indicated a significant variation with particle size of the amount extracted, but also superimposed there is a corresponding v a r i e tion in viscosity, so that the net effect of Wiley milling on the fractionation curve is small, and there is no appreciable effect on the shape of the curve. CONCLUSION
The summative cupriethylenediamine extraction method for the direct fractionation of cellulose possesses all the advantages of the summative method: Fast operation Independence of individual steps High experimental precision Short contact time between cellulose and solvent Constant contact time between cellulose and solvent Direct fractionation of cellulose
measure the proportion of the effect due to the ordered arrangement of the cellulose in the particle. 2. With cupriethylenediamine, there exist in cellulose certain solubility-controlling factors t h a t are more effective than molecular weight. However, this method has been used in the authors’ laboratory with reasonable success with single specie samples of a large variety of pulps and fibers, including wood and linter pulps, even a t incompletc stages of purification, rayons and cellulose regenerated from various steps of processing, staple cotton, and even raw lint. Correlations with other properties havc been made in a number of cases. Fiom this standpoint, the method appears t o be highly versatile ACKNOWLEDGllEhT
The authois wish to thank L. F. Pagel and XI. R. Thom:iq of this laboratory for the characterization of these samples.
However, the method entails certain disadvantages, some of which are inherent with summative methods. The method is indirect, and the final desired results are inferred by expandin mathematically, relatively small experimental differences. g h i l e the precision of the method is very high, a high precision is needed t o obtain any more than the gross differences in molecular weight distribution. Fractionation of closely related substances, such as cellulose molecules which differ only in niolecular weight, and as carried out by extraction or precipitation in heterogeneous mixtures, cannot be expected to be sharp along the line of conditions chosen. The summative method is more susceptible to this error. There results no physically fractionated sample, which can be refractionated or subjected to further experiment.
REFERENCES
Browning, B. L., Propess Report to Joint TAPPI, ACS, and ASTM Disperse Viscosity Subcommittee, Institute of PaBer Chemistry Project 1592, p. 12. 1952. Coppick, Sidney, Battista, 0.A, and Lytton, M. R., IND.Exc. CHEM., 42, 2533-8 (1950). (3) Hatch, R. S., IKD.ENG.CHEX, A N ~ LE.D ,16, 104-7 (1944). 14) Johnson, A. F.. and hlueller. W. -4.. IND. ENG.CHEM.,45, 215-7
(1953). ( 5 ) Nelson, 11.L., and Conrad, C. AI., Testzle Research J., 18, 155-64
119411) ~(6) Gtraus, F. I,., and Levy, R. >I., Paper Trade J., 114, No. 3, 31-34 \
(7)
(1942); TAPPI Section 23-6. Tasman, J. E., and Corey, A. J., Pulp & Paper Mag. Can., 48, Xo.
3, 166-70 (1947).
This particular method has two other disadvantages: 1. It depends largely on the extraction of cellulose from naturally occurring particles. So far it has not been possible t o
(8)
Technical Association of Pulp and Paper Industry, 122 East 42nd St., New York 17, S.Y., “Testing Methods and Recommended Practices,” T230 sm50.
RECEIVED for ieview N a i c h 30, 1933.
ACCEPTEDSeptember 18, 1953.
Precipitation Fractionation of Cellulose Nitrate w i t h the objective of selecting a method for the determination of molecular weight distribution of cellulose, which could he adopted as an ACS standard, 17 laboratories have applied their preferred fractionation procedures to six standard celluloses, which were made available through the chairman of a subcommittee of the Division of Cellulose Chemistry, set up to study the problem. A majority preference was shown for “precipitation” fractionation of the cellulose nitrate derivative, prepared with minimum degradation. -4 tentative standard method has been established as one specific fractionation method, limited in scope but giving useful and reproducible data. Three operations are involved : (1) conversion of the cellulose to cellulose nitrate, (2) separation into several fractions through stepwise precipitation from solution by addition of a nonsolvent, and (3) measurement of the weight and viscosity of each recovered fraction and calculation of its average chain length.
R. L. MITCHELL,
Chairman
Rayonier, Inc., Shelton, Wush.
