INDUSTRIAL AND ENGINEERING CHEMISTRY
1398
from their crystallinity. The higher density crystallinity, hardness, and strength of gutta as compared with rubber can be ascribed to a closer molecular packing in gutta than in rubber.
Conclusions 1. Evaporated latex films and Bolivian fine para contain a chloroform-soluble fraction of about 62 per cent, whereas the soluble portion of crepe and smoked sheets is about 86 per cent. The average molecular weight of these sols, which contain the low polymers and “resin”, range from about 130,000 to 180,000, the more soluble type having the lower value. 2, Diffusion and precipitation methods were employed to fractionate R. C. M. A. crepe, and the following data indicate the approximate composition and molecular weight range of the soluble hydrocarbon fractions separated: Fraction Resins Hexane-acetone Hexane Hexane insol. chloroform sol. Chloroform-idsol. gel protein and ash
+
Mol. W t . Range
.. .......... 9,000-30,000
60,000-160,000 ( 6 ) 160,000-190,000
Content, % ’ 2.7 2.3 50.0 31.0 14.0
.. .. .. .. . ... 3. The chloroform-insoluble portion of crepe contains a nonlinear type of hydrocarbon as judged by x-ray and viscosity studies. These methods also show that the chloroform-insoluble portion of ammonia-preserved latex films contain extremely high-molecular rubber hydrocarbon which is easily oriented to give the regular x-ray crystalline pattern for rubber. 4. Freshly tapped latex contains a large proportion of petroleum-ether-soluble fraction which becomes insoluble in this solvent on standing in the presence of ammonia. Ammonia-preserved latex films are soluble in chloroform or in hexane containing alcohol-acetone or acetic acid; this insolubility is thus an association effect which is overcome by the addition of a polar solvent. 5. Viscosity studies on fractions of balata and gutta-
Vol. 33, No. 11
percha show that their hydrocarbons have an average molecular weight of about 42,000 and cover a narrow polymeric range. Literature Cited (1) Axelrod, S., Gummi-Ztg., 19, 1053 (1905); 20, 105 (1905). (2) Bloomfield, G. F., and Farmer, E. H., J . Inst. Rubber Ind., 16, 69 (1940). Fol, 3 . G., kolloid-Z., 12,131 (1913). Gehman, S. D., Chem. Rev., 26,211 (1940). Kemp, -4.R., and Peters, H., J . Phys. Chem., 43, 923 (1939); Rubber Chem. Tech., 13, 28 (1940). Kemp, A. R., and Peters, H., J. Phys. Chem., 43, 1063 (1939); Rubber Chem. Tech., 13, 11 (1940). Kemp, A. R., and Peters, H., IND. EXG.CaEu., 33, 1263 (1941). Messenger, T. H., TTans. Inst. Rubber Ind., 9, 190 (1933); Rubber Chem. Tech., 7, 297 (1934).
(10) (11) (12) . , (13) (14)
Meyer, K. H., and Mark, H., “Der Aufbau der hochpolymeren organisohen Naturstoffe”, pp. 199, 205, Leipzig, Akad. Verlagsgesellschaf t, 1931. Midgley, T., and Henne, A. L., J . Am. Chem. SOC., 59, 706 (1937); Rubber Chem. Tech., 10,641 (1937). Midgley, T., Henlie, A. L., and Renoll, M.W., J . Am. Chem. SOC.,53, 2733 (1931); Rubber Chem. Tech., 4, 547 (1931). Pummerer. R.. and Pahl, H.. Ber.. 60. 2152 (1927): . . . Rubber Chem. Tech., 1, 167 (1925). Schidromitz, P., and Goldsbrough, H. A., J . SOC.Chem. Ind., 28, 3 (1909). Staudinger, H., Ber., 63, 921 (1930); Rubber Chem. Tech., 3,
.-
556 11930). ,
(15) Staudinger, H., “Die hochmolekularen organischen Verbindungen: Kautsohuk und Cellulose”, Berlin, Julius Springer, 1932. (16) Staudinger,
H., and Bondy, H. F., Ann., 488, 153 (1931); Rubber Chem. Tech., 5 , 275 (1932). (17) Staudinger, H., and Bondy, H. F., Ber., 63, 724 (1930); Rubber Chem. Tech., 3, 511 (1930). (15) Staudinger, H., and Mojen, H. P., Kautsohuk, 12, 121 (1936); Rubber Chem. Tech.. 9. 573 (1936). (19) Vries, 0. de, “Estate Rubber”, Batavia, Rugrak and Co., 1920. (20) Whitby, G. S., Trans. Inst. Rubber Ind., 5, 184 (1929); 40 (1930); Rubber Chem. Tech., 4, 465 (1931).
