MOLECULAR PROPERTIES O F NITROCELLULOSE,
I
569
MOLECULAR PROPERTIES OF NITROCELLULOSE. I
STUDIESOF VISCOSITY~ GEORGE J. DOI-LE, GARMAN HARBOTTLE, RICHARD M. BADGER, AND RICHARD M. NOYES
Gates and Crellin LaDoratories of Chemistry, California Institute of Technology, Pasadena, California Receiaed September S, 1946 IXTRODUCTIOX
Probably the procedures most commonly used for the characterization of samples of high polymers involve measurements of viscosity on solutions of these polymers. Many of thc procedures which are used commercially involve measurements on concentrated solutions, because results of great use in the empirical characterization of samples can be obtained from experiments in which the control of conditions need not be inconveniently precise. However, more valuable results from the theoretical standpoint can be obtained from measurements of viscosity on very dilute solutions and the extrapolation of the data t,o infinite dilution. In the course of studies of the properties of nitrocellulose we have had occasion to measure the viscosities of dilute and concentrated solutions of several nitrocelluloaes in various solvents and have developed procedures for the empirical correlation of results obtained under different conditions. The use of these measurements for evaluating molecular weights will be discussed in a subsequent paper. E X P E R M E N T A L PROCEDURE
Materials 'I'echnicnl butyl acetate was dried over calcium oxide and fractionally distilled under reduced pressure. The middle fraction, irhich boiled at 53°C.at 55 mm. pressure, was used for the solvent in the experiments described below. Chemically pure acetone was stored for a day s i t h potassium permanganate and distilled. The distillate \vas dried over potassium carbonate, decanted into a flask containing anhydrous calcium sulfate, and redistilled. The resulting material was used for studies of dilute solutions; untreated acetone was used for preparing the concentrated solutions, xhich were intended to resemble those used in standard commercial nieasurements of viscosity. The alcohol used in preparing the conrentrated solutions \vas commercial 95 per cent ethanol denatured with about 4 per cent by volume of methanol. Moat of the nitrocelluloses used in these studies \\-ererepresentative commercial samples \vith various properties.
' Contiibution S o . lOT6 f r o i n the G:ttes :Lnd Crrllin T.:~bomtoricsof C l ~ e ~ n i s t rCalifornia y, Institute of Teclindog!. This paper is based in wholc or in part o n work done for the Office of Scientific Itcaearch and Development undrr Contract Ol?Msr-881 with tllp California Institut,r of Technology.
570
Q.
J. DOYLE, Q. HARBOITLE, R. M. BADGER, AND R. M. NOYES
Method of measurement The viscosities of dilute solutions in purified acetone and butyl acetate were measured a t 25°C. with previously calibrated Ostwald-type capillary viscometers. Concentrated solutions were prepared to contain 10 per cent of nitrocellulose in a solvent mixture prepared from 10 parts (by weight) of denatured alcohol and 90 parts of acetone. The viscosities of these solutions were measured with a capillary-type viscometer of special design (2) instead of with the falling-ball viscometer used commercially (3). RESULTS AND DISCUSSION
“he “intrinsic viscosity”, ‘[VI, of a solute in a particular solvent is deiined by the expression
in which
qrsl
= relative viscosity = q,o~ution/qao~v.nt,
1, and c = concentration in grams per 100 ml.
qBp = specific viscosity = qre1-
The precise determination of the intrinsic viscosity of a nitrocellulose involves making measurements at several concentrations and extrapolating the results to infinite dilution. However, if the dependence of viscosity on concentration is known with sufficient precision, it is possible to calculate the intrinsic viscosity from the result of a single measurement on a solution of moderate concentration such that the viscosity can be determined with good precision. The equation of Martin (1) is the most satisfactory expression that we have found for the dependence of viscosity on concentration up to about 1 per cent of nitrocellulose. This equation states that log
= log [VI
+ kblc
in which k is a constant dependent upon the solvent and upon the chemical composition but not the molecular weight of the solute. The precision with which this equation fits the data is illustrated in table 1. In this table the results of measurements on solutions of four representative nitrocelluloses are presented with the intrinsic viscosities obtained by extrapolating these results to infinite dilution. In the last column of the table are presented the intrinsic viscosities calculated from individual measurements by equation 2 with the use of k = 0.22 if the solvent is acetone and k = 0.18 if it is butyl acetate.* The calculated intrinsic viscosities agree with the extrapolated values 2 Subsequent experiments with other preparations of the same solvents indicated different but self-consistent values of k in the neighborhood of 0.2. The differences were not enough to cause serious errors in intrinsic viscosities calculated with the use of equation 2, hut they do suggest that viscometric measurements in pure solvents are very sensitive to small traces of impurities and that each preparation should be checked before equations are applied blindly to measurements made with it.
oendence NITROGEN
1087..
....
.
2917.. . . .
10405.. . . ,
2,465.. . .
