Studies on the Yellow Fraction of Latex G. E. VrlN GILS Indonesian Rubber Research Institute, Bogor, Indonesia
T
HE investigations described in this paper are part of the
highspeed De Lava1 or Sharplcs centrifuge. They are found 011 the walls of the centrifuge bowl as a butterlike niass ( 4 ) . Owing t,othe small size, separation is possible only by high-speed centrifugation. The existence of lutoid remnants i n niiimoniated latex has also been mentioned by Ruinen ( 6 ) . Another indication of the existence of undissolved lutoids in ammoniated latex is the following: Homans has made a large number of viscositj- determinations of ammoniated field latex and of the white fraction prepared from this latex. By calculating the voluminosity ( = 1'8) from theee figures it was found that, the BR of ordinar!, iimmoniated latex is much higher than the V Eof ammoniated white fraction latex ( 7 ) . The voluminosity is defined as the ratio between the rheologically active volume of the dispersed phase and the volume as determined by analytical means. I n other words, besides the rubber phase there must be another phase present which contributes to the viscosity of ammoniated latex as well. The importance of this fact for processes involved in the concentration of latex is only indicated here.
studies on fresh latex carried out a t the I S I R O (Indonesian Rubber Research Institute). For readers not acquainted with the special subject, i t may be useful to mention that Homans and Van Gils ( 2 , 3) have found that fresh Hevea latex is not solely a dispersion of rubber globules in an aqueous medium, the serum. but that there are also present large colloidal jellylike bodies or agglomerations of them, constituting a separate phase in the rubber dispersion. These bodies were called lutoids by the discoverers, because they contained the yellow coloring matter of the rubber. Under a microscope, however, these lutoids look like clear, transparent islands against a darker background of rubber particles.
2
4
10
ADDITION OF WATER
P N P O T A S S I U M CHLORIDE, M L . PER 10 M L . O F L A T E X Figure 1. Reduction of Volume of the
In contrast t o the addition of ammonia, the addition of water stiffens and immobilizes the lutoids. If latex is diluted with water, one expects the viscosity- to be lowered owing to the decrease of the D.R.C. (dry rubber content). However, the first effect observed is an increase of the viscosity as can be seen from the following experiment:
Yellow Fraction by Addition of Salts
After centrifugation, the lutoids are separated a t the bottom of the tube and look like a viscous, yellowish, jellylike mass, containing a low percentage of rubber. It is also possible to separate this mass by other means. As a whole, these agglomerations of lutoids are called the yellow fraction. The remaining latex is called the white fraction. Investigations carried out a t the Rubber Research Institutes in Indonesia and llalaya have shown that the lutoids are responsible for many phenomena occurring in fresh latex. Recent studies of Ruinen (6) seem to indicate that the lutoids are also involved in the rubber formation in the tree.
Water Added t o 5 0 h l l . Latex, 3I1.
21.2 21.7 22.8 23.0 25.2 30.7 Not measurable with capillary \. isco&iieter
0 0.5 1 2 4 8 1:
DISSOLUTION O F THE LUTOIDS
Latex:
According to the previous investigation mentioned, the lutoids dissolve completely on addition of ammonia t o latex. They become invisible under the microscope and can no longer be separated by centrifugation in tubes. However, i t has now been established that this dissolution is only partial and that an undissolved part is dispersed into small round globules of semisolid consistency. On careful examination in a microscope with high magnification the author saw that the rubber globules were not regularlv distributed throughout the space, but that there were small empty spots between them. Brownian movement of the particles interfered with these observations. xIn very thin layers, however, these empty spots are easier t: to observe and then they look like round globules, or droplets 3 to lop in diameter. Pressing down the coverglass by means of a clamp causes these globules to increase in size. These phenomena are not discernible in centrifuged latex. Thes- round globules can be separated by centrifuging with a
D.R.C
Viscosity a t 30' C., Centipoises
=
36.8%;
T.8. (total solids)
=
39.ZYO
In connection with the mentioned phenomenon, the author observed that after dilution, the separation of the yellow fraction by centrifugation was nearly impossible. When the dilution is accompanied by mechanical treatment, stirring, or, even better,
I
P
452
Figure 2.
SALT, M E Q . PER LITER OF L A T E X Influence of Salts on the Viscosity of Latex
February 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
rolling in a ball mill, the lutoids are forced to cohere thus forming agglomerates and even clots. After some time the whole yellow fraction can be separated as one coherent coagulum. When a current of air is Passed through the latex, the lutoids move UPM’ard with the air bubbles and separate in the foam. DISSOLUTION OF THE LUTOIDS BY SALTS
Originally it was believed that the lutoids would remain the same if the latex was not diluted with water but with a solution of about the same ionic strength as the latex itself.
