Depolymerization of Cellulose in Viscose Production Effect of Manganese on Depolymerization Rate F. E. BARTELL AND HALE COWLING University of Michigan, Ann Arbor, Mich. Introduction of various metals into alkali cellulose by dissolving compounds of the metal in the sodium hydroxide steeping solution alters the rate of lowering of viscose viscosity with length of time of aging the alkali cellulose. Manganese and iron increase the rate of change of viscosity while copper decreases it. The effect of mangaflese in lowering the viscosity is unexpectedly great. During alkali cellulose formation, manganese originally in the sodium hydroxide becomes concentrated in the alkali cellulose. Manganese so introduced into alkali cellulose increases the rate of depolymerization of the cellulose during the aging process, not only by increasing the rate of oxygen absorption during aging but
H E N alkali cellulose is allowed to age in contact with air a t ordinary temperatures, oxygen is absorbed (9, 8), reacts with the long-chain cellulose molecules, and breaks them into shorter chains. The extent of this depolymerization during aging and during the dispersion of the cellulose as viscose is indicated by the viscosity of the resulting viscose solution. Depolymerization lowers the viscosity. Cellulose impregnated with the oxides or hydroxides of iron, nickel, cobalt, cerium, or vanadium ( I , @ before being steeped in alkali to form alkali cellulose shows an acceleration of the rate of depolymerization of the alkali cellulose. This catalytic action of the introduced metal oxide or hydroxide makes possible a shortening of the alkali cellulose aging period necessary for production of viscose solution of a desired viscosity, or makes possible production of a viscose solution of a lower viscosity with the same time of alkali cellulose aging. Preliminary studies on the effect of introducing minute amounts of iron, nickel, copper, and manganese into alkali cellulose by their addition to the sodium hydroxide solution in which the original cellulose was steeped showed that iron and copper produced effects similar to those observed by others (8, 6), who introduced these metals by impregnation of the cellulose with the metal hydroxides before steeping. The effect of nickel was very small, probably because of the small amount of this metal that could be introduced into the alkali cellulose from the steeping solution in which nickelous hydroxide is only slightly soluble. However, when manganese was introduced by the addition of a trace of manganous sulfate to the steeping solution, it exerted an enormous and opposite effect to that observed by others when manganese was introduced by impregnating the cellulose before steeping. Davidson (3) had found that impregnation of cellulose with manganous hydroxide before steeping greatly decreased the rate of oxygen absorption by alkali cellulose. By determining
also by changing the relation between the amount of oxygen absorbed and the viscosity of the final viscose solution. When manganese is present, a given amount of oxygen causes a greater amount of depolymerization of alkali cellulose during aging, and the greater the manganese concentration, the less the amount of oxygen required to produce a given viscose viscosity. Even with high concentrations of manganese, however, some oxygen appears to be necessary for depolymerization of Cellulose to take place. Manganese affects but slightly the rate of depolymerization of cellulose during xanthation. It has no effect upon the relation between degree of polymerization of cellulose in the final viscose solution and the viscose viscosity.
cuprammonium fluidities he also obtained information which indicated that the rate of depolymerization of the alkali cellulose was greatly reduced by impregnation of the cellulose with manganous hydroxide. Our preliminary studies on the introduction of manganese into cellulose by dissolving it in the steeping solution, on the other hand, showed that manganese had an enormous accelerating effect. The introduction of 2.5 parts per million of manganese into the sodium hydroxide used for steeping the cellulose decreased by 59 per cent the time of alkali cellulose aging required to obtain a viscose with a viscosity of 45 poises. An investigation of this newly observed effect of manganese was carried out in the following steps: 1. A series of alkali celluloses was prepared using sodium hydroxide containing added manganese in amounts from 0 to 20 p. p. m. The relation between the concentration of manganese in the sodium hydroxide and the amount of this metal taken up by the cellulose during alkali cellulose formation was determined. 2. The effect of manganese upon the relation between the age of the alkali cellulose and the viscosity of viscose solution prepared from the alkali cellulose was determined. 3. The effect of manganese upon the rate of absorption of oxygen from air during alkali cellulose aging and upon the relation between oxygen absorption and viscose viscosity was determined. 4. The effect of manganese in alkali cellulose upon the rate of depolymerization of the cellulose occurring during alkali cellulose aging and xanthation was determined by degree of polymerization measurements on cellulose taken a t different stages of the processes.