C
ELLULOSE is not a homogeneous material with respect to molecular weight or chain length. It is important, therefore, to have a method for measuring the degree of homogeneity of a particular cellulose, and to be able to express i t in a diagram of chain length distribution. 2526
h number of techniques may be used to obtain an approximate idea of the chain length distribution of a sample of cellulose, but all are difficult and time-consuming, and give different results, depending on the method used; none of them is widely used or well standardized with respect to procedural details.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 45, No. 11
-Cellulose Some years ago a t a round-table discussion in Chicago, the Committee of Standards and Methods of Testing, Division of Cellulose Chemistry, AMERICAN CHEMICAL SOCIETY, was asked t o set up a subcommittee, the function of which would be t o select a method for the determination of molecular weight distribution of cellulose, which could be adopted as an ACS standard. I n September 1948, steps were taken t o initiate the forrnation of this subcommittee and early in 1949 selection of i t s members was completed. As now constituted it consists of the eight members shown in Table I. A fair cross section of the cellulose industry is represented.
Solution and precipitation methods of separation yield cliaracteristioally different curves of chain length distribution, both of which seem capable of revealing significant and reproducible differences among different celluloses (Figures 1 to 5 ) . Although it is recognized that neither method of separation yields 1, “clean” fractions, there is some indication that the precipitation technique gives better subdivision of the nitrate than the solution technique, particularly in the high degree of polym e r i z a t i o n D o r t i o n of t h e sample (11). Data in Table I V show the good agreement in average degree of polymerization values reported for the standard samples by the various participants in the testing program; these values cover a wide range in solvent, cellulose concentration, equation used to determine intrinsic viscosity, and actual constant used to convert intrinsic viscosity t o degree of polymerization. Figures 1 to 5 illustrate the type of curve and the reproducibility of solution and precipitation fractionation of the nitrate for some of the standard celluloses. Results of these fractionations were discussed a t the spring meeting of the AMERICAN CHEMICAL SOCIETY,held in Boston in 1951, and it was agreed that the subcommittee cannot hope t o find a single ideal fractionation technique fitting all needs and giving absolute delineation of chain length; i t has a sufficient basis for setting up one or more specific fractionation techniques, limited in scope but giving useful and reproducible data; it should write up a tentative standard method for “precipitation” fractionation of cellulosenitrate, labeling it as such; and this referee method should include instructions for the nitration of cellulose and measurement of viscosity of the nitrate fraction as well as for the actual separation of fractions, A questionnaire was circulated among all participants in the fractionation program, requesting a preference vote on a large number of procedural details. Based on over 20 replies t o this questionnaire, the following fractionation method has been outr lined.
REPORT OF SUBCOMMITTEE 2 COMMITTEE ON STANDARDS AND METHODS OF TESTING, DIVISION OF AMERICAN CHEMICAL SOCIETY
TABLE I. MEMBERS OF SUBCOMMITTEE 21 J a c k Compton
John Harpham Merle A. Heath Emil Heuser Emil Kline R. L. Mitchell (Chairman) William A. Mueller C . J. B. Thor Former member W. E. Davia
x
Institute of Textile Technology (formerly at Celanese Corp. of America) Hercules Powder Co. Buckeye Cotton Oil Co. (formerly at InsGtute of Paper Chemistry) . La Jolla, Calif. (formerly at Institute of Paper Chemistry) Industrial Rayon Corp. Rayonier, Inc. Buckeye Cotton Oil Co.
Visking Corp.
Hercules Powder Co.
One of the first actions of the subcommittee was to ask interested persons: (1) to list methods for determining chain length distribution which they thought should be considered by the subcommittee; (2) to note methods with which they had had actual experience; and (3) t o state whether they would be willing to fractionate selected samples of cellulose by any of these methods. The replies to this inquiry indicated the definite need for some basis for comparing the various fractionation methods being used. As a start, it was thought that chain length distribution curves, obtained by a number of methods on identical samples of cellulose, would be helpful. Accordingly, in early 1950 a set of six standard celluloses was prepared and made available for use in fractionation studies. These celluloses, listed in Table 11, were selected to cover a wide range in degree of polymerization, cellulose type, and purity.
