted t o 70 to 80% of the original nitrate, those marked B to 70 to 80% of the material in solution B. The two latter precj itates were recovered and their intrinsic viscosities determinei as a check on possible degradation during fractionation. The recipitates and residues across the bottom of Figure 2 containexthe low degree of polymerization material; they were recovered and yields determined as described above. DETERXINATION OF INTRINSIC VISCOSITY. Viscosity determinations were carried out using a n Ostwald-Cannon-Fenske viscometer having a n outflow time of about 100 seconds for water. The solvent for the cellulose nitrate was a mixture of 77.5% n-butyl lactate and 22.5% diacetone alcohol by weight, to which 1.5% by volume of water had been added. The low volatility of this solvent minimized concentration changes during handling of the solutions, and its high viscosity made possible very precise determinations of specific viscosity a t low concentrations without the necessity of using a viscometer of Rmall capillary radius (4). I n some of the earlier work acetone waa used a s a solvent; this required higher nitrate concentrations, making the extrapolation t o infinite dilution more uncertain. However, within experimental error, the same intrinsic viscosities were obtained in acetone as in butyl lactate-diacetone alcohol.
TABLE 11. STABILITY OF CELLULOSE NITRATEIN STORAGE T i m e of Storage Days Months 0
...
... ... a
0 6
’
Conditions of Storage
Viscosity Secondsa Intrinsio
445.3 442.7 450.9 450.3
... ... ... ...
Time of flow of a 2.5% solution in a particular visoometer.
... ... ... ... 3.34
3.38 3.95 4.08
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INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY CELLULOSE
Vol. 43, No. 2
NITRATE
1 , 5 % IN A C E T O N E
1
PRECIPITATE
PRECIPITATE
A
PRECIPITATE
t (SOLUTION
I ADD
HEXANE
7
S O L U T I ON ADD
HEXANE
EVAPORATE
Figure 2.
Flow Sheet f o r Short Fractionation
solvent, a static method was used. The method of determining molecular weight from the osmotic pressure data is also deacrihrd by Fuoss and Mead (8). Log V S P / C = log [n 1 Iz[nlc MISCELLANEOUS PROPERTIES. The carboxyl group contente where of the pulps and rayons were determined by the silver o-nitro?SP = (7 -.l)o)/yo phenolate method of Sookne and Harris ( I C ) , using potentio7 = solution viscosit), metric titration with a silver-silver chloride electrode for drno = solvent viscosity termination of silver. c = concentration in grams per 100 ml. Tensile tests on the rayons were carried out on a Scott tester, k = a constant model DH-2, using samples conditioned for 24 hours at 77' F. [q = intrinsic viscosity and 50% relative humidity. Extrapola.tion was carried out by the method of least squares. Fatigue resistance tests were carried out by two niet,hods. 'Pest 1 has been described in the literature (IS). Briefly, it inRELATIONOF DEGREEOF POLYMERIZATION TO INTRINSIC volves cyclic stressing of the cords under load in air of controlled VISCOSITY. As the fractionation work proceeded and the intemperature and humidity. The distinctive feature of the tmt trinsic viscosities of fractions were determined, fractions having is the arrangement whereby each load is supported by two cords the same or nearly the same intrinsic viscosity were combined. which are connected t o eccentrics in such a way that while one Four samples in quantities sufficient for osmometric work were cord is stretching the other is relaxing; this permits use of a large finally obtained. These were dissolved in acetone; the solutions stroke without appreciable vibration of the load. The load used were decanted from the small amount of dirt which settled out in obtaining the results reported herein was 1 gram per denier. and were poured into 95% ethyl alcohol. The precipitated Details of test 2 have not been published, but it is a method which nitrates were recovered by filtration, washed with ethyl alcohol, does not involve embedding the cords in rubber. For both boiled twice with ethyl alcohol to ensure stability, and air-dried. tests a high value means good resistance