Intrinsic Viscosity of Nitrocellulose J
RELATED TO DEGREE OF NITRATION T h e degree of nitration of nitrocellulose of a given molecular weight has an important effect upon the viscosity of its solutions. As complete nitration is seldom attained, this effect must be considered in determining degree of poly-‘ merization from viscosity measurements. By using a conventional nitrating mixture diluted with phosphoric acid, the nitrogen content of a cellulose sample after nitration may be varied between 10.5 and 13.8% without degradation. An empirical equation has been derived by which the intrinsic viscosity as determined, [a], may be converted into the intrinsic viscosity, [ T ~ ] Tof , the corresponding trinitrate: Iog [ 7 ] T / [ q ] = logf, (14.15 - x ) X B, wheref, is a factor which takes into account the departure of the unit molecular weight from that of cellulose trinitrate because of the lower degree of nitration, x is the percentage of nitrogen in the sample, and B is an empirical constant, having a value 0.114 for all cellulose samples studied. This equation makes it possible to calculate the intrinsic viscosity of any nitrocellulose, independent of the nitrogen content. Values for the Staudinger constant have been recalculated to allow for the effect of variable degree of nitration. The best value appears to be I DETERMIXED BY T W O ASCLYTICAL LIETHODS Type of Cellulose
Nitrated
Rayon Wood p u l p Linters ~
~
Nitrogen Content, Vo Gasometric Gla\ linetilo (nitrometer) (nitron) 13.70, 13.78, 13.78, 13.50 13.70, 13.75, 13.78 13.65, 13.70
13 65, 13.70 13.67, 13.72 13,60, 13.76
p~
DETERMINATION OF SITROGEN COATEST. Two methods n-ere used, the usual gasometric method with the nitrometer and a gravimetric procedure using nitron reagent to precipitate the nitrate. The agreement between results obtained by these two markedly different methods (shown in Table I ) indicates that the accuracy as well as the precision of the determinations is satisfactory. 2492
DETER~IIINATIOX OF F i I S C O S I T Y . 1-iscosities of acetone solutions of the nitrocelluloses were measured a t 25.0' C. in capillary viscometers, with t'he precautions described in an earlier paper (10). Intrinsic viscosit,ies a-ere calculated by means of the BakerPhilippoff equation: [?] = 8(7711s- l)/c, where ?;- is the relative viscosity and c is the concentration in grams per deciliter. The conditions under which this equation is valid are discussed in (10). Because there might be some doubt whether the equation holds as well for low as for high nitrogen contents, viscosity measurements were made at several concentrations for a number of the celluloses nitrated to about 11% nitrogen, and the int'rinsic viscosities found by graphical est'rapolation to zero concent,ration. Table I1 compares the values oht,ained by both methods. For rayon and cotton linters, the agreement is satisfactory. The extrapolated value for cotton is lo^, but this is in agreement with previous observations (10, p. 644) on cotton with high nitrogen content: The Baker equation apparently gives high values of intrinsic viscosity of nitrated cotton a t all nitrogen contents, ijut the relative values are probably representative. The only result in Table I1 seriously in doubt is that for the sulfate 17-ood .pulp. Here the individual values of reduced viscosity, plotted on semilog scale against, concentration, fall close to a straight line, so that t'he extrapolated value should be good. The values calculat,ed from the equatiou for each point, however, shon- a .strong downnard trend, and are significantly higher than t,he ,extrapolated value. Khether such departure from the usual course is characteristic of this sulfate pulp is not known; further study is desirable. 'TABLE11. CALCULATED ASD EXTRAPOLATED VALUESOF IsT R I S q I C VISCOSITY O F hTITROCELLULOSES WITH L O W ?;ITROGEU
CONTEXTS Type of
Cellulose Rayon 3ulfatepulp
Nitrogen Content, 70 11 05
10 81
:Linters
11.36
'Cotton
11.05
Concn. G./DI.' 0 509 0 253 0 166 0 0 0 0
516
109 368 268 0.677 0 230 0.157 0.1332 0 0786 0 0311
