Conclusions
literature Cited Boyd, R. N., Hauser, R. H., J . A m . Chem. SOC.7 5 , 5896 (1953). Fry, E. M., J . Org. Chem. 15,802 (1950). Heine, H. W., Angew. Chem. Intern. Ed. 1, 528 (1962). Jay, R. R., Anal. Chem. 36,667 (1964). Pittman, A. G., Lundin, R. E., J . Polymer Sci. 2A,3803 (1964). Quacchia, R. H., Johnson, D. E., Di Milo, A. J., paper in preparation, 1967. Wehrmeister, H. L., J . Org. Chem. 28, 2587 (1963). RECEIVED for review May 16, 1967 ACCEPTEDAugust 28, 1967 DOD Public Release Approval RA/SA-BSD-4/27/67.
The isomer distribution obtained by rearranging aziridines (specifically BITA and 1-benzoyl-2-ethylaziridine)can be determined by a kinetic method. This method, which involves determining the pseudo-first-order rate of reaction of the isomer mixture in acetic acid, is easily carried out and is applicable to materials which cannot be analyzed by gas chromatography. T h e method was demonstrated for BITA, a n aziridine curing agent of interest to solid rocket propellant technology.
VISCOSITY MEASUREMENTS ON CHEMICALLY MODIFIED CELLULOSES W . B . A C H W A L A N D T. V . N A R A Y A N Defartment of Chemical Technology, University of Bombay, Bombay 19, India
A large number of oxycelluloses were prepared and treated with chlorous acid and sodium borohydride and their degree of polymerization (DP) was determined in a number of alkaline solvents as well as in ethyl acetate after nitration. Comparison of DP values showed that differences in alkalinity of the solvents had practically no effect, but the values for different modified celluloses varied considerably, depending upon the acid and alkali sensitivity of functional groups formed. A pretreatment of degraded samples with sodium borohydride is recommended to get a more representative DP value in alkaline solvents.
of degree of polymerization (DP) of cellulosic materials by viscosity measurement involves either working with highly alkaline solvents or nitration under strong acidic conditions. Chemical modifications, particularly by oxidation, may introduce different functional groups such as carbonyl and carboxyl in various positions of the cellulose molecules and induce alkali or acid sensitivity resulting in apparently low degree of polymerization values. Such discrepancies between the viscosity measurements in alkaline solvents such as cuprammonium hydroxide (cuoxam) or cupriethylenediamine (CED) and nitrate viscosity have been reported by many workers (Davidson, 1941 ; Ellefsen, 1963 ; Sihtola et al., 1958; Virkola, 1958). Pronounced alkali sensitivity of oxycelluloses having reducing groups has been attributed by Davidson (1941) and Brownsett and Davidson, (1945) to the presence of carbonyl groups in certain positions which induce alkali sensitivity in 1-4 glucosidic linkages. Rogovin et al. (1949) and Davidson (1941) had observed that nitration of dialdehyde celluloses of a higher degree of oxidation gave poorly soluble nitrates and high viscosity values, which has been attributed to acetal cross linkages formed during the nitration between the individual cellulose molecules (Sihtola, 1960; Sihtola et al., 1958; Virkola, 1958). Acid and alkali stability of dialdehyde cellulose formed by periodate oxidation and stabilization caused by conversion into dicarboxylic and dialcoholic celluloses on further treatment with sodium chlorite and sodium borohydride have been studied (Betrabet et al., 1965; Meller, 1951, 195G; Rutherford et al., 1942). Ellefsen (1963) had suggested a treatment for pulp DETERMINATION
278
l&EC PRODUCT RESEARCH A N D DEVELOPMENT
