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INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 32, NO. 8
six remaining oils are various lubricating grades sold under the SAE 30 rating. The good agreement of aniline point us. volume increase is indicated b y the curves. From preliminary work on vegetable oils, it appears t h a t the aniline points of nonhydrocarbon oils cannot be compared with the aniline points of mineral oils to determine the relative swelling effect. Fraser (2) pointed out t h a t with commercial neoprene vulcaniaates maximum swelling may be followed by a shrinkage in volume due to extraction of oily or waxy materials from the neoprene compound by the oil under test. Contraction is noted in Figure 2, C, D, and E , where oils known to have a low swelling effect have actually caused a shrinkage in volume. This is particularly true of those synthetics which are least affected by oil and which contain extractable material.
3. The aniline point, determined a t a concentration of equal parts of aniline and oil by weight, appears to be a characteristic of mineral oil which will indicate the probable swelling effect on synthetic rubber compounds. The 50 per cent aniline point is more conveniently determined than is the gravity index and appears to be a t least equally reliable. 4. The viscosity rating of a mineral oil is not a satisfactory criterion of its tendency to swell rubberlike compositions and should not be the sole description of a n oil for acceptancc specification testing of synthetic rubber products.
Conclusions
Literature Cited
1. There is a marked difference in the swelling caused by different mineral oils on compounds made of any synthetic rubber, such as neoprene, Thiokol, or Perbunan; the arrangement of the oils by swelling effect tends to remain the same for the synthetic compounds tested. 2. The change in volume is rapid on initial immersion and then gradually approaches equilibrium, except in the case of those systems where marked swelling is encountered.
Acknowledgment The authors wish to thank F. &I. Gavan for obtaining n i m y of the data and charting them.
Am. SOC.Testing Materials Standards Year Book, Pt. 3, p. 837, Designation D471-37T (1939). (2) Fraser, D. F., IXD.ENG.CHEM., 32,320 (1940). (3) Fuchs, G. H., and Anderson, A. P., Ibid., 29, 319 (1937). (4) Gardner, H. A., and Sward, G . G., “Physical and Chemical E x amination of Paints, Varnishes, Lacquers and Colors”, 9th ed., p. 417, Washington, D. C., Inst. of Paint and Varnish Research, 1939. ( 5 ) Hill, J. B., and Coats, H. B., ISD. EKG.CHEM.,20, 641 (1928). ( 6 ) McCluer, W. B., and Fenske, M. R., Ibid., 24, 1371 (1932). (1)
HEVEALATEX Correlation of Nitrogen and Ash with Total Solids Content J. MCGAVACK AND C. E. RHINES, United States Rubber Company, Passaic, K.J.
T
HE purpose of this paper is to report primarily the correlation of nitrogen and ash with the total solids of Hevea latices. I n addition i t is desired to show t h a t the nitrogen in the rubber, prepared by acid coagulation, is dependent upon the original total solids content of the latex. A further purpose is to show t h a t the residual nitrogen adsorbed, dissolved in, or directly associated with the rubber phase has a constant value independent of the concentration of nitrogen in the aqueous pliase. It is believed t h a t the proper knowledge of such relations will be helpful in the preparation of better crude rubbers. Arisa (1) made a study of the nitrogen content of latex. His work was directed to observing the change in the nitrogen content of latex as influenced by the use of various systems of tapping, both with regard to time and location of the cut. His results indicate t h a t there is a relation between the total solids content and the nitrogen value. Using his data on tree 1 and plotting the nitrogen as a percentage of the total solids against the total solids content of the latex (Figure l), we find t h a t the nitrogen content of the total solids is roughly inversely proportional to the total solids content of the latex. When Arisz’s data were plotted so t h a t the nitrogen content was a percentage of the whole latex, a line parallel to the 2axis seemed to result. Following the leads obtained from the work of Arisz, we decided to determine the nitrogen content of latex from particular areas on our plantations obtained by the usual tapping methods. We also decided while these samples were available to see how the ash varied with the total solids content of the
Nitrogen and ash determinations have been made on Hevea latices of widely varying total solids content, with the result that both of these values have a constant value on the latex, independent of the solids content. These values are approximately 0.25 per cent for the nitrogen and 0.5 per cent for the ash. It is also shown that residual nitrogen directly associated with the rubber is a constant value (0.1 per cent), independent of the purification of the latex. latex, and to determine how the nitrogen would be apportioned when latices of various total solids content were coagulated.