Relative Viscosity 2 72 1 698 1 425 4 15 3 13
2 72
2 06 10.02 2.40 1.841 10.83 3 44 2.31
Intrinsic I-iqcusit>'p Calcd. Extrapolated 2 10 L 21 2 17 2 18 3 03 3 01 2 90 2 83 3.94 4.02 4.04 18.08 17 42 17 26
2 44
4.07 16 06
RESULTS & l D DISCUSSIOR-
In Table 111 are given the values of intrinsic viscosity for the several celluloses nitrated to different nitrogen contents in the various nitrating mixtures and for the same nitrocelluloses lenitrated in tbe 100% mixture. The regularity with which any given mixture introduced approximately the same number of nitrate groups into celluloses of distinctly different types is sonien h a t surprising, for it mas not anticipated that the degiee of -ubstitution could be so easily controlled. I n Figure 1 the values of the intrinsic viscosity are plotted against the nitrogen content; only values for the first nitration are shown, as inclusion of those for the renitrated samples would overcrowd the graphs. Data for Wannow's one sample are included for comparison. These curves show how important the correction for nitrogen content is: The intrinsic viscosity a t ' nitrogen is approsimately half the value a t 14y0, for cellu11% loses of low as well as high degree of polymerization. It has been suggested that this marked change in intrinsic viscosity with degree of nitration may be attributed not only to differences in average degree of esterification, but also to differences in distribution of nitrate groups on cellulose chains, particularly for low degrees of nitration. I n view of the reproducibility of the results obtained by the nitrating procedure used,
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 45, No. 11
-Cellulose it seems unlikely that the obAFTER T.kBLE 111. NITROGEN CONTENTS AND INTRINSIC VISCOSITIES O F NITROCELLULOSE served effects are caused by FIRSTAND SECOND NITRATION heterogeneous distribution Second Nitration First Nitration of nitrate groups. Nitrogen Nitrating Nitrogen content, The results of renitration exmixture, content, [?IT, [?IT, dl./g. % Cellulose Nitrated dL/s. % % periments invite comment. I n 13.40 Insoluble 3.11 3 .’95 35 Rayon, I general, the second nitration 13.50 2.26 (7.13) 3.67 4.51 50 10.51 13,66 2.40 4.39 3.58 4.18 12.25 58 raised the degree of substitu13.74 2.51 4.10 3.56 65 4.06 12.61 tion of low-nitrogen samples t o 13.82 3.14 3.83 4.26 75 13.48 3.89 13.60 4.19 3.80 4.53 5.03 13.58 100 about the maximum v a l u e . 13.38 11.05 2.10 (5.60) 3 . 5 1 50 4.49 Rayon, 11 This is particularly well illus13.52 2.27 11.9 4.64 3.65 4.46 60 13.37 3.03 4.63 3.60 4.62 12.82 70 trated by the data for the two 13.20 3.31 4.63 3.54 4.79 13.10 80 rayon samples. The intrinsic 13.47 3.76 3.77 13.40 4.78 4.68 100 viscosities similarly a p p r o a c h 13.28 10.81 3.03 (8.71) 4.61 50 5.09 Wood pulp (sulfate) 12.79 3.36 6.19 4.13 12.23 6.37 60 limiting values. These results 13.25 4.78 6.37 60 .... .... 5 . 1 9 13.68 4 . 7 8 6 . 1 3 13:37 6.03 70 clearly show that the low vis13.71 5.27 4.92 6.05 13.50 80 6.06 cosity values obtained a t low 13.70 5.57 6.19 7.33 6.43 13.62 100 nitrogen contents are not due 4.21 .... 10.39 (13.79) ... 50 ... Wood pulp (sulfite) 4.46 13.51 11.72 9.64 8.04 60 9.84 t o degradation under the ni13.49 10.87 9.63 7.65 11.88 13.05 70 13.25 13.16 8.6 11.5 9.94 13.27 80 trating conditions used, but 13.58 9.11 8.58 13.39 10.94 10.93 80 rather that viscosity is indeed a 13.15 13.39 10,38 9.78 13.41 12.47 100 function of the degree of nitra3.94 13.40 50 11.36 (9.54) 7.12 9.05 Cotton linters 13.70 4.74 12.28 8.59 8.45 9.75 60 tion. In a few cases, notably 13.69 4.82 9.49 8.27 9.58 12.02 60 12.9 5.82 8.14 7.04 13.1 10,48 70 for cotton a t the highest degrees 13.25 6.46 9.03 7.19 9.58 13.1 70 of substitution, there appears to 13.3 7.38 .... 9.68 70 13.46 13:55 7.29 8:83 6.50 8.10 80 be a small loss of nitrogen dur13.50 8.89 11.30 9.14 80 13,40 7.43 13.6 8.45 10.19 13.68 8.55 9.82 100 ing renitration. I n such in13.4 9.13 7.18 . . . . 