Preparation of Alkali Cellulose and Viscose The cellulose used was cotton linter pulp. The sodium hydroxide was commercial 50 per cent caustic of high purity
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
608
Vol. 34, No. 5
sodium hydroxide steeping solution as dilute manganous sulfate solution. The steeped alkali cellulose pulp was pressed to three times its dry weight and was then shredded in a nickel-lined, nickel-bladed shredder for one hour at 21 C. AGIKG,XAKTHATION, AND MIXIXG. Samples of shredded alkali cellulose of 130 grams each were sealed in quart Mason jars and allowed to age at 21' C. in a thermostatically controlled water bath. After the removal of 5 grams of each alkali cellulose sample for degree of polymerization measurements, the remaining 125 grams mere xanthated by adding 10.8 ml. of carbon disulfide, resealing the jar, and then rotating it slowly in the water bath a t 21 C. for 3 hours. To the cellulose xanthate was added the proper mixture of water and 18 per cent sodium hydroxide to give a visco~eof 7 per cent cellulose and 6 per cent total alkalinity. The viscose solutions were mixed for 2 hours at 21" C. by rapid mechanical stirring. VISCOSE RIPENING .4ND \rISCOSITY MEASUREMENTS. Since the viscosity of viscose solutions is not constant but varies with age, the viscosity after 40-hour ripening at 21 C. was always used in comparison of effects. Viscosity measurements were made by the falling ball method. O
20
60
I00 120 140 160 180 ALKALI C E L L U L O S E AGE IN HOURS
40
80
FIGURE 1. EFFECT OF MANGANESE ON RELATION BETWEEN VISCOSEVISCOSITY AND ALKALICELLULOSE AGINGTIME
diluted with distilled water. rjickel or glass equipment was used throughout to prevent contamination.
By these procedures a series of viscose solutions was produced in each of eight runs. I n these runs the only variable was the amount of manganese added to the sodium hydroxide steeping solutions. The experimental results are given in Table I.
Relation between Concentration of Manganese in Sodium Hydroxide and Amount Introduced into Alkali Cellulose The data in the second and third columns of Table I show
STEEPING, PRESBING, AND SHREDDING. A 600-gram sample of cellulose pulp was steeped for one hour at 21' C. in 16 liters of 18 per cent sodium hydroxide containing some given concentration of manganese. The manganese was introduced into the
that the concentration of manganese taken up by the alkali cellulose is three t o four times the concentration which existed in the sodium hydroxide solution before steeping. The data in column 3 are expreesed as parts of manganese per million parts of sodium hydroxide taken up by the cellulose.
TABLEI. EFFECTOF MANGANESE O S REL.4TIOS BETWEEN VISCOSE VISCOSITY AND ALKALI CELLULOSE AGIKGTIME
Effect of Manganese on Relation between Viscosity and Aging Time
Run
No.
M n Added t o NaOH, P. P. M .
M n Taken Up by Alkali Cellulose, P. P. hl.
3
0.50
1.8
Sample
Cellulose, Hr.
Age of
Viscose Viscosity after 40 Hr., Poises
A
51.6 67.8 76.6 94.5 118.1
73.0 48.9 40.6 28.5 20.0
50.2 66.5 75.2 93.1 116.8
62.0 43.6 32.7 22.5 15.7
29.6 44.5 54.0 70.9 77.3 92.9
98.2 50.8 35.5 21.6 20.0 13.1
27.7 42.7 52.2 69.1 75.6
74.2 35.6 24.8 15.0 12.9
20.5 26.6 45.6 52.1 71.8
86.0 61.7 24.0 18.9 10.6
20.4 27.6 43.6 50.1 69.8
63.6 45.9 22.2 18.5 10.5
Alkali
No.