TABLE 11. STANDARD CELLULOSES
I
Sample 1 2 3 4
5 6
-ibha, % 99 9.5 91 98 99 87
DP 1000, wood cellulose 1000 wood cellulose 1000: wood cellulose 1000, cotton cellulose 2000 cotton cellulose 400: wood cellulose (tire cord)
During about a year these samples were distributed on request t o 17 people or organizations, with the understanding that they would fractionate the cellulose by their preferred method and submit the resultant distribution curves t o the subcommittee. Listed in Table I11 are the people who tested samples. Again, a good cross section of the cellulose industry is represented. Fractionation data and curves collected on these standard celluloses indicate that most people prefer a method based on “precipitation” fractionation of the nitrate derivative of cellulose. November 1953
CHAIN LENGTH UNIFORMITY OF CELLULOSE
A. Principle. The method of determining chain length uniformity of cellulose by fractional precipitation of cellulose nitrate is based on the following steps: 1. Conversion of the cellulose sample into cellulose nitrate by a nitration step which does not degrade the cellulose t o an appreciable extent (1, 3, 4,8, 9, 11, 13, 26, 23, 66). 2. Separation of the cellulose nitrate into several viscosity components through stepwise precipitation by the addition of a nonsolvent to a solution of the sample ( 7 , 11, 14, 17, 65). 3. Measurement of the weight and viscosity of each recovered fraction and calculation of its average chain length (degree of polymerization) ( 2 , 3,5 , 9, 12, 16, 16, 18, 19, 25, 25).
TABLE 111. COLLABC )RATORS Name C . J B. Thor William A. Mueller W. J. Alexander 0. A. Battista Leo Friedman Jack Compton J. L. Bitter Emil Kline H. Mark Kyle Ward Jr. Merle A. Heath H. E. Arnold J. W. Tamblyn Edgar J. Page Sigmund Wang R. de Lacotte R. M. Levy
Company Visking Buckeve
Sample No. 1 to 6 1 to 6 1 to 6 1 to 6 1 to 6 1 to 6 1 to 6 2, 4, 6 Nitrates corresp. to 1 to 0 2 4 6 nitrates of 3’aid 4 1 to 6 4, 5 , 6
Comptoir Ecusta Paper Corp.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1 to 6
1
1 to 6
2521
2500
[ SAMPLE NO 4 FRACTIONATION BY SOLUTION
z
2000-
I
25001
I SAMPLE NO. 6 FRACTIONATION BY SOLUTION
FRACTIONATION BY PRECIPITATION
FRACTIONAT ION BY PRECIPITATION
I
t
ZP2 O 0 O t I-
3
-
B I5O0l W W
I
a W
x
F t
500
1
0 20 40 60 80 100 0 20 40 60 80 I
I 1
1
1
20 40 60 80 Kx)
CUMULATIL PE 2ENT Figure 2. Chain-Length Distribution Curves Obtained by Solution a n d Precipitation Fractionation of a Rayon
CUMULATIVE PERCENT Figure 1. Chain-Length Distribution Curves Obtained b y Solution a n d Precipitation Fractionation of a Cotton Linters P u l p
6 . Weighing ~- bottles, tall-form, 40 X 100 mm.. around-glass stoppeis. 7 . Filter funnels, Buchner type, 50 mm. in diameter, with fritted disk (Corning C) or equivalent. 8. Erlenmeyer flask, 2000 ml., glass Etopper , 9. Spatula, 8 inch (stainless). 10. Tamp, stainless cylinder, 40 mm. in diameter, 100 mm. long. 11. \Tire baskets, 3 X 3 X 2 inches, 200-mesh scieen (stainless). 12. Osterizer or \Taring Blendor. 13. Torsion balance, 500-gram capacity, beam graduated in 0.1-gram divisions. 14. Analytical balance, accurate to 0.001 gram. 15. Drying oven with air circulation, 95" C. (normal convection). 16. Drying oven with air circulation, 50' C. (normal convection). 17. Constant temperature bath, 0' C. (ice-water), 18. Bottles, 2-ounce, wide-mouthed, plastic caps.
Reproducible curves of chain length distribution can be obtained by this method of precipitation fractionation within 24 hours. The curves are characteristic of the method of fraction separation and the individual fractions are not absolutely clean, but the curves afford a useful basis for comparing the relative uniformity in chain length of cellulose samples. The degree of polymerization values as calculated are not presumed to be absolute values. They are, nevertheless, in good agreement with the commonly recognized level of degree of polymerization values and serve as a convenient means for expressing the relative significance of measured differences in viscosity.
I
B. Reagents and Apparatus. FORNITRATION 1. Nitric acid, analytical reagent grade, go%+, light color (not red fuming). 2. Phosphoric pentoxide, analytical reagent grade. 3. Nitrating acid mixture, 64% "03, 26y0 HZP04, 10% PzOs. See Note 1 for details of preparation. 4. Ethyl alcohol, 95% (ethyl alcohol denatured with 0.5% b e y e n e is also satisfactory). a. Methanol, absolute.
