Linseed Oil Changes in Physical and Chemical Properties during Heat-Bodying B. P. CALDWELL AND J. MATTIELLO, Polytechnic lnstitute of Brooklyn, Brooklyn, N . Y . THE CHANGES in certain physical and chemical properties of heat-bodied linseed oil during processing at different temperatures have been observed. The properties studied are viscosity, color, speciJic gravity, apparent mean molecular weight, index of refraction, acid value, and iodine aalue. These
were measured on samples withdrawn from commercial batches (250 gallons) during bodying. The results are presented in connection with the time-rate of change of each property, as well as the rate of change of each property with respect to the others.
I
T IS generally known that, in the process of bodying linseed
oil from its raw state to that of a heavy viscous liquid, many changes, both physical and chemical, are taking place concurrently. While the exact program of these changes is not known, nor all the factors that affect their speed and sequence, it is agreed that reactions of polymerization, condensation, cracking, oxidation, hydrolysis, rearrangement, and gelation are involved. It seemed of interest to ascertain a t what rate these changes took place at different temperatures, and, if possible, what interrelations could be discovered among them. The authors are aware of the fact that separate studies of the changes of individual properties have been made by different investigators on different oils under controlled laboratory conditions, but it seemed worth while to study these changes as they occurred in oils bodied on a commercial scale, notwithstanding the fact that experimental conditions cannot be so accurately controlled as in small-scale operations. For the first runs, two 250-gallon monel-metal kettles, heated by means of fuel oil over a free fire, were filled with neutral oil and heated to 327.7' C. (622' F.) and 307.2' C. (585" F.), respectively. Later three similar kettles of oil were heated to the following maximum temperatures: 287.8' C. (550' F.), 304.4' C. (580" F.), and 329.6' C. (625' F.). The first kettle (327.7' C.) was on the fire for 2l/* hours, the second (307.2' C.) for 91/* hours, the third (329.6' C.) for 3 hours, the fourth (304.4' C.) for 6 hours, and the fifth (287.8' C.) for 22 hours, inclusive of the time necessary to raise t o the maximum temperature, There was no increase in temperature when any kettle was taken off the fire, because during the processing the burners were adjusted as the temperature of the kettle rose or fell. The times necessary to reach the maximum temperatures and the complete record of the changes in
properties which were measured are shown in Tables I, 11,and 111, and in the figures that are presented below. DETERMINATION OF PROPERTIES The oil used was an alkali-refined (neutral) oil which had the following - characteristics: FIRSTTwo KETTLES
Color.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Specifio gravity at 15.5O C . . . . . . . . . . . . . . . 0,9321 Molecular weight. . . . . . . . . . . . . . . . . . . . . . . . 700 Index of refraction. . . . . . . . . . . . . . . . . . . . . 1.4769 Acid value. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0,402 Iodine value
.......................
180.3
LMT THREE KETTLEB 6 0.9242 793 1.4800 0.445 179.3
During the period of bringing up to temperature, two 4-ounce samples were taken from each kettle every half-hour and thereafter every 15 minutes. COLOR.The color value was obtained in the following way: One gram of potassium dichromate was dissolved in 100 cc. concentrated sulfuric acid (specific gravity 1.86). The number of cubic centimeters of this solution which it is necessary to add to 100 cc. of colorless concentrated sulfuric acid to match the tint of the oil is called the color value. SPECIFICGRAVITY. A Westphal balance was employed, and the results were recalculated to specific gravities a t 15.5" C. in terms of water at 4 ' C., using the following data from Fritz (2), giving fractional increase in specific gravity per degree fall in t'emperature: 2 2 . 8 ' t o 170° C ...................... 0.0006707 0.0006857 170; to226' C ...................... 0.0006877 226 to 243O C . . .................... M O L E C U L AW R E I G H T . The freezing-point depression method of Beckmann was employed to give the apparent mean molecular weight. Nitrobenzene was used as solvent Objection may be made, and rightly, to the use of this
-
AND CHEMICAL CONSTANTS OF BODIED LINSEEDOIL TABLE I. PHYS~CAL
OJLBODIEDAT 327.8' C.