B
C D
E 4
1.00
3.6
A
B
C D
E 5
2.50
7.7
A B C D
E F
6
5.00
16
A B C
D
E 7
10.00
31
A
B
C
D
E 8
20.00
63
A B C
D
E
On Figure 1 the viscose viscosity after 40-hour ripening is plotted against the aging time of the alkali cellulose. The data were plotted on log-log paper because straight lines resulted (except curves 7 and 8) from which interpolations could easily be made. Curve 1 represents the decrease of viscose viscosity with age of the alkali cellulose when no manganese was added to the sodium hydroxide. Curves 2 to 8, inclusive, represent the results obtained as the amounts of manganese were increased. The progressive displacement of the other curves from curve 1 shows that very small amounts of manganese change appreciably the relation between viscose viscosity and age of the alkali cellulose. Figure 2 demonstrates even better the effect of manganese upon viscose viscosity. The data mere obtained by interpolation from the curves of Figure 1. Figure 2 shows that the viscosity of the viscose decreases rapidly as the amount of manganese taken up from the sodium hydroxide increases. The viscosity changes most rapidly in the region of the lowest concentration of manganese, and the effect levels off as the amount of manganese taken up by the alkali cellulose becomes progressively larger. The curves for the three different aging times are similar.
Effect of LManganese on and Activity of Oxygen Absorption The results described above showed that manganese had an enormous effect upon the rate of depolymerization of cellulose. Since this depolymerization has been considered to be due mainly to the breaking up of long-chain cellulose molecules by the action of oxygen (3, 8),a detailed study of the effect of manganese upon the oxygen absorption of alkali cellulose during aging in air was undertaken.
May, 1942
INDUSTRIAL A N D ENGINEERING CHEMISTRY
609
the absorbed oxygen in the depolymerization of the cellulose, or to some other unexplained effect of the manganese. Experiments were undertaken to obtain more information on this effect of manganese.
EFFECTOF AGINU IN NITROGENON VISCOSE VISCOSITY. To determine whether any depolymerization of the alkali celluloqe was attributable to an acceleration by the manganese of some depolymerizing reaction, such as hydrolysis, which did not require oxygen, experiments were carried out
OF MAKGANESE IN ALKALI FIGURE 2. EFFECT CELLULOSE UPON VISCOSEVISCOSITY
MEASUREMENT OF OXYGENABSORPTION. The rate of oxygen absorption of the eight alkali celluloses was determined by sealing a 130-gram sample of each in a quart jar equipped with a differential mercury manometer made of 3mm. capillary tubing. The change in pressure as well as the normal barometric pressure was noted from time to time during the aging of the cellulose a t 21' C. Knowing the volume of air enclosed in the jar, it was possible to calculate the amount of oxygen absorbed per 100 grams of alkali cellulose during any time interval. EFFECT OF MANGANESE UPON OXYGENABSORPTION.The results obtained by measuring the rate of oxygen absorption from air for the eight alkali celluloses containing different amounts of manganese are given in Table I1 and Figure 3. The times recorded are the alkali cellulose aging times less a 1.5-hour period required for the sample t o come to a constant temperature of 21' C. The data show that, as the amount of manganese absorbed by the alkali cellulose is increased, the rate of oxygen absorption by the alkali cellulose likewise increases. Figure 4 indicates that, as the manganese content of the alkali cellulose is increased, the amount of oxygen absorbed increases rapidly at first and then the effect levels off. The data for Figure 4 were obtained by interpolation from the curves of Figure 3. EFFECT OF MANGANESE ON RELATION BETWEEN OXYGEN ABSORPTION AND VISCOSITY. On Figure 5 viscose viscosity is plotted against the volume of oxygen absorbed by the alkali