Procedure for Nitrogen and Ash Values The latex samples used were obtained from four areas on alternate monthly tapping. Sampling on the four areas was begun simultaneously, after each area had been through a normal rest period for one month. Twenty-eight samples were taken from each area during the month of study. One hundred and twelve samples were thus collected; of this total, one was lost during handling. The areas selected supplied latex varying greatly in total solids content. The trees supplying the latex included old seedlings, young seedlings, and EI number of young buddings. Some of the samples were preserved with ammonia and others with formaldehyde while being transported from the collecting
AUGUST, 1940
IXDUSTRIAL AND ENGINEERING CHEMISTRY
areas to the laboratory. The weights of preservative used were always obtained accurately so that analyses could be based on the unpreserved latex. On receipt a t the laboratory, each sample was analyzed for solids content, and a portion was poured into a shallow glass dish and dried to a film in a 50" C. oven. Each film \\as analyzed in duplicate for nitrogen. The ash was determined on each film without replication. The Kjeldahl nitrogen determination was used. I
A . ON SOLIDS PHASE O.ON WATER PHASE O.ON LATEX
l
8-
I
1073
one class, samples in the range 25 to 26 per cent in another class, and so on until all samples were grouped. Averaged data for the samples are presented in Table I. T h e nitrogen and ash d a t a of Table I are presented graphically in Figure 2. It is striking that curves practically identical i n shape were obtained for ash and nitrogen data. The data closely follow the rule t h a t the ash content is twice the nitrogen content. Both ash and nitrogen contents increase markedly when expressed on the solids phase, decrease appreciably when expressed on the water phase, and increase very slightly when expressed on the latex as the solids content decreases. Variation is so small for results based on the entire latex t h a t the generalizations t h a t the nitrogen content of latex is 0.25 per cent and the ash content is 0.50 per cent are satisfactory. T h e intimate relation between ash and nitrogen values indicates physiologically that the synthesis of nitrogenous material by the rubber tree is quantitatively dependent on the amount of salts absorbed by the trees. TABLE I. AVERAGED DATAFOR LATEXSAMPLES
40 %TOTAL SOLIDS OF LATEX
7oN
s o . of
Sam-
FIGURE1. VARIBTION O F NITROGENWITH S O L I D S CONTENT 4s C A L C E L A T E D FROM r).4T.i OF ARISZ(TREE 1) As a precaution against inclusion of volatile base in the nitrogen determinations, each sample was creped thin and boiled with 0.33 per cent Xa2HPO4.12H20just before analysis. The sample to be analyzed was placed in a Kleldahl flask with 150 cc. of the alkaline phosphate solution and boiled slowly until 25 to 50 CC. of liquid remained. The nitrogen determination was then carried out on the residue in the flask. Violent agitation was practiced before pouring latex into drying dishes to assure uniform dispersion of sludge. This is a precaution essential for obtaining accurate ash figures for ammoniated latex where an appreciable amount of inorganic sludge forms. Every effort was made to conduct each analysis in exactly the same manner so that results would be directly comparable. The use of two preservatives is the only known source of variation in sample treatment; however, changing from formaldehyde to ammonia as preservative does not seem to make the slightest difference in ash or nitrogen analyses. Formaldehyde is probably the more desirable preservative for nitrogen content studies because of its nonnitrogenous composition.