to fatigue, Intrinsic viscosities were determined in butyl lactate-diacetone alcohol a s described above. The nitrates were analyzed for RESULTS nitrogen to establish the relation between molecular %,eight and degree of polymerization. Number-average molecular weights Data illustrating the precision of deterinination of' intrillsic were then determined by the method described by Fuoss and viscosity are shown in Table 111. The results shown are typical, Mead (8),except that the osmometer membranes were of unboth better and worse agreement with the straight lines required dried cellophane and the solvent was 90 to 10 by volume methyl ethyl ketone-anhydrous ethyl alcohol. Bccause of t,he mixed by the viscosity equation used being obtained occasionally. For the examples shown the average difference between obsorved arid calculated values of log (qep/c) is about the same for the two solvents. However, in butyl lactate-diacetone alcohol it is TABLE111. VIbCOSI'I'Y-C:ONCENTRbllON DATA possible t o carry out the determinations a t much lower concen-Log m / c trat,iori than in acetone, whence extrapolation to iiifinite dilution Solute Conon.. Calcd. (least G./lOO G. is more precise with the former solvent. Stat'istical analysis of Solvent Soln. Obsvd. squares) a long series of determinations in butyl lactate-diacetone alcohol 0.6632 0.8614 0.9631 Acetone 0.6744 0.9041 0.9007 showed that, except for samples of very low degree of polymerisa0.4704 0,8260 0.8277 0.4138 0,7877 0.7879 tion, intrinsic viscosity could be determined with a standard error of about 1%; the error is 2 t o 3 times as great in acetone. 1.216 0.3765 0.3741 Acetone 1.019 0.3282 0.3306 Since the fractions tend t o retain solvent, some error in yield 0.8076 0.2842 0,2839 0.7183 0,2648 0,2641 is expected; the magnitude of this error is illustrated by the da.ta iii Table IV. These show that the standard error in the yield Butyl lactate0.5283 0.3060 0.3057 diaoetone alcohol 0.3147 0,2686 0.2603 of a fraction is on the average about 2% of the average weight 0,2336 0.2458 0.2431 0.1522 0.2235 0,2268 of a fraction; when intrinsic viscosity is included the per cent 0.0444 0.2058 0,2029 standard error increases only slightly. These figures are for Butyl lactate0.2080 0.7147 0.7150 groups of fractions; it is probable t h a t for the individual fracdiaoetone alcohol 0.1239 0.6682 0,6667 0.0923 0.6474 0.6485 tions the variation would be somewhat higher. A figure of 3% 0.0601 0.6294 0,6300 for the uncertainty in the position of points on the distribution 0 017F, 0.8060 0.6056 curves seems reasonable. The equation used to represent, the viscosity-concentration data was that of Martin (11).
+
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1951
TABLEIV.
YIELD CHANGESDURING THIRDSTAGE OF
Solvent-Free Wt. of Material Recovered Entering from third third stage stage 1.327 4.522 3.100 2.750 1.201 2.397 2.963
1.307 4,440 3.129 2.833 1.218 2.376 2.951
18 260
18.264
*
FRACTIONATION
zw
[1IU.t
Difference
Before third stage
After third stage
Difference
-0.020 -0.082 +O. 029 f0.083 +0.017 -0.021 -0.012
0,427 1.217 0.729 0.434 0.143 0.221 0 118
0,433 1.224 0.736 0,457 0.139 0.221 0.113
+0.006 +0.007 +0.007 +0.023 -0,004 0.000 -0.005
3 289
3.323
Std. error =
Std. error = 0.051
W , = weight fraction of fraction. a
itl’
fraction:
(71%=
0.011
intrinsic viscosity of
519
degree of polymerization material. The viscosity drop is less pronounced for samples E and F , which are chemical cottons, and for the corresponding rayons than for the wood pulps a n d wood pulp rayons. The fractionation results for both pulps and rayons are brought together in Table VII, which also includes the results of physical tests and carboxyl analyses on the rayons. Table VI11 presents the results of osmometric determinations of molecular weight on selected fractions, which permit the establishment of the relation between intrinsic viscosity and degree of polymerization. Over the range investigated, the data show the relationship t o be linear. Therefore, intrinsic viscosity is directly proportional t o might-average degree of polymerization.
