Formation and Deterioration of Paint Films
20
00
80
5
F I G U R E 1. CHANGE IN WEIGHT
W
u
a n
60 W
HOURS EXPOSURE
> 40
190
IO
I
1000
F I G U R E 2 . IODINE V A L U E S
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Changes in Films of Glycol Esters of Several Unsaturated Fatty Acids under Exposure to Ultraviolet Light
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J. L. OVERHOLT AND A. C. ELM
HOURS EXPOSURE
The New- Jersey Zinc Company, Palmerton, Penna.
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IO F I G U R E 3.
MALEIC
O
ANHYDRIDE
ADDITION
In a previous paper the authors reported the changes taking place in the films of the methyl esters of several unsaturated fatty acids under exposure to ultraviolet light. This investigation was undertaken to obtain data believed necessary for a better understanding of the processes involved in the formation and deterioration of drying oil and paint films. Continuing this work the authors examined the glycol esters of oleic, linoleic, linolenic, and eleostearic acids. In general, the oxidation of the glycol esters follows similar lines to the oxidation of the methyl esters. The greater complexity of the glycol esters is indicated especially by the fact that in contrast with the methyl esters one of the glycol esters, the linolenate, dried to a tack-free film.
VALUES
60
5
0
a
W
a
I
X
HOURS EXPOSURE
too
IO
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I000
F I G U R E 4. R E F R A C T I V E INDEX
cl.50
PREVIOUS paper' stated that an explanation of the formation and deterioration of drying oil and paint systems might be found in a systematic study of simple esters of unsaturated fatty acids. The changes taking place in films of the methyl esters of the four common unsaturated 18-carbon fatty acids under exposure to ultraviolet light were described'. The present paper discusses the results obtained in a study of the glycol esters of the same four unsaturated fatty acids under exposure to the same conditions and examined by the same testing methods.
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Experimental Procedure The glycol esters used in this investigation were prepared from the corresponding methyl esters previously described 1
L
1. 2.
IND.ENQ.CHEM.,32, 378 (1940).
1348
Glycol oleate Glycol linoleate
HOURS E X P O S U R E 10 100
3. 4.
1000
Glycol linolenate Glycol eleostearate
OCTOBER, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
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FIGURE 5 . PE ROX I D E 5
X
0
FIGURE 8 . A C I D V A L U E S
U
::
100
I 0
Y
HOURS IO
I
L5
EXPOSURE
1000
100
I
50
F I G U R E 6. ALDEHYDES
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HOURS
IO
I
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EXPOSURE 100
1000
HOURS 10
EXPOSURE
IO0
1000
e
400
~~~~
F I G U R E 7. HYDROXYL OXYGEN
300
200
HOURS
s
EXPOSURE
1000
100
10
I
1.
2.
Glycol oleate Glycol linoleate
by effecting an exchange between glycol acetate and the respective methyl esters at a relatively low temperature and removing the resultant methyl acetate. The purity of the glycol esters is as follows:
No.
Wijs Iodine Value
1.2 2.0 3.6
84.5 169.6 247.4
Acid Oleate Linoleate Linolenate
Eleostearate a
...
2.2 Determined at 35O C.
Saponification No. 192 189.5 193 211.5
Maleic Anhydride Addition Value
.. . ... ...
79.8
Density at 25'
FIGURE 9.
C.
0.906 0.916 0.926 0,9210
Viscosity et 25," C., Poises 0.28 0.22 0 .,lo Semisolid
The eleostearate was a pasty mass at room temperature, and the progress of this investigation was greatly hampered because it was almost impossible to obtain films of the desired smoothness and clarity. Attempts to liquefy this ester permanently by heating i t a short time t o 204" C. (400" E".) failed, and we had to melt i t every time a film was to be prepared. It remained liquid during the early stages of exposure. As in the preceding investigation, thin films of the esters were exposed to ultraviolet light and analyzed at more or less regular intervals for change in weight, unsaturation, the various forms of oxygen, density, refractive index, molecular weight, and viscosity. Although satisfactory results were
100
3. 4.
ESTER VALUES
HOURS E X P O S U R E 10 100
I
1000
Glycol linolenate Glycol eleostearate
obtained in applying these analytical methods to the examination of the methyl esters, considerable difficulty was experienced in this investigation with the less soluble films of the glycol esters. The results obtained are shown in a set of curves plotted to the same scale as that used in presenting the data of the investigation of the methyl esters.
