P
I
W. J. ALEXANDER’, OTTO GOLDSCHMID, and R. L. MITCHELL1 Rayonier, Inc., Shelton, Wash.
Relation of Intrinsic Viscosity to Cellulose Chain Length Degree
o f Polymerizafion Range below 400
All industrial operations dealing with isolation, purification, or utilization of cellulose, are directly or indirectly concerned with the length of the polymer chain. Because an absolute measurement of degree of polymerization i s very difficult, if not impossible, it is convenient to measure a property, closely related to the chain length, such as the intrinsic viscosity of the cellulose itself or of one of its derivatives dispersed in a suitable solvent. In many instances, it is sufficient to show differences in terms of intrinsic viscosity. However, at times, the measured viscosity is expressed as degree of polymerization (DP). The value of the DP conversion factor changes very sharply for certain systems ranging from DP 10 to about 400. If a constant value of conversion is used throughout this range, great misjudgments in the degree of polymerization are possible.
N u m R o u s references (8, 72, 74, 17, 24) deal with the calculation of degree of polymerization from intrinsic viscosity measurements. For cellulose and its derivatives, the intrinsic viscosity is usually multiplied by a constant determined from independent measurement of osmotic pressure (6, 17, 24), sedimentation equilibrium (25), sedimentation rate and diffusion (21), or light scattering (2, 3 ) . For example, typical conversion constants widely used are: 260 for cellulose in cuprammonium hydroxide (4, 76), 190 for cellulose in cupriethylenediamine (20, 27), and 75 ( 7 ) or 80 (21) for cellulose nitrate in ethyl acetate. Immergut, R%nby, and Mark (72) have presented a correlation between osmotic molecular weight and viscosity data for a series of celluloses and cellulose nitrates, suggesting the use of two constants-one to apply in the low DP range, and the second to apply in the high range. The difference between actual or contour length of a cellulose chain and its effective “behavior length” in solution depends on the solvent, the temperature, and the type of derivative, and is a function of the chain length itself (5, 7, 77, 75). However, this dependence on chain length may be far greater than is generally realized and may not be properly taken into account when conversions to degree of polymerization are made. This is particularly true in the degree of polymerization range below 400. The present study is to define 1 Present address, Eastern Research Division, Rayonier Inc., Mihippany, N. J.
more clearly these relationships and to suggest a basis for rationalizing degree of polymerization values derived from viscosity measurements in different solvents and for materials of widely varying viscosity levels. Intrinsic viscosities have been determined for some cellulose nitrates of extremely short chain length dissolved in ethyl acetate, and compared directly with cupriethylenediamine (cuene) intrinsic viscosities obtained for the corresponding primary cellulose dissolved in cupriethylenediamine solvent. A similar viscosity comparison has been made for a series of cellulose acetates dissolved in acetone and in cupriethylenediamine which saponifies the acetates without degradation. I n a third comparison, cellulose nitrate intrinsic viscosities were related to corresponding viscosity data obtained for cellulose converted to xanthate and dispersed in a n aqueous caustic soda solution. Of the four systems investigated, the cellulose nitrate in ethyl acetate not only has the highest intrinsic viscosity a t a given degree of polymerization, but is the one for which the ratio of effective chain length to actual chain length is believed to change the least with degree of polymerization. The completely nitrated cellulose chain dissolved a t low concentration in *ethyl acetate solvent is relatively extended and the ratio of effective chain length to extended length can be assumed to be constant. O n this basis the intrinsic viscosities of other cellulose solutions and derivatives plotted against the intrinsic viscosity of the niVOL. 49,
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AUGUST 1957
1303
trate demonstrate the progressive adjustments that should be made in [?]DP conversion if viscosity measurements are to lead to consistent degree of polymerization values. The existence of this sensitive range has been explained by Flory (7), on the basis of differences in the degree of extension, or “coiling” of the molecule. The “degree of coiling” apparently increases from a minimum value a t low chain length up to a near maximum level at chain lengths of about DP 400 and above, for the polymer solutions. The maximum degree of coiling attained ranges from a relatively small amount in ethyl acetate solution of the nitrate to sizable amounts for alkaline solution of cellulose xanthate or the cellulose complexes in cuprammonium hydroxide (cuam) or cupriethylenediamine (cuene). where effective length may be only one half or one third of the actual chain length. Experimental-Intrinsic
Viscosities are measured in this apparatus
DP
0 W
0
- I
Z
W
0 n
c;:
U
I
1
4.0
I
6.O
Cq7 CELLULOSE N I T R A T E IN ETHYL ACETATE Figure 1 . Relation between cupriethylenediamine ethyl acetate
[TI
and cellulose nitrate [ 7 7 ] in
0 . W o o d cellulose depolymerized by alkaline oxidation 0
. .