TIMP
Temp. O
7:45
s:oo
8:30 9:oo 9:30 1o:oo 10:30 11:oo 11:30 12:45 l:oo 1:30 2:oo 2:30 3:OO 3:30 4:OO
4:30 24 hours later
Aoid value
weight
Sp. gr.
1.4769 1.4775 1.4778 1.4782 1.4790 1.4832 1.4851 1.4867 1.4871
...
700
....
c.
27 135 216 293 325 327.8 325 315 299 249 246 229 221 210 190 185 176 112
...
0.40 11.60 0.93 2.79 8.54 12.21 14.78
0.9340
....
...
1000 1678
0.9365 0 9402 0.9569 0.9655 0.9695 0.9702
ii:i3
1620
0.9682
1.4871 1.4871 1.4871 1.4870
ii:io ...
1565
1,4870
15: io ...
.... 1.4871
.... .... ....
14.83
14.80
OIL BODIED A T 307 . Z 0 C.
7
Mpl.
Refractive index
830 *.
913
.. .. ..
le02 1608
I
....
.... ....
....
0.9702
....
158
Temp.
Refractive index
Acid value
Mol, weight
c. 27 116 171 238 291 302 303 307 307 302 303 307 306 305 288 279 306 302
..
1.4769 1.4771 1.4771 1.4771 1,4775 1.4784 1.4792 1.4805 1.4816
.... 1.4829
1,4835 1.4843 1.4850 1.4852 1,4855 1,4858 1.4861
....
o:i1
700
Sp. gr.
....
1.39
..
3:22
795
..
0.9321 0.9333 0.9340 0.9346 0.9371 0.9402 0.9434 0.9453
5:29
883
0.9563
6161
..
1220
7.28
1250
7:77 8.00
1480
0144
..
..
..
753
..
.... ....
..
..
1542
0.9642
.... ....
0,9669
....
INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1932
lo
m
m
w
c
2
j,g g4 .1 ;. ;. $? :g :$ 1: ;: : :z : : : z : : : g : : :s ' 4 : 4 . 4 2 . : : 4 : : :d: : : : *. . . : 4 f
W*Cl
F;
'"
3
3
3
3
3
3
3
- - -
0
: : :% : : : : : : : 4 : : . : 3
159
solvent in molecular-weight determinations on oils, for free fatty acids are polymerized to some extent in s o l u t i o n ( d ) , but it is not believed that g l y c e r i d e s are. The authors are sure that the results show the true trend of change in molecular-weight values during processing, but admit that the results are more in error where greater hydrolysis has taken place, that is, toward the end of the heating. ~ D E X OF REFRACTION. The Abbe instrument was used and the determinations were made a t 21" C. VISCOSITY. These values are expressed in p o i s e s a n d w e r e o b t a i n e d with the Gardner-Holt bubble v i s c o m e t e r a t 25" * 1" c. ACID VALUE. These were obtained by refluxing a mixture of approximately 10 grams of oil with 50 cc. of an equal-volume mixture of benzene and 95 per cent ethyl alcohol on the water bath for 30 minutes, cooling, and titrating with alcoholic potassium hydroxide, using phenolphthalein as indicator. Some acid values in this and other solvents were determined by potentiometric titration, using the quinhydrorie electrode and saturated alcoholic lithium chloridecalomel half-cell. The results of this study h a v e b e e n p r e s e n t e d in another paper (1).
IODINE VALUE. The Hanus method was used and the determinations were made in a dark chamber at 23" * 2" C. for 1 hour.
RESULTS Table I gives the time, t e m p e r a t u r e , specific gravity, index of refraction, molecular weight, and acid value for samples withdrawn from the first two batches of oil during bodying. Figure 1 shows the time-rate of change of temperature, and the molecular weights of the oil samples a t certain times during the bodying are also indicated. It will be noticed that in the case of the 327.7" C. (622" F.) oil, although the molecular weight changes by only 200 units during the 2 hours of bringing up to maximum temperature, during the next hour there is an increase of 687 units in molecular weight, notwithstanding the fact that the oil is cooling. There is also some indication of slight depolymerization on cooling in the last stage. The temperature of the other kettle, 307.2" C. (585" F.), was maintained more constant after t h e m a x i m u m h a d b e e n reached. There is an increase of less than 200 units in molecular weight during the first 5 hours of heating; but between the fifth and sixth hours there is a sudden increase of 337 units, and this increase continues slowly for the rest of the run, reaching a final value over twice as great as the initial one, and approximately equal to the value reached in the oil heated to the higher temperature.