FORT'ISCOSITY
%IEASUREMEKT
19. Ethg-1 lactate, analytical reagent grade, plus 1.5TGadded water (by volume). 20. B o t t l e s , 4 - o u n c e . n a r r o w mouthed, plastic caps. 21. Tin foil, 0.001 inch thick. VALUES REPORTED ON TABLE IV. DEGREEOF POLYMERIZATION 22. Viscometers, C a n non-Fen s k e , ACS SUBCOMMITTEE 21 CELLULOSES 0.4- to 0.5-mm. bore capillary, 1-ml. Sample Number bulb, or Ubbelohde, Type 1. Reported b y Method 1 2 3 4 5 6 23. Constant temperature bath, 25' -c 0.1" c. -4lexander Rayonier Nitrateviscosity 1240 1140 1095 960 1895 335 C E D viscosity 1152 1105 1065 952 1692 332 24. S t o p w a t c h , reading to 0.1 second. Battista -4m. Viscose Nitrate viscosity 1065 973 905 825 1406 357 Basic viscosity 1135 1100 1066 970 1703 420 25. Burrell (wrist action) or InterHeath Inst. Paper Chemistry Nitrate viscosity ,. 830 .. 865 . . 300 national shaker.
Kline 34ueller Bitter
Ind. Rayon Buckeye Am. Enka
Page
Corticelli
Brnold
Du P o n t Visking Ecusta
Thor Levy
2528
Nitrate viscosity on Rayonier nitrate Nitrate viscosity C E D viscosity (est.) Nitrate viscosity CED viscosity Nitrate viscosity Acetate viscosity Nitrate viscosity Kitrate viscosity C E D viscosity
..
970 . . 315 902 311 1053 955 895 . .. 990 935 800 1620 lis7 1167 1085 1039 1776 4'1s .. ., , 926 1750 . , .. .. . . 3'85 .. .. 909 875 . . .. 948 917 980 806 1425 277 1040 1010 1000 885 1450 410
..
.
1010 1078 1005
.
,
.
..
.
.. .
FORFRACTIOXATION 26. Microburet, 10-ml., 0.02-mI. subdivisions. 27. Spatula, stainless steel, curved (Fisher Scoopula). 28. B o t t l e s , 8 - o u n c e , n a r r o w mouthed, plastic caps. 29. C e n t r i f u g e , w i t h h e a d and trunnion cups for 250-mI. c e n t r i f u g e bottles.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 45, No. 11
Cellulose
t 2oool I 1
25001
SAMPLE NO 2
FRACTIONAT ION BY SOLUTION
SAME METHOD
z
0
z
l
0
l
I-
U
1500
A'
-
FRACTIONATION BY SOLUTION
Az
I I
W
I
3 LL
1000 -
0 W W
a 500-
3 CUMULI
Figure 3. Reproducibility of Solution and Precipitation Fractionation of a Wood Pulp
Figure 4.
Multiple fractionations were made by same method and same worker
Fraction separationa were made by similar but not identical technique. and by different workers on different nitrates
30. Centrifuge bottles, 250-ml., round-bottomed. Caps for centrifuge bottles, rubber, 1.5 inch, Sani-Tab (Scientific Supplies). 31. Laboratory stirrer, with a glass auger-type agitator, '/z inch in diameter.
C. Procedure. 1. PREPARATION OF CELLULOSENITRATE. Place about 1 gram of the dry cellulose sample in a n Osterizer or Waring Blendor and mix dry for about 30 seconds until the material is uniformly fluffed. Transfer the fluff t o a glass weighing bottle and dry for 1.5 hours at 50" C. Remove the sample from the oven, cover, and cool in a desiccator.
p1
Weigh a 100-gram portion of the nitrating acid into a glassstoppered weighing bottle by means of the torsion balance. Stopper and place in the 0" C. constant temperature bath until the desired temperature has been attained. Weigh a 1-gram portion of the dried cellulose sample t o the nearest 0.001 gram (Note 2). Transfer the weighed cellulose t o the bottle containing the nitrating acid (0" C.) with stainless steel forceps. Swirl t o mix. Allow the bottle and contents t o remain i n the 0" C. bath for exactly 60 minutes, swirling a t 10-minute intervals (Note 3). At the end of the reaction period, transfer the contents of the bottle t o the Biichner-type fritted-glass funnel. Apply vacuum, pressing the cellulose nitrate down with the stainless tamp (Note 4). Continue pressing the cellulose nitrate with the tamp while applying suction until excess acid has just been removed. With force s quickly transfer the nitrate t o 300 ml. of distilled water (0' and stir rapidly for several seconds. Wash the nitrate with a t least five 300-mI. changes of distilled water. Stabilize the cellulose nitrate by subjecting it t o a t least three 5-minute boils in fresh 200-ml. portions of distilled water. Transfer the nitrate t o the Buchner-type fritted-glass funnel and drain with suction. Rinse with methanol and drain with suction. Place nitrate i n the wire basket (200-mesh stainless) and dry in the 50' C. oven for 1 hour. Remove nitrate from oven, transfer to weighing bottle, cool in desiccator, and weigh. If the nitrate is t o be stored for more than a few days, transfer t o a 2-ounce wide-mouthed bottle, saturate with eth 1 alcohol, seal with tin foil under cap, and place in a cool dark caknet.