I
'
TABLE 1 viscosity. of . nitrocellulose solutions on concentration CONCZNPXATION, C
SOLVENT
11.89
13.26
13.94
INTPINSIC VISCOSITY [VI (CALNLAIED)
g.lIO0 ml.
9n
11.99
SPECIlIC ISCOSITY, 7.p
Acetone
0.667
4.029 3.022 2.015 1.007 0.403
7.339 4.408 2.355 0.884 0.304
0.566 0.588 0.618 0.633 0.659
Butyl acetate
0.848
4.022 3.017 2.011 1.006 0.402
10.34 6.031 3.072 1.136 0.376
0.733 0.756 0.782 0.801 0.813
Acetone
2.81
1.007 0.756 0.504 0.252 0.100
10.37 5.925 2.994 1.024 0.325
2.64 2.73 2.85 2.82 2.81
Butyl acetate
3.99
0.W 0.603 0.402 0.201 0.080
10.91 8.122 3.052 1.099 0.363
3.75 3.81 3.89 3.91 3.94
Acetone
3.00
1.007 0.756 0.504 0.252 0.101
12.40 6.768 3.351 1.131 0.355
2.84 2.91 3.04
3.04 3.02
Butyl acetate
4.30
0.704 0.528 0.352 0.352 0.176 0.070
11.33 6.019 2.960 3.002 1.046 0.348
4.39 4.32 4.37 4.41 4.30 4.34
Acetone
6.25
0.504 0.378 0.252 0.126 0.050
14.65 7.746 3.441 1.175 0.366
6.08 6.20 6.17 6.24 6.19
Butyl acetate
8.88
0.402 0.302 0.201 0.101
14.90 7.894 3.709 1.281 0.398
8.56 8.63 8.73 8.75 8.56
0.040
571
572
G. J. DOYLE, G. HARBOTTLE, R. M. BADGER, AND R. M. NOYES
a t least within 3 per cent, provided c is less than 0.5 g./100 ml. The value of k appears to be independent of nitrogen content for nitrocellulosescontaining from 12 to 14 per cent of nitrogen. The results of measurements of intrinsic viscosity on butyl acetate and acetone solutions of several representative nitrocelluloses are presented in table 2. The data indicate that the ratio of the intrinsic viscosities in these solvents is 1.40 0.04 for commercial nitrocelluloses having intrinsic viscosities greater than about 1. The value of the ratio appears to fall off for low-viscositynitrocelluloses. These results are in qualitative agreement with those of Staudinger and Sorkin (4)for the ratios of viscosities of nitrocellulose fractions, but the absolute values of the ratios found by them were less than the values observed by us? TABLE 2 Comparative viscosities of nitrocelluloses in bL NIIROCELLUIOSE NUMBER
-
11
SIIROGEN
I
per
1948. . . . . . . . . . . . . . . . 1087. . . . . . . . . .
2917. . . . . . . . . . . . . . . . 6278. . . . . . . . . . . . . . . . 5250. . . . . . . . . . . . . . . . 10405. . . . . . . . . . . . . . . 10411 . . . . . . . . . . . . . . 5248. . . . . . . . . . . . . . . .
NTRINSIC VISCOSIIY IN BUIYL ACETATE, [?lbu *o
is ACETONE, IVlUCS
[dbu 80/[71m0
_ _ _ _ ~ _ _
CCd
11.82 11 ,99
11.89 13.40 12.55 13.26 13.23 13.42
0.83 0.85 1.64 1.87 2.35 3.89 3.99 4.22 4.26 4.30 4.45 4.85 4.87 4.92 8.66
1.37 1.69 2.84 2.81 3.07 3.05 3.00 3.12 3.43 3.50 3.44 6.25
___
1.36 1.39 1.37 1.42 1.37 1.40 1.43 1.43 1.41 1.39 1.43 1.39
The data presented do not show any systematic dependence of the ratio of intrinsic viscosities in the tlvo solvents upon the nitrogen content of the nitrocellulose. Evidently such an effect, if present, cannot be very large. Its presence cannot, however, be entirely excluded, since in the materials available for measurement high nitrogen content tended to be accompanied b y high viscosity, and low nitrogen content by loiv viscosity. The viscosities of 10 per cent solutions of several nitrocelluloses in 10:90 alcohol-acetone were measured in stokes, and the results were used to calculate the viscosities in Hercules smokeless seconds (2). The results of these measure3 Subsequent experiments with other preparations of the s a m ~ solvents indicatcd selfconsistent values of the ratio nrarer to the values observed by Staudinger and Sorkin. The intrinsic viscosity in at least one of these solvents appears t o he very dependent up011 the presence of small amounts of impuritics.
MOLECULAR PROPERTIES O F KITROCELLULOSE.