100 . . . stances the intrinsic viscosity 7.21 13.31 50 11.25 (18.06) 12.10 15.83 Absorbent cotton also decreases, the r e l a t i o n 9.26 13.30 12.75 14.47 12.25 16.07 60 10.51 13.23 15.17 13.0 12.31 16.51 70 between nitrogen content and 13.31 17.19 13.42 12.71 16.62 13.61 80 16.4 14.7 13.05 13.8 11.82 16.78 100 viscosity being m a i n t a i n e d ; 12.51 13.5 15.39 100 .... ... ... a p p a r e n t l y some d e n i t r a t i o n 1 4 . 8 4 (40.2) 13.20 25.8 34.9 50 11.00 Cotton (sliver) 13.25 18.09 33.5 24.5 32.7 12.21 60 does actually occur. Finally, 13.25 22.7 33.5 26.7 35.8 70 12.93 in almost every case the in25.3 13.4 33.1 26.2 33.8 13.31 80 38.4 23.9 32.4 100 32.0 13.20 13.58 trinsic viscosity of the samples 32.8 31.5 13.36 39.4 25.3 100 13.45 nitrated only once in the 100% mixture is significantly higher than that of any sample of the variation in nitrogen contents, and constitutes the only evisame series, including those obtained by renitration of these samdence for appreciable degradation of the cellulose during nitraples. This observation persists even after account is taken of the tion. The agreement among all the other samples, however, strongly indicates t h a t even if such degradation does occur, it is nearly the same in all cases except this one, and therefore that 35b 0 Cotton comparison among them is still valid. 0 Absorbent Cotton This comparison may be made in several ways. When an 0 Cotton Linters 30-3 independent measure of the molecular weights of samples is availg @ W o o d p u l p (sulfite) able, it is customary to calculate the ratio of intrinsic visc&T 0 W o o d p u l p (sulfote) to molecular weight or degree of polymerization, thus obtain255% GI R a y o n I ing the Staudinger constant. The value of this “constmt” ig 2 (D R a y o n II then compared for various nitrogen contents. I n the pmsmU. e R a y o n (Wannow) work, no other measure of degree of polymerization was obtained, and therefore only the relative change in intrinsic viscosity for the same cellulose nitrated t o different degrees is considered. For purposes of discussion, the variation may be interpreted as arising from two sources. The first arises solely from the change in molecular weight with degree of nitration. To illustrate, suppose the degree of polymerization of two samples of nitrocellulose is 1000 and their nitrogen contents are 12.00 and 14.00%. The molecular weights of the two are easily shown t o be 263,500 and 294,300, and because of this difference in molecular weight the intrinsic viscosities will also be different. As a logical consequence of the Staudinger relation, this effect should be inversely proportional to the molecular weight. The 0 observedintrinsic viscosity can therefore be adjusted for nitrogen IO ll 12 13 14 content b y multiplying it by the ratio of molecular weight of the NITROGEN CONTENT. ?L trinitrate t o that of the sample containing the observed nitrogen Figure 1. Change in Intrinsic Viscosity of Nitrocelluloses with Nitrogen Content content. This ratio has been designated fi,where 1: is the nitrogen content in per cent, and it is readily shown t h a t Acetone solutions at 2SD C.
&,k.
1
i
I . . .
I
-
.
1y
November 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
2493
297
=
1.833 - 0.0589 x
(1)
If variation in molecular weight for a given degree of polymerization were the only cause of variation of intrinsic viscosity with degree of nitration, then for each series of nitrocelluloses in Table 111, the product of intrinsic viscosity by the appropriate factor from Equation 1 should be constant. Such is far from being the case. The major effect of introducing increasing numbers of nitrate groups into the cellulose chain is not the increase in molecular weight, but rather a marked change in the rheological properties of the molecules in solution. This change may be in the shape, the extent of solvation, the intermolecular bonding, or any of several other physicochemical factors. Witha u t being able t o explain a t present what causes the variation, t h e authors have attempted to evaluate it in the following way.