160
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 24, No. 2
Jw 250
zw 150
IO0
so
Asmight be expected, the higher the temperature the more sudden the increase in index of refraction. For example, the high-temperature oil undergoes approximately the same increase in 3 hours as 1 the low-t e m p e r a t u r e oil e x p e r i e n c e s in 9 hours. A graph of indices of refraction against molecular weights for these oils (Figure 2) shows that, during the first stages of bodying, the refractive index increases considerably with correspondingly small increase of molecular weight, while during the latter part of processing, the increase in molecular weight is large, with correspondingly small increase in refractive index. The turning point, which is quite marked, comes for the high-temperature oil when the molecular weight has reached a value of 915, for the lower-temperature oil when the molecular weight is 885, and the curves for both oils closely approximate each other. Evidently molecular rearrangements take place during the heating to some extent Lefore polymerization reactions set in. It may also be noted that a t this turning point (molecular weight around 900, refractive index around 1.483 for both oils) the viscosities differ by only one-half bubble when tested in the 10.75-mm. Gardner-Holt tube, the higher-temperature oil being the heavier. The experimental results for the latter three oils are, perhaps, more dependable. These are exhibited in Table 11, which gives time, temperature,. specific gravity, color, index of refraction, mean molecular weight, viscosity, acid value, and iodine value. Figure 3 gives the temperature-time relations for the three oils. Upon the curves have been indicated the molecularweight values a t corresponding times. The rate a t which the oils were brought up to their maximum temperatures was the same for all. The 829.6' C. (625" F.) oil was permitted to cool after reaching maximum temperature; the 304.4 ' C. (580" F.) oil was kept on the fire 4 hours after reaching maximum temperature and then permitted to cool; the 287.8' C. (550" F.) oil was kept a t maximun temperature without fluctuation for the remainder of the run, which continued for a day and a half longer than with the other two oils. The same sudden increase in molecular-weight values during
a short period of time such as was noted with the former oils is again seen, especially in the case of the high-temperature oil. In connection with any discussion of the changes in properties which proceed during bodying, it must not be forgotten that the system is a complex one; that different reactions are possible and are going on concurrently; and that the results of the present, or of any single, investigation must be influenced by local conditions (methods of heating, shape and Table 111. PHYSICAL AND CHEMICAL CONSTANTS OF BODIED LINSEED OIL
TIME
(Oil bodied at 287.8O C. for additional ll/: days) REFRACACID IODINE VIESP. MOL. TIV& TEMP.VALUE VALUE COBITY GR. WEIGHTINDEX COLOR O
8:OO
A. M.
9:oo 9:15 9:30 9:45 1o:oo 10:15 10:30 10:45 1i:oo 11:15 11:30 11:45
c.
38 127 177 229 274 291 288 291 291 288 288 288
288 1 2 : o O ~ . 279 12:15P . M. 291 12:30 285 12:45 291 1:oo 285 1:15 288 1:30 288 1:45 285 2:00 287 2:15 285 2:30 288 2:45 3:OO 3:15 288 3:30 288
4:OO 4:15 4:30 4:45 5:OO
.... .. ..
5.59 5.70
..
5:98
.. ..
6131
....
6:63
.. ..
6:85
.. ..
.. ..
134.4
. . . .
. . . .
. . . .
.... . 0.9525 . . . . . . . . . . . . . . . . . . . . . .
. . . .
... . 1.4870 2 . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . .
. . . .
. . . 0.9533 1.4873 2 9 07 1251 9:46 0:9536 .. 1,'48?7 2' 2 10.08 i3i:4 12.27 0:9549 1330 1:liio 2 132:7
...
...
...