Discussion of Results The greater complexity of the glycol esters was responsible for some outwardly visible differences between the glycol and the methyl ester films. Although the glycol oleate and linoleate behaved much like the corresponding methyl esters, changing in the course of the exposure from liquids of relatively low viscosity to tacky balsamlike masses, glycol linolenate set in about 10 hours to a tack-free infusible film which resembled a typical drying-oil film. The glycol eleostearate, however, changed in about 3 to 6 hours to a wrinkled mass similar in appearance to a badly frosted tung oil film, remained in that condition for about 200 hours, and then softened to a sticky but highly viscous material. It is difficult to say a t this stage of the investigation what caused this peculiar behavior of glycol eleostearate, but it is reasonable to
INDUSTRIAL AND ENGINEERING CHEMISTRY
1350
HOURS
EXPOSURE
GEL
1
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F I G U R E 11. V I S C O S I T Y
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HOURS
EXPOSURE
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FIGURE I2.MOLECULAR WEIGHT IN TERTIARY B U T Y L
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HOURS EXPOSURE IO too
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FIGURE 13. D E N S I T Y ?
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HOURS EXPOSURE IO 190
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-0.32
FIGURE 14. S P E C I F I C
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REFRACTION
-0.28
.O.26 0.24 1
1. Glycol oleate 2. Glycol linoleate
HOURS 10
EXPOSURE 100
3. 4.
1000
Glycol linolenate Glycol eleostearate
VOL. 32. NO. 10
assume that the softening may have been the result of the solvent action of oxidative decomposition products. This contention receives some support from the observation that on prolonged exposure the eleostearate loses weight a t a greater rate than does the linolenate (Figure 1); it is somewhat more stable, however, than the linoleate and oleate. Again, as in the case of the methyl esters, the rate of gain in weight and loss in weight on extended exposure fall in the order of oleate, linoleate, and linolenate. Up to the maximum gain in weight, the glycol and methyl ester curves are very much alike. After that, however, the greater film-forming ability of the glycol esters asserts itself and results in a greater resistance to oxidative decomposition. The iodine value (Figure Z), as determined by the additionsubstitution method corrected for free acids, changes as in the case of the methyl esters in three principal stages-the induction period, a second stage characterized by a rapid decrease in iodine value, and a third stage during which the iodine value remains relatively constant. The apparent rise in the iodine values of the glycol linolenate between 10 and 100 hours of exposure is difficult to explain, and there is considerable doubt as to its significance. I n view of the fact that the linolenate film dried to a solid film in about 10 hours and in view of the difficulties generally encountered in determining the true degree of unsaturation under these conditions, i t is reasonable to assume that this portion of the iodine curve might better be represented by a straight horizontal line. The changes taking place in the maleic anhydride addition values (Figure 3), refractive indices (Figure 4), peroxides (Figure 5 ) , aldehydes (Figure 6), hydroxyl oxygen (Figure 7 ) , acid values (Figure 8), and total oxygen concentration as determined by ultimate analysis (Figure 10) did not differ sufficiently from those observed with the methyl esters to warrant detailed discussion a t this time. It should, however, be pointed out that the aldehyde values of the linolenate and eleostearate indicated by the curves are a t best only approximate because of the extreme difficulties encountered in avoiding or breaking the sodium bisulfite solution-benzene emulsions which interfered seriously with the quantitative separation of the aldehyde addition product. The hydroxyl values of the glycol linolenate films after 100 hours of exposure are also only approximate because it was not possible to effect complete solution of the films in the acetic anhydridepyridine reagent. The peculiar shape of the ester value curve of the glycol eleostearate (Figure 9) deserves special attention. It is not possible, however, to formulate a reliable explanation for the sudden rise in these values between 2 and 10 hours of exposure on the basis of the data available. This curve has been checked several times, and the trend indicated appears to be real. Further experimental evidence, however, seems to be necessary for a satisfactory explanation of the mechanism of this reaction. The most striking differences between the glycol and the methyl esters are shown in the rate of viscosity increase during exposure (Figure 11). The glycol ester curves are somewhat smoother than the corresponding methyl ester curves, and the sudden upturn indicating gelation or solidification occurs earlier. Unfortunately it was impossible to measure the viscosity of the glycol eleostearate by the rolling ball method because of the inability to obtain smooth liquid films with this ester and prevent its change to a pasty mass. The determination of the molecular weight changes occurring in the glycol esters during exposure to ultraviolet light was greatly handicapped by the lack of solubility of some of the esters even after relatively short exposure periods (Figure 12). It is interesting to note, however, that the linoleate which had become relatively insoluble in tert-butyl alcohol
OCTOBER, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
1351
could be obtained for the glycol eleostearate for reasons previously mentioned. The general nature of these curves does not differ appreciably from those obtained with the methyl esters.