6,
PRESINTEO before the Division of Rubber Chemistry a t t h e IOlst Meeting of the American Chemical Society, St. Louis, Mo.
Holocellulose from Wheat Straw W. ALLAN SCHENCIC AND E. F. KURT” The Institute of Paper Chemistry, Appleton, Wis.
EVERAL detailed investigations on wood holocellulose
S
have been described since a rapid method for its isolation was published in 1933 (IS). They have shown that the total Carbohydrate component in extracted wood can be isolated unchanged by chlorination and extraction of the chlorolignin with certain organic bases dissolved in alcohol. Since the holocellulose so obtained contains all of the easily hydrolyzable ester constituents (acetyl and formyl groups) and a portion of the methoxyl groups present in the original wood (9, I S ) , it is demonstrated that the cellulose cannot be chemically combined with lignin in wood through either ester or ether linkages. Treatment of the holocellulose with mild hydrolytic agents (1 per cent mineral acids or 2 per cent sodium sulfite solutions) converts the holocellulose into a material comparable with Cross and Bevan cellulose ( I S , 16). Viscosity in cuprammonium solution is higher than that of Cross and Bevan cellulose ( I Y ) , which indicates that the carbohydrate chain lengths in holocellulose are shortened 1 Present
address, Quartermaster Corps, U. S. Army, Washington, D. C.
little if a t all. Therefore, with carbohydrate chains containing glucosidic linkages and with the lignin for the most part concentrated in the middle lamella, it is doubtful that cellulose and lignin are chemically combined in wood through a similar linkage. Further, wood holocellulose pulps hydrate readily and develop maximum physical strengths within a relatively short beating time to give glassine or parchmentlike paper (8). The above significant phenomena made it desirable to extend the study to other natural fibrous materials. The purpose of the present work was to isolate the true holocellulose from wheat straw and to study the papermaking properties of such a cellulose material. Zherebov and Paleev (19) and Paleev ( l a ) reported the isolation of a holocellulose fraction from rye straw. Chemically cereal straws differ from wood in that they have a higher pentosan (xylan) and protein content, a lower percentage of resistant cellulose, and a higher amount of ash which is chiefly silica, and that a portion of the lignin is
November, 1941
INDUSTRIAL AND ENGINEERING CHEMISTRY
UNBLEACHED (left)
AND
1399
BLEACH~D (right) WHEATSTRAW ( x 100)
held to be tenaciously retained by the cellulose (11). It was anticipated that these differences would make the isolation of straw holocellulose more difficult than that of wood holocellulose.
Material Clean wheat straw, of the preceding summer's growth (1939) including stalk and chaff, was passed through a GBsta Hall disintegrator and a microgrinder (Mikrogrinder Company), after which it was screened. The fraction passing a 40-mesh and retained on a 60-mesh screen was taken for further treatment. The straw meal was first extracted for 22 hours with 95 per cent ethanol in a Soxhlet apparatus until the extract was colorless, and then it was air-dried. It was again extracted with hot water and air-dried. For the water extraction 1000 ml. of boiling water were added to 100 grams of straw meal and heated in a boiling-water bath for 1.5 hours". The suspension was then filtered on a Buchner funnel and washed twice with boiling water. This process was repeated three times. Quantitative analytical determinations showed 8.01 per cent soluble in alcohol and 4.24 per cent soluble in hot water, a combined extractive content of 12.25 per cent. The lignin, corrected for ash, was found to be 17.35 per cent of the ovendry weight of the extracted straw. On the same basis, assuming no ash or protein material is lost during the isolation, the theoretical yield of lignin-free holocellulose should be 82.65 per cent (100 - 17.35 = 82.65).
