HEVEA LATEX SLUDGE Existence of a Sludge Fraction in Fresh Unpreserved Latex E. M. McCOLM,~United States Rubber Plantations, Boenoet, Kisaran, Sumatra
Fresh unpreserved latex contains a heavy fraction or fractions in a concentration of 0.1 per cent (in the case examined). This fraction consists of a mixture of rubber, protein not in colloidal dispersion, and acetone extractables; the latter, a t least in part, are present as separate globules and not in solution in the rubber. When latex is ammoniated, this fraction is colloidally dispersed, either through dispersion of the protein or through the formation of ammonia soaps by reaction with the free acids of the acetone-soluble substances. On ammoniation the fraction therefore disappears. It is of interest that a solid, colloidally undispersed protein, apparently closely associated with a certain amount of rubber (or a t least a rubbery fraction) is produced by the tree during the formation of latex.
UBLOADING LATEXI N XEWYORK
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RUCE (1) recorded the results of analysis of the ash of
certain crude rubbers, among them of evaporated latex. He found the sample investigated to contain 5.8 per cent MgO and 24 per cent Pz06. It is evident that ammoniation of a latex containing such ions would result in the formation of insoluble MgXHaP04.6Hz0. Hauser (3) refers to this phenomenon, stating that the precipitated salt settles t o the bottom of the container. This precipitate, sometimes containing occluded rubber, has been known in the plantation industry as latex sludge and has constituted a fouling problem in storage containers. The presence of a sludge fraction in fresh unammoniated latex, just as it is produced by the tree, has not been generally recognized. Van Harpen (2) concentrated fresh unpreserved latex by centrifuging and, on opening the centrifuge, observed a sludge deposit in the bowl. He records that this sludge darkened rapidly and states that it was rubber-free and friable. 4 s a beginning in a study of latex desludging procedures in this laboratory, a quantity of the sludge was obtained and analyzed. The data obtained are reported here.
Experimental Procedure A quantity of fresh latex was obtained by 7 A. hi. on the day of tapping, immediately diluted with an equal volume of distilled water, and then passed twice through the clarifying bonl of a laboratory Sharples supercentrifuge operating a t about 40,000 r. p. m. A considerable volume of sludge was obtained on the first passage and only a trace on the second, which showed that practically all of the sediment PLANT WHERE L.4TEX IS
1 Present address, United States Rubber Company. North Bergen, N.J.
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temperature in vacuo over sulfuric acid. This portion had
TABLE I. COMPOSITIOS OF SLUDGE FROM FRESH UNPRESERVED a bad odor when removed, indicating bacterial or enzymic
LATEX
Moisture in wet sludge 83.5 % Dry sludge in undiluted latex 0.11 Dry sludge in latex total solids 0.27 1. Acetone ext. of dry sludge 29.5% 2. Rubber content of dry sludge0 36.0 3. Nz i,n extd. residue. based on original dry sludge 3 . 4 4 4. Ns In ext., based on original dry sludge 0.63 5. Protein equivalent t o No. 3 (% N , X 6 . 2 5 ) 21.5 6. Ash in extd. residue, based on original dry sludge 1.5 7. Ash in ext., based on original dry sludge 2.5
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Total 91.0 a Obtained by extracting the acetone-extracted sludge with carbon tetrachloride.
which was removable a t this centrifuging speed had been removed. This sludge was immediately suspended in distilled water, the suspension centrifuged, and the process repeated in order to wash out any latex remaining in the sludge. Inasmuch as the diluted latex had a density of about 0.98, it mas possible that a portion of the sludge could have remained in the wash water if it had had a density slightly below 1.00. To prove this, the washings were treated with one per cent of a proprietary emulsifying agent, sold under the name of Emulphor 0, and then made up to contain 20 per cent by volume of ethyl alcohol. The density of such a solution is near that of the latex, and the Emulphor 0 has been found by experiment to prevent coagulation of the small amount of latex rubber in the washings when alcohol is added, but not to prevent sedimentation of such sludge. This mixture 17-as recentrifuged, but only a trace of sludge was obtained; thus the major portion of this fresh latex sludge has a density greater than that of distilled water, since it sediments out almost entirely if a water suspension is centrifuged. A portion of the wet sludge was dried 8 hours in an oven a t 100” C. to constant weight. The dry material was slightly elastic but very “short”, and resembled highly compounded rubber. Each granule was covered by an oily film, and the surface of the dish in which it was dried was oily. The material was found to be sufficiently rubbery so that it would cohere if milled with the rolls set not too close together. Another portion was evaporated nearly to dryness a t room
action. A third portion was treated while wet with three separate quantities of redistilled acetone, filtered, and dried in vacuo over sulfuric acid. The acetone washings were dried on the steam bath, and the acid number of the residue was obtained. From ash, nitrogen, acetone-extract, and carbon tetrachloride-extract analyses of the first and last portions described above, the composition of this sludge appears to be as shown in Table I. The 9 per cent unaccounted for represents error in the analyses, possible error in the use of the factor of 6.28 for calculating the protein content from the nitrogen content, water lost by dehydration of inorganic bodies during ashing, and possibly a small amount of an unidentified substance. Of the acetone extract, 20.6 per cent was present in the acetone washings of the original l\-et sludge. This was quite oily and had an acid value of 71.25, equivalent to a free acid content, calculated as stearic, of 36.13 per cent. The remaining 8.9 per cent was removed slowly by acetone extraction in a Soxhlet type of extractor and had an acid value of 4.8. This latter portion of the extract was a yellow, waxy semisolid resembling the Hevea lipin described by Rhodes and Bishop (4).It should be noted that Hevea lipin prepared in this laboratory was found t o have an acid value of 2.3, whereas Rhodes and Bishop reported a value of 14. The fresh u-et sludge is rapidly dispersible in dilute ammonia or other alkalies to yield a permanent suspension from which only traces of sediment can be removed by even longcontinued and exhaustive centrifugation. The residue after acetone and carbon tetrachloride extraction is only slightly dispersible in dilute ammonia solution, but is sufficiently so to give a strong biuret test for protein.
Literature Cited (1) Bruce, Trop. Agr., 59, 267 (1922). (2) Harpen, van, Arch. Rubbercultuur, 21, 63 (1937). (3) Hauser, “Latex” (tr. by Kelly), p. 101, New York, Chemical Catalog Co., 1930. (4) Rhodes and Bishop, Rubber Research Inst. Malaya Quart. J., 2, 125 (1930).
Hydrogenation of Lignin in Aqueous Solutions ELWIN E. HARRIS, JEROME SAEMAN, AK’D E. C. SHERRARD Forest Products Laboratory, Madison, Wis.
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N PREVIOUS publications ( I , 2 ) it was shown that
lignin reacted with hydrogen in dioxane solution in the presence of copper chromite catalyst. Recently it was found that nickel catalyst promoted the hydrogenation of lignin in water or in an aqueous alkaline solution or suspension, and thus caused approximately 35 moles of hydrogen for each equivalent weight of lignin (900 grams) to be taken up. The time required for the reaction was short, and it would thus be possible to hydrogenate lignin in continuous hydrogenation equipment.
The lignin, obtained from various sources, such as methanol lignin, Cellosolve lignin, lignin from wood after treatment with sulfuric acid, and lignin from pulping liquor, was converted into a mixture of practically colorless products. These products were varied somewhat, depending on the starting material and the alkalinity of the aqueous suspension medium. When alkali was used, the reaction was more rapid than with water alone; a t the same time, the alkali had the effect of protecting the catalyst from various impurities that may