cellulose from which the viscose solutions were prepared. The data were obtained by interpolation from Figure 3. The curves show that the relation between oxygen absorption and viscose viscosity is dependent upon the amount of manganese taken up by the alkali cellulose. As the manganese content of the alkali cellulose is increased, the amount of oxygen required to produce a viscose of a given viscosity is reduced. The effect of manganese on viscose viscosity is thus shown to be due not only to an acceleration of oxygen absorption, which was anticipated from the first part of this research, but also either to a n increase of the effectiveness of
FIGURE 3. EFFECT OF MANGANESE ox OXYGEN ABSORPTION BY ALKALICELLULOSE DURING AGING
TABLE11. EFFECTOF MANGANESEON RATE OF OXYGEN ABSORPTION BY ALKALICELLULOSE Run
No. 1
Alkali Go. 0 2 Cellulose Absorbed/100 0. Age, HI. Alkali Cellulose 0 0 17.9 5.0 26.7 7.4 39.4 10.7 50.9 13.5 63.1 16.3 76.2 19.2 24.8 101.8 27.7 115.6 33.8 141.0
0 20.4 26.6 31.8 44.5 56.9 68.0 93.7 0 9.7 19.8 31.9 46.0 57.9 70.0
0 6.9 9.2 11.3 16.4 21.9 26.5 37.5 0 2.5 6.4 12.0 19.5 26.6 33.8
Run
No. 2
Alkali Cellulose Age, Hr. 0 16.3 24.5 37.0 49.1 60.8 74.3 99.5 113.7 138.6
Go. 0 2 Absorbed/100 G. -4lkali Cellulose 0 5.2 7.3 10.8 14.2 17.2 20.8 26.9 30.1 35.9
0 18.8 24.5 30.1 42.6 55.2 66.0 92.0 0 7.9 17.7 30.2 43.8 56.1 67.8
0 7.3 10.0 12.5 18.4 24.8 30.7 44.5 0 3.0 7.2 13.8 20.7 28.3 36.1
610
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 34, No. 5
TABLE 111. EFFECT ON VISCOSEVISCOSITY OF AGINGOF ALKALI CELLULOSE IN SITROGEN Viscose Visoosity after 40 Hr., Poises 64.6 50.3 49.3 49.3 50.2
Hr. of Alkali Cellulose Aging i n Nitrogen 0.5 23.2 47.0 71.5 96.4 ~~
It seems evident that a t the beginning of the experiment all the oxygen had not been removed from the alkali cellulose, but that a small quantity of it was still available for depolymerization. This small quantity mas used up during the first 24 hours, and since no more oxygen was available, depolymeriyuu&o
0
30 40 50 60 10 20 PARTS O f MANGANESE PER MILLION PARTS OF NaOH IN ALKALI CELLULOSE
1
1
20
40
P.P.M. M r I N A L K A L I CELLULOSE
1 I
800
FIGURE 4. EFFECT OF MANGANESE IN ALKALI CELLULOSE ON OXYGEP; ABSORPTION
z 700 0
on the aging of alkali cellulose in nitrogen. A batch of alkali cellulose was prepared with 2.5 parts of manganese per million parts of sodium hydroxide in the steeping solution. Samples (130 grams) of this alkali cellulose were placed in quart jars equipped with lids that had stopcocks sealed into them. The samples were aged in an atmosphere of air for about 40 hours. The jars were evacuated and then filled with nitrogen. This process was repeated five times. The aging of the alkali cellulose was continued in the nitrogen atmosphere, and daily for 4 days one sample was dispersed as viscose in the usual way and the viscose viscosity was determined. The data obtained are given in Table 111. They indicate that during the first hours of the alkali cellulose aging in nitrogen there was an appreciable amount of cellulose depolymerization, but that after the first 24 hours in the nitrogen atmosphere no further depolymerization occurred.
100
5
I
I
t-Q
N
5 600 f _I
a 0
"0 500 Y
cr w
g400
0
! 60
80
I00
120
TIME I N HOURS
FIGURE 6. CHANGESIN DEGREEOF POLYMERIXATION OF CELLULOSE DURING VISCOSE PRODUCTION
zation did not continue. Upon the evidence of this experiment i t seemed reasonable to conclude that cellulose depolymerization did not occur in the absence of oxygen, and, therefore, that no other effects, such as hydrolysis, were active in bringing about the depolymerization of the cellulose during alkali cellulose aging a t 21' C. Since manganese reduces the amount of oxygen necessary to depolymerize cellulose, and since depolymerization apparently does not occur without oxygen, manganese in alkali cellulose must increase the effectiveness of the absorbed oxygen in depolymerizing cellulose.