130:2
... ...
::
l2:QO 0:9555 1 13 57 14:14 0:9552 1336 1:4882
2 3
::
l6:36 0:9560 1:4888 3" 16.71 i3i:5 18.88 o:Qi60 1433 i:4887 3" . . . 19.30 . . . . . . . . . . . . ... 20.10 0.9566 . . 1.4890 3 21 00 . . . . . . . . 12719 23:56 0:9575 . . 1.4891 3
...
. .,
23:80 0:9597
1.'4890
3''
. . . . . . . . .
...... ... 126.1
::
. .
...
., .
288
7.52
288
288
o:iiio .. 1.4899 ... 7:84 127:s ... 0:9iio iSio 1:iQOo 6 ' ' 7.69 1 2 6 . 0 50.90 0.9610 .. 1.4900 6 7.95 , .. 57.20 0.9603 . . 1.4900 6 . . . . . . 6 s:io 123:~ 0.9610 . . 1.4900 ... ... 72:io . . . . . . . . . . . . . 8:i4 . . . . . . 0.9625 . . 1.4903 . . .
288 288
8165
285 288
288 8 : 0 0 a . ~ . 36
9:30 9:45 10:oo 10:15 i0:30 10:45 ii:oo 11:15 11:30 11:45 i2:ooM.
Poises
5.31
285 291 285 288
288 287
286
279
..
..
.... ..
34.7 36.20 36.20
0,9602
1545 1.4898 4
. . . . . . . . .
" '
S:74
8:84
... ... . . . si:40 . . . . 0:9049 . . . ......
0.9668
ii3:3 85:io
o:i6ii
.........
1.4905 6.5
1057
.. .. ..
.......
1.4907
...
1:liio
i:5
February, 1932
1N D U ST RIAL A N D E N G I N E E R I N G CH E M IS TR Y
material of kettle, and effect of moisture formed by reactions or derived from the air). Numbers are hard to visualize. The changes xn properties with time are made more apparent when plotted. I n a general way it may be observed that the changes experienced by the 287.8' C. (550' F.) oil are slower and more regular than those of the others, The slope of all the curves is gradual. The curves for the 304.4' C. (580" F.) oil are similar but steeper. With the 329.6' C. (625' F.) oil there is, in general, a sudden sharp increase in rate of change beginning during the second hour of heating and attaining a maximum during the third hour. Viscosity means much to the practical paint-and-oil man. Figure 4 shows the relation of viscosity to molecular weight. There is no straight-line relationship. For all temperatures the increase in molecular weight is more rapid a t first than in viscosity, but the viscosity increase preponderates later. I n fact, in the 287.8' C. oil toward the end of the run, quite a large increase in viscosity is accompanied by only a small increase in molecular weight. Here, no doubt, gelation is going on-some sort of mechanical packing of the molecules which inhibits their free flow-but polymerization reactions are not proceeding to any extent. It is of course true that a molecular weight determined in solution does not necessarily indicate the molecular weight of the substance in pure form; the solvent may exert a polymerizing or depolymerizing influence. In the present case the solvent has a polymerizing tendency. The curves for viscosity-specific gravity (Figure 5 ) have the same form. This is to be expected. It is interesting t o note a t the end the large increase in viscosity accompanied by so small an increase in specific gravity. This ties up with the view that gelation is a process of enmeshing of molecules, and does not necessarily involve close packing, which would show itself in increased molecular weight, or specific gravity, or both. The same is shown in the graph of viscosity-index of refraction (Figure 6). The behavior of the 304.4' C. (580" F.) and 287.8' C. (550' F.) oils is the same up to a certain point, possibly indicating that at first a certain program of changes must be gone through, irrespective of the temperature, provided the difference in temperature is not too great. The curve for the 329.6" C. (625' F.) oil goes its own course from the start, but coincides with the low-temperature curve a t
161
viscosity of 27 poises and refractive index 1.4895, a t which point both oils have a like molecular weight of MO 1500. Figure 7 shows the graph for viscosity us. iodine value. Here the same facts as above noted are brought out. The final large rise in viscosity is accompanied by small decrease in iodine value. A change of 50 units (180-130) of iodine value, during which time the molecular weight increases 546 units (790 to 1336),is accompanied by an increase of only 14 poises in viscosity. Later, a decrease of 7 units (130-123) of iodine number is accompanied by an increase of 71 poises, while the molecular weight increases 314 units (1336 to 1650). It seems probable that the formation of gels means also large adsorption of ungelled molecules in such a way as to diminish the possibility of reactions of condensation or of oxidation or reduction a t the double bonds. From the slope of the curve it would appear that complete saturation can never be effected in the reactions that take place during heat-bodying. Among the curves for viscosity-acid value (Figure 