I
40
-
YX
value for any given nitrogen content, iegardless of the degree of polymerization of the cellulose used. From the experimental data on the seven celluloses here studied, the value of B is found to be 0.114. A table or graph (see Figure 3) may therefore be prepared giving the value of the function X(Z) = antilog [log!, 0.114 (!4:5 - z)] for any value of x. The intrinsic viscosity of the trinitrate can then he calculated by multiplying the intrinsic viscosity obtained experimentally for a sample of lower nitrogen content by the corresponding value of R ( x ) :
+
[air =
x R(z)
(5)
If the conclusion just stated is valid and based on sound experimental data, then for a series of nitrocelluloses with different nitrogen contents prepared from a particular sample of cellulose, a constant value of [ 9 ] should ~ be found. When this test is applied to the data in Table 111, reasonably good confirmation is obtained. In columns 5 and 8 of that table are given the values of [qIT so calculated. Since, as stated above, samples with nitrogen contents lower than 11.5% do not seem to fit into the scheme r e p resented by Figure2 or Equation 5, values of [?IT for these samples are enclosed in parentheses. In Table IV are given the average values of [71Tcalculated in each case from all values in Table I11 except those in parentheses. A few values which seem far out of line could justifiably have been omitted in figuring the averages, but were nevertheless included. The average deviation from the mean value of [?IT is 6% or less, except for the sulfite pulp. For this material, greater than usual difficulty was experienced during nitration and purification after nitration, and this fact may account for the greater deviation.
TABLE IV.
X
[?Iexpt!.
A V E R A G E VALUES O F THINITRATE INTRIKSIC
T’ISCOSITY
t
u
Cellulose Nitrated
(From Table 111) Average [?IT 4.29 4.64 6 30
I
1
I
Intrinsic viscosities multiplied by molecular weight factor fz = 1.833 0.0589 x where z = % N
-
When the logarithm of the adjusted intrinsic viscosity,
[q]
X
fi,for any of the series of nitrocelluloses in Table I11 is plotted against the nitrogen content, x,the data for x > 11.5 fall approxi-
mately on a straight line, as illustrated by Figure 2 . Furthermore, the lines so obtained for all the celluloses investigated have very nearly the same slope. This result may be expressed by the following equation: log
[?I
+ log fi = A + Bx
(2)
where A is constant for each series but different for the several celluloses, while B is the same for all samples. If now we designate by [vlT the intrinsic viscosity that would be expected, on th@asis of Equation 2 , for completely nitrated trinitrate in any series, we have log
[?IT
=
A
+ 14.15 B
(3)
sincef, = 1 for x = 14.15. Combining Equations 2 and 3 we have log
[VIP - log [ v ]
10gfz
+ (14.15 -
Z)
B
(4)
The right-hand side of this equation should have the same 2494
0.26
11.5
1.0
8.4 16 0
0.58 0.66 1.9
34.5
!
Average Deviation 0.26 0.08
The scatter in [?IT may be attributed to several causes. Probably the main cause is variation in the small amount of degradation that occurs during nitration. Although the renitration experiments show conclusively that the low viscosity values obtained with low-nitrogen samples are not the result of degradation, some breaking of chains undoubtedly occurs in a way that cannot be controlled. Because of the lack of any independent measure of the average chain length for each nitrated sample, it has been necessary to assume that the degree of polymerization is the same throughout each series. In this investigation, however, we are priniarily interested in relative changes in intrinsic viscosity rather than in absolute values. It is reasonable to assume, therefore, that slight irregular degradation, while causing some scatter among individual values of [?IT, does not seriously affect conclusions based upon averages of such values. Another possible cause for scatter is the use of the Baker equation for calculating intrinsic viscosity from single viscosityconcentration determinations rather than extrapolation from measurements a t several concentrations. The magnitude of the error from this cause is probably not more than 5%. The effect of rate of shear upon viscosity measurements with nitrocellulose solutions has been assumed to be negligible; it may be significant for the samples of high degree of polymerization. In addition to these effects are the usual experimental errors in measuring viscosity, concentration, and nitrogen content. If all sources of error and uncertainty could be eliminated, it is reasonable to suppose that the scatter in the calculated values of [ q ] in Table I11 would be eliminated and that a “true” value for the intrinsic viscosity of a nitrocellulose could be obtained,
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 45, No. 11
-Cellulose I
3.c
2 .!
\
l o g R(x)
I
l o g f(x)
I
+ 0.114 (14.15-X)
R(x) b
2 .(
I.!