after about 50 hours of exposure became soluble again after slightly over 100 hours of exposure, probably as a result of oxidative decomposition. The changes occurring in the density of the esters are shown in Figure 13. The similarity t o the viscosity curves is at once apparent. It was impossible to obtain reliable density values with the micropycnometer after the esters had become highly viscous. Because of its peculiar semisolid nature, glycol eleostearate could not be measured a t all. The specific refraction values calculated from the refractive index and density measurements with the aid of the Lorentz-Lorenz equation are shown in Figure 14. No values
Acknowledgment The assistance of J. G. Smull, Lehigh University, and E. P. Clocker who prepared the esters used in this investigation, and of A. J. Farber of this laboratory who did most of the experimental work is gratefully acknowledged. PRESENTED before the Division of P a i n t and Varnish Chemistry a t t h r 99th Meeting of the .imerican Chemical Socictv. Cincinnati, Ohio.
Solubilitv of Methane in Cvclohexane J
J
E. P. SCHOCH, A. E. HOFFMANN, F. D. MAYFIELD
AND
The University of Texas, .4ust,in, Texas
The solubilities of methane in cyclohexane corresponding to pressures u p to the critical pressures and at temperatures of 100.27', 160°, and 220' F. are reported in the form of bubblepoint data. Specific volumes of the liquid phases, together with their compressibilities up to 6000 pounds per square inch, are reported.
I
temperatures of this study were determined by means of the weighing bottle shown in Figure 1, together with the injection portion of the previously described apparatus (3). For these determinations the weighing bottle was attached to the injection cell through a needle valve, and pump and pressure readings at equilibrium were recorded for a presYure of 800 pounds per square inch absolute and the temperature of the determination. After the weighing Iiottle was evacuated, 20 to 30 cc. of cyclohexane were forced out of the injection cell into the weighing bottle through the .lightly opened needle valve by means of the pump. The needle valve was then closed, and another equilibrium pump and pressure reading a t 800 pounds per aquare inch was recorded. The bulb of the weighing bottle was then immersed in ice until the cyclohexane was frozen and completely distilled over into the bulb. The mass of the cyclohexane forced out of the injection cell was determined by weighing the weighing bottle in the usual manner, and the volume of the cyclohexane a t 800 pounds per square inch corresponding to the mass forced out was obtained from the difference in the two pump readings together with the pump piston calibration. Duplicate determinations were made, and the proper buoyancy corrections were applied to the weighings. The densities thus obtained were employed in the calculations of F~~~~~ 1. 1$rEIGHING B~~~~~ FOR the injections and are presented in CYCLOHEXANE DEMITYSTUDIES Table I.
N A PREVIOUS paper (3) the writers described an apparatus and experimental procedure for the determination of high-pressure P-V-2'-X relations for two-component hydrocarbon systems, and presented bubble-point data on the methane-benzene system a t 100.27" F. The present paper presents similar data on the methane-cyclohexane system a t 100.27", 160°, and 220" F. The experimental d a t a consist of the determined solubilities of methane in cyclohexane, together with the densities and compressibilities of the resultant solutions up to pressures of 6000 pounds per square inch. Two previous reports on this system are found in the literature. Sage, Webster, and Lacey (2') reported results similar to thoseof this paper, but their data are limited to two compositions at each temperature and to maximum pressures of 3000 pounds per square inch. Frolich and co-workers (1) presented data at 77" F. with a reported accuracy of *5.0 per cent.
Apparatus and Procedure The apparatus and experimental procedure have already been described ( 3 ) . In the previous work ( 3 ) the density of benzene a t 800 pounds per square inch could be obtained from the literature. However, no similar data on cyclohexane are available, and the densities of cyclohexane a t 800 pounds per square inch had to be determined in order to calculate the injections made into the equilibrium bomb. These densities a t the three