CUMULATIVE Reproducibility of Solution-Type Fractionation
250C
5 - 2000
SAMPLE NO. 4 FRACTIONATION BY PRECIPITATION
FRACTIONATION BY PRECl PITAT ION
ME HOD 6,
METHOD Be
l-
a
II! a W
E 1500 -t
B LL
0
a
1000
i
2 n 500
8.f
) 20 4 0 60 80 I 0 CUMUL IVI PERCENT Reproducibility of Precipitation-Type Fractionation
20 40 60 80 I
Figure 5.
Fraction separations were made by similar but not identical techniques and by different workers on different nitrates
b. Determination of Per Cent Nitrogen. When desired, the degree of nitration (per cent nitrogen) may be determined with a D u Pont nitrometer (84) (Note 6). Prior t o determination of per cent nitrogen, the sample should be redried for 2 hours a t 95" C. 2 . MEASUREMENTS O N UNFRACTIONATED CELLULOSE NITRATE. c. Measurement of Viscosity. For preliminary check of viscosity, weigh a 0.0500 f 0.0001-gram sample of nitrate (redried a. Determination of Yield. Moisture content must be deterfor 1 hour a t 50" C. and cooled just prior t o weighing), prace in a mined for the pulp as nitrated. The nitrate, dried a t 50' C., is 4-ounce plastic capped bottle, add 100 ml. of solvent (ethyl lacfor all practical purposes moisture-free. Yield in per cent is caltate containing 1.5% added water) from a pipet, cover with tin culated simply by multiplying by 54.6 the quotient of nitrate foil before capping, and place on the shaker until solution is comweight divided by pulp weight (Note 5). plete (Note 7 ) . Measure the viscosities of the solvent and the
November 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
2529
TABLE
v.
listed in Table VI; experience will help judge minor adjustments that may be needed for various nitrates.
SOLCTIONS O F CELLULOSE NITRATE I N ETHYLL.4CTATE COXTAINING 1.5y0 WATERBY VOLUME
(Relationship between rlrel. a n d
[?Ic
where c = grams per 100 ml.)
After precipitation of a fraction, cap (Sani-Tab) the centrifuge bottle and centrifuge the dispersion a t 500 G for [ ~ I c Valuee 5 minutes. Decant the supernatant liquor 1.0 0.00 0,0010 0.0198 0.0298 0.0394 0,490 0.0586 0.0681 0.0775 0.0861 into a second centrifuge bottle and set 0.150 0.159 0.168 0.177 0.133 0.142 0.124 0.115 1.1 0,0962 0,105 aside for precipitation of the next frac0.260 0.244 0.252 0.236 0.219 0.227 0,202 0.211 1.2 0 . 1 8 5 0,194 tion. 0.331 0.322 0.330 0,307 0.315 0.292 0,299 1.3 0.268 0.276 0.284 Transfer the settled residue, compris0.410 0.396 0.403 0.381 0.389 1.4 0.345 0.367 0.374 0.352 0,360 ing the first fraction, to a weighing bottle 1 .. 56 0.417 0.424 0.430 0.437 0.444 0 ,451 0 ,. 5 42 58 0.464 0 .471 0 .471 (Note 14). To facilitate drying, press 0.635 0.541 0 2 0.528 0.510 0.516 0,503 1 0,484 0,490 0,497 the gellike fraction into a thin film using 0.600 0.589 0.595 0.577 0.583 0.571 0.569 0.565 1.7 0.547 0.553 a Scoopula to squeeze out the excess 0.651 0.656 0.640 0.645 0.629 0.634 0.618 0,623 0.606 0.612 1.8 liquid. Add 1 t o 3 ml. of water to agglom0.709 0.699 0.704 0.688 0.694 0.683 1.9 0.662 0.673 0.678 0.667 erate (the higher degree of polymeriza0.754 0.759 0.744 0.749 0.734 0.739 2.0 0.714 0,724 0.729 0.719 tion fractions agglomerate as films and the lower degree of polymerization fractions as powders). M'henever possible to do so without loss of nitrate, pour off the water and excess solution. Place weighing bottle containing solution in a suitable viscometer (6, 10) a t 25" i 0.1" C. (Notes nitrate in 50' C. oven until constant weight is attained (usuallv 8 and 9). about 2 hours). For final determination of viscosity, the nitrate solution concenI n a similar manner, precipitate and recover the next eight fractions. To recover fraction 10, evaporate on a water bath the tration is adjusted to a value indicated by the following formula: supernatant liquor from No. 9 to one half its initial volume, cool, Concn., grams/100 ml. X DP = 50. If approximate sample centrifuge, and decant. Transfer the settled residue (fraction 10) degree of polymerization is known, concentration may be approt o a weighing bottle. I n a similar manner, evaporate supernatant liquor from fraction 10 to one half its volume to recover priately adjusted a t the start and the initial measurement will fraction 11. Evaporate to dryness the supernatant liquor from suffice. fraction 11 to obtain the final fraction, No. 12. 