ith
~~~
r)-
Since subsequent discussion will be limited t o differences involving only the portions of distribution curves with low degree of polymerization, only two complete curves are presented. Figure 3 illustrates the degree of fractionation obtained and shows that the principal effect of a third stage of fractionation is t o improve somewhat the resolution a t the high degree of polymerization end of the curve. Therefore, it should be possible to compare the samples with respect t o content of low degree of polymerization material on the basis of either two or three stages of fractionation. This was done by drawing as smooth a curve as possible through the midpoints of the horizontal portions of a graph similar t o Figure 3 for each sample, and reading off the amount of material with a n intrinsic viscosity less than 2. The results are shown in Table V; in this respect there is little difference between two- and three-stage fractionation. Table V also shows the original intrinsic viscosities and the sums of products of corresponding weight fractions and intrinsic viscosities. These should of course be the same, but the data give some indication of a slight drop in degree of polymerization during fractionation. It does not appear t o be sufficient to have a significant effect on the values for the amount of low degree of polymerization material.
r
-THREE
STAS__
WEIGHT PER CENT
Figure 3.
Typical Fractionation Curves f o r N i t r a t e d Viscose R a y o n DISCUSSION
The data presented in Tables I1 t o VI and Figure 1 show that, as far as the effects of stability of nitrates in storage and during fractionation, precision of viscosity determinations, and thoroughness of fractionation are concerned, the information on average intrinsic viscosity and content of low degree of polymerization material summarized in Table VI1 can be regarded as TABLE V. SUMMARY OF FRACTIONATION RESULTSON RAYONS fairly reliable. The other results in Table VII-namely, te% Of nacity, fatigue resistance, and carboxyl content-as well as the No. of iMateria1 Stages of with [VI Original osmometric molecular weights in Table VIII, were obtained by Rayon Sample Fractionation Less Than 2 1.111 ZW , standard methods, and no attempt was made t o assess their A (wood pulp) 2 27.8 3.60 3.60 accuracy by direct test. It is probable t h a t with the exception 3 29.8 3.60 3.49 of the tests for fatigue resistance, about whose accuracy and reB (wood pulp) 2 29.3 3.30 3.23 producibility very little information is available, the above tests C (wood pulp) 2 30.6 3.33 3.27 give results a t least as good as those of the viscosity and frac3 29.6 3.33 3.24 tionation work. It has also been shown t h a t average intrinsic D (wood pulp) 2 29.8 3.39 3.28 3 30.6 3.39 3.32 viscosity is directly proportional t o weight-average degree of polymerization. E (chemical cotton) 3 19.4 4.08 8.96 Considering all the data in Table VI1 as being fairly accurate F (chemical cotton) 2 24.1 3.20 3.42 3 24.3 3.20 3.36 measures of the respective properties, the principal question to be answered is t h a t of the relationship, if any, of the fatigue resistance t o the other properties. This is most readily done by
Table VI presents the same data for the pulps as are given for the rayons in Table V. These results were obtained using the short fractionation method designed t o give only the low degree of polymerization end of the distribution curve and graphical procedures as above. Because of the higher average degree of polymerization of these samples, the contents of low degree of polymerization material were taken below an intrinsic viscosity of 3 rather than 2. The viscosity again shows a tendency t o drop during fractionation, perhaps t o a greater extent than with the rayon nitrates. However, the drop still appears insufficient t o disturb significantly the relative order in amounts of low
TABLE VI, SUMMARY OF FRACTIONATION RESULTSON PIJLPS %
A B
C
D E F
Pulp Sample wood pulp) wood pulp) wood pulp) (wood pulp) (chemical cotton) (chemical cotton)
1
of
Material with [?I Less Than 3
Original
23.5 21.5 20.6 21.6 7.4 10.5
10 26 11.73 10.80 11.53 11.05 9.91
[? I
1
z Wi 1.I 1% 9.56 10.80 10.21 10.12 10.93 B.92
520
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 43, No. 2