Isolation of Straw Holocellulose Chlorination of the moist straw meal with gaseous chlorine and extraction of the chlorinated material with 3 per cent monoethanolamine in alcohol a t 75" C. under the conditions used for wood analysis (16) gave yields of straw holocellulose from 7 to 17 per cent below the theoretical value of 82.65 per cent. The yields depended upon the number of chlorinations and extractions carried out. I n all cases the cellulose fractions gave a positive monoethanolamine-lignin color reaction and an apparent lignin residue. Since the wood holocellulose procedure when applied to straw removed appreciable amounts of carbohydrate material before all of the lignin was removed, it was necessary
to modify the method. Stepwise chlorination with chlorine water a t consistencies of 1 to 2 per cent to minimize acid hydrolysis was investigated and found to have no advantage. The use of dioxane, which is a better lignin solvent than alcohol, as a diluent for the monoethanolamine effected a better lignin removal but it also had a more degrading effect upon the carbohydrate fraction. The effect of temperature of the lignin solvent upon the yield of holocellulose was next investigated. Extractions carried out a t 20" C., in place of the usual 75", gave consistent results. The procedure used in the subsequent work is as follows: 1.5 grams of extracted straw meal were weighed into a Jena (1G1) crucible, covered with cold water, and soaked for 1 hour. The excess water was removed with suction and
Straw holocellulose has been prepared from wheat straw by a modification of the procedure used for the isolation of wood holocellulose. In general, the relationship of straw holocellulose to the original straw is similar to that found for wood. The acetyl content of straw holocellulose approaches that of the holocellulose isolated from some softwoods. Fibrous straw holocellulose pulp was obtained in 69 per cent yield from raw straw macerated in a rod mill. In contrast to wood holocellulose pulps, the strength of the prepared straw holocellulose developed very slowly on beating. This slow strength development is believed to be caused by the high silica content of the product.
1400
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. 33, No. 11
effect upon the yield of holocellulose for with 1.5 to 2 per cent solutions the yields and the residual lignin were essentially the same as with 3 per cent solutions. Since consistent results approaching the theoretical yields of holocellulose were obtained by extraction a t 20' C., a fraction of straw isolated in this manner was analyzed for its constituents. Eleven chlorinations and extractions produced a white product. The results of the analyses, together with similar analysis on the original extracted straw, are given in Table I. The lignin content of the extracted straw and also of the holocellulose fraction was determined by the 72 per cent sulfuric acid method of Ritter, Seborg, and Mitchell (14). To obtain reproducible results, the SEMICOMMERCIAL PULPING LABORATORY O F T H E INSTITUTE OF PAPER CHEMIBTRY sulfuric acid was cooled to 0" C. before being added to the materials, and the mixture was maintained at the sample chlorinated in an ice-\v.ater-jacketed chlorinator this temperature until all fibrous structure had disappeared (3 It was then held at 20" c. for 2 hours and diluted with hours). for 3 minutes. The sample TT,asremoved from the cillorinator, water, and the determination mas completed in the usual washed twice with cold water (0' C.) and once with alcohol. way. It was then covered with about 75 ml. of a 3 per cent solution Cross and Bevan cellulose was determined by successive chlorinations with gaseous chlorine and extractions with a hot of monoethanolamine in alcohol at 20" C. After 2 minutes 2 per cent solution of sodium sulfite (3). The pentosan, lignin, the solvent was removed by suction and the extraction reand ash contents of the Cross and Bevan cellulose fractions were was then mashed Once with and determined, and the observed percentages corrected for these peated* The three times with cold water. The chlorinations and extracconstituents. tions were repeated the desired number of times. After the last extraction the residue I was washed with alcohol, then with &her, dried, TABLE 11. PHYSICAI. PROPERTIES O F STRAW HOLOCELLULOSE PULP and weighed as holocellulose. With the above procedure the yield of 11010Beating time, min. 0 10 20 30 45 60 90 120 cellulose remained at 79-80 per cent of the ~ ~ ~ $ ~ ~ { ; ~ ~ $ h r i% n k a g e ,. . . . . . 