453
Quantitative considerations have shown t h a t the drop in viscosity cannot be accounted for by the reduction of the volume of the yellow fraction. The answer to this problem of reduced viscosity is found by investigating the white fraction. I n Figure 5 i t is seen t h a t if salt is added to the white fraction of latex, the viscosity is decreased in the same way as with ammonia. Therefore, in the author’s opinion, the coazervate which dissolves in alkali as well as in salt solutions not only constitutes a part of the yellow fraction, but every rubber particle is enveloped with a coating of these coazervates causing the rubber particles to agglomerate and hinder their Brownian movement as may be observed by microscopic examination. Through the addition of alkali or salts the rubber particles are decoated and entirely free to move. TECHNOLOGICAL ASPECTS
I n ordinary estate practice, latex is coagulated after dilution with formic acid. Usually an amount of 4 grams of formic acid per kilogram of rubber is needed. , -7LICL * It is known that by addition of only a quarter of SALT, MEQ. PER LITER OF L A T E X this amount and subsequent stirring the so-called yelFigure 3. Influence of Salts on the Yellow Fraction Volume low precoagulum is formed which is Of the yellow fraction plus a certain amount of adhering white fraction rubber. The rubber obtained after discarding Indeed, i t is possible to make the dilution-for instance, with a the precoagulum is very white and can be worked up t o 0.1 N potassium chloride solution-and still obtain a separation “sole crepe.” The precoagulum gives an inferior quality of the yellow fraction after centrifuging. However, if a certain of rubber. However, if the precoagulation could proceed amount of yellow fraction is redispersed in a salt solution and in such a way t h a t the amount of precoagulum is as low as again centrifuged, a smaller volume is obtained. By repeating possible, this would be an advantage. The author has shown that the procedure, the volume obtained after each separation dethis effect is obtainable through addition of salt to the latex creases. Different salts in varying concentrations and also a combination of primary and secondary phosphates of the same pH as the original latex have been tried in the author’s laboraAMMONIA, G R A M S PER LITER OF L A T E X tory but there was no success in obtaining a yellow fraction ‘[washed out” and in equilibrium with the salt solution. It appears that neutral salts dissolve certain parts of the yellow INFLUENCE OF PH fraction, the amount dissolved depending on the strength of the ON THE VISCOSITY OF I N F L U E N C E OF NH3 AND KCL salt solution. This will be made clear by Figures 1 and 3 showing F R E S H LATEX ON T H E VISCOSITY OF FRESH LATEX the volume of tJheyellow fraction reduced by increasing amounts (ORC=36.9%) t of sodium, lithium, ammonium, and potassium chlorides; sodium sulfate; sodium nitrate; and sodium phosphate. Y Salts with divalent cations have a coagulating effect on the > 15t yellow fraction and are therefore not taken into consideration. The following phenomena are also remarkable: PH 1, The yellow coloring substances of the latex do not dissolve b u t remain in the yellow fraction. Sometimes these substances separate in a ring a little below the boundary of the yellow fraction (see Figure 1). 2 . The addition of salts also reduces the viscosity of the latex considerably. Even lower viscosities are attainable in this 3 25 50 75 100 way than by addition of ammonia (Figure 4). P O T A S S I U M CHLORIDE, M E Q . PER LITER OF L A T E X DISCUSSION Figure 4. Influence of Various Factors on the Viscosity of By examining the curves in Figures 2 and 3, the author has Fresh Latex tried to find some regularity-as, for instance, the influence of the lyotropic series-but he has not succeeded. However, this dissolution by neutral salts is no uncommon pheAMMONIUM, G R A M S PER LITER O F L A T E X nomenon in colloid chemistry. By the interaction under #,,O 1 2 3 4 5 6 7 8 9 10 11 12 proper conditions of hydrophylic colloids of opposite electric charge, so-called complex coazervates may be formed (1). Under the microscope these complex coazervates are very similar in appearance to lutoids. Moreover, on addition of neutral salts, the coazervates are dissolved owing to the removal of the electric charge of the colloids. I 25 50 75 100 It seems reasonable to assume, therefore, that the lutoids P O T A S S I U M CHLORIDE, M E O . PER LITER O F L A T E X consist partly of so-called tricomplex coazervates, constituted out of negatively charged protein and lipoid, and Figure 5. Influence of Ammonia and Potassium Chloride on positively charged magnesium ions. the Viscosity of the White Fraction of Latex (DRC = 44.0%)
L
a 1
P ’b
INDUSTRIAL AND ENGINEERING CHEMISTRY
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before diluting and acidifying. As the yellow coloring matter is not dissolved, the precoagulum contains all the coloring matter that has t o be discarded. A second mode of operation is the following: i t is not necessary to discard the yellow fraction by partial acid coagulation. If the latex can be kept liquid for a t least 20 hours, the heavier lutoids will settle down to a more or less coherent layer a t the bottom of the vessel if a sufficiently low viscosity is provided. The author has been successful in obtaining the result indicated by purposely adding salts and O.lyoformaldehyde to the latex. LITERATURE CITED
(1) Bungenberg de Jong, H. G., see H. R. Kruyt, "Colloid Science 11, Chap. X, Amsterdam, Elsevier Publishing Co., 1949.