4. MEASUREMENTS O N CELLULOSE SITRATE FRACTIONS. a. d. Calculation of Degree of Polymerization ( D P ) . Use the Determine for each fraction (1) weight of cellulose nitrate following formula or Table V. cipitated and (2) degree of polymerization, following procef;:; DP = K [ q ] described in C 2 , c and d. 6. Plot (1) integral (stepwise) distribution curve, degree of polymerization us. cumulative per cent, and (2) differential diswhere [ q ] = qep/C . 1 k'%p tribution curve, amount a t each chain length us. degree of poly? ~ s p= qr. 1 merization (Note 15). viscosity of solution tlr = D. Notes. viscosity of solvent K = 85 (Note 10) 1. One method of preparing this mixture of nitrating acid is k' = 0.40 (Note 10) to add very slowly with a spatula 404 grams of phosphorus c = grams of nitrate per 100 ml. of solution pentoxide t o 1000 grams of 90% nitric acid swirled in a 2-liter 3. FRACTIONATION OF CELLULOSE NITRATE. Weigh to the Erlennieyei flask, keeping the acid ice-cold throughout the time nearest 0,001 gram about 1gram of nitrate redried a t 50" C. for 1 of phosphorus pentoxide addition by immersion in an ice-water hour (Note 11). Transfer t o an 8-ounce plastic capped bottle, bath ( 1 ) . -411alternative method of acid make-up is to add the add 200 ml. of a 91 to 9 (by volume) acetone-water mixture, cap required amount of phosphorus pentoxide to 85 % phosphoric acid using tin foil, and place on the shaker t o dissolve (Note 12). Transfer the solution t o a 250-ml. round-bottomed centrifuge and pour the warm mixture into cold 94 to 99% nitric acid (11). bottle, and place in a constant temperature bath a t 25" f 0.1" C. 2. One gram of cellulose gives sufficient nitrate for viscosity Stir the solution rapidly and add distilled water through a micromeasurement and a single fractionation. If duplicate fractionaburet, the tip of which is immersed in the solution (Note 13). tions, per cent nitrogen, or stability tests are desired, a blend of nitrate from multiple 1-gram nitrations should be used. Larger The successive increment amounts of nater that need be added samples of cellulose may also be used in single nitrations, provided in order t o separate the sample into about 12 fractions of roughly suitable precautions are observed Kith respect to addition of equivalent weight are rather critical. ,4s a guide, sequences of cellulose to the nitrating acid, drowning, and stabilization (Note water additions (which have been found to give satisfactory weight separation a t several initial degree of polymerization levels) are 4). 3. The nitration time of 60 minutes a t 0" C. is to be used for relatively pure bleached pulps. Gnbleached pulps should be nitrated long enough to ensure sufficient attack on the lignin so OF WATERADDITION TABLE VI. SEQUENCE that it may be solubilized and removed in the stabilization procD P Level ess. h workable rule appears to be to nitrate for a time in 3000 2000 1000 500 250 minutes equivalent to about 10 times the TAPPI K number ( 2 7 ) Nitrate Dissolved in 200 M1. of 9 1 :Q Acetone-Water Solvent, G. of the unbleached pulp. Samples of properly prepared raw wood 0.2 0.4 0.6 1.0 1.2 shavings may also be nitrated, but, depending on the type of For Ppt. of Fraction Add MI. of Water as Shown wood, usually require much longer nitration time a t a higher NO. temperature level (20). 0 7 1.2 1 0.5 1.7 2.7 0 2 0 3 2 0.2 0.3 0.3 4. The stainless steel cylindrical tamp provides uniform pres0.3 0 3 0.4 0.4 0.4 3 sure and excludes air while removing excess nitrating acid; i t also 0.35 0.5 0 5 0.6 0.35 4 0 6 0.6 0.4 5 0.4 0.8 tends to form a loose disk of nitrate, which in most cases may be 0.6 0.7 0.8 1.0 6 0.5 handled quickly and conveniently with tweezers for transfer to 7 0.6 0.7 0.8 0.9 1.2 1.2 1.4 1.8 0.9 0.7 8 . the water used for drowning. 2 5 5.0 6.0 9 1.5 4.0 10 Evap. to '/z initial volume, cool, centrifuge decant An alternative procedure for removing the excess nitrating acid 11 Evap. to '/a initial volume, cool, centrifuge: decant and drowning the nitrate (particularly useful for cellulose batches Evap. to dryness 12 larger than 1gram) is to apply vacuum cautiously while squeezing ??A.