8.4 9.0 9.2 .. 11.6 1 4 . 6 Basis weight .. .. .. 3 63 .. 98 376.. 71 375 .. 18 373 .. 68 .. 383..86 393 .. 85 oven-dry weight of extracted straw. The lignin content, calculated on the same basis, Bursting strength, points/lb. Apparent ... 2 5 . 4 3 5 . 1 42.1 5 4 . 5 82.5 99.4 .0 20.5 17.0 12.5 12.1 reached a minimum value of about 1.7 per Tearing strength, grams/sheet .... . . 2 4 . 87 2 343 Folding endurance, KO.folds 64 64 631 782 cent. Contrast ratio . . . 0 , 4 4 9 0 . 4 9 1 0.482 0 . 4 7 6 0.485 0.448 _ . , 39.2 40.3 40.2 39.5 The yields of holocellulose obtained when g:E?ZEEEifi%tion, screeli lnevh Retained on 20 . . . . . . . . . . . . . . . 1 cold alcoholic solutions of monoethanolamine Retained on 35 . . . . . . . . . . . . . . . 34.4 were used to dissolve the chlorolignin were Retained on 65 . . . . . . . . . . . . . . . 29.8 Retained o n 150 . . . . . . . . . . . . . . . 14.1 essentially the same with nine or twelve chlo. . . . . . . . . . . . . . . 6.1 ... Passed 150 15.3 rinations. Less consistent yields were obI tained with dioxane in place of alcohol, but here also the decrease in yield of holocellulose with additional chlorinations and extractions was The pentosan content of the materials was determined by the not so great as when hot solutions were employed. The Launer modification of Tollen's method ( I O ) . Eronic acid was determined by boiling with 12 per cent concentration of monoethanolamine in alcohol had little hydrochloric acid, and the carbon dioxide liberated was measured gravimetrically. The percentage of carbon dioxide multiplied by four gives the amount of uronic anhydride present (4). Ash was determined by ignition in a muffle furnace. The AND ITSHOLOCELLULOSE TABLE I. ANALYSISOF STRAW FRACTIOT silica in the ash was determined by removing it as volatile silicon tetrafluoride and calculating the loss in weight as percentage of (Based on oven-dry extracted straw) silicon dioxide. Determination Extd. Straw, % Holocellulose, 5% Protein content was calculated from the percentage of nitrogen determined by the, Kjeldahl method. Percentage nitrogen multiplied by 6.25 gives the protein content. Volatile acids were determined by the method of Freudenberg and Harder (7). To confirm the presence of acetic acid, the Cross and Bevan cellulose distillate from the determination mas evaporated to 5 cc. on a 62.0 62.5 Total steam bath, Crystals of sodium formate and uranyl formate 1.07 0.86 Lignin were added, and the formation of pale yellow tetrahedral crystals 1 5 . 4 1 6 . 1 Pentosans 1.92 2.02 Ash of sodium uranyl acetate, which are distinctly visible a t one hun43.6 43.5 Corrected dred diameters, proved the presence of acetic acid. 1.80 1.87 Acetvl 0.61 3.24 Methoxyl The method of Zeisel (6)T T - ~used t,o determine the methoxyl content. 855
775
736
685
670
614
510
405
November, 1941
INDUSTRIAL AND ENGINEERING CHEMISTRY
With the exception of an apparent residual lignin content of 1.7 per cent, the data in Table I show about the same general relationship of straw holocellulose to the original straw as is observed in the case of wood. The lignin content of the Cross and Bevan cellulose is of the same magnitude reported by Norman and Jenkins (11). These workers concluded that a portion of the lignin in straw is firmly held and are of the opinion that i t is derived from pentosan groupings. Experimentally all of the acetyl, silica, uronic anhydride, protein, and a part of the methoxyl are present in the straw holocellulose. This is believed to be the first instance where acetyl groups have been reported in straw. The acetyl content approaches that of the holocellulose isolated from some softwoods. For the purpose of investigating further the apparent lignin residue from