The values in Table X indicate the strength of some other relationships yo of Low Degree Fatigue Properties of Rayons among the data. There is good eviof Polymerization Resistance Tenacity, Elonga- COOH COG dence for a relation between weightater rial in -T [ q l of g./ tion at tent, meq. Samale Pulp RayonQ 1 2 nitrate denier break, % per g. average intrinsic viscosity and teA (wood pulp) 23.5 28.8 55 4 3.60 3.77 9.1 0.0412 nacity; this is not, unexpected. The 21.5 29.3 .. , 10 3.30 3.43 8.7 B (wood pulp) correlation with number-average degree C (wood pulp) 20.6 30.1 32 5 3.33 3.29 11.1 0.0400 D (chemical (wood pulp) 271 .. 64 31 09 ..24 39 4 34 .. 30 98 3 .. 8 52 1 10 1 .. 3 8 0.0365 of polymerization is not nearly so good. E cotton) 59 9 3 1 0.0331 F (chemical cotton) 10.5 24.3 50 10 3.20 3.48 12.5 0.0365 The best correlation of all exists between amounts of low degree of polya Average of two- and three-stage results where both are given in Table V. merization material in the rayons and in the corresgonding_pulps. While this .. TABLErrJII. DaT.4 FOR CELLULOSE YITRATE may seem natural, one must consider the (Degree of substitution, 2.8) work of Mitchell ( I f ? ) showing the disappearance of the low degree Fraction Intrinsic AIolecular Weight of polymerization peak in the distribution of sulfite wood pulp on KO. T-lscoslty (Osmometric) preparation of alkali cellulose. It seems fairly probable t h a t 1 1.589 39,700 2.728 67,100 2 with both wood pulp and chemical cotton, the low degree of poly4.712 104,000 3 merization fraction is almost completely removed during steeping 5,572 142,000 4 of the cellulose in 18% sodium hydroxide, and that the low These d a t a yield the following value? for the constants in the equation degree of polymerization fraction appearing in the rayons is DP = klq]": largely generated during aging of the alka!i cellulose. Therefore, k a the results presented here suggest a difference between wood pulp Using all 4 points 87.1 0.98 Omitting fraction 3* 86.9 1.02 and chemical cotton in their response to alkaline oxidation, which Av. 87.0 1.00 is reminiscent of the difference in rate of hydrolysis of these two * This is the point which is farthest from the least-squares line for the four materials ( 6 , 1 6 ) ~ However, the possibility that the difference points. in amount of low degree of polymerization material in the rayons is due in part, t o less complete extraction of low degree of polymerization material from the wood pulp d x i n g steeping cannot be neglected. assuming linear relationships and calculating correlation coefficients, as shown in Tables I X and The first two values of -~ P in Table IX do no more than suggest that the fatigue results may be connected with content of low degree of polymerization TABLE I X . CORRELATION^ OF FATIGUE RESISTANCE material. This is probably as much as could be hoped for with Type of Fatigue Correlation Correlation Test No. Correlated with this small number of samples. Since the correlation is somewhat Coefficient Pa Simole 1 % low degree of - 0 75 0.085 better with fatigue test 1 than tvith test 2 , further calculations polymerization were made with the data of test 1. The third value in Table material IX shows that a relation between fatigue resistance and weightSimple 2 % low degree of - 0 . R9 0,121 polymerization average degree of polymerization is just as probable as the relamaterial tion between the former and the amount of low degree of polySimule 1 Weight arerage +0.73 0.095 degree of polymerization material. Therefore, it was of interest t o calculate merization the multiple correlation coefficient, using both weight-average Multiple 1 % low degree of 0 81 ... degree of polymerization and amount of low degree of polymerizapolymerization material and tion material as independent variables. The result was only a w-eight-arerage degree of polyslight improvement in correlation over that obtained with either merization variable alone. The usual interpretation of such a situation is Partial 1 0.52 70low degree, of that the variables taken as independent are actually related. polynierization material This is no more than aould be expected for two such variables Partial 1 Weight - average 0.47 ... as weight-average degree of polymerization and amount of low degree of polymerization degree of polymerization material, and is confirmed by the Simple 1 Number-average +o 72 0.100 values of the partial correlation coefficents in Table I X . degree of polyThese show that when the effect of either variable is eliminated, merization