Vol. 45, No. 2
(2) Homans, L. N. S., and Van Gils, G . E., Arch. RubbercuEt. Ned.I n d i e , 27, 229 (December 1950). (3) Homans, L. N. S., and Van Gils, G. E., Proceedings of the
(4)
(5) (6) (7)
Second Rubber Technology Conference, edited by T. R. Damson, pp. 292-302, W. Heffer & Sons, Ltd., Cambridge, England. McColm, E. M., IND.ENG.CHEM.,3 2 , 4 3 9 (1940); Rubber Chem. and Technol., 13, 517 (1940). Ruinen, J., Ann. bogoriensis, 1, 27-46 (1950). Ruinen, J., and Homans, L. N. S., Arch. Rubbercult. Ned.-Indie, 27, 243 (December 1950). Van Gils, G. E., Ibid., 29, 81 (1952).
RECEIVEDfor review March 13, 1952. ACCEPTEDNovember 11, 1952. Presented as part of the Symposium on Latex, Natural a n d Synthetic, before the Division of Rubber Chemistry a t the 120th Meeting of t,he A&iERICAN CHEMICAL SOCIETY,September 3-7, 1951, New York, N. Y . This is Communication 83 of the Foundation Indonesian Rubber Research Institute ( I N I R O ) , Bogor, Indonesia.
Ternarv Solubilitv Data for Svsterns Involving 1-Propanol and Water J
J
J
J. F. MCCANTS, J. H. JONES, AND W. H. HOPSON Stanolind Oil and Gas Co., Tulsa, Okla. ITHIK recent years, the production of oxygen-containing chemicals by the oxidation of light hydrocarbons and as by-products from the synthesis of liquid fuels has become increasingly important. The use of hydrocarbons as azeotroping agents in the separation and drying of these oxygenated chemicals has also been widely investigated. These advances have necessitated a knowledge of the equilibria that exist among the osygenated chemicals, hydrocarbons, and water. I n this papw are presented equilibrium data a t 100" F. for the ternary liquid systems of 1-propanol and water with n-hexane, n-heptane, benzene, and 1-butanol. Each of these ternary systems contains one partially miscible and two miscible liquid pairs. The method of obtaining the binodal curves was essentially that described by Washburn and coworkers ( 7 ) . The nirthod consists of titrating the third component into known, hornogcneous binary mixtures to the cloud point. The binary mixturps of the consolute liquids were placed in a constant temperature bath a t
-
100' F. and titrated with a third component a t about the sanie temperature. As the cloud point was approached, each sample was agitated in the constant temperature bath for several minutes between drops of the third component. The temperatures of these systems were raised or lowered slightly (1' F.) to obtain homogeneity and their refractive indices were measured to within =kO.OOOl unit by the use of a Bausch and Lomb Precision refractometer. The tie lines were determined in general by the following procedure: h ternary mixture whose composition was well within the two-phase region was prepared and intermittently shaken for several hours in a constant temperature bath a t 100' F. The two phases were then carefully separated and their refractive indices were determined. The intersections of the tie lines with the binodal curve were then determined by refractive index interpolations between the points of known composition used to define the curve. I n all systems, the general slopes of the tie lines were checked by determining one or more tie lines by the graphical application of the lever rule as outlined by Othmer ( 3 ) . In
A
n PROPANOL Tie line intersections by: Refractive index Lever rule
Tie line intersection a s by refractive index
--0 BY TITRATION
60 A
0
4 0/
$ a F O$ R TIE h 6 LINES 0
OPOINTS BY TITRATION @POINTS FOR TIE LlNES
Figure 1. System 1-Propanol-Water-1-Butanol at 100 O F .
Figure 2. System 1-Propanol-Water-Benzene at 100' F .