straw holocellulose, the methoxyl content of this material was determined on the ash-free basis and compared with that of the lignin isolated similarly from extracted straw. A methoxyl content of 14.7 per cent was found for the straw lignin and of only 3.4 per cent for the lignin retained in the holocellulose. The former figure agrees well with the value of 14.8 per cent reported by Brauns (2) for spruce lignin and of 14.8 per cent found by Beckmann, Liesche, and Lehmann (I) for rye straw lignin. The low methoxyl content of 3.4 per cent for the lignin isolated from the holocellulose indicates a high contamination with materials other than lignin or that it was demethoxylated during the chlorination. On the basis of straw lignin having 14.7 per cent methoxyl, the apparent lignin residue from the holocellulose contains only 23.1 per cent lignin (100 X 3.4/14.7 = 23.1). This amount of lignin in the holocellulose on the basis of the straw is 0.4 per cent (1.7 X 23.1/100 = 0.4).
Papermaking Properties of Straw Lignin Approximately 350 grams of fibrous straw holocellulose pulp were prepared from unextracted straw and evaluated according to standard methods. For uniform chlorination of the straw and to facilitate the extraction of the chlorolignin, the raw straw was macerated in a laboratory-size rod mill for 25 minutes at 12 per cent consistency with the temperature maintained a t 90-95' C. The rod mill had a capacity of 500 grams of dry stock. The weight of the rods was 100 kg. and the rate of rotation was 42 r. p. m. This pretreatment thoroughly broke up the straw but produced a relatively large amount of fines. The fibrous holocellulose was isolated from the above pretreated straw, following the procedure used in the analytical work. After six chlorinations and extractions a white product was obtained in 69.3 per cent yield, calculated on the oven-dry weight of raw material. The pulp retained practically the same form as that of the macerated straw from which it was prepared. The lignin, pentosan, and ash contents were 1.4, 31.1, and 3.2 per cent, respectively, calculated on the oven-dry weight of material. The holocellulose pulp was evaluated according to Standard T 200 m-40 of the Technical Association of the Pulp and Paper Industry. A 1.5-pound Niagara-type laboratory beater with 3600 grams on the bedplate was employed. The freeness of the stock was taken after 0, 5, 10, 20, 30, 45, 90, and 120 minutes with a Schopper-Kegler freeness tester. Hand sheets were formed on a British sheet mold according to T. A. P. P. I. Standard T 205 m-40. The hand-sheet shrinkage a t each time interval was determined as a measure of the degree of hydration of the pulp. This shrinkage is the percentage of decrease in perimeter of a 5-inch (19.7-cm.) square on a pressed hand sheet when it is dried at 104" C. Fiber length distribution was determined on samples taken after 60 and 120 minutes of beating with a Bauer-McNett fiber classifier.
1401
The standard hand sheets were conditioned at 65 per cent relative humidity and 70" F. (21.1' C.) for 48 hours before the basis weight (24 X 36 - 500), caliper, bursting strength, fold (Massachusetts Institute of Technology), tear, brightness (General Electric reflection meter), and opacity (Bausch & Lomb opacimeter) were determined. The results of these tests are given in Table 11. The data reveal that beating properties of this pulp were unusual in that its development was slow. After 120 minutes of beating time, the freeness had dropped only to 400 cc. Over the same time interval the hand-sheet shrinkage indicated that a considerable degree of hydration had taken place. The bursting strength increased slowly; a maximum had not been attained after 120 minutes of beating. Similarly the fold endurance was still increasing after 120 minutes. The tear strength steadily decreased during beating, which indicated that the average fiber length was being shortened. This shortening effect was also shown by the fiber classification. The opacity was never very high and changed little over the total beating period. Because of a rapid color reversion, the brightness of the hand sheets was low.