lA A ON SOLIDS PHASE B O ON WATER PHASE IC X ON WATER PHASE, CORRECTED FOR NITROGEN INTIMATELY I ASSOCIATED WITH THE 1 RUBBER D O ON LATEX
40 % TOTAL SOLIDS OF LATEX
30
FIGURE 2. VARI.4TIOS
IX
%%h on Solids Fraction
Frac-
tion
46.30 45.40 44.89 43.12 42.68
0.522 0.525 0.513 0.613 0.561
0.240 0.238 0.228 0.265 0.239
Water Ffaction 0.447 0.438 0.415 0.465 0,417
41.24 40.16 39.59 38.42 37.55
0.545 0.578 0.625 0.663 0.646
0.227 0.233 0.236 0.255 0,241
0.383 0.385 0,410 0.414 0.403
1.13 1.15 1.35 1.37 1.18
1 1 5 2
36.61 35.62 34.63 33.48 32.58
0.663 0.635 0.740 0.745 0.825
0.241 0.225 0.255 0.250 0.268
0,380 0.350 0.395 0.375 0.395
1.28 1.30 1.35 1.47 1.37
5 4 9 8 9
31.28 30.75 29.52 28.48 27.56
0.765 0,814 0.875 0,921 0.967
0,238 0.251 0.257 0.263 0.268
0.344 0,358 0.364 0,367 0.367
1.44 1.58 1.84 1.76 1.83
6
26.71 25.42 24.56 23.58
0.990 0.966 1.053 1.113
0.265 0.246 0.257 0.263
0.360 0.329 0.343 0.341
1.81 1.99 2.23 2.21
Total 7Solids of Latex
3 2 2 2
8 3 2 3
'P 4
4
5 6
1.01 0.94 1.06 1.09 1.12
70Ash
Caicd. on Water Calcd. Fraco n Latex tion 0.87 0.47 0.73 0.43 0.48 0.87 0.83 0.48 0.48 0.8S 0.47 0.80 0.46 0.77 0.88 0.53 0.53 0.86 0.44 0.71 0.48 0.74 0.46 0.72 0.47 0.71 0.74 0.49 0.66 0.45 0.66 0.45 0.49 0.70 0.54 0.77 0.50 0.70 0.50 0.69 0.48 0.66 0.68 0.51 0.55 0.73 0.52 0.68
70' Ash
Yitrogen in Crepe
1
2.0
cII
212. on
A 100-cc. portion of latex from each tapping area was accumuhted daily. The accumulated samples tvere kest a t 1.25 per cent ammonia to assure uniform preservation. A t the end of each 7-day tapping period into which the tapping month can be conveniently divided, the 700-cc. portion accumulated for each plot was , A. A.ON SOLIDS PHASE diluted with one liter of distilled water, treated B.0. ON WATER PHASE with 10 per cent formic acid until acid to methyl 'C.O.DN LATEX PHASE red, and then treated with 200 cc. of ammonium formate buffer solution. The buffer solution, used to assure uniform acidity in coagulation, was prepared by treating 10 per cent formic acid with 20 I per cent ammonia until the reaction was just acid to methyl red. One stock buffer solution was used for all samples. The latex samples, which coagulated about a minute after adding the buffer, were allowed to stand overnight and were creped and dried. The crepe samples obtained were analyzed for nitrogen in duplicate by the same procedure used for the dried latex films (Table 11). The practice of boiling with dilute caustic before analysis assured the removal of ammonia from the samples.
I
20
70S Calcd. on Latex
ples Averaged
A11 samples analyzed were grouped in classes according to solids content. A 1 per cent range was used for each class. Samples from 24 t o 25 per cent solids content were placed in ~
Detd. on Solids
5 0 20
I
0
- 0 4 U'O
40 %TOTAL SOLIDS OF LATEX
30
so
NITROGEN AND ASH CONTENTS WITH LATEXSOLIDS CONTENT
In Figure 3 the data are presented graphically for the creped samples in curve B. Curve A , a reproduction of curve A from the nitrogen graph of Figure 2, shows the total nitrogen present in the latex before coagulation, expressed on the
INDUSTRIAL AND EYGINEERING CHEMISTRY
1074
solids phase. It is apparent from Figure 3 that the portion of the total nitrogen in the latex which appears in the crepe is nearly 60 per cent. As a rule, acid coagulation results in the inclusion in the crepe of all the nitrogen intimately associated with the rubber fraction in addition to 57 per cent of the nitrogenous material normally dispersed in the latex serum. TABLE 11. NITROGEN CONTENT O F CREPED LATEX YoTotal Solids of Latex
Yo N in Creped Rubber
% T o t a l Solids of Latex
% N in Creped Rubber
44.7 41.6 40.6 38.6 38.3 38.2 37.4 32.5
0.42 0.35 0.37 0.35 0.36 0.40 0.42 0.41
30.9 29.5 28.8 28.5 27.5 27.2 24.7 24.0
0.47 0.51 0.50 0.52 0.56 0.58 0.55 0.66
VOL. 32, NO. 8
show, furthermore, that 0.577 gram of nitrogen was in the samples removed for analyses. The 4.333 grams of nitrogen in the final cream and the sera, combined with the 0.577 gram of nitrogen in the samples, sum up to 4.910 grams, a satisfactory accounting for the 4.970 grams of nitrogen in the original latex. The data presented show that the latex coagulated by acid must have a varying nitrogen content in the coagulum dependent upon the total solids of the original latex. Also, the data show that for uniformity it is essential to bring about this coagulation under the same conditions-that is, with the same total solids content. It may also be noticed that the nitrogen in the crepe varies more as the total solids content of A
A. ON LATEX SOLIDS B.ON CREPE0 RUBBER
IO0
Nitrogen Intimately Associated with Rubber in Latices I n the paragraph just above, reference mas made to the nitrogen intimately associated with the rubber fraction of the latex. This is the nitrogen so tightly fixed on the rubber particles that i t cannot be washed off by repeated creaming operations. Creaming operations normally free the rubber hydrocarbon from soluble serum constituents. I n order to illustrate the fixed character of the residual nitrogen, a typical set of creaming data are presented. The data of Table I11 show nitrogen distribution in latex, serum, and cream fractions throughout four consecutive creaming operations.