Rate of Cellulose Depolymerization during Alkali Cellulose Aging and Xanthation
FIGURE5 . EFFECTOF MANGANESE ON RELATION BETWEES OXYGEN ABSORPTIONAND VISCOSE
VISCOSITY
The oxygen absorption measurements described above were not conducted so as to yield information on the influence of manganese on the extent of cellulose depolymerization during xanthation (4). Neither had the work shown to what extent viscose viscosity is dependent on the degree of polymerization of the cellulose in the viscose. Measurements of degree of polymerization mere therefore made on two series of celluloses. The first sample of each series, S, was taken from the alkali cellulose a t the beginning of the aging process. Other samples in each series were taken just before alkali celluloses A, C, and E were xanthated. Samples of cellulose derived from the viscose produced from samples A, C, and E were also taken. The first series was for run 1 (Table I) where no manganese was added. The second series was for run 5 (Table I) where 2.5 parts of manganese per million parts of
61P
INDUSTRIAL A N D ENGINEERING CHEMISTRY
May, 1942
4 5 400 0
IO
15
20
25
30
C C OF OXYGEN ABSORBED BY 100 G. ALKALI CELLULOSE
FIGURE7. RELATIONOF OXYGEN ABSORPTION FIGURE8. RELATIONBETWEEN VISCOSE VISBY ALKALI CELLULOSE TO DEGREE OF POLY- COSITY AND DEGREEOF POLYMERIZATION OF MERIZATION OF CELLULOSE IN ALKALICELLULOSE CELLULOSE IN VISCOSE
sodium hydroxide in the steeping solution introduced 7.7 parts of manganese per million parts of sodium hydroxide into the alkali cellulose. The determinations of degree of polymerization were made by Staudinger’s viscosity method (7) using cuprammonium solution as the solvent for the cellulose. The specific procedures of Lottermoser and Wultsch (6) were followed with slight modification. The degree of polymerization was calculated from the specific viscosity data by use of the proportionality factor determined by Kraemer (6). The results of degree of polymerization measurements are given in Table IV. On Figure 6 for the two runs, time is plotted against degree of polymerization as the dispersion process is carried from linter pulp to viscose solutiod. The drop in degree of polymerization from 0 to S represents the depolymerization that occurs during steeping, pressing, shredding, and during the 1.5 hours necessary to bring the sample t o constant temperature. Since the degree of polymerization of the two S samples is practically the same, the manganese up to this point in the process has exerted no appreciable effect. The decrease in degree of polymerization during alkali
cellulose aging is represented by those portions of the curves from S to A for the A samples, S to C for the C samples, and S to E for the E samples. The marked divergence of these portions of the two curves shows that the presence of the manganese increased the rate of change of degree of polymerization of the cellulose with time. The decrease in degree of polymerization of the alkali cellulose during xanthation and solution of the cellulose xanthate to produce viscose is represented by the curves from A to A’, C to C’, and E to E’ for samples A, C, and E, respectively. These curves show that in both runs the depolymerization of the cellulose during xanthation was much more rapid than during alkali cellulose aging, but that manganese had practically no effect upon the rate of depolymerization. The total amount of depolymerization during xanthation is relatively small because the xanthation time is short. The data on the change of degree of polymerization during xanthation appear in the last column of Table IV.
RELATION BETWEEN DEQREE OF POLYMERIZATION AND OXYGENABSORPTION.The effect of manganese upon the relation between degree of polymerization and oxygen absorption by alkali cellulose is shown graphically on Figure 7 .
TABLE IV. DEGREE OF POLYMERIZATION CHANQES ‘IN CELLVLOSE DURINGVISCOSEPRODUCTION^ Run No. 1
5
Mn Added t o NaOH, P. P. M. 0.00
2.50
Mn Taken Up b y Alkali Cellulose, P. P. M. 0.00
7.7
Sample No. S A C
E S A C
E
Age of Alkali Cellulose. Hr.
Viscose Viscosity after 40 Hr., Poises
1.5 65.4 84.0 116.5
9i:3
64.4 39.0
16:4 20.6 27.8
1.5 29.6 54.0 77.3
9i:2 35.5 20.0
9:9 20.0 30.0
Cc. On Absorbed/ 100 G. Alkali Cellulose
a The degree of polymerization of cellulose in linter pulp was found to have a valu@of 874. b D. P. (degree of polymerization) signifies the number of glucose residues per molecule.
Degree of Polymerization of Cellulose from: Alkali cellulose Visoose 832 546 518 474 840 577 476 420
..*
Decrease in D . P . b during Xanthation
..
498 463 425
48 55 49
bib
67 5s 40
418 380
..
612
INDUSTRIAL AND ENGINEERING CHEMISTRY
These curves indicate that less oxygen is required to decrease the degree of polymerization by a given amount when manganese is present than when it is absent. The data also show that the introduction of manganese into alkali cellulose by adding it to the sodium hydroxide steeping solution not only increases the rate of absorption of the oxygen of the air by the alkali cellulose, but also makes it possible for the oxygen to cause more breaks in the long-chain cellulose molecules than occur in the absence of manganese. RELATIONBETWEEN VISCOSEVISCOSITYAND DEGREEOF POLYRIERIZATION O F CELLULOSE I N VISCOSE. On Figure 8 viscose viscosity is plotted against degree of polymerization of cellulose for viscose solutions produced with and without manganese. Since the relation is not altered by manganese, i t is evident that manganese exerts its effect on viscose viscosity solely through degree of polymerization changes in the cellulose before its solution as viscose. The enormous effect of manganese on viscose viscosity is thus shown to be due almost entirely t o acceleration of the rate of depolymerization of the cellulose during alkali cellulose aging.