CHLORINATOR FOR PREPARATION OF HOLOCELLULOSE Reaction crucible Rubber stoppers C . Cold water
A. B.
TWOthings are outstanding in this work. The hydration of the pulp as measured by hand-sheet shrinkage and indicated by opacity was high even with only 10 minutes of beating. The same property as measured by freeness and indicated by strength tests was low. Strength properties which are believed to depend on fiber and fiber bonding were slow to develop. These characteristics are unlike those of spruce holocellulose, which develop rapidly on beating. Possibly the high silica content of this pulp is the cause of the observed difference. Clerc (6),in a discussion of the de Vains process for pulping straw, mentions that for successful results the raw material should not contain over 4 per cent silica. Wells (18) reports that lime-cooked straw pulps, in which very little of the silica is removed, give up water more rapidly than caustic-cooked pulps in which a large part of the silica is removed. In view of the reports of Clerc and Wens, together with the slow strength development observed in
1402
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
this work, it is believed that the presence of silica decreased the water-holding capacity of the straw holocellulose and restricted essential fiber-to-fiber bonding.
Literature Cited (1) Beckmann, E., Liesche, O., and Lehmann, F., 2. C Z ~ Q E WChem., . 34, 285-8 (1921). (2) Brauns, F. E.. J . Am. Chem. SOC.,61, 2120-7 (1939). (3) Bray, M. W., Paper Trade J., 87, No. 25, 59-68 (1928). (4) Burkhart, B.. Baur. L.. and Link, I(. P., J . Bid. Chem., 104, 171-81 (1934). (5) Clark, E. P., J . Assoc. Oficial Agr. Chein., 15, 136-40 (1932). Clerc, J. F.. Paper Trade J., 78, No. 8, 43-7 (1924). Freudenberg, K., and Harder, M., Ann., 433, 230-7 (1923). Houtz, H. H., and Kurth, E. F., Paper Trade J . , 109, No. 24, 38-41 (1939); Hajny, G. J., and Ritter, G. J., Ibid., 111, NO.22, 131-4 (1940).
Vol. 33, No. 11
Kurth, E. F., and Ritter, G. J., J . Am. Chem. SOC.,56, 2720-3 (1934). Launer, H. F., and Wilson, W. K., J . Research Natl. Bur. Standards, 22,471-84 (1939). Norman, A. G., and Jenkins, S. H., Nature, 131, 729 (1933); Biochem. J., 27, 818 (1933). Paleev, .4.M . , B i o k h i m i y a , 1, 654-64 (1936). Ritter, G. J., and Kurth, E. F., IND. ENQ.CHIXVL, 25, 1250-3 (1933). Ritter, G. J., Seborg, R . M., and Mitchell, R. L., IND. ENO. CHEM..ANAL.ED., 4, 202-4 (1932). Van Beckum, 1%’.G., and Ritter, G. J . , Paper Trade J., 105, No.
Flooding of Paints Containing Chrome Greens A. E. NEWKIRII: AND S . C. HORNING Krebs Pigment and Color Corporation, Newark, N. J.
HROME greens are inorganic pigment colors which consist of a lead chromate yellow and an iron ferrocyanide blue. When they are used in paints, the blue usually tends to migrate to the surface of the paint film. This action may result in a surface uniformly darker than the mass of the paint, a mottled pattern due to the blue collecting a t the surface in rafts, or a streaked pattern if the paint has flowed after being applied. Some investigators have distinguished between the uniform and the mottled phenomena by calling the former “flooding” and the latter ‘