I.t
12
13
14
Nitrogen Content ( X ) , 2 Figure 3. Factor R(x) for Converting Intrinsic Viscosity at x q c Nitrogen to Intrinsic Viscosity of Trinitrate which would be independent of the degree of nitration and hence suitable for comparison with the corresponding value for any other nitrocellulose. The numerical value of the constant slope (0.114) and therefore of the function R ( z )may well be changed as the result of further and more refined study, but the form of the relationship expressed by Equation 4 may confidently be expected t o remain useful, The evaluation of R ( z ) rests upon an averaging process not only of the individual viscosity values within each series but also for the whole group of nitrated celluloses covering a wide range in degree of polymerization.
viscosity upon degree of nitration. The authors have critically reviewed the available literature, and using their more extensive data on nitrogen dependence have attempted t o determine the best value for K,. It is a matter of personal preference, of course, whether one adjusts the intrinsic viscosity for nitrogen content and uses a constant value of K,, or uses a different value of K , for each nitrogen content and divides the experimental intrinsic viscosity by the appropriate value t o obtain degree of polymerization. The authors prefer the former method, but in some cases it is more convenient t o determine a K a t the actual nitrogen content. For example, when data for several celluloses of different degree of polymerization but nearly the same nitrogen content are considered, the K values for all samples are found thus: K = [7]/DP,and the average value of K is determined. ( K without subscript refers t o the constant a t some nitrogen content other than 14.15010.) Most measurements have been made at 20" C., but a few have been made a t 25' C. Intrinsic viscosity, or K,, is not very sensitive t o small temperature changes, as the viscosity of both solution and solvent is affected to nearly the same degree. The authors have found for nitrocellulose in acetone the following relation: [77] a t 25' = 0.98 X [ v ] a t 20". This agrees with the data of Alexander and Mitchell ( I ) , from which a corresponding factor of 0.97 for nitrocellulose in ethyl acetate is obtained. The correction function, R(z), is assumed to be the same at 20" and 25". A note may be added regarding units. Intrinsic viscosity has the dimensions of reciprocal concentration and is variously expressed in the literature. To avoid confusion, all values have been converted to a common unit, deciliters per gram. Husemann and Schulz (6) in 1942 reported the following average values of K for samples containing from 12.96 t o 13.28% nitrogen; the corresponding K , values are also given: Treatment of Cellulose before Nitration Hydrolytically degraded Fractionated Unfractionated Oxidatively degraded Fractionated Unfractionated
K X 108
K m X 10
8.2 12.8
11.5 17 9
10 2 16.4
14 3 23 0
STAUDINGER CONSTANT FOR NITROCELLULOSE IN ACETONE
i
Unfractionated samples are expected to give high K values I n the preceding sections, the dependence of intrinsic viscosity when degrees of polymerization are determined osmometrically, of nitrocelluloses upon degree of nitration was demonstrated and because of the difference between weight-average and numbera means for converting experimental values t o a common basis average degree of polymerization. The treatment of the os(trinitrate) for comparison was developed (Equation 4). Fremotic data by Schulz t o obtain molecular weights has been critiquently, however, it is desirable to express results in terms of cized by Spurlin ( I S ) , and Jorgensen (7, p. 54) has recalculated degree of polymerization rather than intrinsic viscosity. This the value for hydrolytically degraded, fractionated samples, can be done if the value of the Staudinger constant, K , = [q]/DP, obtaining K = 9.4 X or K m = 13.2 X is known. Wannow's data (14) give [ a l p = 0.368 and osmotic DP = 176 A search of the literature reveals considerable l a c k of agreement among the reported TABLE V. STAUDINQER CONSTANTS FROM DATA OF JULLANDER values for this constant. An Degree of Staudinger Constant, important if not the main source DesignaNitrogen Polymerization K m X 108 of disagreement is the failure t o Type of Cellulose tiona Content, % n w w, w I7Jl.r n w w, w take proper account of the niCotton linters Bleached e.h. 12.28 617 997 * 1 0 . 2 6 16.6 . . . 110.1 0.3 trogen content. T h o s e w h o Hydrolyzed 12.48 3.41 V F 120 212 3io 337 16.1 10.6 12,35 1.436 103 15.3 20.2b VF 3 94 71 13.9 have been aware of this effect VF 1/2 11.94 16.3b 52 0.847 16.6 12.4 51 68 have made use of the very 12.58 1820 16.2 Unbleached Mpt 128 949 1420 l5,39 10.8 8.5 13.78 4040 5.1s FB 9 13.4 ... 20.48 limited data of Wannow pre12.18 11.7 Lnt Sulfate wood pulp 574 6.70 20.8b 12.7 Hnt 212 351 11.1 13.40 18.3 3.89 viously cited. Even while criti12.49 14.5 FK 2 599 a54 10'2 8.8 Sulfite wood pulp 8.68 989 cizing his results because he used FK 3 12.48 8.69 8.4 672 1000 1040 12.9 8.7 1 0.9 453 512 15.3 1 3 . 5 F K 6 1 3 . 9 8 633 6 . 9 2 unfractionated , m a t e r i a l s a n d Average value of K m X 108 10.3 15.5 11.4 Average deviation 1.2 1.2 1.4 did not cover a wide ranee of a Designations used in original aper. degree Of Or Of b These values omitted in calcufating Fverages. cellulose types, they have asn. Number-average measures (osmotic pressure). sumed that his results give the w. Weight-average measwe8. I
w, w.