0.00
0.01
0.02
0.03
[ q ] Values
0.04
0.05
0.06
0.07
0.08
0.09
+-
2530
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 45, No. 1 1
Cellulose the cellulose nitrate until only the minimum amount of nitrating acid necessary t o cover the sample completely remains. The sample is then flooded in the funnel with 50% aqueous acetic acid previously chilled t o 10’ C. Washing should be done on a sintered-glass Buohner-type filter funnel t o avoid loss of loose fibers. 5. Depending on the type of cellulose, yield value gives some indication of degree of nitration and purity of the cellulose. As the specified nitration conditions give high nitrogen content with pure cellulose, low yields should occur only with pulps of high pentosan content (xylan dinitrate) or with pulps of high lignin content. 6. Nitrate prepared by this procedure from a pure cellulose should contain 13.9+% nitrogen and i n no case be below 13.6%; it should have a stability of 20 t o 25 minutes a t 134.5’ C. by the German stability test ( 2 1 ) . Wood pulp nitrates may be lower i n nitrogen content than cotton nitrates, depending on the amount of hemicellulose present-e.g., dinitrate of xylan. Nitrogen content may be determined by other methods than the nitrometer, with suitable calibration. 7. The time needed t o obtain complete solution depends on the degree of polymerization and degree of subdivision of the sample, usually running from a few minutes for rayon or cellophane to several hours for very high viscosity wood pulps or raw cotton. It is best t o pick the nitrate sample into small pieces before weighing out for the dissolving step. 8. I n making viscosity measurements, i t is desirable t o vary the concentration of nitrate t o suit the level of degree of polymerization, a s the flow time and specific viscosity are more constant if one uses, for example, a concentration of 0.10 gram per 100 ml. in the case of rayon or low viscosity pulps and 0.025 gram per 100 ml. or less i n the case of very high viscosity pulps, native cotton, or wood cellulose. 9. The viscometer should have a flow time within the range of 70.0 t o 100.0 seconds per ml. a t 25’ C. for the solvent being used. 10. With the described nitration procedure utilizing about 1 gram of cellulose, the values of 85 for K and 0.40 for k’ give values of degree of polymerization which appear t o be consistent with the accepted level of degree of polymerization for rayon, wood pulp, and cotton (1, 6, 11, I S , 16, 17, 26). Other formulas than Huggins’ ( 1 2 ) may be used in calculating intrinsic viscosity values from viscosity measurements-e.g., Baker ( d ) , Martin (18,19),and Schultz (93). Other solvents than ethyl lactate may be used for measuring viscosity-eg., ethyl acetate using K of 75 and k‘ of 0.35. 11. For satisfactory precipitation it is desirable to vary the initial concentration of nitrate with the level of degree of polymerization. The following sample weights have been found t o work satisfactorily.
-
rT
n
8
D P Level 3000 2000 1000 500 250
Grams Sample/ 200 M1. Solvent 0.2 0.4
0.6 1.0 1.2
12. The use of the 91 t o 9 acetone-water mixture ifistead of pure acetone in the solution step gives faster dissolving action and a t the same time brings the solution t o the point of “threshold” precipitation, avoiding the necessity of adding relatively large amounts of water prior t o the precipitation of the fraction. Mild heating (30’ C.) is sometimes helpful in effecting solution, particularly of material of very high degree of polymerization.