8), that of the 287.8' C. (550' F.) oil is the most interesting, showing again clearly that the final large increase in viscosity, which means gel formation, i s accompanied by only small increase in acid value. The temperature here has been so low that hydrolysis has proceeded slowly and only to a small extent over the long time of heating. The oil has had a chance to gel considerably with production of an acid value of less than 9. With the high-temperature oil hydrolysis has already attained its maximum value before gelation has set in to any extent. Figure 9 shows how the oils change in color on heating. There is a large bleaching a t first, with subsequent darkening. The bleaching takes place a t approximately the same rate for the three oils. However, cracking reaptions taking place a t the sides and bottom of the kettles result in darkening, which is more evident the higher the temperature to which the oil has been heated. The color developed in the 287.8" C. (550' F.) oil on heating for 2l/2 days is not as great as that developed in the 329.6' C. (625" F.) oil in 1 day. The relationship of refractive index to molecular weight is shown in Figure 10. The same facts which were noted in the
162
INDUSTRIAL AND ENGINEERING CHEMISTRY
case of the two previous oils and illustrated in Figure 2 are again presented: a t first a large increase in refractive index corresponding to a small increase in molecular weight; and later the reverse, indicating molecular rearrangements rather than polymerization a t first, and later polymerization or molecular packing. Attention is called to the regularity of the 287.8' C. curve. In the other two, irregularities occur which are not easily explained, but which. nevertheless, are seen in both. The curves for refractive index-specific gravity (Figure 11) show one peculiarity. At a value around 0.956 for the specific gravity of all three oils, there are to be seen sharp changes of inflection of the curves which cannot be interpreted with certainty. Attention will be called below to the same point in connection with the curves for acid value-specific gravity. The graph of refractive index-acid value (Figure 12) shows curves which are nearer straight lines than any of the others. The oil bodied a t the lower temperature undergoes least hydrolysis while undergoing changes which determine greatest increase in index of refraction; and the oil bodied a t the highest temperature undergoes greatest hydrolysis and least rearrangement resulting in increase in refractive index. As mentioned above, there is a peculiarity in the curves for specific gravity-acid value (Figure 13). Toward the end of the processing, all the oils undergo a sudden sharp increase in specific gravity corresponding to small change in acid value. As this packing of molecules (probably gel formation) is going on, the 287.8' C. oil decreases in acid value, the 329.6" C. oil has a fixed value, and the 304.4' C. oil increases in acid value. The processes of hydrolysis and molecular condensation, involving among other factors the joining on of the acid groups, are in opposition to one another. At different temperatures they proceed a t different relative rates. Figure 14 shows the relation of refractive index to iodine value, For the 287.8" C. (550' F.) oil, corresponding to an increase from 1.4870 to 1.4905 in refractive index, the iodine value changes only from 137 to 125. The molecular-weight increase during this period is 525 units. The aggregation of molecules in gel form appears to prevent reduction of unsaturation. This plate shows throughout, the regularity with which the changes in the properties involved are taking place during the early processing a t all temperatures, and throughout the entire processing period for the 287.8" C. oil. Other pairs of properties which might have been presented have been omitted on account of exhibiting no results of special interest. HEATSOF COMBUSTION Long, Zimmermann, and Kevins (3) have already shown by determination of calorific values as well as by ultimate analysis that the hardening of linseed-oil films in dry air is partly oxidation. The few results here reported were obtained not on films, but on the raw and bodied oils in bulk. The amount of surface of oil actually exposed t o the atmosphere during the cooking was necessarily small, but some oxidation was to be expected. The first combustions were carried out in an Atwater calorimeter, with the following results: BODYING TIMEKETTLE T E M P ~ R A T U R E W A B KEPTA T ' C. (" F.) MAX. TEMP. Hours Raw oil
287.8(550) 304.4 (580) 329,6 (625)
..