samples with sodium borohydride to get comparable DP values in CED and on nitration. T h e effect of the presence of functional groups formed by oxidizing agents other than periodic acid on DP values in different solvents has not been thoroughly investigated and most of the D P measurements have been carried out in cuprammonium hydroxide and cupriethylenediamine and after nitration. With the development of iron-tartrate complex solvents a wide range of solvents of different alkalinities are available and variation in alkali content may also have a n effect on the extent of alkali sensitivity. A large number of oxycelluloses of different types were prepared by oxidation with various oxidizing agents a t different p H values. AI1 these samples were further treated with sodium chlorite and sodium borohydride under controlled conditions and D P values compared in three types of iron-tartaric acid complex (FeTNa) solvents, cuoxam, and CED as well as in ethyl acetate after nitration. Experimental
Preparation of Modified Cellulose Samples. Forty grams of standard cellulose was oxidized by the respective oxidizing agent a t room temperature a t a material-liquor ratio of 1 to 40. Oxygen consumption was determined wherever possible from the change in the concentration of oxidant and the samples were washed free from reagents, dried in air, and conditioned a t 65y0 R H a t 30' C. Periodate oxidation was carried out by 0.01M potassium metaperiodate for 17 hours and by 0.005M solution for 8 and 24 hours. Potassium dichromateoxalic acid oxycellulose was prepared by suspending the sample in 2M oxalic acid and adding 140 ml. of 2.ON potassium
dichromate with rapid stirring. Standard cellulose was oxidized by 0.1 A' potassium dichromate-sulfuric acid a t p H 1.0 for 15 hours. Sodium hypobromite oxycelluloses were prepared by using 0 . 0 2 5 solution buffered a t p H 5 and 10 for 4 hours. Standard cellulose was also oxidized by a buffered sodium hypochlorite solution containing 3 grams per liter of active chlorine a t p H 5 and 10 for 4 hours. Oxidations with 0.02.V potassium permanganate solutions were carried out a t p H 5 and 10 for 4 hours. Each of the above oxycelluloses was treated with 0.1M sodium chlorite containing 0.5M phosphoric acid for 18 hours a t room temperature and also separately with 0.02M sodium borohydride solution for 24 hours a t a material-liquor ratio of 1 to 50. Determination of DP Values in Different Solvents. In all the solvents the values of intrinsic viscosity and degree of polymerization were calculated from measurement of viscosity a t one suitable concentration, using the appropriate values of Schulz-Blaschke ( K ' ) and Staudinger ( K m ) constants. Nitration as well as viscosity measurements in ethyl acetate were carried out according to A S T M specifications and degree of polymerization was calculated by taking the value of K' = 0.35 and K , = 75 (American Society for Testing Materials, 1961). D P determinations in solvents CED and FeTNa-I, 11, and I11 were carried out by recently standardized methods using the appropriate values of constants (Achwal, 1967). Cuoxam solvent was also prepared according to ASTM specifications and viscosity was measured a t 0.5% concentration and degree of polymerization calculated by taking the value of constants K' = 0.287 and K m = 3.846 X l o u 3 . Results and Discussion
To investigate the effect of different functional groups in the cellulose molecule o n the determination of degree of polymerization in various solvents, a large number of oxycelluloses were prepared. These include three periodate oxycellulose samples and oxidation products of potassium dichromate in the presence of both oxalic and sulfuric acids. Using sodium hypobromite, potassium permanganate, and sodium hypochlorite, oxidations were carried out under both acidic and alkaline conditions. Periodate is known to oxidize the cellulose mainly a t the 2 and 3 positions, forming a dialdehyde (Davidson, 1941 ; Jayme et al., 1941) and potassium dichromate oxidation takes place predominantly a t the primary hydroxyl group (Nevell, 1948). With other oxidizing agents, oxidation is less specific, but results mainly in formation of reducing groups under acidic conditions and carboxyl groups under alkaline conditions. A hydrocellulose sample was also studied for comparison. Values of copper number and carboxyl content of the modified cellulose samples after treatment with sodium chlorite and sodium borohydride are given in Table I .
Table 1.