right
Sedimentation-velocity measurements.
dependence of intrinsic
November 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
2495
polymerization in each of these other cases, however, is only (Data of Miinster) 1020, 760, and 1310, respecNitrated Cotton Nitrated Wood Pulp tively. Kuhn and Kuhn (9) Fraction Nitrogen DP [?IT Nitrogen DP [7lr, NO. content, % (osmotic) dl./g. K m X 103 content, % (osmotic) dl./g. K,,X 103 have deduced that intrinsic viscosity is proportional to degree la 13.9 2250 15.82 7.03 13.52 8650 31.6 3.0 lh .... 13.62 8090 25.1 3.5 of polymerization only over an 2 13:s 16-0 13:24 8.17 13.90 3270 21.1 6 0 intermediate range in molecular 10.16 8.13 13.85 2730 19 0 6 .. 3 3 13.9 1250 4 13.8 924 8.52 9.22 9 . 4 weight; at low degree of poly1 3 , 6 6 1570 1 7 . 3 5 13.7 792 8.35 10.55 13,69 1270 15.05 10.2 6 13.6 671 7.41 11.05 13.6 1230 13.36 9.1 merization, viscosity is propor7 13.6 097 6.23 10.47 13.59 954 12.15 tional to the square, and a t 8 13.5 439 5.04 11.49 13.58 748 9.88 11 10 .. 07 9 13.4 307 3.88 12.63 13.43 575 8.74 12.1 very high degree of polymeri10 13.5 25 1 3.20 12.74 13.31 499 7.62 11.7 11 13.3 110 1.51 13.72 13.30 373 6.05 12.4 zation, to the square root of the 12 .. ... ... 13.38 312 11.7 chain length. The limit's within 13 ... 13.31 218 34 .. 36 88 11.9 which a single value for K , is valid for nit~rocellulose solutions remain to be determined. (averages); hence K, = 20.9 X l o u 3for unfractionated material. 811 t'heae values for K , (recalculated to 14.15% nitrogen} Wannow and Feickert (16) give results for oxidatively degraded are summarized in Table VII. Except, for Ju]]anderJs values cellulases which lead to K m values Of 19 X for unfractionbased on sedimentat,ion studies, they were obtained from measated and 11.6 X 10- for fractionat'ed material (on the assumpurements of viscosity and osmotic pressure. The K , values tion that the nitrogen content' of all fractions is the same as that for unfractionated saniples depend, of course, upon the of t,he unfractionated material). n~olecularit~y.As this could not be expected to be even approxiJullander (8) has obtained the most extensive data for commately the same for all types of samples, little agreement among paring degree of polymerization and viscosity of nitrocelluloses. these K , values should be found. For fractionated samples, hIolecular weights were determined by osmotic pressure measurehowever, the agreement should be good, provided a]] types of mente and also by sedimentation velocity experiments, using the cellulose behave similarly. There appears to be little evidence ult,racentrifuge,for a dozen commercial and laboratory-prepared that, K, is different for nitrat,& cotton,and wood pulp, except nitrocelluloses; for a few Of the same samples weight-average from the dat,a of Nanster. For the unfractionated samples, in molecular weight's were found from sedimentation equilibrium the ts-o cases in which both types of cellulose have been studied determinations, and in ot,her cases, weight-average molecular weights were obtained from osmotic measurements by means of a three-parameter disTABLE1'11. SCMMARY O F I'ALVES FOR STaUDISGER CONSTAXT tribution function based on ultracentrifugal data. (Cellulose trinitrate in acetone a t 20" C., concn. in g./dl.) Table V summarizes these data and gives the corresponding values of K,. The K,, values obK~ x 103
TABLE VI.
STAUDINO-ERCOXsT.4NTS
-.
....