W o o d cellulose depolymerized b y acid hydrolysis
Cotton cellulose depolymerized b y alkaline oxidation 8 3 . Cotton cellulose depolymerized b y acid hydrolysis
1304
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Viscosity
Cellulose Nitrate Degree of Polymerization. The procedure for nieasuring intrinsic viscosity has been described ( 7 ) . Cellulose was converted to the trinitrate derivative in a nitrating mixture of nitric acid, phosphoric acid, and phosphorus pentoxide in the weight ratio of 64:26:10. Ethyl acetate was the solvent used for the viscosity measurements, and the equation of Huggins (70) was used to calculate the intrinsic visc,osity using K’ = 0.35. Degree of polymerization was calculated according to the equation DP = 75 [ a ] . Cellulose i n Cupriethylenediamine. A method similar to the TAPPI procedure T 230 Sn \vas used. The solvent was 1.OM in copper and 2.0M in ethylenediamine. Viscosity measurements were made at a single concentration of 0.5y~ cellulose, and the intrinsic viscosity was obtained from a nomograph based on Martin’s equation (78, 79). Cellulose Acetate (38% Acetyl). Intrinsic viscosities were determined in acetone and in cupriethylenediamine. Viscosities obtained at several low concentrations of acetone were extrapolated according to Huggins‘ equation (70). 111 the cupriethylenediamine, which saponifies acetatewithout degradation ( 4 , 9 , 2 3 ) , a single viscometric determination was made at a O.jyG concentration based on the cellulose in the cellulose acetate. The effect of the acetic acid generated in the saponification upon the cupriethylenediamine solvent is negligible at this concentration. Cellulose Xanthate in Sodium Hydroxide. The xanthate intrinsic viscosity was obtained by extrapolation of viscosity measurements for several low concentrations of cellulose xanthate in 9% sodium hydroxide. The viscose solutions for this work were prepared by a
CELLULOSE POLYMERIZATION modified procedure of Jayme (73),which is a one-vessel process. The cellulose under nitrogen was treated successively with a solution of sodium hydroxide and with carbon disulfide, then dispersed, and retained a t low temperature. The viscosity determination was made after 24 hours. The substitution level of the xanthate was of the order of one xanthate group per anhydroglucose unit.
DP
a
Discussion of Results
Figure 1 shows intrinsic viscosity data in cupriethylenediamine for four series of celluloses related to the intrinsic viscosities of the corresponding cellulose nitrates in ethyl acetate. The data include cellulose from cotton linters (viscose grade) and rayon-grade wood cellulose. A set from each raw material source was depolymerized by alkaline oxidation as well as by acid hydrolysis. The dotted line (Figure 1) represents the linear relationship between intrinsic viscosities found for the high degree of polymerization range. The slope of this line is equal to 0.429 the ratio between the intrinsic viscosities of cellulose in cupriethylenediamine and the corresponding cellulose nitrates in ethyl acetate for the range above degree of polymerization 400. This linear relationship does not apply in the low degree of polymerization range. From a double-logarithmic plot of these data (Figure 2) which gives a reasonably straight line, the following equation may be derived : [V
INC
=
1 6 3 [VI&%
The dotted line again represents the relationship applying a t the higher degree of polymerization levels (above 400) where equilibrium coiling has been reached. In Figure 3, the intrinsic viscosity relationship for cellulose xanthate dispersed in aqueous sodium hydroxide solution is compared with the corresponding cellulose nitrates in ethyl acetate. The deviation from linearity in the low degree of polymerization range shown previously for the cupriethylenediamine-nitrate relation is evident to an even greater extent in the xanthate-nitrate relationship. Figure 4 illustrates variation of the conversion constant with nitrate degree of polymerization, in the ldw degree of polymerization range for three systemscellulose xanthate in sodium hydroxide, cellulose in cupriethylenediamine, and cellulose acetate in acetone. The ordinate in this plot is the conversion constant used to obtain degree of polymerization from intrinsic viscosity data for each of these three systems. The degree of polymerization in each case was calculated from cellulose nitrate
LOG ql CELLULOSE NITRATE IN ETHYL ACETATE Figure 2. Logarithm of cupriethylenediamine [17] vs. logarithm of [17] for cellulose nitrate in ethyl acetate 0 . Wood cellulose depolymerized by alkaline oxidation. 0 . Wood cellulose depolymerized b y acid hydrolysis 0 Cotton cellulose depolymerized b y alkaline oxidation 0 . Cotton cellulose depolymerized b y acid hydrolysis
.
data. Although some slight change may occur in the conversion constant for the cellulose nitrate too, the change is assumed to be small in comparison with these other systems.
Figure 5 is a double logarithmic plot of two series of data. One series of points is for a group of celluloses; the cupriethylenediamine [ v ] being related to degree of polymerization values
DP I Z
z W
!z I I-
z a X W
cn
3 3 1 W
0 m
6
Cql
CELLULOSE
NITRATE I N ETHYL ACETATE
Figure 3. Relation of [ q ] for cellulose xanthate in 9% sodium hydroxide to [ q ] for cellulose nitrate in ethyl acetate VOL. 49, NO. E
AUGUST 1957
1305
lose acetates. lows :
The equation is as fol-
DP = 120 [olka::,,.