Sample Standard cellulose Hydrocellulose Periodate oxycellulose I (0.01A4, 17 hours) Periodate oxycellulose I1 (0.005A4, 24 hours) Periodate oxycellulose I11 (0.005A4, 8 hours) Dichromate and sulfuric acid oxycellulose I Dichromate and oxalic acid oxycellulose I1 Sodium hypobromite oxycellulose, I , pH 5 Sodium hypobromite oxycellulose 11, pH 10 Potassium permanganate oxycellulose I , pH 5 Potassium permanganate oxycellulose 11, pH 9.2 Sodium hypochlorite oxycellulose I, pH 5.2 Sodium hypochlorite oxycellulose 11, pH 9.8
Sodium chlorite is known to oxidize the aldehyde groups in the oxycelluloses (Meller, 1951, 1956), while sodium borohydride is capable of reducing aldehyde as well as keto groups (Head, 1955). Treatment with sodium chlorite results in a partial reduction of copper number and increase ;n the carboxyl content. Borohydride treatment reduces the copper number almost completely and also reduces carboxyl content to a certain extent. T h e reduction in carboxyl content can be attributed to the presence of certain groups in oxycelluloses which can liberate iodine during the idometric estimation of carboxyl groups but be reduced in borohydride treatment (Meghal et a/., 1964). T h e 11 oxycelluloses studied along with hydrocelluloses and standard cellulose with their corresponding products after sodium chlorite and borohydride treatment represent most of the possible formations of various functional groups in the cellulose molecule. Values of degree of polymerization determined in the various solvents for the modified celluloses after treatment with sodium chlorite and borohydride are summarized in Table 11. One of the periodate oxycelluloses having a higher degree of oxidation and particularly its chlorite-treated sample were found difficult to nitrate and were only partially soluble in ethyl acetate. Their insolubility can be attributed to the formation of crosslinkages between the carboxyl or carbonyl groups in position 2-3 and primary hydroxyl group in the neighboring molecule as suggested by Ellefsen (1963) and Anthoni (Sihtola, 1960). I n general, D P values for all the modified celluloses determined in the various alkaline solvents are in agreement with each other but differ to some extent from the nitrate D P values. T h e different alkaline solvents used-namely, cuoxam and the three FeTNa solvents-vary widely in their alkali content. This difference in alkali content was, however, not reflected in degree of polymerization measurement, indicating that even the minimum alkalinity is sufficient to cause scission of all the chains having alkalisensitive groups during the long periods of dissolution of 16 to 18 hours. For periodate oxycelluloses, the DP values in nitrate are considerably higher than corresponding values in alkaline solvents. Thus the dialdehyde celluloses are stable to acids but exhibit considerable alkali sensitivity. For both the dichromate oxycelluloses and oxycelluloses with other oxidizing agents under acidic conditions, the nitrate D P values are only slightly higher than the D P values in alkaline solvents. Oxycelluloses prepared by the above oxidizing agents under alkaline conditions show comparable D P values in alkaline
Properties of Some Modified Cellulose Samples Milliatoms Oxygen Consumed by 700G. Bone-Dry Sample
... ...
27.6 17.6 8.8 29.3
...
4.4 28.2 13.6 32 . O 3.9 10.2
Original 0,025 1.04 14.03 9.52 7.44 11.70 9.90 1.24 1.24 1.41 2.16 1.41 0.30
Coppei S o . After chlorous acid treatment 0.01 0.60 1.12 0.66 0.34 2.18 0.89 0.77 1.04 0.43 0.89 0.65 0.18