16 4
0
CALORIFIC
VALUES
9434 9299 9408 9326
VISCOSITY, 25' C. Poises Less than 0.5 85.3 12.9 40.4
It is noted that the greater the viscosity, the lower the calorific value; greater oxidation is accompanied by greater viscosity.
Vol. 24, No. 2
To .test whether the bodied oil changed in calorific value on standing, other combustions of the same oils were made 6 months later in an Emerson bomb calorimeter: Raw oil Bodied oil
= =
9425 cal. per gram (compare 9434) 9313 cal. per gram (compare 9299)
These latter results check well with the earlier ones, and indicate that the oils had not measurably changed on standing for this period of time.
SUMMARY A study has been made of the changes in certain physical and chemical properties of linseed oil during the process of bodying a t different temperatures. The properties studied were viscosity, color, specific gravity, molecular weight, index of refraction, and iodine value. The temperatures were 287.8', 304.4", and 329.6' C., and the times were 22, 9, and 9 hours, respectively. Samples were taken a t regular intervals. The changes are shown to progress more regularly at lower temperatures, though slowly. At high temperature the various reactions, sometimes working in opposition to one another, change in their relative rates of speed to such an extent as to produce seeming irregularities in the experimental results. Viscosity increases from less than 0.5 t o 85 poises, specific gravity from 0.925 to 0.967, molecular weight from 790 to 1600, index of refraction from 1.4800 to 1.491, and acid value from 0.445 to 14; iodine value decreases from 179.3 to 123, and color first decreases from 6 to 1, then increases to 8.5. The rates of change, as well as the extent, vary with the temperature to which the oil has been raised and the time at which it is held a t this maximum temperature. Other factors also enter in. The above changes were studied in connection with time and temperature and in connection with each other. One fact that stands out is the influence of the gelation process on the reactions of the system. Not only is there a large increase in viscosity, but the gel adsorbs the ungelled molecules and seems to inhibit their reactions. Further study of t,he matter of gel formation and adsorption is in progress. The relations of index of refraction to molecular weight indicate that, regardless of the temperature a t which the oil is bodied, reactions of rearrangement of molecules take place before actual polymerization begins in earnest. Some work is reported on heats of combustion, showing that the bodying process, which is partly an oxidation reaction, causes a diminution in the calorific value of the oil. ACKNOWLEDGMENT The authors extend their thanks to Messrs. Schuman and the Hilo Varnish Corp., of Brooklyn, N. Y., for the use of their facilities, and to E. J. Cole, chief chemist, for valuable suggestions. The aid of Roger Hess, Henry Stalzer, and Joseph Murray in obtaining some of the results is gratefully acknowledged. The authors wish to thank J. Loew for the use of the Atwater calorimeter in the laboratory of the I. R. Transit CO., New York. LITERATURE CITED (1) Caldwell, B. P., and Mattiello, J., IND.ENQ.CHEM., Anal. Ed., 4 , 52 (1932). (2) Fritz, F., Farbe u. Lack, 1928, 478. (3) Long, J. S., Zimmermann, E. K., and Nevins, S. C., IND.E X . CHEM.,20, 806 (1928). (4) Seaton, M. Y., and Sawyer, G. B., Ibid., 8 , 490 (1916). R E C ~ I V ESeptember D 10, 1931. Presented before the Divieion of Paint and Varnieh Chemietry at the S2nd Meeting of the Amerioan Chemical Society, Buffalo, N. Y., August 31 t o September 4, 1931. This paper is a portion of a thesis presented t o the Polytechnic Institute of Brooklyn in partial fulfilment of the requirementa for the degree of master of scienoe in chemistry by J . Mattiello, who ia now connected with the Hilo Varnish Co., Brooklyn, N. Y ,