November 1953
13. The precipitation should b e carefully watched, and if any precipitate tends t o cling t o the buret nozzle it should be removed promptly t o prevent the formation of large stringy mass-. This tendency is apparent only with the early fractions of a high degree of polymerization nitrate, and particularly if too high a n initial concentration of nitrate has been chosen (Note 11). With proper precipitation technique the fractions appear as finely divided floc, usually several seconds after the addition of water has ceased. Other methods for bringing down the fraction, such as by evaporation of solvent, or by change in temperature, may be used. 14. For all but fractions of very low degree of polymerization the centrifuged residue can be shaken out of the centrifuge bottle in a relatively solid piece and requires no rinsing for a quantitative transfer t o the weighing bottle. The fractions of low degree of polymerization are somewhat more difficult t o transfer, sometimes requiring a rinse for clean removal. 15. I n order t o construct a differential plot, a smooth freehand curve is drawn through the stepwise integral plot, ignoring minor deviations from mid-point of individual fractions:. From this smooth curve the amount (in percentage of total) of material falling within successive suitably spaced degree of polymerization ranges is picked up-e.g., 0-25 DP,25-50, 50-100, 200-300, etc. Each percentage is divided by the increment range of degree of polymerization covered to give the average amount at each chain length in that increment. This “amount for each increment range” is plotted against degree of polymerization t o give a s t e p wise differential curve. A smooth freehand curve is drawn through the stepwise curve, ignoring minor deviations from midpoint of individual steps in such manner t h a t the area under the curve totals 100%. LITERATURE CITED
(1) Alexander, W. J., and Mitchell, R. L., Anal. Chem., 21, 4497 (1949). (2)Baker, F.,J. Chem. Soc., 103, 1653 (1913). (3)Berl, E., IND.ENG.CHEM.,ANALED., 13, 322 (1941). (4) Berl, E., and Rueff, G., Cellulosechemie, 14, 115 (1953). (5)Cannon, M. R., and Fenske, M. P., IND.ENG.CREM.,ANAL. En., 10,297 (1938). (6) Conrad, C. M.,and coworkers, Division of Cellulose Chemistry, 121st Meeting, AM,CHEM.SOC., Milwaukee, 1952. (7) Craik, J., and Miles, F. D., Trans. Faraday SOC.,27,756 (1931). ( 8 ) Davidson, G. F., J . Tertile Inst., 29, T195 (1938). (9)Davis, W.E., IND.ENG.CHEM.,43, 516 (1961). (10)Davis, W.E., and Elliot, J. H., J . Colloid Sci., 4,313 (1949). (11) Heuser, E., and Jorgensen, L., Tappi, 34,57,443(1951). (12)Huggins, M. L.,IND.ENG.CHEM.,35, 980 (1943). (13)Jullander, I., Arkiv Kemi Mineral., Geol., 21A, No. 8 (1945). (14)Jurisoh, I., Chem. Ztg., 64,269 (1940). (15)Kramer, E. O.,IND.ENG.CHEM.,30, 1200 (1938). J . Polymer Sci., 7, 635 (1951). (16)Lindsley, C. H., (17)Mark, H., Paper Trade J., 113, No.3,34 (1941). (18)Martin, A. F.,Division of Cellulose Chemistry, 103rd Meeting, AM.CHEM.SOC., Memphis, Tenn., 1942. (19) Martin, A. F., T a p p i , 34, No. 8, 363 (1951). (20)Mitchell, R. L.,IND.ENG.CHEM.,38, 983 (1946). (21) Reeves, R.,and Giddens, J.,Ibid., 39, 1304 (1947). (22)Schieber, W.,Papier-Fabr., 37, 245 (1939). (23) Schultz, G. V., and Blaschke, F. J., Prakt. Chem., 158, 130 (1941). (24) Scott, “Standard Methods of Chemical Analysis,” 5th ed., Vol. 1, p. 650, New York, D. Van Nostrand Co., 1939. (25) Spurlin, H.M., IND.ENG.CHEM.,30,538 (1938). (26) Staudinger, H., and Mohr, R., Ber., 70B, 2296 (1937). (27)TAPPI Standards, Tentative Method T 214m-50. RECEIVED for review March 30, 1953.
ACCEPTED July 2, 1953.
INDUSTRIAL AND ENGINEERING C H E M I S T R Y
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