After sodium borohydride treatment 0.01 0.38 0.55 0.24 0.01 1.30 0.34 0.01 0.58 0.03 0.45 0.07 0.11
VOL. 6
Original 0.70 0.60 4.80 3.00 1 .oo 6.35 4.35 0.65 3.35 0.70 1.75 0.90 1.95
NO. 4
Carboxyl Content After After chlorous sodium acid borohydride treatment treatment 1.20 0.40 4.40 0.70 31.50 0.30 20.30 0.25 13.20 0.20 12.30 3.75 10.90 2.00 1.05 0.40 5.20 2.80 1 .oo 0.45 2.45 1 .oo 1.10 0.50 0.95 0.85
DECEMBER 1967
279
Table II. DP Values of Modified Celluloses in Various Solvents Solvent Oxycellulose
Periodate oxycellulose I Periodate oxycellulose I borohydride-treated Periodate oxycellulose I chlorite-treated Periodate oxycellulose I1 Periodate oxycellulose I1 borohydride-treated Periodate oxycellulose I1 chlorite-treated Periodate oxycellulose 111 Periodate oxycellulose I11 borohydride-treated Periodate oxycellulose I11 chlorite-treated Dichromate and sulfuric acid oxycellulose I Dichromate and sulfuric acid oxycellulose I, borohydride-treated Dichromate and sulfuric acid oxycellulose I, chlorite-treated Dichromate and oxalic acid oxycellulose I1 Dichromate and oxalic acid oxycellulose 11, borohydride-treated Dichromate and oxalic acid oxycellulose 11, chlorite-treated Sodium hypobromite oxycellulose I , pH 5 Sodium hypobromite oxycellulose I, pH 5 borohydride-treated Sodium hypobromite oxycellulose I, pH 5 chlorite-treated Sodium hypobromite oxycellulose 11, pH 10 borohydride-treated Sodium hypobromite oxycellulose 11, pH 10 Sodium hypobromite oxycellulose 11, pH 10 chlorite-treated Potassium permanganate oxycellulose I, pH 5 borohydride-treated Potassium permanganate oxycellulose I, pH 5 Potassium permanganate oxycellulose I , pH 5 chlorite-treated Potassium permanganate oxycellulose 11, pH 9.2 Potassium permanganate oxycellulose 11, pH 9.2 f borohydridetreated Potassium permanganate oxycellulose 11, pH 9.2 chlorite-treated Sodium hypochlorite oxycellulose I, pH 5.2 Sodium hypochlorite oxycellulose I , pH 5.2 borohydride-treated Sodium hypochlorite oxycellulose I, pH 5.2 chlorite-treated Sodium hypochlorite oxycellulose 11, pH 9.8 Sodium hypochlorite oxycellulose 11, pH 9.8 borohydride-treated chlorite-treated Sodium hypochlorite oxycellulose 11, pH 9.8 Standard cellulose Standard cellulose borohydride-treated Standard cellulose chlorite-treated Hydrocellulose Hydrocellulose borohydride-treated Hydrocellulose chlorite-treated
+ + ++ ++
+ +
+ + + +
+
+ + ++
+ +
+ +
Table 111.
Cuoxam 180 640 340 220 790 440 210 960 490 240 520 380 320 720 570 770 1250 770 290 300 260 480 620 500 300
CED 170 670 300 220 810 380 260 1200 550 220 450 360 280 720 530 940 1880 960 360 380 380 540 760 660 370
I 180 650 290 220 780 360 250 1180 500 210 420 280 270 680 420 550 1570 610 300 330 310 49 0 730 560 320
390 360 840 1080 800 750 760 680 2280 2280 2280 680 660 610
440 390 1120 1460 1000 900 950 860 2200 2280 1810 650 660 630
420 340 740 1300 730 760 870 740 2200 2240 1570 700 710 620
Fe Th’a~_ 11 180 640 320 220 760 400 240 1170 550 210 420 270 270 710 410 510 1420 580 290 340 330 470 730 570 330
420 350 710 1320 780 760 900 740 2120 2030 1470 700 660 620
I11 180 670 310 220 810
Nitrate in Ethyl Acetate , . .
180 ... 730 240
... 1110 270
410 270 1190 570 210 440 310 290 720 410 530 1470 590 310 330 330 480 760 560 320
350 450 350 570 730 460 2140 1810 1030 360 370 360 750 700 690 360
440 350 740 1360 750 780 900 740 2010 2000 1410 680 690 620
390 340 1360 1430 1070 910 950 840 2010 2200 1700 570 610 560
...