the correlation of the other variable m ith fatigue resistance Probability of obtaining the observed correlation coefficient when the true value is zero. If P is less t h a n 0.0;1, it is a fairly strong indication t h a t decreases markedly. The values of the partial correlation cothe correlation coefficient is not zero, while if P is greater t h a n 0.20 i t is efficients are still fairly high, however, and one may conclude fairly probable t h a t there is no corre!ation: intermediate values of P oan be taken as indicatinm t h a t a correlation may or may not exist, more evidence that fatigue resistance is probably affected by both weightbeing required t o deFide between the two alternatires. average degree of polymerization and amount of low degree of polymerization material, and that both have about the same T A B L E x. SIMPLECORRELATIONS O F OTHER PROPERTIES amount of influence, but t h a t other factors, not identified in Dependent Correlation this study, are also important. The data on elongation in Table Variable Correlated with Coefficient fa VI1 suggest that variation in this property, which is known t o Weight - average 0.83 0,020 Tenacity affect the results of fatigue testrs, may be one such factor. One degree of polymerization other possibility was tested-namely, t h a t use of number-average h-umber-average 0.50 0.171 Tenacity degree of polyinstead of weight-average degree of polymerization in the correlamerization 0.96 0.0004 tion would cover the effects of both average degree of polymeriza% low degree of % low degree of polymerization polymerization tion and amount of IOK degree of polynierization material. The material in material in rayon pulp last value in Table I X shows, however, that this is not the case, the correlation being no stronger with number-average than with See footnote t o Table IX. weight-average degree of polymerization.
TABLE VTT. SUMMARY OF PULP AND RAYON PROPERTIES
I
x.
~
I . .
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1951
The values of carboxyl content for the rayons given in Table. VI1 are of interest principally in that they show little difference between the two types of rayon. The small variation which does exist is certainly inadequate t o account for the wide spread in fatigue resistance. It should be mentioned, finally, that the constant in the relation found between degree of polymerization (DP)and intrinsic viscosity-name1 y,
DP
0
=
ACKNOWLEDGMENT
The osmometer membranes of undried cellophane were obtained from the Sylvania Industrial Corp., now Sylvania Products Division, American Viscose Corp. The fatigue resistance tests were carried out by the staff of the Rayon Department, E. I. du Pont de Nemours & Co., Inc., Richmond, Va. LITERATURE CITED
87 [ q ]
Coppick, S., Battista, 0 . A., and Lytton, M. R., presented before Division of Cellulose Chemistry at the 106th Meeting, AM. CHEM.SOC., Pittsburgh, Pa. Cragg, L. H., and Hammerschlag, H.,Chem. Revs., 39,79 (1946). Davidson, G. F., J . Teztile Inst., 29, T195 (1938). Davis, W. E., and Elliott, J. H., J . Colloid Sci., 4, 313 (1949). DenigBs, G., Compt. rend., 171,802 (1920). Ekenstam, A,, Ber., 69B,553 (1936). Flory, P. J., J . Chem. Phys., 12, 114, 425 (1944). Fuoss, R. M., and Mead, D. J , J . Phys. Chem., 47, 59 (1943). Husemann, E., and Schulz, G. V., Z . physik. Chem., B52,
is in fair agreement with the value of 96 deduced by Jullander (10)on the basis of the work by Husemann and Schulz (9) and Wannow (18). SUMMARY
*
The fractionation of cellulose nitrates prepared by a nondegradative procedure from a series of six high-tenacity viscose rayons and tho corresponding pulps has been described. The results of the study, in terms of average degree of polymerization and amounts of low degree of polymerization material in the rayons, have been correlated with physical properties of the rayons, such as tenacity and fatigue resistance. *Thelatter correlates fairly well with amount of low degree of polymerization material, while there is a good correlation between tenacity and weight-average degree of polymerization. A strong correlation has been shown between amounts of low degree of polymerization material in the rayons and in the corresponding pulps. The results of a brief investigation of the relation between degree of polymerization and intrinsic viscosity have been presented. The relation appears t o be linear over the range investigated.