~
5 .75
?:h.j$ 0 W
a
30
I 40
50
X TOTAL SOLIDS OF LATEX
TABLE111. NITROGEN DISTRIBTJTIOK IN LATICES Tptal % N of Grams of N Associated .U in with 100 G . Grams of Solids Sample Sample Sample of Sample (Wet Basis) Sample of R u b b e r 1st serum 1287 6.53 0.228 2.930 ... 0.078 0.670 ... 859 2.70 2nd serum 0.029 0.181 ... 625 0.763 3rd serum 0.012 0.066 ... 4th serum 549 0.798 Original 4.970 0.100 latex 2524 32. 7a 0.197 1.968 0.106 60.15 0.158 1st cream 1243 58.8 0.092 0.960 0.102 2nd cream 1046 3rd cream 923 55.1 0.072 0.667 0.106 0.486 0.108 57.7 0.067 4 t h cream 726 The latex was 39.7570 in total solids content before treatment with creaming agent and dilution a t the beginning of the creaming operation; the value 32.7% is for the latex as i t was ready for t h e creaming step.
Calculation of Nitrogen Associated with Rubber An example is given to clarify the calculation procedure for those unfamiliar with creaming operations. The residual nitrogen in 100 grams of first cream is calculated as follows: One hundred grams of the first cream contains 60.15 grams of solids and 39.85 grams of water. The cream may be considered as consisting of rubber particles suspended in the first serum fraction. With the first serum analyzing 6.53 per cent solids, it follows that 100 grams of cream contain 39.85 X (6.53/93.47) or 2.78 grams of serum solids. The total serum in 100 grams of cream is then 2.78 39.85 or 42.63 grams. The nitrogen content of this serum is 42.63 X 0.00228 or 0.097 gram. The serum nitrogen, 0.097 gram, subtracted from the total nitrogen in the cream, 0.158 gram, leaves 0.061 gram of nitrogen associated directly with the rubber fraction of the cream. This rubber fraction amounts to 60.15 - 2.78 or 57.37 grams. It follows that (0.061/57.37) X 100 or 0.106 gram of nitrogen is associated with each 100 grams of rubber in the cream. This value of approximately 0.1 per cent nitrogen is in good agreement with the data of McGavack ( 2 ) determined in a somewhat different manner. The nitrogen found in the four serum fractions and in the final cream fraction totaled 4.333 grams. Sample records
+
the latex decreases, whereas a t a total solids content of from 34 t’o40 per cent the slope is not so great. Hence there will be less variation in the crepe prepared over this range than there would in the crepe prepared from latices below 34 per cent total solids content. Rubbers a t various points along this curve have been examined. The results on the characteristics of such rubbers will be reported a t a later date.
Acknowledgment We want to thank the Plantations Division of the United States Rubber Company for help in obtaining part of the experimental data.
Literature Cited (1) Arise, Arch. Rubbercultuur, 4, 30 ( 1 9 2 0 ) ; 8, 425 (1924). ESG.CHEY.,31, 1509 (1939). (2) McGavack, IND.
PRESENTED before the Division of Rubber Chemistry a t t h e 99th Meeting of the American Chemical Society, Cincinnati, Ohio.
Correction-Thermodynamic Properties of Fluorochloromethanes and -Ethanes In the fifth paper in this series, “Heat Capacity of the Liquid and Vapor of Three Fluorochloromethanes and Trifluorotrichloroethane”, which appeared in the July, 1940, issue of INDUSTRIAL AND ENGINEERING CHEMISTRY, an unfortunate error appears on page 979. The equation for CJC. at the bottom of the second column should read:
R. C. MCHARNESS