Intrinsic Viscosity of Modifled Celluloses as Well a s after Chlorous Acid Treatment Expressed as Percentages of the Value after Sodium Borohydride Treatment Solvent
Fe T N a Sample
Periodate oxycellulose I Periodate oxycellulose I chlorite-treated Periodate oxycellulose I1 Periodate oxycellulose I1 chlorite-treated Periodate oxycellulose 111 Periodate oxycellulose I11 chlorite-treated Dichromate and sulfuric acid oxycellulose Dichromate and sulfuric acid oxycellulose chlorite-treated Dichromate and oxalic acid oxycellulose chlorite-treated Dichromate and oxalic acid oxycellulose Sodium hypobromite oxycellulose I, pH 5 chlorite-treated Sodium hypobromite oxycellulose I, p H 5 Sodium hypobromite oxycellulose 11, pH 10 Sodium hypobromite oxycellulose 11, pH 10 chlorite-treated Potassium permanganate oxycellulose I, pH 5 Potassium permanganate oxycellulose I, pH 5 chlorite-treated Potassium permanganate oxycellulose 11, pH 9.2 chloritePotassium permanganate oxycellulose 11, pH 9.2 treated Sodium hypochlorite oxycellulose I, p H 5.2 Sodium hypochlorite oxycellulose I, p H 5.2 chlorite-treated Sodium hypochlorite oxycellulose 11, pH 9.8 Sodium hypochlorite oxycellulose 11, pH 9.8 chlorite-treated Standard cellulose chlorite-treated Standard cellulose Hydrocellulose chlorite-treated Hydrocellulose
+ +
+
+ + +
+ +
+
+ +
+
+
280
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
CED 25 44
Z 27 44
zz
28 49
27 46
44 78 45 73 62 62 77 74 77 80 79
38 73 48 80 50 50 76 68 71 88 84
39 76 48 65 35 38 57 56 66 76 75
37 57 50 63 35 40 54 58 63 78 78
40 58 48 71 36 40 54 54 63 74 73
95 98 89 97 99 io0 99 103 92
86 94 89 93
81 84 84 90 94 97 69 99 87
82 84 81 84 97 104 72 107 93
79 86 81 95
Cuoxam 29 54
100
96 79 96 95
IZI
100 100
70 98 89
solvents as well as o n nitration. This indicates that the presence of carboxyl groups which are predominantly formed in alkaline conditions causes no particular acid or alkali sensitivity. For all the oxycelluloses, the samples after borohydride treatment show considerably higher D P values in alkaline solvents as compared to the oxycelluloses themselves. Increase in D P value is maximum for the periodic acid oxycelluloses and appreciable for samples oxidized under acidic conditions, while the D P value is practically unaltered for samples oxidized under alkaline conditions. Even for the periodate oxycelluloses, the D P of the borohydride-treated material is low compared to the D P of unoxidized material. Thus even in periodate oxidation certain chain scission takes place during oxidation because of side reactions or the weak alkalinity of the borohydride solution itself. Conversion of the dialdehyde groups into dialcoholic groups on reduction of periodate oxycelluloses with sodium borohydride induces acid sensitivity, as can be seen from the lower values of the nitrate DP. T h e nitrate D P value of the periodic acid oxycelluloses is of a n order similar to the borohydride-treated samples in alkaline solvents and the D P values for these oxycelluloses in alkaline solvents are comparable with the nitrate D P values of the borohydride-treated samples. D P values of standard cellulose as well as hydrocellulose samples are unaltered by borohydride treatment and are of similar order in all the solvents. Borohydride treatment causes a partial reduction of the potential aldehyde groups in the hydrocellulose, as seen from the lowering in copper number. Thus the presence of potential aldehyde groups as such has no effect on the alkali or acid sensitivity of the cellulose molecule and justifies the choice of hydrocelluloses as standard samples of varying degree of polymerization for establishing the viscosity degree of polymerization relations in any solvent. Chlorite treatment of the oxycelluloses also results in increase in degree of polymerization value but to a lesser extent as compared to borohydride treatment. This can be explained by the fact that even after chlorite treatment, a n appreciable copper number is observed due to the presence of keto groups and during the chlorite treatment under acidic conditions a certain degradation of the sample takes place, as is reflected in the lower degree of polymerization values for standard cellulose as well as for hydrocellulose. Nitrate D P values after chlorite treatment of the samples oxidized under acidic