Figure 5 shows excellent agreement between these two independently calibrated degree of polymerization scales. The relative degree of polymerization conversion factors for the several systems are listed in the table. They are all based on degree of polymerization values calculated from nitrate [7], K = 7 5 ; and represent a n attempt to compensate for deviations existing in intrinsic viscosity---chain length relationships, particularly in the low degree of polymerization range,
0 Literature Cited
NITRATE - DP Figure 4. Relation between the conversion factor polymerization I. II. 111.
and nitrate
degree of
Cellulose xanthate in 9% sodium hydroxide Cellulose in cupriethylenediamine Cellulose acetate-38% acetyl in acetone
obtained from nitrate [77] using the conversion factor 75. The other series of points is for cellulose acetates; the cupriethylenediamine [ 7 ] being related to degree of polymerization values ob-
tained from cellulose acetate [ 7 ] in acetone. The degree of polymerization calculated by the Phillip and Bjork equation (22) is based on osmotic pressure data obtained for a series of cellu-
Factors for Converting Intrinsic Viscosity to Degree of Polymerization Degree of Polymerization ‘Level 10 Cellulose nitrate in ethyl acetate Cellulose acetate in acetone or C E D Cellulose in C E D Cellulose xanthate in N a O H
75 75
75 75
60
100
200
400
75 95 100 105
75 105 115 130
75 130 140 165
75 135 170 200
’
1000 75 e ,
175 210
0.1I DP Figure 5.
Intrinsic viscosity vs. nitrate degree of polymerization
0 . Cellulose in cupriethylenediamine I
Cellulose acetate-38%
1 306
acetyl in cupriethylenediamine vs. acetate degree of polymerization
INDUSTRIAL A N D ENGINEERING CHEMISTRY
(1) Alexander, W. J., Mitchell, R. L., Anal. Chem. 21, 1497 (1949). ( 2 ) Badger, R. M., Blaker, K. H., J . Phys. &+ Colloid Chem. 53, 1056-69 (1949). ( 3 ) Blaker, R. H., Badger, R. M., Gilmann. T. S.. Ibid. 53. 794 (1949). Cox, L.k,Battista, 0: A., IND.~ N G . CHEM. 49, 893 (1952). (1952). Debye, P., Buech Bueche, A. hf., .I. Cheni. Phys. 16, 573 (1948). Doty, P., Spurlin, H. M., in “High Polymers,” vol. V. V,~pt. t 1,. “Cellulose and Cellulose Derivatives” (Emil Ott, H. M. Spurlin, M. W. Grafflin, editors), Interscience, New York, 1954. ( 7 ) F o x , T : G., Flory, P. J., J . Am. Chern, SOC. 73, 1904, 1909, 1915 (1951). ( 8 ) Heuser, F., Jorgensen, L., Tappi 34, 450-2 (1951). ( 9 ) Howlett, F.. Minshall. E.. Urauhart. H. R.’, J.‘ Textile I& 35, 7i23-3i (1949). (10) Hdggini, M. L., IKD.ENG.CHEM.35, 980 (1943). (11) Immergut, E. H., Eirich, F. R., Ibid., 45, 2500 (1953). (12) Immergut, E, H., R%nby, B. G., Mark, H. F.. Ibid.. 45. 2483 (19531. (13) Jayme, ’ G., Cellulosec&mie 18, 38 (1940). (14) Juhanddr, I . , Arkiv Kemi, Mineral Geol. ZlA, No. 8 (1945). (15) Kirkwood, J. G., Riseman, J. J., J . Chem. Phys. 16, 565 (1948). (16) Kraemer, E. O., IND.ENG.CHEM.30, 1200-3 (1938). (17) Mark, H., “Der Feste Korper,” p. 103, Hirzel, Leipzig, 1938. (18) Martin, A. F., Division of Cellulose Chemistry, 103rd Meeting, ACS, Memphis, Tenn., 1942. (19) Martin, A. F., Ta@i 34, 363 (1951). (20) Mueller, Wm. A , , Rogers, L. N., Iiw. ENG.CHEM.45, 2522-26 (1953). (21) Newman. S.. Loeb. L.. Conrad. C. M., J . Polymer‘Sci. 10, 463-87 (1’953). (22) Phillip, H. J., Bjork, C. F., Ibid., 6, 549-62 (1951 ). (23) Staudinger, H., Daumiller, G., Ann. 529, 219-65 (1937). (24) Staudinger, H., Mohr, R., Haas, H., Feuerstein, K., Ber. 70B, 2296 (1937). (25) Svedberg, T., Pedersen, K. O., “The Ultracentrifuge,” Oxford Univ. Press, New York, 1940.
.,
RECEIVED for review June 18, 1956 ACCEPTED January 31, 1957 Division of Cellulose Chemistry, 128th Meeting, ACS, Minneapolis, Minn., September 1955. Contribution No. 16 from Research Department, Rayonier, Inc.