573
I
ments are compared in table 3 with the intrinsic viscosities of the same nitrocelluloses in acetone. The data can be fitted empirically by an equation of the form log V = 3.55 log
1771
- 0.71
(3)
in which V is the viscosity in Hercules smokeless seconds. The values of V calculated by means of this expression are presented in the last column of table 3. They indicate that it is not possible from the results of measurements on dilute solutions to predict the viscosities of concentrated solutions within thc apparent accuracy of experimental determinations, but that it is nevertheless possible to obtain a reasonably satisfactory correlation between the results of measurements of the two types. TABLE 3 Comparative viscosities of dilute and concentrated solutions of nitrocellulose NlIROCELLULOSl
’
NUMBER
1948 . . . . . . . . . . . . . . . . 3875 . . . . . . . . . . . . . . . . 3293 . . . . . . . . . . . . . . . . 2936 . . . . . . . . . . . . . . . . 8432. . . . . . . . . . . . . . . 2917 . . . . . . . . . . . . . . . . 6278 . . . . . . . . . . . . . . . . 10411. . . . . . . . . . . . . . . 5248 . . . . . . . . . . . . . . . . 5246.. . . . . . . . . . . . . . .
NITROCEX
I,
VISCOSITY,
v,I X
EEPCELES SXOKEIESS SECONDS
11.82 10.93 11.95 12.17 12.67 11.89 13.40 13.23 13.42 13.45
,1
ISIRINSlC VISCOSITY IS AC;,T””,
0.04 0.33 0.50 1.24 7.8 12.0
iO.0 10 14.2 13
0.64 1.20
1.37 1.69 2.65 2.81 3.07 3.12 3.43 3.44
I ’
-
YIsCOSITY,1‘ (CALCUL.$IED)
0.04 0.a7
0.59 1.26 6.2 7.6 10.5 11.0 15.5 15.8
Measurements of viscosity have been made on dilute solutions of several nitrocelluloses in acetone and in butyl acetate, and it has heen found that the results can be expressed by an equation of the form
vre, =
1
+ [v]c x loL’”‘“
in ahich qrel is the relative viscosity of the solution, 171 is the intrinsic viscosity of the solute, and c is the concentration in grams per 100 ml. The constant k is close to 0.2 for both acetone and butyl acctate and appears to rary for different preparations of solvent. The ratio of the intrinsic viscosities in butyl acetate and in acetone is about 1.40 for nitrocelluloses having intrinsic viscosities greater than about 1, but the value of the ratio appears to fall off for lo\\ -viscosity nitrocelluloses. The value of this ratio appears to vary for different preparations of solvents but is constant within about +0.04 for measurements made with specific preparations.
574
R. H. BLAKER, R. M. BADQER, .LID R. M. NOYES
The viscosity of a nitrocellulosein Hercules smokelessseconds can be estimated approximately from its intrinsic viscosity in acetone by means of the expression log V = 3.55 log [q] - 0.71
in which V is the viscosity in smokeless seconds. We are indebted to Messrs. Robert H. Blaker, John Hardy, Earl Hoerger, and Thomas J. O'Neill for assistance in the measurements. We are also indebted to Dr. Robert B. Corey for helpful suggestions during the progress of the research. REFERENCES
(1) PFEIFFER, G. H . , AND OSBORX, R. H.: In Cellulose and Cellulose Derivatives, Emil Ott (Editor), p. 966. Interscience Publishers, Inc., New York (1943). (2) SHOEMAKER, D. P., HOERGER, E A R L ,NOYES,R. M.,ASD BLAKER, R. H . : Ind. Eng. Chem., Anal. Ed. 19, in press (1917). The smokeless second is defined in respect to the standard falling-ball viscometer, but the solution employed contains 10 per cent by weight of nitrocellulose in a solvent consisting of 10 parts (by weight) of acetone and 10 parts of denatured alcohol. The viscosity in poises is approximately equal to this time multiplied by the factor 3.77. (3) SPEICHER, J. K . : Cellulose 1, 2 3 2 4 (1930\. (4) STALTDINGER, H., A K D SOREIN,M . : Ber. 70, 1993 (1937).
MOLECULAR PROPERTIES OF NITROCELLULOSE.
I1
STUDIESOF MOLECULAR HETEROGENEITY' ROBERT H . BLAKER, RICHARD M. BADGER,
AND
RICHARD M. NOYES
Gates and Crellin Laboratories of Chemistry, California Institute of Technology, Pasadena, California Received September 3, 1946 INTRODUCTION
Of the methods currently employed for determining the average molecular weights of high polymers, procedures involving measurements of osmotic pressure and viscosity are probably the most frequently used. These procedures require comparatively simple apparatus and are capable of precision satisfactory for many purposes; however, they lead to different results when used for measurements on mixtures of polymeric species of different molecular weight. When measurements of osmotic pressure on solutions of a polymeric mixture Contribution No. 1077 from the Gates and Crellin Laboratories of Chemistry, California Institute of Technology. This paper is based in whole or in part on work done for the Office of Scientific Research and Development under Contract OEMsr-881 with the California Institute of Technology.