52 1
1 (1942).
Jullander, I., Arkiv Kemi, Mineral. Geol., 21A, No. 8 (1945). Martin, A. F., presented before Division of Cellulose Chemistry, at the 103rd Meeting, AM. CHZM.SOC., Memphis, Tenn. Mitchell, R. L., IND.ENG.CHEM.,38, 843 (1946). Roseveare, W. E., and Waller, R. C., Testile Research J . , 19, 633 (1949).
Sookne, A. M., and Harris, M., J . Research Natl. Bur. Standarda, 26, 205 (1941).
Stamm, A. J., and Cohen, W. E., J . Phys. Chem., 42,921 (1938). Staudinger, H., and Mohr, R., Be?., 70B,2296 (1937). Strauss, F. L., and Levy, R. M., Paper Trade J . , 114, No. 18, 33 (1942).
Wannow, H. A., Kolloid Z., 102,29 (1943). RECEIVED July 5 , 1050. Presented before the Division of Cellulose Chemist r y at the 116th Meeting of the AMERICANCHEMICALSOCIETY,Atlantio City, N. J.
Breaking Water-Tar Emulsions with Surface-Active Agents IRVING PINCUS’, KARL F. OCKERT, AND CORLISS R. KINNEY The Pennsylvpnia State College, State College, P a .
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Very stable tar-water emulsions are produced frequently during the manufacture of enriched water gas. The dehydration of these emulsions constitutes an important problem to the gas industry, particularly when thermal means of dehydration are to be avoided. A number of these plant emulsionswere found to undergo demulsification with a variety of surface-active agents. Little correlation was observed between the ease of brealcing the emulsions and the percentages of “free carbon,” uncracked oil, or asphaltenes. Emulsions with high water content were most easily broken when cold. Heat usually increased the activity of those agents which were not active when cold, but generally did not increase materially the amount of demulsification obtained with those agents which were active when cold. Tars taken from different sources in the same plant seemed to have similar demulsification properties even though their water contents or other properties varied. The addition of sodium carbonate usually produced little demulsification beyond that of surface-active agent alone. The fact that the emulsions tested were broken to some extent by several of the reagents suggests that all emul-
sions of this type may be broken effectively by finding suitable reagents and conditions. A more extensive survey of reagents, conditions, and types of emulsions is needed.
T
AR-water emulsions of remarkable stability are often produced during the manufacture of water gas enriched by the cracking of heavy oils. Water contents vary but emulsions with as much a s 80% water are frequently encountered. Because of their high water content and their stability, the processing and utilization of these emulsions constitute a problem of importance to the gas industry. If the tar is to be used as a fuel or for road building, the emulsions are usually dehydrated by thermal processes. However, this results in a marked increase in the viscosity of the tar because of the polymerization of unsaturates. This is not only undesirable when the tar is used as a fuel but, for the production of chemicals, particularly the resin-forming monomers, i t should be avoided. For these reasons a study of the demulsification of these tars with several surface-active agents was begun. Eight reagents and nine commercial water gas t a r emulsions were examined. Six of the reagents were cationic in character and two were nonionic. Because of the beneficial action 1
Present address, Great Lakes Carbon Corp., Morton Grove, Ill.