FOR
FRACTIONS O F NITRATED COTTOX AND
...
tained from osmotic data depend upon the polymerheterogeneity of the samples and would therefore be expected to vary considerably from sample to sample. The other two sets of values, being based upon weight-average and modified Tveight-average molecular weights, should be less dependent upon heterogeneity. The scatter in all three sets of data is about the same, however. Blaker, Badger, and Koyes ( 2 ) found for frac-
UnfracFracType of Cellulose tionated tionated Hydrolyzed cotton 17.9 11.5 Data recalcd. by Jorgenaen Hydrolyzed cotton 13.2 Husemann and Schulz Oxidatively degraded cotton 23:o 14.3 Wannow Rayon 20.9 ... Oxidatively degraded wood pulp 19 11.6 Feickert Hydrolyzed linters a n d pulp 15.6 11.4O Blaker, Badger, a n d Noyes Hydrolyzed cotton 21.6 12.2 Hydrolyzed wood pulp 26.8 Heuser a n d JBrgensen Hydrolyzed cotton 13.4 Hydrolyzed wood pulp 16.2 ... Munster (data for fractions Hydrolyzed cotton .. 12.2 with D p Hydrolyzed wood pulp 15.5 a Average value obtained from weight-average D P measurements on unfraotionated samples. I t should be equivalent to number-average values for fractionated samples. Investigators
H~~~~~~~~ and Schuls
,"UEt$Tyd
tionated containing 13,4% nitrogen the value K = 9.4 X 10-3 at, 25' C.; adjusted for nitrogen content and temperature, this becomes 12.2 x 10-3. Similarly their data for unfract,ionated samples give 26.8 x 10-3 for wood pulps and 21.6 X 10-3 for cotton; they interpret the difference as demonstrating t,he greater heterogeneity of nitrocelluloses prepared from wood. Heuser and Jorgensen ( 5 ) made osmot,ic and viscosity measurement.s on hydrolyzed cot,ton and wood pulp nitrocelluloses containing 13.0 to 13.2% nitrogen, Their values for K , (adjusted to 14.15% nitrogen) are 13.4 and 16.2 x 10-3. The difference they attribute to basic differences in t,he original materials which are not eliminated by hydrolysis; t,hey state that differences in polpmolecularity alone do not, afford sufficient explanation. Recently MCinster (11) has found that, in agreement wit,h conclusions drawn from theoretical considerations, the Staudinger relat,ion [q] = K , X DP holds only for degree of polymerization below 600; a better representation is given by the relation 01 log DP, where the value of O( is 1 for DP log [q] = log K , 600, but decreases as degree of polgmerizationincreasesabove600. This behavior is illustrated by the follou~ingdata (Table VI) for two fractionated samples. Yone of the other investigators using fractionated samples (5, 6, 16) found any such falling off of K values for their highest fractions; the maximum degree of
+
2496
JTOOD P U L P
...
I
.
by t'he same iuvestigat,ors, the constant for wood pulp is higher than that for cotton. The difference could be explained as indicat,ing greater heterogeneity for wood cellulose. From a less complete survey of the literature, Nioolas (12) arrived at, the value K = 10.5 X l o w 3calculated, according to Wannow's relation, to 13.8% nitrogen; this corresponds t o 11.7 X 10-3at 14.15%. Fromthc datasummariaedinTableVI1, the best value for the St'audinger constant for cellulose trinitrate dl. per gram at20" c. dissolved in acetone appears to be 12 X The value a t 25' is about 2% lower than that a t 20", but this is well within the uncertainty of the above value. CONCLUSIONS
The degree of nit,ration of cellulose samples can be varied over wide limits by varying t'he pot'ency of the nitrating mixt,ure; this last can be reduced by diluting t,he usual mixture of nitric acid and phosphoric anhgrdride with 85y0 phosphoric acid. Dilution of the nitrating mixture does not cause degradation. The lower the nitrogen content of a nitrocellulose sample, the lower the intrinsic viscosity for a given degree of polymeriza-
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 45, No. 11
-Cellulosetion. The effect is pronounced: The intrinsic viscosity a t 13$% nitrogen is only about two thirds the value for the trinitrate and approximately one half a t 12%.
5
A relationship has been developed which permits the intrinsic viscosity for the trinitrate to be calculated from the experimentally determined viscosity ahd nitrogen content of any nitrocellulose. This relationship makes it possible t o compare the intrinsic viscosities, and hence the degree of polymerization, of nitrocellulose‘ samples containing different amounts of nitrogen, so long as the latter is greater than 11.5%. The present best value of the Staudinger constant for cellulose trinitrate dissolved in acetone is 12 x 10-3 dl. per gram for polymer-homogeneous material. For unfractionated samples, the value is greater, depending upon the heterogeneity. ACKNOWLEDGMENT
n
The authors express their appreciation to the A4mericanEnka Corp. for permission t o publish this paper. LITERATURE CITED
(1) Alexander, W. J., and Nitohell, R. L., A?zuZ. Chenz., 21, 1497500 (1949).