Vol. 34, No. 5
Acknowledgment The authors wish to acknowledge their indebtedness for the valuable assistance and financial support given by The Michigan Alkali Company who made this work possible as part of its contribution to the rayon industry.
Literature Cited (1) Courtaulds, Ltd., and Wilson, L. P., Brit. Patent 14,675 (June 18, 1914). (2) Courtaulds, Ltd., and Wilson, L. P., Swiss Patent 71,681 (Fob. 1, 1916). (3) Davidson, G. F., J . TeztileInst., 23, 95T (1932). (4) Heuser, E., and Schuster, M., Cellulosechem., 7, 17 (1926). (5) Kiaemer, E. O., IND. ENQ.C H ~ M30, . , 1200 (1938). (6) Lottermoser, A,, and Wultsch, F., Kolloid-Z., 83, 180 (1938). (7) Staudinger, H., Trans. Faraday Soc., 29, 18 (1933). (8) Weltzein, W., and zum Tobel, G., Seide, 32, 371 (1928). THE material presented in this paper is from a dissertation submitted b y Hale Cowling to the Horace H. Rackham School of Graduate Studies of t h e University of Michigan in partial fulfillment of the requirements of t h e degree of doctor of philosophy.
Solvent Extraction of Tung Oil W. GORDON ROSE, A. F. FREEMAN, S. MCKINNEY
Bureau of Agricultural Chemistry and Engineering, U. S. Department of Agriculture, Washington, D. C.
AND R.
EGETABLE oils are chiefly obtained by expression or by extraction with solvents. The latter method is used extensively in Europe, but has been employed in this country for the extraction of soybean oil and for the extraction of corn oil from dried distillery residues. The plants in the United States for the production of tung oil utilize the expression principle and employ presses of the expeller type. The resulting oil is of high quality and requires no refining, other than filtering. The residual oil in the expeller press cake usually approximates 5 per cent. The oil in the press cake can be reduced t o about 4
V
0
FIGURE1. LARGE LABORATORY EXTRACTOR
per cent with a resulting decrease in the capacity of the expeller; conversely, it is possible to increase the capacity of the expeller by leaving more oil in the press cake. The 1940 tung crop amounted to about 30,000,000 pounds of fruits that yielded approximately 5,000,000 pounds of oil. The oil discarded in the press cake was probably in excess of 250,000 pounds. Because of the increased acreage now entering production, future yields of tung oil will be much greater, except in years when frost injury decreases the crop. Therefore, the solvent extraction of tung oil was studied with the idea of removing the oil more completely from the oil-bearing seeds. A large size laboratory extractor having a capacity of about 35 pounds of ground kernels was assembled. The extractor was similar to that described by Drake and Spies ( I ) , and is illustrated in Figure 1. The material to be extracted is placed in A , a 22-liter, three-necked flask having an outlet tube sealed to the bottom for return of the solvent-oil solution to the three-necked, 22-liter flask, B , which serves as a solvent reservoir. Solvent is vaporized in flask B by steam and is partially condensed in the glass Friedrichs condenser, D. Solvent vapor not condensed in D is condensed in the metal condenser, C. Condensed solvent from C and D permeate the material to be extracted in A; the solvent-oil solution is intermittently siphoned into B. Extraction of tung kernels ground in grinders of the meat grinder type gave a marc that contained 8 to 10 per cent of oil. Attempts to decrease the amount of residual oil in the marc by grinding the kernels in an experimental flouring mill gave an oily, mucilaginous paste that was not readily handled and still retained 6 to 8 per cent oil in the marc. Complete extraction of the oil from tung kernels has been obtained only by removing the solvent from the marc, followed by regrinding and a second extraction with solvents. Because of the inability to grind tung kernels so that all the oil could be removed by one extraction, it appeared desirable to study also the solvent extraction of tung press cake t o recover the residual oil from the expression process.