conditions are higher than the values in alkaline solvents, while for chlorite-treated materials, oxidized under alkaline conditions, the values of degree of polymerization in all solvents are comparable. Conversion of dialdehyde groups into dicarboxyl groups by chlorite treatment seems to improve the acid sensitivity appreciably but cause only a partial stabilization toward alkali. For all types of oxycelluloses a higher D P value is obtained in alkaline solvents after borohydride treatment and this value might be considered as a better representative value of degree of polymerization approaching the real D P value of the oxycellulose sample. To compare the alkali sensitivity of various oxycelluloses, the intrinsic viscosity values for the oxycelluloses as well as the chlorite-treated samples are expressed as percentage of value obtained for the borohydride-treated samples in various alkaline solvents in Table 111. Results in all alkaline solvents of various types are in agreement with each other. Periodate oxycelluloses show maximum alkali sensitivity, the values of
degree of polymerization being only 20 to 30% of borohydridetreated samples. O n chlorite treatment the values increase to only about SOTO,although the residual copper numbers are low. These results suggest that aldehyde groups and carboxyl groups in positions 2 and 3 in the anhydroglucose unit induce maximum alkali sensitivity to the cellulose chain. Samples oxidized by dichromate come next in order of alkali sensitivity and there is no essential difference between oxidations in presence of oxalic acid and sulfuric acid. Oxidations by acid hypobromite and alkaline hypochlorite come next in order of alkali sensitivity and no appreciable change on chlorite treatment is observed. I n case of the remaining oxidizing agents, samples prepared by oxidation under alkaline conditions show practically no alkali sensitivity, as the D P values of oxycelluloses and their chlorite-treated samples are more than 90% of the value on borohydride treatment. I n some cases, the chlorite treatment has a reverse effect and the lowering in degree of polymerization is probably caused by some degradation during the chlorite treatment. T h e presence of carboxyl groups in these oxycelluloses, probably in the G position, formed during alkaline oxidation has no effect on alkali sensitivity. Conclusions
A study of the oxidation products formed by different oxidizing agents has shown that the formation of functional groups in various positions, characteristic of the different oxidizing systems, induces appreciable alkali sensitivity and causes a n apparent lowering in D P value determined in alkaline solvents. Degradation of cellulosic materials during processing or by various agencies such as heat, light, and radiation always involves a n oxidation process as a part of the degradation. During determination of the extent of degradation it would therefore be advisable to carry out degree of polymerization estimations only after treatment of the degraded samples with sodium borohydride. literature Cited
Achwal, W. B., Tappi, in press, 1967. Am. SOC. Testing Materials, Philadelphia, Standards, ASTM D 539-53,1961. Betrabet, S. M., Daruwalla, E. H., Munshi, V. G., Jacob, C. J., J . Abbl. Polvmer Sci.9. 1437 11965). Brown’sktt,T.; Davidson, G. F.‘, J . Textile Znst. 36, T1 (1945). Davidson, G.F.,J . TextileZnst. 32,T109 (1941). Ellefsen, Q.,J . Polymer Sci.C2, 321 (1963). Head, F.S. H., J . Textile Znst. 46, T400, T584 (1955). Jayme, G., Satre, M., Maris, S., Naturwissenschaften 22, 768 (1941). Meghal, S. M., Nabar, G. M., Shenai, V. A.,Current Sci. ( I n d i a ) 33,229 (1964). Meller, A , , Tappi34,171 (1951); 39,722 (1956). Nevell. T.P.. J . Textiie Znst. 39. T118 11948). Rogovin, Z. ’A., Shorygina, N.’ N., Yashunskaya, A. G., Trevias, M. G., Z h . Priklad. Khzm. 22, 857 (1949). Rutherford, H. A., Minor, F. W., Martin, A. R., Hark, M., J . Res. Natl. Bur. Stand. 29, 131 (1942). Sihtola, H., Li4akromol. Chem. 35, 250 (1960). Sihtola, H., Anthoni, B., Virkola, N. E., J . Polymer Sci. 30, 1 (1958). Virkola, N. E., Paperi Puu 40, 367 (1958). RECEIVED for review December 28, 1966 .\CCEPTED July 24, 1967 Research financed in part by a grant from the U S . Department of Agriculture under PL480.
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