(2) Blaker, R. H., Badger, R. XI., and Noyes, R. M., J . Phys. Chenz., 51,574-9 (1947). (3) Chbdin, J., and Tribot, A., Kolloid-Z., 125, 65-72 (1952). (4) Goldberg, A. I., Hohenstein, W. P., and Mark, H., J . Polymer SC~., 2,503-10 (1947). (5) Heuser, E., and Jorgensen, L., T a p p i , 34,450-2 (1951). (6) Husemann, E., and Schulz, G. V., 2. p h y s i k . Chem., B52, 1-22 (1942). (7) Jorgensen, L., “Studies on the Partial Hydrolysis of Cellulose,” Oslo, Trykt Hos Eniil hloestue A/S, 1950. ( 8 ) Jullander, I., Arkiv Kemi,M i n e d . Geol., 21A, No. 8 (1943). (9) Kuhn, H., and Kuhn, W., J . POlylneT Sci., 9, 1-33 (1952). (10) Lindsley, C. H., Ibid., 7, 835-52 (1951). (11) Munster, A., 2. physik. Chem., 197, 17-38 (1981); J . Polynzer SC~., 8,633-49 (1952). (12) Nioolas, L., Assoc. tech. ind. papetihre, Bull. 5, 427-35 (1951). (13) Spurlin, H. M., in “Cellulose and Cellulose Derivatives,” E. Ott, editor, pp. 920 et seq., New York, Interscience Publishers, 1943. (14) Wannow, H. A,, Kolloid-Z., 102,ZQ-34 (1943). (15) Wannow, H. A , , and Feickert, C., Ibid., 108, 103-13 (1944). RECEIVED for review March 30, 1953.
ACCEPTED August 17, 1953
Intrinsic Viscosity of Cellulose REPORT OF THE CELLULOSE DISPERSE VISCOSITY SUBCOMMITTEE A
study of the solvent power and stability of cupriethylene and cuprammonium solvents as a function of the amount of copper and of base has been completed. Work is being started on the preparation of cellulose solutions in the optimum solvents and on the viscosity behavior of such solutions. The Cellulose Disperse Viscosity Subcommittee is considering a tentative method in which results will be reported in terms of intrinsic viscosity and/or intrinsic fluidity. Factors for converting to degree of polymerization will be included. Viscosity measurements will be made at a concentration such that the product of concentration and intrinsic viscosity equals 3.0. Preliminary data indicate excellent reproducibility at a level within 10% of the true intrinsic viscosity. This tentative method is being tested in several laboratories, but a choice of solvent should be made before a standard method is published.
A. F. MARTIN, Chairman 1
Hercules Experiment Station, Hercules Powder Co., Wilmington, Del.
T
HE need for simplification and standardization of methods for determining cellulose disperse viscosity is apparent to all
those working with cellulosics. The Cellulose Disperse Viscosity Subcommittee, now sponsored jointly by the Division of Cellulose CHEMICAL SOCIETY, the TAPPI Chemical Chemistry, AMERICAN Methods Committee, and ASTM Subcommittee D-23, feels that no present standard method is well adapted to the diverse needs of the cellulose industry. Methods suitable for infrequent use in a referee laboratory are too awkward and expensive for use in routine testing in cellulose manufacturing operations. The present methods differ greatly in such features solvents, concentrations, and techniques of measuring viscosity. This report summarizes the committee’s efforts t o date on standardization, emphasizing in particular the necessity for ensuring wide applicability while retaining operating simplicity. The method under development differs SO greatly from present methods that it will supplement rather than completely rep]ace them. The subcommittee must now make a decision concerning the merits of immediate revision and republication of the standard
November 1953
ACS method. This report is concerned entirely with the progress on the new method, The new method will undoubtedly follow in general the standard outline given in Table I, each topic of which has been the subject of correspondence among the members of the subcommittee, DETERMINATION OF VISCOSITY
REPORTING RESULTS. Opinion of committee members is almost unanimous that cellulases be characterized by the fundamental characteristics intrinsic viscosity, ], degree of polymerization (Dp), or intri,?sic fluidity, The method under consideration will give intrinsic viscosity directly. Degree of Polymerization can be determined by multiplying by a factor of about 200, while intrinsic fluidity is merely the reciprocal of intrinsic viscosity. Degree of polymerization is a concept easily understood by nontechnical people who must interpret technical
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